Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Tada, Kenichi; Aizawa, Naoto*; Fujita, Tatsuya*; Fukushima, Masahiro; Pyeon, C. H.*
Journal of Nuclear Science and Technology, 63(1), p.1 - 2, 2026/01
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)This document is the preface to "Special Issue on Progressive Reactor Physics for Current and Future Challenges" published in the Journal of Nuclear Science and Technology.
Np, 
Am, and 
Am reaction rates in highly enriched uranium fuel cores at Kyoto University Critical AssemblyPyeon, C. H.*; Oizumi, Akito; Katano, Ryota; Fukushima, Masahiro
Nuclear Science and Engineering, 199(3), p.429 - 444, 2025/03
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Experimental analyses of neptunium-237 (Np), americium-241 (Am), and Am fission and Np capture reaction rates are conducted by the Serpent 2 code together with ENDF/B-VIII.0 and JENDL-5, using experimental data at neutron spectra of thermal and intermediate regions obtained in the solid-moderated and solid-reflected cores with highly-enriched uranium fuel at the Kyoto University Critical Assembly. Also, uncertainty quantification of fission and capture reaction rate ratios of test samples of Np, Am and Am with reference samples of uranium-235 (
U) and gold-197 (
Au) are evaluated by the MARBLE code system. In terms of fission reaction rate ratios of Np/U, Am/U and Am/U, a comparison between experiments and Serpent 2 calculations shows an accuracy about 5, 15 and 10%, respectively, together with ENDF/B-VIII.0 and JENDL-5. For capture reaction rate ratios of Np/Au, Serpent 2 calculations reveal a fairly good accuracy at the thermal neutron spectrum. The total uncertainties of Np/U, Am/U and Am/U fission reaction rate ratios by MARBLE with the covariance data of ENDF/B-VIII.0 and JENDL-5 are found to be about 4% at most in all cores, except for about 8% of Am/U with ENDF/B-VIII.0 at the intermediate neutron spectrum.
Katano, Ryota; Fukushima, Masahiro; Pyeon, C. H.*
Nuclear Science and Engineering, 11 Pages, 2025/00
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Proposed here is a novel method involving integral experiments effective in reducing nuclear-data-induced uncertainty. The method is formulated by the Extended Bias Factor method and the L1-norm-based sparse modeling to address computational difficulty in combinational optimization. The pseudo-design parameters only sensitive to specific microscopic reactions are defined for the validation of nuclear data. The method is applied to two pseudo parameters: neptunium-237 capture and bismuth-209 inelastic scattering cross sections, while considering integral experimental data used in ADJ2017 together with sample worth measurements made at the Kyoto University Critical Assembly. The results indicate that the proposed method successfully identifies a small subset of effective integral experiments.
Katano, Ryota; Oizumi, Akito; Fukushima, Masahiro; Pyeon, C. H.*; Yamamoto, Akio*; Endo, Tomohiro*
Nuclear Science and Engineering, 198(6), p.1215 - 1234, 2024/06
Times Cited Count：1 Percentile：13.31(Nuclear Science & Technology)In this study, we have demonstrated that data assimilation using lead and bismuth sample reactivities measured in the Kyoto University Critical Assembly A-core can successfully reduce the uncertainty of the coolant void reactivity in accelerator-driven systems derived from inelastic-scattering cross-sections of lead and bismuth. We re-evaluated and highlighted the experimental uncertainties and correlations of the sample reactivities for the data assimilation formula. We used the MCNP6.2 code to evaluate the sample reactivities and their uncertainties, and performed data assimilation using the reactor analysis code system MARBLE. The high-sensitivity coefficients of the sample reactivities to lead and bismuth allowed us to reduce the cross-section-induced uncertainty of the void reactivity of the accelerator-driven system from 6.3% to 4.8%, achieving a provisional target accuracy of 5% in this study. Furthermore, we demonstrated that the uncertainties arising from other dominant factors, such as minor actinides and steel, can be effectively reduced by using integral experimental data sets for the unified cross-section dataset ADJ2017.
Pyeon, C. H.*; Katano, Ryota; Oizumi, Akito; Fukushima, Masahiro
Nuclear Science and Engineering, 197(11), p.2902 - 2919, 2023/11
Times Cited Count：3 Percentile：41.66(Nuclear Science & Technology)Sample reactivity and void reactivity experiments are carried out in the solid-moderated and solid-reflected cores at the Kyoto University Critical Assembly (KUCA) with the combined use of aluminum (Al), lead (Pb) and bismuth (Bi) samples, and Al spacers simulating the void. MCNP6.2 eigenvalue calculations together with JENDL-4.0 provide good accuracy of sample reactivity with the comparison of experimental results; also experimental void reactivity is attained by using MCNP6.2 together with JENDL-4.0 and ENDF/B-VII.1 with a marked accuracy of relative difference between experiments and calculations. Uncertainty quantification of sample reactivity and void reactivity is acquired by using the sensitivity coefficients based on MCNP6.2/ksen and covariance library data of SCALE6.2 together with ENDF/B-VII.1, arising from the impact of uncertainty induced by Al, Pb and Bi cross sections. A series of reactivity analyses with the Al spacer simulating the void demonstrates the means of analyzing the void in the solid-moderated and solid-reflected cores at KUCA
Am and U fission reaction rates at Kyoto University Critical AssemblyPyeon, C. H.*; Oizumi, Akito; Fukushima, Masahiro
Nuclear Science and Engineering, 195(11), p.1144 - 1153, 2021/11
Times Cited Count：1 Percentile：7.35(Nuclear Science & Technology)Measurements of Am and U fission reaction rates are conducted with the use of two single fission chambers in the solid-moderated and solid-reflected core at the Kyoto University Critical Assembly (KUCA). Critical irradiation experiments of Am and U foils are carried out, and the measured result of Am/U is 0.0424 
0.0019; also, calculation/experiment values between calculated (MCNP6.1 with JENDL-4.0, ENDF/B-VIII.0, and JEFF-3.3) and measured results of Am/U range among 0.93 0.04, 0.94 0.04, and 0.93 0.04, respectively. Through a comparison between the measured and calculated results, the Am fission cross-section data of the three major nuclear data libraries are successfully validated, demonstrating the same accuracy as that of previous minor actinide irradiation experiments at KUCA. Importantly, the comparison also provides the complemental data of integral experiments of Am fission reaction rates that confirm the accuracy of the Am fission cross-section data.
Np and Am fission reaction rates in lead region at A-core of KUCAOizumi, Akito; Katano, Ryota; Kojima, Ryohei; Fukushima, Masahiro; Tsujimoto, Kazufumi; Pyeon, C. H.*
KURNS Progress Report 2020, P. 104, 2021/08
In the nuclear transmutation system such as ADS, the nuclear data validation of MA is required to reduce the uncertainty caused by the nuclear data of MA. This study aims to measure the fission reaction rate ratios (FRRRs) of Neptunium-237 (Np) or Americium-243 (Am) to Uranium-235 (U) by using a single fission chambers in the KUCA. The results showed that the measured FRRRs of Np/U and Am/U were 0.0480.003 and 0.0420.004, respectively. The measured values will be used for verification of evaluated nuclear data by conducting detailed analyses.
Pyeon, C. H.*; Yamanaka, Masao*; Fukushima, Masahiro
Nuclear Science and Engineering, 195(8), p.877 - 889, 2021/08
Times Cited Count：6 Percentile：46.95(Nuclear Science & Technology)Uncertainty quantification of lead (Pb) and bismuth (Bi) sample reactivity worth is numerically determined using the SCALE6.2 code system and experimental results obtained from the solid-moderated and solid-reflected core at the Kyoto University Critical Assembly (KUCA) to demonstrate the sensitivity coefficients of aluminum (Al) and Bi scattering reactions. From the results of the numerical analyses, the impact of 
Al and 
Bi scattering cross sections obtained using SCALE6.2/TSAR is disclosed on the Bi sample reactivity worth using Al reference and Bi test samples, although the uncertainty itself is small in the Bi sample reactivity worth.
Katano, Ryota; Oizumi, Akito; Fukushima, Masahiro; Pyeon, C. H.*
KURNS Progress Report 2020, P. 102, 2021/07
For the design study of ADS, integral experimental data of LBE is necessary to validate cross sections of lead (Pb) and bismuth (Bi). In this study, we conducted Pb and Bi void reactivity measurements using aluminum (Al) void space in Kyoto University Critical Assembly (KUCA). We found that the calculations overestimate the void reactivities of Pb and Bi by about 20 pcm.
Am fission rates in low-enriched uranium region at A-core of KUCAOizumi, Akito; Fukushima, Masahiro; Tsujimoto, Kazufumi; Yamanaka, Masao*; Pyeon, C. H.*
KURNS Progress Report 2019, P. 14, 2020/08
In the nuclear transmutation system such as ADS, the nuclear data validation of MA is required to reduce the uncertainty caused by the nuclear data of MA. This study aims to measure the fission reaction rate ratios (FRRs) of Americium-243 (Am) to Uranium-235 (U) by using a single fission chambers in the KUCA. The result showed that the measured FRR of Am/U were 0.042 0.002. These measured values will be used for verification of evaluated nuclear data by conducting detailed analyses.
Fukushima, Masahiro; Oizumi, Akito; Yamanaka, Masao*; Pyeon, C. H.*
KURNS Progress Report 2019, P. 143, 2020/08
For the design study of ADS, integral experimental data of nuclear characteristics of LBE is necessary to validate cross sections of lead (Pb) and bismuth (Bi). The calculation agree with experiment for the Bi sample worth. On the other hand, the calculation overestimates for the Pb sample worth.
Pyeon, C. H.*; Talamo, A.*; Fukushima, Masahiro
Journal of Nuclear Science and Technology, 57(2), p.133 - 135, 2020/02
Times Cited Count：4 Percentile：95.53(Nuclear Science & Technology)Katano, Ryota; Yamanaka, Masao*; Pyeon, C. H.*
Journal of Nuclear Science and Technology, 57(2), p.169 - 176, 2020/02
Times Cited Count：4 Percentile：29.84(Nuclear Science & Technology)We proposed the linear combination method as a subcriticality measurement method which estimates the prompt neutron decay constant (
) correlated with the subcriticality using measurement results obtained at multiple detector positions. In the previous study, we confirmed applicability of the linear combination method through the pulsed neutron experiment with DT neutron source at Kyoto University Critical Assembly (KUCA). In this study, we conduct the pulsed neutron source experiment with spallation neutrons at KUCA and confirm the robustness of the linear combination to neutron sources.
Katano, Ryota; Yamanaka, Masao*; Pyeon, C. H.*
Nuclear Science and Engineering, 193(12), p.1394 - 1402, 2019/12
Times Cited Count：6 Percentile：42.77(Nuclear Science & Technology)The author proposed the linear combination method as a subcriticality measurement method which estimates the prompt neutron decay constant (alpha) correlated with the subcriticality using measurement results obtained at multiple detector positions. In this study, we conduct the pulsed neutron experiment at Kyoto University Critical Assembly (KUCA) and measure alpha by the linear combination method using measured neutron counts. Through experiment, we experimentally show that the linear combination method can reduce the higher-mode effect compared to the conventional method. In addition, experimentally show that the linear combination has capability of the different mode extraction.
Np and Am by accelerator-driven system at Kyoto University Critical AssemblyPyeon, C. H.*; Yamanaka, Masao*; Oizumi, Akito; Fukushima, Masahiro; Chiba, Go*; Watanabe, Kenichi*; Endo, Tomohiro*; Van Rooijen, W. G.*; Hashimoto, Kengo*; Sakon, Atsushi*; et al.
Journal of Nuclear Science and Technology, 56(8), p.684 - 689, 2019/08
Times Cited Count：12 Percentile：68.26(Nuclear Science & Technology)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 (Np) and americium-241 (Am), and capture reactions of Np. Subcritical irradiation of Np and Am 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 (Np or Am) and reference (uranium-235) foils. The first nuclear transmutation of Np and Am 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.
Oizumi, Akito; Fukushima, Masahiro; Tsujimoto, Kazufumi; Chiba, Go*; Yamanaka, Masao*; Sano, Tadafumi*; Pyeon, C. H.*
KURNS Progress Report 2018, P. 38, 2019/08
In the nuclear transmutation system such as ADS, the nuclear data validation of MA is required to reduce the uncertainty caused by the nuclear data of MA. This study aims to measure the fission reaction rate ratios (FRRs) of Neptunium-237 (Np) or Americium-241 (Am) to Uranium-235 (U) by using a back-to-back (BTB) fission chamber in the KUCA built as a sub-critical core (k
= 0.998) with the nuclear spallation neutron source. The result showed that the measured FRRs of Np/U and Am/U were 0.014 0.002 and 0.023 0.005, respectively. These measured values will be used for verification of evaluated nuclear data by conducting detailed analyses.
Fukushima, Masahiro; Oizumi, Akito; Yamanaka, Masao*; Pyeon, C. H.*
KURNS Progress Report 2018, P. 143, 2019/08
For the design study of ADS, integral experimental data of nuclear characteristics of LBE is necessary to validate cross sections of lead (Pb) and bismuth (Bi). In present study, sample worth measurements were carried out with systematically changed mixing ratios of lead and bismuth, which would be complementary to the previous data of Pb and Bi samples individually measured in FY 2013 and FY 2017, respectively.
Am neutron capture and total cross sections with ANNRI at J-PARCKimura, Atsushi; Nakamura, Shoji; Terada, Kazushi*; Nakao, Taro*; Mizuyama, Kazuhito*; Iwamoto, Nobuyuki; Iwamoto, Osamu; Harada, Hideo; Katabuchi, Tatsuya*; Igashira, Masayuki*; et al.
Journal of Nuclear Science and Technology, 56(6), p.479 - 492, 2019/06
Times Cited Count：15 Percentile：75.62(Nuclear Science & Technology)Pyeon, C. H.*; Yamanaka, Masao*; Oizumi, Akito; Fukushima, Masahiro; Tsujimoto, Kazufumi
Journal of Nuclear Science and Technology, 55(11), p.1324 - 1335, 2018/11
Times Cited Count：9 Percentile：56.46(Nuclear Science & Technology)Sample reactivity worth experiments are carried out by substituting aluminum (Al) plates for bismuth (Bi) ones at the Kyoto University Critical Assembly. At the beginning, uncertainty quantification of bismuth isotope is conducted by deterministic calculations with nuclear data library JENDL-4.0, with the use of experimental results of sample reactivity worth. Then, with the combined use of current (Bi) and previous (Pb) experimental results that demonstrate the comparative difference in the sensitivity and uncertainty of Bi and Pb isotopes, experimental results of cross-section uncertainties of Bi isotope are available for examination of neutron characteristics of Pb-Bi coolant material in the accelerator-driven system. From the experimental analyses, further uncertainty analyses by neutron transport calculations are needed for several reactions of Bi isotope, especially with the use of the covariance data of capture, elastic scattering and inelastic scattering reactions in another nuclear data library.
Am with ANNRI at J-PARCTerada, Kazushi*; Kimura, Atsushi; Nakao, Taro*; Nakamura, Shoji; Mizuyama, Kazuhito*; Iwamoto, Nobuyuki; Iwamoto, Osamu; Harada, Hideo; Katabuchi, Tatsuya*; Igashira, Masayuki*; et al.
Journal of Nuclear Science and Technology, 55(10), p.1198 - 1211, 2018/10
Times Cited Count：18 Percentile：79.93(Nuclear Science & Technology)
