Fresh Fuel Transportation Package in a Hypothetical Accident Condition of Fire: Thermal Analysis and Evaluation of the Potential for Criticality

摘要

This paper discusses a computer modeling analysis of a Type A fissile package for radioactive materialunder hypothetical accident conditions (HACs). The base model developed for this benchmarkcomputation explores the impact of thermal heat transfer and flow phenomena on the fuel claddingtemperatures, the effect of boundary conditions on both fuel cladding and resin temperatures, and theperformance 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 theregulations for the safe transport of radioactive material.COBRA-SFS predicts (1) higher fuel cladding temperatures for the case in which fire gas penetrates thecavity and (2) higher resin temperatures for the case in which no fire gas penetrates the cavity. COBRASFSprovides a conservative estimate of the peak cladding temperature of the package for the 30-minuteHAC fire transient. The model simulates the fire gas penetration into the package cavity and estimatesthe local effect of hot gas on the fuel rods nearest the open corner of the package. COBRA-SFS providesa conservative estimate of neutron-shield resin temperatures.Given the potentially high temperatures predicted to occur in the resin, the uncertainty in how muchfire/combustion gas would actually penetrate the cavity in a realistic fire scenario, and the uncertainty inhow uniformly it would penetrate the cavity, it is important to understand how the material properties ofthe resin vary with the high temperature, including how the temperatures associated with the HAC firetest affect the neutron-absorbing properties of the resin. A criticality analysis is performed that confirmsthe importance of the neutron absorber resin in the criticality safety design of the package.