Who's next?

August 12, 2015

Next reactor to be reactivated following Sendai restart remains unknown

http://mainichi.jp/english/english/newsselect/news/20150812p2a00m0na011000c.html

After the No. 1 reactor at the Sendai Nuclear Power Plant in Kagoshima Prefecture was reactivated on Aug. 11, attention is being focused on which reactor will be brought back online next.

The No. 3 and No. 4 reactors at Kansai Electric Power Co.'s Takahama Nuclear Power Plant in Fukui Prefecture and the No. 3 reactor at Shikoku Electric Power Co.'s Ikata Nuclear Power Plant are deemed viable candidates for reactivation as they have already cleared safety screenings. But it is difficult to predict when they will be reactivated because the two nuclear plants face some challenges.

Of a total of 46 reactors at 17 nuclear plants in Japan, including three reactors that have been under construction, applications for the Nuclear Regulation Authority's safety screenings have been filed for 25 reactors at 15 nuclear plants. Of those reactors under application for safety screenings, 10 reactors at eight nuclear power plants are boiling water reactors (BWRs) -- the same type as that of the crippled reactors at the Fukushima No. 1 Nuclear Power Plant -- and 15 other reactors at seven nuclear plants are pressurized water reactors (PWRs) that are different from the Fukushima reactors.

The No. 3 and No. 4 reactors at the Takahama Nuclear Power Plant and the No. 3 reactor at the Ikata Nuclear Power Plant, all of which have passed the NRA's safety screenings, are PWRs -- the same type as that of the reactors at the Sendai Nuclear Power Plant. The reactors at the two nuclear plants are closest to reactivation, but the Takahama reactors cannot be reactivated for the time being because the Fukui District Court handed down a provisional injunction against their reactivation. The reactor at the Ikata nuclear plant looks difficult to be reactivated by the end of this year as Ehime Gov. Tokihiro Nakamura said he had not decided whether to give the green light for its reactivation.

PWRs are not required to be equipped with filtered vent systems -- which are designed to curb the discharge of radioactive substances in the event of a severe accident -- for now because their containment vessels are larger in capacity than those of BWRs so that pressure cannot build up easily in the vessels.

On the other hand, it takes longer to conduct safety screenings on BWRs that are not free of such requirements. The NRA plans to carry out safety screenings intensively on the No. 6 and 7 reactors that are of a new type at Tokyo Electric Power Co.'s Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture as a model case to make the screening process efficient. But it remains unclear when the NRA will do so. It is also difficult to reactivate Hokuriku Electric Power Co.'s Shika Nuclear Power Plant in Ishikawa Prefecture because the NRA's experts suggested the possibility of active fault lines running under the premises of the nuclear complex.

The NRA, meanwhile, has set the lifespan of a reactor at 40 years as a general rule after starting to operate. Therefore, the earlier a reactor started its operation, the more difficult it becomes to conduct a safety screening. One of the reasons is that new standards require measures to make electric cables flame-retardant. Seven reactors, including those at the Takahama Nuclear Power Plant, use electric cables made of flammable materials. Therefore, unless fire prevention measures are taken for an electric cable of several hundred kilometers at each reactor, it cannot pass a safety screening.

The government plans to give the green light for reactivation of nuclear reactors that have passed "new regulatory standards," but NRA Chairman Shunichi Tanaka has said, "The requirements under the new standards are considerably high. Utility firms are struggling over screenings, but we can't make them easy."