With Quest to Cool Fuel Rods Stumbling, U.S. Sees 'Weeks' of Struggle

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Evacuees receiving radiation scans in Nihonmatsu, Japan. Americans were advised by their embassy to evacuate a radius of 50 miles from the Fukushima plant. More Photos »

By NORIMITSU ONISHI, DAVID E. SANGER and MATTHEW L. WALD

Published: March 17, 2011

TOKYO — Amid widening alarm in the United States and elsewhere about Japan's nuclear crisis, military fire trucks began spraying cooling water on spent fuel rods at the country's stricken nuclear power station late Thursday after earlier efforts to cool the rods failed, Japanese officials said.

The United States' top nuclear official followed up his bleak appraisal of the grave situation at the plant the day before with a caution that it would "take some time, possibly weeks," to resolve.

The developments came as the authorities reached for ever more desperate and unconventional methods to cool damaged reactors, deploying helicopters and water cannons in a race to prevent perilous overheating in the spent rods of the No. 3 reactor.

Moments before the military trucks began spraying, police officers in water cannon trucks were forced back by high levels of radiation in the same area. The police had been trying to get within 50 yards of the reactor, one of six at the plant.

The five specially fitted military trucks sprayed water for about an hour, but the full impact of the tactic was not immediately clear.

The Japanese efforts focused on a different part of the Fukushima Daiichi Nuclear Power Station, 140 miles northeast of here, from the reactor — No. 4 — depicted in Washington on Wednesday as presenting a far bleaker threat than the Japanese government had offered.

The decision to focus on the No. 3 reactor appeared to suggest that Japanese officials believe it is a greater threat, since it is the only one at the site loaded with a mixed fuel known as mox, for mixed oxide, which includes reclaimed plutonium.

Western nuclear engineers have said that the release of mox into the atmosphere would produce a more dangerous radioactive plume than the dispersal of uranium fuel rods at the site. The Japanese authorities also expressed concern on Wednesday that the pressure in the No. 3 reactor had plunged and that either gauges were malfunctioning or a rupture had already occurred.

After the military's effort to cool the spent fuel atop the reactor with fire trucks, Hidehiko Nishiyama, deputy director-general of the Nuclear and Industrial Safety Agency, said it was too early to assess the success of the attempt.

Mr. Nishiyama also said that radiation of about 250 millisievert an hour had been detected 100 feet above the plant. In the United States the limit for police officers, firefighters and other emergency workers engaged in life-saving activity as a once-in-a-lifetime exposure is equal to being exposed to 250 millisieverts for a full hour. The radiation figures provided by the Japanese Self-Defense Force may provide an indication of why a helicopter turned back on Wednesday from an attempt to dump cold water on a storage pool at the plant.

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