Considering the up-scattering in resonance interference treatment in APOLLO3

TRIPOLI-4 $^R$ is a registered trademark of CEAInternational audienceThe use of the exact elastic scattering in resonance domain introduces the neutron up-scattering which must be taken into account in the deterministic transport code. The existing resonance interference treatment method in APOLLO3 is not able to take into account the resonance up-scattering phenomenon, since this method employs the asymptotic scattering kernel in the calculation of the infinite homogeneous medium reaction rates of mixture. It is known that the use of the asymptotic kernel instead of the realistic free-gas model has non-negligible impact on the calculated results. In order to consider both the resonance interference phenomenon and the resonant up-scattering, the resonance interference factor method was implemented in APOLLO3. The numerical results showed that this method gived good results in both k-eff values and reaction rates.An improved method was also proposed for the solution of the mixture heterogeneous equation by the fine-structure self-shielding method. Compared to the existing method, it requires less storage memory and less solution time, but it gives the same numerical results as those of the existing method