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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.
Matsumura, Taichi; Okumura, Keisuke; Sakamoto, Masahiro; Terashima, Kenichi; Riyana, E. S.; Kondo, Kazuhiro*
Nuclear Engineering and Design, 432, p.113791_1 - 113791_9, 2025/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Emura, Yuki; Matsuba, Kenichi; Kikuchi, Shin; Yamano, Hidemasa
Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 8 Pages, 2024/11
Yoshida, Kazuo; Hiyama, Mina*; Tamaki, Hitoshi
JAEA-Research 2024-007, 24 Pages, 2024/08
JAEA-Research-2024-007.pdf:2.1MB
An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. It has been observed experimentally that volatility of RuO
is suppressed by HNO
generated by HNO
radiolysis. The analysis of chemical reactions of NO
including HNO and HNO in the waste tank is essential to simulate of these phenomena. To resolve this issue, an analytical approach has been attempted to couple dynamically two computer codes SHAWED and SCHERN. The simulation of boiling behavior in the tank is conducted with SHAWED. SCHERN simulates chemical behaviors of HNO, HNO and NO in the tank. A programmatic coupling algorithm and a trial simulation of the accident are presented in this report.
Emura, Yuki; Takai, Toshihide; Kikuchi, Shin; Kamiyama, Kenji; Yamano, Hidemasa; Yokoyama, Hiroki*; Sakamoto, Kan*
Journal of Nuclear Science and Technology, 61(7), p.911 - 920, 2024/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Zablackaite, G.; Shiotsu, Hiroyuki; Kido, Kentaro; Sugiyama, Tomoyuki
Nuclear Engineering and Technology, 56(2), p.536 - 545, 2024/02
Times Cited Count：1 Percentile：62.55(Nuclear Science & Technology) dissolution in bicarbonate solution with HO; The Effect of temperatureMcGrady, J.; Kumagai, Yuta; Kitatsuji, Yoshihiro; Kirishima, Akira*; Akiyama, Daisuke*; Watanabe, Masayuki
RSC Advances (Internet), 13(40), p.28021 - 28029, 2023/09
Times Cited Count：2 Percentile：11.92(Chemistry, Multidisciplinary)Upon nuclear waste canister failure and contact of spent nuclear fuel with groundwater, the UO matrix of spent fuel will interact with oxidants in the groundwater generated by water radiolysis. Bicarbonate (HCO
) is often found in groundwater, and the HO induced oxidative dissolution of UO in bicarbonate solution has previously been studied under various conditions. Temperatures in the repository at the time of canister failure will differ depending on the location, yet the effect of temperature on oxidative dissolution is unknown. To investigate, the decomposition rate of HO at the UO surface and dissolution of U
in bicarbonate solution (0.1, 1, 10 and 50 mM) was analysed at various temperatures (10, 25, 45 and 60 
C). At [HCO] 
1 mM, the apparent equilibrium concentration of U decreased with increasing temperature. This was attributed to the formation of U-bicarbonate species at the surface and a change in the mechanism of HO decomposition from oxidative to catalytic. At 0.1 mM, no obvious correlation between temperature and U dissolution was observed, and thermodynamic calculations indicated this was due to a change in the surface species. A pathway to explain the observed dissolution behaviour of UO in bicarbonate solution as a function of temperature was proposed.
Abe, Takeyasu; Iida, Yoshihisa; Sasamoto, Hiroshi; Ishii, Eiichi
Proceedings of Water-Rock Interaction (WRI-17)/ Applied Isotope Geochemistry (AIG-14), 6 Pages, 2023/08
Cation exchange is one of important elementary reactions among water-rock interactions in sedimentary rocks. In order to model non-constant Na-K-Ca-Mg-H exchange selectivity of sedimentary rocks, exchange isotherms and pH dependence on cation exchange capacity of smectite were analyzed following active fraction model. As the result of comparison of exchangeable cationic composition between measured and calculated, selectivity coefficients determined in this study were preferred to those presented by previous studies. Using the coefficients and groundwater hydrochemistry reported previously, expected compositions of exchangeable cations were calculated. The results suggested that pH and total Na-K-Ca-Mg-H concentration of groundwater are important factors to interpret observed compositional variation in exchangeable base cations.
Thwe Thwe, A.; Kadowaki, Satoshi; Nagaishi, Ryuji
Journal of Nuclear Science and Technology, 60(6), p.731 - 742, 2023/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)In this study, we performed numerical calculations of unsteady reaction flow considering detailed chemical reactions, investigated the unstable behavior of hydrogen-air dilute premixed flame due to intrinsic instability, and clarified the effects of unburned gas temperature and pressure. I made it. The unstable behavior of the flame in a wide space was simulated, and the burning rate of the cellular flame was obtained. Then, the effects of heat loss and flame scale on flame unstable behavior were investigated. The burning velocity of a planar flame increases as the unburned-gas temperature increases and it decreases as the unburned-gas pressure and heat loss increase. The normalized burning velocity increases when the pressure increases and heat loss becomes large, and it decreases when the temperature increases. This is because the high unburned-gas pressure and heat loss promote the unstable behavior and instability of flame.
Yoshida, Kazuo; Tamaki, Hitoshi; Hiyama, Mina*
JAEA-Research 2023-001, 26 Pages, 2023/05
JAEA-Research-2023-001.pdf:1.61MB
An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. To resolve this issue, an analytical approach has been developed using computer simulation programs to assess the radioactive source term from those facilities. The proposed approach consists analyses with three computer programs. At first, the simulation of boiling behavior in the HLLW tank is conducted with SHAWED code. Next step, the thermal-hydraulic behavior in the facility building is simulated with MELCOR code based on the results at the first step simulation such as flowed out mixed steam flow rate, temperature and volatilized Ru from the tank. The final analysis step is carried out for estimating amount of released radioactive materials with SCHERN computer code which simulates chemical behaviors of nitric acid, nitrogen oxide and Ru based on the condition also simulated MELCOR. Series of sample simulations of the accident at a hypothetical typical facility are presented with the data transfer between those codes in this report.
Patronis, N.*; Kimura, Atsushi; 130 of others*
EPJ Techniques and Instrumentation (Internet), 10, p.13_1 - 13_10, 2023/05
rays from a neutron-induced 
-wave resonance of 
XeOkudaira, Takuya*; Tani, Yuika*; Endo, Shunsuke; Doskow, J.*; Fujioka, Hiroyuki*; Hirota, Katsuya*; Kameda, Kento*; Kimura, Atsushi; Kitaguchi, Masaaki*; Luxnat, M.*; et al.
Physical Review C, 107(5), p.054602_1 - 054602_7, 2023/05
Times Cited Count：5 Percentile：71.53(Physics, Nuclear)no abstracts in English
Yamamoto, Tomohiko; Kato, Atsushi; Hayakawa, Masato; Shimoyama, Kazuhito; Ara, Kuniaki; Hatakeyama, Nozomu*; Yamauchi, Kanau*; Eda, Yuhei*; Yui, Masahiro*
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 6 Pages, 2023/04
Saito, Tatsuo; Yamazawa, Hiromi*; Mochizuki, Akihito
Journal of Environmental Radioactivity, 255, p.107035_1 - 107035_14, 2022/12
Times Cited Count：0 Percentile：0.00(Environmental Sciences)The seasonal variation of dissolved U (DU) in Lake Biwa was reproduced by the following model and parameter research. The introduced models are the water-DU mass balance, and the ion exchange between UO
and H
on the lakeshore soil. The optimized parameters were the CEC of the lakeshore, TU as the sum of DU and AU (soil adsorbed U), kads and kdes as the first order reaction rate coefficients during rapid soil adsorption and desorption of U, respectively. Tabulated by the chemical equilibria constituting DU and analyzed the contribution of each chemical species, it is shown that the seasonal variation of DU is caused by the seasonal variation of pH. A correction to the ion-exchange equilibrium to shift to first order rate reaction only when the daily AU ratio increased above kads or decreased below kdes, improved the reproducibility of DU measurements and reproduced the delay of the DU peak from the pH peak.
Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*
ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08
Times Cited Count：4 Percentile：30.07(Chemistry, Multidisciplinary)Matsuda, Shohei; Yokoyama, Keiichi; Yaita, Tsuyoshi; Kobayashi, Toru; Kaneta, Yui; Simonnet, M.; Sekiguchi, Tetsuhiro; Honda, Mitsunori; Shimojo, Kojiro; Doi, Reisuke; et al.
Science Advances (Internet), 8(20), p.eabn1991_1 - eabn1991_11, 2022/05
Times Cited Count：8 Percentile：43.80(Multidisciplinary Sciences)no abstracts in English
Nakano, Keita; Matsuda, Hiroki*; Meigo, Shinichiro; Iwamoto, Hiroki; Takeshita, Hayato*; Maekawa, Fujio
JAEA-Research 2021-014, 25 Pages, 2022/03
JAEA-Research-2021-014.pdf:2.1MB
For the development of accelerator-driven transmutation system (ADS), measurement of nuclide production cross-sections in proton-induced reactions on 
Be, C, 
Al, 
Sc, and V have been performed. The measured data are compared with the calculations by the latest nuclear reaction models and with the nuclear data library to investigate the reproducibilities.
Yoshida, Kazuo; Tamaki, Hitoshi; Hiyama, Mina*
JAEA-Research 2021-013, 20 Pages, 2022/01
JAEA-Research-2021-013.pdf:2.35MB
An accident of evaporation to dryness by boiling of high level liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into atmosphere. An idea has been proposed to implement a steam condenser as an accident countermeasure. This measure is expected to prevent nitric acid steam diffusing in facility building and to increase gaseous Ru trapping ratio into condensed water. A simulation study has been carried out with a hypothetical typical facility building to analyze the efficiency of steam condenser. In this study, SCHERN computer code simulates chemical behaviors of Ru in nitrogen oxide, nitric acid and water mixed vapor based on the conditions obtained from simulation with thermal-hydraulic computer code MELCOR. The effectiveness of steam condenser has been analyzed quantitively in preventing mixed vapor diffusion and gaseous Ru trapping effect. Some issues to be solved in analytical model has been also clarified in this study.
Kosaka, Wataru; Uchibori, Akihiro; Yanagisawa, Hideki*; Takata, Takashi; Jang, S.*
Nihon Kikai Gakkai Rombunshu (Internet), 88(905), p.21-00310_1 - 21-00310_9, 2022/01
If a pressurized water/water-vapor leaks from a heat transfer tube in a steam generator (SG) in a sodium-cooled fast reactor (SFR), sodium-water reaction forms high-velocity, high-temperature, and corrosive jet. It would damage the other tubes and might propagate the tube failure in the SG. Thus, it is important to evaluate the effect of the tube failure propagation for safety assessment of SFR. The computational code LEAP-III can evaluate water leak rate during the tube failure propagation with short calculation time, since it consists of empirical formulae and one-dimensional equations of conservation. One of the empirical models, temperature distribution evaluation model, evaluates the temperature distribution in SG as circular arc isolines determined by experiments and preliminary analyses instead of complicated real distribution. In order to improve this model to get more realistic temperature distribution, we have developed the Lagrangian particle method based on engineering approaches. In this study, we have focused on evaluating gas flow in a tube bundle system, and constructed new models for the gas-particles behavior around a tube to evaluate void fraction distribution near the tube. Through the test analysis simulating one target tube system, we confirmed the capability of the models and next topic to improve the models.
Takino, Kazuo; Sugino, Kazuteru; Oki, Shigeo
Annals of Nuclear Energy, 162, p.108454_1 - 108454_7, 2021/11
Times Cited Count：1 Percentile：10.40(Nuclear Science & Technology)