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Journal Articles

Disorder-induced exceptional and hybrid point rings in Weyl/Dirac semimetals

Matsushita, Taiki*; Nagai, Yuki; Fujimoto, Satoshi*

Physical Review B, 100(24), p.245205_1 - 245205_9, 2019/12

 Times Cited Count:1 Percentile:76.22(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Influence of linear energy transfer on the scintillation decay behavior in a lithium glass scintillator

Koshimizu, Masanori*; Iwamatsu, Kazuhiro*; Taguchi, Mitsumasa; Kurashima, Satoshi; Kimura, Atsushi; Yanagida, Takayuki*; Fujimoto, Yutaka*; Watanabe, Kenichi*; Asai, Keisuke*

Journal of Luminescence, 169(Part B), p.678 - 681, 2016/01

We analyzed the effects of linear energy transfer (LET) on the scintillation properties of a Li glass scintillator, GS20. The scintillation time profiles were measured by using pulsed ion beams having different LETs. The rise in the scintillation time profiles was faster for higher LET, whereas the decay part was not significantly different for largely different LETs. The LET effects in the rise was ascribed to the effects of excited states interaction during the energy transfer process from the host glass to the luminescent centers, Ce$$^{3+}$$ ions. Supposing that the light yield decreases with LET, the fast rise at high LET was explained in terms of the competition between the energy transfer and the quenching due to the excited states interaction.

Journal Articles

Linear energy transfer effects on time profiles of scintillation of Ce-doped LiCaAlF$$_{6}$$ crystals

Yanagida, Takayuki*; Koshimizu, Masanori*; Kurashima, Satoshi; Iwamatsu, Kazuhiro*; Kimura, Atsushi; Taguchi, Mitsumasa; Fujimoto, Yutaka*; Asai, Keisuke*

Nuclear Instruments and Methods in Physics Research B, 365(Part B), p.529 - 532, 2015/12

 Times Cited Count:8 Percentile:28.72(Instruments & Instrumentation)

We measured temporal profiles of scintillation of Ce-doped LiCaAlF$$_{6}$$ scintillator crystals at different linear energy transfers (LETs). Based on the comparison of the high-LET temporal profiles with those at low LET, we found that a fast component was observed only at low LET. The disappearance of the fast component at high LET is tentatively ascribed to quenching of excited states at defects owing to the interaction between excited states via Auger process. In addition, the rise and the initial decay behavior was dependent on the LET. This LET-dependent behavior is explained by a seeming acceleration process and a slowing down process in energy transfer at high LET. The LET-dependent temporal profiles provide a basis of discrimination technique of $$gamma$$-ray and neutron detection events using these scintillators based on the nuclear reaction, $$^{6}$$Li(n,$$alpha$$)t.

Journal Articles

Colossal thermomagnetic response in the exotic superconductor URu$$_2$$Si$$_2$$

Yamashita, Takuya*; Shimoyama, Yusuke*; Haga, Yoshinori; Matsuda, Tatsuma*; Yamamoto, Etsuji; Onuki, Yoshichika; Sumiyoshi, Hiroaki*; Fujimoto, Satoshi*; Levchenko, A.*; Shibauchi, Takasada*; et al.

Nature Physics, 11(1), p.17 - 20, 2015/01

 Times Cited Count:32 Percentile:11.24(Physics, Multidisciplinary)

Journal Articles

Long-term high-temperature operation in the HTTR, 2; Core physics

Goto, Minoru; Fujimoto, Nozomu; Shimakawa, Satoshi; Tachibana, Yukio; Nishihara, Tetsuo; Iyoku, Tatsuo

Proceedings of 5th International Topical Meeting on High Temperature Reactor Technology (HTR 2010) (CD-ROM), 8 Pages, 2010/10

In the High Temperature Engineering Test Reactor (HTTR), which is a Japanese block-type HTGR, reactivity is controlled by control rods (CRs) and burnable poisons (BPs). The CRs insertion depth into the core should be retained shallow during burnup period, because the large insertion depth leads to significant disturbance of the power distribution, and consequently fuel temperature rises above the limit. Thus, the controllable reactivity with the CRs during operation is small, and then reactivity control through the burnup period largely depends on the BPs. It has not been confirmed an effectiveness of BPs on reactivity control on block-type HTGRs. The HTTR succeeded in long-term high temperature operation, and its burnup reached about 370EFPD. Thereby it became possible to confirm the effectiveness of BPs on reactivity control on the HTTR using its burnup data. We focused on a burnup change in the CRs insertion depth into the core to confirm whether the BPs functioned as designed. Additionally, we compared the change in the CRs insertion depths between analysis results and the experimental data to confirm validity of a whole core burnup calculation with the SRAC/COREBN. As a result, the experimental data showed that although the CRs insertion depth into the core was increased with burnup, it was retained the allowable depth. Meanwhile, the analysis result of the CRs insertion depth was in good agreement with the experimental data.

Journal Articles

Characteristic test of initial HTTR core

Nojiri, Naoki; Shimakawa, Satoshi; Fujimoto, Nozomu; Goto, Minoru

Nuclear Engineering and Design, 233(1-3), p.283 - 290, 2004/10

 Times Cited Count:9 Percentile:44.08(Nuclear Science & Technology)

This paper describes the results of core physics test in start-up and power-up of the HTTR. The tests were conducted in order to ensure performance and safety of the high temperature gas cooled reactor, and was carried out to measure the critical approach, the excess reactivity, the shutdown margin, the control rod worth, the reactivity coefficient, the neutron flux distribution and the power distribution. The expected core performance and the required reactor safety characteristics were verified from the results of measurements and calculations.

JAEA Reports

Core dynamics analysis of control rod withdrawal test in HTTR (Contract Research)

Takada, Eiji*; Nakagawa, Shigeaki; Takamatsu, Kuniyoshi; Shimakawa, Satoshi; Nojiri, Naoki; Fujimoto, Nozomu

JAERI-Tech 2004-048, 60 Pages, 2004/06

JAERI-Tech-2004-048.pdf:4.18MB

The HTTR (High Temperature Engineering Test Reactor), which has thermal output of 30MW, coolant inlet temperature of 395$$^{circ}$$C and coolant outlet temperature of 850$$^{circ}$$C/950$$^{circ}$$C, is a first high temperature gas-cooled reactor (HTGR) in Japan. The HTGR has a high inherent safety potential to accident condition. Safety demonstration tests using the HTTR are underway in order to demonstrate such excellent inherent safety features of the HTGR. The reactivity insertion test demonstrates that rapid increase of reactor power by withdrawing the control rod is restrained by only the negative reactivity feedback effect without operating the reactor power control system, and the temperature transient of the reactor is slow. The best estimated analyses have been conducted to simulate reactor transients during the reactivity insertion test. A one-point core dynamics approximation with one fuel channel model is applied to this analysis. It was found that the analytical model for core dynamics could simulate the reactor power behavior.

JAEA Reports

Evaluation for the models of neutron diffusion theory in terms of power density distributions of the HTTR

Takamatsu, Kuniyoshi; Shimakawa, Satoshi; Nojiri, Naoki; Fujimoto, Nozomu

JAERI-Tech 2003-081, 49 Pages, 2003/10

JAERI-Tech-2003-081.pdf:2.6MB

In the case of evaluations for the highest temperature of the fuels in the HTTR, it is very important to expect the power density distributions accurately; therefore, it is necessary to improve the analytical model with the neutron diffusion and the burn-up theory. The power density distributions are analyzed in terms of two models, the one mixing the fuels and the burnable poisons homogeneously and the other modeling them heterogeneously. Moreover these analytical power density distributions are compared wtih the ones derived from the gross $$gamma$$-ray measurements and the Monte Carlo calculational code with continuous energy. As a result the homogeneous mixed model isn't enough to expect the power density distributions of the core in the axial direction; on the other hand, the heterogeneous model improves the accuracy.

JAEA Reports

Test plans of the high temperature test operation at HTTR

Sakaba, Nariaki; Nakagawa, Shigeaki; Takada, Eiji*; Nojiri, Naoki; Shimakawa, Satoshi; Ueta, Shohei; Sawa, Kazuhiro; Fujimoto, Nozomu; Nakazawa, Toshio; Ashikagaya, Yoshinobu; et al.

JAERI-Tech 2003-043, 59 Pages, 2003/03

JAERI-Tech-2003-043.pdf:2.54MB

HTTR plans a high temperature test operation as the fifth step of the rise-to-power tests to achieve a reactor outlet coolant temperature of 950 degrees centigrade in the 2003 fiscal year. Since HTTR is the first HTGR in Japan which uses coated particle fuel as its fuel and helium gas as its coolant, it is necessary that the plan of the high temperature test operation is based on the previous rise-to-power tests with a thermal power of 30 MW and a reactor outlet coolant temperature at 850 degrees centigrade. During the high temperature test operation, reactor characteristics, reactor performances and reactor operations are confirmed for the safety and stability of operations. This report describes the evaluation result of the safety confirmations of the fuel, the control rods and the intermediate heat exchanger for the high temperature test operation. Also, problems which were identified during the previous operations are shown with their solution methods. Additionally, there is a discussion on the contents of the high temperature test operation. As a result of this study, it is shown that the HTTR can safely achieve a thermal power of 30MW with the reactor outlet coolant temperature at 950 degrees centigrade.

JAEA Reports

Rise-to-power test in High Temperature Engineering Test Reactor; Test progress and summary of test results up to 30MW of reactor thermal power

Nakagawa, Shigeaki; Fujimoto, Nozomu; Shimakawa, Satoshi; Nojiri, Naoki; Takeda, Takeshi; Saikusa, Akio; Ueta, Shohei; Kojima, Takao; Takada, Eiji*; Saito, Kenji; et al.

JAERI-Tech 2002-069, 87 Pages, 2002/08

JAERI-Tech-2002-069.pdf:10.12MB

Rise-to-power test in the HTTR has been performed from April 23rd to June 6th in 2000 as phase 1 test up to 10MW, from January 29th to March 1st in 2001 as phase 2 test up to 20MW in the rated operation mode and from April 14th to June 8th in 2001 as phase 3 test up to 20MW in the high temperature test operation mode. Phase 4 test to achieve the thermal reactor power of 30MW started from October 23rd in 2001. On December 7th it was confirmed that the thermal reactor power reached to 30MW and the reactor outlet coolant temperature reached to 850$$^{circ}$$C. JAERI obtained the certificate of pre-operation test from MEXT because all the pre-operation tests by MEXT were passed successfully. From the test results of rise-up-power test up to 30MW, the performance of reactor and cooling system were confirmed, and it was confirmed that an operation of reactor facility could be performed safely. Some problems to be solved were found through tests. By means of solving them, the reactor operation with the reactor outlet coolant temperature of 950$$^{circ}$$C will be achievable.

Journal Articles

Analysis of HTTR's core with Monte Carlo code MVP

Fujimoto, Nozomu; Nojiri, Naoki; Yamashita, Kiyonobu; Shimakawa, Satoshi; Ando, Hiroei; Mori, Takamasa

Nippon Genshiryoku Gakkai Monte Karuro Ho Ni Yoru Ryushi Shimyureshon No Genjo To Kadai, p.201 - 210, 2002/01

no abstracts in English

Oral presentation

LET effects on the scintillation properties of a Ce-doped Ca$$_{3}$$B$$_{2}$$O$$_{6}$$6 scintillator

Koshimizu, Masanori*; Fujimoto, Yutaka*; Yanagida, Takayuki*; Iwamatsu, Kazuhiro; Kimura, Atsushi; Kurashima, Satoshi; Taguchi, Mitsumasa; Asai, Keisuke*

no journal, , 

no abstracts in English

Oral presentation

Three-dimensional simulation of solid-particle sedimentation using a particle-grid coupled method

Ohara, Yohei*; Fujimoto, Takuya*; Nishida, Satoshi*; Morita, Koji*; Guo, L.*; Tagami, Hirotaka; Suzuki, Toru

no journal, , 

In order to assess sedimentation behavior of fuel debris during core disruptive accidents in sodium-cooled fast reactors, a three-dimensional particle-grid coupled method was developed. Through the analyses of basic experiments on the sedimentation behavior of solid particles, fundamental adequacy of the modeling approach was confirmed.

Oral presentation

Numerical simulation of solid-particle sedimentation using a particle-grid coupled method

Kawata, Ryo*; Ohara, Yohei*; Fujimoto, Takuya*; Nishida, Satoshi*; Morita, Koji*; Guo, L.*; Tagami, Hirotaka; Suzuki, Toru

no journal, , 

no abstracts in English

Oral presentation

Numerical simulation of mixed particle sedimentation using a particle-grid coupled method

Kawata, Ryo*; Ohara, Yohei*; Fujimoto, Takuya*; Nishida, Satoshi*; Morita, Koji*; Guo, L.*; Tagami, Hirotaka; Suzuki, Toru

no journal, , 

no abstracts in English

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