The Mainichi Shimbun answers some common questions readers may have about the decontamination of areas that were heavily exposed to radiation in the nuclear crisis at the Fukushima No. 1 Nuclear Power Plant.
Question: What is the situation right now with the decontamination of areas that were exposed to radioactive materials in the Fukushima nuclear incident, where residents were ordered to evacuate?
Answer: In April 2012, areas that were under evacuation orders were separated into three categories based on annual radiation exposure dosages. Decontamination work has not been carried out in areas of the Fukushima Prefecture towns of Okuma, Futaba, Namie, Tomioka, and the prefectural villages of Iitate and Katsurao and the city of Minamisoma -- classified as "difficult-to-return zones" with annual radiation exposure dosages topping 50 millisieverts -- save for a few areas that were decontaminated on a trial basis.
Meanwhile, in "restricted residence zones," where the annual radiation exposure dosage is between 20 and 50 millisieverts, and in "preparing for lifting of evacuation order zones," which have annual radiation exposure dosages of 20 millisieverts or lower, the government is aiming to have decontamination completed by March 2017.
Q: Why haven't "difficult-to-return zones" been decontaminated?
A: In addition to the fact that all residents had evacuated, it was determined immediately after the disaster broke out that decontamination efforts would be ineffective because of the high levels of radiation there. However, radiation has the property of decreasing as time passes. Indeed, according to measurements taken by an airplane that was released by the Nuclear Regulation Authority in February this year, radiation levels had gone down significantly. And in some areas, where decontamination was attempted on a trial basis, there was some success.
Q: How much does radiation go down through the decontamination process?
A: According to the Environment Ministry, in a trial decontamination of the Akougi district in Namie, Fukushima Prefecture -- designated a "difficult-to-return zone" -- radiation levels went down by half. However, a ministry official explains that radiation levels there cannot be brought down to zero because even if the area is decontaminated, radiation seeps in via rain and other means.
Q: What is done with the waste that results from decontamination?
A: The Environment Ministry estimates that 16 million to 22 million cubic meters of radioactively contaminated waste will result from decontamination work. That waste will be stored temporarily in municipalities in Fukushima Prefecture, then transported to interim storage facilities in the prefectural towns of Okuma and Futaba. However, only 5 percent of the entire land area needed for storing radioactive waste had been secured as of late July. (Answers by Hanayo Kuno, Science and Environment News Department)