Development of a fine and ultra-fine group cell calculation code SLAROM-UF for fast reactor analyses

Hazama, Taira ; Chiba, Go; Sugino, Kazuteru

A cell calculation code SLAROM-UF has been developed for fast reactor analyses to produce effective cross sections with high accuracy in practical computing time, taking full advantage of fine and ultra fine group calculation schemes. The ultra fine group calculation below 52.5keV solves the slowing down equation and can treat resonance structures directly and precisely including resonance interference effects. The fine group calculation covers the other energy range in a group structure with a minimum lethargy width of 0.008. Calculation accuracy and improvements from conventional 70 group cell calculations were investigated through comparisons with reference values obtained with a continuous energy Monte Carlo calculation. It was confirmed that SLAROM-UF reduces the difference in k-infinity from 0.15% to 0.01% on a "JOYO" MK-I fuel subassembly lattice cell calculation, and also reduces the difference in criticality from -0.21% to less than a statistical uncertainty of the reference calculation of 0.03% on a ZPPR-10A core calculation.