Ina, Takuya*; Idomura, Yasuhiro; Imamura, Toshiyuki*; Yamashita, Susumu; Onodera, Naoyuki
Proceedings of 12th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems ScalA21) (Internet), 8 Pages, 2021/11
A new mixed-precision preconditioner based on the iterative refinement (IR) method is developed for preconditioned conjugate gradient (P-CG) and multigrid preconditioned conjugate gradient (MGCG) solvers in a multi-phase thermal-hydraulic CFD code JUPITER. In the IR preconditioner, all data is stored in FP16 to reduce memory access, while all computation is performed in FP32. The hybrid FP16/32 implementation keeps the similar convergence property as FP32, while the computational performance is close to FP16. The developed solvers are optimized on Fugaku (A64FX), and applied to ill-conditioned matrices in JUPITER. The P-CG and MGCG solvers with the new IR preconditioner show excellent strong scaling up to 8,000 nodes, and at 8,000 nodes, they are respectively accelerated up to 4.86 and 2.39 from the conventional ones on Oakforest-PACS (KNL).
Gonzalz, M. A.*; Borodin, O.*; Kofu, Maiko; Shibata, Kaoru; Yamada, Takeshi*; Yamamuro, Osamu*; Xu, K.*; Price, D. L.*; Saboungi, M.-L.*
Journal of Physical Chemistry Letters (Internet), 11(17), p.7279 - 7284, 2020/09
Oba, Takashi*; Ishikawa, Tetsuo*; Nagai, Haruyasu; Tokonami, Shinji*; Hasegawa, Arifumi*; Suzuki, Gen*
Scientific Reports (Internet), 10(1), p.3639_1 - 3639_11, 2020/02
Internal doses of residents after the Fukushima Daiichi Nuclear Power Station accident have been reconstructed. In total 896 behaviour records in the Fukushima Health Management Survey were analysed to estimate thyroid doses via inhalation, using a spatiotemporal radionuclides concentration database constructed by atmospheric dispersion simulations. After a decontamination factor for sheltering and a modifying factor for the dose coefficient were applied, estimated thyroid doses were close to those estimated on the basis of direct thyroid measurement. The median and 95th percentile of thyroid doses of 1-year-old children ranged from 1.2 to 15 mSv and from 7.5 to 30 mSv, respectively.
Rossi, F.; Rodriguez, D.; Takahashi, Tone; Seya, Michio; Koizumi, Mitsuo
Nihon Kaku Busshitsu Kanri Gakkai Dai-39-Kai Nenji Taikai Rombunshu (CD-ROM), 3 Pages, 2018/11
This paper (presentation) reports on the design study for seeking compactness of moderator (and reflector) structure for the Delayed Gamma-ray Spectroscopy Non Destructive Assay system to be applied for verification of fissile isotopic (Pu-239, Pu-241 and U-235) composition ratio in High Radioactive Nuclear Material sample such as dissolved solution of reprocessing facility. We first investigated advantages and disadvantages of using different compact neutron sources as DT and DD neutron generators. This led us to the conclusion of using DD sources to achieve a compact (and practical) NDA system. Based on MCNP simulations, with the use of a DD neutron generator, a preliminary optimization study was performed and will be shown here.
Nuclear Instruments and Methods in Physics Research B, 365(Part B), p.592 - 595, 2015/12
Ikeda, Takashi; Boero, M.*
Journal of Chemical Physics, 143(19), p.194510_1 - 194510_7, 2015/11
By resorting to a novel implementation of the first-principles-based van der Waals correction based on maximally localized Wannier functions, we inspect its performance and assess its reliability for aqueous solutions of alkali metal ions. We find that van der Waals interactions, when added to the widely used revPBE gradient corrected functional, influence substantially both structural and dynamical properties of water molecules, with particular emphasis on the hydration shell of the alkali cations. These effects are more evident for strong structure-making and -breaking cationic species. Moreover, self-diffusion coefficients and reorientation correlation times of solvating water molecules change systematically, showing a trend in better agreement with experiments with respect to simulations neglecting the long-range dispersion contributions.
Kim, S.-Y.; Asakura, Toshihide; Morita, Yasuji; Uchiyama, Gunzo*; Ikeda, Yasuhisa*
Journal of Radioanalytical and Nuclear Chemistry, 262(2), p.311 - 315, 2004/11
no abstracts in English
Tamura, Itaru; Aizawa, Kazuya; Harada, Masahide; Shibata, Kaoru; Maekawa, Fujio; Soyama, Kazuhiko; Arai, Masatoshi
Proceedings of ICANS-XVI, Volume 1, p.529 - 539, 2003/07
Moderator components of the McStas code have been created for the design of the spectrometers of JSNS. Three cryogenic moderators are adopted in JSNS, One is a coupled H moderator for high intensity experiments and other two are decoupled H with poisoned or unpoisoned for high resolution moderators. Monte Carlo simulations have turned out to be useful for design of neutron scattering instruments with high complexity. The software package McStas is selected for its own flexibility. Since the characteristics of neutron beams generated from moderators make influence on the performance of pulse neutron spectrometers, it is important to perform the simulation with neutron source component written precisely. Both Energy dependence of neutron spectrum and time structure of neutrons were calculated using NMTC/JAERI97 and MCNP4a codes.The simulation parameters, which describe the pulse shape as a function of time, are optimized. The creation of neutron source components viewed to coupled H moderator and viewed to decoupled H moderator of JSNS are reported.
Onuki, Akira; Nakamura, Hideo; Anoda, Yoshinari; Obata, Hiroyuki*; Saishu, Sadanori*
Proceedings of 9th International Conference on Nuclear Engineering (ICONE-9) (CD-ROM), 10 Pages, 2001/00
A passive containment cooling system (PCCS) is under planning to use in a next-generation-type BWR for long-term cooling by condensing steam using horizontal heat exchangers. Heat transfer behavior in a secondary water pool is one of important phenomena governing heat removal performance of the PCCS. Boiling and condensation can be supposed under high heat flux regions and the two-phase natural circulation might enhance the heat transfer due to an increase of flow rate and a flow agitation. However, some heat transfer tubes might be covered only by steam and the heat transfer is degraded in such region (Steam-blanket effect). This study evaluated the characteristics of the heat transfer behavior in the secondary water pool by multi-dimensional two-fluid model code ACE-3D. It was found from the analyses that no any heat transfer tubes are covered only by steam and the heat transfer is enhanced due to the nucleate boiling and the increase of local liquid flow rate.
Takase, Kazuyuki; Kunugi, Tomoaki; Seki, Yasushi
Proc. of Int. Topical Meetig on Advanced Reactors Safety, 2, p.1268 - 1275, 1997/00
no abstracts in English
Proceedings 6th Intern.Symp. on Space Tech. and Sci., p.719 - 728, 1966/00
no abstracts in English
El-Asaad, H.; Chirayath, S.*; Hecker, S.*; Fuhrmann, M.*
no journal, ,