The International Atomic Energy Agency (IAEA) published the Specific Safety Guide (SSG)-91, “Protection of Workers Against Exposure Due to Radon” in November 2024, providing recommendations for protecting workers from radon exposure in workplaces. Section 2 of SSG-91 introduces the framework to determine appropriate approaches for the protection. Sections 3 and 4 provide guidance on protecting workers in existing exposure situations and planned exposure situations, respectively. These sections also include recommendations for the protection, along with detailed explanations of the responsibilities and functions of the government, the regulatory body or other relevant authority, and employers. This paper provides an overview of SSG-91, summarizing key points from each chapter. Additionally, it discusses the background behind the development of SSG-91 and explains related developments in Japan.

In nuclear power generation, which utilizes the energy released through nuclear fission, various radioactive nuclides are inevitably generated. In particular, the long-term safe disposal of high-level radioactive waste (HLW), which contains radionuclides with high radioactivity levels and long half-lives, has long been a concern in countries that use nuclear power. These countries plan to dispose of HLW deep underground (i.e., geological disposal) so that it would not affect human health and the environment in the distant future. However, they face difficulties in reaching a social consensus on the selection of burial disposal sites and the method of ensuring the safety of disposal facilities. It would take a long time before geological disposal will be implemented. The authors recognize that in order to improve this current worrying situation, it is important to consider the issue from humanity and social science perspectives, in addition to explanations from a science and engineering perspective as has been done so far and have exchanged information and opinions at the “Special Study Group on Considerations from a Humanities and Social Science Perspective on the Management and Disposal of Radioactive Waste,” which was established by the Japan Health Physics Society in 2022. This paper reports on the knowledge and ideas shared and agreed upon through these discussions over approximately two years.

As nuclear power plants are increasingly being restarted, it is extremely important for Japan to develop an emergency monitoring system that reflects the lessons learned from the accident at the TEPCO Fukushima Daiichi Nuclear Power Station. Although much research and development has been carried out in the world, how and by whom the new emergency monitoring system will be operated is not yet fully developed. In particular, based on the lessons learned from the Fukushima nuclear accident, there is a need to develop a screening system for evaluation of radiation dose from radioactive iodine in the thyroid glands of children and pregnant women. This paper reviewed the reports on emergency monitoring of the ICRP, ICRU and IAEA, and summarizes their main points. In addition, a questionnaire survey on emergency monitoring was conducted among organizations with which the authors have personal connections, the results were shown in the Appendix. This paper summarized the results of the two years of committee's activities from 2020 and the results of a further year. It also described relevant ICRP reports and reports on the concept of radiation protection in emergency situation, monitoring and the development of a radiation protection culture in the community. Furthermore, ICRU reports on radiation monitoring in emergency exposure situation, data required for radiation assessment, monitoring programs, individual monitoring programs and evaluation of organizational responses were reviewed.

The authors release a homemade code named DIRAP (Dosimetry for Inhaled Radon Progeny), which is used to calculate the effective dose per exposure to ²²²Rn progeny. The accuracy of the code was verified by comparing its calculations to the values reported in ICRP publications for the adult Reference Person engaged in light work. This code can also calculate the doses for the adult Reference Person at the four reference levels of physical exertion: sleep, sitting, light exercise and heavy exercise. A copy of the source code is available in text format by contacting one of the authors via email at dirap@qst.go.jp.

In a previous report of the authors, changes in aerosol number concentrations before and after passing through four types of masks (non-woven masks, N-95 masks, urethane masks, and gauze masks) were investigated. In the present study, reduction rates of aerosol-attached radon progeny concentrations were calculated from the changes in aerosol number concentrations and attachment coefficients for four particle size ranges, based on a theory of attachment of radon progeny to aerosol particles. Additionally for comparison, reduction rates of radon progeny concentrations before and after passing through the masks were measured by an alpha-counting method. The calculated and measured reduction rates were in good agreement. Reduction rates of inhalation dose due to radon progeny were estimated for the four types of masks at the same two experimental conditions as in the previous study. The reduction rates for the four types of masks were 23 to 99.5% for experiments without simulation of a person wearing a mask. Those for the same masks were 31% to 75% for experiments with simulation of a person wearing a mask. The results for experiment at the two different conditions indicated that the reduction rates depended on the adhesiveness of the mask to the face as well as the mask types.