Year
2012
Abstract
This paper discusses a computer modeling analysis of a Type A fissile package for radioactive material under hypothetical accident conditions (HACs). The base model developed for this benchmark computation explores the impact of thermal heat transfer and flow phenomena on the fuel cladding temperatures, the effect of boundary conditions on both fuel cladding and resin temperatures, and the performance of the neutron-absorbing resin under the high temperatures of the thermal test. In addition, the model is used to verify that the package design satisfies the thermal safety requirements in the regulations for the safe transport of radioactive material. COBRA-SFS predicts (1) higher fuel cladding temperatures for the case in which fire gas penetrates the cavity and (2) higher resin temperatures for the case in which no fire gas penetrates the cavity. COBRASFS provides a conservative estimate of the peak cladding temperature of the package for the 30-minute HAC fire transient. The model simulates the fire gas penetration into the package cavity and estimates the local effect of hot gas on the fuel rods nearest the open corner of the package. COBRA-SFS provides a conservative estimate of neutron-shield resin temperatures. Given the potentially high temperatures predicted to occur in the resin, the uncertainty in how much fire/combustion gas would actually penetrate the cavity in a realistic fire scenario, and the uncertainty in how uniformly it would penetrate the cavity, it is important to understand how the material properties of the resin vary with the high temperature, including how the temperatures associated with the HAC fire test affect the neutron-absorbing properties of the resin. A criticality analysis is performed that confirms the importance of the neutron absorber resin in the criticality safety design of the package.