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Yoshida, Naoki; Amano, Yuki; Yoshida, Ryoichiro; Ono, Takuya; Tashiro, Shinsuke; Yamane, Yuichi
Journal of Hazardous Materials, 513, p.142332_1 - 142332_20, 2026/07
Times Cited Count：0Volatile ruthenium tetroxide (RuO
) formed during evaporation-to-dryness accidents (EDA) of high-level liquid waste (HLLW) combines high chemical toxicity with radiotoxicity from isotopes such as 
Ru and 
Ru, making it a primary hazard in nuclear-fuel reprocessing. This study experimentally elucidates the mechanisms governing RuO formation while testing the validity of the pragmatic nitrosyl-ruthenium ([RuNO]) surrogate model, an experimental model that assumes Ru in HLLW exists as [RuNO], and evaluates gaseous Ru release using nitric acid solutions of [RuNO], commonly used in RuO release assessments by comparing it with the behavior of simulated HLLW (s-HLLW). We systematically investigated potential pathways, including oxidation by liquid-phase nitric acid (HNO
(l)), gas-phase nitric acid (HNO(g)), and oxygen (O2); thermal decomposition of [RuNO]; and matrix effects of coexisting nitrates. The results identify oxidation by activated HNO(l), oxidation by HNO(g) and thermal decomposition of [RuNO] as the principal routes to RuO, with HNO(g) playing a far more significant role than previously recognized. Crucially, the RuO release profile from s-HLLW differed markedly from that predicted by the [RuNO] surrogate model, demonstrating that this model fails to capture the complex matrix effects and time-dependent chemical changes of Ru species inherent to real HLLW. These findings have significant implications for improving the accuracy of hazard assessments related to RuO release during HLLW EDAs, particularly by highlighting the limitations of commonly used [RuNO] surrogate models.
Ono, Takuya; Tashiro, Shinsuke; Amano, Yuki; Yoshida, Naoki; Yoshida, Ryoichiro; Yamane, Yuichi
Journal of Nuclear Science and Technology, 63(6), p.603 - 611, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)This paper reports the first case of hot zone formation in a combustion test simulating an organic solvent fire in a reprocessing plant. Our goal is to add a boilover component to a computational model for quantitatively predicting the accident progression of the fire. Although the scale of boilover combustion increases when hot zones are formed in the solvent, it has not been clarified whether or not a hot zone is formed in the combustion of a 30 percent tributyl phosphate (TBP)/dodecane solvent mixture. To clarify this point, we conducted beaker-scale combustion tests and measured the temperature distribution in the burning solvent with thermocouples to obtain the following results. (1) No hot zone was formed by the combustion of only dodecane. (2) In the combustion of TBP/dodecane, hot zones were not formed as long as dodecane remained in the solvent. (3) A hot zone was formed when only TBP was burned.
Tashiro, Shinsuke; Uchiyama, Gunzo; Ono, Takuya; Amano, Yuki; Yoshida, Ryoichiro; Watanabe, Koji*; Abe, Hitoshi; Yamane, Yuichi
Nuclear Technology, 211(3), p.429 - 438, 2025/03
Times Cited Count：1 Percentile：20.46(Nuclear Science & Technology)Contributing to the confinement safety evaluation of glove-box (GB) connected with high efficiency particle air (HEPA) filters for radioactive materials under fire accidents, combustion tests of a flammable polymer, Polymethyl methacrylate (PMMA), and a flame retardant polymer, Polycarbonate (PC), as typical GB panel resins have been conducted with an engineering-scale combustion apparatus. The combustion properties such as the mass loss rate (MLR) and the heat release rate (HRR) of PMMA and PC were investigated in the combustion tests. In the tests with the same shapes, it was found the followings; MLRs and HRRs of PMMA were larger than those of PC under the same supply flow rate into the combustion cell (Fv); MLRs and HRRs of PMMA and PC were constant under different Fv. Moreover, in the tests of PMMA with different cross section areas (S), MLRs and HRRs were found to be proportional to S. Using these results, the relationships of MLR and HRR to S of PMMA and PC were deduced.
Yoshida, Naoki; Ono, Takuya; Amano, Yuki; Yoshida, Ryoichiro; Abe, Hitoshi; Yamane, Yuichi
Nuclear Technology, 210(10), p.1999 - 2007, 2024/10
Times Cited Count：3 Percentile：20.46(Nuclear Science & Technology)A malfunction of the cooling system of high-level liquid waste (HLLW) and failure of countermeasures may lead to the "evaporation to dryness due to the loss of cooling functions" (EDLCF) of HLLW. In the EDLCF, ruthenium (Ru) can be released at a greater fraction to initial amount than other elements in HLLW by forming gaseous Ru. It is important to identify the chemical form of the released gaseous Ru to achieve a comprehensive understanding of the events impacting the source term assessment of Ru in this accident, such as particle formation, gas absorption and deposition on migration pathways. In this study, we observed the ultraviolet/visible spectroscopy of the off-gas generated during the heating of an HLLW simulant. Employing a program that allows the separation and quantification of known components within the spectrum (ruthenium tetroxide (RuO), nitrogen dioxide, and nitric acid), we attempted to analyze the composition of gaseous Ru within the generated off-gas. Our findings reveal RuO as the main component of the gaseous Ru in off-gas after comparing the total amount of released Ru and the RuO released amount obtained via spectroscopic analysis.
Watanabe, Tomoaki; Yamane, Yuichi
Journal of Nuclear Science and Technology, 61(7), p.958 - 966, 2024/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The total fission energy released in a criticality accident involving fissile solution boiling tends to be high because the relatively high fission power continues during boiling. Simulating fission power change correctly during boiling seems essential to estimate the total fission energy. Fission power during boiling changes depending on fissile concentration and volume as the solution evaporates. In this study, we investigated the effect of concentration and volume change on estimated total fission energy for a long time of boiling. We introduced a model calculating the evaporation of fissile solution into the modified quasi-steady-state method to simulate power change during boiling. Three CRAC experiments and the Idaho Chemical Processing Plant (ICPP) criticality accident in 1959 were analyzed. As a result, the calculated energy considering concentration and volume change during boiling reproduced the measured energy well.
Fukuda, Kodai; Yamane, Yuichi
Journal of Nuclear Science and Technology, 60(12), p.1514 - 1525, 2023/12
Times Cited Count：1 Percentile：12.78(Nuclear Science & Technology)This study aims to clarify the effect of fuel particle radius on the criticality transient behavior and the total number of fissions in water-moderated solid fuel dispersion systems. Neutronics/thermal hydraulics-coupled kinetics analysis was performed in a hypothetical fuel debris system, where small fuel particles aggregate in water and become supercritical. Results showed that the number of fissions is 10 times larger when the fuel particle radius is reduced by one order of magnitude under conditions where heat transfer, i.e. from fuel to water, is emphasized. Moreover, there is a possibility that lower reactivity could give a larger number of fissions when the fuel particle size is very small. In addition, the number of fissions may be overestimated or underestimated to an unexpected extent unless appropriate fuel particle size is set on the analysis.
Suyama, Kenya; Ueki, Taro; Gunji, Satoshi; Watanabe, Tomoaki; Araki, Shohei; Fukuda, Kodai; Yamane, Yuichi; Izawa, Kazuhiko; Nagaya, Yasunobu; Kikuchi, Takeo; et al.
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 6 Pages, 2023/10
To remove and store safely the fuel debris generated by the severe accident of the Fukushima Daiichi Nuclear Power Station in 2011 is one of the most important and challenging topics for decommissioning of the damaged reactors in Fukushima. To validate the adopted method for the evaluation of criticality safety control of the fuel debris through comparison with the experimental data obtained by the criticality experiments, the Nuclear Regulation Authority (NRA) of Japan funds a research and development project which was entrusted to the Nuclear Safety Research Center (NSRC) of Japan Atomic Energy Agency (JAEA) from 2014. In this project, JAEA has been conducting such activities as i) comprehensive computation of the criticality characteristics of the fuel debris and making database (criticality map of the fuel debris), ii) development of new continuous energy Monte Carlo code, iii) evaluation of criticality accident and iv) modification of the critical assembly STACY for the experiments for validation of criticality safety control methodology. After the last ICNC2019, the project has the substantial progress in the modification of STACY which will start officially operation from May 2024 and the development of the Monte Carlo Code "Solomon" suitable for the criticality calculation for materials having spatially random distribution complies with the power spectrum. We present the whole picture of this research and development project and status of each technical topics in the session.
Fukuda, Kodai; Yamane, Yuichi
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 9 Pages, 2023/10
This study presents the results of multiphysics analysis, which investigates the change of reactivity caused by the motion of fluids, of Windscale Works criticality accident. The purpose of this study is to confirm previously reported trends of emulsion formation and increase in reactivity by the multi-physics analysis which takes the motion of fluids into account. Continuous energy Monte Carlo code MVP3 was used to calculate reactivity based on the material distribution obtained by CFD calculation using OpenFOAM. An interface program in python was developed to transfer data from OpenFOAM to MVP3. The change of reactivity caused by the motion of solutions was calculated without considering the generation of heat by fissions in a system that simulated the transfer vessel at Windscale Works. As a result, trends of emulsion formation and increase in reactivity were confirmed. The influence of the resolution of the calculation system on the results was also discussed.
Yamane, Yuichi
Journal of Nuclear Science and Technology, 59(11), p.1331 - 1344, 2022/11
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The reactivity was estimated from a time profile of neutron count rate or a simulated data in a quasi-steady state after sudden change of reactivity or external neutron source strength. The estimation was based on the equation of power in subcritical quasi-steady state. The purpose of the study is to develop the method of timely reactivity estimation from complicated time profile of neutron count rate. The developed method was applied to the data simulating neutron count rate created by using one-point kinetics code, AGNES, and Poisson-distributed random noise and to the transient subcritical experiment data measured by using TRACY. The result shows that the difference of the estimated and reference value was within about 5% or less for (
-1) for simulated data and within about 7% or less for 
-1.4 and -3.1 for the experimental data. It was also shown that the possibility of the reactivity estimation several ten seconds after the status change.
Takeuchi, Yutaro*; Yamane, Yuta*; Yoon, J.-Y.*; Ito, Ryuichi*; Jinnai, Butsurin*; Kanai, Shun*; Ieda, Junichi; Fukami, Shunsuke*; Ohno, Hideo*
Nature Materials, 20(10), p.1364 - 1370, 2021/10
Times Cited Count：181 Percentile：99.07(Chemistry, Physical)
random mediaAraki, Shohei; Yamane, Yuichi; Ueki, Taro; Tonoike, Kotaro
Nuclear Science and Engineering, 195(10), p.1107 - 1117, 2021/10
Times Cited Count：2 Percentile：15.52(Nuclear Science & Technology)Criticality control of random media such as fuel debris is one of the most important safety issues in post-accident management. 
spectrum randomizing model is expected to simulate such random media because it is well known that the noise can describe a diverse range of random and disordered natural phenomena. In this paper, we focused on the relationship between the multiplication factor and moderation condition in the random media. A number of random media were realized with the spectrum randomizing model that is based on the Randomized Weierstrass function (RWF). The volume ratio of concrete to fuel was adopted as an index for the moderation condition. The multiplication factors were calculated with a two-energy group Monte Carlo calculation. The calculation results were analyzed by using variance, skewness, and kurtosis. Those statistical parameters had an extreme value around the optimum moderation condition. This result suggested that it is possible to predict the rough trend of variation range, distortion, and outlier of multiplication factors in the random media.
spectrum model of randomizationSimanullang, I.; Yamane, Yuichi; Kikuchi, Takeo; Tonoike, Kotaro
Annals of Nuclear Energy, 147, p.107675_1 - 107675_6, 2020/11
Times Cited Count：2 Percentile：14.22(Nuclear Science & Technology)Yamane, Yuichi
Journal of Nuclear Science and Technology, 57(8), p.926 - 931, 2020/08
Times Cited Count：1 Percentile：7.07(Nuclear Science & Technology)An equation of power in subcritical quasi-steady state has been derived based on one-point kinetics equations for the purpose of utilizing it for the development of timely reactivity estimation from complicated time profile of neutron count rate. It linearly relates power, 
, to a new variable 
, which is a function of time differential of the power. It has been confirmed by using one-point kinetics code, AGNES, that the calculated points (
) are perfectly in a line described by the new equation and that points () calculated from transient subcritical experiments by using TRACY made a line with a slope indicated by the new equation.
on effective multiplication factor in 1/f
spectrum random systemAraki, Shohei; Yamane, Yuichi; Ueki, Taro; Tonoike, Kotaro
Proceedings of International Conference on the Physics of Reactors; Transition To A Scalable Nuclear Future (PHYSOR 2020) (USB Flash Drive), 8 Pages, 2020/03
We investigated the dependence of the effective multiplication factor (k
) in the 1/f noise model. We conducted the two-group Monte Carlo calculations. We found that the standard deviation of the k distribution showed the positive correlation with the value because the spatial distribution of the fuel became less uniform as the value increased.
Yamane, Yuichi
Nihon Genshiryoku Gakkai-Shi ATOMO
, 62(1), p.42 - 46, 2020/01
The combination of philosophy and technology to keep safety against the risk specific to the facility containing nuclear fuel materials is criticality safety. The first target of criticality safety is to keep subcriticality. Its essence is to make the subcriticality condition clear and to keep that condition. Criticality safety control utilizes the leak and absorption of neutrons. From the view point of the improvement of risk assessment, it is expected to study the relation between inhomogeniety and subcriticality condition.
Yamane, Yuichi
Genshiro No Butsuri, p.357 - 380, 2019/12
This chapter introduces knowledge on criticality safety as a part of introductory book on reactor physics. From the view point of reactor physics, the purpose, target and method are explained, and the issues relating prevention of criticality, the history and mechanism of criticality accident, etc. are described.
Yamane, Yuichi; Numata, Yoshiaki*; Tonoike, Kotaro
Proceedings of 11th International Conference on Nuclear Criticality Safety (ICNC 2019) (Internet), 10 Pages, 2019/09
For the criticality safety of the operation treating the fuel debris in Fukushima Daiichi Nuclear Power Plant, the reactivity effect of its geometrical change has been investigated and the developed procedure has been applied to a trial analysis of a postulated scenario for the purpose of its verification.
Tonoike, Kotaro; Watanabe, Tomoaki; Gunji, Satoshi; Yamane, Yuichi; Nagaya, Yasunobu; Umeda, Miki; Izawa, Kazuhiko; Ogawa, Kazuhiko
Proceedings of 11th International Conference on Nuclear Criticality Safety (ICNC 2019) (Internet), 9 Pages, 2019/09
Criticality control of the fuel debris in the Fukushima Daiichi Nuclear Power Station would be a risk-informed control to mitigate consequences of criticality events, instead of a deterministic control to prevent such events. The Nuclear Regulation Authority of Japan has administrated a research and development program to tackle this challenge since 2014. The Nuclear Safety Research Center of Japan Atomic Energy Agency, commissioned by the authority, is conducting activities such as computations of criticality characteristics of the fuel debris, development of a criticality analysis code, preparation of criticality experiments, and development of a criticality risk analysis method.
Yoshida, Ryoichiro; Yamane, Yuichi; Abe, Hitoshi
Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.408 - 414, 2019/09
In a criticality accident, it is known that some kinds of radiolysis gases are generated mainly due to kinetic energy of fission fragments. Hydrogen gas (H
) is one of them, which is able to initiate explosion. The rate of H generation and its total amount can be estimated from the number of fission per second if its G value is known. In this study, it was tried to estimate G value of hydrogen gas (G(H)) by using the H concentration measured as time-series data in Transient Experiment Critical Facility (TRACY) which was carried out by Japan Atomic Energy Agency. There was time lag in the measured H concentration from its generation. To overcome those problems, measured profile of H concentration was reproduced based on a hypothetical model and its total amount was evaluated. Based on the model, the obtained G(H) was 1.2.
Yoshida, Naoki; Tashiro, Shinsuke; Amano, Yuki; Yoshida, Kazuo; Yamane, Yuichi; Abe, Hitoshi
NEA/CSNI/R(2017)12/ADD1 (Internet), p.293 - 305, 2018/01
The "Evaporation to Dryness due to the Loss of Cooling Functions" (EDLCF) of highly-active liquid waste (HALW) was newly defined as one of the severe accidents in Japan's nuclear safety standard for the reprocessing plant. Studies on accident scenarios and their source terms have led to an increased need for the development of accident management measures and the assessment of their effectiveness. Previous studies have shown that ruthenium was released at a greater rate than other elements because it formed volatile species such as ruthenium tetroxide (RuO). In addition, ruthenium isotopes, Ru and Ru, have radiotoxicity. Accordingly, the accident management measures require the experimental information on the release and transport behavior of the gaseous ruthenium (Ru(g)). This paper summarizes our experimental results on the characteristics of Ru(g) in the EDLCF. This work includes the results of the experiments carried out under the agreement among JAEA, Japan Nuclear Fuel Ltd. and Japan Nuclear Energy Safety Organization.
