Resonance Self-Shielding Methods for Fast Reactor Calculations-Comparison of a New Tone's Method with the Subgroup Method in APOLLO3

This paper presents two resonance self-shielding methods recently implemented in APOLLO3 for fast reactor calculations: a recently developed method, based on Tone's method, and the subgroup method. Both methods utilize the so-called mathematical probability tables. Numerical results for a pin cell and for a sodium-cooled fast reactor assembly show that Tone's method produces precision similar to that of the subgroup method while reducing greatly the CPU time. The results also show that utilization of the approximated multicell model in the calculation of collision probabilities noticeably decreases the CPU time as compared to the direct-integration approach, while keeping equivalent accuracy. Finally, our tests show the improvement in the fast neutron spectrum gained by using an incident-energy-dependent fission spectrum instead of the traditional average fission spectrum. (authors)