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Journal Articles

Application of quasi-Monte Carlo and importance sampling to Monte Carlo-based fault tree quantification for seismic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Tanaka, Yoichi; Hakuta, Yuto*; Arake, Daisuke*; Uchiyama, Tomoaki*; Muramatsu, Ken

Mechanical Engineering Journal (Internet), 10(4), p.23-00051_1 - 23-00051_17, 2023/08

The significance of probabilistic risk assessments (PRAs) of nuclear power plants against external events was re-recognized after the Fukushima Daiichi Nuclear Power Plant accident. Regarding the seismic PRA, handling correlated failures of systems, components, and structures (SSCs) is very important because this type of failure negatively affects the redundancy of accident mitigation systems. The Japan Atomic Energy Research Institute initially developed a fault tree quantification methodology named the direct quantification of fault tree using Monte Carlo simulation (DQFM) to handle SSCs' correlated failures in detail and realistically. This methodology allows quantifying the top event occurrence probability by considering correlated uncertainties related to seismic responses and capacities with Monte Carlo sampling. The usefulness of DQFM has already been demonstrated. However, improving its computational efficiency would allow risk analysts to perform several analyses. Therefore, we applied quasi-Monte Carlo and importance sampling to the DQFM calculation of simplified seismic PRA and examined their effects. Specifically, the conditional core damage probability of a hypothetical pressurized water reactor was analyzed with some assumptions. Applying the quasi-Monte Carlo sampling accelerates the convergence of results at intermediate and high ground motion levels by an order of magnitude over Monte Carlo sampling. The application of importance sampling allows us to obtain a statistically significant result at a low ground motion level, which cannot be obtained through Monte Carlo and quasi-Monte Carlo sampling. These results indicate that these applications provide a notable acceleration of computation and raise the potential for the practical use of DQFM in risk-informed decision-making.

Journal Articles

A Scoping study on the use of direct quantification of fault tree using Monte Carlo simulation in seismic probabilistic risk assessments

Kubo, Kotaro; Fujiwara, Keita*; Tanaka, Yoichi; Hakuta, Yuto*; Arake, Daisuke*; Uchiyama, Tomoaki*; Muramatsu, Ken*

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 8 Pages, 2022/08

After the Fukushima Daiichi Nuclear Power Plant accident, the importance of conducting probabilistic risk assessments (PRAs) of external events, especially seismic activities and tsunamis, was recognized. The Japan Atomic Energy Agency has been developing a computational methodology for seismic PRA, called the direct quantification of fault tree using Monte Carlo simulation (DQFM). When appropriate correlation matrices are available for seismic responses and capacities of components, the DQFM makes it possible to consider the effect of correlated failures of components connected through AND and/or OR gates in fault trees, which is practically difficult when methods using analytical solutions or multidimensional numerical integrations are used to obtain minimal cut set probabilities. The usefulness of DQFM has already been demonstrated. Nevertheless, a reduction of the computational time of DQFM would allow the large number of analyses required in PRAs conducted by regulators and/or operators. We; therefore, performed scoping calculations using three different approaches, namely quasi-Monte Carlo sampling, importance sampling, and parallel computing, to improve calculation efficiency. Quasi-Monte Carlo sampling, importance sampling, and parallel computing were applied when calculating the conditional core damage probability of a simplified PRA model of a pressurized water reactor, using the DQFM method. The results indicated that the quasi-Monte Carlo sampling works well at assumed medium and high ground motion levels, importance sampling is suitable for assumed low ground motion level, and that parallel computing enables practical uncertainty and importance analysis. The combined implementation of these improvements in a PRA code is expected to provide a significant acceleration of computation and offers the prospect of practical use of DQFM in risk-informed decision-making.

Journal Articles

Mesospheric ionization during substorm growth phase

Murase, Kiyoka*; Kataoka, Ryuho*; Nishiyama, Takanori*; Nishimura, Koji*; Hashimoto, Taishi*; Tanaka, Yoshimasa*; Kadokura, Akira*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Ogawa, Yasunobu*; et al.

Journal of Space Weather and Space Climate (Internet), 12, p.18_1 - 18_16, 2022/06

 Times Cited Count:0 Percentile:24.42(Astronomy & Astrophysics)

We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.

Journal Articles

Chemical species of iodine during sorption by activated carbon; Effects of original chemical species and fulvic acids

Kato, Tomoaki; Kozai, Naofumi; Tanaka, Kazuya; Kaplan, D. I.*; Utsunomiya, Satoshi*; Onuki, Toshihiko

Journal of Nuclear Science and Technology, 59(5), p.580 - 589, 2022/05

 Times Cited Count:3 Percentile:58.27(Nuclear Science & Technology)

This study reports the effect of fulvic acids, which is a natural organic substance generally contained in groundwater, on the oxidation states of radioactive iodine anions (iodide and iodate). Iodide and iodate are contained in the contaminated water of the Fukushima Daiichi Nuclear Power Plant and supposed to be removed by activated carbon (AC) via adsorption. When fulvic acids does not exist in the experimental system, the adsorption of iodide on AC was less than that of iodate and their oxidation states after the adsorption were not changed. When fulvic acids existed, a fraction of the adsorbed iodate was reduced to iodide. This result indicates that the reduction of the adsorbed iodate progresses during the storage of the spent AC.

Journal Articles

Evaluation of gas entrainment flow rate by free surface vortex

Torikawa, Tomoaki*; Odaira, Naoya*; Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki

Konsoryu, 36(1), p.63 - 69, 2022/03

On free surface of a sodium cooled fast reactor, gas entrainment can be caused by free surface vortices, which may result in disturbance in core power. It is important to develop an evaluation model to predict accurately entrained gas flow rate. In this study, entrained gas flow rate a simple gas entrainment experiment is conducted with focusing on effect of pressure difference between upper and lower tanks. Pressure difference between upper and lower tanks are controlled by changing gas pressure in lower tank. As a result, it is confirmed that the entrained gas flow rate increases with increasing pressure difference between upper and lower tanks. By visualization of swirling annular flow in suction pipe, it is also observed that pressure drop in suction pipe increases with increase in entrained gas flow rate, which implies that entrained gas flow rate can be predicted by evaluation model based on pressure drop in swirling annular flow region.

Journal Articles

An Automotive intelligent catalyst that contributes to hydrogen safety for the Decommissioning of Fukushima Daiichi Nuclear Power Station (1FD)

Tanaka, Hirohisa*; Masaki, Sayaka*; Aotani, Takuro*; Inagawa, Kohei*; Iwata, Sogo*; Aida, Tatsuya*; Yamamoto, Tadasuke*; Kita, Tomoaki*; Ono, Hitomi*; Takenaka, Keisuke*; et al.

SAE Technical Paper 2022-01-0534 (Internet), 10 Pages, 2022/03

Journal Articles

Performance tests of catalysts for the safe conversion of hydrogen inside the nuclear waste containers in Fukushima Daiichi

Reinecke, E.-A.*; Takenaka, Keisuke*; Ono, Hitomi*; Kita, Tomoaki*; Taniguchi, Masashi*; Nishihata, Yasuo; Hino, Ryutaro; Tanaka, Hirohisa*

International Journal of Hydrogen Energy, 46(23), p.12511 - 12521, 2021/03

 Times Cited Count:4 Percentile:23.47(Chemistry, Physical)

The safe decommissioning as well as decontamination of the radioactive waste resulting from the nuclear accident in Fukushima Daiichi represents a huge task for the next decade. At present, research and development on long-term safe storage containers has become an urgent task with international cooperation in Japan. One challenge is the generation of hydrogen and oxygen in significant amounts by means of radiolysis inside the containers, as the nuclear waste contains a large portion of sea water. The generation of radiolysis gases may lead to a significant pressure build-up inside the containers and to the formation of flammable gases with the risk of ignition and the loss of integrity. In the framework of the project "R&D on technology for reducing concentration of flammable gases generated in long-term waste storage containers" funded by the Japanese Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), the potential application of catalytic recombiner devices inside the storage containers is investigated. In this context, a suitable catalyst based on the so-called intelligent automotive catalyst for use in a recombiner is under consideration. The catalyst is originally developed and mass-produced for automotive exhaust gas purification, and is characterized by having a self-healing function of precious metals (Pd, Pt and Rh) dissolved as a solid solution in the perovskite type oxides. The basic features of this catalyst have been tested in an experimental program. The test series in the REKO-4 facility has revealed the basic characteristics of the catalyst required for designing the recombiner system.

Journal Articles

Transient ionization of the mesosphere during auroral breakup; Arase satellite and ground-based conjugate observations at Syowa Station

Kataoka, Ryuho*; Nishiyama, Takanori*; Tanaka, Yoshimasa*; Kadokura, Akira*; Uchida, Herbert Akihito*; Ebihara, Yusuke*; Ejiri, Mitsumu*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Sato, Kaoru*; et al.

Earth, Planets and Space (Internet), 71(1), p.9_1 - 9_10, 2019/12

 Times Cited Count:7 Percentile:40.92(Geosciences, Multidisciplinary)

Transient ionization of the mesosphere was detected at around 65 km altitude during the isolated auroral expansion occurred at 2221-2226 UT on June 30, 2017. A general-purpose Monte Carlo particle transport code PHITS suggested that significant ionization is possible in the middle atmosphere due to auroral X-rays from the auroral electrons of $$<$$10 keV.

Journal Articles

Reduction behaviors of permanganate by microbial cells and concomitant accumulation of divalent cations of Mg$$^{2+}$$, Zn$$^{2}$$+, and Co$$^{2+}$$

Kato, Tomoaki*; Yu, Q.*; Tanaka, Kazuya; Kozai, Naofumi; Saito, Takumi*; Onuki, Toshihiko

Journal of Environmental Sciences, 86, p.78 - 86, 2019/12

 Times Cited Count:1 Percentile:4.44(Environmental Sciences)

This paper investigated the fate of the dissolved permanganate in aqueous solution after contact with bacterial cells and metal accumulation during precipitation of Mn oxides. When Mn(VII) was contacted with bacterial cells, cells were damaged and Mn(VII) was reduced by cells to lower valence and precipitated as Mn oxides (biomass Mn oxides). When Co$$^{2+}$$ ions were present, Co was incorporated into Mn oxides as Co$$^{3+}$$. These results suggest that Mn(VII) can be used to remove metal ions when introduced to wastewater as disinfectant.

Journal Articles

Research on hydrogen safety technology utilizing the automotive catalyst

Ono, Hitomi*; Takenaka, Keisuke*; Kita, Tomoaki*; Taniguchi, Masashi*; Matsumura, Daiju; Nishihata, Yasuo; Hino, Ryutaro; Reinecke, E.-A.*; Takase, Kazuyuki*; Tanaka, Hirohisa*

E-Journal of Advanced Maintenance (Internet), 11(1), p.40 - 45, 2019/05

Journal Articles

Development of radiation resistant monitoring camera system

Takeuchi, Tomoaki; Otsuka, Noriaki; Watanabe, Takashi*; Tanaka, Shigeo*; Ozawa, Osamu*; Komanome, Hirohisa*; Ueno, Shunji*; Tsuchiya, Kunihiko

Proceedings of 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC 2017) (Internet), 3 Pages, 2018/11

no abstracts in English

Journal Articles

Gamma irradiation effects of image sensor for radiation-resistant camera

Takeuchi, Tomoaki; Otsuka, Noriaki; Tsuchiya, Kunihiko; Tanaka, Shigeo*; Ozawa, Osamu*; Komanome, Hirohisa*; Watanabe, Takashi*; Ueno, Shunji*

Nihon Hozen Gakkai Dai-13-Kai Gakujutsu Koenkai Yoshishu, p.391 - 394, 2016/07

no abstracts in English

Journal Articles

Angular dependence of critical current density in YBCO films with columnar defects crossing at widespread angles

Sueyoshi, Tetsuro*; Furuki, Yuichi*; Tanaka, Eiki*; Fujiyoshi, Takanori*; Mitsugi, Fumiaki*; Ikegami, Tomoaki*; Ishikawa, Norito

IEEE Transactions on Applied Superconductivity, 23(3), p.8002404_1 - 8002404_4, 2013/06

 Times Cited Count:8 Percentile:42.26(Engineering, Electrical & Electronic)

To investigate whether one dimensional pinning centers (1D PCs) can attain the isotropic critical current density ($$J_{c}$$) properties, columnar defects (CDs) crossing at widespread angles were installed by heavy-ion irradiations into YBCO thin films. For the sample containing the CDs crossing relative to the $$c$$-axis, the plateau-like behavior of $$J$$$$_{c}$$ is realized over a wide range of magnetic field orientations, except for around B $$||$$ $$ab$$-plane where a dip structure is accompanied by a rapid decline of the $$J_{c}$$. For the bimodal splay configuration consisting of CDs crossing relative to the $$c$$-axis, a single peak around the $$c$$-axis is observed in the angular dependence of $$J_{c}$$, suggesting the splay effect at B $$||$$ $$c$$-axis by the crossed CDs. Two parallel families of CDs crossing relative to the $$ab$$-plane, on the other hand, bring about not a peak but a dip around B $$||$$ $$ab$$-plane on the angular dependence of $$J_{c}$$.

Journal Articles

Standard for prevention of gas entrainment phenomena in fast reactors, 1; Validations of CFD methods for reproducibilities of gas entrainment phenomena

Ohshima, Hiroyuki; Tanaka, Nobuatsu*; Eguchi, Yuzuru*; Nishimura, Motohiko*; Kunugi, Tomoaki*; Uchibori, Akihiro; Ito, Kei; Sakai, Takaaki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 11(4), p.316 - 328, 2012/12

It is of importance for stable operations of sodium-cooled fast reactors (SFRs) to prevent gas entrainment (GE) phenomena due to free surface vortices. Therefore, the authors have been developing an evaluation method for GE based on computational fluid dynamics (CFD) methods. In this study, we determine the suitable CFD method for GE phenomena from several candidates through some numerical benchmarks. As the results, we obtain the following guideline for the vortex-induced gas entrainment. Free vortex flow around the vortex core can be correctly evaluated by using the appropriate numerical models such as enough mesh resolution, suitable advection solver, suitable turbulence and free surface modeling.

Journal Articles

Identified charged hadron production in $$p + p$$ collisions at $$sqrt{s}$$ = 200 and 62.4 GeV

Adare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Yasuyuki*; Al-Bataineh, H.*; Alexander, J.*; Aoki, Kazuya*; Aphecetche, L.*; Armendariz, R.*; et al.

Physical Review C, 83(6), p.064903_1 - 064903_29, 2011/06

 Times Cited Count:176 Percentile:99.41(Physics, Nuclear)

Transverse momentum distributions and yields for $$pi^{pm}, K^{pm}, p$$, and $$bar{p}$$ in $$p + p$$ collisions at $$sqrt{s}$$ = 200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at the RHIC. We present the inverse slope parameter, mean transverse momentum, and yield per unit rapidity at each energy, and compare them to other measurements at different $$sqrt{s}$$ collisions. We also present the scaling properties such as $$m_T$$ and $$x_T$$ scaling and discuss the mechanism of the particle production in $$p + p$$ collisions. The measured spectra are compared to next-to-leading order perturbative QCD calculations.

Journal Articles

Azimuthal correlations of electrons from heavy-flavor decay with hadrons in $$p+p$$ and Au+Au collisions at $$sqrt{s_{NN}}$$ = 200 GeV

Adare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Yasuyuki*; Al-Bataineh, H.*; Alexander, J.*; Aoki, Kazuya*; Aphecetche, L.*; Aramaki, Y.*; et al.

Physical Review C, 83(4), p.044912_1 - 044912_16, 2011/04

 Times Cited Count:7 Percentile:49.81(Physics, Nuclear)

Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled $$p+p$$ collisions. Here we extend these studies to two particle correlations where one particle is an electron from the decay of a heavy flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interaction between heavy quarks and the quark-gluon matter. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to $$p+p$$ collisions.

JAEA Reports

Description of "Design guideline for gas entrainment prevention using CFD method" (Cooperative research)

Ohshima, Hiroyuki; Sakai, Takaaki; Kamide, Hideki; Kimura, Nobuyuki; Ezure, Toshiki; Uchibori, Akihiro; Ito, Kei; Kunugi, Tomoaki*; Okamoto, Koji*; Tanaka, Nobuatsu*; et al.

JAEA-Research 2008-049, 44 Pages, 2008/06

JAEA-Research-2008-049.pdf:42.3MB

Japan Atomic Energy Agency has conducted a conceptional design study of a sodium-cooled fast reactor in a frame work of the FBR feasibility study. The plant system concept for a commercial step is intended to minimize a vessel diameter to achieve an economical competitiveness. Therefore, the coolant in the vessel has relatively higher velocity and gas entrainment (GE) prevention from a liquid surface in the reactor vessel becomes one of important issues for the thermal-hydraulic design. In order to establish a design criteria for the GE prevention, the GE from vortex dimples at the liquid surface was investigated by a working group. The 1st proposal of "Design Guideline for Gas Entrainment Prevention Using CFD Method" was established based on the knowledge gained from the working group activities. This report introduces each study in the working group to clarify the basis of the design guideline.

Journal Articles

Hydrogen isotope distributions and retentions in the inner divertor tile of JT-60U

Oya, Yasuhisa*; Hirohata, Yuko*; Tanabe, Tetsuo*; Shibahara, Takahiro*; Kimura, Hiromi*; Oyaizu, Makoto*; Arai, Takashi; Masaki, Kei; Goto, Yoshitaka*; Okuno, Kenji*; et al.

Fusion Engineering and Design, 75-79, p.945 - 949, 2005/11

 Times Cited Count:9 Percentile:53.26(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Feasibility Study on Commercialization of Fast Breeder Reactor Cycle Systems Interim Report of Phase II; Technical Study Report for Reactor Plant Systems

Konomura, Mamoru; Ogawa, Takashi; Okano, Yasushi; Yamaguchi, Hiroyuki; Murakami, Tsutomu; Takaki, Naoyuki; Nishiguchi, Youhei; Sugino, Kazuteru; Naganuma, Masayuki; Hishida, Masahiko; et al.

JNC TN9400 2004-035, 2071 Pages, 2004/06

JNC-TN9400-2004-035.pdf:76.42MB

The attractive concepts for Sodium-, lead-bismuth-, helium- and water-cooled FBRs have been created through using typical plant features and employing advanced technologies. Efforts on evaluating technological prospects of feasibility have been paid for these concepts. Also, it was comfirmed if these concepts satisfy design requierments of capability and performance presumed in the feasibilty study on commertialization of Fast Breeder Reactor Systems. As results, it was concluded that the selection of sodium-cooled reactor was most rational for practical use of FBR technologies in 2015.

Journal Articles

Analyses of hydrogen isotope distributions in the outer target tile used in the W-shaped divertor of JT-60U

Oya, Yasuhisa*; Morimoto, Yasutomi*; Oyaizu, Makoto*; Hirohata, Yuko*; Yagyu, Junichi; Miyo, Yasuhiko; Goto, Yoshitaka*; Sugiyama, Kazuyoshi*; Okuno, Kenji*; Miya, Naoyuki; et al.

Physica Scripta, T108, p.57 - 62, 2004/00

no abstracts in English

32 (Records 1-20 displayed on this page)