The SMORES capability for minimum critical mass determination

The purpose of the present work is to illustrate the capability of SMORES - a new sequence incorporated in SCALE-5, for automated minimum critical mass (MCM) determination. The illustration is done by identifying the MCM of spherical systems of 233U, 235U or 239Pu moderated and reflected with either D2O or a combination of polyethylene and Be. The latter provide the lowest critical mass of, respectively, 151.7 g, 202.2 g and 119.0 g. These masses are close to a factor of 2 lower than the MCM of the corresponding fissile material with D2O and close to a factor of 4 for the MCM in H2O. The fissile material concentration exhibit a spike near the core outer boundary, at the interface between the polyethylene and Be. The SMORES sequence of SCALE 5 could be useful for determining margins of subcriticality and for other applications encountered by the criticality safety community. (author)