Japanese nuclear plant hit by quake shut down safely, UN expert team concludes

A Japanese nuclear power plant damaged by a strong earthquake last month shut down safely, and the very small amount of radioactivity released was well below the authorized limits for public health and environmental safety, according to a United Nations-sponsored fact-finding team of international nuclear safety experts.

But physical stresses resulting from the quake could affect the long-term safe operation of some plant components at the Kashiwazaki Kariwa plant and the mission’s findings and Japanese analyses include important lessons, both positive and negative, that will be relevant to other nuclear plants worldwide, UN International Atomic Energy Agency (IAEA) Director General Mohamed ElBaradei said.

The six-member team, assembled by the IAEA at the request of the Japanese Government, found that damage appears less than expected, and in a statement Mr. ElBaradei welcomed the cooperation and transparency afforded by the authorities. The mission’s full report will be issued shortly.

The team, which conducted a three-day physical examination of the seven-unit complex as well as an analysis of instrument logs and other records, concluded that plant safety features performed as required during the quake, supporting the Japanese authorities’ conclusion that the radioactivity released was well below authorized limits for public health and environmental safety.

Damage appears to be limited to those sections that would not affect the reactor or systems related to reactor safety. Detailed checks and inspections by the operator and Japanese authorities are ongoing and significant work, such as detailed examination of the reactor vessels, cores and fuel elements, has still to be performed, the mission said.

Additional engineering analysis of some components would be an important consideration for determining whether they should be replaced earlier than otherwise anticipated, the team of two IAEA experts and four other specialists added.

The quake significantly exceeded the level of seismic activity for which the plant was designed, but as with most nuclear plants additional robustness in design, known as a design safety margin, had been incorporated into the structures, systems and components, probably explaining why damage was less than could have otherwise been expected.

However, experts cautioned that conduct further technical analysis is essential to understand the precise design elements that resulted in the plant performance.