14 Aug (NucNet): The Kashiwazaki Kariwa nuclear power plant in Japan, affected by a strong earthquake on 16 July 2007, shut down safely and damage appears less than expected, a team of nuclear safety experts has concluded.
The International Atomic Energy Agency (IAEA) team was dispatched after a request from the Japanese authorities. The team’s report will be issued within a few days, the IAEA said in a statement today.
The team carried out a three-day physical examination covering the complex of seven nuclear units, as well as analysis of instrument logs and other records from the time of the event. The team has concluded that plant safety features performed as required during the earthquake.
The IAEA said the team’s review supports the Japanese authorities’ conclusion that the very small amount of radioactivity released was well below authorised limits for public health and environmental safety.
Damage from the earthquake appears to be limited to sections of the plant that would not affect the reactor or systems related to reactor safety, the IAEA said.
Detailed inspections are being carried out by the operator and Japanese authorities, with work such as detailed examination of the reactor vessels, cores and fuel elements, still to be performed.
The earthquake “significantly exceeded” the level of seismic activity for which the plant was designed, the IAEA said. However, as with most nuclear plants, additional robustness in design had been incorporated into plant structures, systems and components. The IAEA team said these conservative seismic design measures probably explain why damage was less than could otherwise have been expected. However, it was essential to conduct further technical analysis to understand the precise design elements that resulted in the plant performance, today’s statement said.
The team noted that the plant owner, Tokyo Electric Power Company (Tepco), was at the time of the event already performing a seismic hazard re-evaluation based on new guidelines for seismic design that had been issued in September 2006 by Japan's Nuclear Safety Commission (NSC). Because of the July earthquake, these evaluations will be expanded to account for the potential existence of active faults underneath the site, the team said.
The earthquake led to the automatic shut-down of three units at the plant. Units 3, 4 and 7 shut down safely. Units 1, 5 and 6 were already shut down at the time of the quake for periodic inspections. Unit 2 was technically undergoing a periodic inspection and start-up operations had just begun, but the unit was also shut down safely.
