Improvements in LFR fuel pin cell calculation by DRAGON

Deterministic lattice calculations for lead-cooled fast reactors require fine-group cross section libraries, with accurate self-shielding data for both actinides and structural materials. In this work, improvements in library preparation are presented and the libraries are shown to perform well for a LFR fuel pin cell. Two self-shielding methods implemented in DRAGON5, the subgroup method with physical probability tables and Tone’s method, are compared against OpenMC reference calculations. A fine 1962-group structure is used, reducing the discrepancy on the multiplication factor by some hundreds pcm with respect to legacy 315-group libraries. Additional self-shielding data for lead isotopes and iron are included, further improving accuracy. Particular attention is paid to the treatment of unresolved resonances, where the standard UNRESR module of NJOY exhibits a behaviour of the dilution-dependent cross sections of 239Pu different from that of the PURR module, which is used to generate a new set of libraries. With the improved libraries, DRAGON5 achieves agreement with OpenMC within 30 pcm on the multiplication factor and sub-percent discrepancies on condensed quantities across most of the energy region of interest. To the autors’ knowledge, this is the first published calculation with DRAGON5 which uses libraries specifically created for fast reactor applications.