Fire at Japan nuclear reactor heightens radiation threat

(Reuters) - Japan raced to avert a catastrophe after fire broke out on Wednesday at a nuclear plant that has sent low levels of radiation wafting into Tokyo, prompting some people to flee the capital and triggering growing international alarm.

Public broadcaster NHK said flames were no longer visible at the building housing the No.4 reactor of the plant in Fukushima, 240 km (150 miles) north of Tokyo, hours after the operator reported fire had broken out at the quake-crippled facility.

Experts say spent fuel rods in a cooling pool at the No. 4 reactor could be exposed by the fire and spew more radiation into the atmosphere. Operator Tokyo Electric Power said it was considering using a helicopter to dump boric acid, a fire retardant, on the facility.

Japan's Nuclear and Industrial Safety Agency said two workers were missing after blasts at the facility a day earlier blew a hole in the building housing the No. 4 reactor.

In the first hint of international frustration at the pace of updates from Japan, Yukiya Amano, director general of the International Atomic Energy Agency, said he wanted more timely and detailed information.

"We do not have all the details of the information so what we can do is limited," Amano told a news conference in Vienna. "I am trying to further improve the communication."

The U.S. Department of Energy said it had sent a team of 34 people to help Japan with the crisis.

Japanese Prime Minister Naoto Kan on Tuesday urged people within 30 km (18 miles) of the facility -- a population of 140,000 -- to remain indoors, as authorities grappled with the world's most serious nuclear accident since the Chernobyl disaster in Ukraine in 1986.

Officials in Tokyo said radiation in the capital was 10 times normal at one point but not a threat to human health in the sprawling high-tech city of 13 million people.

The best advice experts could give them was to stay indoors, close the windows and avoid breathing bad air -- steps very similar to those for handling a smog alert or avoiding influenza.

While these steps may sound inconsequential, experts said the danger in Tokyo, while worrisome, is slight -- at least for now.

"Everything I've seen so far suggests there have been nominal amounts of material released. Therefore, the risks are generally low to the population," Jerrold Bushberg, who directs programs in health physics at the University of California at Davis, said in a telephone interview.

Winds over the plant will blow from the north along the Pacific coast early on Wednesday and then from the northwest toward the ocean during the day, the Japan Meteorological Agency said.

Fears of transpacific nuclear fallout sent consumers scrambling for radiation antidotes in the U.S. Pacific Northwest and Canada. Authorities warned people would expose themselves to other medical problems by needlessly taking potassium iodide in the hope of protection from cancer.

The nuclear crisis and concerns about the economic impact from last week's earthquake and tsunami have hammered Japan's stock market.