IAEA says Japan underestimated tsunami threat

TOKYO: Japan underestimated the hazard posed by tsunamis to nuclear plants, the UN atomic watchdog said on Wednesday, while praising Tokyo's response to the March 11 disaster as "exemplary".

The massive seabed quake and tsunami caused the world's worst nuclear disaster since Chernobyl 25 years ago at the Fukushima Daiichi plant, which has since leaked radiation into the soil, air and sea.

The UN's International Atomic Energy Agency (IAEA) sent an 18-member team of its own experts and specialists from 12 countries including the United States, China, Russia and South Korea on a fact-finding mission to Japan.

"The tsunami hazard for several sites was underestimated," said the IAEA team in a preliminary report to Japan's government, ahead of a full report to be presented in Vienna later this month.

"Nuclear designers and operators should appropriately evaluate and protect against the risks of all natural hazards, and should periodically update those assessments and assessment methodologies," it said.

The 14-metre (45-foot) wave that slammed into the plant knocked out reactor cooling systems and backup power systems, causing partial fuel meltdowns and forcing emergency crew to douse reactors with water since then.

The IAEA report on lessons learnt from the disaster said that plants should be designed to withstand "extreme external events, particularly those with common mode implications such as extreme floods".

The report also said that at nuclear plants "simple effective robust equipment should be available to restore essential safety functions in a timely way for severe accident conditions".

The IAEA mission also said that the independence of nuclear watchdogs must be ensured. Japan's system has been criticised because its regulatory agency is part of a ministry that actively promotes nuclear power.

"Nuclear regulatory systems should address extreme external events adequately, including their periodic review, and should ensure that regulatory independence and clarity of roles are preserved in all circumstances in line with IAEA Safety Standards," said the preliminary report.

The team said Japan's government, plant operators and agencies had been "extremely open in sharing information" during their visit, and praised the country's initial response to the disaster.

"The response on the site by dedicated, determined and expert staff, under extremely arduous conditions has been exemplary and resulted in the best approach to securing safety given the exceptional circumstances," it said.

"The Japanese government's longer term response to protect the public, including evacuation, has been impressive and extremely well organised."

It added that "a suitable and timely follow-up programme on public and worker exposures and health monitoring would be beneficial."

Copyright AFP (Agence France-Presse), 2011