Thermal Analysis of Regulatory Fire Conditions on a Transport Package for Radioactive Material

Abstract

MDS Nordion, a division of Canadian-based MDS Inc., maintains and operates transport packages for the distribution of radioactive materials used in the medical, sterilization and pharmaceutical industries. Each of these packages must be proven to meet international regulatory standards, often including the analysis of the packages under accident fire conditions. Actual physical fire tests are costly and time consuming. Therefore, it is beneficial to simulate such fire tests with numerical models validated against previous tests. This paper describes the thermal simulation of the IAEA TS-R-1 regulatory fire conditions (800°C fire for a period of 30 minutes and left to cool naturally in the heat of the sun) on atransport package using the ANSYS finite element code. The analyzed transport package is a steel-encased cylindrical lead-filled radiation shield welded to a support frame. A cylindrical cavity in the center of the shield, sealed by a lead-filled shielding plug, holds the radioactive material. The radiation shield is wrapped in thermal insulation, which is held in place by wire mesh. A two-dimensional, axi-symmetric model was developed to simulate the thermal behavior of the transport package during and after the regulatory fire. Mechanical deformations and stresses induced from the temperature distributions in the package are not considered in this paper. The mesh (solid model, radiation enclosure calculations, convection and radiation elements), material properties (non-linear), boundary conditions (radiation and convection) and loading (thermal transient, heat generation) used in the ANSYS simulations are discussed. Test data from physical steady state and transient fire tests was used to develop and validate the model. The finite element model was then used to predict and evaluate the response of the package to the S-R-1 fire transient.