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Nakayama, Shinsuke; Iwamoto, Osamu; Kimura, Atsushi
EPJ Web of Conferences, 294, p.07001_1 - 07001_6, 2024/04
Graphite is a candidate of moderator in innovative nuclear reactors such as molten salt reactors. Scattering of thermal neutrons by the moderator material has a significant impact on the reactor core design. To contribute to the development of innovative nuclear reactors, an evaluation method of thermal neutron scattering law for reactor grade graphite was studied. The inelastic scattering component due to lattice vibration was evaluated based on the phonon density of states computed with first-principles lattice dynamics simulations. The simulations were performed for ideal crystalline graphite. The coherent elastic scattering component due to crystal structure was evaluated based on neutron transmission and scattering experiments recently performed in the J-PARC/MLF facility. In comparison with the neutron transmission experiments, it was found that the quantification of small-angle neutron scattering due to structures larger than crystal, such as pores in graphite, is important. Based on the above methods, thermal neutron scattering law data for reactor-grade graphite at room temperature were evaluated.
U(n
,fission) prompt gamma energy spectrum by FIFRELINOgawa, Tatsuhiko; Litaize, O.*; Mancusi, D.*; Chebboubi, A.*; Serot, O.*
no journal, ,
Thermal fission of U-235 is fundamental for nuclear energy engineering, whose details were observed through neutrons and gamma-rays. Among them, gamma-rays above 8 MeV, which come from immediate gamma deexcitation of fission fragments, were recently measured as a probe to observe fission more directly. The energy spectrum measured by a theoretical model CoH3 (Coupled-Channels Hauser-Feshbach Code) reproduced a peak around 4 MeV and a shoulder from 6 to 8 MeV, however, underestimated the components above 14 MeV. In this study, we used FIFRELIN developed by the French Atomic Energy, Alternative Energy Commission (CEA) to reproduce the gamma-ray energy spectrum. In addition to the peak around 4 MeV and a shoulder from 6 to 8 MeV, gamma spectrum up to 20 MeV was reproduced. This calculation also discovered that the level-density model for fission fragments plays the critical role. It was thus illustrated that FIFRELIN is useful to reproduce the spectra of gamma-ray from fission and investigate the reaction processes responsible for gamma-ray spectrum.
