Machine learning molecular dynamics simulations for evaluation of high-temperature properties of nuclear fuel materials

Kobayashi, Keita; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko

Materia, 62(3), p.175 - 181, 2023/03

https://doi.org/10.2320/materia.62.175

no abstracts in English

Machine learning potentials for tobermorite minerals

Kobayashi, Keita; Nakamura, Hiroki; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko

Computational Materials Science, 188, p.110173_1 - 110173_14, 2021/02

https://doi.org/10.1016/j.commatsci.2020.110173

no abstracts in English

Neutron scattering study of yttrium iron garnet

Shamoto, Shinichi; Ito, Takashi; Onishi, Hiroaki; Yamauchi, Hiroki; Inamura, Yasuhiro; Matsuura, Masato*; Akatsu, Mitsuhiro*; Kodama, Katsuaki; Nakao, Akiko*; Moyoshi, Taketo*; et al.

Physical Review B, 97(5), p.054429_1 - 054429_9, 2018/02

https://doi.org/10.1103/PhysRevB.97.054429

Nuclear and magnetic structure and full magnon dispersions of yttrium iron garnet YFeO have been studied by neutron scattering. The lowest-energy dispersion below 14 meV exhibits a quadratic dispersion as expected from ferromagnetic magnons. The imaginary part of -integrated dynamical spin susceptibility "() exhibits a square-root energy-dependence in the low energies. The magnon density of state is estimated from the "() obtained on an absolute scale. The value is consistent with a single chirality mode for the magnon branch expected theoretically.

Realization of a phase bunching effect for minimization of beam phase width in a central region of an AVF cyclotron

Miyawaki, Nobumasa; Fukuda, Mitsuhiro*; Kurashima, Satoshi; Okumura, Susumu; Kashiwagi, Hirotsugu; Nara, Takayuki; Ishibori, Ikuo; Yoshida, Kenichi; Yokota, Wataru; Nakamura, Yoshiteru*; et al.

Nuclear Instruments and Methods in Physics Research A, 636(1), p.41 - 47, 2011/04

https://doi.org/10.1016/j.nima.2011.01.174

A phase bunching effect has been achieved for the first time using a rising slope of the dee voltage waveform produced at the first acceleration gap between the RF shielding cover of the inflector and the puller in the new central region of the JAEA AVF cyclotron. The feasibility of the phase bunching effect in the central region for a two-dee system with a span angle of 86 in three acceleration harmonic modes was assessed by a simple geometrical analysis of particle trajectories and a three-dimensional beam orbit simulation. The simulation indicated that the initial beam phase width of 40 RF degrees is compressed to 11 RF degrees in the second harmonic mode. A phase width of 1.5 RF degrees FWHM for a 260 MeV Ne beam accelerated in the second harmonic mode was reduced by the bunching effect, compared with the beam phase width of 7.3 RF degrees FWHM in the same harmonic mode for a 10 MeV H beam accelerated in the original central region.

Recent progress in the energy recovery linac project in Japan

Sakanaka, Shogo*; Akemoto, Mitsuo*; Aoto, Tomohiro*; Arakawa, Dai*; Asaoka, Seiji*; Enomoto, Atsushi*; Fukuda, Shigeki*; Furukawa, Kazuro*; Furuya, Takaaki*; Haga, Kaiichi*; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.2338 - 2340, 2010/05

http://accelconf.web.cern.ch/AccelConf/IPAC10/papers/tupe091.pdf

Future synchrotron light source using a 5-GeV energy recovery linac (ERL) is under proposal by our Japanese collaboration team, and we are conducting R&D efforts for that. We are developing high-brightness DC photocathode guns, two types of cryomodules for both injector and main superconducting (SC) linacs, and 1.3 GHz high CW-power RF sources. We are also constructing the Compact ERL (cERL) for demonstrating the recirculation of low-emittance, high-current beams using above-mentioned critical technologies.

Reliability of core exit thermocouple (CET) for accident management action during SBLOCA and abnormal transient tests at ROSA/LSTF

Suzuki, Mitsuhiro; Nakamura, Hideo

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) (CD-ROM), 17 Pages, 2009/09

Presented are experiment results on performance of core exit thermocouple (CET) and applicability to PWR accident management (AM) during 12 tests of small-break loss-of-coolant accident (SBLOCA) and abnormal transient conducted at the Large Scale Test Facility (LSTF) of Japan Atomic Energy Agency, which is the largest PWR simulator with full-height and 1/48 volume scaling. General CET performances are derived including (1) CETs are capable in most cases to detect core overheating with delay of time and temperature increase from core heat-up, (2) one of the reasons of this delay is attributed to cooling effects of structural materials at the core exit and peripheral region, (3) CETs were incapable to detect core overheating in a very small break under steam generator depressurization action as well as a 10% cold leg break due to significant water fall-back from hot legs, and (4) an alternative indication by CET superheat is necessary in extremely high and low pressure conditions.

Single-turn extraction from a K110 AVF cyclotron by flat-top acceleration

Kurashima, Satoshi; Miyawaki, Nobumasa; Okumura, Susumu; Ishibori, Ikuo; Nara, Takayuki; Agematsu, Takashi; Yoshida, Kenichi; Yokota, Wataru; Nakamura, Yoshiteru*; Arakawa, Kazuo; et al.

Review of Scientific Instruments, 80(3), p.033302_1 - 033302_9, 2009/03

https://doi.org/10.1063/1.3093810

Single-turn extraction from the JAEA AVF cyclotron with a K number of 110 using a flat-top (FT) acceleration system has been achieved to reduce the energy spread of an ion beam for microbeam formation with energy up to hundreds of MeV and to increase extraction efficiency from the cyclotron. In order to generate an FT waveform voltage using the fifth-harmonic frequency on a dee electrode, an FT resonator was designed using MAFIA code to achieve downsizing and low power consumption. The FT resonator, coupled to the main resonator through a coupling capacitor, covered the full range of the fifth harmonic frequency from 55 to 110 MHz. Various ion beams, accelerated using different acceleration harmonic mode of h = 1 and 2, such as 220 MeV C (h = 2), 260 MeV Ne (h = 2), and 45 MeV H (h = 1) were developed by FT acceleration. A clear turn separation of the beam bunches was successfully observed at the extraction region of the large-scale AVF cyclotron with number of revolutions greater than 200. As a result, high extraction efficiency (over 95%) from the cyclotron was achieved. Single-turn extraction was confirmed by counting the number of beam bunches out of the cyclotron for an injected beam pulsed by a beam chopping system in the injection line. The energy spread of the 260 MeV Ne beam was measured using an analyzing magnet and we verified a reduction of the energy spread from E/E = 0.1% to 0.05% by single-turn extraction.

A Study on ROSA/LSTF SB-CL-09 test simulating PWR 10% cold leg break LOCA; Loop-seal clearing and 3D core heat-up phenomena

Suzuki, Mitsuhiro; Nakamura, Hideo

JAEA-Research 2008-087, 148 Pages, 2008/10

JAEA-Research-2008-087.pdf:22.6MB

This report presents major results observed in LOCA test (SB-CL-09) conducted at the ROSA/LSTF test facility simulating 10% cold leg break in a 4-loop Westinghouse-type PWR. Following are found in this test with an assumption of high pressure injection system. (1) The relatively large break size resulted in pressure inverse within 2 minutes between the primary and steam generator secondary sides. (2) During a loop-seal clearing (LSC) process started at about 1 minutes after the break, the core water level was suppressed to almost lower end and then it recovered to the middle core height. The water level remained at the middle height was due to remained water levels in the SG U-tube inlet sides which were higher than their outlet sides. (3) Significant core heat-up was observed above the water level at the middle height and core power was tripped off at 111s. (4) The effects of fall-back water from the intact loop hot leg was observed by the local core cooling.

RELAP5 analysis of ROSA/LSTF vessel upper head break LOCA experiment

Takeda, Takeshi; Asaka, Hideaki; Suzuki, Mitsuhiro; Nakamura, Hideo

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-12) (CD-ROM), 3 Pages, 2007/09

RELAP5 code analysis was performed to validate the code predictability by using ROSA/LSTF experiment data that simulated a PWR vessel upper head small break loss-of-coolant accident (SBLOCA) with a break equivalent to 1% cold leg break. The JAEA-modified RELAP5/MOD3.2.1.2 code was used by incorporating a break model that employs maximum bounding flow theory with a discharge coefficient (Cd) of 0.61 for two-phase break flow. In the experiment, liquid level in the upper head was found to control break flow rate as coolant in the upper plenum entered the upper head through control rod guide tubes (CRGTs) until the penetration holes at the CRGT bottom were exposed to steam in the upper plenum. The upper head noding and flow paths between the upper plenum and the CRGT were thus modeled to simulate well the liquid level and coolant flow around the upper portion of pressure vessel. The code, however, overpredicted the break flow rate due to the underprediction of break-upstream void fraction especially during two-phase flow discharge period. Cd for two-phase break flow was thus adjusted to be 0.58. Effects of break area on the core cooling were investigated further. The parameter analyses showed that peak cladding temperature (PCT) is the maximum at 1% break case, while the PCT would be lower than 1200 K in the larger break size cases because vapor condensation on injected accumulator coolant induces loop seal clearing and effectively enhances core cooling thereafter.

A Study on timing of rapid depressurization action during PWR vessel bottom break LOCA with HPI failure and AIS-gas inflow, ROSA-V/LSTF test SB-PV-06

Suzuki, Mitsuhiro; Takeda, Takeshi; Asaka, Hideaki; Nakamura, Hideo

JAEA-Research 2007-037, 150 Pages, 2007/03

JAEA-Research-2007-037.pdf:7.55MB

A small break LOCA experiment (SB-PV-06) was conducted at the LSTF of ROSA-V program to study effects of rapid secondary depressuriza-tion action on core cooling as one of accident management (AM) measures for a PWR in case of high pressure injection system failure and non-condensable gas inflow from the accumulator injection system. The break simulated 10 instrument tubes rupture equivalent to 0.2% cold leg break. It was clarified through comparison with former experiments that (1) the depressurization initiated by detecting the vessel level below the primary loop (4545s) was degraded by the gas inflow resulting in whole core uncovery prior to the start of low pressure injection and (2) an alternative start of the depressurization by detecting level decrease at the SG outlet plenum (2330s), would limit the core uncovery suggesting more effective parameter for the AM measures. The report presents the experiment results with the effects of rapid depressurization initiation timing.