The decontamination workers cleaning up the hot zone around the Fukushima No. 1 power plant received as much as 13.9 millisieverts of radiation from 2011 to 2013, well within government-mandated levels, the Radiation Effects Association said in its first report on the subject.
The average cumulative dose was 0.6 millisievert among the 26,382 workers tasked with decontaminating 11 municipalities in Fukushima Prefecture tainted by fallout from the March 2011 core meltdowns, said the association, which is in charge of managing their radiation exposure.
The Health, Labor and Welfare Ministry’s present limit for decontamination workers is 50 millisieverts a year and 100 millisieverts over five years.
According to the association’s tally, the cumulative radiation received by 22,015 workers, or 83.4 percent of the total, was 1 millisievert or lower, but 34 workers, or 0.1 percent, received a dose of over 10 millisieverts.
The association reported on Wednesday that a group of 6,037 people, or 22.9 percent, worked on different projects, with seven of them completing seven assignments. Their average radiation dose came to 2.6 millisieverts for workers who engaged in six different decontamination projects.
Exposure levels were higher for decontamination workers in municipalities in the northern part of Fukushima, including the village of Iitate and the city of Minamisoma, with the average in 2012 standing at 0.8 millisievert.
The number of decontamination workers in the northern municipalities was about half the number in the southern ones, including the village of Kawauchi.
Some 15.4 percent of the total in 2013 were aged 60 to 64. Most were men, with women only accounting for 2.6 percent.
Quarterly records show that the number of decontamination workers is climbing and totaled 17,988 in the July-September quarter of 2014, according to the association.
The average radiation dose peaked at 0.8 millisievert in January-March 2012 but leveled off to 0.2 to 0.3 millisievert after October-December 2012.
The association is commissioned to keep records of worker radiation doses in a database linked to general contractors and other companies that undertake the decontamination work. Since 2014, the database has covered at least 99 percent of the workers, according to the association.
Separately, a Fukushima Labor Bureau survey of 1,152 companies in charge of the decontamination work found some 800 violations of safety and sanitary regulations had been committed, including the failure to measure aerial radiation levels and have workers carry dosimeters.
If violations of labor regulations are included, nearly 70 percent of the companies committed violations, according to the bureau of the ministry.
According to the Environment Ministry, which is supervising the decontamination effort, some 12,000 people work on the cleanup every day. Work is complete in four of the 11 municipalities, and the ministry aims to finish the rest by March 2017.