High-level waste canister corrosion studies pertinent to geologic isolation

The compatibility of candidate high-level waste (HLW) canister materials with deep geologic isolation environments is addressed. Results are presented which are applicable to the following repositories or test facilities: bedded and domed salt, sub-seabed sediment, and various types of hardrock. Such studies are an essential portion of the technological basis for terminal waste management. These studies will identify HLW canister or overpack materials satisfying appropriate requirements for barrier lifetime. Mechanical properties, as well as constraints on cost and consumption of critically limited materials, are also selection criteria. Lifetime objectives range from a minimum of several years for retrievability constraints up to several hundred years for retardation of near-field interactions (e.g., waste form leaching with potential radionuclide release to the geosphere) during the period of greatest HLW thermal output. A review of present and prior applicable corrosion results is presented. However, emphasis is on the results obtained from current laboratory and in situ HLW canister/corrosion programs at Sandia Laboratories. The effects of multiple variables on corrosion susceptibility and rates are briefly discussed and some applicable data given. It is possible to provide a canister/overpack barrier which can survive geologic isolation environments for periods of several hundred years