Measures for inadvertent human intrusion at radioactive waste disposal facility based on defence-in-depth approach

The Nuclear Regulation Authority, Japan, established the regulatory requirements for the intermediate-depth disposal of intermediate-level radioactive waste in October 2021. Regarding the inadvertent human intrusion to the intermediate-depth disposal facility, some measures are required in the requirements and will be taken in the design of the facility or in the site selection process. The international standards provided by the IAEA and ICRP have stipulated the needs for measures against human intrusion and the evaluation of human intrusion scenarios as part of safety case. In this paper, we attempt to classify these measures against inadvertent human intrusion and clarify their objectives and functions from the viewpoint of the defence-in-depth approach that has been widely applied in the safety strategy of nuclear installations for preventing accidents and mitigating their consequences. Additionally, effectiveness evaluations of such measures are discussed taking into account some examples of scenarios that have been proposed thus far. (author)