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During the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station (1F) accident on March 11, 2011, many members of the Japan Health Physics Society, including researchers and radiation workers, were involved in 1F accident-related work. The resulting articles covered a wide range of topics such as lessons learned and future challenges, risk communication, environmental monitoring, dosimetry, radiation medicine, and radioactive waste. In March 2022, a working group was established to review the articles related to the 1F accident published in the Japanese Journal of Health Physics. This article shows the types and number of 1F-related articles published in this journal over a period of about 10 years.

Background: The Korean Peninsula is split between the South Korea and Democratic People’s Republic of Korea (DPRK, North Korea), with North Korea possessing nuclear weapons. There are rising concerns over legacy sites, areas contaminated primarily by nuclear activities. In North Korea, these sites lack regulatory oversight and are likely neglected even if inactive. Hence, it is vital to devise strategies to manage and assess these sites. Yongbyon, a prominent nuclear site in North Korea, has been proposed for environmental sampling to gauge contamination levels. The goal is to determine contamination by suggesting sample collection points in Yongbyon. Materials and Methods: Using recent data and satellite imagery from the International Atomic Energy Agency’s periodic Safety Measures Report, we selected legacy sites to assess their contamination levels with recent data and satellite imagery. We identified sampling locations using the Visual Sample Plan (VSP) to check nuclear contamination. From these results, we devised a scenario evaluating accessibility and the local environment. Results and Discussion: For Yongbyon in North Korea, this study created two sampling scenarios based on interior access feasibility. Given North Korea’s constraints, we finalized the scenario without interior access. The sampling areas include two steam lines, four vehicle paths, and five green zones outside the facility. Conclusion: Nuclear facility operations worldwide are concerning. When halted, these become legacy sites requiring contamination management. Despite North Korea’s limited recordkeeping and challenges in determining contamination, we devised a sampling scenario using VSP software, factoring in accessibility and movement paths.

Background: A portable gamma irradiation system was developed for on-site calibration of environmental radiation monitoring devices. This system uses a portable collimator and gammaray sources such as 57Co, 133Ba, 137Cs, and 60Co, each with a nominal radioactivity of 10 MBq or less. Materials and Methods: The air kerma rate produced by the system was measured using a spherical ionization chamber with a 10 L sensitive volume. This chamber was calibrated against the air kerma rate measured with primary standard ionization chambers. The system’s performance was evaluated by comparing the calibration results of the monitoring device with those obtained using a conventional method involving a standard ionization chamber for outdoor use. Results and Discussion: The calibration coefficient of the spherical ionization chamber was within ±2% of the value of 3.029×103 Gy/C for photon energies ranging from 50 keV to 1,250 keV. The air kerma rate of the irradiation field produced by the portable system ranged from 0.17 μGy/hr to 4.7 μGy/hr, with an uncertainty between 2.4% and 10%. The calibration coefficients obtained using the portable system were consistent with those from the conventional method. Conclusion: The portable gamma irradiation system offers significant advantages, including preventing damage to standard ionization chambers used outdoors and reducing measurement time compared to conventional methods. Due to its ease of construction and implementation, the system is expected to be useful not only for on-site calibration of monitoring devices but also in various radiation safety management scenarios.

Background: A NaI(Tl) survey meter was used in the pediatric thyroid screening conducted after the Fukushima Daiichi Nuclear Power Plant accident. However, this measurement method has the weakness that it is difficult to selectively identify 131I. In this study, we analyzed the performance of an energy-analyzable NaI(Tl) spectrometer using the Particle and Heavy Ion Transport code System (PHITS), which allows Monte Carlo simulation of radiation transport. Materials and Methods: The spectrum of energy emitted by the NaI(Tl) spectrometer was simulated for a total energy absorption peak by adjusting factors that affect pulse wave height. From these simulation results, the detection limits of the NaI(Tl) spectrometer were obtained using Monte Carlo simulation. Results and Discussion: The energy spectrum results were reproduced with an accuracy of 0.1% to 44.0% for total energy absorption peaks. The calculated detection limit for 131I activity equivalent to 100 mSv in the thyroid under a 0.2 μSv· hr−1 ambient dose rate was approximately 80–90 Bq, which could be detected for up to 38 days after 131I intake in a 1-year-old child. Conclusion: This study demonstrated that pediatric thyroid screening using an NaI(Tl) spectrometer can practically provide greater accuracy than NaI(Tl) survey meters.

Background: The installation and removal of nozzle dam work is one of the representative maintenance works in the steam generator primary side and can result in high levels of exposure due to the Chalk River unidentified deposit deposited inside the steam generator. Therefore, it is necessary to assess the radiation dose to workers installing and removing the nozzle dam to determine the exposure level for each task. This study assessed the radiation dose to workers installing and removing the nozzle dam during the overhaul period. Materials and Methods: The work scenarios for installation and removal of the nozzle dam were analyzed based on Advanced Power Reactor 1400 (APR1400) mock-up operation video and worker questionnaire. Then, based on the steam generator design data presented in the APR1400 design criteria document (DCD), the steam generator was simulated using Monte Carlo N-Particle (MCNP) code. Based on analyzed work scenarios and simulated steam generator, the radiation doses to workers were assessed. Results and Discussion: The work scenarios were analyzed for the four sub-works and the steam generator was simulated using MCNP6. The simulated steam generator was used to derive dose rates for each work location. For each sub-work, the assessment results of radiation doses were in the range of 2.13–4.51 man·mSv. For each worker, the radiation doses were in the range of 1.01–2.70 mSv. The highest radiation dose to workers was about 5.4% of the annual dose limit for workers (based on a maximum of 50 mSv per year). In this study, the source term was set using the specific activity of each radionuclide provided as conservative values in the APR1400 DCD. Consequently, the results of the dose assessment are likely to be somewhat conservative. Conclusion: The results of this study can be used for optimizing radiation exposure to workers installing and removing nozzle dam during the overhaul period.

Background: This study is a comparative analysis of legal decisions by the Korean judiciary regarding human health effects of radiation exposure in lawsuits related to the linear no threshold hypothesis of the International Commission on Radiological Protection (ICRP), particularly following the Fukushima nuclear power plant accident in 2011. Materials and Methods: The legal cases related to radiation exposure and human health effects were searched and compiled using legal databases such as ‘national law information center,’ ‘case note,’ and ‘LBOX.’ Keywords such as ‘radiation,’ ‘human health effects,’ ‘lawsuit,’ ‘radiation effects,’ and ‘disease’ were used to search for relevant legal cases, leading to the identification of a total of nine legal decisions. The original texts of these cases were analyzed. The analysis categorized the cases based on the distinction between the plaintiff, radiation doses, types of diseases, and the results of the lawsuits. Results and Discussion: Four lawsuits ruled that there is a causal relationship between radiation exposure and human health effects. These rulings were made in 2016 (two cases), 2018, and 2022. In cases where the radiation exposure doses were precisely recorded as 1.71 mSv and 2.09 mSv, the rulings also concluded that there was a causal relationship between radiation exposure and human health effects. In contrast, five lawsuits concluded that there was no causal relationship between low-dose radiation exposure and human health effects, ruling that a radiation exposure of 12.25 mSv was not related to the disease. Conclusion: Judicial rulings on radiation risks must be consistent and equitable. The ICRP recommends standards for radiation protection and dose limits. Based on these recommendations, the executive branch must establish consistent guidelines, and judicial rulings must maintain consistency in accordance with these standards.