At 10:13 am on July 16 a magnitude 6.8 earthquake struck off the coast of Niigata Prefecture on the Japan Sea side of Honshu, Japan's largest island. As a result of the quake, four reactors (units 2,3,4 & 7) at Tokyo Electric Power Company's (TEPCO) Kashiwazaki-Kariwa nuclear power plant shut down automatically. At the time, Unit 2 was being started up after a periodic inspection, while the other three units (1, 5, & 6) were still shut down for periodic inspection.
The suffering of the affected residents will continue for some time. The only fortunate thing amidst this misery is that the nuclear reactors shutdown. If they had not done so, there could have been a nuclear disaster in which large quantities of radioactive material was released into the environment.
As a result of the quake, a fire occurred in a transformer in unit 3. The transformer was part of the external electric power supply system. It is believed that the fire started in leaked insulating oil. The cause has not been announced, but it is likely that the oil leaked from cracks formed in equipment as a result of the earthquake. It took nearly two hours to extinguish the fire, apparently because of the time required to obtain the extinguishing agent. The fact that the plant was not prepared for an oil fire of this type was a serious oversight.
If transformers fail to operate, this can lead to a loss of external power supply. This is a very serious type of accident. In these circumstances diesel generators are supposed to start up, but emergency diesel generators are not completely reliable and it is possible that they could fail to start up in the case of an earthquake. Even after automatic shutdown, the fuel in the reactor core is still extremely hot, so it is necessary to maintain a continual flow of coolant. If it is not maintained, the fuel could melt, leading to the release of highly radioactive material into the environment. Under some circumstances, it could also result in an explosion. Despite the potential seriousness of this fire, TEPCO failed to announce whether the transformer continued to operate, or whether the emergency generator started up.
It was announced that water containing radioactive material was leaked from unit 6 into the sea. If the figure for the quantity of radioactivity released is correct (60,000 becquerels), one would not expect there to be any impact on the environment or on human health, but data should be published about the type of radionuclides released. Also, it must be said that TEPCO took much too long (six hours) to announce that the leak had occurred.
A proper analysis of the cause of the leak must be carried out. It is likely that the spent fuel pool overflowed, but TEPCO says it does not yet know the cause. Spent fuel pools frequently overflow during earthquakes. The fact that on this occasion radioactive material was released to sea shows that this problem had not been adequately addressed.
Information about the condition inside the plant buildings has not been announced, but there is no doubt that there would have been damage to walls and equipment. The earthquake design basis for this nuclear power plant assumed a so-called "extreme design earthquake". (The "extreme design earthquake" was thought to be impossible in reality, but it was chosen just to be on the safe side.) On this occasion the earthquake exceeded this so-called "extreme design earthquake". Indeed, based on the information released by TEPCO, for Unit 1 it was 2.5 times as strong as the "extreme design earthquake". It is said that this earthquake was caused by movement of a 30km long, 25km deep fault. This fault was not discovered during the surveys carried out for the design of the Kashiwazaiki-Kariwa nuclear power plant. Instead, a fault located 20 kilometers away was identified. The fault identified at that time was part of the fault which caused an earthquake in the same region in 2004.
Clearly Japan's earthquake safety standards are inadequate. This fact can no longer be disputed. Given that the size and location of this earthquake was not predicted, it is essential that a thorough geological survey be carried out of the surrounding area, both on land and at sea. This should be a top priority for TEPCO.
In just two years three earthquakes (off the coast of Miyagi Prefecture on 16 August 2005, off the Noto Peninsula in Ishikawa Prefecture on 25 March 2007, and now this one) have exceeded the "extreme design earthquake" assumed at the time the plants were built. In September 2006, for the first time in 28 years, the Nuclear Safety Commission revised Japan's earthquake guidelines. Japan's nuclear power companies are now carrying out earthquake safety checks on the basis of the new guidelines. By rights, all nuclear power plants should be shut down until these checks have been completed. The Nuclear Industrial and Safety Agency should review its approach of allowing safety checks to be carried out over a period of three years while the reactors continue to operate.
Hideyuki Ban (Co-Director)
Philip White (International Liaison Officer)
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