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A six-member team from the International Atomic Energy Agency’s Nuclear Installation Safety Division has finished a four-day inspection of Tokyo Electric Power Co.’s Kashiwazaki-Kariwa nuclear-power station, which was damaged by a major earthquake July 16. The IAEA team’s task was to find out what actually happened at the power station, the world’s largest in terms of electrical output. It is hoped that not only the Japanese government and nuclear-power industry but also the governments and power industries of other countries can learn from the IAEA inspectors’ findings and implement measures as needed.

The Kashiwazaki-Kariwa nuclear plant was hit by tremors stronger than those assumed possible in the design — casting doubts on design guidelines that had been revised in September 2006 for the first time in 25 years. The design strength was for a magnitude-6.5 earthquake occurring directly beneath the power station. But a magnitude-6.8 quake occurred in the Sea of Japan, only 9 km northeast of the nuclear-power plant. It is possible that the fault that caused the quake runs directly beneath the nuclear plant. The government and industry cannot avoid reconsidering the assumptions used in the design.

Although water and exhaust gas containing tiny amounts of radioactive materials were released into the sea and air, there was no major radioactive leakage. Four of the plant’s seven reactors automatically shut down; the other three were undergoing regular checks. The IAEA team discussed operational management with TEPCO, but reportedly did not inspect reactor pressure vessels. TEPCO will have to carefully examine the pressure vessels and reactor cores before resuming operation. The IAEA team leader said restarting the plant could take as long as a year.

Some local government officials had expressed the hope that the IAEA team would dispel rumors that the area might have been contaminated with radioactive material. But this task must be borne by TEPCO and the central and local governments. It is their job to explain what happened fully and, by so doing, regain the trust of the people.

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