SMALL-SCALE FIRE TESTING OF POLYMER AS AN ENCAPSULANT FOR MAGNOX WASTE

At Patram 04 in Berlin, a paper was presented on fire testing of polyurethane foam – a material that is used to mitigate the effect of fire on a transport package. A fire test using a five gallon steel pail was adopted by General Plastics Manufacturing Co. to understand the linear heat front and thermal degradation of transport containers. This paper confirms that the approach has wider applications as a cost-effective approach to demonstrating fire safety. Magnox is a metallic alloy applied as fuel cladding in the first generation reactors in the UK. The high magnesium content (>95% magnesium) is a challenge to package safely. Two of the main encapsulants in the UK are Blast Furnace Slag / Ordinary Portland Cement (BFS/OPC) and Pulverised Fly Ash / Ordinary Portland Cement (PFA/OPC). As these contain water in the cement pores there is a concern that a fire accident could result in a steam reaction with the immobilised Magnox. These cement-based grouts are also not suitable for a specific number of Magnox-containing waste packages, as the material has been subjected to compaction which does not allow adequate infiltration of the grout to produce an acceptable wasteform. A polymer matrix has been proposed as an alternative encapsulant because of its improved flow and infiltration characteristics and lack of water content. Instead of conducting a full-scale fire test using a 500 litre Drum waste package an approach was developed, similar to the technique discussed at Patram 04. This involved representing part of the side-wall of the 500 litre Drum waste container using a 'bucket' containing an encapsulated simulant. 1 Our main interest was the propagation of the heat front and its impact on the contents, especially the Magnox metal. The safe performance demonstrated in the test was due to a combination of several factors: • A gap developing behind the steel wall of the bucket - due to loss of vaporised polymer; • A distinct char layer of part degraded polymer; • There was evidence of some metal loss but no sustained Magnox combustion – even though negligible sources of oxygen (air or water) were identified in the simulant.