A New Model to Predict the Oxidation Kinetics of Zirconium Alloys in a Pressurized Water Reactor

Abstract

The previous CEA corrosion code COCHISE provided satisfactory simulations of in-reactor corrosion of the fuel cladding when used in its validity range. In contrast, it could lead to hazardous predictions if applied out of this range due to the strongly linked parameters mainly based on the analysis of French pressurized water reactor (PWR) data. To predict the oxidation kinetics for new operating conditions or new materials, the CEA and EDF decided to develop a new model, named CORCY, which is based on a more phenomenological approach and uses separate parameters deduced from analytical experiments. The aim of this paper is to present the new model for Zircaloy-4 in PWR. The phenomenological approach is described. It is based on out- and in-pile data. Typically, since (1) the oxidation kinetics of zirconium alloys in autoclave are periodic, and (2) the oxide films formed in autoclave, in out-of-pile loop, and in-reactor all exhibit periodic lateral cracks with a period similar to the oxide thickness to transition, the oxidation kinetics in CORCY are characterized by a cyclic repetition of semi-parabolic law. Each model parameter is detailed. They are deduced separately from (a) oxidation tests performed in autoclave on fresh alloys to determine their kinetics; (b) oxidation tests performed in the out-of-pile corrosion loops Corail and Reggae to quantify the effects of thermo-hydraulic conditions; (c) data provided by Testing Material Reactors (OSIRIS and Halden reactor) during isothermal oxidation to determine the effects of irradiation; and (d) oxidation tests performed on pre-hydrided alloys to take into account the accelerated corrosion phase occurring, in reactor, for Zircaloy-4 at high burn-up. After describing both the phenomenological approach and the different model parameters, a comparison of measured and calculated corrosion data from French PWRs at a burn-up up to 65 GWd/tU is provided.

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

“…Approaches that are formulated starting from fundamental transport equations and interface physics have subsequently been developed [41e45], shedding light on issues such as the role of electron transport, effects of charge distributions, transition from 1=2 to 1=3 time kinetics, etc. Extension to irradiation conditions has been undertaken typically using empirical correlations linking oxide growth to burnup [37,40,41]. While these models can yield good quantitative estimates of oxide thickness growth in a variety of conditions, they do not help us answer any of the fundamental questions raised above.…”

Influence of light ion irradiation of the oxide layer on the oxidation rate of zircaloy-4: Irradiation of the post-transition oxide layer

“…The main assumptions suggested in the literature to explain this acceleration are the precipitation of zirconium hydrides under the metal/oxide interface resulting from the hydrogen uptake by the matrix during the corrosion process, the tin distribution evolution, the amorphization of the Second Phases Particles (SPPs) and their dissolution under irradiation [3][4][5][6][7][8][9][10][11][12][13][14]. This high burnup acceleration could also be partially caused by the accumulation of irradiation damage in the cladding material or the radiolysis of the water.…”