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Journal Articles

Adjoint-weighted correlated sampling for -eigenvalue perturbation in Monte Carlo calculation

Tuya, D.; Nagaya, Yasunobu

Annals of Nuclear Energy, 169, p.108919_1 - 108919_9, 2022/05

https://doi.org/10.1016/j.anucene.2021.108919

Times Cited Count：2 Percentile：35.75(Nuclear Science & Technology)

Estimating an effect of a perturbation in a fissile system on its -eigenvalue requires special technique called perturbation theory when the considered perturbation is small. In this study, we develop an adjoint-weighted correlated sampling (AWCS) method based on the exact perturbation theory without any approximation by combining the correlated sampling (CS) method with iterated-fission probability (IFP) based adjoint-weighting method. With the advantages of the CS method being good at providing very small uncertainty for small perturbations and the IFP-based adjoint-weighting method being suitable for continuous-energy Monte Carlo calculation, the developed AWCS method based on the exact perturbation theory offers a new rigorous approach for perturbation calculations. The obtained results by the developed AWCS method for verification problems involving Godiva and simplified STACY density perturbations showed good agreement with the reference calculations.

Journal Articles

Criticality configuration design methodology applied to the design of fuel debris experiment in the new STACY

Gunji, Satoshi; Tonoike, Kotaro; Clavel, J.-B.*; Duhamel, I.*

Journal of Nuclear Science and Technology, 58(1), p.51 - 61, 2021/01

https://doi.org/10.1080/00223131.2020.1798825

Times Cited Count：2 Percentile：19.64(Nuclear Science & Technology)

The new critical assembly STACY will be able to contribute to the validation of criticality calculations related to the fuel debris. The experimental core designs are in progress in the frame of JAEA/IRSN collaboration. This paper presents the method applied to optimize the design of the new STACY core to measure the criticality characteristics of pseudo fuel debris that simulated Molten Core Concrete Interaction (MCCI) of the fuel debris. To ensure that a core configuration is relevant for code validation, it is important to evaluate the reactivity worth of the main isotopes of interest and their k $_{rm eff}$ sensitivity to their cross sections. In the case of the fuel debris described in this study, especially for the concrete composition, silicon is the nucleus with the highest k $_{rm eff}$ sensitivity to the cross section. For this purpose, some parameters of the core configuration, as for example the lattice pitches or the core dimensions, were adjusted using optimization algorithm to find efficiently the optimal core configurations to obtain high sensitivity of silicon capture cross section. Based on these results, realistic series of experiments for fuel debris in the new STACY could be defined to obtain an interesting feedback for the MCCI. This methodology is useful to design other experimental conditions of the new STACY.

Journal Articles

Pressure resistance thickness of disposal containers for spent fuel direct disposal

Sugita, Yutaka; Taniguchi, Naoki; Makino, Hitoshi; Kanamaru, Shinichiro*; Okumura, Taisei*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 19(3), p.121 - 135, 2020/09

https://doi.org/10.3327/taesj.J19.007

A series of structural analysis of disposal containers for direct disposal of spent fuel was carried out to provide preliminary estimates of the required pressure resistance thickness of the disposal container. Disposal containers were designed to contain either 2, 3 or 4 spent fuel assemblies in linear, triangular or square arrangements, respectively. The required pressure resistance thickness was evaluated using separation distance of the housing space for each spent fuel assembly as a key model parameter to obtain the required thickness of the body and then the lid of the disposal container. This work also provides additional analytical technical knowledge, such as the validity of the setting of the stress evaluation line and the effect of the model length on the analysis. These can then be referred to and used again in the future as a basis for conducting similar evaluations under different conditions or proceeding with more detailed evaluations.

Journal Articles

Sensitivity and uncertainty analysis of $beta_{rm eff}$ for MYRRHA using a Monte Carlo technique

Iwamoto, Hiroki; Stankovskiy, A.*; Fiorito, L.*; Van den Eynde, G.*

EPJ Nuclear Sciences & Technologies (Internet), 4, p.42_1 - 42_7, 2018/11

https://doi.org/10.1051/epjn/2018023

This paper presents a nuclear data sensitivity and uncertainty analysis of the effective delayed neutron fraction $beta_{rm eff}$ for critical and subcritical cores of the MYRRHA reactor using the continuous-energy Monte Carlo transport code MCNP. The $beta_{rm eff}$ sensitivities are calculated by the modified -ratio method proposed by Chiba. Comparing the $beta_{rm eff}$ sensitivities obtained with different scaling factors introduced by Chiba shows that a value of is the most suitable for the uncertainty quantification of $beta_{rm eff}$ . Using the calculated $beta_{rm eff}$ sensitivities and the JENDL-4.0u covariance data, the $beta_{rm eff}$ uncertainties for the critical and subcritical cores are determined to be 2.2 0.2% and 2.0 0.2%, respectively, which are dominated by delayed neutron yield of $^{239}$ Pu and $^{238}$ U.

Journal Articles

Sensitivity analysis of source term in the accident of Fukushima Dai-ichi Nuclear Power Station Unit 1 using THALES2/KICHE

Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of Asian Symposium on Risk Assessment and Management 2018 (ASRAM 2018) (USB Flash Drive), 6 Pages, 2018/10

In the accidents at Fukushima Dai-ichi Nuclear Power Station, Tsunami caused loss of electric power supply and this event led to core melt and failure of Containment vessel. Finally, fission products were released to the environment. Currently, the activities for understanding of accident progressions are carried out based on the measured data during the accident, accident progression analysis using integrated severe accident analysis codes and investigation of inside of reactor buildings and containment vessels. On the other hand, there are some research activities with combination of accident progression analysis and accident consequence analysis. In Japan Atomic Energy Agency (JAEA), the research project of combination of these analyses using the computational simulation codes has been started. The results obtained from the combination analysis are expected to have broad width of uncertainty because of many uncertainty factors in this combined analysis. In order to perform the analysis efficiently, sensitivity analysis for failure location on containment vessel and its failure size were carried out by THALES2/KICHE developed by JAEA at first. This analysis was performed on unit 1, since it was the first plant to release radioactive materials to the environment during the accident and its consequence had no effect from other plants. The authors focused on the failure of containment vessel head flange, penetration seal and vacuum breaker pipe, and possibility of partial open of vent valve based on the investigations of reactor building inside performed by TEPCO. This paper presents the results obtained from this sensitivity analysis.

Journal Articles

Factors affecting the effectiveness of sheltering in reducing internal exposure

Hirouchi, Jun; Takahara, Shogo; Komagamine, Hiroshi*; Watanabe, Masatoshi*; Munakata, Masahiro

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 11 Pages, 2017/11

no abstracts in English

Journal Articles

Reliability enhancement of seismic risk assessment of NPP as risk management fundamentals; Quantifying epistemic uncertainty in fragility assessment using expert opinions and sensitivity analysis

Choi, B.; Nishida, Akemi; Itoi, Tatsuya*; Takada, Tsuyoshi*; Furuya, Osamu*; Muta, Hitoshi*; Muramatsu, Ken

Proceedings of 13th Probabilistic Safety Assessment and Management Conference (PSAM-13) (USB Flash Drive), 8 Pages, 2016/10

In this study, we address epistemic uncertainty in structure fragility estimation of nuclear power plants (NPPs). In order to identify and quantify dominant factors in fragility assessment, sensitivity analyses of seismic analysis results are conducted for a target NPP building using a three-dimensional finite element model and a conventional lumped mass model (embedded sway rocking model), and the uncertainty caused by the major factors is then evaluated. The results are used to classify epistemic uncertainty levels in a fragility estimation workflow for NPPs in several stages, and a graded knowledge tree technique, which can be used for future fragility estimations, is proposed.

Journal Articles

An Integrated approach to source term uncertainty and sensitivity analysis for nuclear reactor severe accidents

Zheng, X.; Ito, Hiroto; Tamaki, Hitoshi; Maruyama, Yu

Journal of Nuclear Science and Technology, 53(3), p.333 - 344, 2016/03

AA2014-0796.pdf:0.84MB

https://doi.org/10.1080/00223131.2015.1044262

Times Cited Count：12 Percentile：72.01(Nuclear Science & Technology)

Journal Articles

Application of Bayesian nonparametric models to the uncertainty and sensitivity analysis of source term in a BWR severe accident

Zheng, X.; Ito, Hiroto; Kawaguchi, Kenji; Tamaki, Hitoshi; Maruyama, Yu

Reliability Engineering & System Safety, 138, p.253 - 262, 2015/06

https://doi.org/10.1016/j.ress.2015.02.004

Times Cited Count：10 Percentile：40.96(Engineering, Industrial)

JAEA Reports

Sensitivity analysis on flammable gas dispersion and explosion in HTTR hydrogen production system with fire and explosion analysis code system -P2A- (Contract research)

Inaba, Yoshitomo; Nishihara, Tetsuo

JAERI-Tech 2005-033, 206 Pages, 2005/07

JAERI-Tech-2005-033.pdf:34.71MB

In this report, we investigated the effects of jet for the dispersion and explosion analysis of leaked gas, obstacles, position of an ignition point and cell size for the gas explosion analysis, and atmospheric stability for the dispersion analysis of the leaked gas, with PHOENICS, AutoReaGas, and AUTODYN. Then, we carried out two accident analyses about combustible fluid leakage based on the investigation results of these effects. As a result, it was shown that important buildings related to safety was hardly affected by the explosion of the leaked gas.

Journal Articles

Effects of process parameters of the IS process on total thermal efficiency to produce hydrogen from water

Kasahara, Seiji; Hwang, G.*; Nakajima, Hayato; Choi, H.*; Onuki, Kaoru; Nomura, Mikihiro

Journal of Chemical Engineering of Japan, 36(7), p.887 - 899, 2003/07

https://doi.org/10.1252/jcej.36.887

Times Cited Count：69 Percentile：88.17(Engineering, Chemical)

Thermal efficiency of the IS thermochemical hydrogen production process was evaluated. Sensitivities of operation conditions (HI conversion ratio, pressure and reflux ratio at HI distillation and concentration of HI after EED) and nonidealities of the process (electric energy loss in EED, loss at heat exchangers and loss of waste heat recovery as electricity) were investigated. Concentration of HI after EED had the most significant effect of 13.3 % on thermal efficiency in operation conditions. Nonidealities had importance on thermal efficiency. Thermal efficiency was 56.8 % with optimized operation conditions and no nonidealities.

Journal Articles