The effect of dancoff equivalent pitch on voided CANDU and SCWR lattice cells

The current method with which the DAN2PITCH call in CENTRM calculates the Dancoff Equivalent Pitch (DEP) seems to be overly sensitive to changes in coolant density. When evaluating the Coefficient of Void Reactivity (CVR) for the 64-element pressure tube type Super Critical Water Reactor (SCWR) [1] and 37-element CANDU reactor [2], this sensitivity can lead to large inaccuracies. The difference becomes noticeable and potentially problematic when coolant densities drop below ∼0.3 g/cm³. There is also a significant discontinuity below ∼0.01 g/cm³ which is largely attributable to the self-shielding methods specific to SCALE. The inaccuracies are determined by comparing NEWT calculations using the 238 energy group ENDF/B-VII Release 0 which utilize DAN2PITCH [3] to continuous energy KENO [4] calculations which does not.