Corrosion Model Validation in High Level Nuclear Waste Package Research
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CORROSION MODEL VALIDATION IN HIGH LEVEL NUCLEAR WASTE PACKAGE RESEARCH M. B. McNEIL* and J.B. Moody**, *Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555. **J. B. Moody and Associates, 25 W. Washington St. , Athens, Ohio 45701. ABSTRACT: The strategies for waste package (WP) performance validation will be based on site specific geologic and hydrogeochemical information plus models which can be used to predict potential WP lifetimes. The development and application of such models will include the evaluation of natural analogues (NA). These analogues are needed to resolve issues related to the validation of models. Natural analogues have not had extensive use or widespread acceptance in the area of waste package failure prediction. This lack of acceptance is due to the anticipated choice of alloys for waste package containers. Few of these alloys are similar to naturally occurring metals, and the proposed HLW repositories are in general in geologic settings not very similar to those in which naturally occurring metals are generally found. Natural and archaeological analogues can be used, however, in analysis of possible waste package failures as a means of testing proposed models for failure. In fact, the analogues are the only available mechanisms for testing models of long-term waste package behavior. A strategy is outlined for incorporating natural and archaeological analogue studies into waste package research, and examples are discussed. The natural/archaeological analogues approach which appears most promising is to use archaeological and mineral samples to develop an understanding of the identities and rates of the mineral alteration reactions at or near the surface of the package, improving present capability for estmating the lifetimes of metallic waste package containers. INTRODUCTION
Waste packages (WP) used to contain high-level nuclear waste (HLW) must be so designed that there is reasonable assurance of containment for a period as yet to be determined but in the range of 300-1000 years [1]. Bounds are also needed for release rates beyond 1000 years. One potential cause of WP failure is corrosion. To offer the legally required assurance and to establish needed bounds on potential corrosion rates it is necessary to go beyond the range of conventional corrosion testing. Although some corrosion tests have been conducted over periods of as long as 20 years [2], available test data on corrosion beyond a year or two are largely on a very small range of materials under a few conditions, mostly water or near-surface saturated soils. These data cannot be used directly in predicting WP behavior in the potential Yucca Mountain (YM)HLW repository, which is in unsaturated welded tuff. The development of predictive models for corrosion has led to useful predictions of general corrosion [3]. Extensive research on localized corrosion has led to successful qualitative predictions, but rarely meaningful rate predictions [4,5]. Predictions of general corrosion can often be ma
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