We have developed a test to simulate corrosion processes that might occur when pore water or modifications thereof drips onto a high-level radioactive waste canister. Alloy C-22 has been chosen by the U.S. Department of Energy as the construction material for the outer cylinders of the waste packages used to permanently store high-level radioactive waste in the vadose zone at Yucca Mountain. Our study focuses on looking at the corrosion behavior of C-22 in simulated fluids that might occur in the repository. C-22 is a hastelloy made of primarily nickel, chromium, and molybdenum with small amounts of iron, tungsten, and manganese. C-22 has been shown to be exceptionally corrosion-resistant. However, dripping of pore water or pore water distillation products onto spots on the canister surface can produce unusual phenomena not typically observed in conventional corrosion tests.

 

The test consists of a bent strip of C-22 alloy heated from below while solution is dripped onto the surface of the strip from above. Because the experiment functions as a mixed flow reactor, the corrosion rate can be determined by analyzing the effluent for concentrations of nickel, iron, and chromium. For example, dripping 0.5 m nitric acid, which might form under these conditions as a result of the distillation of pore water solutions and radiolysis, onto a test strip heated to 120°C produces a corrosion rate of 1.2 mils per year. Conversely, J-13 groundwater dripped onto the surface produces a strongly adherent precipitate that coats the surface and no measurable release of Ni, Cr, or Fe. J-13 groundwater has been a standard test water in the DOE program, but it only occurs below the level of the proposed repository.