Evaluation of Tin Plating for Multi Canister Overpack Seals

The Multi-Canister Overpack (MCO) incorporates plated seals for use with (1) the port cover plates, (2) process valves of the shield plug, and (3) test plug ofthe cover cap. These seals are required to maintain leakage rates as low as 10{sup -7} scc/atm-sec. in the cover cap to test plug seal. The seals are manufactured by EG&G division of Perkin Elmer. Currently, the MCO design calls for use of silver or gold plated seals in these locations. The seal plating materials are deposited on Inconel 718 or X-750 substrates. Some of these seals are reused several times in service on the MCO. The MCO manufacturer has built several MCOs and is in the leak testing stage and has had great difficulty obtaining acceptable leakage rates at their plant in Camden, New Jersey. The seal manufacturer was called in to evaluate the situation and now the seal manufacturer recommends tin plated seals. This evaluation examines the Corrosion resistance and thermal stability of tin plating on the seals. The use of tin plating on MCO seals was evaluated for corrosion resistance and thermal stability. The corrosion resistance of tin in the expected MCO environments is acceptable. The effect of radiation hardening will offset creep deformation results. However, a low melting point indicates unsuitability at significantly elevated temperatures