The Fukushima Daiichi Nuclear Power Plant (FDNPP) suffered reactor damage in the 2011 Great East Japan Earthquake and the subsequent Fukushima Daiichi Nuclear Accident (Fukushima Accident), leading to the release of radioactive materials into the environment. Decommissioning operations are currently underway. Tokyo Electric Power Company (TEPCO), which plays a central role in the decommissioning process, estimates that decommissioning will take at least several decades to complete. 1 This study aims to assess the situations involving potential risks of over-exposure to radiation faced by workers during decommissioning operations and propose effective medical countermeasures.
Discussion
Characteristics of Injuries and Illnesses Occurring at the FDNPP Decommissioning Site
Worker mortality events have occurred at the FDNPP decommissioning site at regular intervals. The daily number of workers on-site, the temporal changes in the number of patients visiting the on-site emergency room visits, and the dates and causes of on-site deaths are presented in Figure 1. Until fiscal year 2019, on-site death due to injury or illness occurred every few months, with over half attributed to heart disease, which is endogenous. Although the frequency of such incidents has declined in recent years, the total number of fatalities has reached 15. Notably, none of these deaths can be linked to radiation exposure or contamination as a direct cause of DNA damage.
Figure 1. ACS: acute coronary syndrome.
Radiation Risks During Decommissioning Operations
Radiation exposure doses for decommissioning workers are strictly maintained within international regulatory limits.Reference Valentin2 To date, no confirmed deterministic or stochastic effects of radiation have been observed among FDNPP workers. The highest-risk areas are the reactor buildings, which have a risk of contamination from α radionuclides, and filtration systems for contaminated cooling water.
The external radiation exposure dose for workers at the FDNPP is controlled to an average of <0.3 mSv/month. Over the past 5 years (April 2021-July 2024), the cumulative external and internal exposure doses averaged 4.77 mSv (maximum, 57.62 mSv).3 These figures indicate that radiation exposure in the current decommissioning operations remains within the regulatory dose limits.
Two areas within the FDNPP present relatively high radiation risks (Figure 2). The first is inside the reactor buildings of Units 1-4, where there is a risk of high-concentration contamination and high-dose exposure from radioactive materials linked to the Fukushima Accident (Figure 2 Area 1). This area contains a mixture of α, β, and γ radionuclides, raising the risk of internal exposure through inhalation of α radionuclides, which have high radiation weighting factors and Relative Biological Effectiveness (RBE). Medical personnel should be vigilant regarding potential internal contamination. A recent incident on December 10, 2023, involved the first case of internal exposure from α radionuclides since decommissioning began (Table 1).
Figure 2. Two processes in the decommissioning work are recognized as having relatively high radiation risks for workers.
Table 1. Recent events of internal and external contamination in the FDNPP (2021.03~2024.09)
Record levels: 2 mSv;level by which TEPCO determines that there was “no significant ingestion” based upon the Exposure Measurement/Assessment Manual issued by the Nuclear Safety Technology Center, criteria for exiting radiation-controlled zone: 4 Bq/cm2, R/B: reactor building, T/B: turbine building
The second area considered to have high radiation risks is the contaminated water filtration systems and storage facilities for filtered waste, including the Advanced Liquid Processing System (ALPS) and high-integrity containers (HIC) used for storing high-density radioactive waste (molten slag) (Figure 2 Area 2). In this area, there is a risk of external exposure and contamination from β radionuclides such as strontium and yttrium, including contamination through wounds. High-density skin contamination from strontium occurred in the area on October 25, 2023. As the criteria for exiting radiation-controlled zones (4 Bq/cm2) could not be met and local skin radiation injuries could not be ruled out, the affected individuals were hospitalized at Fukushima Medical University Hospital for decontamination and observation of the skin condition (Table 1). To date, no deterministic skin effects have been observed in these cases. Including the above 2 cases, all instances of external and internal exposure and contamination have resulted in committed effective doses below the record level set by TEPCO (2 mSv), and no cases have required medical intervention involving the administration of internal decontamination.
Medical Challenges and Countermeasures for Perceived Radiation Risk in Future Decommissioning Operations
As of September 2024, nuclear fuel removal operations have resumed at the FDNPP, with radiation exposure and contamination risks from radioactive materials anticipated to increase accordingly. However, the absence of clear medical criteria for initiating treatment for internal exposure resulting from radioactive material uptake is a challenge for medical personnel. As medical professionals, we aim to avoid deterministic effects (tissue reactions). While the absorbed dose is used to assess deterministic effects, internal exposure varies significantly by tissue and organ, complicating the estimation of effects based solely on whole-body absorbed dose. Consequently, internal exposure is currently estimated using the “committed effective dose,” which considers factors such as wound contamination, injury severity, treatment side effects, life expectancy, and available medical resources.4-6 However, the committed effective dose was designed as an “indicator for stochastic risk assessment” and a “reference value for radiation protection,” not to guide individual medical interventions. This presents a fundamental issue for use as standards for medical decisions. Additionally, in cases of α radionuclide uptake, dose assessment may overestimate actual exposure due to the conservative values assigned to RBE and radiation weighting factors for α radionuclides.7 To address these issues, the Ministry of Economy, Trade and Industry, in collaboration with decommissioning stakeholders, is developing a protocol for medical responses to internal contamination incidents at the FDNPP.
Another issue is that Japan’s system for stockpiling and administering emergency drugs is inadequate. Japan lacks a fully developed system for “compassionate use,” to allow the emergency use of medications approved abroad but not yet authorized domestically in crises or disasters. Consequently, we must apply for specific clinical research using medications as emergency responses, obtain approval from certified clinical review boards, and subsequently import medications for stockpiling, maintenance, and management. 8
On-site nuclear disaster response and preparedness in Japan: Establishing the On-site Medical System Development Committee
Japan has learned many lessons from the Great East Japan Earthquake and Fukushima Nuclear Power Plant accident, which have been implemented into policy. For example, a medical system has been built to cope with this disaster.Reference Tanigawa, Hosoi and Hirohashi9, Reference Hasegawa, Tanigawa and Ohtsuru10 Since 2015, a nuclear disaster medical system centered on nuclear disaster base hospitals has been established,11 with the aim of minimizing the effects of radiation on the residents living near a nuclear power plant (off-site) in the event of a nuclear accident. Four nuclear disaster medical support centers currently oversee the prefectures of nuclear power plants and the neighboring prefectures in each region, while support centers conduct various educational and training programs. However, this new medical system is not responsible for caring for workers injured or exposed to radiation inside (on-site) nuclear power plants at the time of accidents, because, in Japan, different ministries are responsible for nuclear disaster response within and outside of nuclear power plants. The Ministry of Health, Labor, and Welfare (MHLW) plays a crucial role in on-site medical care at power plants, and in exercising jurisdiction over this area. In contrast, the Nuclear Regulation Authority is responsible for off-site medical care around power plants. Under the current regulations, the Disaster Medical Assistance Team (DMAT)Reference Kondo, Koido and Morino12 and Emergency Medical Information System (EMIS),Reference Anan, Akasaka and Kondo13 which operate during natural disasters, are also administered the MHLW, and cannot be used during a nuclear disaster. The decommissioning of the FDNPP, a complex and ongoing process, thus presents unique challenges. With more than 3000 workers inside the plant daily, the need for medical care remains constant. An on-site emergency room, open 24/7, is staffed by 65 registered physicians working in shifts, most of them are board certified emergency physician in all over Japan, ensuring round-the-clock care for injuries and illnesses.
Japan has more than 50 nuclear reactors, some of which are currently operational. The MHLW recently notified the electric power companies that own nuclear power plants to establish a nationwide on-site medical system in preparation for future nuclear accidents and disasters. Following the 2011 accident at the FDNPP, gathering registered physicians during the initial stages of establishing an emergency room was challenging, which led to the establishment of the On-Site Medical System Development Committee in 2021. This committee, comprising a working group of 12 electric power companies, experts in radiation disaster medicine, related academic societies, and electric power companies, was formed to address this issue. The committee’s working group surveyed the 65 doctors registered in the FDNPP’s emergency room network to establish an effective on-site medical care system (Figure 3).
Figure 3. Sixty-five physicians registered with the 1F ER Network were asked whether 24-hour on-site support by physicians registered with the 1F ER Network would be possible in case of an accident or disaster at another nuclear facility in Japan. Of these, 52 of the 65 physicians responded.
Many physicians indicated availability to work in the emergency room if an accident occurred at another nuclear power plant. However, they noted several challenges in establishing this system (Table 2). Currently, Japan’s on-site medical system for disasters is insufficient, and requires a proactive approach for recruiting registered physicians, focusing on recruiting emergency physicians in prefectures with nuclear power plants and neighboring prefectures, subsequently extending to a nationwide recruitment strategy. In complex disasters, the participation of DMAT is essential, and collaboration beyond the boundaries of the responsible ministries and agencies must be promoted.
Table 2. Unresolved issues in the establishment of a nationwide nuclear power plant on-site medical system
Conclusion
The perceived risk of exposure and contamination for workers at the FDNPP is expected to increase as the decommissioning process progresses. Consequently, it is anticipated that medical responses to incidents involving radioactive materials may still encounter confusion. We hope that these considerations will serve as a reference for onsite medical interventions and contribute to the progress of decommissioning operations.
Acknowledgements
We would like to thank the staff of Fukushima Medical University and Hiroshima University, and all the stakeholders in the decommissioning of the Fukushima Daiichi Nuclear Power Plant for their valuable work.
Author contribution
The corresponding authors had full access to all data in the study and had the final responsibility to submit the article for publication. AH contributed to manuscript writing and research design of the conclusion and discussion, and NH to the discussion. All authors contributed to the review of the entire manuscript.
Funding statement
This study was supported by the Nuclear Regulatory Agency Japan.
Competing interest
The authors declare no competing interests.
Ethical standard
Not required.
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