Impact assessment of ionizing radiation on human and non-human biota from the vicinity of a near-surface radioactive waste repository.

This work describes the radiological assessment of the near-surface Maisiagala radioactive waste repository (Lithuania) over the period 2005-2012, with focus on water pathways and special emphasis on tritium. The study includes an assessment of the effect of post-closure upgrading, the durability of which is greater than 30 years. Both human and terrestrial non-human biota are considered, with local low-intensity forestry and small farms being the area of concern. The radiological exposure was evaluated using the RESRAD-OFFSITE, RESRAD-BIOTA and ERICA codes in combination with long-term data from a dedicated environmental monitoring programme. All measurements were performed at the Lithuanian Institute of Physics as part of this project. It is determined that, after repository upgrading, radiological exposure to humans are significantly lower than the human dose constraint of 0.2 mSv/year valid in the Republic of Lithuania. Likewise, for non-human biota, dose rates are below the ERICA/PROTECT screening levels. The potential annual effective inhalation dose that could be incurred by the highest-exposed human individual (which is due to tritiated water vapour airborne release over the most exposed area) does not exceed 0.1 μSv. Tritium-labelled drinking water appears to be the main pathway for human impact, representing about 83 % of the exposure. Annual committed effective dose (CED) values for members of the public consuming birch sap as medical practice are calculated to be several orders of magnitude below the CEDs for the same location associated with drinking of well water. The data presented here indicate that upper soil-layer samples may not provide a good indication of potential exposure to terrestrial deep-rooted trees, as demonstrated by an investigation of stratified (3)H in soil moisture, expressed on a wet soil mass basis, in an area with subsurface contamination.