EPDM and Fluorocarbon Seal Materials: A Comparison of Performance for Nuclear Fuel Transport Flasks

The lid seals on the flasks used to transport spent fuel from U.K. AGR and Magnox Power Stations are fluorocarbon elastomer 'O' rings. Currently, only this material is qualified for the purpose and it was decided to investigate the possibility of qualifying other materials. One material that is already in use in similar applications is an Ethylene Propylene Diene Monomer (EPDM). The work presented in this paper compares the performance of the existing material with three candidate types of EPDM. The areas considered were: • Extrusion and blow-out resistance when subjected to various steam pressures and temperatures at a range of flange separations, • Permeability to water, caesium salt solution and hydrogen (as a typical ‘benchmark’ gas) • Radiation resistance in warm (60°C) aqueous conditions It is concluded that the performance of the EPDM materials is good in respect of mechanical properties, radiation and water resistance. However, while permeation rates for gas and water can be higher than for fluorocarbon, this might be mitigated by assessing the actual radioactive burden in the permeate. In the case of dissolved salts, the test results indicate that this will be very low.