The Kashiwazaki-Kariwa Nuclear Power Plant in Japan, affected by a strong earthquake on 16 July, shut down safely and damage appears less than expected, a fact-finding mission of international nuclear safety experts has concluded. The six member expert team of the International Atomic Energy Agency was dispatched upon the request of the Japanese authorities. The mission report will be issued within a few days. The Director General of the IAEA, Mohamed ElBaradei, said today that he welcomed the cooperation and transparency the team had received from the Japanese authorities. The mission´s findings and the Japanese analyses of the event include important lessons learned - both positive and negative - that will be relevant to other nuclear plants worldwide, he said. The team conducted a three-day physical examination covering the complex of seven units, as well as analysis of instrument logs and other records from the time of the event. It has concluded that plant safety features performed as required during the earthquake. The team´s review of plant operator records and analyses support the Japanese authorities´ conclusion that the very small amount of radioactivity released was well below the authorized limits for public health and environmental safety. Damage from the earthquake appears to be limited to those sections of the plant that would not affect the reactor or systems related to reactor safety. Detailed checks and inspections by the operator and Japanese authorities are ongoing. According to the IAEA team, significant work, such as detailed examination of the reactor vessels, cores and fuel elements, has still to be performed. Physical stresses resulting from the earthquake could affect the long-term safe operation of some plant components, the team said. Additional engineering analysis of such components would be an important consideration for future examination, to determine whether they should be replaced earlier than otherwise anticipated. The earthquake significantly exceeded the level of seismic activity for which the plant was designed. However, as with most nuclear plants, additional robustness in design (known to the industry as "design safety margin") 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 it could have otherwise been expected. However, it was essential to conduct further technical analysis to understand the precise design elements that resulted in the plant performance. 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). With the occurrence of the 16 July 2007 earthquake, these evaluations will be expanded to account for the potential existence of active faults underneath the site, the team said. Analyses of safety events at nuclear facilities are routinely communicated to other nuclear operators and nuclear regulators, so that lessons learned can be incorporated where relevant at other plants. An opportunity for such feedback on the earthquake that affected the Kashiwazaki-Kariwa plant will occur in September, when Japan will present a report on the event to a Senior Regulators Meeting at the IAEA General Conference.
