Thermal Testing of Waste Packages for a Storage Environment

The Pipe Overpack Container (POC) was developed at Rocky Flats to transport plutoniumresidues (waste containing higher levels of plutonium than standard TRU waste) to WIPP fordisposal. The POC consists of an inner containment vessel (pipe) surrounded by organic fiberdunnage inside of a 200-liter (55 gal.) 7A drum. This inner container, called a Pipe Container(PC), was designed to maintain separation of fissile material (which allowed the total fissilematerial loading of the TRUPACT-II container to go from 325 grams to 2.8 kg) and toprovide shielding from radiation. The POC is also used for on-site storage of this type ofmaterial.In 1997 Sandia National Laboratories (SNL) conducted a series of tests and analyses on POCsto determine the degree of protection they provide during storage accident events. One ofthese tests exposed four of the POCs to a 30-minute engulfing pool fire, resulting in one of the7A drums generating sufficient internal pressure to pop off its lid and expose the top of the PCto the fire environment. The O-ring seal of this PC eventually failed due to the hightemperature, and this PC could have released some of its contents if the internal pressure wassufficiently high.The residues at Rocky Flats were inert materials, which would not generate large internalpressure within the PC if heated. However, POCs are now being used to store combustibleTRU waste at Los Alamos (and other DOE sites). Therefore, starting in 2015 SNL conducteda new series of fire tests, this time to examine whether the contents of the PC would reach atemperature that would result in generation of sufficient gas to cause over-pressurization ofthe PC, and eventual release of some of its content. This paper will describe the various testconducted thus far, present some preliminary results from these tests, and discuss theirimplications, both for POCs and 7A drums.