Effect of Added Scatterers on Nuclear Criticality

Abstract

Experience involving basic concept of nuclear criticality has shown that there are many complex effects involved, some of which have been little studied and are not well understood. One of these involves the effect of added scatterers on criticality.
A study has been made of the effect of added scatterers (O, C, N) on criticality by means of transport theory calculations utilizing the DTE-IV codes. This study pertains to plutonium compounds likely to be encountered throughout the nuclear industry - in fuel processing and fabrication operations. It is shown that in some cases of undermoderated thin slab with hydro-genous reflectors, the effect of added scatterers can cause an increase in the critical dimension contrary to the usual expectation that the size should be reduced in such cases.
Interpretation of the reswksrobtained for water-reflected and nickel-reflected slabs, including scatterers added homogeneously to the core region, contribute to a better understanding of the observed effects. The dominant factor causing the increase in slab thickness is the decrease of neutron leakage into the moderating reflector.