COMPARISON BETWEEN THE UNIFORM AND NODULAR FORMS OF ZIRCALOY CORROSION IN WATER-REACTORS

This paper considers the kinetics of the in-reactor oxidation of zircaloy, using results from the post-irradiation examination of fuel from both BWRs and PWRs. It is shown that the growth rate of the continuous film type of oxide is similar in all reactors considered, at about 2-3 times the out-of-reactor rate, and that stainless steel components do not accelerate the oxidation. It is concluded that the rate-limiting factor is anion diffusion. By contrast, the nodular form of zircaloy oxidation is affected by both coolant chemistry and the presence of stainless steel components nearby, and it is shown that both these effects probably occur at the nodule nucleation stage. Subsequent growth must then be controlled by similar factors to the continuous oxide form. These observations support a simple, repeated mechanical cracking model of nodule growth. © 1979.