Thermal Analysis of the Mound One Kilowatt Package

The Mound One Kilowatt (1 KW) package was designed for the shipment of plutonium (Pu-238) with not more than 1 kW total heat dissipation. To comply with regulations, the Mound 1 kW package has to pass all the requirements under Normal Conditions of Transport (NCT; 38 degrees C ambient temperature) and Hypothetical Accident Conditions (HAC; package engulfed in fire for 30 minutes). Analytical and test results were presented in the Safety Analysis Report for Packaging (SARP) for the Mound 1 kW package, revision 1, April 1991. Some issues remained unresolved in that revision. In March 1992, Fairchild Space and Defense Corporation was commissioned by the Department of Energy to perform the thermal analyses. 3-D thermal models were created to perform the NCT and HAC analyses. Four shipping configurations in the SARP revision 3 were analyzed. They were: (1) The GPHS graphite impact shell (GIS) in the threaded product can (1000 W total heat generation); (2) The fueled clads in the welded product can (1000 W total heat generation); (3) The General Purpose Heat Source (GPHS) module (750 W total heat generation); and (4) The Multi-Hundred Watt (MHW) spheres (810 W total heat generation). Results from the four cases show that the GIS or fuel clad in the product can is the worse case. The temperatures predicted under NCT and HAC in all four cases are within the design limits. The use of helium instead of argon as cover gas provides a bigger safety margin. There is a duplicate copy