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Fukaya, Yuji; Okita, Shoichiro; Kanda, Shun*; Goto, Masaki*; Nakajima, Kunihiro*; Sakon, Atsushi*; Sano, Tadafumi*; Hashimoto, Kengo*; Takahashi, Yoshiyuki*; Unesaki, Hironobu*
KURNS Progress Report 2021, P. 101, 2022/07
The Japan Atomic Energy Agency (JAEA) started the Research and Development (R&D) to improve nuclear prediction techniques for High Temperature Gas-cooled Reactors (HTGRs) in 2018. The objectives are to intro-duce the generalized bias factor method to avoid full mock-up experiment for the first commercial HTGR and to improve neutron instrumentation system by virtue of the particular characteristics due to a graphite moderation system. For this end, we composed B7/4"G2/8"p8EU(3)+3/8"p38EU in the B-rack of Kyoto University Critical Assembly (KUCA) in 2021.
Sakon, Atsushi*; Hashimoto, Kengo*; Sano, Tadafumi*; Nakajima, Kunihiro*; Kanda, Shun*; Goto, Masaki*; Fukaya, Yuji; Okita, Shoichiro; Fujimoto, Nozomu*; Takahashi, Yoshiyuki*
KURNS Progress Report 2021, P. 100, 2022/07
The R&D of reactor noise analysis to obtain HTGR nuclear characteristics have been performed with Kyoto University Critical Assembly (KUCA). In the last study, a neutron detector located about 55 cm away of fuel assembly measured the auto power spectral density. However, the prompt neutron decay constants obtained by this detector was different from that of other detectors. The objective of this study is experimental study of reactor noise analysis by the power spectrum method using neutron detector placed outside reactor core.
Fukaya, Yuji; Goto, Minoru; Nakagawa, Shigeaki; Nakajima, Kunihiro*; Takahashi, Kazuki*; Sakon, Atsushi*; Sano, Tadafumi*; Hashimoto, Kengo*
EPJ Web of Conferences, 247, p.09017_1 - 09017_8, 2021/02
The Japan Atomic Energy Agency (JAEA) started the Research and Development (R&D) to improve nuclear prediction techniques for High Temperature Gas-cooled Reactors (HTGRs). The objectives are to introduce a generalized bias factor method to avoid full mock-up experiment for the first commercial HTGR and to introduce reactor noise analysis to High Temperature Engineering Test Reactor (HTTR) experiment to observe subcriticality. To achieve the objectives, the reactor core of graphite-moderation system named B7/4"G2/8"p8EUNU+3/8"p38EU(1) was newly composed in the B-rack of Kyoto University Critical Assembly (KUCA). The core is composed of the fuel assembly, driver fuel assembly, graphite reflector, and polyethylene reflector. The fuel assembly is composed of enriched uranium plate, natural uranium plate and graphite plates to realize the average fuel enrichment of HTTR and it's spectrum. However, driver fuel assembly is necessary to achieve the criticality with the small-sized core. The core plays a role of the reference core of the bias factor method, and the reactor noise was measured to develop the noise analysis scheme. In this study, the overview of the criticality experiments is reported. The reactor configuration with graphite moderation system is rare case in the KUCA experiments, and this experiment is expected to contribute not only for an HTGR development but also for other types of a reactor in the graphite moderation system such as a molten salt reactor development.
Sakon, Atsushi*; Nakajima, Kunihiro*; Takahashi, Kazuki*; Hohara, Shinya*; Sano, Tadafumi*; Fukaya, Yuji; Hashimoto, Kengo*
EPJ Web of Conferences, 247, p.09009_1 - 09009_8, 2021/02
In graphite-reflected thermal reactors, even a detector placed far from fuel region may detect a certain degree of the correlation amplitude. This is because mean free path of neutrons in graphite is longer than that in water or polyethylene. The objective of this study is experimentally to confirm a high flexibility of neutron detector placement in graphite reflector for reactor noise analysis. The present reactor noise analysis was carried out in a graphite-moderated and -reflected thermal core in Kyoto University Critical Assembly (KUCA). BF
proportional neutron counters (1" dia.) were placed in graphite reflector region, where the counters were separated by about 35cm and 30cm -thick graphite from the core, respectively. At a critical state and subcritical states, time-sequence signal data from these counters were acquired and analyzed by a fast Fourier transform (FFT) analyzer, to obtain power spectral density in frequency domain. The auto-power spectral density obtained from the counters far from the core contained a significant degree of correlated component. A least-squares fit of a familiar formula to the auto-power spectral density data was made to determine the prompt-neutron decay constant. The decay constant was 63.3
14.5 [1/s] in critical state. The decay constant determined from the cross-power spectral density and coherence function data between the two counters also had a consistent value. It is confirmed that reactor noise analysis is possible using a detector placed at about 35cm far from the core, as we expected.
Fukaya, Yuji; Goto, Minoru; Nakagawa, Shigeaki; Nakajima, Kunihiro*; Takahashi, Kazuki*; Sakon, Atsushi*; Sano, Tadafumi*; Hashimoto, Kengo*
Proceedings of International Conference on the Physics of Reactors; Transition To A Scalable Nuclear Future (PHYSOR 2020) (USB Flash Drive), 8 Pages, 2020/03
The Japan Atomic Energy Agency (JAEA) started the Research and Development (R&D) to improve nuclear prediction techniques for High Temperature Gas-cooled Reactors (HTGRs). The objectives are to introduce a generalized bias factor method to avoid full mock-up experiment for the first commercial HTGR and to introduce reactor noise analysis to High Temperature Engineering Test Reactor (HTTR) experiment to observe subcriticality. To achieve the objectives, the reactor core of graphite-moderation system named B7/4"G2/8"p8EUNU+3/8"p38EU(1) was newly composed in the B-rack of Kyoto University Critical Assembly (KUCA). The core is composed of the fuel assembly, driver fuel assembly, graphite reflector, and polyethylene reflector. The fuel assembly is composed of enriched uranium plate, natural uranium plate and graphite plates to realize the average fuel enrichment of HTTR and it's spectrum. However, driver fuel assembly is necessary to achieve the criticality with the small-sized core. The core plays a role of the reference core of the bias factor method, and the reactor noise was measured to develop the noise analysis scheme. In this study, the overview of the criticality experiments is reported. The reactor configuration with graphite moderation system is rare case in the KUCA experiments, and this experiment is expected to contribute not only for an HTGR development but also for other types of a reactor in the graphite moderation system such as a molten salt reactor development.
Tsuji, Akihiro*; Zhang, S.*; Hashimoto, Tadafumi*; Okano, Shigetaka*; Shobu, Takahisa; Mochizuki, Masahito*
Zairyo, 65(9), p.665 - 671, 2016/09
It is necessary to control weld residual stress which has negative influence on fracture strengths. In structural steel welds, complex residual stress fields are formed due to phase transformation that occur according to the thermal cycles. In this study, in-situ evaluation of phase transformation and transitional stress simultaneously during welding is discussed. In the test using SM490A, after cooling process, stress evaluated by this system showed good agreement with that evaluated by lab X-ray. During austenite to ferrite transformation in weld metal, tensile stress occurred in austenite and compressive stress occurred in ferrite. Moreover, stress concentration was occurred in ferrite phase immediately after the start of phase transformation. Also, stress concentration was occurred in austenite phase just before the end of phase transformation.
Ihara, Ryohei*; Hashimoto, Tadafumi*; Mikami, Yoshiki*; Katsuyama, Jinya; Onizawa, Kunio; Mochizuki, Masahito*
Nihon Hozen Gakkai Dai-7-Kai Gakujutsu Koenkai Yoshishu, p.611 - 616, 2010/07
In light-water reactor nuclear power stations, stress corrosion cracking (SCC) has been observed near the welded joint in recirculation piping made of low-carbon austenitic stainless steel. Residual stress is one of the most important factors in the occurrence and propagation of SCC. The joining process of pipes which usually consists of surface machining and welding results in high tensile residual stress. In this study, finite element analysis method was developed to evaluate residual stress generated by surface machining considering the shape of machining tool and machining condition. Residual stress due to surface machining was measured by X-ray diffraction method and analysed the method developed. It was shown that high tensile residual stress due to machining occurred very limited surface region. It was also shown that surface machining affected SCC growth behavior significantly from the SCC analysis results based on residual stress distributions due to surface machining and welding.
Ihara, Ryohei*; Katsuyama, Jinya; Onizawa, Kunio; Hashimoto, Tadafumi*; Mikami, Yoshiki*; Mochizuki, Masahito*
Yosetsu Kozo Shimpojiumu 2009 Koen Rombunshu, p.393 - 396, 2009/11
Stress Corrosion Cracking (SCC) has been observed near the weld zone of the primary loop recirculation pipes made of SUS316L. For the evaluation of initiation and propagation of SCC for non-sensitization material, residual stress distribution generated by surface-machining is the most important factors. In this study, residual stress distributions generated are evaluated by varying cutting speed, and crack growth analysis are performed using evaluated residual stress distributions. As a result, crack growth highly depends on residual stress distributions by surface-machining.
Ihara, Ryohei*; Katsuyama, Jinya; Onizawa, Kunio; Hashimoto, Tadafumi*; Mikami, Yoshiki*; Mochizuki, Masahito*
no journal, ,
Stress corrosion cracking (SCC) has been observed near the weld zone of core shroud and recirculation pipes made of Type316L stainless steel. Residual stress distribution generated by welding and/or surface machining is very important for the evaluation of occurrence and propagation of SCC in such a non-sensitized material. In this work, residual stress distribution due to surface machining at the piping-weld has been evaluated by numerical simulations with the cutting speed varied. Analysis results showed that the thickness of hardened layer due to surface machining was limited only to a thin area of 0.2 mm, although higher cutting speed caused higher residual stress at the surface.
Zhang, S.; Shobu, Takahisa; Shiro, Ayumi; Hashimoto, Tadafumi*; Tsuji, Akihiro*; Okano, Shigetaka*; Mochizuki, Masahito*
no journal, ,
no abstracts in English
Zhang, S.; Shobu, Takahisa; Shiro, Ayumi; Hashimoto, Tadafumi*; Tsuji, Akihiro*; Okano, Shigetaka*; Mochizuki, Masahito*
no journal, ,
Fukaya, Yuji; Goto, Minoru; Nakagawa, Shigeaki; Nakajima, Kunihiro*; Takahashi, Kazuki*; Sakon, Atsushi*; Hashimoto, Kengo*; Sano, Tadafumi*
no journal, ,
To improve accuracy of nuclear prediction for HTGR, we performed the critical experiment and reactor noise measurement to obtain HTGR nuclear characteristics by configuring the graphite moderation system mock-up core at the solid moderator rack (B rack) in Kyoto University Critical Assembly (KUCA). This report states the overview of the criticality experiment and future perspective of this R&D.
Takahashi, Kazuki*; Nakajima, Kunihiro*; Sakon, Atsushi*; Hohara, Shinya*; Hashimoto, Kengo*; Fukaya, Yuji; Sano, Tadafumi*
no journal, ,
A Mock-up core for HTTR was configured on the B rack of the Kyoto University Critical Assembly (KUCA), and control rod and center core drop experiments were conducted to obtain time-series data. As a result of performing inverse kinetics analysis on the acquired time-series data, position dependency of each detector was confirmed. Furthermore, in the case with large reactivity worth, such as C1 and the central core, significant differences were found between the analysis results of the integration method and the least squares inverse kinetics method.
analysis for HTTR simulated core in KUCANakajima, Kunihiro*; Sakon, Atsushi*; Takahashi, Kazuki*; Hohara, Shinya*; Hashimoto, Kengo*; Fukaya, Yuji; Sano, Tadafumi*
no journal, ,
Time series data of neutron detector was obtained under Am-Be steady neutron source driven condition and neutron source from fuel in the graphite core system configured on B rack of the Kyoto University Critical Assembly (KUCA), and the reactor noise analysis with Rossi- method was performed. As a result, neutron correlation component could not be observed under Am-Be neutron source driven condition, but a significant correlation component was observed under fuel neutron source driven condition, and prompt neutron decay constant could be determined.
Sakon, Atsushi*; Nakajima, Kunihiro*; Takahashi, Kazuki*; Hohara, Shinya*; Sano, Tadafumi*; Fukaya, Yuji; Hashimoto, Kengo*
no journal, ,
Subcriticality measurement experiment by reactor noise analysis was performed in mock-up core for HTTR configured on B rack of the Kyoto University Critical Assembly (KUCA). The experiments were carried out in low power critical state and in the subcritical state driven by Am-Be neutron source, and the measurements were performed with several neutron detectors at different positions. We analyzed neutron detector time series data acquired by experiment by power spectrum method, and tried to estimate the prompt neutron decay constant of the system.
Nakajima, Kunihiro*; Nagaya, Yasunobu; Sakon, Atsushi*; Sano, Tadafumi*; Hashimoto, Kengo*
no journal, ,
Reactor noise analysis have been performed with the MVP3.0 code for subcritical experiments at KUCA A-core. The prompt neutron decay constant has been calculated with Feynman- simulation capability of the code. It has been confirmed that the calculated values agree with the measured ones within the range of 10%.
Okita, Shoichiro; Fukaya, Yuji; Goto, Masaki*; Kanda, Shun*; Nakajima, Kunihiro*; Sakon, Atsushi*; Sano, Tadafumi*; Hashimoto, Kengo*; Takahashi, Yoshiyuki*; Unesaki, Hironobu*
no journal, ,
no abstracts in English
