WASHINGTON - The US Navy on Tuesday recommended personnel and families stationed at two bases in Japan take precautions after detecting low-levels of radioactivity, including limiting outdoor activities.

"These measures are strictly precautionary in nature. We do not expect that any United States federal radiation exposure limits will be exceeded even if no precautionary measures are taken," the Seventh Fleet said in a statement.

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The International Atomic Energy Agency said the explosion at the Fukushima Daiichi unit 2 "may have affected the integrity of its primary containment vessel."

The IAEA said primary containment vessels of units 1 and 3 appeared intact despite explosions there. It said units at the Fukushima Daini, Onagawa, and Tokai nuclear power plants were in a safe and stable condition.

On a scale of one to seven, Japan's current nuclear crisis in Fukushima is equivalent to a number six on the INES's scale of nuclear accidents the French Nuclear Safety Authority said. In comparison, the 1986 Chernobyl disaster was a seven.

Prime Minister Naoto Kan urged people within 30 km (18 miles) of the facility north of Tokyo -- a population of 140,000 -- to remain indoors amid the world's most serious nuclear accident since the Chernobyl disaster in Ukraine in 1986.

Around eight hours after the explosions, the UN weather agency said winds were dispersing radioactive material over the Pacific Ocean, away from Japan and other Asian countries. The Geneva-based World Meteorological Organization added that weather conditions could change.

Radiation levels in the city of Maebashi, 100 km (60 miles) north of Tokyo, and in Chiba prefecture, nearer the city, were up to 10 times normal levels, Kyodo news agency said. Only minute levels were found in the capital itself, which so far were "not a problem", city officials said.



Two of the reactors exploded on Tuesday at the Fukushima Daiichi plant after days of frantic efforts to cool them. Kyodo news agency said the nuclear fuel pool at the No. 4 reactor may be boiling, suggesting the crisis is far from over at the plant, 240 km (150 miles) north of Tokyo.

"The possibility of further radioactive leakage is heightening," a grim-faced Kan said in an address to the nation. "We are making every effort to prevent the leak from spreading. I know that people are very worried but I would like to ask you to act calmly."

Levels of 400 millisieverts per hour had been recorded near the No. 4 reactor, the government said. Exposure to over 100 millisieverts a year is a level which can lead to cancer, according to the World Nuclear Association. The government later said radiation levels around the complex had plunged.

The plant operator pulled out 750 workers, leaving just 50, and a 30-km no-fly zone was imposed around the reactors.

"Radioactive material will reach Tokyo but it is not harmful to human bodies because it will be dissipated by the time it gets to Tokyo," said Koji Yamazaki, professor at Hokkaido University graduate school of environmental science. "If the wind gets stronger, it means the material flies faster but it will be even more dispersed in the air."


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