A hypothetical nuclear criticality accident in a waste supercompactor is examined. The material being compressed in the compactor is a homogeneous mixture of beryllium and 239Pu. The point-kinetics equations with simple thermal-hydraulic feedback are used to model the transient behavior of the system. A lumped-parameter energy balance is used to determine the bulk temperature of the system. A computer code has been developed to solve the model equations. The computer code calculates the fission power history, fission yield, bulk temperature of the system, and several other thermal-hydraulic parameters of interest. Calculations have been performed for the waste supercompactor for various material misloading configurations. The peak power for the various accident scenarios varies from 1.04 × 1017 to 4.85 × 1020 fissions per second (fps). The total yield varies from 8.21 × 1017 to 7.73 × 1018 fissions, and the bulk temperature of the system varies from 412 to >912 K.