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沖田 将一朗; 後藤 実
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 10 Pages, 2023/10
The recently released JENDL-5 and ENDF/B-VIII.0 have adopted porosity-dependent thermal neutron scattering law (TSL) data for reactor graphite, and they improve neutronic calculation accuracy of criticality for graphite-moderated cores. Currently, we can only handle neutronic calculations for three graphite porosities of 0%, 10%, and 30%. The uncertainties associated with the difference between the porosity of actual reactor graphite (
20%) and the porosity remains. Toward the future update of JENDL-5, we are planning to preparing new TSL data of reactor graphite. As a first step, it is essential to evalute phonon density state distribution of reactor graphite. In this study, in order to evalute it, molecular dynamic (MD) analysis is performed for three MD models: ideal crystalline graphite (Ideal model), 20%-porous reactor graphite with monoatomic random pore (Monoatomic random model), and 20%-porous reactor graphite with atomic cluster random pore (Cluster random model). The ideal crystalline graphite is modeled without any pores for reference. The 20%-porous reactor graphite with monoatomic random pore is modeled by randomly removing atoms from the ideal crystalline graphite. The 20%-porous reactor graphite with cluster random pore is modeled by randomly removing atomic clusters of approximately 2 nm in diameter from the ideal crystalline graphite. Their interatomic interactions are on the basis of Reactive Empirical Bond Order (REBO) potential. Velocity autocorrelation functions and phonon density of states distributions are calculated for these models. For validation, specific heat for each model is evaluated, and they are compred with experimental values.
沖田 将一朗; 長家 康展; 深谷 裕司
Journal of Nuclear Science and Technology, 58(9), p.992 - 998, 2021/09
被引用回数：2 パーセンタイル：30.55(Nuclear Science & Technology)The latest ENDF/B-VIII library adapted new porosity-dependent cross-section data of graphite. However, the porosity of the actual graphite does not necessarily correspond to the porosity given in the data. We have proposed a method to perform neutronic calculations at the desired porosity on the basis of the pseudo-material method. We have performed calculation benchmarks to confirm the applicability of this method for the porosity-dependent cross-sections of graphite. We have also compared the 
values calculated by the pseudo-material method with the experimental values for the VHTRC. In addition, we have investigated the temperature dependance of the calculation values obtained by this method. From these results, we have concluded that this method allows us to perform the neutronic calculations in which we can reflect detailed information on the porosity of graphite.
権 セロム*; 今野 力; 太田 雅之*; 佐藤 聡*
no journal, ,
JAEA/FNSで行った銅ベンチマーク実験を核データライブラリENDF/B-VIII.0及びJEFF-3.3を用いて解析したところ、10MeV以上の中性子に感度を有する
Nb(n,2n)
Nb反応の反応率をENDF/B-VIII.0を用いた計算値は実験値を大幅に過小評価、JEFF-3.3を用いた計算値は実験値を大幅に過大評価した。今回、この原因を調べ、数MeV以上の(n,np)や(n,n')反応等のデータに起因することがわかった。
