Radiation levels around the boundary of the crippled Fukushima No. 1 nuclear plant have risen to eight times the government standard of 1 millisievert per year, Tokyo Electric Power Co. said.
The Nuclear Regulation Authority is scheduled to hold a meeting Jan. 10 to discuss countermeasures for a southern area on the plant site that has long been a source of problems.
A level of 8 millisieverts per year was estimated as of December near an area with many storage tanks containing highly radioactive water, company officials said.
After water leaks from underground tanks on the plant’s premises were found last April, the utility transferred radioactive water to the aboveground storage tanks near the southern boundary, TEPCO officials said. The readings there were estimated at 7.8 millisieverts per year as of May.
TEPCO said the main factor behind the increase in radiation levels was X-rays from the storage tanks.
Beta rays released from radioactive strontium and other substances in the water reacted with iron and other elements in the storage tank containers to generate the X-rays, the officials said.
The reactor decommissioning plan for the Fukushima plant stipulates that radiation levels around the boundaries of the facility should be below 1 millisievert per year. That way, TEPCO can minimize the negative impact of radiation on areas outside the plant, according to the plan.
With a succession of high radiation levels reported on the plant premises and elsewhere, the NRA set up radiation monitoring devices at an additional 400 locations in 12 cities, towns and villages around the stricken facility, including ones in evacuation zones.
According to the NRA, the number of locations where such instruments are set up has risen from 446 to 815. The newly installed devices started full-scale operations on Jan. 10.
The additional instruments were installed at centers for local community meetings and other places where residents will likely gather after they are allowed to return home.
The NRA measures air dose rates 0.5 to 1 meter above the ground every 10 minutes.
The monitoring results are available on the NRA’s website at http://radioactivity.nsr.go.jp/en/
(Akira Hatano contributed to this article.)
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