Japan underestimated tsunami threat at Fukushima, U.N. experts say

Japan did not properly protect its nuclear plants against the threat of tsunami before the March 11 disaster that caused radiation to spew from the Fukushima Daiichi facility, concludes a preliminary report released Wednesday by international nuclear experts.

“The tsunami hazard for several sites was underestimated,” says a three-page summary released by a United Nations nuclear safety team investigating the aftermath of a magnitude 9 earthquake that triggered a nearly 50-foot-high wall of water, deluging the plant.

That miscalculation led to meltdowns in three of the facility’s six reactors, which caused the release of harmful radioactive isotopes into the air, soil and seawater. The emergency prompted the evacuation of more than 80,000 residents.

The report by the International Atomic Energy Agency, which was compiled by nuclear experts from a dozen nations, including the United States, France, Russia and China, says the tsunami was the cause of power failures that quickly caused the disaster to spiral out of control. Inspectors said waves believed to have reached 49 feet in height overwhelmed the plant’s defenses.

“In terms of the cause, it is clear: The direct cause was a tsunami, associated with an earthquake of tremendous size,” fact-finding team leader Michael Weightman, a Briton, told reporters in Tokyo.

Although characterizing Japan’s response to the disaster as “exemplary,” the report calls for nuclear plant designers and operators to better coordinate safety preparations at more than a dozen facilities nationwide.

Investigators also urge regulatory officials to better monitor the effects of prolonged radiation exposure on the public and nuclear workers at the crippled plant, 150 miles north of Tokyo.

The full report is scheduled for release this month at an IAEA conference in Vienna.

The report summary was released a day after Japan’s Health Ministry ordered Tokyo Electric Power Co., which operates the stricken plant, to correct deficiencies in protection of workers from radiation exposure.

The company, known as Tepco, acknowledged this week that two employees who were in the plant’s central control room when a hydrogen explosion occurred during the March disaster might have been exposed to radiation in excess of the government limit of 250 millisieverts for male workers. The utility company says the men are undergoing further tests and show no immediate health issues.

Tepco says the two workers apparently did not take the protective potassium iodide pills required by the company. Potassium iodide is believed to prevent the buildup of radioactive iodine in the thyroid gland. Both workers recorded high iodine levels in their thyroid glands, company executives acknowledge.

The utility has come under fire for failing to fully disclose the extent of radiation exposure faced by plant workers or measures taken to ensure their safety.

Tepco spokesman Ken Matsuda said Wednesday that the utility company was working on better protecting his employees. “We will be taking appropriate measures to prevent what we’ve been asked to correct from the government,” he said.

After an on-site inspection, officials at the Ministry of Health, Labor and Welfare said the utility allowed some employees to work without wearing dosimeters, which measure radiation exposure, despite laws that require nuclear workers to wear the devices on the job.

A Tokyo-based electrical engineering company also permitted workers to enter a turbine building flooded with highly radioactive water without wearing protective boots, ministry officials said.

Separate research released Wednesday by Greenpeace indicated uncontrolled leaks of extremely radioactive water from the Fukushima Daiichi plant have caused “severe” radioactive contamination in the ocean.

The environmental group said research conducted by Greenpeace and the Japanese government suggested that the radioactive water leakage was “considerably worse and more continuous” than Tepco had acknowledged.

The IAEA inspectors arrived in Japan last week and conducted inspections at the Fukushima plant. Inspectors praised government efforts to evacuate more than 80,000 people living near the plant as “impressive and well organized.”

john.glionna@latimes.com

Special correspondent Yuriko Nagano in Tokyo contributed to this report.