A model for uniform Zircaloy clad corrosion in pressurized water reactors

Integrated Computational Modeling of Water Side Corrosion in Zirconium Metal Clad Under Nominal LWR Operating Conditions

“…The corrosion kinetics is generally interpreted as diffusion controlled, 2 with a one-third power law dependency with time. [2][3][4][5] At a certain thickness, the oxide scale cracks, 6,7 which opens up pathways for the water to reach the metallic substrate, leading to a loss of the protective layer and a sudden jump in corrosion rates. Fracture is attributed to the contribution of several factors, such as (1) compressive stresses in the oxide due to volumetric expansion during oxidation (Pillar-Bedworth ratio of 1.56), 2 (2) tensile stresses in the oxide layer due to thermal and irradiation induced expansion on the fuel side, and (3) dynamic embrittlement caused by hydride precipitation.…”

“…[2][3][4][5] At a certain thickness, the oxide scale cracks, 6,7 which opens up pathways for the water to reach the metallic substrate, leading to a loss of the protective layer and a sudden jump in corrosion rates. Fracture is attributed to the contribution of several factors, such as (1) compressive stresses in the oxide due to volumetric expansion during oxidation (Pillar-Bedworth ratio of 1.56), 2 (2) tensile stresses in the oxide layer due to thermal and irradiation induced expansion on the fuel side, and (3) dynamic embrittlement caused by hydride precipitation. [8][9][10][11][12] Due to the highly complex and synergistic nature of corrosion kinetics, with coupled oxygen/hydrogen transport, diffusion/ reaction kinetics, temperature effects, and complex oxide microstructures, to name but a few, a multipronged approach that includes modeling as an essential element must be adopted to improve our understanding of the process.…”

Zirconium Alloys for Fuel Element Structures

“…The boiling temperature of BWRs (slightly below 300 °C at 7 MPa pressure) being approximately 30-40 °C lower than the exit temperature of the PWRs (operating at 14 MPa), typically leads to 3-4 times lower general corrosion rates (cr), as can easily be seen when evaluating a typical rate law curve [11] for the post transition Zircaloy corrosion regime: cr = C 2 exp (-Q 2 /RT) with Q 2 /R = 14000 K -1 C 2 = frequency factor, T = temperature This is the reason why today BWRs can still use the old BWR cladding variant Zircaloy-2 even with higher burn-up. The boiling temperature of BWRs (slightly below 300 °C at 7 MPa pressure) being approximately 30-40 °C lower than the exit temperature of the PWRs (operating at 14 MPa), typically leads to 3-4 times lower general corrosion rates (cr), as can easily be seen when evaluating a typical rate law curve [11] for the post transition Zircaloy corrosion regime: cr = C 2 exp (-Q 2 /RT) with Q 2 /R = 14000 K -1 C 2 = frequency factor, T = temperature This is the reason why today BWRs can still use the old BWR cladding variant Zircaloy-2 even with higher burn-up.…”

Advanced Proliferation Resistant, Lower Cost, Uranium-Thorium Dioxide Fuels for Light Water Reactors (Progress report for work through June 2002, 12th quarterly report)

“…Currently, FRAPCON-3 uses a two-stage corrosion model by Forsberg et al (1995) for standard Zircaloy-4. The oxidation proceeds via a cubic rate law until the transition thickness (taken to be 2.0µm) is accumulated.…”