Some effects of water sprinklers on array criticality safety analyses

The criticality safety of water-sprinkled arrays of enriched uranium metal on 20-in. center-to-center spacing was investigated using KENO, a multigroup Monte Carlo criticality calculation program. The effects of array size and unit apparent density on the optimum-density interspersed water moderation were analyzed. It was shown that larger arrays of enriched uranium require a lower density of interspersed hydrogenous moderator for optimum moderation than do similar smaller arrays. Also, it was shown that when the density of dry uranium metal units is decreased from full density without changing the mass or the center-to-center spacing of the units, while maintaining optimum interspersed hydrogenous moderation, the neutron multiplication of the array at first decreases, then increases beyond that of the array of full density units. The initial decrease of the neutron multiplication of the array may not be true in general for all arrays.