Operating Experience with the 21PF Overpack

Abstract

This paper (a) outlines the development of the 21PF overpack, including moisture absorption by the fire resistant phenolic foam insulation and the change from mild steel to stainless steel cladding; (b) summarises recent operating experience with stainless steel overpacks that pitting perforation occurs from the inside of the shell in <6 years with high chloride foam (0·5–1%), whereas no pitting occurs in >12 years for overpacks with low chloride foam <0·05%); and (c) concludes that there is a need to standardise on low chloride foam <0·05%) and possibly also to consider less susceptible combinations of foam and shell materials.