9 Mars 2014
March 9, 2014
THREE YEARS AFTER: Risks of radiation exposure remain high for Fukushima workers
THE ASAHI SHIMBUN
About half of the workers at the Fukushima No. 1 nuclear power plant in the three years since the triple meltdown have been exposed to more than 5 millisieverts of radiation, a level used as a radiation exposure reference for humans.
The levels of radiation exposure among workers at the crippled Fukushima plant have decreased since the 2011 nuclear accident, but there was a spike from last summer with the problem of dealing with the growing volume of radiation-contaminated water.
The labor ministry instructed Tokyo Electric Power Co., the plant operator, at the end of last year to improve the measures taken to deal with radiation exposure.
About 3,000 people work at the Fukushima No. 1 plant on any given day. Workers who are exposed to radiation in excess of 50 millisieverts over the course of a year or greater than 100 millisieverts over a five-year period are prohibited from working at a nuclear plant.
The 5-millisievert annual radiation level is used to determine eligibility for the government's workers' compensation insurance program for those who develop leukemia, as well as to establish radiation control zones that restrict entry by residents.
According to TEPCO statistics, there were a total of 32,034 workers at the Fukushima No. 1 plant between the March 2011 nuclear accident and January 2014. Of that number, 1,751 workers were exposed to a combined total in excess of 50 millisieverts. Of that number, 173 workers were exposed to more than 100 millisieverts.
Close to half the overall number of workers, or 15,363, were exposed to more than 5 millisieverts.
While there were 2,925 workers who were exposed to more than 5 millisieverts over the course of one month in March 2011, that number has gradually decreased. In June 2013, 98 workers were exposed to more than 5 millisieverts in one month's time.
However, the number increased subsequently as TEPCO admitted in July 2013 that radiation-contaminated water had flowed into the ocean and began work to install an underground wall to shut off the seepage of water.
The number of workers exposed to more than 5 millisieverts over a one-month period was 117 in July, 186 in August, 312 in September and 398 in October.
The labor ministry became concerned about the increase and inspected the Fukushima plant site in November and December. Ministry officials instructed TEPCO to install shielding plates against radiation and to rotate workers at shorter intervals.
The Nuclear Regulation Authority also instructed TEPCO in October 2013 to develop more specific measures to deal with radiation exposure among workers.
In January, TEPCO came up with measures such as decontaminating the plant site, removing debris with high radiation levels, paving asphalt on the plant site, installing more than 50 radiation level indicators and more than 10 dust monitors, as well as shielding off areas in the plant site with high radiation levels.
However, the utility has set a March 2015 deadline for completing all of those measures.
"We will accelerate the rate at which we implement such measures," said Akira Ono, head of the Fukushima No. 1 nuclear plant.
(This article was written by Toshio Tada and Shinichi Sekine.)