JRR-2 decommissioning activity (2)

The Japan Research Reactor No.2 (JRR-2) was a 10 MW, heavy water moderated and cooled, multi purpose research reactor which used enriched uranium fuel. Since the first criticality in October 1960, JRR-2 had been operated approximately 36 years for various experiments, such as irradiation of fuels and materials, neutron beam experiment, radioisotope production and Boron Neutron Capture Therapy (BNCT). However, JRR-2 was permanently shut down in December 1996 in accordance with JAERI's long term plan released in January 1996 and the legal application for the decommissioning of JRR-2 was submitted to the Science and Technology Agency (STA) in May 1997. Decommissioning of the JRR-2 was planed for 11 years from 1997 to 2007 and the program was divided into 4 phases. Decommissioning activity started in August 1997 according to the program that reactor building to be remained after one piece removal of the reactor at the phase-4 would be used for effective demand. The phase-1 (permanent reactor shutdown), phase 2 (isolation of cooling system and seal of reactor) and the phase-3 (dismantling of the reactor cooling systems) had already completed as planned in March 1998, February 2000, February 2004, respectively. In the original decommission program of JRR-2, the phase-4 was expected to start in 2004 and would finish at 2007. However, in order to reduce radioactive wastes arising from the phase-4 activity, the decommissioning program was revised to maintain the reactor to be kept in safe storage. In this report which is a sequel of 'JRR-2 decommissioning activity (1)' the decommissioning activities, radioactive wastes and exposure dose of workers in the latter half of phase-3 are described. (author)