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Mihama: What happened to 40-year rule?

August 4, 2016 (Mainichi Japan)


40-year rule for Japan's nuclear reactors sidelined as Mihama unit passes screening



The aging No. 3 reactor at Mihama Nuclear Power Plant in Fukui Prefecture, which Kansai Electric Power Co. is attempting to keep running beyond a designated 40-year lifespan for Japan's reactors, has cleared government screening under new safety standards.

The idled reactor, which started operating in December 1976, needs two additional sets of approval by the end of November before it can be restarted, but it has cleared the first hurdle in a process that could see the reactor kept in operation up until 2036.

It is the third time a reactor has effectively been given a pass for operating beyond the 40-year limit, indicating that the 40-year rule is being hollowed out.

In the wake of the meltdowns at the Fukushima No. 1 Nuclear Power Plant following the March 2011 Great East Japan Earthquake and tsunami, a change to Japanese law set the life of Japan's nuclear reactors at 40 years in principle. Under legislation, it is possible to extend the life of each reactor once for an additional 20 years, but such a move is designated as an "exception."

It had been thought that extending the life of the Mihama reactor would be difficult due to its old design and the deadline for screening, but Kansai Electric set apart 165 billion yen for safety measures and overcame these difficulties.

The power company raised the estimate for standard ground motion at the No. 3 reactor -- a measure of the maximum level of shaking that it would be subjected to during an earthquake -- to 993 gals, 1.3 times higher than the original figure. A gal is a unit of acceleration, with 1 gal defined as 1 centimeter per second squared. The company also announced major design changes, including the conversion of a storage rack for spent nuclear fuel at the reactor, whose design was old and was deemed unable to endure the maximum level of shaking, into a movable system, and the renewal of structures supporting nuclear fuel within the reactor.

There are no movable racks at other nuclear power plants in Japan, but the Nuclear Regulation Authority (NRA) judged that the design was suitable. Work to confirm whether new structures within the reactor would be able to withstand shaking was delayed until after the screening deadline.

Extended operation of the Mihama No. 3 reactor will be permitted by the end of November, and the power company hopes to restart the reactor as early as the spring of 2020. Shunichi Tanaka, chairman of the NRA, has stated, "If power companies are prepared to make any level of investment, then 40 years is not an issue."

His comment indicates that the extension of the operating life of reactors as an "exception" would be permitted if the utility spent money on safety measures.



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