Aging and Phase Stability of Waste Package Outer Barrier
This report was prepared in accordance with ''Technical Work Plan for: Regulatory Integration Modeling and Analysis of the Waste Form and Waste Package'' (BSC 2004 [DIRS 171583]). This report provides information on the phase stability of Alloy 22, the current waste package outer barrier material. The goal of this model is to determine whether the single-phase solid solution is stable under repository conditions and, if not, how fast other phases may precipitate. The aging and phase stability model, which is based on fundamental thermodynamic and kinetic concepts and principles, will be used to provide predictive insight into the long-term metallurgical stability of Alloy 22 under relevant repository conditions. The results of this model are used by ''General Corrosion and Localized Corrosion of Waste Package Outer Barrier'' as reference-only information. These phase stability studies are currently divided into three general areas: Tetrahedrally close-packed (TCP) phase and carbide precipitation in the base metal; TCP and carbide precipitation in welded samples; and Long-range ordering reactions. TCP-phase and carbide precipitates that form in Alloy 22 are generally rich in chromium (Cr) and/or molybdenum (Mo) (Raghavan et al. 1984 [DIRS 154707]). Because these elements are responsible for the high corrosion resistance of Alloy 22, precipitation of TCP phases and carbides, especially at grain boundaries, can lead to an increased susceptibility to localized corrosion in the alloy. These phases are brittle and also tend to embrittle the alloy (Summers et al. 1999 [DIRS 146915]). They are known to form in Alloy 22 at temperatures greater than approximately 600 C. Whether these phases also form at the lower temperatures expected in the repository during the 10,000-year regulatory period must be determined. The kinetics of this precipitation will be determined for both the base metal and the weld heat-affected zone (HAZ). The TCP phases (P, {mu}, and {sigma}) are present in the weld metal in the as-welded condition. It may be possible to eliminate these phases through a solution anneal heat treatment, but that may not be possible for the closure weld because the spent nuclear fuel cladding cannot be heated to more than 350 C. The effects of any stress mitigation techniques (such as laser peening or solution heat treating) that may be used to reduce the tensile stresses on the closure welds must also be determined. Cold-work will cause an increase in dislocation density, and such an increase in dislocation density may cause an increase in diffusion rates that control precipitation kinetics (Porter et al. 1992 [DIRS 161265]; Tawancy et al. 1983 [DIRS 104991]). Long-range order (LRO) occurs in nickel (Ni)-Cr-Mo alloys (such as Alloy 22) at temperatures less than approximately 600 C. This ordering has been linked to an increased susceptibility of Ni-Cr-Mo alloys to stress corrosion cracking and hydrogen embrittlement (Tawancy et al. 1983 [DIRS 104991]). These analyses provide information on the rate at which LRO may occur in Alloy 22 under repository conditions. Determination of the kinetics of transformations through experimental techniques requires that the transformations being investigated be accelerated due to the fact that the expected service life is at least 10,000 years. Phase transformations are typically accelerated through an increase in temperature. The rate of transformation is determined at the higher temperature and is extrapolated to the lower temperatures of interest.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC28-01RW12101
- OSTI ID:
- 839522
- Report Number(s):
- ANL-EBS-MD-000002, REV 02; DOC.20041005.0003, DC42582; TRN: US0502959
- Resource Relation:
- Other Information: PBD: 28 Sep 2004
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
36 MATERIALS SCIENCE
AGING
CORROSION RESISTANCE
GRAIN BOUNDARIES
HEAT TREATMENTS
HYDROGEN EMBRITTLEMENT
NUCLEAR FUELS
PHASE STABILITY
PHASE TRANSFORMATIONS
SERVICE LIFE
SHOT PEENING
SOLID SOLUTIONS
SOLUTION HEAT
SPENT FUELS
STABILITY
STRESS CORROSION
THERMODYNAMICS
WASTE FORMS
WASTES