Air radiation drops after snowfall / But decontamination necessary, levels will rise once snow melts, experts say

The Fukushima prefectural government has received many inquiries because air radiation levels across the prefecture following the crisis at the Fukushima No. 1 nuclear power plant declined considerably late January and have since remained constant, perhaps due to fallen snow blocking radiation above the ground.

According to monitoring by the Education, Culture, Sports, Science and Technology Ministry and others, the rate of decline was particularly large in the Akougi district in Namie and the Nagadoro district in Iitate, located in the expanded evacuation zone around the nuclear plant.

Radiation measuring found that the Akougi district had a reading of 19.7 microsieverts per hour in the morning of Jan. 25, down from 30 microsieverts per hour recorded in the morning of Jan. 18.

Air radiation levels also decreased to 5.9 microsieverts per hour from 10 microsieverts per hour over the same period in the Nagadoro district.

It is believed there were no major changes in air radiation levels before Jan. 18 and after Jan. 25.

According to the ministry’s Nuclear Emergency Response Headquarters, the decline can be attributed only to snowfall since decontamination operations were not conducted in the areas at the time.

The Fukushima Meteorological Observatory said snow accumulation is not monitored in Namie and Iitate, but temperatures and other factors suggest the town and the village had snow from Jan. 20 to 22.

The prefectural emergency response headquarters said radiation levels also declined in the city of Fukushima. While such levels measured 0.84 microsievert per hour at 6 p.m. on Jan. 21 when snow began to fall, at 9 p.m. on Jan. 22, after snowfall, radiation levels in the air measured 0.62 microsievert per hour.

Farmer Masuo Kaneko, 63, who evacuated to the city from Nagadoro district, said after reading the newspapers he thought the radiation levels were dropping rapidly. But he was disappointed to hear the decline was due to snowfall.

“I expected radiation levels to halve in about two years time,” he said.

Tokyo Institute of Technology Associate Professor Keiji Saneyoshi said air radiation levels may halve if about 20 centimeters of snow falls in certain areas. “Yet decontamination work needs to continue since the levels will rise again once the snow melts,” Saneyoshi said.


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