Japan to Widen Evacuation Zone

TOKYO—Japan's government will move people out of some areas outside of the current evacuation and sheltering zones because radiation doses could accumulate to high levels over the coming year.

The government, the International Atomic Energy Agency, a Kyoto University group, and Greenpeace have all found elevated levels of radiation beyond the 20-kilometer evacuation zone and even the 30-kilometer zone within which people are urged to minimize time outdoors. Japan's Nuclear Safety Commission is now recommending that those living in areas where the annual accumulated dose will reach 20 millisieverts over the next year move to safer areas, Masanori Shinano told reporters. Prior to the current emergency, nuclear power plant workers in Japan were limited to annual doses of 100 millisieverts. Protecting ordinary citizens is not an emergency situation but rather a "deliberate evacuation" that will be carried out over the next month after consultations with the affected communities, according to government spokesman Noriyuki Shikata, speaking at a press conference.

The areas with elevated radiation levels are northwest of the stricken Fukushima nuclear power plant and apparently got the worst of a radioactive plume blown in that direction by weather patterns in the early days of the crisis.

Towns south of the plant seem to be much safer. Radiation levels throughout the entire region have dropped significantly over the past month. But the downward curve has been flattening out, indicating that iodine, with a half-life of 8 days, is decaying but that cesium-134 and cesium-137 "account for the majority of radiation you can measure today; that is very bad news," said Greenpeace radiation expert Jan Vande Putte at a briefing today. The half-life of cesium-134 is 2 years; that of cesium-137 is 30 years. This means dangerous levels of radiation could persist for years if not decades.

Government officials could not immediately say how many people will need to move under the new evacuation policy or how long they will need to stay away from their homes. "There has to be more intensive monitoring to answer such questions," Shinano said. In a related development, the Ministry of Agriculture on Friday banned the planting of rice in soil found to contain more than 5000 becquerels per kilogram of cesium. Several of the handful of locations sampled by Greenpeace exceed those limits, said Rianne Teule, another Greenpeace radiation expert. The agricultural ministry said that it will take more extensive test to determine which fields are off limits. The ministry also intends to boost testing of harvested rice.

Posted in Asia, Physics Japan Quake 2011