PWR Zircaloy Fuel Cladding Corrosion Performance, Mechanisms, and Modeling

Abstract

Oxide axial profiles for Zircaloy-4 cladding measured for 17 fuel rods irradiated from 50 to 60 GWD/t in three different pressurized water reactors (PWRs) were studied. Computer simulation of the magnitude and shape of the various profiles involved five contributing interrelated effects: (1) thermal feedback, (2) radial thermal redistribution of corrosion hydrogen, (3) metallurgical variables (tin content and radiation-induced changes in intermetallic particle size distribution), (4) lithium hydroxide exposure history, and (5) radiation effects in the oxide film. Published research results supporting each separate effect are reviewed, and the selection of a predictive simulation for each phenomenon and the effect of varying its relative weight are reported. The effect on cladding corrosion of hydrogen thermal redistribution to the oxide-metal interface, coupled with thermal feedback, was found to be a predominant factor in predicting the magnitude and shape of cladding oxide profiles at high burnups for PWR fuel rods. Tin content, coupled with thermal feedback, was also found to have a very important effect on the predicted magnitude of oxide profiles at all burnups. Radiation-induced dissolution of fine Zr(Cr,Fe)2 intermetallic particles in the Zircaloy-4 cladding primarily affected the predicted shape of the oxide profiles at the colder inlet region of the fuel rods. Lithium hydroxide (LiOH) exposure history and radiation effects in the oxide film appeared to play non-negligible secondary roles in determining the oxide profiles at all burnups.

BISON Theory Manual The Equations behind Nuclear Fuel Analysis

“…15.15. Activiation energy in the post-transition period is found to be dependent on hydrogen content [130]: where F HU = hydrogen enhancement factor at hydride rim ([H 2 ] = 18811.25 ppm), Q 2L = 24825 cal/mol, and Q 2U = 9135.6 cal/mol.…”

FRAPCON-3: Modifications to fuel rod material properties and performance models for high-burnup application

“…Staff at EPRI have recently published a revised PWR corrosion model, which includes cladding annealing and alloying effects, hydride layer effects, and coolant chemistry history effects (Cheng et al 1996). This model will be evaluated as a possible future improvement to the FRAPCON-3 code; however, the coeffcients of this model are not publicly available at this time.…”

Determination of dose rate effects on Zircaloy oxidation using proton irradiation and oxygen transport modeling

“…The graph shows the experimental results (of Zircaloy-4 exposed to irradiation for 24 h in pure water with 3 wt ppm dissolved H 2 at a temperature of 320 + C), an exponential fit to the measurements (denoted by Rð _ fÞ), and predictions from the present model. conditions [31]. In general, the observed microstructures in these tests consisted primarily of columnar monoclinic grains elongated in the growth direction of the oxide layer, with an interspersed distribution of smaller and more equiaxed grains within the columnar structure.…”