A government study has found poor monitoring of the radiation doses suffered by workers at the disaster site, citing 19 breaches including data input errors and cases of personnel not wearing one of two required dosimeters.
The Ministry of Health, Labor and Welfare reported the failings on Oct. 30, after studying dose records for hundreds of individuals employed in cleanup and stabilization work at the Fukushima No. 1 nuclear power plant.
But the ministry admitted that the survey had a limited scope. The cases it identified may represent only the tip of an iceberg, and it offers little in either confirmation or rebuttal to those who have speculated about the widespread falsification of workers' dose readings.
In July, The Asahi Shimbun revealed that some workers shielded their dosimeters with lead plates to keep dose readings within safe limits--and to remain on the job.
The plant operator, Tokyo Electric Power Co., then said in August it had identified 27 cases of inadequate dose control.
In the latest study, conducted separately, the health ministry screened 1,813 workers who wore both electronic dosimeters, which indicate daily doses, and badge-type dosimeters, which record long-term accumulated doses. All workers had been exposed to high radiation levels between November and June.
In 28 cases the cumulative electronic dosimeter readings were at least 25 percent higher or lower than those recorded by the badge-type dosimeter. Of these, 19 were due to erroneous procedures.
The ministry identified instances where workers had not worn one of the two required dosimeters. It also found cases of erroneous data input, by officials of a major construction company.
The ministry acknowledged the survey's small scope.
"We only investigated the most suspicious cases because of the limited survey personnel available," said a health ministry official.
On Oct. 30, the ministry ordered TEPCO and 37 general contractors involved in work at the site to check their data and take measures to prevent violations from recurring.
Masayuki Ono, acting general manager of TEPCO's Nuclear Power and Plant Siting Division, said the company would deliver its response by the end of November.
"We will respond after verifying the facts," Ono told a news conference Oct. 30.
The health ministry's survey included only those workers with monthly dose records exceeding 5 millisieverts. Furthermore, officials interviewed less than 0.1 percent of all relevant workers.
The ministry is far from having investigated all individuals who have been at the site since the nuclear disaster in March 2011.
In particular, there has been no survey relating to the first seven months, through October 2011, a time of elevated radiation levels.
Nor has there been any investigation of conditions in the immediate aftermath of the disaster, when TEPCO issued teams of workers only one dosimeter between them.
The Asahi Shimbun has learned of one case this spring where workers left both the electronic and badge-type dosimeters somewhere on site, but continued working without wearing them.
That kind of breach would never have come to notice in the health ministry's latest study, because it would have created no disparity in the readings of the two dosimeters.
(This article was compiled from reports by Toshio Tada and Jun Sato.)
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