Lessons learned from experiences on the first approval for clearance in Japan

In Japan, in December 2004, the special committee on radioactive waste disposal safety and decommissioning safety under the Nuclear Safety Commission (NSC) concluded that it would be appropriate to adopt the International Atomic Energy Agency (IAEA) safety guide RS-G-1.7 values as Japanese clearance levels from an international harmonization standpoint. Relevant regulations governing clearance levels in Japan have been in force since December 2005. The Standards Committee (SC) of the Atomic Energy Society of Japan (AESJ) started examining a nongovernmental standard of a clearance judgment method in May 2003. In the process of drafting the standard 'Monitoring for Compliance with Clearance Level', there were significant discussions on how to solve the problem of satisfying the clearance criterion while considering the uncertainties of the measurement and the nuclide spectrum. Taking into consideration the theoretical background to the definition of the dose criteria for exemption and clearance, a new approach to establishing an appropriate safety factor for the uncertainties of measurements and nuclide spectra was proposed, which was adopted as an AESJ standard and was also used in the first application and approval for clearance in Japan. (author)