Journal of Nuclear Science and Technology, 14 Pages, 2022/04
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*; Ono, Hideo*
Nature Materials, 20(10), p.1364 - 1370, 2021/10
Araki, Shohei; Yamane, Yuichi; Ueki, Taro; Tonoike, Kotaro
Nuclear Science and Engineering, 195(10), p.1107 - 1117, 2021/10
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.
Simanullang, I.; Yamane, Yuichi; Kikuchi, Takeo; Tonoike, Kotaro
Annals of Nuclear Energy, 147, p.107675_1 - 107675_6, 2020/11
Journal of Nuclear Science and Technology, 57(8), p.926 - 931, 2020/08
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.
Araki, 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.
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.
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.
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.
Yamane, Yuichi; Amano, Yuki; Tashiro, Shinsuke; Abe, Hitoshi; Uchiyama, Gunzo; Yoshida, Kazuo; Ishikawa, Jun
Journal of Nuclear Science and Technology, 53(6), p.783 - 789, 2016/06
The release behavior of radioactive materials from high active liquid waste (HALW) has been experimentally investigated under boiling accident conditions. In the experiments using HALW obtained through laboratory scale reprocessing, release ratio was measured for the FP nuclides such as Ru, Tc, Cs, Sr, Nd, Y, Mo, Rh and actinides such as Cm, Am. As a result, the release ratio was 0.20 for Ru and 1 for the FP and Ac nuclides. Ru was released into the gas phase in the form of both mist and gas. For its released amount, weak dependency was found to the initial concentration in the test solution. The release ratio decreased with the initial concentration. For other FP nuclides and actinides as non-volatile, released into the gas phase in the form of mist, the released amount increased with the initial concentration. The release ratio of Ru and NOx concentration increased with temperature of the test solutions. They were released almost at the same temperature between 200 and 300C. Size distribution of the mist and other particle was measured.
Tashiro, Shinsuke; Amano, Yuki; Yoshida, Kazuo; Yamane, Yuichi; Uchiyama, Gunzo; Abe, Hitoshi
Nihon Genshiryoku Gakkai Wabun Rombunshi, 14(4), p.227 - 234, 2015/12
The release characteristics of Ru from highly active liquid waste (HALW) have been investigated under the condition of accidental evaporation to dryness by boiling of HALW. Using a laboratory-scale apparatus, non-radioactive simulated HALW (s-HALW) was heated with an external heater to dryness to observe the release characteristics of Ru and gaseous nitrogen oxides. As a result, Ru was significantly released between 120 and 300 C of the s-HALW. The cumulative release ratio of Ru was 0.088. It was also found that the partially released amount of Ru against the temperature of the s-HALW had two peaks with one maximal at about 140 C and maximum at about 240 C. Referring to the results of the release rate of gaseous nitrogen oxides and the volume of condensate, which was a collection of the mixed vapors of steam and nitric acid released from the s-HALW, we discussed the causes of Ru release around these peaks.
Journal of Nuclear Science and Technology, 52(11), p.1425 - 1435, 2015/11
A simple equation for the first peak power in a criticality accident due to instantaneous reactivity insertion into nuclear fuel solution system has been developed to improve the accuracy in the estimation of the first peak power keeping the easiness of calculation. The equation is based on the assumption that temperature feedback reactivity is a second order function of an increase in fuel temperature. Peak power estimated using the equation was in a range between about a half and twice of experimental value. Its applicability to a wide range of initial reactivity and accuracy of estimation have been confirmed in the comparison to one-point kinetics numerical calculation. The expression suggests the first peak power increases with the square of small initial reactivity and three-halves power of large initial reactivity.
Uchiyama, Gunzo; Tashiro, Shinsuke; Amano, Yuki; Abe, Hitoshi; Yamane, Yuichi; Yoshida, Kazuo; Ishikawa, Jun
Proceedings of 21st International Conference & Exhibition; Nuclear Fuel Cycle for a Low-Carbon Future (GLOBAL 2015) (USB Flash Drive), p.1056 - 1063, 2015/09
The experimental study for source term data of radioactive materials has been conducted at a boiling accident of high active liquid waste (HALW) in reprocessing plants. In the study, three kinds of tests have been conducted including a cold small scale test, a cold engineering scale test and a hot small scale test. The following results were obtained: Ruthenium and Technetium were released into the gas phase in the form of both mist and gas under the boiling accident conditions of a simulated HALW. Non-volatile fission products (FPs) such as Nd and Cs were released into the gas phase in the form of mist. The release ratios of non-volatile FPs from a vessel of the simulated HALW were about 10. The release ratios of actinide nuclides such as Am were almost the same as those of non-volatile FPs.
Tonoike, Kotaro; Yamane, Yuichi; Umeda, Miki; Izawa, Kazuhiko; Sono, Hiroki
Proceedings of International Conference on Nuclear Criticality Safety (ICNC 2015) (DVD-ROM), p.20 - 27, 2015/09
From the viewpoint of safety regulation, 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 set up a research and development program to tackle this challenge. The Nuclear Safety Research Center of Japan Atomic Energy Agency, commissioned by the authority, has launched activities such as computations of criticality characteristics of the fuel debris, development of criticality risk assessment method, and preparation of criticality experiments to support them.
Amano, Yuki; Watanabe, Koji; Tashiro, Shinsuke; Yamane, Yuichi; Ishikawa, Jun; Yoshida, Kazuo; Uchiyama, Gunzo; Abe, Hitoshi
Nihon Genshiryoku Gakkai Wabun Rombunshi, 14(2), p.86 - 94, 2015/06
Radioactive materials could be released into air due to the accidental boiling of high active liquid waste (HALW) in reprocessing plants. Volatile radioactive nuclides, such as ruthenium, are released from the tanks into the atmosphere. Nitrogen oxides (NOx) are also released due to the thermal decomposition of metal nitrates in HALW. The released NOx transport volatile ruthenium and cause redox reactions associated with the composition or decomposition of volatile ruthenium. In this study, NOx release data were obtained by heating simulated HALW up to 600C. As a result, the release of NOx from the simulated HALW was observed from 200C to 600C, and the main release of NOx was observed at about 340C. All the lanthanide nitrates were found to decompose in the simulated HALW, and the thermal decomposition temperature of the lanthanide nitrates decreased after the addition of ruthenium dioxide to the mixed lanthanide nitrates solution.
Tashiro, Shinsuke; Uchiyama, Gunzo; Amano, Yuki; Abe, Hitoshi; Yamane, Yuichi; Yoshida, Kazuo
Nuclear Technology, 190(2), p.207 - 213, 2015/05
The release behavior of radioactive materials from high active liquid waste (HALW) has been investigated under boiling accident conditions. Results of the experiment using a nonradioactive simulated HALW found Ru to be a volatile element under the accident conditions and to be released into the gas phase in the form of both mist and gas. The Ru release rate and the apparent Ru volatilization rate constant were obtained under the boiling conditions of simulated HALW. The other fission product elements such as Cs were found to be nonvolatile and to be released into the gasphase in the form of mist. The mist size distribution near the surface of the simulated HALW in the reactor vessel was found to range from 0.05 to 20 m with a peak diameter of 2 m.
Tonoike, Kotaro; Sono, Hiroki; Umeda, Miki; Yamane, Yuichi; Kugo, Teruhiko; Suyama, Kenya
Nuclear Back-end and Transmutation Technology for Waste Disposal, p.251 - 259, 2015/00
In the Three Mile Island Unit 2 reactor accident, a large amount of fuel debris was formed whose criticality condition is unknown except the possible highest U/U enrichment. The fuel debris had to be cooled and shielded by water in which the minimum critical mass is much smaller than the total mass of fuel debris. To overcome this uncertain situation, the coolant water was borated with sufficient concentration to secure the subcritical condition. The situation is more severe in the damaged reactors of Fukushima Daiichi Nuclear Power Station, where the coolant water flow is practically "once through". Boron must be endlessly added to the water to secure the subcritical condition of the fuel debris, which is not feasible. The water is not borated relying on the circumstantial evidence that the xenon gas monitoring in the containment vessels does not show a sign of criticality. The criticality condition of fuel debris may worsen due to the gradual drop of its temperature, or the change of its geometry by aftershocks or the retrieval work, that may lead the criticality. To avoid criticality and its severe consequences, a certain principle of criticality control must be established. There may be options, such as prevention of the criticality by coolant water boration or by neutronic monitoring, prevention of the severe consequences by intervention measures against criticality, etc. Every option has merits and demerits that must be adequately evaluated toward selection of the best principle.
Yoshida, Kazuo; Tashiro, Shinsuke; Amano, Yuki; Yamane, Yuichi; Uchiyama, Gunzo; Abe, Hitoshi
Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(4), p.155 - 166, 2014/12
An accident of evaporation to dryness by boiling of high level liquid waste (HLLW) is postulated as one of the severe accidents to occur caused by the loss of cooling function at a fuel reprocessing plant. In this case, a large amount of ruthenium (Ru) will be volatilized and transfer to the vapor phase in the tank, and could be released to the environment. Therefore, the quantitative estimation of released Ru is one of the key issues in the assessment of the accident consequence. To resolve this issue, an empirical correlation for Ru transfer rate to vapor phase with the temperature, nitric acid mol fraction and activity of HLLW has been developed based on the data obtained from the accelerated experiments using simulated HLLW. A simulation study with the developed correlation demonstrated that amount of Ru transfer to vapor phase was in a good agreement with the long term experiment using actual HLLW.
Tonoike, Kotaro; Izawa, Kazuhiko; Sono, Hiroki; Umeda, Miki; Yamane, Yuichi
Transactions of the American Nuclear Society, 110(1), p.282 - 285, 2014/06
no abstracts in English