Leaking radiation in Japan 'a new threat'

An explosion at a nuclear power plant on Japan's devastated coast destroyed a building today and made leaking radiation the central threat menacing a nation just beginning to grasp the scale of a catastrophic earthquake and tsunami.

The Japanese government said radiation emanating from the plant appeared to have decreased after the blast, which produced an intensifying cloud of white smoke that swallowed the complex.

Authorities did not say why, and the precise cause of the explosion and the extent of the ongoing danger were not clear.

Japan dealt with the nuclear threat as it struggled to determine the scope of the earthquake, the most powerful in its recorded history, and the tsunami that ravaged the north-east of the country yesterday with breathtaking speed and power.

The official count of the dead was 686, but the government said the figure could far exceed 1,000.

Teams searched for the missing along hundreds of miles of the Japanese coast, and thousands of hungry survivors huddled in darkened emergency centres that were cut off from rescuers and aid.

At least a million households had gone without water since the quake struck. Large areas of the countryside were surrounded by water and unreachable.

The explosion at the nuclear plant, Fukushima Dai-ichi, 170 miles north-east of Tokyo, appeared to be a consequence of steps taken to prevent a meltdown after the quake and tsunami knocked out power to the plant, crippling the system used to cool fuel rods there.

The blast destroyed the building housing the reactor, but not the reactor itself, which is enveloped by stainless steel six inches thick.

Inside that superheated steel vessel, water being poured over the fuel rods to cool them formed hydrogen.

When officials released some of the hydrogen gas to relieve pressure inside the reactor, the hydrogen apparently reacted with oxygen, either in the air or the cooling water, and caused the explosion.

"They are working furiously to find a solution to cool the core," said Mark Hibbs, a senior associate at the Nuclear Policy Program for the Carnegie Endowment for International Peace.

Nuclear agency officials said Japan was injecting sea water into the core - an indication, Hibbs said, of "how serious the problem is and how the Japanese had to resort to unusual and improvised solutions to cool the reactor core".

Chief Cabinet Secretary Yukio Edano said radiation around the plant had fallen, not risen, after the blast.

Virtually any increase in dispersed radiation can raise the risk of cancer, and authorities were planning to distribute iodine, which helps protect against thyroid cancer. Authorities urged people within 12 miles of the reactor to leave.

It was the first time Japan had confronted the threat of a significant spread of radiation since the greatest nightmare in its history - the 1945 atomic bombings of Hiroshima and Nagasaki by the US, which resulted in more than 200,000 deaths from the explosions, fallout and radiation sickness.

Officials have said that radiation levels at Fukushima were elevated before the blast: At one point, the plant was releasing each hour the amount of radiation a person normally absorbs from the environment each year.

The Japanese utility that runs the plant said four workers suffered fractures and bruises and were being treated at a hospital.

As Japan entered its second night since the magnitude-8.9 quake, there were grim signs that the death toll could soar.

One report said no one could find four whole trains. Others said 9,500 people in one coastal town were unaccounted for and that at least 200 bodies had washed ashore elsewhere.

The government said 642 people were missing and 1,426 injured.

Atsushi Ito, an official in Miyagi prefecture, among the worst hit states, could not confirm the figures, noting that with so little access to the area, thousands of people in scores of towns could not yet be reached.

"Our estimates based on reported cases alone suggest that more than 1,000 people have lost their lives in the disaster," Edano said. "Unfortunately, the actual damage could far exceed that number considering the difficulty assessing the full extent of damage."