Carbon Steel Canister Performance Assessment: Iron Transfer Study

Abstract

ABSTRACTCarbon steel has been chosen in the Czech disposal concept of spent fuel disposal in a granite host rock as a reference material for disposal canisters. On the basis of the results of performance assessment studies, it could be decided whether this material is suitable or whether a more corrosion resistant, and also more expensive, material should substitute it. A number of papers have convincingly shown that iron transfer constraints contribute to a significant decrease in corrosion rate, but no study hasso far been devoted to modeling this process. In this paper the effects of initial corrosion rate, corrosion product solubility and porosity and other repository parameters on the transfer of iron to the host rock are modeled using a numerical transport computer code. It was found that the critical parameter for iron transfer is the solubility of corrosion products, considerably affecting the steady state corrosion rate. The initial corrosion rate of carbon steel and the sorption properties of bentonite primarily affect the time needed to achieve a steady state of corrosion. The results of the calculations strongly suggest that the constraints on iron transfer from the canister surface will govern the corrosion rate of carbon steel canisters, whose lifetime, owing to this effect, can stretch to millions of years.