Radioactive fallout from the crippled Fukushima No. 1 nuclear plant has caused widespread fear, prompting the government in August to adopt basic targets for decontamination efforts in and around Fukushima Prefecture.
But the government’s plan falls short and efforts should focus in particular on residential areas with more aggressive decontamination measures and goals, including reducing current radiation levels by 90 percent, two radiation experts said when interviewed by The Japan Times.
“I really doubt their seriousness (about decontamination),” said radiation expert Tomoya Yamauchi, a professor at the Graduate School of Maritime Sciences at Kobe University.
Areas with radiation exposure readings representing more than 20 millisieverts per year have been declared no-go zones, and the government has shifted the focus of its decontamination plan to areas with radiation readings, based on an annual accumulative amount, of between 20 millisieverts and more than 1 millisievert, with the goal of reducing the contamination by 50 to 60 percent over two years.
Decontamination efforts by humans, however, are expected to only yield a reduction of 10 to 20 percent.
Nature, including the impact of rain, wind and the normal degradation of the radioactivity of cesium-134, whose half-life is roughly two years, is assumed to do the rest, thus reaching the best-case scenario of cutting the contamination by 60 percent.
The experts said the government’s goal of human effort achieving a 10 to 20 percent reduction is not ambitious enough.
“A 10 percent reduction doesn’t really mean anything. I mean, 40 percent of the radiation would be reduced just by natural causes, so I think the government is almost saying it is just going to wait for the radioactive materials to decrease naturally,” said Shunichi Tanaka, former chairman of the Atomic Energy Society of Japan.
The main radioactive materials that spewed from the Fukushima No. 1 plant are cesium-134 and -137, the second of which has a half-life of 30 years. Given the relatively short half-life of cesium-134, the total radiation will naturally be halved in four years and fall to one-third in six years, although the threat from the latter will remain for a longer time.
The government is now trying to reduce contamination mainly by using high-power water hoses, known as pressure washers, on structures and removing surface soil and vegetation in limited areas.
But radioactive cesium can find its way into minute cracks and crevices. It is hard to remove, for example, from roofs made of certain materials, or surfaces that are rusted or whose paint is peeling, Yamauchi said.
He has monitored radiation in areas in the city of Fukushima and found that the levels were still quite high after the city performed cleanup operations.
To lower the contamination to pre-March 11 levels, Yamauchi said drastic, and highly costly, efforts by the government are needed, including replacing roofs and removing the surface asphalt of roads.
Tanaka meanwhile pointed out that the government has not even floated a plan for decontaminating the no-go zones where the radiation exceeds 20 millisieverts per year — areas where there isn’t even a timetable for when evacuees will be able to return.
If the government doesn’t speed up the decontamination work, it will be years before the evacuees may be able to return home, he said, adding that the government can’t set a target date because it isn’t sure how the cleanup effort will fare.
The government’s stance regarding the no-go zone is largely based on recommendations by the International Commission on Radiological Protection and other scientists that call for the maximum radiation exposure of between 20 and 100 millisieverts per year under an emergency situation.
The ICRP theorizes that cumulative exposure of 100 millisieverts could increase the cancer mortality risk by about 0.5 percent, meaning about 50 out of 10,000 people exposed to that level could die of cancer caused by radiation.
Scientists are split over whether exposure to less than 100 millisieverts is harmful. Yamauchi maintains that low-level exposure could pose risks to residents in Fukushima, and he heard from many that they don’t want to continue living there due to the fear. The government should thus widen the evacuation zone, he said.
Because the decontamination process is closely connected with the people living in the affected areas, Tanaka said their participation in the process is crucial.
He has been conducting cleanup work in Fukushima while serving as a decontamination adviser for the municipal government of Date, Fukushima Prefecture. He noted decontamination also entails cleaning up private spaces.
Another issue is the need for communities to reach consensus on where to temporarily store contaminated waste.
“Municipalities need to communicate closely with residents (to solicit their involvement) . . . without the participation of the residents, they can’t find space for the storage,” Tanaka said.