14 Novembre 2012
A study released Thursday by a U.S. research team links protracted exposure to low-level radiation to a higher risk of leukemia among workers engaged in the cleanup of the 1986 Chernobyl nuclear disaster, and points to the need to protect those involved in dealing with the Fukushima crisis.
In the U.S. study, scientists did a followup health survey covering 110,645 cleanup workers through 2006 and found 137 developed leukemia.
After excluding genetic and other factors, it estimated that around 16 percent of the leukemia cases confirmed during the 20-year followup period were attributable to radiation exposure from the disaster.
Most of the victims were involved in efforts to contain the Chernobyl disaster until 1990. Their cumulative exposure was less than 200 millisieverts.
According to Tokyo Electric Power Co., around 6,000 workers are currently involved in efforts to decommission the four crippled reactors at the Fukushima No. 1 power plant.
After the March 2011 meltdowns and hydrogen explosions, the Health, Labor and Welfare Ministry raised the allowable cumulative radiation exposure threshold to 250 millisieverts for workers so Tepco wouldn't run out of workers too quickly because of overexposure.
After the government declared the completion of "Phase 2" of the road map for containing the disaster, the limit was lowered last December to 50 millisieverts per year and 100 millisieverts per five years, the same level as before the crisis.
But six workers were exposed to more than 250 millisieverts.
"All of the six have already left the work site," Tepco said. "At this moment, there has been no observable impact on their health."
By the end of September this year, 167 workers registered more than 100 millisieverts. Workers exposed to 50 to 100 millisieverts numbered 941.
High radiation zones, including the structures housing the reactors, remain off-limits. As work progresses, concern will likely increase about what to do to reduce the health risk of workers.
Tepco meanwhile apparently lacks adequate procedures and discipline to minimize the radiation exposure.
Reports show workers have either misplaced dosimeters for measuring their radiation exposure or have worked without them. There was also an ethically questionable case in which dosimeters were covered by a lead sheet to suppress exposure readings, so workers could undertake operations beyond the exposure limit.
"In Japan, nobody exactly knows workers' conditions at nuclear facilities," said Masako Sawai of Citizens' Nuclear Information Center. "Even after the Fukushima crisis started, there have been moves to conceal exposure. In that sense, the latest U.S. data are very instructive and show the need for Japan to grasp what is going on."
Earlier this month, a 46-year-old man from Iwaki, Fukushima Prefecture, pleaded for better conditions at Fukushima No. 1. He said he was told to ignore dosimeter alerts and continue working in a high-radiation environment.
He told reporters Nov. 1 at the health ministry, "Rank-and-file people cannot raise their voices even when there is a problem." He filed a complaint with a Fukushima labor office against Tepco and Kandenko Co., the Tepco subcontractor that oversaw the man's work.