An international team of nuclear safety experts has said that nuclear safety equipment suffered no significant damage at Kashiwazaki Kariwa, and that the lessons of last year's earthquake should be fed back into updated safety standards.
The International Atomic Energy Agency (IAEA) team was headed by Philippe Jamet, who led an August 2007 mission to the plant. Both of the fact-finding efforts came at the request of Japanese Nuclear and Industrial Safety Agency (Nisa), which took part in "open and constructive" discussions with the IAEA.
Jamet's group said that a lot of data had been gathered on the effects of the 6.8 magnitude Niigata-Chuetsu-Oki earthquake on the power plant's reactors. More data is still being collected and this must all be examined as a whole to understand the real effects of earthquakes on nuclear power plants. The IAEA team called for "an international cooperative effort which could expand ongoing Japanese studies and make a contribution to the evolution of international safety standards."
This event is a good example with which to build knowledge because of the size of the plant - seven reactors - and that the earthquake was unexpectedly large. It was not beyond the limit of the plant's ultimate safety, but it was beyond the strength the plant was designed to cope with without some damage. The plant was designed to contain potentially dangerous nuclear material for that strength of earthquake, but not necessarily to operate afterwards without serious repairs.
When the tremor hit on 16 July 2007 three reactors were in operation; one was in the start-up process; and three were already shut down to undergo periodic inspection. None suffered any significant damage, but checks and repairs continue.
The size of the earthquake had come as a surprise. The plant site is above deep fault lines, but these had been thought to be stable. Work to establish the status of the fault lines is underway.