Kashiwazaki-Kariwa: Some Things Becoming Clearer Nuke Info Tokyo No. 122
In the six months since the Chuetsu-Oki Earthquake, several things which were hazy at first have become clearer. For example, the stance of Niigata Prefecture is clearer than it was before.
(1) Length of the fault
For the earthquake resistance design of the Kashiwazaki-Kariwa (K-K) nuclear power plant (based on the old guidelines) estimates were made of the length of the active faults in the vicinity of the plant, the magnitude of the earthquake if these faults were to shift and the seismic acceleration for the “maximum design earthquake” (S1) and “extreme design earthquake” (S2). However, as explained in NIT 121, the measured seismic acceleration far exceeded even the S2 estimate.
When applying for permission to construct K-K, in regard to the region of the seabed where the Chuetsu-Oki Earthquake occurred, the Tokyo Electric Power Company (TEPCO) informed the government that there were no prominent active faults. The government’s safety assessors accepted this judgment. However, when a team of geomorphologists reanalyzed the sonic testing data in the original application, they found that, even considering the level of scientific understanding at the time, it was clear that there was a fault exceeding 20 kilometers on the seabed. For the whole seabed the fault was 30 ~ 50 kilometers long, so an earthquake exceeding magnitude 7.3 could occur. On December 5, shortly after the team announced its findings, TEPCO acknowledged the existence of a 23-kilometer fault. In fact, TEPCO had reassessed the length of the fault and reported to the Nuclear Industrial and Safety Agency (NISA) in 2003 that the original figure was an under-estimate. They must have realized that the seismic acceleration might also be an underestimate, but neither TEPCO nor NISA disclosed this failure of the safety assessment system. As things have turned out, however, it is public knowledge now.
(2) Predictable earthquake
There was considerable debate about the fault surface that caused the Chuetsu-Oki Earthquake. No consensus had emerged, but on December 11 the government’s Earthquake Research Committee (within the Headquarters for Earthquake Research Promotion) handed down its conclusion. It found that the fault surface was 27 kilometers long and sloped south-east. The Committee also found a 10-kilometer north-west sloping fault surface that intersected the other fault in an X shape. The head of the survey team stated that had a detailed survey had been carried out it would have been possible to predict the earthquake, so the slipshod nature of the survey carried out by TEPCO and the government’s safety assessors is plain for all to see.
(3) Niigata Prefecture’s Stance
Niigata Prefecture, which is lumbered with the problem of what to do about the K-K nuclear power plant, set up a committee to develop a vision for recovery from the earthquake. The committee released its vision on December 27. It identified the high dependence of the affected region on the K-K nuclear power plant and the considerable loss of tax revenue and employment that this entails, due to the fact that it will be difficult to restart the plant in the short term. It recommended that dependence on the nuclear power plant be reduced and presented two scenarios, one assuming that the plant will be restarted and one assuming that it will not be restarted.
This is the first time in Japan that an official document has canvassed the possibility of closing down a nuclear power plant. Since the September session of the prefectural assembly, the governor has not changed his position, saying, “[The situation] is under review. Depending on the outcome of the review, it is possible that the plant will be closed down.” Also, Niigata Prefecture is strengthening its own technical committee and, rather than swallowing whatever the central government says, it intends to make its own judgments.
For its part, the central government has invited the IAEA to send a second investigation team. Twelve people will visit Japan from January 28 to February 1. Then on February 26 & 27, nuclear energy proponents who hope the plant will be restarted will gather in Kashiwazaki-Kariwa for an international symposium. The theme will be how nuclear reactors, equipment and materials withstand earthquakes.
Meanwhile, the government has established several review committees aimed at restarting the plant. The Group of Concerned Scientists and Engineers Calling for the Closure of the K-K Nuclear Power Plant is busily critiquing the activities of these committees. It has publicly submitted questions concerning the geology and ground on which the plant is based and it is preparing a second set of questions concerning equipment and materials of the reactor.
Yukio Yamaguchi (CNIC Co-Director)