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Journal Articles

Reactor physics experiment in a graphite moderation system for HTGR, 3

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.

Journal Articles

Preliminary experiment in a graphite-moderated core to avoid full mock-up experiment for the future first commercial HTGR

Okita, Shoichiro; Fukaya, Yuji; Sakon, Atsushi*; Sano, Tadafumi*; Takahashi, Yoshiyuki*; Unesaki, Hironobu*

Proceedings of International Conference on Physics of Reactors 2022 (PHYSOR 2022) (Internet), 9 Pages, 2022/05

Journal Articles

Reactor physics experiment in a graphite-moderation system for HTGR

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.

Journal Articles

Reactor noise analysis for a graphite-moderated and -reflected core in KUCA

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$$_{3}$$ 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$$pm$$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.

Journal Articles

Reactor physics experiment in a graphite-moderation system for HTGR

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.

Oral presentation

R&D to improve accuracy of nuclear prediction for HTGR, 1; Experiment of first mock-up reactor with graphite system in KUCA

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.

Oral presentation

R&D to improve accuracy of nuclear prediction for HTGR, 2; Inverse kinetics analysis for HTTR simulated core in KUCA

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.

Oral presentation

R&D to improve accuracy of nuclear prediction for HTGR, 3; Rossi-$$alpha$$ analysis for HTTR simulated core in KUCA

Nakajima, 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-$$alpha$$ 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.

Oral presentation

R&D to improve accuracy of nuclear prediction for HTGR, 4; Power spectrum analysis for HTTR simulated core in KUCA

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.

Oral presentation

Reactor noise analysis using MVP code for subcritical systems in KUCA

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 $$alpha$$ has been calculated with Feynman-$$alpha$$ simulation capability of the code. It has been confirmed that the calculated values agree with the measured ones within the range of 10%.

Oral presentation

Reactor physics experiment using graphite-moderated core in KUCA to improve accuracy of nuclear prediction for HTGR designs

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

Oral presentation

Reactivity estimation of UTR-KINKI subcritical cores; Estimation based on power profile in quasi-steady state

Yamane, Yuichi; Araki, Shohei; Sakon, Atsushi*

no journal, , 

A new reactivity estimation method was applied to the data obtained from some subcritical cores of UTR-KINKI for comparison to other existing methods. The estimated reactivity value for about several dollars subcritical cores by using the method based on the power profile in quasi-steady state showed almost the same result as other methods such as Feynman-$$alpha$$ and source jerk.

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