Neutron Up-Scattering Effect in Refined Energy Group Structure

摘要

Aiming at generating a 361-group library, this paper investigated neutron up-scattering effect in the 361-group Santamarina-Hfaiedh Energy Mesh (SHEM). Firstly, the Doppler Broadening Rejection Correction (DBRC) method is implemented to consider the neutron up-scattering effect in Monte Carlo (MC) method. Then the MC method is employed to prepare resonance integral table and scattering matrix for afterward calculation. Numerical results show that the neutron up-scattering affects k_(inf) by ～200 pcm at most for UO_2 pin cell problems in the 361-group SHEM, while the fuel temperature coefficient (FTC) is also influenced by 12～13%. It has also been found that both of the above two influences acts through scattering matrix rather than self-shielded absorption cross sections. In addition, the self-shielding effect of cladding is studied and it's been found that it affects k_(inf) by 30～70 pcm.