Criticality Safety of Transuranic Storage Arrays at the Waste Isolation Pilot Plant

Abstract

The Waste Isolation Pilot Plant (WIPP) facility is designed to store transuranic waste that will consist mainly of surface contaminate articles and sludge. The fissile material in the waste is predominantly [sup 239]Pu. The waste is grouped into two categories: contact-handled waste, which will be stored in 55-gal steel drums or in steel boxes, and remote-handled waste, which will be stored in specially designed cylindrical steel canisters. To show that criticality safety will be acceptable, criticality analyses were performed to demonstrate that a large number of containers with limiting loadings of fissile material could be stored at the site and meet a k[sub eff] limit of 0.95. Criticality analyses based on the classic worst-case moderated plutonium sphere approach would severely limit the capacity for storage of waste at the facility. Therefore, these analyses use realistic or credible worst-case assumptions to better represent the actual storage situation without compromising the margin of safety. Numerous sensitivity studies were performed to determine the importance of various parameters on the criticality of the configuration. It was determined that the plutonium loading has the dominant effect on the system reactivity. Nearly all other reactivity variations from the sensitivity studies were found to be relatively small.more » The analysis shows that criticality of the contact-handled waste storage drums and boxes and the remote-handled canisters is prevented by restrictions on maximum fissile loading per container and on the size of handling/storage areas.« less