20 Juillet 2012
July 20, 2012
FUKUI — Reactor 4 at the Oi nuclear power plant in Fukui Prefecture reached criticality Thursday morning following its reactivation the night before by Kansai Electric Power Co.
The 1.18-million-kw reactor is scheduled to begin generating and transmitting power Saturday after turbine checks, and reach full operation on July 25.
The reactor is the second to be brought back online since the use of nuclear power briefly ceased earlier this year. All commercial reactors were kept offline after regular checks as the Fukushima nuclear crisis rekindled nuclear safety fears in March 2011. The first to resume operation was Oi's reactor 3, which resumed full operation on July 9.
When reactor 4 reaches full operation, the power-saving targets issued by Chubu Electric Power Co., Hokuriku Electric Power Co. and Chugoku Electric Power Co. are expected to be scrapped, and the target for Shikoku Electric Power Co. is expected to be cut from 7 percent to 5 percent. The target for Kepco, however, is expected to be kept at 10 percent, following an earlier reduction from 15 percent.
On Wednesday, the Nuclear and Industrial Safety Agency told Kepco to re-examine fault fracture zones, or soft earth layers, running under the Oi plant, after experts pointed out the earthquake risks the previous day.
Seishu Makino, senior vice minister of economy, trade and industry, said he does not believe the danger is great enough to justify halting the restart process.
Kepco reactivated reactor 4 at 9 p.m. Wednesday by extracting the control rods used to moderate the fission reaction in the core. As Makino watched, the utility began adjusting the control rods and the boron level in the primary coolant water through early Thursday until it achieved a self-sustaining fission reaction.
Reactor 4 was idled on July 22 last year for regular checks. After the government decided June 16 to restart it, the unit was tested with reactor 3 under a special monitoring regime hastily drawn up by the nuclear safety agency, Kansai Electric and the Fukui Prefectural Government so its reactivation could proceed despite regional opposition.