左近 敦士 (サコン アツシ)

  • 原子力研究所 講師
Last Updated :2024/02/01

コミュニケーション情報 byコメンテータガイド

  • コメント

    加速器駆動炉などの新型炉における原子炉物理について、臨界集合体を使った実験研究をしています。

研究者情報

学位

  • 博士(工学)(2014年03月 近畿大学)

ホームページURL

J-Global ID

現在の研究分野(キーワード)

    加速器駆動炉などの新型炉における原子炉物理について、臨界集合体を使った実験研究をしています。

研究分野

  • エネルギー / 原子力工学

経歴

  • 2020年04月 - 現在  近畿大学原子力研究所講師
  • 2015年10月 - 2020年03月  近畿大学原子力研究所助教
  • 2014年04月 - 2015年09月  国立研究開発法人日本原子力研究開発機構福島研究開発部門 原子力科学研究所 福島技術開発試験部 臨界技術第1課

学歴

  • 2011年04月 - 2014年03月   近畿大学大学院   総合理工学研究科   エレクトロニクス系工学専攻 博士後期課程
  • 2009年04月 - 2011年03月   近畿大学大学院   総合理工学研究科   エレクトロニクス系工学専攻 博士前期課程
  • 2007年04月 - 2009年03月   近畿大学   理工学部   電気電子工学科
  • 2005年04月 - 2007年03月   近畿大学工業高等専門学校   電気情報工学科
  • 2002年04月 - 2005年03月   大阪市立都島工業高等学校   機械電機科

所属学協会

  • 日本原子力学会   

研究活動情報

論文

  • Sin-Ya Hohara; Tomohiro Endo; Kazuki Takahashi; Kunihiro Nakajima; Atsushi Sakon; Tadafumi Sano; Kengo Hashimoto
    Journal of Nuclear Science and Technology 1 - 7 2022年11月
  • Shoichiro Okita; Yuji Fukaya; Atsushi Sakon; Tadafumi Sano; Yoshiyuki Takahashi; Hironobu Unesaki
    NUCLEAR SCIENCE AND ENGINEERING 2022年07月 
    In this paper, integral experiments on a graphite-moderated core were conducted at the B-rack of the Kyoto University Criticality Assembly in order to develop an integral experiment database for the applicability of data assimilation techniques to the neutronic design of a high-temperature gas-cooled reactor. The calculation/experiment-1 (C/E-1)values for the k(eff) values at critical cores with the major nuclear data libraries, such as JENDL-4.0, JENDL-5, JEFF-3.2, ENDF/B-VII.1, and ENDF/B-VIII.0, were calculated for the core. Of these, the k(eff) values with JENDL-5 with thermal neutron scattering law data for 30% porous graphite showed the best agreement with experimental values within 0.02% accuracy.
  • Kengo Hashimoto; Kunihiro Nakajima; Sin-ya Hohara; Atsushi Sakon; Tadafumi Sano
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 59 6 748 - 756 2022年06月 
    An improved Rossi-alpha formula is derived to consider a delayed-neutron contribution to a conditional counting probability defined in the Rossi-alpha technique. The improved formula has an additional constant term and another additional term proportional to time interval tau to the original formula. For an university training and research reactor of Kindai University, the Rossi-alpha analyses based on the original and the improved formulae are carried out to examine the applicability of these formulae to the subcritical thermal reactor. The original formula results in an inconsistent prompt-neutron decay constant with that determined from a previous Feynman-alpha analysis considering delayed neutrons. This difficulty of the original formula originates from the neglect of delayed neutrons. Applying the improved formula leads to a consistent prompt-neutron decay constant. The additional constant term of the improved formula should be considered to determine accurately the decay constant, while the additional proportional term is much too small to consider. The additional constant term obtained from the present analysis is consistent with that from the previous Feynman-alpha analysis.
  • Rei Kimura; Yuki Nakai; Satoshi Wada; Atsushi Sakon; Tadafumi Sano
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 59 12 1487 - 1498 2022年05月 
    A novel core power distribution reconstruction method based on ex-core detectors is demonstrated at the Kindai University Reactor UTR-KINKI. Technology to monitor the interior of the core is critical for assuring nuclear safety. Typical core monitoring systems utilize in-core detectors. However, the harsh environment inside the core degrades detector maintainability and reliability. On the other hand, monitoring using ex-core detectors is difficult due to the lack of information of neutrons. A previous study, therefore, proposed a new power distribution reconstruction method using power correlation between fuel regions, PHOEBE. However, PHOEBE has not been verified experimentally. Thus, the present study demonstrates PHOEBE at UTR-KINKI. The experiment measures the neutron counts using four detectors outside the reflector, and the power distribution was found to be well reconstructed. Furthermore, the present study estimates the power distribution using only two detectors for confirming the effect of power correlation. When the control rod had a large impact on detectors, estimated power distribution was emphasized. By contrast, small control rod effect cases suggested the advantage of PHOEBE. However, a more complex experimental geometry, such as a multi-layered fuel region, is required to more clearly evaluate the effect of considering the power correlation between fuel regions.
  • Kazuki Takahashi; Kunihiro Nakajima; Tadafumi Sano; Atsushi Sakon; Sin-Ya Hohara; Kengo Hashimoto
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 59 2 240 - 246 2022年02月 
    Time-sequence count data of a neutron counter were acquired at subcritical states of UTR-KINKI reactor and then a Feynman-alpha analysis considering delayed neutrons was carried out to determine a measured ratio of delayed to prompt neutron contribution to the correlation amplitude Y. The zero-power reactor was driven by a neutron source inherent in highly enriched uranium fuels to reduce any spatial effect. The delayed-to-prompt ratio was also calculated using several sets of delayed-neutron group parameters for thermal fission of U-235 nuclide, to validate these sets by comparing with the measured ratio. The ratios calculated using Keepin's 6-group and Spriggs' 8-group sets agreed very well with the measured ratio. However, the ratios calculated using the other sets were almost the same as each other and in a very poor agreement with the measured ratio.
  • Shoichiro Okita; Yuji Fukaya; Atsushi Sakon; Tadafumi Sano; Yoshiyuki Takahashi; Hironobu Unesaki
    Proceedings of International Conference on Physics of Reactors; Making Virtual a Reality: Advancements in Reactor Physics to Leap Forward Reactor Operation and Deployment (PHYSOR 2022) 2338 - 2346 米国原子力学会 2022年 [査読有り]
  • Kunihiro Nakajima; Sin-Ya Hohara; Atsushi Sakon; Tadafumi Sano; Kengo Hashimoto
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 58 10 1145 - 1156 2021年10月 
    For an university training and research reactor of Kindai University, the Feynman-alpha analyses based on several formulae are carried out to examine the applicability of these formulae to the subcritical thermal reactor system. The original formula, in which the effect of delayed neutrons is neglected, results in a prompt-neutron decay constant sensitive to an upper limit of the gate time range of the analysis and consequently has difficulty in determining the decay constant. This difficulty originates from the neglect of delayed neutrons. An improved formula, where a term proportional to the gate time is added to the original formula, gives a desirable decay constant insensitive to the upper limit and the insensitive decay constant well agrees with that obtained from the Rossi-alpha analysis. The application of a difference filtering technique also leads to a successful result similar to the above improved formula. An alternative index Z to the traditional index Y of the original formula has been sometimes employed as an indication of the non-Poisson nature of the counting statistics. The Z is defined as dividing the Y by the mean number of neutron counts accumulated in the gate time. The formula for the Z never results in a reasonable decay constant even though the effect of delayed neutrons is considered. This study suggests that the improved formula considering delayed neutrons for the Y and the formula for the difference filtering technique should be employed to determine the prompt-neutron decay constant of thermal reactors.
  • Sin-ya Hohara; Atsushi Sakon; Tomohiro Endo; Tadafumi Sano; Kunihiro Nakajima; Kazuki Takahashi; Kengo Hashimoto
    EPJ Web of Conferences 247 09008 - 09008 2021年 
    In these years, reactor noise analysis methods have been studied to apply for the Debris’ criticality management at the Fukushima Daiichi NPP, Japan. The Feynman-α analysis with bunching method is one of the candidate techniques, however the bunching method itself has never been validated in detail. This synthesis technique is useful to reduce a time required for the experiment, however it is known that a non-physical trend unrelated to the state of a nuclear reactor is generated by the multiple use of time series data, and this phenomenon (we call “pseudo trend phenomenon”) has never been systematically studied in detail. In this study, Poisson events, whose statistical characteristics were clarified, were employed to investigate the pseudo trend phenomenon of the bunching method. The time-sequence count data for various statistical parameters were generated by the Monte Carlo time series simulator. Comparing the two results obtained by applying the conventional bunching method and the moving-bunching method for the same Poisson event time series, and it was found that the same pseudo trend component appears in both results of the bunching method and the moving bunching method. In addition, it was also found that the fluctuation width of the pseudo trend component is smaller than the statistical fluctuation range.
  • Tomohiro Endo; Sho Imai; Kenichi Watanabe; Akio Yamamoto; Atsushi Sakon; Kengo Hashimoto; Masao Yamanaka; Cheol Ho Pyeon
    EPJ Web of Conferences 247 09004 - 09004 2021年 
    From zero-power reactor noise measurement, the second- and third-order neutron correlation factors Y and y3 can be evaluated by analyzing mean, variance, the third-order central moment of neutron count data. Theoretically, it is expected that the neutron-correlation ratio y3/Y2 converges to the unique combination number “3” at a near-critical state in an arbitrary system without depending on the fissile material and the neutron-energy spectrum of core, as the neutron counting gate width T increases sufficiently. Thus, the information about the difference between y3/Y2 and “3” has the potential to judge whether a target unknown system is critical or not and to roughly guess the absolute value of subcriticality. In this study, the detector dead-time effect on y3/Y2 is theoretically investigated based on the heuristic method using the single-, pair-, and trio-detection probabilities with the fundamental mode approximation. As a result, it is clarified that the saturation value of y3/Y2 converges to “3” independent of the dead time, when a target system is a critical state. For validation, actual experimental results are presented for a non-multiplication system driven by 252Cf spontaneous source, and shallow and deep subcritical systems at Japanese experimental facilities (UTR-KINKI and KUCA) under the shutdown state. Consequently, it is demonstrated that y3/Y2 shows a significant difference from “3” in the non-multiplication system. In the case of subcritical systems driven by inherent neutron sources, it is confirmed that the ratios y3/Y2 are close to the unique combination number “3,” and the slight difference from “3” is measurable by the long-time reactor noise measurement for the deep subcritical system.
  • Kunihiro Nakajima; Tadafumi Sano; Kazuki Takahashi; Atsushi Sakon; Masao Yamanaka; Sin Ya Hohara; Cheol Ho Pyeon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 57 10 1152 - 1166 2020年10月 
    © 2020 Atomic Energy Society of Japan. All rights reserved. For a highly enriched uranium subcritical core driven by an inherent or an external Am-Be source in Kyoto University Critical Assembly (KUCA), a series of the source multiplication measurements, the Feynman-α and the Rossi-α neutron correlation analyses was carried out to demonstrate quantitatively that the use of the former inherent source had some advantages over that of the latter external source. Under a reactor drive by the external source, the subcriticality obtained by the neutron source multiplication method (NSM) significantly depended on neutron counter position and was consequently in very poor agreement with that calculated by the continuous-energy Monte Carlo code MVP (version 3) with the nuclear data library JENDL-4.0. In contrast to the above drive, the other drive by the inherent source spectacularly reduced the counter-position dependence and lead to a good agreement with the calculation by the MVP. The prompt-neutron decay constant determined from the Feynman-α analysis under the external source was also significantly dependent on the counter position. The Rossi-α analysis had a relatively slight counter-position dependence of the decay constant to the Feynman-α analysis but had a very low S/N ratio, which indicated an inferior applicability of the Rossi-α analysis to the reactor drive and enlarged a statistical uncertainty of the decay constant. On the other hand, the reactor drive by the inherent source considerably reduced the counter-position dependence of the Feynman-α analysis and spectacularly enhanced the S/N ratio of the Rossi-α analysis. An effective strength of the inherent source could be also determined from the S/N ratio. When the prompt-neutron decay constant obtained under this reactor drive was transformed into each subcriticality by the Simmons and King method, where a subcritical dependence of the generation time and the effective delayed-neutron fraction was neglected, the subcriticality transformed seemed to agree well with that calculated by the MVP. When the decay constant was transformed by the inhour method, where the subcritical dependence of these kinetic parameters was considered, a systematic disagreement between the transformed and the calculated subcriticality appeared.
  • Tomohiro Endo; Asahi Nonaka; Sho Imai; Akio Yamamoto; Atsushi Sakon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 57 5 607 - 616 2020年05月 
    © 2019, © 2019 Atomic Energy Society of Japan. All rights reserved. To estimate the subcriticality in dollar units for an arbitrary state-change, the time-domain decomposition-based integral method (TDDI) is proposed using the point kinetics theory based on the fundamental mode approximation. In a general transient subcritical system, reactivity, neutron source intensity, and point kinetics parameters can vary simultaneously. Furthermore, the state-change may not necessarily be a stepwise change. For such a transient, the TDDI method can estimate the subcriticality after the transient using only the time variation of the neutron count rate. Therefore, the proposed method is useful to approximately estimate the subcriticality in a system where a detailed core configuration is unknown. To investigate the applicability of the TDDI method, transient experiments with simultaneous reactivity and source changes or to two successive safety rods dropping were performed at the Kindai University Training and Research Reactor (UTR-KINKI). By comparing with reference values using excess reactivity and control rod worth, it was validated that the subcriticality values obtained by the TDDI method better agree with the reference values than the previous integral method.
  • Atsushi Sakon; Tadafumi Sano; Kazuki Takahashi; Kunihiro Nakajima; Sin Ya Hohara; Cheol Ho Pyeon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 57 3 335 - 343 2020年03月 
    © 2019, © 2019 Atomic Energy Society of Japan. All rights reserved. Solid-moderated cores of the Kyoto University Critical Assembly (KUCA) have an emergency shutdown system to avoid any reactivity-initiated accidents. When a reactor protection system of KUCA detects some abnormal conditions, the emergency system withdraws downward several fuel and reflector assemblies assigned as a central fuel loading from the core in 10 and several seconds. The withdrawal of the fuel loading inserts a very large negative reactivity into the core. The negative reactivity has been measured by the integral count technique; however, the application of the integral count technique to this measurement must have been impossible in principle. The integral count technique assumes an instantaneous insertion of a large negative reactivity but the assumption must fail for this measurement. An accurate measurement of the negative reactivity is of extreme importance from the viewpoint of reactor safety. In this study, the least-squares inverse kinetics method was employed to determine the negative reactivity from time-sequence counts data of a neutron counter. The negative reactivity determined by this method was in good agreement with that calculated by the continuous-energy Monte Carlo code MVP (version 3) with the nuclear data library JENDL-4.0.
  • Kunihiro Nakajima; Tadafumi Sano; Sin Ya Hohara; Atsushi Sakon; Kazuki Takahashi; Masao Yamanaka; Cheol Ho Pyeon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 58 1 117 - 135 2020年 
    © 2020 Atomic Energy Society of Japan. All rights reserved. For a subcritical reactor system driven by a periodically pulsed spallation neutron source in Kyoto University Critical Assembly (KUCA), the Feynman-α and the Rossi-α neutron correlation analyses were carried out to determine the prompt-neutron decay constant and quantitatively to confirm a non-Poisson characteristics of the neutron source. In these correlation analyses, a non-negligible contribution of delayed neutrons and a non-Poisson character of the source were considered, and each pulse was assumed to be a delta function. When a neutron counter was placed closely to the reactor core, the prompt-neutron decay constant determined from the present Feynman-α analysis well agreed with that done from a previous analysis for the same subcritical system driven by an inherent neutron source. However, the decay constant determined from the present Rossi-α analysis was in poor agreement with that done from the above previous analysis. This disagreement originated from an inevitable excitation of a higher mode. In the Rossi-α counting probability distribution, the excitation deformed a sharp cusp arising from the delta function to a smooth convex shape. When the data around the convex top were masked for least-squares fitting of the present Rossi-α formula, the disagreement could be successfully resolved. Compared with the previous Feynman-α and Rossi-α analyses under the Poisson inherent source, the non-Poisson spallation source definitely enhanced the respective prompt-neutron correlation amplitudes. The enhancement rate increased with an increase in subcriticality. Moreover, the Degweker’s factor (m 2-m 12)/m 12 of 0.067 ± 0.011, which indicated a non-Poisson character of the present spallation source, could be determined from the present correlation analysis and the non-zero value of the factor convinced us that the present source had a different statistical distribution from the Poisson.
  • Kunihiro Nakajima; Atsushi Sakon; Tadafumi Sano; Sin Ya Hohara; Kazuki Takahashi; Masao Yamanaka; Cheol Ho Pyeon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 58 3 374 - 382 2020年 
    © 2020 Atomic Energy Society of Japan. All rights reserved. For a subcritical reactor system driven by a periodically pulsed spallation neutron source in Kyoto University Critical Assembly, a series of power spectral analysis on frequency domain is carried out to determine the prompt-neutron decay constant and quantitatively to confirm a non-Poisson characteristics of the neutron source. Not only the cross-power but also the auto-power spectral density has a considerable correlated noise component even at a deeply subcritical state, where no correlated component could be observed under a pulsed DT(14MeV) neutron source. The non-Poisson character of the spallation source must enhance the correlation amplitude of these power spectral densities. Moreover, the Degweker’s factor (m 2-m 12)/m 12 of 0.082 ± 0.021, which is a quantitative indication of the non-Poisson character, is determined from the present analysis and is consistent with that obtained by a previous Rossi-α analysis for the same subcritical system driven by the spallation source. The non-zero value of the factor convinces us again that the present source has a different statistical distribution from the Poisson. The prompt-neutron decay constant obtained from the present analysis well agreed with that done from the above previous Rossi-α analysis.
  • Atsushi Sakon; Tadafumi Sano; Sin Ya Hohara; Cheol Ho Pyeon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 56 11 935 - 944 2019年11月 
    © 2019, © 2019 Atomic Energy Society of Japan. All rights reserved. In a variety of highly enriched uranium cores of Kyoto University Critical Assembly, many different subcriticality measurements have been strenuously performed. However, any influence of neutron source inherent in the highly enriched uranium fuels on these measurements has hardly been studied. This is because the influence has been expected to be negligible in the fuels. In this study, we revaluated the influence on pulsed neutron, accelerator-beam trip and rod drop measurements to reveal an unexpected impact of the weak inherent source. Especially, the inherent source was injurious to most of the beam trip and the rod drop measurements based on the integral count method. The least-squares inverse kinetics analysis also had a significant influence on the inherent source. In the area ratio analysis for a pulsed neutron measurement, a considerable number of neutrons from the inherent source was mixed into delayed-neutron area. When the influence was considered in these data analyses, the subcritical reactivity of the above measurements was in good agreement with that calculated by the continuous-energy Monte Carlo code MVP.
  • Cheol Ho Pyeon; Masao Yamanaka; Akito Oizumi; Masahiro Fukushima; Go Chiba; Kenichi Watanabe; Tomohiro Endo; Wilfred G. Van Rooijen; Kengo Hashimoto; Atsushi Sakon; Naoto Aizawa; Yasutoshi Kuriyama; Tomonori Uesugi; Yoshihiro Ishi
    Journal of Nuclear Science and Technology 56 8 684 - 689 2019年08月 
    © 2019, © 2019 Atomic Energy Society of Japan. All rights reserved. This study demonstrates, for the first time, the principle of nuclear transmutation of minor actinide (MA) by the accelerator-driven system (ADS) through the injection of high-energy neutrons into the subcritical core at the Kyoto University Critical Assembly. The main objective of the experiments is to confirm fission reactions of neptunium-237 (237Np) and americium-241 (241Am), and capture reactions of 237Np. Subcritical irradiation of 237Np and 241Am foils is conducted in a hard spectrum core with the use of the back-to-back fission chamber that obtains simultaneously two signals from specially installed test (237Np or 241Am) and reference (uranium-235) foils. The first nuclear transmutation of 237Np and 241Am by ADS soundly implemented by combining the subcritical core and the 100 MeV proton accelerator, and the use of a lead-bismuth target, is conclusively demonstrated through the experimental results of fission and capture reaction events.
  • Atsushi Sakon; Kunihiro Nakajima; Sin ya Hohara; Kengo Hashimoto
    Journal of Nuclear Science and Technology 56 2 254 - 259 2019年02月 
    © 2018, © 2018 Atomic Energy Society of Japan. All rights reserved. Even a zero-power reactor core containing highly enriched uranium has a weak neutron source inherent in uranium 235, and consequently, a neutron counter placed closely to the core without external neutron source registers a certain counting rate. The study of the counting is very important for zero-power reactor physics experiments with a high precision. In this experimental study, first, at a shutdown state of the UTR-Kinki reactor without start-up neutron source, a pulse height distribution of output signals from a neutron proportional counter was measured to confirm that these signals resulted from neutron detections. At several subcritical states of the UTR, then, the Feynman-α analysis was carried out to confirm that the neutrons detected by the counter must be fission neutrons multiplied by fission chain reactions. The correlation amplitude measured in the Feynman-α analysis was much higher than that measured in a previous drive by start-up source. Further, it was also confirmed that the subcriticality dependence of neutron counting rate followed the source multiplication formula. This feature indicated that the one-point model was very successful in the subcritical range including the shutdown state.
  • Sin ya Hohara; Kunihiro Nakajima; Atsushi Sakon; Kengo Hashimoto
    Journal of Nuclear Science and Technology 55 11 1309 - 1316 2018年11月 
    © 2018, © 2018 Atomic Energy Society of Japan. All rights reserved. Feynman-α method is used as the representative method in reactor noise analysis for the criticality monitoring. Feynman-α analysis needs a large amount of measurement time in its original process, though many researchers use the bunching method and its derived methods for the experimental data processing to shorten the measurement time. However, the detailed characteristics and the application limit of the bunching method have not been researched and discussed enough. This paper shows a possibility that the Bunching method is a method to reduce the probability fluctuation with the Y value only in the appearance. Moreover, the criteria for determining that the Y value is not an accidental product are also provided in this paper.
  • Ryohei Okuda; Atsushi Sakon; Sin Ya Hohara; Wataru Sugiyama; Hiroshi Taninaka; Kengo Hashimoto
    Journal of Nuclear Science and Technology 53 10 1647 - 1652 2016年10月 [査読有り]
     
    © 2016 Atomic Energy Society of Japan. All rights reserved. The bunching technique has been widely utilized in Feynman-α neutron correlation analysis to synthesize neutron counts within longer gate widths by bunching time-sequence neutron counts stored in multichannel scaler channels. An alternative technique referred to as “moving–bunching technique” was proposed to reduce a statistical scatter of variance-to-mean ratio of neutron counts. The conventional bunching technique has no overlap of adjacent bunches, while the present technique makes adjacent bunches overlap as long as possible similarly to the moving average technique. A Feynman-α experiment was performed in the UTR-KINKI, to confirm the advantage of the proposed bunching technique. When a neutron detector was placed far from the core, a Feynman-α analysis with the conventional bunching technique led to a scattered variance-to-mean ratio from which the prompt-neutron decay constant was never determinable. However, another analysis with the proposed technique remarkably reduced the above scatter and enabled the determination of the decay constant. For a neutron detector close to the core, the proposed technique also reduced statistical error of the decay constant.
  • Atsushi Sakon; Kengo Hashimoto; Wataru Sugiyama; Sin Ya Hohara; Cheol Ho Pyeon; Tadafumi Sano; Takahiro Yagi; Takaaki Ohsawa
    Journal of Nuclear Science and Technology 52 2 204 - 213 2015年02月 
    © 2014 Atomic Energy Society of Japan. All rights reserved. A unique power spectral analysis for a subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at the Kyoto University Critical Assembly (KUCA). In this analysis, a complex cross-power spectral density between time-sequence signal data from an accelerator beam ammeter and a neutron detector was measured to determine the prompt-neutron decay constant of an accelerator-driven system (ADS) from the phase data of the spectral density. Assuming the one-point kinetics model, in theory, the decay constant can be arithmetically derived from the phase at the integral multiples of the pulse repetition frequency. However, the actual derivation from the phase at a pulse repetition frequency of 20 Hz considerably underestimated the prompt-neutron decay constant, compared with that obtained by a previous pulsed neutron experiment, and the derived decay constant apparently decreased with an increase in the multiple of the pulsed repetition frequency. Considering a lag time in detector response, the above underestimation and the above apparent decrease were solved to obtain the consistent decay constant. While both previous power spectral analysis and Feynman-α analysis for pulsed neutron source require non-linear least-squares fits of the respective complicated formulae, the present analysis makes the fitting unnecessary except at regular calibration of the lag time. This feature is advantageous for a robust online monitoring of subcritical reactivity of an actual ADS.
  • Y. Miyoshi; K. Izawa; H. Sono; T. Kida; M. Murazaki; A. Sakon; K. Tonoike
    ICNC 2015 - International Conference on Nuclear Criticality Safety 1308 - 1319 2015年 
    A modification program of the Static Experiment Critical Facility, STACY is now undergoing in Japan Atomic Energy Agency, JAEA, in order to accumulate fundamental critical data relating the critical control technology for fuel debris treatment in the Fukushima Daiichi Nuclear Power Station, 1FNPS. In accordance with the new regulatory requirement for research reactors established by Nuclear Regulatio n Authority of Japan, NRA in December 2013, fundamental design policies and basic nuclear properties of STACY have been confirmed for the critical experiments which are oriented to research on criticality control in the 1FNPS. Reactivity control in the STACY experiments is made by adjusting the water level in a core tank. The moderating ratio of the heterogeneous system which determines neutron spectrum can be adjusted by changing lattice plates. Safety review by NRA for revised basic design started in March, 2015. This paper described main specifications of experimental cores for license procedure, the availability of re activity control system, and the range of nuclear characteristics such as reactivity control, reactivity coeffi cients and kinetic parameters, which dominate static and transient characteristics of the STACY cores.
  • Atsushi Sakon; Kazuhiko Izawa; Hiroki Sono; Kotaro Tonoike; Yoshinori Miyoshi
    ICNC 2015 - International Conference on Nuclear Criticality Safety 1320 - 1330 2015年 
    Decommissioning is underway in the Fukushima Daiichi Nuclear Power Station (1FNPS). Criticality control is one of the important safety issues in the decommissioning, especially during fuel debris removal. In 1FNPS, part of fuel debris might be in the form of molten-core-concrete-interaction (MCCI) product. It has been shown that the MCCI product can be critical not only under water but even with water bound in concrete. Further study of criticality characteristics by computation is being conducted to clarify its criticality risk. Furthermore, the risk assessment by computation needs validation by experiment. Japan Atomic Energy Agency is preparing critical experiments with simulated fuel debris in the Static Experiment Critical Facility (STACY), whose solution core will be converted into a new core using fuel rods and light-water moderator. It is difficult to build core configurations composed of water and fuel rods which contain homogeneous mixtures of uranium dioxide (UO2) and structural materials of boiling light water reactors. In the modified STACY, it is being planned to simulate fuel debris by arranging UO2 fuel rods and structural material rods in water. In this study, difference in heterogeneity between the experimental core and possible fuel debris conditions is evaluated by comparing infinite multiplication factors and neutron energy spectra.
  • Power Spectral Analysis for a Subcritical Reactor System Driven by a Pulsed Spallation Neutron Source
    A.Sakon; S.Hohara; W.Sugiyama; K.Hashimoto; C.H.Pyeon; T.Sano; T.Yagi
    PHYSOR 2014: The Role of Reactor Physics Toward a Sustainable Future, Kyoto, Japan 2014年09月 [査読有り]
  • Atsushi Sakon; Kengo Hashimoto; Muhamad Aiman Bin Maarof; Masahiro Kawasaki; Wataru Sugiyama; Cheol Ho Pyeon; Tadafumi Sano; Takahiro Yagi; Takaaki Ohsawa
    Journal of Nuclear Science and Technology 51 1 116 - 126 2014年01月 
    Large negative reactivity of a subcritical system driven by a pulsed 14 MeV neutron source has been measured in the Kyoto University Critical Assembly. The subcriticality of the accelerator-driven system (ADS) ranged in effective multiplication factor roughly from 0.98 to 0.92, which corresponded to an operational range of an actual ADS proposed by Japan Atomic Energy Agency. As the measurement technique, pulsed neutron method, power spectral analysis for pulsed neutron source, accelerator-beam trip method were employed. From neutron count decay data obtained by the pulsed neutron experiment, not only the prompt-neutron decay constant of fundamental mode but also a higher spatial mode could be derived. The subcriticality was also determined from the fundamental decay constant. The measured cross-power spectral density consisted of a familiar correlated reactor-noise component and many uncorrelated delta-function-like peaks at the integral multiple of pulse repetition frequency. The fundamental prompt-neutron decay constant, i.e., the subcriticality determined from the latter uncorrelated peaks was consistent with that obtained by the above pulsed neutron experiment. However, the magnitude of the former correlated component was reduced with an increase in the subcriticality and eventually this component became almost white at deeply subcritical state ranging in the multiplication factor under 0.95. Consequently, the determination of the decay constant from the correlated component was impossible under such a subcritical state. As data analysis method for the beam trip experiment, both the conventional integral count method and the least-squares inverse kinetics method (LSIKM) were employed. The LSIKM analysis led to the consistent subcriticality with that obtained by the pulsed neutron experiment, while the integral count method significantly underestimated the subcriticality. This underestimation originated from a residual background count, which was maintained after the beam trip. The LSIKM was mostly not influenced by such a slight count rate. © 2013 Atomic Energy Society of Japan.
  • Atsushi Sakon; Kengo Hashimoto; Wataru Sugiyama; Hiroshi Taninaka; Cheol Ho Pyeon; Tadafumi Sano; Tsuyoshi Misawa; Hironobu Unesaki; Takaaki Ohsawa
    Journal of Nuclear Science and Technology 50 5 481 - 492 2013年05月 
    A series of power spectral analyses for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at Kyoto University Critical Assembly (KUCA), to determine the prompt-neutron decay constant of the accelerator-driven system (ADS). The cross-power spectral density between time-sequence signal data of two neutron detectors was composed of a familiar continuous reactor noise component and many delta-function-like peaks at the integral multiple of pulse repetition frequency. The prompt-neutron decay constant inferred from the reactor noise component of the cross-power spectral density was consistent with that obtained by a pulsed neutron experiment. However, the reactor noise component of the auto-power spectral density of each detector was hidden by a white chamber noise in the higher-frequency range and this feature resulted in a considerable underestimation of the decay constant. For several runs with a low pulse-repetition frequency, furthermore, we attempted to infer the decay constant from point data of the delta-function-like peaks. The analysis for a run under a slightly subcritical state resulted in the consistent decay constant; however, those for other runs under significantly subcritical states underestimated the decay constant. Considering the contribution of a spatially higher mode to the point data, the above underestimation was solved to obtain the consistent decay constant. While the Feynman-α formula for a pulsed neutron source is too complicated to be fitted directly to variance-to-mean ratio data, the present analysis on frequency domain is much simpler and the conventional formula based on the first-order reactor transfer function is available for fitting to power spectral density data. © 2013 Taylor and Francis Group, LLC.
  • 河崎 将大; ビンマーロフ ムハマドアイマン; 左近 敦士; 橋本 憲吾; 杉山 亘; 卞 哲浩; 佐野 忠史
    日本原子力学会 年会・大会予稿集 2013s 130  一般社団法人 日本原子力学会 2013年 
    京都大学臨界集合体固体減速炉心の中心架台の反応度価値を、中心架台落下実験、加速器ビームトリップ実験、炉雑音解析、パルス中性子法実験により測定した。数値計算結果は、これら測定結果をよく再現した。
  • 前田 拓哉; 梅田 和輝; 左近 敦士; 杉山 亘; 芳原 新也; 橋本 憲吾
    日本原子力学会 年会・大会予稿集 2013s 493  一般社団法人 日本原子力学会 2013年 
    原子力発電所を運営するにあたり、日々、ゴム手袋などの資材を利用する。これら資材は、使用後、たとえ放射性物質が付着していなくても低レベル放射性廃棄物として処分される。原子力発電所に保管される低レベル放射性廃棄物は増加傾向にある。焼却処分できない難燃性廃棄物を減容するために様々な手法が検討されている。しかしながら、決定的な手法は導入されていない。そこで、本研究では、難燃性廃棄物を飛躍的に減容するとともにこのような廃棄物から液体燃料を得る方法を検討した。
  • 左近 敦士; ムハマド アイマン ビン マーロフ; 橋本 憲吾; 杉山 亘; 卞 哲浩; 佐野 忠史
    日本原子力学会 年会・大会予稿集 2013s 131  一般社団法人 日本原子力学会 2013年 
    14MeVパルス中性子源により駆動された京都大学臨界集合体の未臨界炉体系において、未臨界度を2%から8%の間で設定し、2系統の中性子検出器信号間および、加速器ビーム電流系と中性子検出器信号間のクロスパワースペクトル密度を測定した。このクロスパワースペクトル密度のゲインと位相差から算出した即発減衰定数は、パルス中性子源による結果を再現した。
  • Atsushi Sakon; Kengo Hashimoto; Cheol Ho Pyeon
    Transactions of the American Nuclear Society 107 1032 - 1034 2012年
  • 左近 敦士; 冨塚 慎吾; 橋本 憲吾; 卞 哲浩; 佐野 忠史; 三澤 毅; 杉山 亘
    日本原子力学会 年会・大会予稿集 2011s 164 - 164 一般社団法人 日本原子力学会 2011年 
    パルスモード運転下の加速器により駆動された京都大学臨界集合体の未臨界炉体系において、検出器出力のパワースペクトル密度を測定した。このパワースペクトル密度から算出した即発減衰定数は、固定中性子源下での結果と一致した。
  • 冨塚 慎吾; 左近 敦士; 橋本 憲吾; 杉山 亘
    日本原子力学会 年会・大会予稿集 2011s 152 - 152 一般社団法人 日本原子力学会 2011年 
    高次モード計算の源反復に対してWielandtの加速法を適用した。高速原型炉クラスの体系の空間高次モード計算に適用した結果、基本モードのみならず高次モードの源反復の収束の著しい加速が確認された。

講演・口頭発表等

  • Reactor Physics Experiment in a Graphite-Moderation System for HTGR  [通常講演]
    Yuji Fukaya; Sigeaki Nakagawa; Kunihiro Nakajima; Kazuki Takahashi; Atsushi Sakon; Tadafumi Sano; Kengo Hashimoto
    PHYSOR 2020: Transition to a Scalable Nuclear Future, Cambrige, United Kingdom 2020年 口頭発表(一般)
  • Experiment of Unique Combination Number due to the Third-Order Neutron-Correlation  [通常講演]
    Tomohiro Endo; Sho Imai; Kenichi Watanabe; Akio Yamamoto; Atsushi Sakon; Kengo Hashimoto; Masao Yamanaka; Cheol Ho Pyeon
    PHYSOR 2020: Transition to a Scalable Nuclear Future, Cambrige, United Kingdom 2020年 口頭発表(一般)
  • Basic Study on a Pseudo Trend Phenomenon of the Feynman-a Analysis with Bunching Method  [通常講演]
    Sin-Ya Hohara; Atsushi Sakon; Tomohiro Endo; Tadafumi Sano; Kunihiro Nakajima; Kazuki Takahashi; Kengo Hashimoto
    PHYSOR 2020: Transition to a Scalable Nuclear Future, Cambrige, United Kingdom 2020年 口頭発表(一般)
  • Reactor noise analysis for a graphite-moderated and -reflected core in KUCA  [通常講演]
    Atsushi Sakon; Kunihiro Nakajima; Kazuki Takahashi; Sin-Ya Hohara; Tadafumi Sano; Yuji Fukaya; Kengo Hashimoto
    PHYSOR 2020: Transition to a Scalable Nuclear Future, Cambrige, United Kingdom 2020年 口頭発表(一般)
  • Experimental Study on Neutron Correlation Analysis for a Subcritical System Driven by a Pulsed Spallation Neutron Source in KUCA  [通常講演]
    Kunihiro Nakajima; Kazuki Takahashi; Atsushi Sakon; Sin-Ya Hohara; Tadafumi Sano; Masao Yamanaka; Cheol Ho Pyeon; Kengo Hashimoto
    PHYSOR 2020: Transition to a Scalable Nuclear Future, Cambrige, United Kingdom 2020年 口頭発表(一般)
  • A Verification of Delayed Neutron Dataset with Comparing Theoretical and Experimental Delayed-to-Prompt Ratio Index Defined in Feynman- Analysis  [通常講演]
    Kazuki Takahashi; Kunihiro Nakajima; Atsushi Sakon; Tadafumi Sano; Sin-Ya Hohara; Kengo Hashimoto
    PPHA19: Reactor Physics Asia 2019 2019年12月 口頭発表(一般)
  • A Correlation Characteristics of Spurious Counts of Fission Counter Installed in Kyoto University Reactor for Reactor Operation  [通常講演]
    Sin-Ya Hohara; Atsushi Sakon; Tadafumi Sano; Kunihiro Nakajima; Kazuki Takahshi; Kengo Hashimoto
    PPHA19: Reactor Physics Asia 2019 2019年12月 口頭発表(一般)
  • Neutron Correlation Analysis for a Subcritical Reactor System Driven by a Pulsed Spallation Neutron Source in KUCA  [通常講演]
    Kunihiro Nakajima; Atsushi Sakon; Sin-Ya Hohara; Kazuki Takahashi; Masao Yamanaka; Tadafumi Sano; Cheol Ho Pyeon; Kengo Hashimoto
    PPHA19: Reactor Physics Asia 2019 2019年12月 口頭発表(一般)
  • Research of Measurement Condition for a Reactor Noise Measurement in the Power Operation of Kyoto University Reactor, KUR,  [通常講演]
    S.Hohara; K.Nakajima; A.Sakon; K.Hashimoto; T.Sano
    PHYTRA4 – The Fourth International Conference on Physics and Technology of Reactors and Applications, Marrakech, Morocco 2018年09月 口頭発表(一般)
  • Feynman- Analysis for a Subcritical Reactor System Driven by an Unstable Spallation Neutron Source in the Kyoto University Critical Assembly  [通常講演]
    K.Nakajima; A.Sakon; S.Hohara; K.Hashimoto; M.Yamanaka; T.Sano; C.H. Pyeon
    PHYTRA4 – The Fourth International Conference on Physics and Technology of Reactors and Applications, Marrakech, Morocco 2018年09月 口頭発表(一般)
  • Power Spectral Analysis for a Thermal Accelerator-Driven System of the Kyoto University Critical Assembly  [通常講演]
    A.Sakon; K.Hashimoto; C.H.Pyeon
    OECD Second International Workshop Technology and Components of Accelerator-driven systems 2013年05月 口頭発表(一般)
  • 左近 敦士; ムハマド アイマン ビン マーロフ; 橋本 憲吾; 杉山 亘; 卞 哲浩; 佐野 忠史
    日本原子力学会 年会・大会予稿集 2013年 一般社団法人 日本原子力学会
     
    14MeVパルス中性子源により駆動された京都大学臨界集合体の未臨界炉体系において、未臨界度を2%から8%の間で設定し、2系統の中性子検出器信号間および、加速器ビーム電流系と中性子検出器信号間のクロスパワースペクトル密度を測定した。このクロスパワースペクトル密度のゲインと位相差から算出した即発減衰定数は、パルス中性子源による結果を再現した。
  • 河崎 将大; ビンマーロフ ムハマドアイマン; 左近 敦士; 橋本 憲吾; 杉山 亘; 卞 哲浩; 佐野 忠史
    日本原子力学会 年会・大会予稿集 2013年 一般社団法人 日本原子力学会
     
    京都大学臨界集合体固体減速炉心の中心架台の反応度価値を、中心架台落下実験、加速器ビームトリップ実験、炉雑音解析、パルス中性子法実験により測定した。数値計算結果は、これら測定結果をよく再現した。
  • Cross-Power Spectral Analysis between Beam Current and Neutron Detection Signals for a Thermal Accelerator-Driven System  [通常講演]
    A.Sakon; K.Hashimoto; C.H.Pyeon
    2012 ANS Winter Meeting, SanDiego, USA 2012年11月 口頭発表(一般)
  • 左近 敦士; 橋本 憲吾; 杉山 亘; 卞 哲浩; 佐野 忠史; 三澤 毅
    日本原子力学会 年会・大会予稿集 2012年 一般社団法人 日本原子力学会
     
    14MeVパルス中性子源により駆動された京都大学臨界集合体の未臨界炉体系において、加速器ビーム電流計と中性子検出器信号間のクロスパワースペクトル密度を測定した。このパワースペクトル密度のゲインと位相差から算出した即発減衰定数は、パルス中性子実験による結果を再現した。
  • Experimental Investigation of Power Spectral Analysis for Periodic and Pulsed Neutron Source  [通常講演]
    A.Sakon; K.Hashimoto; W.Sugiyama; T.Ohsawa; C.H.Pyeon; T.Sano; H.Unesaki
    PHYTRA2 – Second International Conference on Physics and Technology of Reactorsand Applications 2011年09月 口頭発表(一般)

MISC

受賞

  • 2014年03月 一般財団法人 日本原子力学会 炉物理部会 平成25年度 日本原子力学会 炉物理部会賞
     加速器駆動システムに対するパワースペクトル解析に基づいた未臨界度測定 
    受賞者: 左近敦士
  • 2009年03月 一般財団法人 日本原子力学会 日本原子力学会 フェロー賞
     
    受賞者: 左近敦士

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