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Journal Articles

Study for estimation of snow depth by using DSM made by SfM method

Miyasaka, Satoshi*; Unome, Sota*; Tamura, Ayako*; Ito, Yoshiaki*; Ishizaki, Azusa; Sanada, Yukihisa

Nihon Rimoto Senshingu Gakkai Dai-63-Kai (Heisei-29-Nendo Shuki) Gakujutsu Koenkai Rombunshu (CD-ROM), p.81 - 84, 2017/11

Information of snow depth is important to improve the airborne radiation measurement in the winter. The snow depth is enable to estimate by the aerial photograph which is obtained at the same time with the radiation measurement before and after the snowfall. We attempted optimization parameters which used to make a Digital Surface Model (DSM) using Structure from Motion (SfM) method for estimation of the snow depth. As a result, to enable to measure precisely the snow depth was indicated. However, the estimated snow depth in the forest area was relatively not so accurate because fallen leaves and a tree move were prevented to measure DSM precisely.

Journal Articles

Event sequence assessment of deep snow in sodium-cooled fast reactor based on continuous Markov Chain Monte Carlo method with plant dynamics analysis

Takata, Takashi; Azuma, Emiko*

Journal of Nuclear Science and Technology, 53(11), p.1749 - 1757, 2016/11

 Times Cited Count:1 Percentile:14.27(Nuclear Science & Technology)

Margin assessment of a nuclear power plant against external hazards is one of the most important issues after Fukushima Dai-ichi Nuclear Power Plant Accident. In this paper, a new approach has been developed to assess the plant status during external hazards and countermeasures against them in operation quantitatively and stochastically. A Continuous Markov chain Monte Carlo (CMMC) method is applied and coupled with a plant dynamics analysis. In the CMMC method, a subsequence plant status is determined by the latest state (Markov chain) and the status is evaluated from the plant dynamics analysis. A failure or success of safety function of plant component is also evaluated stochastically based on a latest state of plant or hazard. A numerical investigation of plant dynamics analysis against a snow hazard is also carried out in a loop type sodium cooled fast reactor so as to assess the margin against the hazard.

Journal Articles

Development of probabilistic risk assessment methodology against extreme snow for sodium-cooled fast reactor

Yamano, Hidemasa; Nishino, Hiroyuki; Kurisaka, Kenichi

Nuclear Engineering and Design, 308, p.86 - 95, 2016/11

 Times Cited Count:4 Percentile:45.9(Nuclear Science & Technology)

This paper describes snow probabilistic risk assessment (PRA) methodology development through external hazard and event sequence evaluations mainly in terms of decay heat removal (DHR) function of a sodium-cooled fast reactor (SFR). Using recent 50-year weather data at a typical Japanese SFR site, snow hazard categories were set for the combination of daily snowfall depth (snowfall speed) and snowfall duration which can be calculated by dividing the snow depth by the snowfall speed. For each snow hazard category, the event sequence was evaluated by event trees which consist of several headings representing the loss of DHR. Snow removal action and manual operation of the air cooler dampers were introduced into the event trees as accident managements. Access route failure probability model was also developed for the quantification of the event tree. In this paper, the snow PRA showed less than 10$$^{-6}$$/reactor-year of core damage frequency. The dominant snow hazard category was the combination of 1-2 m/day of snowfall speed and 0.5-0.75 day of snowfall duration. Importance and sensitivity analyses indicated a high risk contribution to secure the access routes.

Journal Articles

Analysis of variations in observed ambient dose rates due to rainfall or snowfall at JAEA Ningyo-toge

Tanaka, Hiroshi; Sakoda, Akihiro; Ando, Masaki; Ishimori, Yuu

Hoken Butsuri, 51(2), p.107 - 114, 2016/06

Ambient dose rates are continuously monitored in Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency. The present study discussed the variations in ambient dose rates, observed from April 2014 to March 2015, due to snowfall as well as rainfall. It is much snowy as one of climatic features in this area. Rain or snow was sampled for a certain period in the day of interest (17 cases in total), and then the concentration of radon progeny was measured. With the measured data, the variation in ambient dose rate was calculated considering the accumulation of the radon progeny on the ground. As a whole, this calculation was found to reasonably reproduce the time trends of observed dose rates, except for four cases. Based on the backward trajectory analysis, it was explained that the discrepancy in two cases out of the four was induced by changes of radon progeny concentration in precipitation around sampling period. It was suggested that the other two cases were caused by the run-off of rain from the ground surface.

Journal Articles

Development of risk assessment methodology of decay heat removal function against external hazards for sodium-cooled fast reactors, 1; Project overview and margin assessment methodology against snow

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.

Journal Articles

Replication of individual snow crystals for their subsequent chemical analysis using micro-PIXE

Kasahara, Mikio*; Ma, C.-J.*; Okumura, Motonori*; Kojima, Takuji; Hakoda, Teruyuki; Sakai, Takuro; Arakawa, Kazuo

JAERI-Review 2003-033, TIARA Annual Report 2002, p.270 - 272, 2003/11

A snow crystal scavenges earozol particles and trasfer various elements in atomosphere through heterogenious nucleation. The snow has many complicated crystal shapes which results in difficulty in comparison of its environmental purification function directly with that of raindrops. The replica of individual snow crystal grain was prepared by their immobilization on the collodion film. The replica samples were analized by micro-PIXE at JAERI and PIXE st Kyoto university. The following results are obtained: (1) Size(circumscribed diameter) of individual snow crystal are in the range of 0.12-2.5mm, (2)snow crystal grows from hexagnal plate to dendritic sectored plate, (3) major elements captured by a snow crystal are Si,S,K,Ca,Fe,S, (4)there is relation between snow crystal size and captured-element masses. The result leads us to presume the chemical inner-structure and the elemental mixing state in/on single snow crystal.

Journal Articles

Diminution of terrestrial gamma ray dose rate due to snow cover, II; In situ measurement on a flat terrain

Nagaoka, Toshi; Sakamoto, Ryuichi; Tsutsumi, Masahiro; Saito, Kimiaki; Moriuchi, Shigeru

Hoken Butsuri, 27, p.113 - 121, 1992/00

no abstracts in English

JAEA Reports

Diminution of terrestrial gamma ray exposure rate due to snow cover; Ground survey and aerial survey

Nagaoka, Toshi; Sakamoto, Ryuichi; Saito, Kimiaki; Tsutsumi, Masahiro; Moriuchi, Shigeru

JAERI-M 91-210, 20 Pages, 1991/12


no abstracts in English

Journal Articles

External doses due to terrestrial gamma rays on the snow cover

Saito, Kimiaki

Radiation Protection Dosimetry, 35(1), p.31 - 39, 1991/00

 Times Cited Count:8 Percentile:67.1(Environmental Sciences)

no abstracts in English

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