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The compilation of Metal Waste Form (MWF) immersion test data in this document is part of the effort initiated to qualify the stainless steel-15% zirconium (SS-15Zr) alloy for repository disposal. The SS-15Zr alloy was developed as part of the waste stream from the Argonne National Laboratory (ANL) electrometallurgical process for spent nuclear fuel. There were four areas of significant relevance concerning MWF performance in a long-term repository setting addressed in the test model. The areas encompassed the study of the effects of (1) the solution aggressiveness [simulated by concentrated J13 solution (CJ13)], (2) high-chloride content of the solution [simulated by 10,000 ppm chloride solution (10KCl)], (3) solution pH [simulated by acidified J13 solution (AJ13)], and (4) the state of the metal surface--polished vs. oxidized on the releases. The simulated J-13 solution was intended to replicate the groundwater in the J-13 well at the Yucca Mountain geologic repository. A fifth area of interest was to determine if the releases were limited by iron saturation of the solution. The data obtained from the entire study will be compared with the data from the High Level Waste Glass (HLWG) form previously qualified for repository disposal. Even though the MWF samples used in thesemore » tests contained no actinides and no Tc, conclusions can be made with respect to the releases of the noble metal fission products and the stainless steel constituents. Fe releases are an order of magnitude or higher than the releases of the noble metal fission-product elements in all solutions. Releases of noble metal fission products and Cr and Ni in SJ13 and CJ13 solutions at 90 C are close to the limits of detection. Solution concentration increased the Zr release. Zr releases from CJ13 were about a factor of 2 lower than the Fe release. In CJ13, Zr releases from oxidized samples were higher than from polished samples. Releases of all elements increased in the AJ13, pH=2 solution. Total cumulative releases as a function of time continued to increase for the 308 days of tests unlike the behavior in other test solutions. Tests in solutions with pH between 2 and 8 are needed to understand the different behavior. Except for high chloride solutions, (10KCl), release rates of stainless steel elements and noble metal fission products from the MWF samples are lower than release rates from HLWG.« less |
