Recent progress in safety assessments of Japanese water-cooled solid breeder test blanket module

This paper presents summary of preliminary safety assessment of the water-cooled solid breeder (WCSB) test blanket module (TBM) proposed by Japan for the ITER TBM test program. For the purpose of basic evaluation of source terms on nuclear heating and radioactivity generation, distribution of neutron flux, tritium breeding ratio, nuclear heating, decay heat and induced activity of radioactive waste are calculated. For the purpose of occupational radiological exposure evaluation, radiological isotope (RI) inventories, i.e., tritium in the breeder pebble bed, tritium in purge gas, permeated tritium in cooling system and active corrosion product (ACP) in the cooling system, are estimated. Failure mode effect analysis (FMEA) has been carried out for identification of the postulated initiating events (PIEs) that need safety evaluation. The PIEs are summarized into three groups, i.e., release of RI, pressurization and heatup. With respect to PIEs about release of RI, the maximum released RI is evaluated for three RI inventories, i.e., RI in vacuum vessel (VV) (tritium and radioactive dust), RI in purge gas (tritium) and RI in coolant (tritium and ACP). With respect to the PIEs about pressurization, the maximum pressures of the compartments nearby the pipes of cooling system are evaluated.