Canister corrosion process

Conditioning of the near field geochemistry by the canister corrosion processes... 

The main perturbations associated with the massive steel canister are canister failure through corrosion, hydrogen gas production due to anaerobic corrosion and redox changes around the canister following canister failure (Nagra 1994a). Gas has already been treated above and the discussion here will concentrate on corrosion processes during the first 1000 a after repository closure (when complete containment... 

Figure 1 also compares redox couples that are of importance to the performance and safety of a deep geological repository for spent nuclear fuel. They reflect the performance assessment issues raised in the introduction to this paper, and have been reviewed by Banwart et al. (1997). The couples Cu20(s)/Cu and CU2S/CU reflect corrosion processes that can destabilize the copper canister in which spent fuel rods will be placed. These couples represent oxic and sulphidic corrosion of copper, respectively. 

The transport process from the repository is schematically illustrated in Figure 3. Radionuclides and corrosion products would diffuse from the canister into the groundwater, and the migration will then be retarded first in the backfill barrier and after that in the bedrock. 

In many CVD processes, toxic, explosive, and corrosive materials are produced as one component of the vapor phase reaction co-product. In order to remove them prior to atmospheric venting, scrubbers are employed, which must be appropriate for the process used. For example, halides frequently are neutralized in a water scrubber. Carbon monoxide and hydrogen often are burnt. Arsine generally is removed by heating the exhaust gas in a cracking furnace. Charcoal canisters often are used to absorb vapor phase species. Sulfur has been employed to getter thallium. Very fine particle filters also are used to catch a diversity of solids entrained within the exhaust stream. 

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