More than 170,000 people have been moved out of the zone, a virtual no-man’s land, since an earthquake and 10-meter (30-ft) tsunami smashed into the Fukushima Daiichi nuclear power complex on March 11, threatening nuclear disaster.
“At the moment, there is no need to expand the evacuation area,” Chief Cabinet Secretary Yukio Edano told a briefing.
Latest available readings from an area 10 km (6 miles) outside the evacuation zone show a level of 110 microsieverts per hour in the air, well below a level that would cause health risks but much higher than normal background levels.
It is unclear what background levels would have been this far away from the plant before the tsunami struck, but a reading of 110 microsieverts is roughly 3,000 times Tokyo’s normal pre-disaster background level.
Exposure to 100,000 microsieverts a year is the lowest level at which any increase in cancer risk is clearly evident.
The government is advising people living within 10 km of the evacuation zone to stay indoors, but radiation in the atmosphere is not the only problem for these people. Some food and even tap water have been found to be contaminated.
Elevated levels of radioactive cesium particles in the air are causing particular concern, because cesium can linger longer than, say, radioactive iodine, another element that has been found not only in the atmosphere but also in tap water.
Edano said there were no health risks, even at the highest cesium readings.
