Management of decommissioning low level radioactive wastes and clearance materials in Japan

For a commercial nuclear power plant, MITI (Ministry of International Trade and Industry, currently METI) recommended (June 1985) the following standard decommissioning process: system decontamination, safe storage for 5∼10 years, dismantling and removal. The decommissioning project on the first commercial power reactor, the Tokai power station of JAPCO, the Japan Atomic Power Co. was started in December 2001. The project will take 17 years and is therefore divided into three phases, and reactor structure will be dismantled at the third phase from 2011, after 10 years safe storage. At present, conventional facilities are removed, and radioactive wastes raised from these activities are of small amount and they are stored at the Tokai site. All radioactive wastes raised from decommissioning of the commercial nuclear power plants are classified as low level radioactive wastes in Japan. Those are divided into 3 categories from the viewpoint of disposal, in other words, 3 different types of disposal facility will be constructed. The Atomic Energy Commission (AEC) and the Nuclear Safety Commission (NSC) have concluded a disposal policy and basic regulatory concept of disposal of these wastes. Relatively high radioactive concentration waste, such as reactor internals, with relatively higher contamination, will be disposed of at 50-100m depth, so called intermediate depth repository. Based on the concept, utilities and Japan Nuclear Fuel Ltd. (JNFL) are carrying out basic study and site investigation. With respect to very low level radioactive wastes, whose radioactive nuclide concentration are exceeding clearance level, JAPCO started investigation on site characterization, to gather data on ground water level and flow rate, which will be utilized for safety assessment of VLLW disposal facility. NSC reviewed clearance level based on RG-S-1.7 'Application of the concept of Exclusion, Exemption and Clearance' issued by the IAEA. Establishment of regulations of clearance is now forwarded by NISA. JAPCO is preparing clearance measuring devices and rules of quality assurance. Public acceptance is also a very important issue for non-restricted use. The Tokai-1 decommissioning project plays an important role in demonstrating that the decommissioning of commercial nuclear power plant can be executed safely and economically, and for establishing the key technologies for future LWR decommissioning in Japan. (author)