Test strategy and development achievements of ITER solid breeder test blanket modules in Japan

This paper presents progresses of the test strategy development, design and supporting R and Ds of solid breeder TBMs in Japan. Japan is proposing to test its unique designs of water cooled solid breeder (WCSB) and helium cooled solid breeder (HCSB) TBMs from the beginning of the ITER operation. Water cooled solid breeder blanket has the better capability of heat removal and applicability to the more compact and economical fusion reactors. On the other hand, if it uses beryllium pebble beds as the neutron multiplier, it has the potential safety concern of thermo-chemical excursion of water and beryllium reaction in the case of the coolant water ingress in the beryllium pebble beds. Safety analysis of the WCSB TBM showed the possible preventive measures to such a case in TBM tests in ITER. Also, to void such potential safety concern, the advanced multiplier material, Be-Ti alloy, is under development in Japan because it has very low reactivity with water even in high temperature. Helium gas coolant has less heat removal capability but higher safety to thermo-chemical excursion phenomena. As for the design work, structure design showed steady progress and clarified detailed structure taking into account the fabrication procedure. As for supporting R and Ds, the corrosion characteristics of the structural material by high temperature and pressure water was clarified as one of critical structure integrity issues. Also, important design data of the breeder pebble bed has been clarified. Along with the development progress, the test strategy has been investigated to obtain the most effective results of test blanket module test program. (author)