EFFECTS OF PROTON IRRADIATION ON THE MICROSTRUCTURAL EVOLUTION AND UNIFORM CORROSION-RESISTANCE OF ZIRCALOYS

In previous studies of irradiation effects on the nodular corrosion resistance of Zircaloys, the authors proposed a mechanism which involved solute redistribution during irradiation and which enhanced the nodular corrosion resistance of these alloys. Further study of the uniform corrosion resistance of proton-irradiated Zircaloys was performed using a similar technique. Specimens of Zircaloys (with various initial conditions) were irradiated with 1 MeV protons at 350-degrees-C up to total dose of 1 dpa at the 2 mum depth. Uniform corrosion tests were performed in an autoclave filled with 400-degrees-C and 10.3 MPa steam for up to 130 days. It was found that irradiation increased the uniform corrosion rate. For example, in the as-received (alpha + beta quenched) specimen, the weight gain of the irradiated specimen was three times higher than that of the unirradiated one. The microstructures before and after irradiation were also studied using analytical electron microscopy. Precipitate microchemistry was studied using an attached energy dispersive spectrometer. It was also demonstrated that irradiation-induced precipitate dissolution and solute redistribution in the matrix of Zircaloys occurred. In summary, it is believed that irradiation induced the dissolution of intermetallic precipitates and redistributed solutes more evenly which, in tum, affected the nodular corrosion resistance and the uniform corrosion resistance of Zircaloys in opposite ways. The increased solute concentrations in the Zircaloy matrix enhanced the nodular corrosion resistance of Zircaloys but made the uniform corrosion resistance worse. This result is important in designing high burnup fuel cladding for future advanced light water reactors.