#Radiation in Japan: Government Believes Radiation Level Will Drop by 40% in 2 Years

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):

政府の原子力災害対策本部は２４日、東京電力福島第１原発周辺の今後の放射線量を予測する考え方や計算方法を原子力安全委員会に報告、了承された。安全委によると、原発周辺の田畑では除染をしなくても、２年後に線量が約４割減少する試算結果になるという。政府は周辺の除染について２６日に基本方針を決めるが、今回の試算を参考にするという。



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.



　対策本部は、周辺で検出される放射性物質のうち、影響が残るセシウム１３４と１３７を重視。過去の核実験などで国内の田畑に蓄積したセシウムに関する研究に基づき試算した。放射性物質が半分になる「半減期」が約３０年のセシウム１３７は、雨などによる拡散効果を考慮すると約１８年で半分になる。半減期が短く現在は検出されていない放射性ヨウ素や、線量への寄与が小さい放射性ストロンチウムは考慮しないとした。



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.

More about → #Radiation in Japan: Government Believes Radiation Level Will Drop by 40% in 2 Years

"Ecological Half Life" of Cesium-137 May Be 180 to 320 Years?

A Wired Magazine article dated December 15, 2009 cites a poster session presentation of the research of the Chernobyl exclusion zone at the American Geophysical Union conference in 2009, and says radioactive cesium may be remaining in the soil far longer than what the half life (30 years) suggests.



To note: it was a poster session presentation, and I'm looking to see if it has been formally published in a scientific paper since then.



From Wired Magazine (12/15/2009):

SAN FRANCISCO — Chernobyl, the worst nuclear accident in history, created an inadvertent laboratory to study the impacts of radiation — and more than twenty years later, the site still holds surprises.



Reinhabiting the large exclusion zone around the accident site may have to wait longer than expected. Radioactive cesium isn’t disappearing from the environment as quickly as predicted, according to new research presented here Monday at the meeting of the American Geophysical Union. Cesium 137’s half-life — the time it takes for half of a given amount of material to decay — is 30 years. In addition to that, cesium-137’s total ecological half-life — the time for half the cesium to disappear from the local environment through processes such as migration, weathering, and removal by organisms is also typically 30 years or less, but the amount of cesium in soil near Chernobyl isn’t decreasing nearly that fast. And scientists don’t know why.



It stands to reason that at some point the Ukrainian government would like to be able to use that land again, but the scientists have calculated that what they call cesium’s “ecological half-life” — the time for half the cesium to disappear from the local environment — is between 180 and 320 years.



“Normally you’d say that every 30 years, it’s half as bad as it was. But it’s not,” said Tim Jannik, nuclear scientist at Savannah River National Laboratory and a collaborator on the work. “It’s going to be longer before they repopulate the area.”



In 1986, after the Chernobyl accident, a series of test sites was established along paths that scientists expected the fallout to take. Soil samples were taken at different depths to gauge how the radioactive isotopes of strontium, cesium and plutonium migrated in the ground. They’ve been taking these measurements for more than 20 years, providing a unique experiment in the long-term environmental repercussions of a near worst-case nuclear accident.



In some ways, Chernobyl is easier to understand than DOE sites like Hanford, which have been contaminated by long-term processes. With Chernobyl, said Boris Faybishenko, a nuclear remediation expert at Lawrence Berkeley National Laboratory, we have a definite date at which the contamination began and a series of measurements carried out from that time to today.



“I have been involved in Chernobyl studies for many years and this particular study could be of great importance to many [Department of Energy] researchers,” said Faybishenko.



The results of this study came as a surprise. Scientists expected the ecological half-lives of radioactive isotopes to be shorter than their physical half-life as natural dispersion helped reduce the amount of material in any given soil sample. For strontium, that idea has held up. But for cesium the the opposite appears to be true.



The physical properties of cesium haven’t changed, so scientists think there must be an environmental explanation. It could be that new cesium is blowing over the soil sites from closer to the Chernobyl site. Or perhaps cesium is migrating up through the soil from deeper in the ground. Jannik hopes more research will uncover the truth.



“There are a lot of unknowns that are probably causing this phenomenon,” he said.



Beyond the societal impacts of the study, the work also emphasizes the uncertainties associated with radioactive contamination. Thankfully, Chernobyl-scale accidents have been rare, but that also means there is a paucity of places to study how radioactive contamination really behaves in the wild.



“The data from Chernobyl can be used for validating models,” said Faybishenko. “This is the most value that we can gain from it.”



Update 12/28: The second paragraph of this story was updated after discussion with Tim Jannik to more accurately reflect the idea of ecological half-life.



Image: flickr/StuckinCustoms



Citation: “Long-Term Dynamics of Radionuclides Vertical Migration in Soils of the Chernobyl Nuclear Power Plant Exclusion Zone” by Yu.A. Ivanov, V.A. Kashparov, S.E. Levchuk, Yu.V. Khomutinin, M.D. Bondarkov, A.M. Maximenko, E.B. Farfan, G.T. Jannik, and J.C. Marra. AGU 2009 poster session.

More about → "Ecological Half Life" of Cesium-137 May Be 180 to 320 Years?