No abstract

Cortest Columbus Technologies, Inc. (CC Technologies) investigated the long-term performance of container materials used for high-level waste packages as part of the information needed by the Nuclear Regulatory Commission (NRC) to assess the Department of Energy's application to construct a geologic repository for high-level radioactive waste. At the direction of the NRC, the program focused on the Tuff Repository. This report summarizes the results of Stress-Corrosion-Cracking (SCC) studies performed in Tasks 3,5 and 7 of the program. Two test techniques were used; U-bend exposures and Slow-Strain-Rate (SSR) tests. The testing was performed on two copper-base alloys (Alloy CDA 102 and Alloy CDA 71 5) and two Fe-Cr-Ni alloys (Alloy 304L and Alloy 825) in simulated J-13 groundwater and other simulated solutions for the Tuff Repository. These solutions were designed to simulate the effects of concentration and irradiation on the groundwater composition. All SCC testing on the Fe-Cr-Ni Alloys was performed on solutionannealed specimens and thus issues such as the effect of sensitization on SCC were not addressed. Both Alloy 825 and Alloy 304L was resistant to SCC in the J-13 well water and in the J-13 well. water that was concentrated by a factor of about 80 by evaporation. Alloy 825 was resistant to SCC in all other environments evaluated including chloride solutions containing up to 100 000 pprn CI in the presence of H, O, , even though crevice corrosion occurred in some of these environments. Alloy 304L was resistant to SCC in 5-13 well containing 1000 ppm added CI. Alloy 304L underwent SCC in only one liquid phase exposure condition; J-13 well water with 100 000 ppm added CI. Alloy 304L also underwent SCC in four vapor phase exposure conditions, all in the presence of H;02 Of the four solutions in which Alloy 304L underwent cracking, three were prepared with simulated J-13 well water and added CI (1000 ppm CI and 10 000 ppm CI as NaCl and 10 000 ppm CI as CaCI,) while one solution, Solution Number 20, was taken from the Task 2 experimental test matrix. Solution Number 20 contained 1000 ppm CI as well as 200 ppm F and 200 ppm NO& Both Alloy CDA 102 and Alloy CDA 715 were found to be resistant to SCC in Solution Number 7 from the Task 2 experimental test matrix, in simulated J-13 well water and in the simulated water concentrated approximately 80 times. Alloy CDA 715 was also resistant to SCC in all other environments evaluated including NaNO, at concentrations up to 1 M. Alloy CDA 102 underwent SCC in NaNO, environments at concentrations as low as approximately 200 ppm. The presence of species from simulated J-13 well water appeared to inhibit SCC of Alloy CDA 102 in the dilute NaNO, solution. On the other hand, anodic polarization of Alloy CDA 102 specimens in NaNO, solutions, to simulate radiolysis products, increased susceptibility to SCC. In SSR tests performed on Alloy CDA 102 at 90°C in NaNO, solutions, cracking only occurred under anodic polarization, suggesting that the potential range, relative to the fr...

No abstract

An assessment was performed of approaches to life prediction for high-level nuclear waste containers. It was concluded that the commonly used remaining life assessment techniques are inadequate for the prediction of performance of the waste canisters primarily because of the reliance on empirical damage accumulation laws. The best hope for prediction of performance of the repository relies on utilizing mechanistic models based on first principles. It was further concluded that prediction of performance of the waste containers should rely primarily on propagation phenomenon, because of the uncertainties in proving that initiation will not occur. The above philosophy imposes significant restrictions on the selection of container materials, and selection of the repository site. The materials selection for the waste canister should focus on corrosion allowance materials because the general corrosion rate can be bounded and the rates of pitting corrosion are expected to be much lower than for corrosion resistant materials. Corrosion resistant materials should be avoided because the probability of pit initiation is high for the range of possible environments and the rates of pitting corrosion are expected to be high, as a result of hydrolysis reactions. In order to reduce possible rates of localized corrosion, an anoxic repository should be selected. Because of the uncertainties in the predictive capability of the mechanistic models, corrosion monitoring, and a multiple barrier design for the waste package should be used.