Following internal confusion, the science and technology ministry retracted a plan to end yearlong measurements of accumulated radiation doses at nine locations in Fukushima Prefecture.
"I will deal with the matter from the viewpoint of assurance and safety for residents for the time being instead of discontinuing the practice immediately," Hirofumi Hirano, the science and technology minister, told a news conference on May 15.
The ministry announced on May 14 that it would end the accumulated dose measurements to simplify and streamline its radiation monitoring operations.
A senior ministry official said Hirano was not informed of the decision to end the measurements, and only learned about the move after reading a May 15 newspaper report. Hirano immediately said he would continue the measurements for the time being, the official said.
By March, the ministry had installed new radiation-measurement devices that automatically obtain readings at 545 locations across Fukushima Prefecture. The accumulated doses are being updated daily on the Internet.
That setup prompted the ministry to announce on May 14 an end to the old measurement system.
But the online figures are available only from April this year, meaning there is no continuity in the data. The measurement locations are also different.
"We concluded there would be no major problem (by discontinuing the old measurement setup) because the increased number of measurement stations now allows us to get a broader picture," a ministry official said. "We will consult experts to consider whether to end (the old measurement setup) in the future and how to release (data) to the public."
The science ministry is considering a review of the current setup, which releases measurement results once a week.
Under the conventional method, accumulated doses have been calculated by tallying hourly measurements from simple dosimeters at nine outdoor locations outside the 20-kilometer radius of the crippled Fukushima No. 1 nuclear power plant.
Those dosimeters were installed between March 23 and April 8 last year, shortly after the Great East Japan Earthquake and tsunami triggered the crisis at the Fukushima plant on March 11.
Ministry employees visit the measurement sites once a week to obtain the readings.
The data have not been used directly to help in the health management of residents or to draw up measures for their evacuation and return. But the numbers are still considered useful indicators that can be compared with reference levels.
For example, the Akogi district of Namie, 31 km northwest of the nuclear plant, had the highest accumulated dose of 137.63 millisieverts, as of May 8, for a hypothetical subject who stays outdoors 24/7. That reading exceeds 100 millisieverts, the threshold for enhanced cancer risks.
(This article was compiled from reports by Hiroshi Ishizuka and Hisae Sato.)
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