Behind the Environment Ministry's controversial decision to allow reuse of highly radioactive soil emanating from the Fukushima nuclear disaster in public works projects was an estimate that the reuse could cut the costs of reducing radiation levels of such soil by over 1.5 trillion yen, it has been learned.
The estimate in question was presented during a closed-door meeting of the ministry in January and stated that reuse of radioactive soil generated from Fukushima decontamination work could cut the cost for purifying such soil from 2.9127 trillion yen in case the levels of radioactive cesium are reduced to 100 becquerels per kilogram to 1.345 trillion yen in case the cesium levels are cut down to 8,000 becquerels per kilogram. The estimate calls the latter option "reasonable from economic and social points of view."
The Environment Ministry decided in June to allow reuse of soil with radioactive cesium of no more than 8,000 becquerels per kilogram in mounds under road pavements and other public works projects. The decision sparked criticism that it runs counter to the safety standards of 100 becquerels or less for recycling metals generated from the decommissioning of nuclear reactors under the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors. The ministry has insisted that the radiation levels of tainted soil used in road mounds can be held down from 8,000 becquerels to around 100 becquerels by covering those mounds with concrete among other measures.
A ministry working group on safety evaluation of radiation effects held closed-door meetings over the issue on six occasions between January and May this year. In June, the Mainichi Shimbun reported that an estimate presented to one of those meetings stated, "For example, it will take 170 years for radiation levels to reduce to 100 becquerels if tainted soil of 5,000 becquerels is put to reuse," sparking controversy. In response, the ministry on Aug. 1 released the minutes of the closed-door meetings and other documents on its website.
At the second meeting of the working group on Jan. 27, the copies of a document titled "About reasonable radioactivity concentrations of recycled materials" were handed out to attendants. The document, which was drawn up by the Japan Atomic Energy Agency, includes an estimate that the cost for reducing the radiation levels of tainted soil to 100 becquerels for recycling would reach 2.9127 trillion yen, with a volume reduction rate of 40 percent, adding that 40 percent of contaminated soil could not be put to reuse. Meanwhile, the estimate says it would cost 2.1185 trillion yen to drop the radiation levels of tainted soil to 3,000 becquerels, with a volume reduction rate of 0.5 percent, while it would cost 1.345 trillion yen to decrease the radiation levels of soil to 8,000 becquerels, with a volume reduction rate of 0.2 percent. The latter option could make 99.8 percent of tainted soil available for reuse, the estimate says.
"Considering economic and social factors, it is appropriate to set the radioactivity concentration of recycled materials at several thousand becquerels," the document stated. A note of caution in the document states, "Apart from this, it is necessary to project the cost for final disposal (of tainted soil)."
A ministry official in charge of the issue told the Mainichi Shimbun, "The document was produced in response to a request by a member of the working group. As the document states, it is difficult to (set the standards for reusing tainted soil) at 100 becquerels from a realistic point of view."