Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Yoshida, Tadayoshi; Sato, Tetsuro*; Seki, Akiyuki; Yamamoto, Hideaki*; et al.
Journal of Environmental Radioactivity, 210, p.105878_1 - 105878_12, 2019/12
Aihara, Jun; Yasuda, Atsushi*; Ueta, Shohei; Ogawa, Hiroaki; Honda, Masaki*; Ohira, Koichi*; Tachibana, Yukio
Nippon Genshiryoku Gakkai Wabun Rombunshi, 18(4), p.237 - 245, 2019/12
Development of fabrication and inspection technologies of oxidation resistant fuel element for improvement of safety of high temperature gas-cooled reactors (HTGRs) in severe oxidation accident was carried out. Simulated coated fuel particles (CFPs), alumina particles, were over-coated with mixed powder of Si, C and small amount of resin to form over-coated particles, and over-coated particles were molded and hot-pressed to sinter simulated oxidation resistant fuel elements with SiC/C mixed matrix. Simulated oxidation resistant fuel elements with matrix whose Si/C mole ratio is 1.00 were fabricated. Failure fraction of CFPs in fuel elements is one of very important inspection subjects of HTGR fuel. It is essential that CFPs are extracted from fuel elements without additional failure. Development of method for extraction of CFPs was carried out. Desolation of SiC by KOH method or pressurized acidolysis method should be applied to extraction of CFPs.
Physics of Plasmas, 26(12), p.120703_1 - 120703_5, 2019/12
This Letter presents the impacts of the hydrogen isotope mass and the normalized gyroradius on L-mode like hydrogen (H) and deuterium (D) plasmas dominated by ion temperature gradient driven (ITG) turbulence using global full-f gyrokinetic simulations. In ion heated numerical experiments with adiabatic electrons, the energy confinement time shows almost no isotope mass dependency, and is determined by Bohm like scaling. Electron heated numerical experiments with kinetic electrons show clear isotope mass dependency caused by the isotope effect on the collisional energy transfer from electrons to ions, and the H and D plasmas show similar ion and electron temperature profiles at an H to D heating power ratio of . The normalized collisionless ion gyrokinetic equations for H and D plasmas become identical at the same , and collisions weakly affect ITG turbulence. Therefore, the isotope mass dependency is mainly contributed by the scaling and the heating sources.
Ali, Y.*; Onodera, Naoyuki; Idomura, Yasuhiro; Ina, Takuya*; Imamura, Toshiyuki*
Proceedings of 10th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA 2019), p.1 - 8, 2019/11
Iterative methods for solving large linear systems are common parts of computational fluid dynamics (CFD) codes. The Preconditioned Conjugate Gradient (P-CG) method is one of the most widely used iterative methods. However, in the P-CG method, global collective communication is a crucial bottleneck especially on accelerated computing platforms. To resolve this issue, communication avoiding (CA) variants of the P-CG method are becoming increasingly important. In this paper, the P-CG and Preconditioned Chebyshev Basis CA CG (P-CBCG) solvers in the multiphase CFD code JUPITER are ported to the latest V100 GPUs. All GPU kernels are highly optimized to achieve about 90% of the roofline performance, the block Jacobi preconditioner is re-designed to extract high computing power of GPUs, and the remaining bottleneck of halo data communication is avoided by overlapping communication and computation. The overall performance of the P-CG and P-CBCG solvers is determined by the competition between the CA properties of the global collective communication and the halo data communication, indicating an importance of the inter-node interconnect bandwidth per GPU. The developed GPU solvers are accelerated up to 2x compared with the former CPU solvers on KNLs, and excellent strong scaling is achieved up to 7,680 GPUs on the Summit.
Yamano, Hidemasa; Nishida, Akemi; Choi, B.; Takada, Tsuyoshi*
Proceedings of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08
The objective of this study is to assess cliff edge effects, which are greatly important for nuclear power plants. Through assessments of failure probabilities (fragility), this study examined seismic margins of simulated two kinds of thin- and thick-walled reactor vessels by using response waveforms of the reactor building with/without a seismic isolation system obtained by seismic response analyses. The fragility analyses showed that the seismic isolation technology largely reduced the structural response effects nearly twice as much as that of the non-isolated plant. In focusing on uncertainty of response factor of components, the seismic isolation plant has a significant margin compared to the non-isolated plant even if factors from 0.5 to 2.0 are taken into account. This study concluded that the seismic isolation technology is effective to avoid cliff-edge effects.
Hashidate, Ryuta; Onizawa, Takashi; Wakai, Takashi; Kasahara, Naoto*
Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 10 Pages, 2019/07
Under the severe accident conditions, structural materials of nuclear power plants are subjected to excessive high temperature. Although it is very essential to clarify how the structure collapses under the severe accident conditions, the failure mechanisms in such high temperatures are not clarified. However, it is very difficult and expensive to perform structural tests using actual structural materials. Therefore, we propose to use lead alloys instead of actual structural materials. Because the strength of lead alloys is much poorer than that of the actual structural materials, failure can be observed at low temperature and by small load. For demonstration of analogy between the failure mechanisms of lead alloys structure at low temperature and those of the actual structures at high temperature, numerical analyses are required. So, we confirm the material characteristics of lead alloys and develop inelastic constitutive equations of lead alloy required for finite element analyses.
Kimura, Atsushi; Nakamura, Shoji; Terada, Kazushi*; Nakao, Taro*; Mizuyama, Kazuhito*; Iwamoto, Nobuyuki; Iwamoto, Osamu; Harada, Hideo; Katabuchi, Tatsuya*; Igashira, Masayuki*; et al.
Journal of Nuclear Science and Technology, 56(6), p.479 - 492, 2019/06
Idomura, Yasuhiro; Watanabe, Tomohiko*; Todo, Yasushi*
Shimyureshon, 38(2), p.79 - 86, 2019/06
We promote the research and development of exascale fusion plasma simulations on Post-K towards estimation and prediction of core plasma performance, and exploration of improved operation scenarios on the next generation fusion experimental reactor ITER. In this paper, we review developed exascale simulation technologies and outcomes from validation studies on existing experimental devices, and discuss perspectives on exascale fusion plasma simulations on Post-K.
Asahi, Yuichi*; Grandgirard, V.*; Sarazin, Y.*; Donnel, P.*; Garbet, X.*; Idomura, Yasuhiro; Dif-Pradalier, G.*; Latu, G.*
Plasma Physics and Controlled Fusion, 61(6), p.065015_1 - 065015_15, 2019/05
The role of poloidal convective cells on transport processes is studied with the full-F gyrokinetic code GYSELA. For this purpose, we apply a numerical filter to convective cells and compare the simulation results with and without the filter. The energy flux driven by the magnetic drifts turns out to be reduced by a factor of about 2 once the numerical filter is applied. A careful analysis reveals that the frequency spectrum of the convective cells is well-correlated with that of the turbulent Reynolds stress tensor, giving credit to their turbulence-driven origin. The impact of convective cells can be interpreted as a synergy between turbulence and neoclassical dynamics.
Aihara, Jun; Honda, Masaki*; Ueta, Shohei; Ogawa, Hiroaki; Ohira, Koichi*; Tachibana, Yukio
Nippon Genshiryoku Gakkai Wabun Rombunshi, 18(1), p.29 - 36, 2019/03
Japan Atomic Energy Agency carried out development of fabrication technology of oxidation resistant fuel element for improvement of safety of high temperature gas-cooled reactors in serious oxidation accident, based on precursor research in former JAEA. Dummy coated fuel particles (alumina particles) were over-coated with mixed powder of Si, C and small amount of resin to form over-coated particles, and over-coated particles were molded and hot-pressed to sinter dummy oxidation resistant fuel elements with SiC/C mixed matrix. We fabricated dummy oxidation resistant fuel elements with matrix whose Si/C mole ratio (about 0.551) is three times as large as that in precursor research. Si peak was not detected by X-ray diffraction of matrix. Better oxidation resistant was confirmed with oxidation test in 20% O at 1673 K than that of ordinal fuel compact with ordinal graphite/carbon matrix. All dummy coated fuel particles were held in specimen after 10 h oxidation.
Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Nunami, Masanori*
Computer Physics Communications, 235, p.9 - 15, 2019/02
We have implemented the Sugama collision operator in the gyrokinetic Vlasov simulation code, GKV, with an implicit time-integration scheme. The new method is versatile and independent of the details of the linearized collision operator, by means of an operator splitting, an implicit time integrator, and an iterative Krylov subspace solver. Numerical tests demonstrate stable computation over the time step size restricted by the collision term. An efficient implementation for parallel computation on distributed memory systems is realized by using the data transpose communication, which makes the iterative solver free from inter-node communications during iteration. Consequently, the present approach achieves enhancement of computational efficiency and reduction of computational time to solution simultaneously, and significantly accelerates the total performance of the application.
Ando, Masaki; Mikami, Satoshi; Tsuda, Shuichi; Yoshida, Tadayoshi; Matsuda, Norihiro; Saito, Kimiaki
Journal of Environmental Radioactivity, 192, p.385 - 398, 2018/12
Car-borne surveys using KURAMA systems have been conducted over a wide area in eastern Japan since 2011. The measurement data collected until 2016 was analyzed, and decreasing trend of the dose rates in regions within 80 km of Fukushima Dai-ichi Nuclear Power Plant were examined. The averaged dose rates tended to decrease considerably with respect to the physical decay of radiocaesium, and the ecological half-lives of the fast and slow decay components were estimated. The decrease of the dose rate in the forest was slower than its decrease in other regions, and the decrease of the dose rate in urban area was the fastest. The decrease in the dose rates obtained via the car-borne survey was larger than that obtained on flat ground with few disturbances using survey meters approximately 1.5 y after the accident; hereafter, the decrease in the dose rates obtained via the car-borne survey was same as the latter measurement.
Oikawa, Kenichi; Su, Y.; Kiyanagi, Ryoji; Kawasaki, Takuro; Shinohara, Takenao; Kai, Tetsuya; Hiroi, Kosuke; Harjo, S.; Parker, J. D.*; Matsumoto, Yoshihiro*; et al.
Physica B; Condensed Matter, 551, p.436 - 442, 2018/12
Hiroi, Kosuke; Shinohara, Takenao; Hayashida, Hirotoshi*; Parker, J. D.*; Su, Y.; Oikawa, Kenichi; Kai, Tetsuya; Kiyanagi, Yoshiaki*
Physica B; Condensed Matter, 551, p.146 - 151, 2018/12
Hiroi, Kosuke; Shinohara, Takenao; Hayashida, Hirotoshi*; Parker, J. D.*; Oikawa, Kenichi; Su, Y.; Kai, Tetsuya; Kiyanagi, Yoshiaki*
JPS Conference Proceedings (Internet), 22, p.011030_1 - 011030_7, 2018/11
Idomura, Yasuhiro; Ina, Takuya*; Yamashita, Susumu; Onodera, Naoyuki; Yamada, Susumu; Imamura, Toshiyuki*
Proceedings of 9th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA 2018) (Internet), p.17 - 24, 2018/11
A communication avoiding (CA) multigrid preconditioned conjugate gradient method (CAMGCG) is applied to the pressure Poisson equation in a multiphase CFD code JUPITER, and its computational performance and convergence property are compared against CA Krylov methods. In the JUPITER code, the CAMGCG solver has robust convergence properties regardless of the problem size, and shows both communication reduction and convergence improvement, leading to higher performance gain than CA Krylov solvers, which achieve only the former. The CAMGCG solver is applied to extreme scale multiphase CFD simulations with billion DOFs, and it is shown that compared with a preconditioned CG solver, the number of iterations is reduced to , and speedup is achieved with keeping excellent strong scaling up to 8,000 nodes on the Oakforest-PACS.
Suzuki, Yoshio; Iigaki, Kazuhiko
JAEA-Data/Code 2018-009, 41 Pages, 2018/09
Toward Verification & Validation (V&V) of a seismic simulation of entire nuclear plant, an approach to estimate errors included in observed acceleration data is proposed. On the comparison between simulation results and experimental/observational results in the process of V&V, errors which might be included in experimental/observational data should be estimated. It is considered that there exist following two causes for errors in observed acceleration data; measurement accuracy of an accelerometer measurement system and disturbance included in measured data. Techniques based on the specification of an accelerometer measurement system and the time series analysis are respectively adopted to estimate those errors. To clarify the actual procedure, those techniques are applied to acceleration data observed at High Temperature engineering Test Reactor (HTTR) at the Oarai Research and Development Institute of Japan Atomic Energy Agency.
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 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. In addition, sensitivity analyses have investigated the effects of a tephra arrival reduction factor and pre-filter covering.
Oizumi, Akito; Fukushima, Masahiro; Tsujimoto, Kazufumi; Yamanaka, Masao*; Sano, Tadafumi*; Pyeon, C. H.*
KURRI Progress Report 2017, P. 50, 2018/08
In the nuclear transmutation system such as ADS, the nuclear data validation of MA is required to reduce the uncertainty caused by the nuclear data of MA. This study aims to measure the reaction rates of Neptunium-237 (Np) and Americium-241 (Am) using the nuclear spallation neutron source in the KUCA for 3 hours. The observed distributions of pulse-height of Np and Am fission reactions were significantly different from the ones generally observed in critical and pulsed neutron source (PNS) experiments because of the influence of the -ray generated by the nuclear spallation reaction. On the other hand, the capture reaction rate of Np was measured in this experiment. The capture reaction rate of the critical experiment which was available to be measured the fission reaction rate of Np and Am was almost 8 times larger than that of this experiment. Consequently, reducing the influence of the generated by the nuclear spallation reaction and extending the duration of the irradiation to 24 or more hours would be necessary for detecting signals of fission reactions under the spallation neutron source.
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.