Multistage Corrosion of Fuel Element Materials in Nuclear Reactors

Abstract

One of the factors limiting the operation time of nuclear reactor is corrosive wear of the reactor core structural materials and fuel element cladding due to continuous action of water coolant. Thus, for VVER (water-water energetic reactor) type reactors, local galvanic corrosion, which occurs between the surface of fuel element cladding made of zirconium alloy and various grade steel parts of other structural elements is peculiar. A short-circuited galvanic cell formed on the inner wall of Zr + 1% Nb alloy fuel elements is shown. Changes in oxide films thicknesses depending on the time at different water medium acidity are analyzed. A generalized model demonstrating that dissimilar metals in the reactor core (zirconium alloy and steel) form a short-circuited galvanic cell, resulting from which an increase in local corrosion of zirconium alloy occurs is presented.