MAINICHI, Japan -- Japan's government’s Nuclear and Industrial Safety Agency (NISA) has demanded that the Health Ministry raise the allowable radiation exposure limit to 350 millisieverts effectively for emergency workers trying to bring the crippled Fukushima nuclear power station under control shortly after the ministry lifted the legal exposure limit to 250 millisieverts from 100 millisieverts on March 14, 2011, it has been learned.
NISA demanded the change to the radiation exposure limit after receiving a request from Tokyo Electric Power Co. (TEPCO), the operator of the troubled Fukushima No. 1 Nuclear Power Plant, according to NISA’s internal documents disclosed after an organization specializing in issues of radiation exposure requested the materials through information disclosure laws. The internal documents disclosed are NISA’s internal memos and solicitation documents TEPCO, Toshiba Corp. and Hitachi-GE Nuclear Energy, Ltd. sent to NISA.
It was already known that then Prime Minister Naoto Kan talked about the possibility of raising the exposure limit to 500 millisieverts at the Prime Minister’s Office three days after it was raised to 250 millisieverts. But it is the first time that specific exchanges between the government ministries and agencies concerned have been revealed through internal documents.
Regulations enforced under the Industrial Safety and Health Act set the radiation exposure limit at 50 millisieverts per year for workers under “usual” conditions and at 100 millisieverts for five years, while the rules set the limit at 100 millisieverts for people working under an emergency situation. To cope with the worsening nuclear crisis at the Fukushima nuclear power complex, the Health, Labor and Welfare Ministry raised the emergency exposure limit to 250 millisieverts for workers at the Fukushima nuclear power plant three days after the outbreak of the disaster.
Meanwhile, the health ministry had planned to maintain the “usual” limit and combine it with the emergency limit to set the overall upper threshold. Under the scheme, a worker who is exposed to more than 50 millisieverts of radiation in Fukushima will not be allowed to work at other nuclear power plants for one year. Likewise, the worker who is exposed to more than 100 millisieverts of radiation in Fukushima will not be allowed to work at other nuclear power plants for five years.
Seeing that the scheme was unfavorable for workers, TEPCO and nuclear plant makers, therefore, demanded the health ministry set a separate exposure limit, rather than combine the “usual” limit with the emergency limit. If a separate limit was set, the worker would be allowed to be exposed to the “usual” level of radiation exposure at other nuclear facilities even if he was exposed to 250 millisieverts of radiation in Fukushima. On March 22, 2011, Hitachi Ltd., the parent company of Hitachi-GE Nuclear Energy which dispatched emergency workers to the Fukushima plant, asked then health minister Ritsuo Hosokawa to set a separate exposure limit.
NISA was later told by TEPCO and Toshiba Corp that it would be difficult to secure enough workers at other nuclear power plants. NISA then prepared a written document on March 25, 2011, saying, “Unless a separate limit is set it will create grave problems in preventing the nuclear disaster from worsening.” With that document, NISA urged the health ministry to review the exposure limit.
After repeatedly exchanging opinions, the health ministry decided to maintain its original plan to combine the “usual” limit with the emergency exposure limit and conveyed its decision to NISA. But the health ministry decided to take out the stipulation of “50 millisieverts per year.” Under the revised scheme, a worker who was exposed to radiation between 50 and 100 millisieverts in Fukushima would be allowed to work at other nuclear plants later for five years within the limit of 100 millisieverts. NISA, TEPCO and others continued to have complaints thereafter. But work to bring the troubled nuclear power plant under control passed the critical stage and the emergency exposure limit was lowered back to 100 millisieverts at the end of last year.