29 Mars 2012
The nuclear safety agency on Wednesday endorsed Kansai Electric Power Co.'s assessment that the idled Nos. 3 and 4 reactors at its Oi nuclear power plant would be able to withstand a powerful multi-fault earthquake, officials said.
By concluding KEPCO's earthquake-resistance safety projection was "appropriate," the Economy, Trade and Industry Ministry's Nuclear and Industrial Safety Agency has completed its technical evaluation concerning the safety of the two reactors at the plant in Oi, Fukui Prefecture, according to the officials.
The reactors have been idle since being taken offline for regular safety checkups.
Prime Minister Yoshihiko Noda and three ministers in charge of nuclear policies will make a final confirmation of the reactors' safety. Following this, Economy, Trade and Industry Minister Yukio Edano will visit Fukui Prefecture as early as next month to brief local governments on the central government's stance and ask their opinions on resuming the reactors. The central government will then make a final decision on reactivation, the officials said.
KEPCO conducted stress tests on the two reactors as part of preconditions for resuming their operations. Its primary stress test results showed they could withstand a quake 1.8 times the strength of a quake predicted to hit the area.
While assessing the results, however, NISA instructed nuclear power plant operators to consider scenarios in which active fault lines at least five kilometers from each other move simultaneously.
If estimated seismic waves were upwardly revised, the results of previous stress tests would have to be reviewed.
In the case of the Oi nuclear power plant, the focus has been placed on a scenario in which three nearby active faults shift together, according to the officials.
NISA on Wednesday concluded such a phenomenon is unlikely "because each fault is located far from the others." It also approved KEPCO's projection that seismic waves triggered by the three active faults' synchronization would not exceed 1.8 times the conventional projection, the officials said.
However, the agency concluded that two or more active faults could move simultaneously at six other nuclear power plants, and instructed their operators to recalculate seismic wave assumptions.
The six facilities are Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture; Hokuriku Electric Power Co.'s Shika nuclear power plant in Ishikawa Prefecture; the Japan Atomic Power Co.'s Tsuruga nuclear power plant, Japan Atomic Energy Agency's Monju prototype fast-breeder reactor and KEPCO's Mihama nuclear power plant, which are in Fukui Prefecture; and Chugoku Electric Power Co.'s Shimane nuclear power plant in Shimane Prefecture.
Regarding the Japan Atomic Power's Tokai No. 2 nuclear power plant and JAEA's Tokai Reprocessing Plant--both in Ibaraki Prefecture--NISA concluded seismic waves associated with the movements on nearby active faults would not exceed those of a presumed subduction quake in the Pacific, according to the officials.
The agency also said it would instruct the operators of other nuclear power plants to examine whether they could withstand a magnitude-9 subduction quake. These facilities include Chubu Electric Power Co.'s Hamaoka nuclear power plant in Shizuoka Prefecture; Tohoku Electric Power Co.'s Higashidori nuclear power plant in Aomori Prefecture; and Tohoku Electric's Onagawa nuclear power plant in Miyagi Prefecture, the officials said.
(Mar. 29, 2012)