Disposal of very low-level radioactive waste: Lithuanian case on the approach and long-term safety aspects.

Decommissioning of nuclear power plants typically requires management of hundreds of thousands of cubic meters of waste with very low levels of radioactivity. Such very low-level waste (VLLW) is suitable for disposal in simple landfill type facilities. The only nuclear power plant in the Republic of Lithuania, the Ignalina NPP, was finally shut down at the end of 2009. Final management of the existing operational radioactive waste and that arising during the decommissioning will require the disposal of 60,000 m3 of very low-level short-lived solid waste. An overview of the implementation of the landfill disposal facility for very low-level radioactive waste at the Ignalina NPP site and the main aspects of long-term safety assessments based on national regulations as well as the IAEA's recommendations including the siting process are presented in this paper as well as a short description of the disposal concept and the characteristics of the waste intended for disposal in the landfill. Water pathway scenarios as well as intrusion scenarios have been investigated following an IAEA methodology. It has been defined that 14C is the greatest contributor to the total dose in the case of water pathway scenarios. In the case of intrusion scenarios, the main contribution to the total dose is from radionuclides 94Nb and 137Cs. In all the considered cases, the total value of the annual effective exposure dose remains quite well (orders of magnitude) below the value of the dose constraint established by regulations of Lithuania. Uncertainty analysis is carried out to define the influence of various factors on the obtained results of the safety assessment.