Radiation Leaks Force 140,000 Indoors.

Radiation Leaks Force 140,000 Indoors.

Radiation falls at Japan nuke plant, officials say

SOMA, Japan — Japanese data indicate that radioactivity levels fell during a six-hour period on Tuesday at a nuclear power plant damaged by last week's earthquake and tsunami, the U.N. nuclear watchdog said.

"These observations indicate that the level of radioactivity has been decreasing at the site," the International Atomic Energy Agency (IAEA) said in a statement.

The Vienna-based U.N. agency said a radiation dose level of 11.9 millisieverts (mSv) per hour was observed at the main gate of the Fukushima nuclear power plant at midnight GMT on Tuesday (8 p.m. ET Monday).

Six hours later, the rate had declined to 0.6 millisieverts, the agency said in a statement. The IAEA uses the unit to measure doses of radiation received by people. It quantifies the amount of radiation absorbed by human tissue.

Exposure to more than 100 millisieverts (mSv) a year is a level that can lead to cancer, the World Nuclear Association says. People are exposed to natural radiation of 2-3 mSv a year.

Earlier on Tuesday, the IAEA said Japan had told it radioactivity was being released "directly" into the atmosphere from the site and that a 400 mSv per hour radiation dose was observed, between the plant's reactor units 3 and 4.

That figure would be 20 times the annual exposure for some nuclear-industry employees and uranium miners.

Orders from the government 

"This is a high dose-level value, but it is a local value at a single location and at a certain point in time," the IAEA statement said.

"It should be noted that because of this detected value, non-indispensable staff were evacuated from the plant ... and that the population around the plant is already evacuated."

The radiation releases also prompted Japanese officials to issue orders for 140,000 people to seal themselves indoors Tuesday.

The IAEA said about 150 people had received monitoring for radiation levels and that measures to "decontaminate" 23 of them had been taken.

Clearing up nuclear questions

Though Japanese officials urged calm, Tuesday's developments fueled a growing panic in Japan and around the world amid widespread uncertainty over what would happen next.

In the worst-case scenario, the reactor's core would completely melt down, a disaster that would spew large amounts of radioactivity into the atmosphere.

Tokyo reported slightly elevated radiation levels, but officials said the increase was too small to threaten the 39 million people in and around the capital, about 170 miles away. Closer to the stricken nuclear complex, the streets in the coastal city of Soma were empty as the few residents who remained there heeded the government's warning to stay indoors.

Officials just south of Fukushima reported up to 100 times the normal levels of radiation Tuesday morning, Kyodo News agency reported. While those figures are worrying if there is prolonged exposure, they are far from fatal.

'Please do not go outside' 

Officials warned there is danger of more leaks and told people living within 19 miles of the Fukushima Dai-ichi complex to stay indoors to avoid exposure that could make people sick.

"Please do not go outside. Please stay indoors. Please close windows and make your homes airtight," Chief Cabinet Secretary Yukio Edano told residents in the danger zone.

"These are figures that potentially affect health. There is no mistake about that," he said.

Interactive: How a nuclear plant works

Weather forecasts for Fukushima were for snow and wind from the northeast Tuesday evening, blowing southwest toward Tokyo, then shifting and blowing west out to sea. That's important because it shows which direction a possible nuclear cloud might blow.

Radiation Leaks Force 140,000 Indoors.