Chemical, biological, radiological, and nuclear decontamination: Recent trends and future perspective.

Chemical, biological, radiological, and nuclear (CBRN) decontamination is the removal of CBRN material from equipment or humans. The objective of the decontamination is to reduce radiation burden, salvage equipment, and materials, remove loose CBRN contaminants, and fix the remaining in place in preparation for protective storage or permanent disposal work activities. Decontamination may be carried out using chemical, electrochemical, and mechanical means. Like materials, humans may also be contaminated with CBRN contamination. Changes in cellular function can occur at lower radiation doses and exposure to chemicals. At high dose, cell death may take place. Therefore, decontamination of humans at the time of emergency while generating bare minimum waste is an enormous task requiring dedication of large number of personnel and large amount of time. General principles of CBRN decontamination are discussed in this review with emphasis on radiodecontamination.

Decontamination in general is defined as the removal of hazardous material from areas where it is not wanted. Decontamination is utilized to reduce the dose that worker may receive from a component or surface, to reduce the potential for airborne Chemical, biological, radiological, and nuclear (CBRN) agents, or to reduce the disposal cost associated with the component or the material. Decontamination serves to loose CBRN contaminants and fix the remaining contamination in place in preparation for protective storage or permanent disposal work activities. Some decontamination procedures have been utilized to reuse or recycle the material.

The decontamination technology is similar to the cleaning of dirt, oil, or corrosion products. Chemical decontamination can be defined as a method essentially involving the conversion of toxic chemicals into harmless products, either by degradation[1] or detoxification. Decontamination plays a vital role in the defense against Chemical Warfare agents. The toxic chemicals must be eliminated by application of efficient decontamination methods as quickly as possible for resuming routine activities. Biological decontamination means giving symptomatic and therapeutic medications to the individuals exposed to biological warfare agents. Radioactive contamination can be categorized into smearable and fixed type. The smearable contamination can be removed by wiping the surface with a cloth rag. It can be compared with dust that is found in all houses. The fixed contamination is held tightly to the surface and typically is associated with corrosion products on metal or concrete surface. In these cases, the contaminants have diffused into the material or other material on which the radionuclide could form some type of electrostatic or chemical bond with the surface materials. The removal of fixed contaminants typically requires harsh removal techniques. Techniques such as chemical dissolution of corrosion films or concrete scabbling are required to remove the fixed contamination. Smearable contamination can be generated by treating or attempting to remove fixed contamination. Some decontamination will loosen the fixed contamination, rendering it amenable to remove as smearable.

The effectiveness of the decontamination can be expressed as decontamination factor (DF). It is the ratio of contamination level of material before decontamination to the contamination level of material after decontamination.

A decontamination process that removes material will result in a DF greater than 1. The percentage of contamination removed from the surface can be given by

Percent contamination removed = (1-1/DF) × 100

If DF = 10, percent contamination removed = 90%

If DF = 100, percent contamination removed = 99%

There are varieties of decontamination methods available. An evaluation of several considerations will determine which specific methods shall be applied [Table 1].

Table 1

Determining selection of decontamination methods

There is no single technology that will be applicable in all situations and all type of contaminations, because nature and extent of contamination is different at different places. Like corrosion films found in boiling water reactors differ from those found in pressurized water reactors (PWRs). The main difference in these types of corrosion films is the concentration and oxidation state of chromium. Decontamination technologies[2] include mechanical methods, such as shaving, scabbling, and blasting; application of chemicals; biological methods; and electrochemical techniques. Materials to be decontaminated are primarily concrete or metal. Concrete materials include walls, floors, ceilings, bio-shields, and fuel pools. Metallic materials include structural steel, valves, pipes, glove boxes, reactors, and other equipments. Porous materials such as concrete can be contaminated throughout their structure, although contamination in concrete normally resides in the top quarter-inch below the surface. Metals are normally only contaminated on the surface. Contamination includes a variety of alpha, beta, and gamma-emitting radionuclides and can sometimes include heavy metals and organic contamination.

Decontamination of Chemical Agents

Chemical emergencies can arise from some chemical accidents, human errors, natural calamities, sabotage activities, or in the form of chemical agents released deliberately in air. Chemical emergencies can result in fire, explosion, and/or toxic release. Apart from normal emergencies, the chemical emergencies have another aspect and that is contamination. The contamination if not taken care can be fatal. The removal of contamination is termed as decontamination.

Patient decontamination for chemical emergencies

If it is suspected that skin has been exposed to liquid agents then it must be decontaminated immediately (within a minute). All experience confirms that the most important factor is time; the means used in decontamination are of minor importance. Good results can be obtained with such widely differing means such as talcum powder, flour, soap and water,[3] or special decontaminants or some polymers.[4]

If clothes have been exposed to contamination then extreme care must be taken when undressing to avoid transferring chemical warfare agent (CWA) to the skin. There may be particular problems when caring for injured persons, because it may be necessary to remove their clothes by cutting them off. This must be performed in such a way that the patient is not further injured through skin contact with CWAs. During subsequent treatment, ensuring that the entire patient is decontaminated is essential to avoid the risk of exposing the medical staff to the CWAs.

ED staff has the following three primary goals in treating a patient who has been exposed to a hazardous material and may be contaminated or who has not undergone adequate decontamination before arrival at the hospital: (1) isolate the chemical contamination; (2) appropriately decontaminate and treat the patient(s) while protecting hospital staff, other patients, and visitors; and (3) reestablish normal service as quickly as possible.

Health care providers caring for the patient should put on the appropriate PPE before coming into contact with contaminated patients. In most instances, this is level B PPE.

Ideally, decontamination occurs outside the hospital by EMS providers. If this does not occur, prepare a decontamination area for the patient. If possible, the ideal location is outdoors.

If indoor decontamination is necessary, a decontamination room is the next ideal location. Indoor decontamination only should occur in cases in which a controlled indoor environment may be maintained safely.

Controlled volatilization of the chemical to prevent displacement of ambient room oxygen, to prevent combustion, and to prevent levels of the chemical from reaching air concentrations deemed immediately dangerous to life or health for that specific hazard. In order to monitor this hazard effectively, the hospital requires testing equipment capable of identifying the chemical, its ambient air concentration, and ambient room oxygen concentrations.

If such a room is not available, try to isolate the patient in a single large room after removing nonessential and nondisposable equipment. Ideally, this room should be away from other patient care areas. Maintain ventilation to the area in which the patient is located, but be wary of further contaminating the hospital with recycled ventilation.

Establish a secure zone with yellow tape and permit only appropriately protected individuals to enter as needed. Include in the secure zone any area the patient may contaminate while entering the ED.

Upon arrival of the patient, determine whether the patient requires any immediate life-saving interventions. If these are required, stabilize the patient before or during decontamination.

General principles of chemical emergencies

The hot zone or immediate isolation zone is the area of immediate contamination. Entry into a hot zone requires special technique and equipment. It is imperative that the hot zone be isolated immediately and entry restricted, to avoid additional unnecessary casualties. Chemical agents are especially likely to spread downwind, creating an at-risk area, protective action zone, which is potentially amenable to evacuation. Notably, dispersion dynamics are such that ‘downwind’ is rarely a straight line and is more likely to be an expanding plume. Gases spread differently in the atmosphere during day and night. Meteorologic conditions, population concentrations, communication capabilities, the specific agent and amount released, and evacuation routes must be identified and are factors in decisions to either evacuate or shelter in place.

The hot zone must be approached from an upwind direction, an area that is also a potential evacuation and treatment area. The indicators of nerve gas release will resemble the consequences of other weapons of mass destruction (WMD), such as immediate casualties of similar presentation; a suspicious site characterized by a dispersal device, unexplained gaseous clouds, vapors, or odors; or an absence of animal, bird, or insect life.

Alternatively, there may be intelligence based on reports, remote detection, or point use chemical detectors. Victims must be identified, decontaminated, and evacuated, and general and specific therapy administered as rapidly and efficiently as possible. Considerations include triage and prioritization, communication with a central command center, and identification of all potential sources of important resources such as medications, monitors, and life-support equipments. For example, local supplies of drugs, such as atropine, amyl nitrite, and thiosulfate, will be exhausted rapidly in a mass casualty scenario, so alternative supplies need to be identified and efficiently procured.

Casualties will also be individuals who sustained secondary trauma during exposure to chemical agents, falls and blunt trauma, motor vehicle injuries, burns, or aggravation of preexisting comorbidities such as chronic lung disease and myocardial ischemia. These patients will need to be treated according to established medical principles, including the ABCDs of acute care.

Treatment area

There are various guidelines for setting up of treatment areas and decontamination facilities for the chemical emergencies, which are as follows:

When responding to a disaster involving hazardous materials and WMD, it is critical that the treatment area be at least 300 yards upwind of the contaminated area.

Having the patient perform as much of the decontamination as possible is preferable to decrease the amount of cross-contamination.

Remove the patient's clothes and jewelry and place them in plastic bags.

Wash the patient from head to toe with soap and water. Avoid vigorous scrubbing to prevent skin breakdown.

Decontaminate open wounds by irrigation with saline or water for an additional 5 to 10 min.

Try to avoid contaminating unexposed skin of the patient. Use surgical drapes if necessary.

Flush exposed areas with soap and water for 10 to 15 min with gentle sponging.

Irrigate exposed eyes with saline for 10 to 15 min, except in alkali exposures, which require 30 to 60 min of irrigation.

Clean under fingernails with a scrub brush.

Ideally, collect runoff water in steel drums if possible.

Special considerations for the chemical warfare patient

The best universal liquid decontamination agent for CWAs is 0.5% hypochlorite solution. It is prepared easily by diluting household bleach to one-tenth strength (i.e., nine parts water or saline to one part bleach). Hypochlorite solution works through physical removal and oxidation and/or hydrolysis of the agent; water does this at a much slower rate. Hypochlorite solutions are for use on the skin and soft-tissue injuries, including open lacerations. Do not use it in penetrating abdominal wounds (leads to development of peritoneal adhesions), in the eye (leads to corneal opacities), in open chest wounds, or in open brain or spinal cord injuries (effects unknown). Irrigate these areas with copious amounts of sterile saline solution. After using hypochlorite solution on either the skin or soft-tissue wounds, subsequently irrigate these areas with sterile saline solution.

The military also has access to a universal dry decontaminant known as M291 resin, which is available as pads packaged in small individual packets. M291 resin is a dry black carbonaceous material that decontaminates by absorption and physical removal of the CWA from the victim. M291 resin is used for spot decontamination of skin exposed to CWAs.

Organization of the military treatment area in chemical warfare

A full discussion of the military medical team response to a chemical warfare attack is beyond the scope of this article. A basic understanding of the structure of the military's medical treatment facility is important for civilian health care providers, because they most likely will be working with the military in the event of a chemical warfare incident. The military medical treatment facility is divided into dirty and clean sides. The demarcation of the sides is known as the hotline. The concept of the hotline is to keep all contaminated equipment, personnel, and casualties out of the clean side until decontamination is completed.

The dirty side consists of a triage station, emergency treatment station, and decontamination area. The triage station is the single entry point into the medical treatment facility. If the patient has an emergent medical condition that requires immediate medical intervention before decontamination, the patient is sent from triage to the emergency treatment station. The emergency treatment station is equipped to handle contaminated patients with emergent medical issues and stabilize them for either decontamination at the medical treatment facility or dirty evacuation to another facility for a higher level of care. The decontamination area is divided into ambulatory and nonambulatory patient decontamination areas.

The clean side consists of part of the decontamination area and the clean treatment area. The hotline extends through the decontamination area. Patients are decontaminated on the dirty side and are brought to the hotline nude, except for their PPE mask. These patients are transferred across the line to a team on the clean side of decontamination area. The clean side decontamination team then brings patients into the clean treatment area.

The clean treatment area is located 30 to 60 m upwind of the dirty side. The clean side decontamination team removes the patient's mask before transferring the patient to the clean treatment area. In the clean treatment area, the patient can be treated definitively or transferred to another facility if needed.

Defence Research and Development Organisation (DRDO) Venture for Chemical Emergencies

Chemical decontamination converts the toxic CWAs into innocuous products which can be handled safely, whereas in the physical process they are just removed from the site. Chemical decontamination procedures include nucleophilic reactions, electrophilic reaction (oxidations), thermal destruction, and photochemical and radiochemical reactions.

In general, sodium hydroxide dissolved in organic solvent breaks down most substances, but should not be used in decontaminating skin other than in extreme emergencies when alternative means are not available. Chloramines are effective against mustard and V agents, but ineffective against G agents. Soda solution renders nerve agents of G type harmless, but as far as V agents are concerned, it produces a product, which is as toxic as the original substance.

(a)DS-2 (Decontamination solution-2) contains 2% Sodium hydroxide (NaOH - 2%); Ethylene glycol monomethyl ether - 28%, and diethylene triamine - 70%. The active ingredient in this formulation is Ethylene glycol monomethyl ether [Figure 1] , which works as nucleophile and hydrolyses the toxic agents into their nontoxic counterparts. DS2 solution is used to decontaminate equipment that has been contaminated with liquid, blister or nerve agents, and biological agents (except bacterial spores). It is a clear, amber colored solution and is used in the portable decontamination apparatus. DS2 reacts with GB and HD to effectively reduce their hazards within 5 min. Within 30 min contact time, DS2 neutralizes all known toxic chemical agents.

Figure 1

Decontamination solution (DS2)

(b)Decontamination kit personal: The active ingredients of this kit are Ethanol: 72%; Phenol: 10%; Sodium hydroxide: 5%; Ammonia: 0.2%; Water: 12%. The components are contained in foil-packed pairs of towelettes in a plastic carrying case. These formulations are effective against nerve agents and can be used for decontaminating the skin and personal equipment [Figure 2].

Figure 2

Personal decontamination kit (PDK)

(c)Portable decontamination apparatus: The apparatus is made up of stainless steel sheet, with provision for pressurizing the apparatus by an inbuilt pump as well as from a vehicle compressor. A lance with a scrubber, a brush, a scraper, and an adjustable nozzle are provided for working at a safe distance from the contaminated surface. A pressure gauge indicates the pressure inside the apparatus. A shoulder strap for manual handling and brackets for fixing it on a vehicle are also provided. The DAP is meant for use by a small party or with the vehicle to be employed in contingencies involving the aftermath of an attack using nuclear, biological, chemical (NBC) agents for decontamination purposes on a small scale [Figure 3].

Figure 3

Potable decontamination apparatus

Surfactants-based formulations: Because decontamination of hydrophobic CWAs is hampered by their low solubility in the aqueous medium, formulations have been developed with surfactants (detergents) which not only enhance the solubility of the agents in aqueous medium, but also contribute to catalyze their detoxification. The main ingredients of such formulations are surfactants like Sodium dodecylsulphate or cetyltrimethylammonium halide and nuclease like hydroperoxides or hypochlorites. The variables which determine the effectiveness of decontamination include contamination time, temperature, contamination density, decontamination medium, nature of agent, and nature of decontaminants.

(d) Mobile decontamination system: It is a vehicle which is used for decontamination of the materials like vehicle, rescue teams with protective clothings , gloves, boots, etc [Figure 4].

Figure 4

Mobile decontamination system

Biological Emergencies

Biological emergencies are those in which the microbes are released in the air causing illnesses and death. During biological emergencies, the decontamination procedures include all the universal safety precautions and procedures that are required to maintain sanitized environment in and around the wards, and especially diagnostic laboratories. External decontamination in such cases is to maintain sanitation and hygienic environment. The isolation (quarantine) and prevention of various types of infections are discussed below.

Patient isolation precautions for biological emergencies

During medical management of biological emergencies, the standard precautions to be followed by health workers include (a)hand wash after patient contact; (b)wearing gloves when touching blood, body fluids, secretions, excretions, and contaminated items; (c)wearing a mask and eye protection, or a face shield during procedures likely to generate splashes or sprays of blood, body fluids, secretions, or excretions; (d)handling used patient-care equipment and linen in a manner that prevents the transfer of microorganisms to people or equipment; and (e)care when handling sharp objects and using a mouthpiece or other ventilation device as an alternative to mouth-to-mouth resuscitation when practical. These standard precautions are required to be practiced for all such emergencies.

Standard precautions for biological emergencies

During airborne infections, in addition to standard precautions, the following precautions should be practiced: (a)placing the patient in a private room that has monitored negative air pressure, a minimum of six air changes/hour, and appropriate filtration of air before it is discharged from the room; (b)wearing respiratory protection when entering the room; (c)limiting movement and transport of the patient, placing a mask on the patient if they need to be moved. The conventional diseases requiring airborne precautions include measles, varicella, and pulmonary tuberculosis, though small pox is the biothreat disease requiring such precautions.

In case of infections spread by droplet, the additional precautions to be practiced include (a)placing the patient in a private room or cohort them with someone with the same infection. If not feasible, maintaining at least 3 ft distance between patients; (b)wearing a mask when working within 3 ft of the patient; (c)limit movement and transport of the patient, place a mask on the patient if they need to be moved. Conventional diseases requiring droplet precautions include Invasive Haemophilus influenzae and meningococcal disease, drug-resistant pneumococcal disease, diphtheria, pertussis, mycoplasma, GABHS, influenza, mumps, rubella, parvovirus, though pneumonic plague is a biothreat disease requiring such precautions.

Contact precautions (in addition to standard precautions) that need to be practiced during MRSA, VRE, Clostridium difficile, RSV, parainfluenza, enteroviruses, enteric infections in the incontinent host, skin infections (SSSS, HSV, impetigo, lice, scabies), hemorrhagic conjunctivitis, or biothreat disease, i.e., viral hemorrhagic fevers, include (a)placing the patient in a private room or cohort them with someone with the same infection if possible; (b)wearing gloves when entering the room and changing gloves after contact with infective material; (c)wearing a gown when entering the room if contact with patient is anticipated or if the patient has diarrhea, a colostomy, or wound drainage not covered by a dressing; (d)limiting the movement or transport of the patient from the room; (e)ensuring that patient-care items, bedside equipment, and frequently touched surfaces receive daily cleaning; and (f)dedicated use of noncritical patient-care equipment (such as stethoscopes) to a single patient, or cohort of patients with the same pathogen. If not feasible, adequate disinfection between patients is necessary.

Radiological Decontamination Methods for Materials

Radiological decontamination methods can be broadly classified into following categories:

Chemical decontamination

Mechanical decontamination

Electrokinetic/electrochemical decontamination

Human decontamination

Chemical decontamination

Chemical decontamination uses concentrated or dilute reagents in contact with the contaminated item, to dissolve the contamination layer covering the base metal and eventually part of the base metal. Chemical solutions are generally most effective on nonporous surfaces. The choice of the decontamination agents is based upon the chemistry of the contaminant, the chemistry of the substrate, and the ability to manage the waste generated during the process.[5] Chemical decontamination is usually carried out by circulating the selected reagents in the system. However, segmented parts may be decontaminated by immersing them in tank containing the reagent, which is then mostly agitated. Chemical decontamination processes are basically divided into two groups. Mild chemicals include noncorrosive reagents such as detergents, complexing agents, dilute acids, and alkalies. Aggressive chemicals include concentrated strong acids and alkalies and other corrosive reagents. The dividing line between these two groups of processes is usually at about 1 to 10% concentration of the active reagent. Mild chemical decontamination techniques have generally been used for items where the objective is to remove contamination without attacking the base material. Their advantages are low corrosion rates and low chemical concentrations, which facilitates the treatment of the spent decontamination solution (secondary waste). Although some low concentration decontamination techniques have low DFs and require long contact times, they may be made more effective by combining with processes using noncorrosive oxidizing or reducing agents, and complexing and chelating agents, and applying them in several stages. In many cases, the effectiveness may also be improved by increasing the treatment temperature usually in the range of 20 to 90°C. The selection of redox and chelating agents will depend on the composition of the surface corrosion products to be removed.

Aggressive chemicals and electrochemical decontamination techniques may involve one or more stages using different chemical solutions. A multistep process (i.e., the application of a strongly oxidized solution followed by a complexing acid solution) is a common technique for removal of the contaminated oxide layer from metal surfaces, such as stainless steel. The first (alkaline) stage is intended to oxidize the chromium oxide to yield soluble chromate ions. The second (acid) stage is a primary dissolution reaction for the complexing of dissolved metals. The required decontamination level may necessitate repeating the process a number of times. The chemical reagents at excessively high temperature may result in undesirable effects, such as toxic or explosive gases, e.g., hydrogen. In order to keep secondary waste at minimum in more recent years, the regeneration of chemicals has become a fundamental part in all chemical decontamination processes. Several conventional chemical processes may be used for regenerating the spent solutions, eventually in combination with, for example, ion exchange, evaporation/distillation, and electrodialysis.

Chemical decontamination involves techniques like using chemical solutions, multiphase treatment processes, foam decontamination, chemical gels, decontamination by pastes, decontamination by chemical fog, and gas phase decontamination.

Chemical solutions

Strong mineral acids—acids like HNO3, H2SO4, phosphoric acid, fluoroboric acid, and fluoronitric acid are used. The main purpose of these is to attack and dissolve metal oxide films and lower the pH of solutions in order to increase solubility or ion exchange of metal ion.[5]

Nitric acid is widely used for dissolving metallic oxide films and layers in stainless steel and Inconel systems. The nitric acid/potassium permanganate/oxalic acid (NPOx) system is being used for remote operation. This system performs very well with high decontamination efficiencies and very low quantities of waste generated during decontamination.[5] Sulphuric acid is an oxidizing agent used to a limited extent for removing deposits that do not contain calcium compounds. In order to reduce low-level radioactive liquid wastes, evaporation at atmospheric pressure was carried out for aqueous solutions containing a sub-volatile fission product in both nitric acid and sodium nitrate solutions.[6] DFs of the distillates for Pd, Mo, Te, and Sb were the order of 10,000, and the percentages per square meters adhering to the condenser and the inside of the evaporator lid were between 0.001 and 0.0001. Tests with sulphuric acid-cerium(IV) solution have been reported.[78] The dismantling of the BR3-PWR reactor led to the production of large masses of contaminated metallic pieces, including structural materials, primary pipings, tanks, and heat exchangers. One process called MEDOC (Metal Decontamination by Oxidation with Cerium) has been reported and is based on the use of cerium (IV) as strong oxidant in sulphuric acid, with continuous regeneration using ozone.[9] Cerium (IV) ions are added to increase the hardness of the reagents in order to balance the temperature decrease. Phosphoric acid is generally used for the decontamination of carbon steel, because it rapidly defilms and decontaminates carbon steel surfaces. Fluoroboric acid technology was designed especially for decontamination and decommissioning. The acid attacks nearly every metal surface and metallic oxide.Fluoronitric acid has been used for decontamination of stainless steel. The basis for the dissolution of corrosion films and therefore mechanism for decontamination is the destabilization of the oxide lattice by attack with proton.

The salts of various weak and strong acids can be used in place of the acids themselves or more effectively, in combination with various acids to decontaminate metal surfaces. Salts like sodium phosphate and polyphosphates, sodium bisulphates, sodium sulphate, ammonium oxalate, ammonium citrate, sodium fluoride, and ammonium bifluoride have been used. One new process called In-Situ-Mixed Iron Oxide process, removes strontium and actinides from waste streams with faster reaction kinetics than the monosodium titanate (MST) process.[10] Use of in-situ-formed magnetite[11] for the removal of Sr, Pu, Np, U, Am, and Cs from tank waste has also been reported. In-situ-formed ‘magnetite’ is actually a mixture of Fe(II) and Fe(III) oxides and hydroxides, including magnetite. DF values were measured for both magnetite and MST. Magnetite DF values were found to be superior to MST for all isotopes studied.

Sodium permanganate and strontium nitrate have been used to remove the actinides and radiostrontium from waste supernate.[12] The strontium DFs far exceeded the required values. Within the ARP application, the use of peroxide as the reductant for permanganate produced higher plutonium DFs than the use of sodium formate. In the formate, application increasing the reductant concentration and mixing energy resulted in higher Sr and Pu decontamination. The use of AGS (silica-gel impregnated with silver nitrate)[13] column for iodine-129 removal with a DF more than 36,000 has been reported. One technology called Small-Tank Tetraphenylborate Process[14] uses sodium tetraphenylborate to precipitate and remove radioactive cesium from the waste and MST to sorb and remove radioactive strontium and actinides.

The use of organic acids is for decontamination mainly during plant operation. They are used not only for metal surfaces, but also on plastics and other polymeric compounds. The material is treated with formic acid, complexing agent and corrosion inhibitor, and simultaneous agitation by ultra sound in a purpose-built bath. The process allowed the fast and effective removal of surface contamination from level of 103 to 104 Bq/cm2 to below release levels.[15] Oxalic acid is effective for removing rust from iron and is an excellent complexer for niobium and fission products. However, secondary deposits of ferric oxalate containing radionuclides may be formed on the decontaminated surfaces.Oxalic acid is a basic component of circuit decontamination technology.Oxalic peroxide is used for the simultaneous dissolution of UO2 and for the defilming and decontamination of metals. Citric acid is used as a reducing agent, and it is very effective for decontaminating stainless steel in a two step process following alkaline permanganate treatment.

Caustic compounds are used both solely and in solution with other compounds to remove grease and oil films, to neutralize acids, to act as surface passivators, to remove paint and other coatings, to remove rust from mild steel, to act as a solvent for species that are soluble at high pH, and as a means of providing the right chemical environment for other agents, mainly oxidizing ones. Examples include sodium carbonate, trisodium phosphate, and ammonium carbonate.

Complexing agents form stable complexes with metal ions, solubilize them, and prevent their redeposition out of solution. Agents like oxyethylidenediphosphonic acid, diethylenetriaminepentaacetic acid (DTPA), ethylenediamine-tetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid, organic acids, sodium and ammonium salts of organic acids, Nitrilotriacetic acid and picolinic acid have been used. Problems may occur with conditioning if the secondary waste contains complexing agents, i.e., solidification of concrete and stability of resins.[16] Uranium (U) and other radioactive actinides and lanthanides are embedded within the mixed oxide structures of the passivity layers of corroded iron and steel. These toxic metals can be dissolved out of the surface layers by a naturally occurring bacterial siderophore called Desferrioxamine B (DFB). DFB is a trihydroxamate ligand with one amine and three hydroxamate groups, which chelates with metals through hydroxamate coordination. Complexation of DFB with U can be utilized in decontamination strategy of the passivity layers.[17] There are a wide variety of compounds that are naturally occurring biodegradable organic chelates (siderophores) that appear to be more effective at oxide dissolution and actinide complexation than EDTA or other organic acids now used in decontamination processes. These chelates bind hard acids (Fe[III] and actinides[IV]) with extraordinarily high affinities. For example, the binding constant for the siderophore enterobactin with iron is about 10 (sub 50), and its binding constant for Pu(IV) is estimated to be high.[18]

Bleach is most effective in removing chemical agents from surfaces. Traditionally calcium hypochlorite has been used. Use of sodium-based bleach formulations have found some applications.

Detergents are effective, mild, all-purpose cleaners for treating all facility surfaces, equipment, clothes, and glassware. They are not effective in dealing with metal corrosion and long standing contamination. Surfactants are used as wetting agents, detergents, and emulsifiers.

Organic solvents have been used in decontamination for removing organic materials, like grease, wax, oil, and paint from surfaces and for cleaning clothes.Kerosene, 1,1,1-trichloroethane, tetrachloroethane, trichlorethylene, perchloroethylene, xylene, petroleum ethers, and alcohols fall under this category.

Multiphase treatment processes combine a variety of chemicals and processes to achieve a more effective decontamination, and are widely used.Reducing oxidizing agents or REDOX agents increase or reduce the oxidation state of the superficial metallic oxide layer on the contaminated metal, thereby making it more soluble. Most of the REDOX decontamination processes are multistep applications. An initial oxidation step (commonly alkaline or acidic permanganate) is used to increase the oxidation state of the metal ions. This is followed by a reduction step aimed at dissolving the metal cations.

Low oxidation state of metal ion process was primarily developed for a steam-generating heavy water reactor. It is applied to structural materials such as different types of carbon and stainless steel, Inconels, and Zircaloy.In PWRs, it is normally followed by an oxidizing stage. This process employs a strong reducing agent to attack the ferric ion in the oxide matrix. The strong reducing agent is the vanadous ion that is in solution, chelated with picolinic acid. The vanadous ion is oxidized to vanadic ion while reducing the ferric ion to ferrous ion.

Once the various metal species are solubilized, they are complexed with picolinic acid which is added to the solution at the beginning of the step. This process is utilized at a pH of 4 to 5, thus sodium hydroxide also is added to the concentrated chemicals before injection.

Alkaline permanganate is used to oxidize Cr(III) oxides (which are insoluble in acids and alkalis) present in the corrosion films to Cr(VI) in the form of CrO42- anion, which are soluble over a wide range of pH values.

Ammonium citrate has been successfully used after alkaline permanganate pretreatment and water rinsing to decontaminate stainless steel and carbon steel.EDTA can be added to former process, i.e., alkaline permanganate followed by ammonium citrate, to keep the iron oxide in solution and inhibit its redeposition.A mixture of oxalic acid, citric acid, and an inhibitor is an effective decontaminant of stainless steel as the second step after alkaline permanganate pretreatment. Alkaline permanganate treatment can be followed by sulphamic acid treatment. This technique is effective in removing the contaminated film from stainless steel piping without causing redeposition of a precipitate.Alkaline permanganate pretreatment can be followed by oxalic acid treatment. This process has been successful in removing aged films on high-temperature stainless steel water piping, but it has the disadvantage of causing redeposition in the form of a tenacious oxalate film on the metal.This can be avoided by using an acidic permanganate solution. To prevent the formation of secondary oxalate deposits, hydrogen peroxide (H2O2) was used in the final stage.The main disadvantage of this process (as for other multistage technologies) is the large volume of spent solution and flushing water generated. This can exceed the original circuit volume by up to a factor of ten.

In CORD (chemical oxidation/reduction decontamination) process, permanganic acid (HMnO4) is added to the system to oxidize Cr(III), and dicarboxylic acid (oxalic acid) is then added directly. In this process, HMnO4 acts as oxidizing agent and oxalic acid as dissolution and chelating agent. Dissolved metal may be removed by ion exchange using ‘on-line’ systems or by subsequent evaporation of the solvent.

Ultraviolet light and H2O2 are used to reduce the concentration of the oxalic acid which in turn reduces total waste volumes.

POD (PWR oxidizing decontamination) method is similar to CORD and other methods, and is based on the reduction of an oxidizing solution using organic acid (e.g., oxalic acid).

A combination of nitric acid, permanganate, and hydrofluoric acid has also been used.Use of ozone and Ce(IV) in an acid solution[19] has been reported for the decontamination of steam generator. A solution of nitric acid, Ce(IV), and ozone was also used successfully for the decontamination of Inconel tube bundles at several steam generators in Europe.[20] Ce(IV) nitrate in a nitric acid solution and proprietary commercial solutions that include acid and sequestering agents have been used for decontamination of glove boxes in Plutonium Finishing Plant.[21]

CAN-DECON chemical decontamination process was developed for heavy water reactors. This is a low concentration, chemical decontamination process in which the only radioactive waste generated is an ion exchange resin. This process is composed of EDTA, citric acid, and oxalic acid in a molar ratio of approximately 2 : 1 : 1. The CAN-DEREM process eliminated oxalic acid from CAN-DECON process, as CAN-DECON solvent may lead to intergranular attack/intergranular stress-cracking corrosion in heavily sensitized stainless steel (SS304). As EDTA, citric acid, and oxalic acid dissolve, the oxide deposits are solubilized. Online generation removes the iron from the chelant, i.e., EDTA by passing the decontamination liquid through cation exchange resin. The CAN-DEREM process is less aggressive due to the absence of oxalic acid, and therefore, can be used without corrosion concern on both stainless steel as well as carbon steel surfaces.

The CITROX reagent consists of citric acid (0.3M) and oxalic acid (0.2M). Inhibitors are also used due to its corrosive nature. It was used in carbon steel systems. This process remains popular for use on BWR and PWR component decontamination, but has not been qualified for application on a full reactor recirculation system in a BWR or a reactor coolant system on a PWR. The online demineralization should be maintained at a high enough rate in order to keep the concentration of ferric ion to less than 10 ppm. The corrosion is substantially reduced if the ferric ion in solution is maintained at concentration of less than 10 ppm (10 mg/l).

Decontamination for decommissioning (DFD) process utilizes fluoroboric acid as the active ingredient. The DFD process was developed to remove the radioactive materials from metallic surfaces by corroding the metal surfaces. The corrosion on the base metal would release any radionuclides deposited in pits or crevices within base metal. After several cycles of DFD, the component's radiation levels are reduced and the component may be able to be free-released. This process also uses potassium permanganate and oxalic acid. Potassium permanganate raises the oxidation potential of the solution to dissolve protective chromium layer. Oxalic acid is used to dissolve MnO2 that is generated by the reduction or decomposition of the potassium permanganate. The Cr (C2O4)3 can be removed by anion portion of the mixed bed resin.

CORPEX™ chemical process is a nondestructive cleaning method that removes only the contaminant and the matrix that fixes the contaminant to the surface. It uses oxidizers leaving only water, CO2, nitrogen gases, and the secondary waste sludge.

LTLT process or gas phase decontamination is an in-situ technique that uses a mixture of treatment gases to decontaminate diffusion-cascade equipment. The treatment gases are injected into the diffusion cell at low pressure and allowed to react with the solid U deposits. Once the reactions have progressed to the desired level, the cell gases are removed and either returned to the operating cascades where recovered uranium hexafluoride is eventually withdrawn as low-enriched U product or passed through cold traps to remove recovered uranium hexafluoride.

TechXtract Technology is a sequential chemical extraction process for the removal of radionuclides, PCBs, and other hazardous organic and inorganic substances from solid materials, such as concrete, brick, and steel. The technology uses chemical formulations and engineered applications to achieve significant penetration and removal of these contaminants at and below the surface of these materials. The spent chemical solution does not contain any hazardous constituents (except for extracted contaminants) and have been disposed of by incineration, solidification (and land disposal), and discharge to liquid-effluent treatment systems.

Foam decontamination is achieved by using foam such as that produced by detergents and wetting agents. Foam acts as a carrier for chemical decontamination agents. The process is widely used, especially for large components with complex shapes or large volumes. It can be applied to surfaces in any orientationand produces low volume of secondary waste. It has been applied to a series of large carbon steel valves having complex internal configuration, yielding very low residual contamination levels. It was used effectively with a sulphonitric mixture during the decontamination of a graphite/gas cooler made of ferritic steel and brass.[2223] Experimental use of foam[24] was only 59% effective in removing the radioactive contamination in the first attempt, and that even after two more attempts at decontamination (first using the same material with a different method, and finally with French material and methods), the overall decontamination efficacy was only 72%.

Chemical gels are used as carriers of chemical decontamination agents and are sprayed or brushed onto a component or surface, allowed to work, then scrubbed, wiped, rinsed, or peeled off.Techniques using aggressive agents in liquid and gel-like forms have been developed.[25] This method is effective in situations where long contact time are required, together with the need to minimize waste.[26] Use of this technique with sulphuric/phosphoric acid and Ce(IV) gels has been reported.[27] Use of a new and more environmentally acceptable technology for decontamination of actinides, especially Pu, on steel and concrete surfaces has been reported. The key component of this technology is isosaccharinate (ISA), a degradation product of cellulose materials that is biodegradable. ISA will be incorporated into foams/gels for safe and easy use in decontamination of actinides from steel, concrete, and other surfaces.[28]

Pastes have been used for treating metal surfaces, particularly stainless steel. They consists of a filler, a carrier, and an acid or mixture of acids as the active agents.[29] In modified technique, an abrasive is included within paste. Mechanical action with the abrasive assists in breaking down surface films, increasing the effectiveness of the chemical reagents.

Decontamination can also be achieved by dispersing chemical agents as a fog.[29] Water and/or acidic fogs have been used for decontamination of equipment removed from liquid metal cooled reactors.

A solvent extraction process to recover U and technetium[30] from solutions of irradiated commercial reactor fuel while sending the plutonium to waste with the fission products and higher actinides has been reported. A caustic-side solvent extraction process[31] has been used to remove cesium from high-level waste. The cesium was removed from the waste with DFs greater than 40,000, and the recovered cesium was concentrated by a factor of 15 in dilute nitric acid.

Few more techniques like DECOFOR, based on formic acid, and DECOPAINT, based on alkalies, and the concrete decontamination process DECONCRETE, based on phosphoric acid, and mechanical stripping with steel brushes have also been reported.[32] A new enhanced membrane technology[33] for the liquid salt-bearing radioactive waste processing based on the state-of-the-art membrane unit design, namely, the filtering units equipped with the metal-ceramic membranes of TruMem brand, as well as the electrodialysis and electroosmosis concentrators has been used. Application of the above mentioned units in conjunction with the pulse pole changer will allow the marked increase of the radioactive waste concentrating factor and the significant reduction of the waste volume intended for conversion into monolith and disposal. Besides, the application of the electrodialysis units loaded with an ion exchange material at the end polishing stage of the radioactive waste decontamination process will allow the reagent-free radioactive waste treatment that meets the standards set for the release of the decontaminated liquid radioactive waste effluents into the natural reservoirs of fish-farming value. Use of membrane ultrafiltration[34] in conjunction with water-soluble polymers or surfactants with added metal-selective chelating agents has also been reported for U, thorium, lead, cadmium, and mercury along with chromium (as chromate). Laboratory scale tests showed removal of 99.0 to 99.9% of each metal tested in a single separation stage.

Soil decontamination

Soil may be decontaminated using a biochemical method for the decontamination of radioactively contaminated soil by bioleaching of the soil in tanks. This technique uses thiobacteria and capillary action, and has already been tested on semi-industrial scale.[35]

Advantages

Chemical decontamination is relatively simple and similar to classical cleaning. It may also be relatively inexpensive as additional equipment is not required.

Chemical decontamination is a known practice in many nuclear plants and facilities.

With proper selection of chemicals, almost all radionuclides may be removed from contaminated surfaces. Problem of recontamination may be reduced by continuously rinsing the surface with water.

With strong mineral acids, a DF of 100 : 1 decrease in activity levels may be achieved, and in many cases, the item may be decontaminated up to releasable levels.

Chemical decontamination may also remove radioactivity from internal and hidden surfaces. However, in this case, its effectiveness may be low, and measurement at release levels will be a problem.

Chemical decontamination involves relatively minor problems of airborne contamination, similar to those of the closed-system approach.

Disadvantages

The main disadvantage of chemical decontamination is the generation of secondary liquid waste, resulting in relatively high volumes compared with other processes, such as electropolishing. The treatment and conditioning of the secondary waste requires appropriate processes to be considered when selecting the decontamination option. Moreover, in some cases (e.g., internal and hidden surfaces), the effectiveness of the decontamination may be relatively low.

Usually the solution must be heated up to 70 to 90°C in order to improve the kinetics of the decontamination process.

A further disadvantage in obtaining high DF is that corrosive and toxic reagents may need to be handled.

Chemical decontamination is mostly not effective on porous surfaces.

Mechanical decontamination

Mechanical decontamination methods can be used on any surface where contamination is limited to near material. Mechanical decontamination methods work best on large, regular surfaces that are readily accessible and unencumbered by other structures. As with chemical decontamination, the selection of the most effective technique depends on many variables, such as contaminants involved, surface material, and cost. The selected treatment may have to be applied several times to meet the established decontamination objectives. The techniques required in the removal of contaminated material are identical to the techniques required to remove dust, dirt, or corrosion products that are nonradioactive. The difference is that more waste may be generated in the cleaning of radioactively contaminated surfaces since cross contamination, the contamination of surfaces previously free of contamination, needs to be avoided.

Flushing with water is the simplest technique. Water acts by dissolving chemical species or by eroding and flushing loose debris from the surface. Flushing can be used for areas that are too large for wiping or scrubbing,involves flooding a surface with hot or cold water, followed by water collection.

Dusting, vacuuming, wiping, and scrubbing involve the physical removal of dust, aerosol, and particles from building and equipment surfaces using common cleaning techniques.Suction cleaning is most useful as a pretreatment for removing large quantities of loose contaminants.

Stripping coating technique is also used and consists of a two-stage process; first, the application of a polymer and decontamination mixture to a contaminated surface and second, the removal of the stabilized polymer layer after setting. It is applicable to a wide range of contaminants and materials, with the best results achieved on large nonporous surfaces that are easily accessible.

Steam cleaning combines the solvent action of hot water with kinetic energy effect of blasting. It is recommended for removing contamination from complex shapes and large surfaces, even if grease or similar substances are present,and for removing contaminated soil particles from earth moving and drilling equipments.Secondary waste volumes produced by the process are relatively low as the steam can be collected by vacuum extract, or similar means, and condensed.[3637]

Abrasive cleaning process uses an abrasive medium such as plastic, glass or steel beads, or grit such as garnet, soda or aluminium oxide. It is used to remove smearable or fixed contamination from metal surfaces such as structured steel components and hand tools, and also from concrete surfaces and coatings. In the case of concrete surfaces and coatings, a significant amount of the base material is also removed. This process is most effective on flat surfaces and can also be used on ‘hard to reach’ areas such as ceiling or behind equipments. The process produces comparatively large amounts of secondary waste. The decontamination process can be carried out wet or dry, with the abrasive medium being driven against the surface by mechanical means, e.g., vibrating bed for small objects (this technique is sometimes called vibratory finishing) or blasted on to the surface using water or compressed air as the propellant. Water or compressed air is generally used for large surfaces.

Sponge blasting technique uses sponge made of water-based urethane; when theses sponges are blasted on to the surface, it creates a scrubbing effect by expanding or contracting. An ‘aggressive’ grade of sponge, impregnated with abrasives, can be used to erode material such as paints, protective coatings, and rusts.

CO2 blasting is a variation of grit blasting in which CO2 pellets are used as the cleaning medium. The technique has proven effective with plastics, ceramics, composites, and stainless steel, although soft materials can be damaged by the process and brittle materials may shatter.One advantage of the process is that the bulk of the secondary waste is in the form of a gas which is easy to treat.

High-pressure liquid nitrogen blasting is a variation of grit blasting whereby abrasive is injected into a liquid nitrogen jet, the jet propelling the grit on to the surface to be decontaminated. The contamination is removed by the embrittlement induced by the liquid nitrogen and the abrasive action of the grit.

Decontamination by Freon jetting is affected by directing a high-pressure jet of a Freon cleaning solvent on to the surface to be cleaned. It is usually used on discrete components inside a glove box, but experimental units have been developed for in-situ cleaning. However, regulatory restrictions on the use of freon can limit the application of this technique.[29]

Wet ice blasting is a variation of grit blasting where a compressed air jet is used to propel a mixture of water and ice crystal on to the surface to be decontaminated. This technique will remove coatings and some fixed surface contaminants, but will not remove more than the surface layer from concrete.

High-pressure water processes use a pressurized water jet to remove contamination from the surface of the work piece, the contamination being removed by the force of the jet. Pressure can range from 105 Pa to more than 108 Pa; the pressure and flow rates being optimized for individual requirements. Recirculation and treatment systems can also be used to minimize secondary waste production. Typical applications include the cleaning of inaccessible surfaces such as the interiors of pipes, structural steel work, and cell interiors.[22] Depending on the pressure used, water jetting will remove paint, coatings, galvanized layers from sheet steel, and tenacious deposits without damaging the underlying surfaces.[38] Variation of this technique includes the use of glycerin as the pressurized mediumor the entrainment of grit in the water jet. When grit is entrained, this is the same process as grit blasting.

Grinding/shaving uses coarse grained abrasive in the form of either water-cooled or dry diamond grinding wheels or multiple tungsten carbide surfacing discs. It is recommended for use where thin layers of contamination need to be removed.

Scarifying/scabbling/planning are used to abrade the surface of concrete structures to remove contamination. One method uses scabblers consisting of several pneumatically operated piston heads to simultaneously strike a concrete surface. Another method is a needle gun, which is used on both concrete and steel surfaces and consists of uniform sets of several millimeter long needles, which are pneumatically driven. These processes are very effective for removing the thin contaminated layer from the surface of concrete.

Metal milling uses rotating cutters to shave off layers of material, and is most effective where there are a large number of similarly shaped items or large areas requiring decontamination.

The drilling and spalling technique involves drilling 25 to 40 mm diameter holes, approximately 75 mm deep in to which a hydraulically operated spalling tool having an expandable tube is inserted. A tapered mandrel is then hydraulically forced into the hole to spread the ‘fingers’ and spall off the concrete. It is mainly applicable to concrete and is recommended for removing contamination which penetrates a few centimeters below the surface.

Expansive grout is used as a dismantling technique, but can also be used for decontamination through its ability to remove a thick layer of contaminated concrete.

Equipment such as paving breaker and chipping hammer is primarily used in demolition activities and is also referred to as ‘jack hammer.’ It is mainly used to remove surface contamination and the rough surface left on completion of operations.[39]

One technique called electrohydraulic scabbling (EHS) removes surface layers of contaminated concrete while generating minimal secondary waste. The EHS device delivers powerful shock waves to the concrete surface originated by a pulsed, high-voltage electric discharge between two electrodes. The hydraulic shock wave propagates through water between the discharge channel and the concrete, causing the concrete to crack and peel.

VecLoader is an integrated trailer mounted system comprised of a diesel-engine-powered-vacuum, a cyclone separator, and a HEPA filter. It uses a flexible smooth vacuum and is used to remove insulation. The powerful vacuum shreds and sucks the insulation from the wall. The insulation waste stream is drawn first into a cyclone separator where it is sprayed with water as it enters. The wet insulation begins to clamp as it spins at high speed in the cyclone separator. Large particles of insulation clumps together, decelerate, settle to the bottom of the separator. Insulation that collects on the sides of the cyclone separator is conveyed to the bottom of the separator by a built-in hydraulic auger.

Electrokinetic decontamination is a technique for in-situ removal of contaminants from porous concrete. This method provides a viable alternative to scabbling or physical abrasion. This technique applies on electric field to induce migration of ionic components from within the porous concrete into the decontamination unit. The components of the system are electrokinetic extraction concept (SEEC) pad, electrolyte solution, and electrode. The electrolytic solution contains various complexing agents, as well as other materials to promote formulation of a soluble ionic complex of each specific contaminant present. The electrolyte solution is in contact with the concrete surface through the SEEC pad, which consists of a fabric or carpet-like material that partially removes contaminants from the electrolyte solution and limits the solution's flow. All contaminants are collected in either the aqueous electrolyte solution and/or in the SEEC pad. Both of these are treated and disposed of by conventional technologies. This process generates minimal secondary waste and no airborne particulate matter common to conventional scabbling or physical abrasion techniques. Furthermore, compared with conventional systems, this process is capable of removing contaminants diffused deeply into concrete. It can be used for soil cleanup, concrete decontamination, contaminant separation of ground water and waste water, containment structures, underground mapping, and barrier detection.[4041]

Decontamination by electropolishing of components and systems in the turbine house and of the primary water system has been reported.Electropolishing is generally an anodic dissolution technique, where a controlled amount of material is stripped from the surface of the workpiece along with the contamination. The process works for any conductive metal, provided protective surface coatings are not present. The components are decontaminated following removal by immersing them in a bath of fluid[7222629] or treated in-situ using close circuit systems, which can be deployed from manipulators or operated manually.[42] Typical electrolytes are based on phosphoric acid,[43] nitric acid,[44] and organic acids.[22]

In ultrasonic cleaning, high-frequency energy is converted into low-amplitude mechanical energy, i.e., vibrations. The vigorous scrubbing action produced by the cavitation of a cleaning solution is then imparted to a submerged object. This technique is usually applied to small objects with primarily loose deposits and adhered contamination. It is not applicable for concrete or for materials which absorb ultrasonic energy. Radiometric measurements indicate that the synergy between ultrasonics and chemical will enhance the DF and also reduce the time needed for the chemical decontamination.

Melting can also be considered a decontamination technique. It has three-fold purpose. The main goal of melting is the recycling of metals; simultaneous decontamination of the metal occurs during melting, because many of the radioactive isotopes separate from the melt and concentrate in the slag. Melting also provides a means of volume reduction. Melt decontamination of radioactively contaminated stainless steel by electro slag remelting (ESR) has been reported.[45] ESR is industrially used for the production of specialty steels and superalloys to remove a variety of contaminates and to improve metal chemistry. Correctly applied, it could maintain the specified chemistry and mechanical properties of the original material while capturing the radioactive transuranic elements in a stable slag phase. The ESR process also produces a high-quality metal ingot free of porosity that can be directly forged or rolled into final shapes. One case to melt the scrap at Siempelkamp's melting plant[46] has been reported. For safety reasons, the furnace is widely operated by remote handling. A highly efficient filter system of cyclone, bag filter and HEPA-filter in two lines retains the dust and aerosol activity from the off-gas system. The slag is solidified at the surface of the melt and gripped before pouring the liquid iron into a chill. DFs could be achieved between 80 and 100 by the high affinity of the U to the slag former. The activity is transferred to the slag up to nearly 100%. All produced ingots showed a remaining activity less than 1 Bq/g and could be released for industrial reuse.

The light ablation technique uses the absorption of light energy and its conversion to heat to achieve the selective removal of surface coatings or contaminants. Surface coatings such as epoxy paints, adhesives, corrosion products, accumulated airborne pollutants, and up to 6 mm thick layers of concrete can be removed using this technique. Laser and xenon flashlights sources for this application are commercially available, and a pinch plasma lamp is under development. Laser decontamination might have two advantages over other methods; first, the production of secondary waste is reduced owing to it being a ‘dry’ process, and second, because the laser beam can be transmitted through an optical fiber, the whole decontamination process can be operated remotely.

Microwave scabbling is a new method of removing the surface of concrete which use microwave energy to heat the moisture present in the concrete matrix. Continued heating produces steam under pressure which generates internal mechanical and thermal stresses, bursting the surface layer of the concrete. The analysis showed that the main factors affecting scarification are the pore dimensions and the evaporable water content of the cement.

Thermal degradation uses a controlled high-temperature flame or arc, which is applied to the surface of a noncombustible workpiece in order to thermally degrade organic surface coatings. Scarifying of concrete has also been undertaken using both high-temperature flames[22] and plasma[47]. The local heating caused by the passage of the flame or arc causes differential expansion and spalling of the concrete surface.

In biodecontamination, a microbial solution is applied to the contaminated area, allowing the microbes to penetrate the surface and contact and consume the contamination. A detergent or solvent wash is then used to remove the reaction products. The technique could be useful for the in-situ removal of hazardous residues from the walls and floors, abandoned process equipment, storage tanks, sumps, piping, etc.

A new technique uses the flameless burning of powders containing Al, Mg, NaNO3, and oil. The powder is applied as a flat layer, approximately 10 mm thick, and is used to remove surface coatings from the concrete, e.g., asphalt.

In supercritical fluid extraction methods, liquefied CO2 is used as a solvent together with other chemical reagents. Tests show that 95 to 99% of radionuclides can be removed from the treated surfaces and CO2 evaporated to minimize residual volumes.[48]

Other emerging technologies include vapor-phase transport separation, gaseous decontamination,[49] catalytic extraction solvent washing,explosive removal,[2650] use of atmospheric pressure plasma tool[5152] for surface decontamination, and use of diamond wire cutting technology[53] for cutting of the vacuum vessel in tritium-fueled Fusion Test Reactor (TFTR). One oxidative tritium decontamination system[54] has been reported to reduce tritium surface contamination on various components and items. The system is configured to introduce gaseous ozone into a reaction chamber containing tritiated items that require a reduction in tritium surface contamination. Tritium surface contamination (on components and items in the reaction chamber) is removed by chemically reacting elemental tritium to tritium oxide via oxidation, while purging the reaction chamber effluent to a gas holding tank or negative pressure HVAC system. Implementing specific concentrations of ozone along with catalytic parameters, the system is able to significantly reduce surface tritium contamination on an assortment of expendable and nonexpendable items.

Generally abrasive-blasting techniques have proved effective. In many cases, the equipment is well-developed and commercially available. Industrial equipment is also available for remote operations.

Several methods remove tightly adherent material, including corrosion layers. Special tool for cleaning the inside of tanks and pipes are also available.

The abrasive-blasting techniques give results in a relatively short time.

Abrasive-blasting techniques generally produce a large amount of waste, if recirculation and/or recycling of abrasives and/or water is not available. In some cases, it is difficult to control the amount of base metal removed. In dry abrasive systems, dust-control measures are needed to control dust and/or airborne contamination. Wet abrasive systems also produce a mixture of dust and water droplets that might be difficult to treat.

Care must be taken not to introduce the contamination into the material surface (hammering effect) in order for the ability to meet clearance levels not to be jeopardized.

Electrochemical decontamination

Electrochemical decontamination may be considered in principle to be chemical decontamination assisted by an electrical field. Electropolishing is a process widely used in nonnuclear industrial applications to produce a smooth polished surface on metals and alloys. It may be considered the opposite of electroplating, as metal layers are removed from a surface rather than added as a coating.

Electrochemical decontamination uses direct electric current, which results in the anodic dissolution and removal of metal and oxide layer from the component. The dissolution may be conducted by immersing items to be decontaminated in an electrolyte bath as anode or fitted with anodes. This method is useful for decontaminating items with easily accessible surfaces. Current may also be delivered to a submerged component by moving a pad over the surface to be decontaminated, as an efficient method for regular surfaces. The electrolyte is continuously regenerated by recirculation.

For in-tank electropolishing, at least two (stainless steel) tanks are required. One tank contains the electrolyte, electrode, and parts to be contaminated. The other tank holds the water used for rinsing the parts after decontamination. Power supply amperages of up to 2700 A are common. To control vapors released from the electrolyte during the electropolishing process, an extraction hood is located along side the electropolishing tank. Provisions for heating and agitating the electrolyte as well as rinsing the tank are also required.

Electrochemical decontamination process may only be applied for removing radionuclide contamination from conducting surfaces, such as iron-based alloys (including stainless steel), copper, aluminium, lead, and molybdenum. They are highly effective and give high DF. Important operating parameters for electrochemical decontamination are electrolyte concentration, operating temperature, electrode potential, and current density.

The effectiveness of the decontamination may be limited by the presence of adhering materials on the surface of the items to be decontaminated. Materials such as oil, grease, oxide (rust) and paint, or other coatings should be removed before decontamination. The use of electrochemical decontamination is limited

when immersion is used, by the size of the bath and

when a pad is used by the geometry of the surfaces, and the available free space around the part being treated.

This makes this method almost inapplicable for all industrial decontamination of complex geometries (e.g., small-diameter pipes).

Chemical reagents

Phosphoric acid is normally used as electrolyte in electropolishing because of its stability, safety, and applicability to a variety of alloy systems. Moreover, the nondrying nature of the phosphoric acid helps minimize airborne contamination, and the good complexing characteristics of phosphoric acid for metal ions is a significant factor in minimizing recontamination from the electrolyte.

Other electrolytes, such as nitric acid and sodium sulphate have been proposed as alternatives to phosphoric acid and sulphuric acid.

Secondary waste generation

Electrochemical decontamination by electropolishing causes a steady increase of dissolved iron in the phosphoric acid. If the iron content exceeds 100 g/dm3, a precipitation of iron phosphate occurs, which stops the efficiency of the decontamination process. Therefore, the acid has to be exchanged or regenerated periodically. In doing so, the volume of effluents is limited; however, handling the parts to be immersed or the pad may lead to additional exposure to workers.

Electropolishing is commercially available. Major equipment is relatively inexpensive, and process and processing procedures fairly simple. It is capable of decontaminatingto background levels for decommissioning purposes, removing practically all radionuclides covering the surface, including plutonium, U, cobalt, strontium, cesium, and americium, giving typically DF of more than 100 : 1 decrease in activity levels.

Electropolishing may decontaminate flat area, corners, recessed geometries, tanks, etc. where measurements up to release level do not cause any problem. EIt produces a smooth polished surface with a low inherent ability to be recontaminated. The thickness of metal removed during decontamination is generally less than 25 μm.

When compared with the volume of liquids required for chemical decontamination, electrolyte volumes for electrode contamination are relatively low.

For the most widely used process (i.e., in tank), the items to be decontaminated must be removed from the plant and immersed in the tank with electrolyte. For the in-situ process, access or entry for the device into the item to be decontaminated is required. Therefore, the use of electrochemical decontamination is limited by the size of the bath when immersion is used, and by the geometries of the surfaces and the available free space around the part being treated, when a pad is used. This makes the method less applicable for industrial decontamination of complex geometries (e.g., small diameter pipes).

The treatment of the electrolyte for disposal (if not recyclable) requires neutralization and processing in a treatment system for liquid radioactive waste.

Electropolishing does not remove (or removes with difficulty) fuel fines, sludge, or any insulating material from the surfaces.

Hidden parts as the inside of tubes are treated poorly.

Handling of components may lead to additional exposure to workers.

Human decontamination for radiological emergencies

Like materials, humans may also be contaminated with radiological contamination. This may result from a radiation dispersal device or a nuclear reactor accident. The two most significant radiosensitive organ systems in the body are the hematopoietic and the gastrointestinal (GI) systems. The relative sensitivity of an organ to direct radiation injury depends upon its component tissue sensitivities. Cellular effects of radiation, whether due to direct or indirect damage, are basically the same for the different kinds and dose of radiation. The simplest effect is cell death. With this effect, the cell is no longer present to reproduce and perform its primary function.[55]

Changes in cellular function can occur at lower radiation doses than those that cause cell death. Changes can include delays in phases of the mitotic cycle, disrupted cell growth, permeability changes, and changes in motility.[56] In general, actively dividing cells are most sensitive to radiation. Radiosensitivity also tends to vary inversely with the degree of differentiation of the cell.

The severe radiation sickness resulting from external irradiation and its consequent organ effects is a primary medical concern. When appropriate medical care is not provided, the median lethal dose of radiation, the LD50/60 (which will kill 50% of the exposed persons within a period of 60 days), is estimated to be 3.5 Gy.

Recovery of a particular cell system is possible if a sufficient fraction of a given stem cell population remains after radiation injury. Although complete recovery may appear to occur, late somatic effects may have a higher probability of occurrence because of the radiation damage.[56]

A human may be contaminated externally or internally. External contamination by radionuclides will occur when a soldier traverses a contaminated area without appropriate barrier clothing. If the individual is wounded while in contaminated area, he will become an externally contaminated patient. The simple removal of outer clothing and shoe will, in most instances, effect a 90% reduction in the patient's contamination.[57] Open wound should be covered before decontamination. Contaminated clothing should be carefully removed, placed in marked plastic bag, and removed to a secure location within a contaminated area. Bare skin and hair should be thoroughly washed, and if practical, the effluent should be sequestered and disposed off appropriately. Radiological decontamination should never interfere with medical care. Unlike chemical agents, radioactive particles will not cause acute injury, and decontamination sufficient to remove chemical agents is more than sufficient to remove radiological contamination.[58]

Internal contamination will occur when unprotected personnel ingest, inhales, or wounded by radioactive material. An externally contaminated causality who did not have respiratory protection should be evaluated for internal contamination. The routes of intake are inhalation, ingestion, wound contamination, and skin absorption.

Within the respiratory tract, particles less than 5 μ in diameter may be deposited in the alveolar area. Larger particles will be cleared to the oropharynx by the mucociliary apparatus. Soluble particles will be either absorbed into the blood stream directly or pass through the lymphatic system. Insoluble particles, until cleared from the respiratory tract, will continue to irradiate surrounding tissues. In the alveoli, fibrosis and scarring are more likely to occur due to the localized inflammatory response.[59]

All swallowed radioactive material will be handled like any other element in the digestive tract. Absorption depends on the chemical makeup of the contaminant and its solubility. For example, radioiodine and cesium are rapidly absorbed; plutonium, radium, and strontium are not. The lower GI tract is considered the target organ for ingested insoluble radionuclides that pass unchanged in feces.[59]

The skin is impermeable to most radionuclides. Wounds and burns create a portal for any particulate contamination to bypass the epithelial barrier. All wounds must therefore be meticulously cleared and debrided, if they occur in a radiological environment. Any fluid in the wound may hide weak beta and alpha emission from detectors.[59]

Once a radionuclide is absorbed, it crosses capillary membrane through passive and active diffusion mechanisms and then it is distributed throughout the body. The rate of distribution to each organ is related to organ metabolism, the ease of chemical transport, and the affinity of the radionuclide for chemicals within the organ. The liver, kidney, adipose tissue, and bone have higher capacities for binding radionuclides because of their high protein and lipid makeup.[59]

General Aspects of Radiological Decontamination

Radiological decontamination is performed in an identical manner to doctrinal chemical decontamination. The main difference is in timing. In case of humans, if both types of contaminations are found, then chemical decontamination is the priority, as it is an emergency.[57]

Decontamination of causality is an enormous task. The process requires dedication of both large numbers of personnel and large amounts of time. Even with appropriate planning and training, the requirement demands a significant contribution of resources.

Removal of outer clothing and rapid washing of exposed skin and hair removes 95% of contamination. The 0.5% hypochlorite solution used for chemicals will also remove radiological contaminants. Care must be taken to not irritate the skin. If the skin becomes erythematous, some radionuclides can be absorbed directly through the skin. Surgical irrigation solutions should be used in liberal amounts in wounds, the abdomen, and the chest. All such solutions should be removed by suction instead of sponging and wiping. Only copious amounts of water, normal saline, or eye solution are recommended for the eye.

Radiological particulate transfer is a potential problem that can be resolved by a second deliberate decontamination. Decontamination at the medical treatment facility prevents spread of contamination to areas of the body previously uncontaminated, contamination of personnel assisting the patient, and contamination of the medical facility.[57]

Protection from hazard

The manpower working in a nuclear power plant may be at risk if enemy strikes these reactors and containment facilities. Downward service members could internalize significant amounts of iodine-131 and other fission byproducts.[59] MOPP (mission oriented protective posture) equipment will provide more than adequate protection from radiological contamination. The standard NBC protective mask will prevent inhalation of any particulate contamination. After prolong use in a contaminated area, filter should be checked with a radiac before disposal.

Normal hospital barrier clothing will provide satisfactory emergency protection for hospital personnel. Ideally, personnel attending a contaminated patient before his decontamination will wear anticontamination coveralls. After decontamination, no special clothing is indicated for medical personnel, as the patient presents no risk to medical care providers.[59]

Medical management of casualties of radiological emergencies

Treatment of internal contamination reduces the absorbed radiation dose and the risk of future biological effects. Administration of diluting and blocking agents enhances elimination rates of radionuclides.[59] Treatment with mobilizing or chelating agents should be initiated as soon as practical when the probable exposure is judged to be significant. Gastric lavage and emetics can be used to empty the stomach promptly and completely after the ingestion of poisonous materials. Purgatives, laxatives, and enemas can reduce the residence time of radioactive materials in the colon.

Ion exchange resins limit GI uptake of ingested or inhaled radionuclides.[59] Ferric ferrocyanide (Prussian blue; an investigational new drug, IND) and alginates have been used in humans to accelerate fecal excretion of cesium-137.

Blocking agents, such as stable iodine compounds, must be given as soon as possible after the exposure to radioiodine. A dose of 300 mg of iodide, as administered by a dose of 390 mg potassium iodide, blocks the uptake of radioiodine. When administered before exposure to radioiodine, 130 mg of daily oral potassium iodide will suffice.[59]

Mobilizing agents are more effective the sooner they are given after the exposure to the isotope. Propylthiouracil or methimazole may reduce the thyroid's retention of radioiodine. Increasing oral fluids increases tritium excretion.[59]

Chelating agents may be used to remove many metals from the body. Calcium edetate (EDTA) is used primarily to treat lead poisoning, but must be used with extreme caution in patients with preexisting renal disease. DTPA as IND is more effective in removing many of the heavy metals, multivalent radionuclides.[59]

The chelates are water soluble and excreted in urine. DTPA metal complexes are more stable than those of EDTA and are less likely to release the radionuclide before excretion. Repeated use of calcium salt can deplete zinc and cause trace metal deficiencies. Dimercaprol forms stable chelates with mercury, lead, arsenic, gold, bismuth, chromium, and nickel, and therefore may be considered for the treatment of internal contamination with the radioisotopes of these elements. Penicillamine chelates copper, iron, mercury, lead, gold, and possibly other heavy metals.[59]

Decontamination of patient in radiological emergencies

Routine patient decontamination is performed under the supervision of medical personnel. Moist cotton swabs of the nasal mucosa from both sides of the nose should be obtained, labeled, and sealed in separate bags. Significant decontamination will occur in the normal emergency evaluation of patients by careful removal and bagging of clothing.

In practical skin wash, water should be contained and held for disposal. If this water cannot be collected, flushing down standard drains is appropriate. Local water purification units should be notified of this action.[60]

Contaminated tourniquets are replaced with clean ones, and the sites of the original tourniquets are decontaminated. Splints are thoroughly decontaminated, but removed in the operating room, placed in a plastic bag, and sealed. Wounds should be covered when adjacent skin is decontaminated,[60] so that skin contaminants do not enter the wound.

Wound decontamination for radiological contamination

Removal of MOPP and other exterior garments during the course of resuscitation will remove nearly all contamination, except where the suit has been breached. During initial decontamination in the receiving areas, bandages are removed and the wounds are flushed; the bandages are replaced only if bleeding recurs. After determination that adequate decontamination has been obtained, the wound should again be thoroughly irrigated with saline or other physiologic solution. Aggressive surgery such as amputation or extensive exploration should not be undertaken to ‘eliminate radioactive contamination.’ Partial-thickness burns should be thoroughly irrigated and cleaned with mild solution to minimize irritation of the burned skin. Blisters should be left closed; open blisters should be irrigated and treated in accordance with appropriate burn protocols. In full-thickness burns, radioactive contaminants will slough in the eschar. As there is no circulation in the burned tissues, contaminants will remain in the layers of the dead tissue. Excision of wound is appropriate when surgically reasonable.[60] Radioactive contaminants will be in the wound surfaces and will be removed with the tissue.

DRDO Venture for Radiological Emergencies: Shudhika and Protective Clothing for Quick Response Medical Teams

The efficiency and effectiveness of the Management of emergencies, particularly for nuclear/radiation events, lies in judicious use of technologies and proper training. First and foremost thing of the medical management of nuclear and radiological emergency is adequate medical preparedness and capacity development needed for quick response. To effectively manage such scenario, item suitable for field conditions having ability to save time is an utmost requirement. Keeping this in view, INMAS has been working for development of such products and devices. A skin decontamination kit named ‘Shudhika’ has been developed as a part of INMAS initiative to achieve the target of converting the tacit knowledge related to medical management of radiation emergencies into explicit knowledge and to convert the same into ready-to-use techniques/products.

This kit named ‘Shudhika’ has been made in accordance with the Atomic Energy Regulatory Board and International Atomic Energy Agency guidelines issued from time to time for skin decontamination with respect to radioactive contaminants [Figure 5].

Figure 5

Shudhika-the skin decontamination kit

The skin decontamination kit, ‘Shudhika’ has been developed for use by the members of Quick Response Medical Teams (QRMT) for reducing the radiation load on the skin of the personnel exposed to radiation after the nuclear eventualities. Nuclear fallout will mostly be in the form of radioactive dust or rain. The main advantages of this kit include ease of use and user friendliness. The complete material of Shudhika is housed in a portable light-weight water-proof case with locking system. The case can be hanged around the neck and the kit material used for one-to-one decontamination. This kit also falls in the line of quick response category material to externally decontaminate the casualties exposed to radioactive contamination. Shudhika contains various items required for the skin decontamination under the broad category of Decontaminants and Medicare items. This kit is designed for managing/handling radiological emergencies including accidental spillage resulting in human contamination at various medical, agriculture, and industrial centers using radioactive nuclides.

Overall weight and dimensions

Length: 300 mm

Width: 250 mm

Height: 250 mm

Weight: 5.00 kg

Protective Clothing for the Quick Reaction Medical Team

Protective clothing [Figure 6] for QRMT has been designed and developed for the medical and paramedical staff of the QRMT, to manage and control radiocontamination in the event of radiological and nuclear disaster. Protection from radiocontamination needed for the medical first responders involved in evacuating the casualties and the medical and paramedical staff who will be responsible for their treatment.

Figure 6

Protective clothing for quick response al teams

The cloth material is water-proof and breathable. The later is important to comfort as it prevent accumulation of sweat that can cause dampness. The suit is made from high-strength polyester fabric, which is coated with a breathable polymer in the inner side of the clothing and water-proof coating on the outer side. The coated fabric (mean pore size of the fabric ≅ 3 μ) is impervious to wind, rain, sleet, snow, and α-particles and yet allows water vapor transmission by a molecular mechanism involving adsorption-diffusion- desorption. This protective clothing has been made as an integrated suit with built-in hood. Polyester adjustable cord with toggle is attached with hood. Two pockets are provided below the waist part. The pockets are protected with flaps. A legging bolt is provided for the adjustment of waist. Velcro is fitted to adjust the bottom part of the legging. One pair of detachable shoe cover is provided with this clothing. A nonmetallic anticorrosive zipper is attached at front.

There is a set of five protective clothing per QRMT and with different color codes and signage for the members of the QRMT. Overall weight and dimensions of the protective clothing are as follows.

Incident Site Decontamination

At the incident site, the dynamics of scenario with respect to meteorological condition (like rate of flow of wind and its direction), level of exposure, or contamination spread keeps on drifting. Thus, development of an ideal Incident Command Post is a complex process. In such post, there is an overlapping region of outward boundary of warm zone, i.e., where contamination spread is less than its threshold and main boundary of safe zone. The basic principle is that anybody entering in the safe zone (treatment or evacuation areas) needs to be decontaminated first.

Hospital Level Decontamination

An emergency response plan for hazardous materials incidents must be supported by adequate trained staffs who are able to respond to hazardous materials, because most likely they will have to tackle the exposed patients who have not been decontaminated at the scene. QRMTs should be developed with trained first-responders who are able to decontaminate contaminated victims. For response to an unknown hazard, necessary personal protective equipment should be available with teams. At the hospital level, the patient decontamination plan requires professional input from medical toxicologists, hazardous materials teams, industrial hygiene experts, and radiation safety officers. Among them, hazardous material specialist should lead the team for safety of decontamination operations. Hazardous materials specialists are individuals who respond with and provide support to technicians trained to perform decontamination activities at the hospital level. They also liaise with government and nongovernmental officials/stakeholders. They are trained as skilled technicians as well as competency training to lead the decontamination process.

An ideal one should have the following features: neutralization of all agents, safety (compound to be both nontoxic and noncorrosive), ease of application by hand, ready availability, rapid action, nonproduction of toxic end products, stability in long-term storage, short-term stability (after issue to unit/individual), affordability, nonenhancement of percutaneous agent absorption, no irritation potential, hypoallergenicity, and ease of disposal. Primarily salt water solution, soap, and warm (not hot) water are used to wash the wounds.

The most important and most effective decontamination of any radioactive chemical exposure is that decontamination is done within the first minute or two after exposure. This is self-decontamination, and this early action by the soldier will make the difference between survival (or minimal injury) and death (or severe injury). DRDO has developed a skin decontamination kit SHUDHIKA, which is widely acceptable for the purpose of contamination on the exposed victim or responder by the other person. However, self-decontamination, ready-to-use formulations are required to be developed to enhance the level of confidence and to reduce the chances of cross contamination. Therefore, there is an inevitable need of developing new modified decontamination formulations to minimize or mitigate the radiation injury risk. Literature review revealed that there is an urgent requirement to develop effective bioassays for screening of synthetic and herbal-based pharmaceutical alternatives for decontamination that can be applicable for self-utility with ease.

Knowledge about decontamination is widespread, though fitting into an integrated context is yet to be achieved by combining discrete islands of information. There is a need for the effective networking of these knowledge repositories based on standard products available world-wide. Self-decontamination procedures need to be broad spectrum and easy to use based on its multifunctionality. A product of such kind is not available as per the requirements of effectiveness posed by emergencies and its stockpile, by evaluating its usage in the normal operations in predisaster phase. Cosmetic effectiveness of cleanliness needs to be superimposed to enhance the requirement of removing the overburden of the agents from the body, which is the key for effective management of CBRN emergencies. Utility management and integration of technologies followed by dose optimization is a strategy envisioned in this process.

Conclusion

There are varieties of decontamination methods available. An evaluation of several considerations will determine which specific methods shall be applied. There is not a single comprehensive technology that will be applicable in all situations and all type of contamination, because nature and extent of contamination is different at different places. Therefore, a combination of methods chosen from various available methods is used to achieve optimum decontamination level.