http://www.japantimes.co.jp/text/nn20120727a1.html
Friday, July 27, 2012
Shika site faces seismic scrutiny
Tunnel eyed to probe fault at nuke plant
Jiji
Hokuriku Electric Power Co. plans to tunnel under the reactor 1 building at its Shika nuclear power plant in Ishikawa Prefecture to investigate a suspected active fault.
The utility submitted the plan to the Nuclear Industry and Safety Agency Wednesday. If experts give their approval at a hearing Tuesday, the company will begin boring this autumn. A final report is expected around January.
After re-examining documents submitted at the time of the plant's construction, the industry ministry's agency noted the S-1 fault under the southwestern part of the reactor 1 building may have been active in the late Pleistocene Epoch, 120,000-130,000 years ago, or later.
Under guidelines for evaluating the seismic resistance of nuclear plant designs, the fault could be deemed active, so NISA ordered the utility to check it again.
According to the plan, Hokuriku Electric will bore a vertical hole nearly 2 meters in diameter to a depth of 40 meters alongside the reactor building, then a horizontal 50-meter-long tunnel until just under the building.
The company will check the S-1 fault directly and conduct boring surveys at the nuclear plant's site. It will also examine faults around the plant site that could move with the S-1 fault.
On Wednesday, Kansai Electric Power Co. submitted a plan to study the F-6 fault under its Oi nuclear power plant in Fukui Prefecture. Kepco said it will draw up a final report by year's end.
Safety specifications of nuclear plants have long been questioned in quake-prone Japan. Among other things, the Fukushima nuclear crisis has highlighted safety concerns of those living around nuclear plants.
In a fresh development adding to local worries, Chubu Electric Power Co. said Wednesday that many parts of reactor 5 at its Hamaoka nuclear power station in Shizuoka Prefecture have been confirmed corroded.
The corrosion was apparently caused by the seawater that was found to have flowed into the reactor in May last year during work to halt the plant, Chubu Electric told a meeting with experts hosted by the NISA.
In announcing the interm results of its probe, Chubu Electric said corrosion affects the equipment that raises and lowers the control rods, which moderate the chain reaction in the core.
Work to halt the plant, which is in Omaezaki, Shizuoka Prefecture, began on orders from then Prime Minister Naoto Kan amid warnings that the poorly protected site could suffer the same quake-tsunami double-punch that knocked out Tokyo Electric Power Co.'s Fukushima No. 1 power plant in March 2011.
Some 400 tons of seawater are believed to have flowed into the reactor because 43 narrow tubes in a steam condenser were broken, and 5 tons of the total apparently reached the pressure vessel.
In addition, tubes in a different condenser have been deformed, apparently because of corrosion, the firm said.
Chubu Electric will carry out the probes until December before announcing full details. The industry ministry's agency said it will take years before it can tell prospects for the reactor.
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