Blog Archive

Sunday, 20 July 2014

New radiation measurement method spreads confusion

Fukushima Minpo
Confusion is spreading among towns and cities tasked with radiation cleanup in the face of a new decontamination policy to be released by the Environment Ministry as early as this month.

The government has been decontaminating areas whose aerial radiation reading is 0.23 microsievert per hour or more, based on its policy of keeping annual radiation exposure for individuals at 1 millisievert or less. It arrived at the estimated dose of 0.23 microsievert per hour by assuming that an individual spends eight hours outdoors and 16 hours indoors.

Under the new policy, however, the government will determine decontamination needs by using radiation exposure data collected from individual dosimeters, which tend to be lower than the estimated dose, thus reducing the areas subject to government-mandated decontamination.

While some municipalities welcome the move, saying it will allow them to scale down decontamination efforts in areas where radiation levels are unlikely to go down significantly, others are worried that residents will be confused.

The Environment Ministry unveiled its plan to use the individual dosimeter data last month at its meetings with officials from the cities of Fukushima, Koriyama, Soma and Date. According to Date officials, the city measured the radiation exposure of its 52,000 citizens wearing dosimeters from July 2012 through June 2013. The results showed that per-year exposure levels for nearly 70 percent of residents, even in areas where aerial radiation levels exceeded 0.23 microsievert per hour, was less than 1 millisievert in total.
“We should break the spell of aerial radiation soon,” said a Date official, pinning hopes on the ministry plan.

An official of the city of Tamura, on the other hand, expressed shock, saying the city has been cleaning up contaminated areas based on aerial readings, and if the cleanup projects are scaled back as a result of a policy change, it would cause anxiety among residents. Tamura, therefore, will not change its decontamination plan, the official said.

Experts are similarly divided. Junichiro Tada, a member of the board of directors at nonprofit organization Radiation Safety Forum, said he agrees with the ministry. “We should change the way radiation doses are managed from an aerial radiation basis to an individual exposure basis,” he said. “That way, we will do away with ineffective decontamination work.”

But Keizo Ishii, director of the Research Center for Remediation Engineering of Living Environments Contaminated with Radioisotopes at Tohoku University, remains cautious.
“Many residents of Fukushima have deliberately stayed indoors since the nuclear disaster. If they start to go out like they used to before the quake, the individual radiation doses might go up and will not necessarily fall below the 1 millisievert threshold,” Ishii said. “As such, we should aim for continued use of aerial figures for decontamination.”

Sanae Sato, a 54-year-old homemaker from the city of Fukushima, said she wants standards that are easy to understand. “I hope the national, prefectural, municipal governments, as well as experts, will come to a consensus and create the same standards,” she said.




Post a Comment