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Fukuda, Kodai; Yamane, Yuichi
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 9 Pages, 2023/10
This study presents the results of multiphysics analysis, which investigates the change of reactivity caused by the motion of fluids, of Windscale Works criticality accident. The purpose of this study is to confirm previously reported trends of emulsion formation and increase in reactivity by the multi-physics analysis which takes the motion of fluids into account. Continuous energy Monte Carlo code MVP3 was used to calculate reactivity based on the material distribution obtained by CFD calculation using OpenFOAM. An interface program in python was developed to transfer data from OpenFOAM to MVP3. The change of reactivity caused by the motion of solutions was calculated without considering the generation of heat by fissions in a system that simulated the transfer vessel at Windscale Works. As a result, trends of emulsion formation and increase in reactivity were confirmed. The influence of the resolution of the calculation system on the results was also discussed.
Okuno, Hiroshi; Suyama, Kenya
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 8 Pages, 2023/10
The criticality accident that resulted in the evacuation of residents occurred on September 30, 1999, at JCO's nuclear fuel fabrication plant in Ibaraki prefecture, Japan. This paper presents the outline, technical issues and background of the accident and the situations that followed. The review of this accident was one of the hot issues in the last ICNC2003 organized in Tokai-mura. At the this turn of ICNC in Japan, we would like to revisit the accident to reaffirm and share the idea that the response and preparedness should be strengthened to protect people and the environment from nuclear disasters. The accident occurred in a factory of JCO during the informal and unusual process of preparing a uranium nitrate solution of medium-enriched (18.8 weight% 
U) uranium from U
O
using the precipitation tank of 45 cm in diameter, which exceeded the critical diameter (ca. 23 cm) of an infinite cylinder with a full thick water reflector. A 2.2-cm-thick water "jacket" surrounded and enclosed the tank, and the jacket was connected to the cooling tower beside the factory. The jacket not only functioned as the neutron reflector but also prevented the evaporation of the solution, and then the criticality continued for about 20 hours. Because JCO's plant had not anticipated the criticality accident, the response to the accident was confusing. During the accident, the JAERI and JNC, both the predecessors of the Japan Atomic Energy Agency (JAEA), acted to terminate the criticality and reduce the residents' exposure to radiation. After the accident, the JAERI and the National Institute of Radiological Sciences provided the telephone consultation at the village office of Tokai-mura. The JNC did the same things at the prefectural building of Ibaraki to advise the residents. The presentation may include issues of applying the Slide rule, identifying a nuclear criticality accident to occur, and responding to the emergency.
Fukaya, Yuji; Goto, Minoru
Annals of Nuclear Energy, 164, p.108617_1 - 108617_6, 2021/12
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)A reasonable source term of a hypothetical criticality accident for fuel fabrication facility with solution system has been proposed. The public exposure must not exceed the limitation of 5 mSv during an accident. Then, we proposed the reasonable source term of the first burst peak due to the hydrogen gas generation by radiation decomposition of water. With the criticality control system composed of the Criticality Accident Alarm System (CAAS) and soluble neutron absorber, safety is ensured by the reduced fission number. We confirmed the effect by environmental impact assessment during a criticality accident by using site condition of a fuel fabrication facility in Tokai-mura, Japan. As a result, the public exposure is reduced at a site boundary from 68 mSv to 0.6 mSv under the current regulatory guideline.
Tsujimura, Norio; Takahashi, Fumiaki; Takada, Chie
Progress in Nuclear Science and Technology (Internet), 6, p.148 - 151, 2019/01
Abe, Hitoshi; Tashiro, Shinsuke; Miyoshi, Yoshinori
Nihon Genshiryoku Gakkai Wabun Rombunshi, 6(1), p.10 - 21, 2007/03
In MOX fuel fabrication facility, zinc stearate will be added into the MOX powder as addition material. If the material is added in large excess by miss operation, criticality characteristics of the MOX fuel would be influenced because it has neutron moderation effect. If criticality condition should be induced by the excess addition, physical variations, such as melting and pyrolysis of the material, must be caused by the fission energy and dynamic characteristics of the MOX fuel must be affected. To contribute quantitative evaluation of the dynamic characteristics, thermal properties data such as exo/endothermic calorific values, reaction rates, etc. with the respective physical variations and release behavior of pyrolysis gas were measured. It was found the exo/endothermic behavior with rinsing temperature of the material could be divided into six regions and rapid pressure rise caused by the pyrolysis reaction over about 400 
C. Furthermore, on the basis of the results, evaluation model for the thermal properties under the criticality condition was also investigated.
Nomura, Yasushi*; Okuno, Hiroshi; Miyoshi, Yoshinori
Nuclear Technology, 148(3), p.235 - 243, 2004/12
Times Cited Count：3 Percentile：23.52(Nuclear Science & Technology)no abstracts in English
-ray monitorTonoike, Kotaro; Nakamura, Takemi*; Yamane, Yuichi; Miyoshi, Yoshinori
Nuclear Technology, 143(3), p.364 - 372, 2003/09
Times Cited Count：2 Percentile：19(Nuclear Science & Technology)no abstracts in English
Miyoshi, Yoshinori; Yamamoto, Toshihiro; Nakajima, Ken
JAERI-Research 2002-002, 30 Pages, 2003/03
JAERI-Research-2002-002.pdf:1.42MB
no abstracts in English
Umemoto, Michitaka; Ishigami, Tsutomu; Kobayashi, Kensuke
Chiiki Anzen Gakkai Rombunshu, 4, p.231 - 240, 2002/11
no abstracts in English
Yamamoto, Toshihiro; Miyoshi, Yoshinori
Nuclear Science and Engineering, 142(3), p.305 - 314, 2002/11
Times Cited Count：2 Percentile：10.15(Nuclear Science & Technology)Mechanisms of a positive temperature reactivity coefficient that occurs in a dilute plutonium solution are investigated based on the perturbation theory and the four-factor formula. The temperature coefficient of a solution fuel is positive if the adjoint flux or 
f between 0.05eV and 0.2eV increases with neutron energy. As compared to Pu-239, Pu-241 has a tendency to make the temperature coefficient of a plutonium solution. As Pu-241 in a plutonium solution decays into Am-241 with time, the temperature coefficient becomes more positive. Since the capture cross sections of most neutron absorbers such as boron and gadolinium decreases with increasing neutron energy, soluble absorbers make the temperature coefficient positive for higher concentration plutonium solution. Cadmium and samarium solved in a dilute plutonium solution exceptionally can keep the temperature coefficient. A fixed neutron absorber generally makes the temperature coefficient negative regardless of the property of absorber materials.
-ray exposure rate from short-lived fission products under criticality accident conditionsYanagisawa, Hiroshi; Ono, Akio; Aizawa, Eiju
Journal of Nuclear Science and Technology, 39(5), p.499 - 505, 2002/05
Times Cited Count：4 Percentile：29.25(Nuclear Science & Technology)no abstracts in English
Watanabe, Shoichi; Miyoshi, Yoshinori; Yamane, Yuichi
JAERI-Tech 2002-043, 93 Pages, 2002/03
JAERI-Tech-2002-043.pdf:6.74MB
no abstracts in English
Nakajima, Ken; Yamane, Yuichi; Ogawa, Kazuhiko; Aizawa, Eiju; Yanagisawa, Hiroshi; Miyoshi, Yoshinori
JAERI-Data/Code 2002-007, 123 Pages, 2002/03
JAERI-Data-Code-2002-007.pdf:4.34MB
no abstracts in English
Nakajima, Ken; Yamane, Yuichi; Ogawa, Kazuhiko; Aizawa, Eiju; Yanagisawa, Hiroshi; Miyoshi, Yoshinori
JAERI-Data/Code 2002-006, 176 Pages, 2002/03
JAERI-Data-Code-2002-006.pdf:6.33MB
no abstracts in English
Nakajima, Ken; Yamane, Yuichi; Ogawa, Kazuhiko; Aizawa, Eiju; Yanagisawa, Hiroshi; Miyoshi, Yoshinori
JAERI-Data/Code 2002-005, 158 Pages, 2002/03
JAERI-Data-Code-2002-005.pdf:6.55MB
no abstracts in English
Nakajima, Ken; Yamane, Yuichi; Miyoshi, Yoshinori
JAERI-Data/Code 2002-004, 42 Pages, 2002/03
JAERI-Data-Code-2002-004.pdf:1.51MB
no abstracts in English
Kanamori, Masashi
JNC TN8440 2001-018, 50 Pages, 2001/12
JNC-TN8440-2001-018.pdf:1.31MB
On September 30 at around 10:35 AM, criticality accident occurred at the JCO's conversion building in Tokai-mura. Since criticality accident had not been anticipated, neither devices for termination of criticality accident nor neutron detectors were available. Immediately after the information of the accident, our emergency staff (Japan Nuclear cycle development institute staff) went to JCO site, to measure the intensity of neutrons and gammas. There were four main tasks, first one was to measure the radiation intensity, second one was to terminate the criticality accident, third one is to alert the residents surrounding the JCO site, fourth one is to evacuate the employees in the site. These tasks were successfully performed until October 1. This paper describes about how these operations were performed by the relevant staffs.
Sakurai, Kiyoshi
Nihon Genshiryoku Gakkai-Shi, 43(11), P. 1113, 2001/11
no abstracts in English
Abe, Hitoshi; Tashiro, Shinsuke; Koike, Tadao; Okagawa, Seigo; Uchiyama, Gunzo
Proceedings of the 2001 Topical Meeting on Practical Implementation of Nuclear Criticality Safety (CD-ROM), 8 Pages, 2001/11
no abstracts in English
Yamahara, Takeshi
Dai-26, 27-Kai NS Netto Anzen Kyaraban Koenroku, p.1 - 30, 2001/10
no abstracts in English
