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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 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. 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; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; et al.
Proceedings of 2015 International Congress on Advances in Nuclear Power Plants (ICAPP 2015) (CD-ROM), p.454 - 465, 2015/05
This paper describes mainly strong wind PRA methodology development in addition to the project overview. In developing the strong wind PRA methodology, hazard curves were estimated by using Weibull and Gumbel distributions based on weather data recorded in Japan. The obtained hazard curves were divided into five discrete categories for event tree quantification. Next, failure probabilities for decay heat removal related components were calculated as a product of two probabilities: i.e., a probability for the missiles to enter the intake or outtake in the decay heat removal system, and fragility caused by the missile impacts. Finally, based on the event tree, the core damage frequency was estimated about 610
/year by multiplying the discrete hazard probabilities in the Gumbel distribution by the conditional decay heat removal failure probabilities. A dominant sequence was led by the assumption that the operators could not extinguish fuel tank fire caused by the missile impacts and the fire induced loss of the decay heat removal system.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; et al.
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 10 Pages, 2015/05
This paper describes mainly snow margin assessment methodology development in addition to the project overview. For the snow margin assessment, the index is a combination of a snowfall rate and duration. Since snow removal can be expected during the snowfall, the developed snow margin assessment methodology is such that the margin was regarded as the snowfall duration up to the decay heat removal failure which was defined as when the snow removal rate was smaller than the snowfall rate.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Okano, Yasushi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; et al.
Proceedings of 10th International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10) (USB Flash Drive), 12 Pages, 2014/12
This paper describes mainly snow probabilistic risk assessment (PRA) methodology development in addition to the project overview. In snow hazard category, the accident sequence was evaluated by producing event trees which consist of several headings representing the loss of decay heat removal. Snow removal action and manual operation of the air cooler dampers were introduced into the event tree as accident managements. The snow PRA showed less than 10/reactor-year of core damage frequency.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; Takata, Takashi*
Proceedings of 12th Probabilistic Safety Assessment and Management Conference (PSAM-12) (USB Flash Drive), 11 Pages, 2014/06
This paper describes mainly preliminary risk assessment against snow in addition to the project overview. The snow hazard indexes are the annual maximum snow depth and the annual maximum daily snowfall depth. Snow hazard curves for the two indexes were developed using 50 year weather data at the typical sodium-cooled fast reactor site in Japan. In this paper, the snow risk assessment showed less than 10/reactor-year of core damage frequency. The dominant snow hazard category was the combination of 1-2m/day of snowfall velocity and 0.75-1.0 day of snowfall duration. Sensitivity analyses indicated important human actions, which were the improvement of snow removal velocity and the awareness of snow removal necessity.
Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi; Sakai, Takaaki; Yamamoto, Takahiro*; Ishizuka, Yoshihiro*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; Takata, Takashi*
no journal, ,
This study aims to develop margin evaluation methodology for decay heat removal function in sodium cooled fast reactors against representative external hazards such as external weather (Snow pack, strong wind, tornado and rainfall), volcanic eruption, and forest fire. This report describes four-year project overview and establishing concept for margin evaluation methodology as part of the first year result.
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*; Geshi, Nobuo*; Furukawa, Ryuta*; Nanayama, Futoshi*; et al.
no journal, ,
This paper describes mainly snow margin assessment methodology development in addition to the project overview. For the snow margin assessment, the index is the combination of a snowfall rate and duration. Since snow removal can be expected for the snowfall, this study developed the snow margin assessment methodology that the margin was regarded as the snowfall duration to the decay heat removal failure which was defined as when the snow removal rate was smaller than the snowfall rate.
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; 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.
