Status of fast pulsed reactors in Japan

In this country, there exist two fast pulsed reactor projects, that is, pulsed YAYOI project and Linac Booster type pulsed reactor project. YAYOI is open to joint use of all universities in Japan and LB type pulsed reactor program is also a joint project of university union in Japan. For discussing and investigating these projects, the committee on fast pulsed neutron source reactor has been set up at Nuclear Engineering Research Laboratory of Univ. of Tokyo since 1972. The preliminary experiments for pulsed operation of YAYOI was started in 1973 and the pulsed operation was attained last December. The pulsed operation combined with Linac is also promised next year. Four kinds of pile oscillators are available as reactivity varying devices for YAYOI. Each oscillator can be used alone or combined with each other to make many different modes of reactivity addition. This reactivity pulsing procedure is a original one which has not yet been explored in the world. Linac program started in 1974 and the main machine is scheduled to be completed in this fiscal year. The repetitive fast pulsed reactor in Japan is based on the original concepts and is the combination of Booster, i.e., a sub-prompt critical reactor and electron Linac. This concept was selected from the stand point of safety and research benefit. This project is a long term research and development program. The investigation was started about 10 years ago as the research committee in Atomic Energy Society of Japan and the activity has been continued increasingly to performing fundamental research and mock up testing. (auth.)