Evaluation of Internal Criticality of the Plutonium Disposition MOX SNF Waste Form

The purpose of this calculation is to perform a parametric study to determine the effects of fission product leaching, assembly collapse, and iron oxide loss (Me203) on the reactivity of a waste package (WP) containing mixed oxide (MOX) spent nuclear fuel (SNF). Previous calculations (CRWMS M&O 1998a) have shown that the criticality control features of the WP are adequate to prevent criticality of a flooded WP for all the enrichment/ burnup pairs expected for the MOX SNF. Therefore, the objective of this calculation is to determine the increase in reactivity that might result from possible degradation of the WP criticality control features. Specifically, this calculation tests the sensitivity of effective neutron multiplication factor (keff) to loss (from the WP) of the following: (l) fission product neutron absorbers, or (2) moderator displacement material (principally, the iron oxide that results from the corrosion of carbon steel).