Case study activities for nuclear security culture development in JAEA

Amano, Tsukasa; Shibata, Ryodai; Sato, Yoshiharu; Yamazaki, Katsuyuki; Shiromo, Hideo; Nakamura, Hironobu

Proceedings of INMM & ESARDA Joint Annual Meeting 2023 (Internet), 6 Pages, 2023/05

In Japan, about 10 years have passed since the law obligated nuclear operators to develop and maintain a nuclear security culture. During this period, the global nuclear situation has changed significantly, and it is becoming important to maintain a stance that emphasizes compliance with regulations and nuclear security culture. In JAEA, the policy of legal compliance and developing nuclear security culture is determined by the president of JAEA. For legal compliance and developing nuclear security culture, many activities are carried out based on that policy. Finally, these activities are evaluated and improved it every year. Case study is the one of activities that can obtain skills for legal compliance and developing nuclear security culture, such as sensitivity of nuclear security risks, correct understanding of the laws. The procedure for the case study was created with reference to a method called KY-Training which is often applied to safety training program in Japan. KY-Training is a training that participants (groups) can reach the conclusion how to respond to cases through four questions. Firstly, participants are given illustrations and descriptions which has potential of nuclear security risks. Then, participants make discussion according to four questions. Consequently, participants can effectively become aware of nuclear security risks. In the 2022 case study, we prepared 23 cases so that they can select choose freely according to role of participants such as in charge of nuclear security, guards, general employees. Finally, participants are asked to fill a questionnaire to evaluate effectiveness of case study. The result of questionnaires indicated that the case study was able to lead to improvement sensitivity of nuclear security risks and correct understanding of the laws. Overall, case study results suggested that JAEA's efforts were implying sufficiently to develop and maintain a nuclear security culture.

Laboratory experiment on runoff of particles deposited on land surface by rainfall at accidents in the decommissioning stage

Shimada, Taro; Namekawa, Masakazu*; Miwa, Kazuji; Takeda, Seiji

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02

It is supposed that radioactive dust deposited at the land surface will be moved downstream and concentrated at the depression by overland flow at heavy rain after the accidental release of radioactive dusts accumulated at the filters in the decommissioning stage of nuclear facilities. The authors are developing a calculation code to evaluate distribution changes of radioactivity on the surface and public dose considering the conditions such as rainfall, topography and types of cover surface. It is necessary to construct methods for setting parameter values used for the calculations based on the actual situation. Therefore, the parameter values were obtained by the experiments where FeO powder spread on the cover surface such as smooth and aged-asphalt, concrete and bare soil, was eroded by overland flow and raindrops and they were collected at the lower end of the slope at a minute interval. The collected weights of overland flow and FeO powder were measured. Based on the Manning's roughness coefficient for smooth asphalt already known as a fixed value, the erosion velocity coefficient was evaluated. Then Manning's roughness coefficients for other cover surfaces were obtained using the erosion velocity coefficient. Manning's roughness coefficients were slightly smaller than the range of literature values. In addition, elevations for the cover surface were measured by 3D scanner as point cloud data, and the surface roughness were evaluated. The values of surface roughness and Manning's roughness coefficients had a correlation. It indicated a possibility to utilize the surface roughness to set the Manning's roughness coefficient for the evaluation of radioactivity distribution change by heavy rainfall.

Vibration test and fatigue test for failure probability evaluation method with integrated energy

Kinoshita, Takahiro*; Okamura, Shigeki*; Nishino, Hiroyuki; Yamano, Hidemasa; Kurisaka, Kenichi; Futagami, Satoshi; Fukasawa, Tsuyoshi*

Transactions of the 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 7 Pages, 2022/07

The seismic evaluation of key components such as reactor vessel is important for the Seismic Probabilistic Risk Assessment (S-PRA) in a Sodium-Cooled Fast Reactor (SFR). Many components were damaged by cumulative damage like fatigue damage during seismic ground motion. However, general evaluation method for key components under seismic ground motion has been based on static loads and elastic region of materials. More accurate evaluation method for S-PRA, which can evaluate the failure of key components such as reactor vessels, has been actually required. In this study, failure probability evaluation method with integrated energy was developed by comparing the energy with vibration tests and fatigue tests. Vibration tests were performed to evaluate integrated vibration energy at failure by energy balance equation and fatigue tests were performed to evaluate integrated vibration energy at failure based on experimental results of fatigue tests.

Development of seismic safety assessment method for piping in long-term operated nuclear power plant

Yamaguchi, Yoshihito; Li, Y.

Haikan Gijutsu, 63(12), p.22 - 27, 2021/10

no abstracts in English

Lifetime risk assessment of lung cancer incidence for nonsmokers in Japan considering the joint effect of radiation and smoking based on the life span study of atomic bomb survivors

Shimada, Kazumasa; Kai, Michiaki*

Journal of Radiation Protection and Research, 46(3), p.83 - 97, 2021/09

https://doi.org/10.14407/jrpr.2020.00255

[Background] The lifetime risk of lung cancer incidence owing to radiation for non-smokers is overestimated because the average cancer baseline among a population including smokers is used. In recent years, the generalized multiplicative (GM) excess relative risk (ERR) model has been developed in the life span study of atomic bomb survivors to consider the joint effect of radiation and smoking. Based on this background, the issues of radiation risk assessment considering smoking will be discussed in this paper in 2 parts. [Materials and Methods] Part 1: We proposed a simple method of estimating the baseline risk for non-smokers using current smoking data. We performed sensitivity analysis on baseline risk estimation to discuss the birth cohort effects of birth year effect and smoking history. Part 2: We applied the GM ERR model for Japanese smokers to calculate lifetime attributable risk (LAR). We also performed a sensitivity analysis with other ERR models (e.g., simple additive (SA) ERR model). [Results] Part 1: The lifetime baseline risk (LBR) for non-smokers were 54% (44% - 60%) or males and 24% (18% - 29%) for females, which were lower than the LBRs for all adults including smokers. Part 2: When comparing the LAR between the SA ERR model and the GM ERR model, if the radiation dose was 200 mGy or less, the difference between these ERR models was within the standard deviation of the LAR owing to the uncertainty of the smoking information.

Concept of radiation protection for low-dose risks

Takahara, Shogo

Hoshasen Seibutsu Kenkyu, 55(2), p.162 - 172, 2020/06

http://rbrc.kenkyuukai.jp/special/index.asp?id=33566

no abstracts in English

Development of human resources socially requested for nuclear and radiation technology

Yoshinaka, Kazuyuki

Gijutsushi, (634), p.8 - 11, 2019/10

AA2019-0232.pdf:0.4MB

Since the FUKUSHIMA-DAIICHI Nuclear Power Plant accident, a significant issue to develop human resources for nuclear and radiation technology has been growing up. A strong effort will be made, based on the serious experiences of troubles/accidents, to restore social confidence by developing engineers having high sense of ethics beyond logic of organization.

Development of seismic counter measures against cliff edges for enhancement of comprehensive safety of nuclear power plants, 10; Avoidance of cliff edge for reactor vessel

Yamano, Hidemasa; Nishida, Akemi; Choi, B.; Takada, Tsuyoshi*

Transactions of the 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08

The objective of this study is to assess cliff edge effects, which are greatly important for nuclear power plants. Through assessments of failure probabilities (fragility), this study examined seismic margins of simulated two kinds of thin- and thick-walled reactor vessels by using response waveforms of the reactor building with/without a seismic isolation system obtained by seismic response analyses. The fragility analyses showed that the seismic isolation technology largely reduced the structural response effects nearly twice as much as that of the non-isolated plant. In focusing on uncertainty of response factor of components, the seismic isolation plant has a significant margin compared to the non-isolated plant even if factors from 0.5 to 2.0 are taken into account. This study concluded that the seismic isolation technology is effective to avoid cliff-edge effects.

Visualized measurement of extremely high-speed droplets in Venturi scrubber

Horiguchi, Naoki; Yoshida, Hiroyuki; Abe, Yutaka*

Journal of Nuclear Science and Technology, 56(3), p.278 - 290, 2019/03

https://doi.org/10.1080/00223131.2018.1564707

Venturi scrubber (VS) has been installed in NPPs as one of the components of filtered venting systems. It can eliminate fine aerosol particles including fission products from polluted gas. Under extremely high-velocity conditions during severe accident, the data related to the droplet in the VS, which affects decontamination performance, is insufficient. This objective is to obtain the diameter of the extremely high-speed droplets and clarify an applicability of the existing correlations for the diameter. To visualize the extremely high-velocity droplet, an optical system with high frame rate and high resolution was developed. Visualization experiment using the VS under air-water condition was conducted, and droplet diameter distributions and Sauter mean diameter (SMD) were obtained. By comparing experimental data with values evaluated by existing correlations, it was clarified that the Nukiyama-Tanasawa equation can evaluate the SMD with good accuracy in the gas velocity range 82-250 m/s.

Analysis of the trends on minimization of proliferation risk

Suda, Kazunori; Shimizu, Ryo; Tazaki, Makiko; Tamai, Hiroshi; Kitade, Yuta

Nihon Kaku Busshitsu Kanri Gakkai Dai-38-Kai Nenji Taikai Rombunshu (Internet), 9 Pages, 2018/04

Since India's nuclear explosion in 1974, there has been continued discussion on nuclear non-proliferation. At first, to prevent proliferation of nuclear weapons, the International Nuclear Fuel Cycle Evaluation (INFCE) was established to discuss reprocessing, plutonium handling, and so on. After that, to respond to the threat of proliferation posed by DPRK, the international community desired to further enhance nuclear non-proliferation by strengthening the IAEA safeguards system. In recent years, some researchers at universities and national laboratories are studying proliferation resistance from the standpoint of nuclear materials that may be inherently self-protecting. This paper discusses minimization of proliferation risk and future prospects based on alternative measures for reprocessing, plutonium handling, and recycling described in INFCE-WG4.