2020 年 55 巻 2 号 p. 86-91
Safety cases for disposal of uranium bearing waste and NORM with uranium has not yet been fully developed in Japan, because of safety assessment of extraordinary long timespan and uncertainty in unexpected incidents with uncompleted radon impact evaluation measures arising from uranium waste disposal facility in far future. Our task group of radiation protection for wastes with natural radioactive nuclides studied some safety cases with disposal of uranium bearing waste and NORM in terms of nuclides, 235U, 238U and their progenies, and comprehensively discussed the current state of their disposal in comparison to the ideas of international organizations such as ICRP and IAEA. We developed our ideas with the knowledge of experts in each related area of direction, repeating discussions, focusing out the orientation of each directions, and outlined the recommendations with our suggestions of solving important issues in the future to be addressed.
1. As for the exemption, for the dose levels for NORM and NORM waste, it is desirable that 10 μSv per year is not applicable and the dose shall not exceed approximately 1 mSv/year, considering the regional differences of natural background in Japan.
2. Regarding safety assessment of waste disposal, establishing radiological protection criteria is desirable, which divides the assessment period in two stages, namely, with relatively small uncertainty period (previous period) and a large uncertainty period with less accurate prediction phase (latter period).
3. The following three points are suggested as the most important issues that should be urgently resolved.
1) Safety assessment for radon from disposal facility in uranium waste mainly with regard to the potential exposure, exemption by low activity specific concentrations, or existing situation as combination of natural radon at the disposal site and radon generated from the waste.
2) Examination of the clearance level for disposal in uranium bearing waste.
3) Consideration to the sociological aspect.