Quantitative evaluation of conservatism included in the derivation of clearance level: a case study for major radionuclides

Clearance levels, which are estimated by the International Atomic Energy Agency as the activity concentration corresponding to an effective dose of 10 μSv per year, are widely used; however, it has been pointed out that there is a large conservatism in their estimation. In the present study, we have attempted to examine the conservatism included in the derivation of clearance levels by selecting major radionuclides, considering the “factor of conservatism” included in the parameter settings and applying data on the latest statistical information from Japan. As a result, the factor of conservatism for activity concentration corresponding to an effective dose of 10 μSv per year was evaluated to be approximately 2–17 for major radionuclides. It is useful to take into account the fact that such conservatism is presented in the treatment of uncertainty in conformity assessment or in discussions on the stability of regulatory standards.