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Yokoyama, Sumi*; Hamada, Nobuyuki*; Tsujimura, Norio; Kunugita, Naoki*; Nishida, Kazutaka*; Ezaki, Iwao*; Kato, Masahiro*; Okubo, Hideki*
International Journal of Radiation Biology, 99(4), p.604 - 619, 2023/04
Times Cited Count：2 Percentile：19.1(Biology)In April 2011, the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens. Such a new occupational lens dose limit has thus far been implemented in many countries, and there are extensive discussions toward its regulatory implementation in other countries. In Japan, discussions in the Japan Health Physics Society (JHPS) began in April 2013 and in Radiation Council in July 2017, and the new occupational lens dose limit was implemented into regulation in April 2021. To share our experience, we have published a series of papers summarizing situations in Japan: the first paper based on information available by early 2017, and the second paper by early 2019. This paper (our third paper of this series) aims to review updated information available by mid-2022, such as regarding regulatory implementation of the new occupational lens dose limit, recent discussions by relevant ministries based on the opinion from the council, establishment process of safety and health management systems, the JHPS guidelines on lens dose monitoring and radiation safety, voluntary countermeasures of the licensees, development of lens dose calibration method, and recent studies on exposure of the lens in nuclear workers and biological effect on the lens.
-iron under cascade damage conditionAbe, Yosuke; Jitsukawa, Shiro; Okubo, Nariaki; Matsui, Hideki*; Tsukada, Takashi
Effects of Radiation on Nuclear Materials; 25th Volume (ASTM STP 1547), p.313 - 337, 2013/01
Times Cited Count：0 Percentile：0.1(Materials Science, Characterization & Testing)It is known that the mechanical properties degradation of reactor pressure vessel steels caused by neutron irradiation is partly due to the formation of nanometer-size solute and point-defect (PD) clusters. Therefore, the rationalization of radiation induced effects on the microstructure and their consequences on the material properties by developing predictive models is thus of great importance. Cluster dynamics (CD) simulation with rate equations has been used to estimate the long-term evolution of point defect clusters. We have extended the CD simulation code to allow hopping motion for all the self-interstitial atom (SIA) clusters to be mobile. Results of calculation on 316 stainless steel and -iron have been compared. The difference and underlying mechanism of microstructural evolution between austenitic stainless steel and -iron is discussed with regard to the dose dependence.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14) (CD-ROM), 13 Pages, 2011/09
Toward the commercialization of fast reactors, a design study of Japan Sodium-cooled Fast Reactor (JSFR) is being performed, in which fully natural circulation system is adopted as the decay heat removal system. A new evaluation method of core hot spot which can be applied to natural circulation decay heat removal has been developed. The new method consists of three-step thermal hydraulics analyses in order to consider the effects of physical phenomena particular to natural circulation, such as inter-fuel-assembly heat transfer and flow redistribution in the core due to buoyancy force. From the viewpoint of calculation cost reduction, we have also developed a simplified model substituting for the third step analysis (subchannel analysis). The new method was applied to the evaluations of a loss-of-external-power event and of a sodium leakage accident in a secondary loop of a large scale reactor.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
Proceedings of 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8) (CD-ROM), 11 Pages, 2010/10
Toward the commercialization of fast reactors, design study of JSFR is being performed. Adoption of fully natural circulation system is being examined as the decay heat removal system. In order to confirm feasibility of the system, we are developing a new evaluation method of core hot spot in transition from rated operation to natural circulation decay heat removal conditions, which requires uncertainty factor assessment for the natural circulation conditions as well as for the rated operation conditions. In this paper, we focus on effects of wire-spacer contact and pellet- cladding eccentricity on the peak cladding temperature as typical uncertainty factors and evaluated these two effects under natural circulation conditions quantitatively.
Ohshima, Hiroyuki; Doda, Norihiro; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
Nihon Kikai Gakkai Rombunshu, B, 76(763), p.448 - 450, 2010/03
Toward the commercialization of fast reactors, a design study of Japan Sodium Cooled Fast Reactor is being performed. In this design study, the adoption of decay heat removal system operated by fully natural circulation is being examined from viewpoints of economic competitiveness and passive safety. This paper describes a new evaluation method of core hot spot that is necessary for confirming feasibility of the fully natural circulation decay heat removal system. The new method consists of three analysis steps in order to include effects of thermal hydraulic phenomena particular to the natural circulation decay heat removal and therefore it enables more rational hot spot evaluation rather than conventional ones. This method was applied to a hot spot evaluation of loss-of-external-power event and the result was compared with those by conventional simulations. It was confirmed that the proposed method can estimate the hot spot with reasonable degree of conservativeness.
Nagai, Ryoji; Kobayashi, Hideki*; Sasaki, Shigemi; Sawamura, Masaru; Sugimoto, Masayoshi; ; Kikuzawa, Nobuhiro; Okubo, Makio; Minehara, Eisuke; *; et al.
Nuclear Instruments and Methods in Physics Research A, 358, p.403 - 406, 1995/00
Times Cited Count：13 Percentile：76.15(Instruments & Instrumentation)no abstracts in English
Ohshima, Hiroyuki; Kamide, Hideki; Tanaka, Masaaki; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
In the design study of commercialized sodium-cooled fast reactor, the adoption of decay heat removal by entire natural circulation is being examined from the viewpoint of enhancing economical competitiveness and safety. In this study, an evaluation method is proposed, in which the hot spot in the core can be rationally evaluated under transient conditions from rated operation to natural circulation decay heat removal.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
no abstracts in English
Ohshima, Hiroyuki; Kamide, Hideki; Doda, Norihiro; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
In the conceptual design study of Japan Sodium-cooled Fast Reactor (JSFR), adoption of a decay heat removal system (DHRS) utilizing passive natural circulation is being examined as one of innovative technologies to improve economical competitiveness and reactor safety at the same time. In order to adopt such a passive DHRS in a large scale SFR, it is necessary to clarify the core cooling capability. In this presentation, a new evaluation method of core peak temperature is proposed, which takes account of buoyancy force effects (e.g., flow redistribution in core/fuel assemblies and inter-assembly heat transfer) and uncertainty factors under the natural circulation conditions.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
Toward the commercialization of fast reactors, adoption of fully natural circulation system is being examined as the decay heat removal system from the viewpoints of economic competitiveness and passive safety. This paper introduces a new evaluation method for hot spot in core of fast reactor under natural circulation. The new method consists of three step analysis in order to include the effects of thermal hydraulic phenomena particular to natural circulation decay heat removal, inter-assembly heat transfer and flow redistribution in fuel assemblies and in the core by buoyancy force. The method was applied to an analysis of loss-of-external-power event and the result was compared with those by a conventional method and a detailed 3D simulation. It was confirmed that the proposed method can estimate the hot spot with a reasonable degree of conservativeness.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
Toward the commercialization of sodium cooled fast reactors, adoption of fully natural circulation system is being examined as the decay heat removal system. This paper introduces investigations on a simplified evaluation method for hot spot in core of fast reactor under natural circulation.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
A new simplified evaluation method of core hot spot under transient conditions has been developed for feasibility study of decay heat removal operation by natural circulation in sodium cooled fast reactors. Its applicability was confirmed through an evaluation of a typical transient event of FBR.
Doda, Norihiro; Ohshima, Hiroyuki; Kamide, Hideki; Watanabe, Osamu*; Okubo, Yoshiyuki*
no journal, ,
Toward the commercialization of fast reactors, a design study of Japan Sodium Cooled Fast Reactor (JSFR) is being performed. In this design study, adoption of fully natural circulation system is being examined as the decay heat removal system. We are developing a new evaluation method of core hot spot in transition from rated operation to natural circulation decay heat removal conditions. This paper summarises the evaluation method and its future developments.
