Radioactive contamination may keep some areas around the stricken Fukushima Daiichi nuclear complex off limits for years, Japan's government said Monday.
In its first detailed survey of the evacuation zone around the plant, the education ministry said it found spots—mostly within three kilometers (nearly two miles) of the plant—where annual radiation exposure could reach 200 to 500 millisieverts. The government requires people to evacuate if the cumulative dosage is likely to exceed 20 millisieverts per year. The annual limit for nuclear-plant workers in normal circumstances is 50 millisieverts (250 millisieverts in emergency conditions).
"Some places may have to be kept off-limits to residents for a long period of time even after clean-up operations are undertaken," Chief Cabinet Secretary Yukio Edano said at a news conference. His comments followed Friday's announcement that levels of radioactive contamination were higher in some areas in the 20-kilometer evacuation zone than were found in the plant compound itself.
Mr. Edano said various options are under consideration to help people who may be displaced for a long time, including government purchase or rental of their land. Policy details will be determined in consultation with local authorities based on the results of a further radiation survey and decontamination programs, he said.
On Sunday, reconstruction minister Tatsuo Hirano said the government also is considering providing long-term housing for evacuees rather than the prefabricated temporary homes the government currently is building.
Other government officials noted that decontamination is possible but will take time. Goshi Hosono, minister in charge of the Fukushima crisis, stressed that "nothing has been decided on the evacuation policy, and the desires of local residents will come first in any decision."
The government had hoped to narrow the evacuation zone gradually after January, the target date for Tokyo Electric Power Co. to bring the damaged reactors fully under control and stop deadly radiation emissions. But the education ministry's measurements of radiation levels at 50 locations within the 20-kilometer radius showed annual exposure could exceed 100 millisieverts in 15 locations, including one where it could reach 508 millisieverts, compared with the government 20 millisieverts per year standard for evacuation.
The discovery of elevated radiation came as Tepco reported a sharp drop in levels inside the plant. Tepco has said the level stands at just 0.4 millisievert per year along the boundary of the plant compound, well below the normal limit of one millisievert for ordinary citizens.
"Radiation spreads like a typhoon," said an official with the Nuclear and Industrial Safety Agency, the main nuclear regulator. "The amount of radioactive substance can be small at the eye of the typhoon, but very large outside."