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Kobayashi, Tetsuro*; Takata, Takashi; Narumiya, Yoshiyuki*; Iida, Susumu*
Nihon Genshiryoku Gakkai-Shi ATOMO
, 63(1), p.50 - 54, 2021/01
Since December 2019, the new coronavirus infectious disease COVID-19, which has occurred mainly in Wuhan City, Hubei Province, China, rapidly spread as a pandemic (a global pandemic of infectious diseases). And thus it affected financial and social issues extremely. In this paper, the current status and issues of non-medical measures in Japan and overseas are explained with regard to the safety of nuclear facilities against pandemics.
Takata, Takashi*; Yamano, Hidemasa; Narumiya, Yoshiyuki*
Nihon Genshiryoku Gakkai-Shi ATOMO, 62(8), p.448 - 451, 2020/08
This report describes risk analysis applicable to selection and evaluation of external hazards in risk assessment. Volcanic ash hazard evaluation is shown as one of hazard evaluations. The objective of the risk assessment is to secure and improve the safety of nuclear installation. This report also describes discussion on the process of response informed based on risk evaluation against external hazards.
Okano, Yasushi; Nishino, Hiroyuki; Yamano, Hidemasa; Kurisaka, Kenichi
Proceedings of International Topical Meeting on Probabilistic Safety Assessment and Analysis (PSA 2019), p.274 - 281, 2019/04
A sodium-cooled fast reactor uses the ambient air as an ultimate heat sink to remove decay heat, thus meteorological phenomena can potentially pose risks to the reactor. If a rare and intense external hazard occurs concurrently with another external hazard, it would affect the systems (i.e. air cooler of decay heat removal system). In this study, a new scheme of screening of the external hazard combinations was proposed. The authors classified simultaneous or sequential combinational hazards, and identified associated potential effects in terms of hazard duration and sequential order. As a result, this study identified scenarios of the external hazard combinations of preceding rare and intense external hazard with an following additional external hazard.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Yamamoto, Takahiro*
ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part B; Mechanical Engineering, 4(3), p.030902_1 - 030902_9, 2018/09
This paper describes volcanic probabilistic risk assessment (PRA) methodology development for sodium-cooled fast reactors. The volcanic ash could potentially clog air filters of air-intakes that are essential for the decay heat removal. The degree of filter clogging can be calculated by atmospheric concentration of ash and tephra fallout duration and also suction flow rate of each component. The atmospheric concentration can be calculated by deposited tephra layer thickness, tephra fallout duration and fallout speed. This study evaluated a volcanic hazard using a combination of tephra fragment size, layer thickness and duration. In this paper, each component functional failure probability was defined as a failure probability of filter replacement obtained by using a grace period to a filter failure limit. Finally, based on an event tree, a core damage frequency was estimated about 3
10
/year in total by multiplying discrete hazard probabilities by conditional decay heat removal failure probabilities. A dominant sequence was led by the loss of decay heat removal system due to the filter clogging after the loss of emergency power supply. In addition, sensitivity analyses have investigated the effects of a tephra arrival reduction factor and pre-filter covering.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi
Mechanical Engineering Journal (Internet), 5(4), p.18-00093_1 - 18-00093_19, 2018/08
This paper describes the development of a probabilistic risk assessment (PRA) methodology against a combination hazard of strong wind and rainfall. In this combination hazard PRA, a hazard curve is evaluated in terms of maximum instantaneous wind speed, hourly rainfall, and rainfall duration. A scenario analysis has provided event sequences resulting from the combination hazard of strong wind and rainfall. The typical event sequence was characterized by the function loss of auxiliary cooling system, of which heat transfer tubes could crack due to cycle fatigue caused by cyclic contacts with rain droplets. This cycle fatigue crack could occur if rain droplets enter into the air cooler of the system following the coolers roof failure due to strong-wind-generated missile impact. This event sequence has been incorporated into an event tree which addresses component failure caused by the combination hazard. As a result, a core damage frequency has been estimated to be about 10/year in total by multiplying discrete hazard frequencies by conditional decay heat removal failure probabilities. The dominant sequence is the manual operation failure of an air cooler damper following the failure of external fuel tank due to the missile impact. The dominant hazard is the maximum instantaneous wind speed of 20-40 m/s, the hourly rainfall of 20-40 mm/h, and the rainfall duration of 0-10 h.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi
Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 12 Pages, 2017/07
This paper describes probabilistic risk assessment (PRA) methodology development against combination hazard of strong wind and rainfall. In this combination hazard PRA, a hazard curve has been evaluated in terms of maximum instantaneous wind speed, hourly rainfall, and rainfall duration. A scenario analysis provided event sequences resulted from the combination hazard of strong wind and rainfall. The event sequence was characterized by the function loss of auxiliary cooling system, of which heat transfer tubes could crack due to cycle fatigue by cyclic contact of rain droplets. This situation could occur if rain droplets ingress into air cooler occurs after the air cooler roof failure due to strong-wind-generated missile impact. This event sequence was incorporated into an event tree which addressed component failure by the combination hazard. Finally, a core damage frequency has been estimated the order of 10
/year in total by multiplying discrete hazard frequencies by conditional decay heat removal failure probabilities. A dominant sequence is the failure of the auxiliary cooling system by the missile impact after the failure of external fuel tank by the missile impact. A dominant hazard is the maximum instantaneous wind speed of 40-60 m/s, the hourly rainfall of 20-40 mm/h, and the rainfall duration of 0-10 h.
Yamano, Hidemasa
Genshiryoku Shisutemu Kenkyu Kaihatsu Oyobi Eichi O Kesshushita Genshiryoku Kagaku Gijutsu, Jinzai Ikusei Suishin Jigyo Heisei-28-Nendo Seika Hokokukai Shiryoshu (Internet), 4 Pages, 2017/01
This study has carried out R&D of margin assessment methodology of decay heat removal function for sodium-cooled fast reactors against external hazards in the MEXT innovative nuclear system R&D project from 2012 to 2016. In 2014, the development has been completed for hazard evaluation and event sequence evaluation methods against combination hazards of snow and low temperature as well as strong wind and rainfall. In forest fire, a combination hazard evaluation methodology has been developed by taking into account lightning.
Takata, Takashi; Azuma, Emiko*; Nishino, Hiroyuki; Yamano, Hidemasa; Sakai, Takaaki*
Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 6 Pages, 2016/11
A new approach has been developed to assess event sequences under external hazard condition considering a plant status quantitatively and stochastically so as to take various scenarios into account automatically by applying a Continuous Markov Chain Monte Carlo (CMMC) method coupled with a plant dynamics analysis. In the paper, a strong wind is selected as the external hazard to assess the plant safety in a loop type sodium cooled fast reactor. As a result, it is demonstrated that the plant state is quite safe in case of the strong wind because multiple failures of the air coolers in the auxiliary cooling system (ACS) has a quite low probability. Furthermore, a weight factor is introduced so as to investigate the low failure probability events with a comparative small number of the sampling.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; et al.
Proceedings of 11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-11) (USB Flash Drive), 12 Pages, 2016/10
This paper describes mainly volcanic margin assessment methodology development in addition to the project overview. The volcanic tephra could potentially clog filters of air-intakes that need the decay heat removal. The filter clogging can be calculated by atmospheric concentration and fallout duration of the volcanic tephra and also suction flow rate of each component. In this paper, the margin was defined as a grace period to a filter failure limit. Consideration is needed only when the grace period is shorter than the fallout duration. The margin by component was calculated using the filter failure limit and the suction flow rate of each component. The margin by sequence was evaluated based on an event tree and the margin by component. An accident management strategy was also suggested to extend the margin; for instance, manual trip of the forced circulation operation, sequential operation of three air coolers, and covering with pre-filter.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; et al.
Proceedings of 24th International Conference on Nuclear Engineering (ICONE-24) (DVD-ROM), 10 Pages, 2016/06
This paper describes mainly volcanic probabilistic risk assessment (PRA) methodology development for sodium-cooled fast reactors in addition to the project overview. The volcanic ash could potentially clog air filters of air-intakes that are essential for the decay heat removal. The degree of filter clogging can be calculated by atmospheric concentration of ash and tephra fallout duration and also suction flow rate of each component. The atmospheric concentration can be calculated by deposited tephra layer thickness, tephra fallout duration and fallout speed. This study evaluated a volcanic hazard using a combination of tephra fragment size, layer thickness and duration. In this paper, each component functional failure probability was defined as a failure probability of filter replacement obtained by using a grace period to a filter failure limit. Finally, based on an event tree, a core damage frequency was estimated about 310/year in total by multiplying discrete hazard probabilities by conditional decay heat removal failure probabilities. A dominant sequence was led by the loss of decay heat removal system due to the filter clogging after the loss of emergency power supply. A dominant volcanic hazard was 10
kg/m
of atmospheric concentration, 0.1 mm of tephra diameter, 50-75 cm of deposited tephra layer thickness, and 1-10 hr of tephra fallout duration.
Yamano, Hidemasa; Nishino, Hiroyuki; Okano, Yasushi; Yamamoto, Takahiro*; Takata, Takashi*
Earthquakes, Tsunamis and Nuclear Risks, p.111 - 121, 2016/01
The present study is developing risk assessment methodologies that include probabilistic risk assessment (PRA) and margin assessment methodologies against snow, tornado, strong wind, rain, volcanic eruption and forest fire mainly for a sodium-cooled fast reactor. The present paper describes briefly the project overview and then mainly the development of PRA and margin assessment methodologies against strong wind. In the strong wind PRA, the hazard curve was estimated using the Gumbel distributions based on weather data. Next, failure probabilities for components were calculated and event trees were developed. Using them, the strong wind PRA methodology was developed to quantify a core damage frequency. The present study also developed the wind margin assessment methodology that the margin was regarded as wind speed leading to the decay heat removal failure.
Yamano, Hidemasa
Genshiryoku Shisutemu Kenkyu Kaihatsu Oyobi Eichi O Kesshushita Genshiryoku Kagaku Gijutsu, Jinzai Ikusei Suishin Jigyo Heisei-27-Nendo Seika Hokokukai Shiryoshu (Internet), 4 Pages, 2016/01
This study is carrying out R&D of margin assessment methodology of decay heat removal function for sodium-cooled fast reactors against external hazards in the MEXT innovative nuclear system R&D project from 2012 to 2016. In 2014, the development has been completed for hazard evaluation and event sequence evaluation methods against external precipitation and volcanic eruption hazards. In forest fire, a hazard evaluation methodology has been developed using fire spread simulations.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Furukawa, Ryuta*; Geshi, Nobuo*; Nanayama, Futoshi*; et al.
no journal, ,
PRA and margin assessment methodologies are being developed for sodium-cooled fast reactors against representative external hazards. This report describes the overview of second-year (JPY2015) outcomes and the development of the margin assessment methodology against snow and tornado.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Furukawa, Ryuta*; Geshi, Nobuo*; Nanayama, Futoshi*; et al.
no journal, ,
PRA and margin assessment methodologies are being developed for sodium-cooled fast reactors against representative external hazards. This report describes the overview of Third-year (JPY2014) updates and the development of the sequence assessment methodology against volcanic eruption hazard.
Yamano, Hidemasa; Nishino, Hiroyuki; Okano, Yasushi; Kurisaka, Kenichi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Furukawa, Ryuta*; Geshi, Nobuo*; Nanayama, Futoshi*; et al.
no journal, ,
A four-year research project since 2012 is being performed to develop risk assessment methodologies that include probabilistic risk assessment (PRA) and margin assessment methodologies against external hazards mainly for a sodium-cooled fast reactor. The present paper describes briefly the project overview and then mainly the development of PRA and margin assessment methodologies against strong wind. In this project, by 2014, PRA methodologies against snow, tornado, rain and strong wind were developed as well as their hazard evaluation methodologies. For a volcanic eruption hazard, tephra fallout simulations were carried out to contribute to the hazard evaluation methodology development. In developing the strong wind PRA methodology, hazard curves were estimated using the Gumbel distributions based on weather data recorded in Japan. Next, failure probabilities for components related to the decay heat removal function were calculated as a product of two probabilities: a probability for the missiles to enter the intake/outtake in the decay heat removal system, and fragility caused by the missile impacts. After developing event trees, a core damage frequency was estimated about 610
/year by multiplying discrete hazard frequencies and conditional decay heat removal failure probabilities. The present study also developed the wind margin assessment methodology that the margin was regarded as wind speed leading to the decay heat removal failure.
Yamano, Hidemasa; Kawasaki, Nobuchika; Kubo, Shigenobu
no journal, ,
Tentative external hazard conditions assumed for a next-generation SFR design in 2011 were not reasonable because of an envelope range covering severe conditions. This report proposed a reasonable definition method of external hazard conditions and defined specific design basis and design extension conditions against various external hazards.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Takata, Takashi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Furukawa, Ryuta*; Geshi, Nobuo*; et al.
no journal, ,
PRA and margin assessment methodologies have been developed for sodium-cooled fast reactors against representative external hazards. This report describes the overview of last year (JPY2015) updates and the development of the sequence assessment methodology against a combination hazard of strong wind and rainfall.
Okano, Yasushi; Yamano, Hidemasa
no journal, ,
For an evaluation of a combination hazard curve of forest fire and thunder, it is necessary to take into account not only the overlap occurrence frequency but also meteorological effect on a forest fire intensity. The logic tree of a forest fire hazard curve evaluation was utilized in this study for quantitative estimation of the hazard curve of the combination event of forest fire and thunder.
Takata, Takashi
no journal, ,
In the present paper, a numerical quantification of a plant status in sodium-cooled fast reactor has been carried out based on a continuous Markov chain Monte Carlo (CMMC) method under a strong rainfall hazard. For this purpose, a numerical tool where a water level of each compartment is calculated considering such as a penetration to compartment, a transport via opening or pathway and a drain and is coupled with the CMMC method.
Okano, Yasushi; Yamano, Hidemasa; Takata, Takashi; Nishino, Hiroyuki; Kurisaka, Kenichi
no journal, ,
External hazard related to meteorological phenomena may impact on decay heat removal system using ambient air as an ultimate heat sink such as in sodium-cooled fast reactor system. This study identify the combination of external hazards to be considered and the items to be quantified for probabilistic risk assessment from the view point of strength and affecting duration of the hazard in case that secondary external hazard which has predicted appearance frequency overlaps after an primary external hazard which is very rare but high consequence.
