even if they don't do any decontamination.
Well I guess they don't buy the argument of Russian scientists about the "ecological half life" of radioactive cesium in Chernobyl area being 62 to 420 years.
From Mainichi Shinbun (6:48PM JST 8/24/2011):
The Nuclear Disaster Countermeasures Headquarters of the Japanese government reported its plans on how to predict the future radiation levels in the area around Fukushima I Nuclear Power Plant to the Nuclear Safety Commission on August 24, and the Commission approved. According to the NSC, in the fields around the plant, the calculation shows the radiation will decrease by 40% in two years even without decontamination. The national government will determine its basic policy on decontamination of the area around the plant, and this calculation will be used as a guide.
The Countermeasures Headquarters focused on cesium-134 and cesium-134 among all the radioactive materials being detected around the plant, because they have longer-lasting effects. The calculation was based on radioactive cesium deposited in the fields from the past nuclear tests. Cesium-137, whose half life is about 30 years, would be half in 18 years considering the effect of dispersion by rain. Radioactive iodine whose half life is short and currently is not detected, and radioactive strontium which has little impact on the radiation level are not to be considered.
If they have decided to ignore strontium, it's safe to assume they have also decided to ignore plutonium or any other alpha and beta emitters. When they say radiation, it most likely means "air radiation".
Mainichi Shinbun also reports on the "Fukushima decontamination task force" set up by the national government. (Note that it's only for Fukushima Prefecture.) The key members of this task force are: the Ministry of the Environment, the cabinet office, and the Japan Atomic Energy Agency (JAEA) which is governed by the Ministry of Education and Science and the Ministry of Economy, Trade and Industry.
According to Mainichi, this powerful trio doesn't even know how to do decontamination yet. The trio is going to figure that out by experimenting in the area with relatively high radiation (e.g. Date City in Fukushima) to establish the official decontamination procedure and advise the municipalities.
Now I'm beginning to think that the regulatory agency for the nuclear industry being moved to the Ministry of the Environment was for a very good reason but not the government's stated reason of minimizing the collusion between the nuke industry and the regulators. The Ministry of the Environment has made it sound like it resents having to have the nuclear regulatory agency under the ministry. Au contraire, I think.
Here's the big chance for the minor ministry like the Ministry of the Environment to become a major player by leading the effort on decontamination, which is what the government has clearly decided to promote big time. The Ministry already has its vested interest group - the waste management industry which is going to play a very, very big role in the "cleanup" of 30 years or so worth of debris with varying degrees of radioactive contamination in Tohoku area. The Ministry has its own set of "experts" who will advise on decontamination and cleanup.
If anyone has accumulated a workable decontamination plan and method, that would be the Radioisotope Center of Tokyo University under Professor Kodama. But no, the national government has its own ideas, and the JAEA, of Monju notoriety, will be in charge.