Scientist weighs homecoming risks in Fukushima


Staff Writer

When scientist Junko Nakanishi stepped into radiation-contaminated towns and villages in Fukushima Prefecture 10 months after the nuclear power plant meltdowns of 2011, she realized how difficult the job of decontamination would be.

Surveying the thinly populated areas surrounded by hills and rice paddies, she wondered how much time and money it would take to reduce the radiation.

“I thought decontamination wouldn’t succeed without a concrete plan,” Nakanishi, 76, a leading expert on chemical risk assessment, said in a recent interview with The Japan Times.

Decontamination is the biggest issue when thinking of Fukushima’s future, because it determines when, or even if, residents will be able to return home, she said.

Three years on, however, the government is still stumbling toward a realistic decontamination goal, leaving thousands of evacuees in limbo, she said.

The central government is responsible for decontaminating evacuation zones in 11 municipalities where dosage readings exceed 20 millisieverts per year. But many areas remain untouched or in the midst of decontamination, with their 80,000 residents still displaced as of April 1, by government order.

“The longer their evacuation period gets, the more residents will miss the timing to return home,” said Nakanishi, a fellow at the National Institute of Advanced Industrial Science and Technology. “It’s about time to think of ways to live under a certain level of risk.”

The government did not set a specific radiation goal for decontamination but settled on a threshold instead. The main condition for lifting an evacuation order is that the annual radiation dose must be 20 millisieverts or less.

An annual dose of 1 millisievert has meanwhile been set as a “long-term goal” for decontamination, without a specific time frame.

Nakanishi said that the 20 millisievert threshold is too high for many residents to accept and that the 1 millisievert figure is unrealistic in heavily contaminated areas, given the limits and cost of decontamination technology. As an alternative, she proposes a maximum exposure level of 5 millisieverts per year as a target for decontaminating evacuation zones, based on her assessment of the various risk factors.

“Somebody has to find a common ground where people can return to their homes as early as possible. We need to set a goal for radiation. . . . But no politician, bureaucrat or expert seems to make such suggestions,” she said. As a scientist, Nakanishi said it’s her job to find that magic number.

Since the 1970s, Nakanishi has studied the environmental and health risks of such toxic chemicals as dioxin and mercury. At the core of her research is the concept of risk trade-off, which means reducing one risk while allowing another to rise.

For example, chlorinating the drinking water of a population would reduce its risk of contracting an infectious disease. But it would also increase the risk of cancer. Nakanishi searches for the best mix of acceptable risks when trying to reduce overall risk.

Nakanishi looked at health factors, technological limits, cost and time to assess the tainted areas in Fukushima and concluded that an annual radiation exposure of 5 millisieverts or less would be the best goal for repopulating them.

According to her calculations, a 5-millisievert goal would allow some 65,000 residents to return home in another one to two years and cost around ¥1.8 trillion to execute.

A resident would be exposed to around 38 millisieverts over 15 years, a risk that, when compared to the average risk of exposure to a chemical like dioxin, is not high, Nakanishi said. The dose would drop to less than 1 millisievert a year after 15 years due to natural radioactive decay and land erosion from rain and wind, she said.

According to the International Commission on Radiological Protection, an annual dose of 100 millisieverts increases the risk of dying by cancer by 0.5 percent over one’s lifetime. Below that, the risks are too small to distinguish from the effects of other cancer risks, such as smoking and an unbalanced diet.

“The risk is not zero, but we need to think about the amount we can tolerate,” Nakanishi said. “It’s difficult, but that’s the reality. It’s more honest to say that the risk is not zero rather than it is safe.”

For areas with annual radiation readings over 50 millisieverts, residents need to give up on returning and relocate, with financial support from the state, she said.

Nakanishi also emphasized that there is a need for the government to financially back those who want to relocate even if an annual radiation dose drops to less than 5 millisieverts a year. Given Japan’s experience with the atomic bombings of Hiroshima and Nagasaki, some find it extremely hard to prevent horrific images of the aftermath from entering their minds when they hear the word radiation, she said.

“For a long time, I’ve been analyzing the risk of chemicals, and through the research I have come to realize that Japan has never set a goal for regulating chemicals by itself. It was always based on decisions made by international organizations or other countries,” she said.

“(In Japan, people are) not used to finding a mutually acceptable common ground by considering different conditions and risks,” Nakanishi said. “(Fukushima) was a very unfortunate nuclear disaster. But I see it as a chance for Japan to learn to strike a balance of risks, and find risk levels that we can accept.”

  • nanka
  • nanka

    This way, residents are made guinea pigs of a large scale experiment. Do you like to raise your children under this conditions? This kind of proposal ist just unaccaptable, because this “risks” are not like other daily life risks but adding up to them, if not even much more likely to happen. Japanese government along with Tepco Co. have to accept the fact, that such contaminated land is gone for a generation or two. Tepco should be forced to compensate the displaced residents and to buy out all land, ground and water, for the residents may settle down in other places for good, eventually. After that, Tepco has all time in the world to try out all ways of decontimanation with the long term goal to sell clean land in about fifty to hundred years from now.

  • vlady47

    Outrageous! Repopulate the areas with nuclear proponents and the people like this scientist that think those levels are acceptable.
    Comparing chlorinated water to living surrounded by radiation, with some guesstimated dose and unknown timetable…not even bothering to distinguish the difference of the health effects on the old, young, babies or the unborn.
    Plus who said the Fukushima accident was over?

  • I’m a little confused here. If the radiation limit for perceptible risk is 100 millisieverts, and the condition for lifting an evacuation order is 20 millisieverts, then why is a target of less than 20 millisieverts a bad goal? That seems reasonable.

    • vlady47

      20 msv a year turns into 100 msv in 5 years. Radiation exposures accumulate..
      Remember radiation causes genetic mutations too….one does not have to die to be affected ~ Women, children, babies and the unborn are at the greatest risk.

  • therailer

    Idiots. The only study that needs to be done, is on why the world won’t shut these plants down and put them into cold storage immediately. There is absolutely no way on earth that companies should be allowed to sell something so deadly to the world. This will be our downfall-our inability to adapt to the needs of the planet.