Stress corrosion cracking of Zircaloys. Final report
The overall aim has been to develop an improved understanding of the stress corrosion cracking (SCC) mechanism considered to be responsible for pellet-cladding interaction (PCI) failures of nuclear fuel rods. The objective of the present phase of the project was to investigate the potential for improving the resistance of Zircaloy to iodine-induced SCC by modifying the manufacturing techniques used in the commercial production of fuel cladding. Several aspects of iodine SCC behavior of potential relevance to cladding performance were experimentally investigated. It was found that the SCC susceptibility of Zircaloy tubing is sensitive to crystallographic texture, surface condition, and residual stress distribution and that current specifications for Zircaloy tubing provide no assurance of an optimum resistance to SCC. Additional evidence was found that iodine-induced cracks initiate at local chemical inhomogeneities in the Zircaloy surface, but laser melting to produce a homogenized surface layer did not improve the SCC resistance. Several results were obtained that should be considered in models of PCI failure. The ratio of axial to hoop stress and the temperature were both shown to affect the SCC resistance whereas the difference in composition between Zircaloy-2 and Zircaloy-4 had no detectable effect. Damage accumulation during iodine SCC was found to be nonlinear: generally, a given life fraction at low stress was more damaging than the same life fraction at higher stress. Studies of the thermochemistry of the zirconium-iodine system (performed under US Department of Energy sponsorship) revealed many errors in the literature and provided important new insights into the mechanism of iodine SCC of Zircaloys.
- Research Organization:
- SRI International, Menlo Park, CA (United States)
- OSTI ID:
- 5523320
- Report Number(s):
- EPRI-NP-1329; TRN: 80-007503
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
22 GENERAL STUDIES OF NUCLEAR REACTORS
CLADDING
CRACKS
FUEL PELLETS
IODINE
CORROSIVE EFFECTS
ZIRCALOY
STRESS CORROSION
ZIRCALOY 2
COMPARATIVE EVALUATIONS
ZIRCALOY 4
FAILURES
FUEL RODS
STRESSES
ALLOYS
CHEMICAL REACTIONS
CHROMIUM ADDITIONS
CHROMIUM ALLOYS
CORROSION
DEPOSITION
ELEMENTS
FUEL ELEMENTS
HALOGENS
IRON ADDITIONS
IRON ALLOYS
NONMETALS
PELLETS
REACTOR COMPONENTS
SURFACE COATING
TIN ALLOYS
ZIRCONIUM ALLOYS
ZIRCONIUM BASE ALLOYS
360105* - Metals & Alloys- Corrosion & Erosion
220300 - Nuclear Reactor Technology- Fuel Elements