Effects of different accident scenarios and sites on the reduction factor used for expressing sheltering effectiveness

Hirouchi, Jun; Watanabe, Masatoshi*; Hayashi, Naho; Nagakubo, Azusa; Takahara, Shogo

Journal of Radiological Protection, 45(1), p.011506_1 - 011506_11, 2025/03

https://doi.org/10.1088/1361-6498/adba6e

Public living in areas contaminated by nuclear accidents is exposed to radiation in the early phase and over the long term. Even under similar accident scenarios, radiation doses and sheltering effectiveness, which is one of the protective measures, depend on meteorological conditions and the surrounding environment. Radiation doses and sheltering effectiveness in the early phase of nuclear accidents are crucial information for the public as well as national and local governments planning a nuclear emergency preparedness. In this study, we assessed radiation doses and sheltering effectiveness at sites with nuclear facilities in Japan using the Off-Site Consequence Analysis code for Atmospheric Release accidents, which is one of the level-3 probabilistic risk assessment codes, for five accident scenarios: three scenarios from past severe accident studies, a scenario defined by the Nuclear Regulation Authority in Japan, and a scenario corresponding to the Fukushima-Daiichi Nuclear Power Station accident. The sheltering effectiveness differed by up to approximately 50% among the accident scenarios at the same sites and by approximately 20%50% among sites under the same accident scenario. Differences in the radionuclide composition among the accident scenarios and the differences in wind speeds among the sites primarily caused these differences in sheltering effectiveness.

Construction of new polygon mesh-type phantoms based on adult Japanese voxel phantoms

Sato, Kaoru; Furuta, Takuya; Satoh, Daiki; Tsuda, Shuichi

PLOS ONE (Internet), 19(10), p.e0309753_1 - e0309753_26, 2024/10

https://doi.org/10.1371/journal.pone.0309753

The authors previously developed the adult male (JM-103) and female (JF-103) voxel phantoms with standard Japanese body sizes for dose assessment of radiation accidents and medical exposures. However, JM-103 and JF-103 were not applicable to dose assessment considering posture at the time of exposure due to limitations in description format and resolution. In this study, we developed the polygon mesh-type adult Japanese phantoms (male: JPM, female: JPF) based on JM-103 and JF-103. The detailed models of skin and lens with radiosensitive regions less than 1 mm thick were incorporated into JPM and JPF. The effective doses, and skin and lens (entire and radiosensitive regions) doses were calculated for external irradiation with photons or electrons in anterior-posterior geometry. It was confirmed that dose analysis results by JPM and JPF were consistent with the previous reports. In the future, we will develop a detailed dose assessment method for individuals, taking into account their postures at the time of exposure, by applying the posture deformation technique currently under development to the JPM and JPF.

External exposure assessment in the Fukushima accident area for governmental policy planning in Japan, 2; Matters to be attended for assessments of external exposure

Yoshimura, Kazuya; Sanada, Yukihisa; Sato, Rina; Nakayama, Mariko*; Tsubokura, Masaharu*

Journal of Radiation Research (Internet), 64(2), p.203 - 209, 2023/03

https://doi.org/10.1093/jrr/rrac088

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, individual exposure doses to residents have been assessed by many municipalities, governments and research institutes. Various methods including measurements with personal dosimeters and simulations have been used for this evaluation depending on purposes, but the information of assessments and methods has not been systematically organized. A comprehensive review of the knowledge and experiences of individual exposure doses assessments accumulated so far and understanding the characteristics of the assessment methods will be very useful for radiation protection and risk communication, following to governmental policy planning. We reviewed the efforts made by the Japanese government and research institutes to assess radiation doses to residents after the FDNPS accident in Part1. On the other hand, each method of assessing individual exposure doses includes uncertainties and points to be considered for the appropriate assessment. These knowledge and experiences are important for the assessment implementation and applying the assessment results to the governmental policy planning, and are summarized in Part2 of this article.

Influence of differences in model parameters observed in Europe and Japan, on the effective dose predicted by the European model for inhabited areas (ERMIN)

Hirouchi, Jun; Charnock, T.*

Proceedings of 14th International Conference on Radiation Shielding and 21st Topical Meeting of the Radiation Protection and Shielding Division (ICRS-14/RPSD 2022) (Internet), p.195 - 198, 2022/09

ERMIN (EuRopean Model for Inhabited Areas), which was compared and validated with other models by EMRAS II program, is a code that provides a module to two European nuclear accident decision support systems and calculates doses for people in inhabited areas contaminated by radionuclides. Parameters in ERMIN are principally based on observations after the Chernobyl accident. However, these parameters may differ among countries. In order to understand the uncertainty and variability of calculated doses when applying ERMIN elsewhere, it is important to investigate the degree of influence of each parameter on doses. Therefore, in this study, the parameters in Japan obtained by our literature surveys were compared with those used in ERMIN. We calculated doses using the values and uncertainties of those parameters and investigated the differences in doses and the influence of each parameter on doses. The results showed that the retention parameters, soil migration parameters, air exchange rate, and indoor deposition rate have a significant influence on the dose assessment.

Evaluation of radioactivity concentration corresponding to dose criterion for near surface disposal of radioactive waste generated from research, medical, and industrial facilities, Volume 1

Sugaya, Toshikatsu; Abe, Daichi*; Okada, Shota; Nakata, Hisakazu; Sakai, Akihiro

JAEA-Technology 2021-004, 79 Pages, 2021/05

JAEA-Technology-2021-004.pdf:2.86MB
JAEA-Technology-2021-004(errata).pdf:0.38MB

JAEA has aims to carry out near surface disposal of low-level radioactive waste generated from research, medical, and industrial facilities. Therefore, radioactivity concentration corresponding to dose criteria of near surface disposal for 220 nuclides in the waste were calculated for the purpose of discussion for radioactivity limits between trench and concrete vault disposal, and key nuclides related to them. We calculated the radioactivity concentrations with consideration of not only the exposure pathways used at calculation of the radioactivity concentration limits of waste packages for near surface disposal by Nuclear Safety Commission but also ones used at the concentration limits for intermediate depth disposal. We also assumed the capacities of the disposal facilities as 44,000 m for pit disposal and 150,000 m for trench disposal. The radioactivity concentrations calculated in this report is used as the reference values because the disposal site has not been decided yet. Addition to this, the radioactivity concentrations will be revised according to circumstances of development of disposal facilities and so on. In the future, we will decide the radioactivity and radioactive concentration of a waste package described in the license application documents based on the dose assessment taken into consideration the disposal site conditions.

Evaluation of effective dose for exposures in the environment

Saito, Kimiaki

Annals of the ICRP, 49(2), p.7 - 9, 2020/10

https://doi.org/10.1177/0146645320916969

no abstracts in English

Organ absorbed dose estimation reflecting specific organ masses with simple scaling of reference doses using the organ masses

Manabe, Kentaro; Koyama, Shuji*

Radiation Protection Dosimetry, 189(4), p.489 - 496, 2020/05

AA2019-0343.pdf:0.67MB

https://doi.org/10.1093/rpd/ncaa058

It is important for radiation protection in diagnostic nuclear medicine to estimate organ absorbed doses in consideration of person-specific parameters. This study proposes a straightforward method for estimating organ doses which reflect an individual organ masses by scaling the reference doses based on the reference human models using the inverse ratio of the individual masses to the reference organ masses. The method was tested for the administration cases of Tc-labelled colloids and I-labelled sodium iodine to confirm the effectiveness of the method. The discrepancies of the doses estimated by the method were sufficiently small in terms of solid organs.

Dose estimation for contaminated soil storage in living environment

Takai, Shizuka; Shimada, Asako; Sawaguchi, Takuma; Takeda, Seiji; Kimura, Hideo

Radiation Protection Dosimetry, 188(1), p.1 - 7, 2020/01

https://doi.org/10.1093/rpd/ncz250

After the Fukushima Nuclear Power Plant accident, most of radiocesium-contaminated soil generated from decontamination activities outside Fukushima prefecture has been stored at decontamination sites such as schools, parks and residential lands (storage at sites) according to the Decontamination Guidelines. However, additional exposure due to the present storage has not been evaluated. Moreover, entering storage sites, which is not restricted for storage at sites, was not considered in safety assessment conducted in the guidelines. To continue the storage and confirm the effectiveness, understanding of present possible exposures is important. In this study, we evaluated exposure doses for residents and users of storage sites based on the present situation. As a result, annual doses due to residence were 10 to 10 mSv y and doses due to annual entries were of the order of 10 mSv y. Hence, we confirmed that the exposure due to present storage outside Fukushima is significantly less than 1 mSv y.

Dose estimation in recycling of decontamination soil from the Fukushima Daiichi NPS accident for land reclamation

Shimada, Asako; Nemoto, Hiromi*; Sawaguchi, Takuma; Takeda, Seiji

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 6 Pages, 2019/05

https://doi.org/10.1299/jsmeicone.2019.27.1370

no abstracts in English

Dose estimation in recycling of decontamination soil resulting from the Fukushima NPS accident for road embankments

Takai, Shizuka; Sawaguchi, Takuma; Takeda, Seiji

Health Physics, 115(4), p.439 - 447, 2018/10

https://doi.org/10.1097/HP.0000000000000904

After the Fukushima Nuclear Power Station accident, large quantities of radiocesium-contaminated soil generated from decontamination activities have been stored in the Fukushima Prefecture. To reduce the disposal volume, the Ministry of the Environment of Japan has presented a policy to recycle low-radioactive decontamination soil limited to civil engineering structures. However, there has been no practical instance or safety assessment of decontamination soil recycling. In this study, the way of ensuring the safety for decontamination soil recycling for road embankments was discussed. First, based on Japanese construction standards, additional doses to workers and the public in construction and service scenarios were evaluated. From the result, the radioactive cesium concentration level of recycled materials, where all additional doses meet the radiation criterion of 1 mSv y, was derived to be 6,000 Bq kg. To confine additional doses to the public in a service scenario below 0.01 mSv y, soil slope protection of 40 cm or more was needed. Finally, additional doses in a disaster scenario were confirmed to be below 1 mSv y.