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.