Evaluation of Internal Criticality of the Plutonium Disposition Ceramic Waste Form

The purpose of this calculation is to perform partially and fully degraded mode criticality evaluations of plutonium disposed of in a ceramic waste form and emplaced in a Monitored Geologic Repository. The partially degraded mode is represented by the immobilized plutonium ceramic discs piled in the bottom of the waste package (WP) while neutron absorbers begin to leach out of the discs. The fully degraded mode, which is the final stage of degradation, is represented by a mixture of degradation products and non-degraded materials that have settled in the bottom of the WP producing a uniform "sludge". The criticality evaluations calculate the values of k-eff, the effective neutron multiplication factor, for partial and fully degraded internal WP configurations with various amounts of water added to and various amounts of neutron absorbing materials removed from the sludge. The fully degraded cases were done for different times in life after the breach of the WP, which was assumed to occur 10,000 years after emplacement.