The Nuclear and Industrial Safety Agency has concluded there are no problems in extending the operational life of the decades-old Mihama nuclear plant's No. 2 reactor by 10 years.
In July, the plant in Mihama, Fukui Prefecture, will have been in operation for 40 years.
NISA announced its finding at a NISA panel of nuclear experts on June 6.
Hiromitsu Ino, professor emeritus of materials science at the University of Tokyo who is a member of the expert panel, criticized the decision.
"It is not appropriate for NISA to conclude that the extension is OK," he said. "It's not NISA's job to draw such conclusions. That decision should only be given after a new nuclear regulatory agency (to replace NISA) is set up."
Even if the Mihama No. 2 reactor is granted a 10-year extension, the period will automatically be shortened to three years when an amended law to limit, in principle, the operational life of nuclear reactors to 40 years takes effect.
A further extension would require a re-examination under a new set of standards being drawn up because of the March 2011 disaster at the Fukushima No. 1 nuclear power plant.
The government submitted a bill to the current Diet session to amend the Law on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors. The bill is still under deliberation.
The government expects the provision to take effect in January. When that happens, all nuclear reactors that have operated for more than 40 years will be granted a three-year extension by way of a special exemption for the transitional period.
Although the bill includes a provision to allow for extensions of up to 20 years on request, Goshi Hosono, the Cabinet minister in charge of nuclear policy, has said such cases should be "exceptional."
An application for the extension was filed by Kansai Electric Power Co., operator of the Mihama nuclear plant, last July.
NISA has convened expert meetings since November to screen the application.
A similar extension can be endorsed only when adequate measures to withstand a major earthquake, along with proper maintenance and management, are in place.
NISA has concluded both measures to protect the Mihama reactor in a major earthquake, and KEPCO's maintenance plan for the coming 10 years, are adequate.
Under current legislation, NISA must endorse an extension of the operational life before the expiry of 40 years if an application has been filed, and if all requirements are met.
The Mihama No. 2 reactor has been offline since December for regular inspection, and there is no immediate prospect for its reactivation.
KEPCO has failed to submit to NISA the results of first-stage stress tests for the Mihama No. 2 reactor, although doing so is a precondition for a restart.
"We have yet to decide when to submit (the stress test results)," a KEPCO official said.
(This article was written by Ryuta Koike and Jin Nishikawa.)
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