Oxide Dissolution in Corrosion Of Aluminum Cladding On Nuclear Reactor Fuel Elements

Effect of aluminum oxide dissolution on aluminum corrosion in high temperature deionized water is discussed. Such dissolution promotes corrosion by removing protective oxide and is especially significant in nonisothermal systems, such as aluminum-clad fuel elements in nuclear reactors cooled by pressurized water, where the water cannot be kept saturated with dissolved oxide. Hypothesis is advanced that resistance to dissolution lies principally in mass transfer from oxide-water surface into bulk water; dissolution rate can be estimated by use of general equations for mass transfer, if oxide solubility is known as a function of temperature. Dissolution rates thus calculated were in good agreement with in-reactor corrosion rates of aluminum-clad fuel elements in high temperature deionized water, which had been previously measured at Hanford. Fair agreement was obtained with measurements in recirculating out-of-reactor loops. It is concluded that mass transfer of dissolved oxide into the water may be the principal factor controlling corrosion rate of aluminum-clad fuel elements in many nuclear reactor systems using high temperature pressurized deionized water as coolant.