TEPCO Fukushima Daiichi Nuclear Power Station： Trends and Current State of Work Involving Radioactive Exposure
By Iida Katsuyasu, Tokyo Occupational Safety and Health Center
1 Exposure Limits During Emergencies Raised without Verifying the Validity
March of this year marks 15 years since the nuclear accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) operated by Tokyo Electric Power Co. (TEPCO). In response to the government’s Nuclear Disaster Emergency Declaration on 11 March 2011, the Ministry of Health, Labour and Welfare (MHLW) issued a ministerial decree on 14 March giving special provisions for the Rules on Preventing Ionizing Radiation Damage (below, “IR Damage Prevention Rules”). This decree revised Article 7 of the aforesaid rules, taking steps to raise exposure limits from 100 to 250 millisieverts (mSv) for workers engaged in nuclear accident clean-up operations at FDNPS.
Though it must be admitted that they were under pressure to deal with the nuclear catastrophe, what they did was hastily inquire with the radiation council, submit a report and raise the exposure limits during the emergency by a factor of 2.5, allowing the emergency workers to be subjected to high doses of up to 250 mSv. At that time, what was required was for them to clarify the basis and validity of the special measures regarding exposure limits during emergencies, but the government has never provided a solid explanation, nor has the verification been accomplished.
In 2016, MHLW partially revised Japan’s IR Damage Prevention Rules, enabling “Special Case Emergency Exposure Limits” to be raised to 250 mSv with the issuance of a special decree when a nuclear catastrophe occurs. In addition, they restricted this higher exposure level to “key members of nuclear power disaster prevention organizations” designated as “special case emergency response organizations” under the nuclear power operators’ disaster prevention plans. This constituted confirmation of the emergency dose limit increase, but without verifying its validity, and cannot be considered to have taken into consideration what was learned from the emergency response to the Fukushima Daiichi nuclear accident.
On 16 December 2011, Japan’s government issued a declaration that the accident “had been brought to a conclusion,” as cold shutdown conditions had been achieved in the primary containment vessels, and the emergency response was terminated. The number of workers who had been engaged in the emergency response had come to about 20,000. MHLW formulated “Guidelines on Maintaining and Improving Health of the Emergency Workers at the TEPCO Fukushima Daiichi Nuclear Power Station.” It had registration certificates issued to the emergency workers, creating a lifetime long-term health-maintenance system for radioactive exposure and providing annual cancer screenings for any emergency workers whose exposure had exceeded 100 mSv and cataract screenings for those whose exposure had exceeded 50 mSv. As of the end of October 2025, the number of emergency response workers who had been issued a registration certificate stood at 19,812, of whom 911 had been exposed to over 50 mSv, with 897 of those being issued a “special emergency response worker exposure record booklet.” A long-term health maintenance system needs to be established not only for the emergency response workers, but also for all workers who have engaged and will continue to engage in environmental restoration work as a result of the accident.
2 General Situation Regarding Exposure Doses to Workers at Fukushima Daiichi
Each month, TEPCO releases the results of its evaluations of worker exposure doses and distribution at the Fukushima Daiichi NPS. Ever since the emergency response work was declared completed in December 2011 up to the current day, the numbers of workers involved in this kind of work (from TEPCO and cooperating companies) have been, in months with the fewest workers, in excess of 5,000 people, and from January 2023 to the present time, about 7,000 – 8,000 in the average month. In its Mid-and-long-term Roadmap progress status report overview for 25 December 2025, TEPCO reports, “Each month for the last two years, the average number of workers engaged per weekday (actual values) has tended to be on the scale of 3,500 to 5,000 people,” and “The average dose in FY2022 was 2.16 mSv per person per year; that in FY2023 was 2.18 mSv per person per year; and that in FY2024 was 2.08 mSv per person per year (the legal upper dose limit is 100 mSv per person in five years, or 50 mSv per person per year, and our company’s target limit is 20 mSv per person per year).”
However, the area around and inside the nuclear reactor buildings is a high-dose area. The work involved in retrieving a small fragment of nuclear fuel debris from the Unit 2 reactor in FY2024 necessitated unavoidable high radiation doses. For example, TEPCO has admitted that “establishing an isolation room” and “opening the hatch” as part of the preparatory work involved “a planned dose of 3,000 mSv, and the actual dose was about 3,000 person mSv, resulting in a maximum personal cumulative dose of about 41 mSv” (negotiations on 8 April 2024 between the ministries and TEPCO regarding worker exposure issues).
Regarding work like this that is expected to entail high exposures, TEPCO says they have discussed this with the ALARA Symposium, formulated measures to reduce exposures, and have been implementing the measures while submitting work notifications to the local labour standards inspection office in Tomioka and notifiying the office of their plans. TEPCO has reported the operations it had undertaken with the 10 highest levels of radiation exposure that the ALARA Symposium had addressed, plus its measures to reduce them, to the Labour Safety & Hygiene Subcommittee of the Association for Monitoring of Safety in Decommissioning in Fukushima Prefecture. The fundamental principle of radiation protection under the IR Damage Prevention Rules is that “businesses must make efforts to minimize the amount of ionizing radiation that workers are subjected to in as far as it is possible” (Article 1). TEPCO must fulfill its responsibility to take every measure to control the amount of radiation its workers are exposed to and protect them from radiation.
3 Safety and Health of Fukushima Daiichi Workers and Their Working Conditions
For work toward recovery from the Fukushima Daiichi nuclear accident to proceed, protecting workers’ safety and health and ensuring decent working conditions are extremely important efforts.
During the past 15 years, there have been times when numerous accidents involving fatalities or serious injuries have occurred at FDNPS. In FY2014, the number of work accidents there hit an astounding 64 cases, fully double the number in the preceding fiscal year: 32. At that time, construction work on facilities for treating contaminated water was proceeding at a feverish pace, so there was undue pressure to complete the work in as short a time as possible, with the workers’ safety a secondary consideration. The result was many accidents. In January 2015, a succession of fatal accidents occurred at both the Fukushima Daiichi and Daini nuclear power stations. In January of that year, the Minister of Health, Labour and Welfare addressed a request to TEPCO’s president “regarding thorough measures to prevent work accidents at your nuclear power stations.” Giving uncustomary instructions he said, “We want you to bear in mind that TEPCO is not merely a client placing an order, but the owner of nuclear facilities and that you were furthermore involved in a nuclear accident. You must make that the basis of your efforts to ensure labour disaster prevention at your facilities.” He directed TEPCO together with its primary contractors to establish a safety and hygiene system as its primary responsibility.
From now on, TEPCO must firstly continue its efforts to prevent disasters, including measures to prevent cerebral and cardiac disorders and heat stroke, which can result from severe working environments and long working hours, and also implement measures to promote mental health and steps to prevent harassment, while taking other steps to strengthen the company’s safety and hygiene measures, raising its subcontractors’ wages, improving their treatment, and ensuring decent work conditions.
4 Rethinking the Lack of Formal Occupational Accident Recognition for Exposures below 100 mSv
To date, there have been eight cases of leukemia, one of erythrocythemia, two of laryngeal cancer, two of thyroid cancer, two of lung cancer and two of colon cancer, totaling 17 cases that have been certified as work-related among all the workers engaged in operations at FDNPS since the nuclear accident.
MHLW has determined that only the leukemia cases fall under the certification standard of “5 mSv × (no. of years employed)” and then looks at whether the case is occupational or non-occupational to decide on whether or not to recognize a work-related injury. However, MHLW does not recognize a causal relationship between low-level radiation exposures of under 100 mSv and solid carcinomas.
In contrast, an immunological study (INWORKS2023 Report) on nuclear power plant workers in the UK, France and the US was published by IARC et al., which clarified that health damage (fatalities) could result from radiation exposures of less than 100 mSv (0-50 mSv). The INWORKS2023 Report is highly reliable with strong statistical power, involving 300,000 subjects surveyed, with records kept of their personal exposure levels and follow-up over a long period, and noting numerous instances of damage (fatalities).
The MLHW should take the INWORKS2023 Report seriously, reconsider its current injury compensation policy of considering only exposures of 100 mSv or more as a necessary condition for formal recognition of solid tumors as work-related injuries and recognize cases of solid tumors with less than 100 mSv exposure. In addition, this should not be limited to workers at the FDNPS. It needs to be made widely known that when workers at any nuclear power plant receive cumulative exposures of more than 100 mSv and develop cancer, they can have it certified as work-related. Efforts to encourage workers to seek compensation should be made.
