Oi Nuclear Power Plant's No. 4 Reactor Achieves Criticality
FUKUI (Kyodo)--The No. 4 reactor at the Oi nuclear power plant in Fukui Prefecture reached criticality on Thursday morning following its reactivation the night before by its operator, Kansai Electric Power Co.
The 1.18 million kilowatt reactor is scheduled to begin power generation and transmission possibly on Saturday after checks on its turbines and start full operation on July 25.
The reactor is the second to go back online after all of Japan's commercial reactors were taken offline for regular checks in the wake of the March 2011 Fukushima nuclear crisis. The first to resume operation was the Oi plant's No. 3 reactor which was brought to full operation on July 9.
When the No. 4 reactor begins full operation, the government plans to remove power-saving targets for Chubu Electric Power Co., Hokuriku Electric Power Co. and Chugoku Electric Power Co., while further easing the target for Shikoku Electric Power Co. from 7 percent to 5 percent. However, it intends to maintain the 10 percent target -- recently reduced from 15 percent -- for Kansai Electric.
On Wednesday, the government's Nuclear and Industrial Safety Agency told Kansai Electric to reexamine some fault fracture zones, or soft earth layers, running under the Oi plant, after a number of experts highlighted the risk posed by them at a meeting a day earlier. Commenting on the issue, Senior Vice Minister of Economy, Trade and Industry Seishu Makino said he does not believe that there is a danger as great as to warrant halting of reactivation.
Kansai Electric reactivated the No. 4 reactor at 9 p.m. Wednesday by pulling out control rods which had been suppressing nuclear fission. In the presence of Makino, the utility carried out works for achieving criticality, or self-sustaining nuclear fission chain reaction, such as removal of control rods and adjustment of boron concentration in primary coolant water through early Thursday.
The No. 4 reactor was idled on July 22 last year for regular checks. Following the government's June 16 decision for reactivation, the reactor had been inspected together with the No. 3 reactor under a special monitoring regime involving the nuclear agency, Kansai Electric and the Fukui prefectural government.