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Journal Articles

Probabilistic risk assessment for sodium-cooled fast reactors by the CMMC method; Consideration of operator's recognition probability for accident managements

Koike, Akari*; Nemoto, Masaya*; Nakashima, Risako*; Sakai, Takaaki*; Doda, Norihiro; Tanaka, Masaaki

Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 2 Pages, 2023/04

To evaluate the effect of the operator's recognition of the accident management (AM) necessity on plant safety, the operator's recognition of the AM necessity was modeled as a function of time-dependent success probability, and dynamic PRA analyses were performed for a sodium-cooled fast reactor during abnormal snowfall. The analysis results showed that the operator's recognition of the snowfall can avoid the core damage at an earlier stage after the accident.

Journal Articles

Risk assessment of a sodium-cooled fast reactor for abnormal snowfall with considering global warming

Koike, Akari*; Nakashima, Risako*; Nemoto, Masaya*; Sakai, Takaaki*; Doda, Norihiro; Tanaka, Masaaki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 4 Pages, 2022/10

Due to global warming, the amount of snowfall in abnormal snowfall events may increase in the future. In order to evaluate the effect of global warming on the probability of exceeding the limit temperature at the core outlet as a core damage factor in a sodium-cooled fast reactor, a hazard curve of snowfall was developed considering global warming, and a dynamic PRA was performed. As a result, it was found that the amount of snowfall in abnormal snowfall events increases due to global warming, and the probability of exceeding the limit temperature increases.

Journal Articles

Analysis on cooling behavior for simulated molten core material impinging to a horizontal plate in a sodium pool

Matsushita, Hatsuki*; Kobayashi, Ren*; Sakai, Takaaki*; Kato, Shinya; Matsuba, Kenichi; Kamiyama, Kenji

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-13) (Internet), 9 Pages, 2022/09

During core disruptive accidents in sodium-cooled fast reactors, the molten core material flows through flow channels, such as the control rod guide tubes, into the core inlet plenum under the core region. The molten core material can be cooled and solidified while impinging on a horizontal plate of the inlet plenum in a sodium coolant. However, the solidification and cooling behaviors of molten core materials impinged on a horizontal structure have not been sufficiently studied thus far. Notably, this is an important phenomenon that needs to be elucidated from the perspective of improving the safety of sodium-cooled fast reactors. Accordingly, a series of experiments on discharging a simulated molten core material (alumina: Al$$_{2}$$O$$_{3}$$) into a sodium coolant on a horizontal structure was conducted at the experimental facility of the National Nuclear Center of the Republic of Kazakhstan. In this study, analyses on the sodium experiments using SIMMER-III as the fast reactor safety evaluation code were performed. The analysis methods were validated by comparing the results and experiment data. In addition, the cooling and solidification behaviors during jet impingement were evaluated. The results indicated that the molten core material exhibited fragmentation owing to the impingement on the horizontal plate and was, therefore, scattered toward the periphery. Furthermore, the simulated molten core material was evaluated to be cooled by sodium and subsequently solidified.

Journal Articles

Quantitative risk assessment with CMMC method on abnormal snowfall incident for a sodium-cooled fast reactor

Nakashima, Risako*; Koike, Akari*; Sakai, Takaaki*; Doda, Norihiro; Tanaka, Masaaki

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 6 Pages, 2022/08

In development of a quantitative risk assessment method to the external hazards for a sodium-cooled fast reactor, a dynamic PRA using the Continuous Markov chain Monte Carlo (CMMC) method was performed to evaluate the effect of global warming on the probability of exceeding the temperature limit as a core damage factor. There is a possibility that the amount of snowfall in abnormal snowfall events will increase due to global warming in the future. A hazard curve of snowfall considering global warming was developed. The results show that the probability of exceeding the temperature limit is increased by the abnormal snowfall events due to global warming.

Journal Articles

Gas entrainment phenomenon from free liquid surface in a sodium-cooled fast reactor; Measurements and evaluation on a gas core growth form the liquid surface

Uchida, Mao*; Alzahrani, H.*; Shiono, Mikihito*; Sakai, Takaaki*; Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 16 Pages, 2022/03

Gas entrainment from cover gas is one of key issues for sodium-cooled fast reactors design to prevent unexpected effects to core reactivity. A vortex model based evaluation method has been developed to evaluate the surface vortex gas core growth at the free surface in the reactor vessel. In this study, water experiments were performed to clarify the prediction accuracy for the vortex gas core growth during the vortex drift motion using a circulating water tunnel with an open flow channel test section. Gas core growth were predicted by applying the evaluation method to the numerical analyses performed in the same geometry of the experiments, and compared with the experimental results. It was observed the gas core growth became large at downstream region where downward velocity became large in experiment. However, the gas core length which were predicted from numerical result showed a discrepancy with the experimental result on the peak position and an overestimation of peak value.

Journal Articles

Analysis of gas entrainment phenomenon from free liquid surface for a sodium-cooled fast reactor design (Velocity profile and Strouhal number in a flow field)

Uchida, Mao*; Sakai, Takaaki*; Ezure, Toshiki; Tanaka, Masaaki

Mechanical Engineering Journal (Internet), 8(4), p.21-00161_1 - 21-00161_11, 2021/08

An evaluation method based on numerical analyses has been developed to predict occurrences gas entrainment phenomena at a free surface in a sodium-cooled fast reactor. In this study, experiments were conducted for gas entrainments due to drifting free surface vortexes observed in a circulating water tunnel geometry. Numerical analyses were also conducted in the same geometry using a computational fluid dynamics (CFD) code. Then, Strouhal numbers of vortex frequency and detailed flow velocity profiles were compared between experimental results and numerical results to clarify the evaluation accuracy of CFD calculation. As the results, the Strouhal numbers of the vortex frequency obtained from numerical analyses showed good agreement with the experimental data.

Journal Articles

Validation of analysis models on relocation behavior of molten core materials in sodium-cooled fast reactors based on the melt discharge experiment

Igarashi, Kai*; Onuki, Ryoji*; Sakai, Takaaki*; Kato, Shinya; Matsuba, Kenichi; Kamiyama, Kenji

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 6 Pages, 2020/08

Journal Articles

STRAD project for systematic treatments of radioactive liquid wastes generated in nuclear facilities

Watanabe, So; Ogi, Hiromichi*; Arai, Yoichi; Aihara, Haruka; Takahatake, Yoko; Shibata, Atsuhiro; Nomura, Kazunori; Kamiya, Yuichi*; Asanuma, Noriko*; Matsuura, Haruaki*; et al.

Progress in Nuclear Energy, 117, p.103090_1 - 103090_8, 2019/11

AA2019-0193.pdf:1.29MB

 Times Cited Count:9 Percentile:78.07(Nuclear Science & Technology)

Journal Articles

Quantitative risk assessment of accident managements against volcano ash hazard in a sodium-cooled fast reactor

Suzuki, Minoru*; Sakai, Takaaki*; Takata, Takashi; Doda, Norihiro

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 7 Pages, 2019/05

With an aim to establish a quantitative risk assessment of accident managements (AMs) for various external hazards, the plant dynamics analyses with Continuous Markov Chain Monte Carlo (CMMC) method were carried out to assess repeatedly occurred multi-failures by volcano ash in volcanic eruption event. AM repetition of the filter exchange to recover the cooling function of the air coolers were considered. The results showed that this method can evaluate the effectiveness of AM measures against volcanic ash fall events with respect to time progress.

Journal Articles

Study on gas entrainment from unstable drifting vortexes on liquid surface

Hirakawa, Moe*; Kikuchi, Yuichiro*; Sakai, Takaaki*; Tanaka, Masaaki; Ohshima, Hiroyuki

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 8 Pages, 2018/07

Gas entrainment (GE) from cover gas is one of key issue for Sodium-cooled fast reactors to prevent unexpected effects to core reactivity. By using a computational fluid dynamics (CFD) code, analyses have been conducted to estimate the drifting vortexes on water experiments which were generated as wake vortexes behind a plate obstacle in the circulating water channel. In this paper, the results of comparison between experiments and analyses were discussed and the gas core lengths from the surface vortexes were evaluated by using the evaluation tool named StreamViewer developed by Japan Atomic Energy Agency.

Journal Articles

Surface modifications of hydrogen storage alloy by heavy ion beams with keV to MeV irradiation energies

Abe, Hiroshi; Tokuhira, Shinnosuke*; Uchida, Hirohisa*; Oshima, Takeshi

Nuclear Instruments and Methods in Physics Research B, 365(Part A), p.214 - 217, 2015/12

no abstracts in English

Journal Articles

Surface modification effects on hydrogen absorption property of a hydrogen storage alloy by short pulse laser irradiation

Abe, Hiroshi; Shimomura, Takuya; Tokuhira, Shinnosuke*; Shimada, Yukihiro*; Takenaka, Yusuke*; Furuyama, Yuta*; Nishimura, Akihiko; Uchida, Hirohisa*; Daido, Hiroyuki; Oshima, Takeshi

Proceedings of 7th International Congress on Laser Advanced Materials Processing (LAMP 2015) (Internet), 4 Pages, 2015/08

A short pulse laser (the nanosecond and femtosecond) was applied to hydrogen absorbing alloys surface layer, and a surface modification experiment was put into effective to aim at improvement of hydrogen adsorption functionally. It was investigated about correlation between an initial hydrogen absorption reaction rate of hydrogen alloys and a laser irradiation in this research. The laser irradiation condition was done with pulse width 100 fsec and energy 0.2 - 3.4 mJ/pulse. It blazed down on hydrogen absorbing alloys (LaNi$$_{4.6}$$Al$$_{0.4}$$) and changed local order in the surface. As a result, the initial hydrogen absorption reaction rate was 1.5 - 3.0 times as fast as a irradiated sample, and the result and laser irradiated sample found out that a hydrogen absorption function improves. A laser irradiation can conclude to be effective in surface modification of the hydrogen storage materials.

Journal Articles

Immunofluorescence observation of oxidative damage of DNA induced by heavy ions from TIARA

Kitabatake, Satomi*; Ushiroda, Tota*; Hirayama, Ryoichi*; Furusawa, Yoshiya*; Funayama, Tomoo; Yokota, Yuichiro; Okahata, Yoshio*; Ito, Atsushi*

JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 86, 2015/03

Biological effects of high-LET radiation could be understood in terms of the ion track structure. Therefore the evaluation of the contribution of both core and penumbra regions to biological effects is an important issue for the study of high-LET effects. In the present study, we developed a protocol to make a uniform DNA sheet with insoluble nature in aqueous solution, and explored the applicability to the detection of 8-OHdG distributions after heavy-ion irradiation. Water-insoluble DNA sheet was irradiated with proton and neon ion beams at JAEA-Takasaki. After irradiation DNA samples were incubated with an 8-OHdG antibody followed by with a second antibody containing a fluorescence probe. The preliminary results indicated that upon ion irradiation randomly distributed dot-like fluorescence was observed, suggesting that these dots may be from incident ions.

Journal Articles

Vertical and lateral transport of particulate radiocesium off Fukushima

Otosaka, Shigeyoshi; Nakanishi, Takahiro; Suzuki, Takashi; Sato, Yuhi; Narita, Hisashi*

Environmental Science & Technology, 48(21), p.12595 - 12602, 2014/11

 Times Cited Count:24 Percentile:58.95(Engineering, Environmental)

From August 2011 to July 2013, a sediment trap was deployed at 100 km east of the Fukushima Daiichi Nuclear Power Plant and sinking particles were collected. Sinking flux of $$^{137}$$Cs decreased over time with seasonal fluctuation. The $$^{137}$$Cs fluxes were mainly affected by two principal modes. One was a rapid sinking of radiocesium-bound particles (moderate mode). This mode was dominant especially in the early post-accident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another was the secondary transport of particles attributed to turbulence near the seabed and was observed in winter (turbulence mode). Although the latter process would not drastically change the distribution of sedimentary radiocesium, attention should be paid as this key process redistributing the accident-derived radiocesium may cumulatively affect the long-term distribution.

Journal Articles

Radiocesium derived from the Fukushima Daiichi Nuclear Power Plant accident in seabed sediments; Initial deposition and inventories

Otosaka, Shigeyoshi; Kato, Yoshihisa*

Environmental Science; Processes & Impacts, 16(5), p.978 - 990, 2014/05

 Times Cited Count:41 Percentile:82.59(Chemistry, Analytical)

Since the accident of Fukushima Daiichi Nuclear Power Plant (1FNPP), significant levels of anthropogenic radionuclides have been detected from seabed sediments off the east coast of Japan. In this paper, the approximate amount of accident-derived radiocesium in seabed sediments off Fukushima, Miyagi and Ibaraki prefectures was estimated. As of October 2011, the total amount of sedimentary $$^{134}$$Cs was 0.20$$pm$$0.05 PBq (decay corrected to March 11, 2011) and about 95% of the radiocesium was accumulated in the regions shallower than 200 m depths. The large inventory in the coastal sediments was attributed to effective adsorption of dissolved radiocesium onto sediments. Although rivers are also an important source to supply radiocesium to the coastal regions, the potential was relatively lower than that of the above-mentioned process at least in the early stage, within half a year, after the accident.

Journal Articles

Synergic effects of ion irradiations (La, Ce) and alkaline pretreatment (KOH) on hydriding kinetic property of a Mm-Ni based alloy

Abe, Hiroshi; Aone, Shigeo*; Morimoto, Ryo*; Uchida, Hirohisa*

Journal of Alloys and Compounds, 580(Suppl.1), p.S219 - S221, 2013/12

 Times Cited Count:5 Percentile:31.92(Chemistry, Physical)

no abstracts in English

Journal Articles

Effects of ultra-intense laser driven proton beam on the hydriding property of palladium

Abe, Hiroshi; Orimo, Satoshi; Kishimoto, Masahiko*; Aone, Shigeo*; Uchida, Hirohisa*; Daido, Hiroyuki; Oshima, Takeshi

Nuclear Instruments and Methods in Physics Research B, 307, p.218 - 220, 2013/07

 Times Cited Count:1 Percentile:11.56(Instruments & Instrumentation)

We investigated the structure changes of a hydrogen storage alloy by ion irradiations, and its absorption property in order to obtain basic data and to elucidate relevant mechanisms of hydrogen absorption by the influence of the irradiation. In previous studies, the induction of vacancies in a hydrogen absorption alloy was found to be effective to increase in the hydrogen absorption rate. As well known, the rate of hydrogen absorption strongly depends upon the surface state of a hydrogen storage alloy because the dissociation of hydrogen molecules or water molecules needs electron change with the surface in the H$$_{2}$$ gas or electrochemical reaction process. In this study, ion irradiations were made at a room temperature using the laser driven proton beam method, at Kansai Photon Science Institute, Japan Atomic Energy Agency. The beam treatment has several unique properties such as short pulse duration, high peak current, low transverse emittance, and wide energy range from KeV to MeV. The irradiation was used to modify the alloy surface using this equipment. From obtained results, the initial hydrogen absorption rate was found improved by the laser driven proton beam rather more effectively than a mono-energetic proton beam. Discussion is made on the correlation among proton irradiation (laser driven proton or mono-energetic proton) and the initial hydrogen absorption rate of the alloy. We argue about the usefulness of an energy spread beam.

Journal Articles

Improvement of hydrogen absorption characteristics of Pd using irradiation of heavey ions

Abe, Hiroshi; Aone, Shigeo*; Morimoto, Ryo*; Uchida, Hirohisa*; Oshima, Takeshi

Transactions of the Materials Research Society of Japan, 36(1), p.133 - 135, 2011/03

The introduction of vacancies in Pd was found to be effective for an increase in the initial hydrogen absorption rate in a previous study. Also, it was reported that the initial hydrogen absorption rate depends strongly on the surface conditions of metals. Heavy ions with keV ranges can create severe damage and high densities of vacancy near the surface of materials. As well known, the formation of hydride phases can be facilitated by the presence of vacancy because vacancy acts as hydrogen trapping site to form hydrides. Thus, the hydrogen absorption characteristics of Pd may be improved by the irradiation of heavy ions. As a result, the initial hydrogen absorption rate increased due to ion irradiation, and the value became 3$$sim$$10 times higher than un-irradiated Pd.

Journal Articles

Application of ionic liquid as a medium for treating waste contaminated with UF$$_{4}$$

Ohashi, Yusuke; Asanuma, Noriko*; Harada, Masayuki*; Wada, Yukio*; Matsubara, Tatsuo; Ikeda, Yasuhisa*

Journal of Nuclear Science and Technology, 46(8), p.771 - 775, 2009/08

Most of the metal or bed material wastes generated from uranium enrichment facilities or uranium refining and conversion plants are contaminated by uranium fluoride compounds such as UF$$_{4}$$. The UF$$_{4}$$ powder was completely dissolved in BMICl(1-buthyl-3-methylimidazolium chloride). The uranium concentrations of metal waste dropped below the temporary proposed clearance level (1.0 Bq/g) using BMICl. In the cyclic voltammogram of BMICl solution when dissolving UF$$_{4}$$, uncoupled reduction and oxidation peaks were observed and the reduction peak was considered to correspond to the reduction of uranyl(VI) + e$$^{-}$$ $$rightarrow$$ uranyl(V) followed by further reduction to UO$$_{2}$$.

Journal Articles

Effects of ion irradiation on hydrogen storage characteristics of alkaline pretreatment Mm alloy

Abe, Hiroshi; Aone, Shigeo*; Uchida, Hirohisa*; Oshima, Takeshi

JAEA-Review 2008-055, JAEA Takasaki Annual Report 2007, P. 145, 2008/11

no abstracts in English

101 (Records 1-20 displayed on this page)