Evaluation of Zircaloy-2 Cladding Corrosion Characteristics by Simulated BWR Corrosion Loop Test

Abstract

The effects of irradiation conditions such as neutron flux, β and γ rays, and of heat flux on the corrosion behavior of Zircaloy-2 cladding tubes were studied by using an inreactor corrosion loop simulating BWR conditions. Platinum and hafnium rings were placed in the rigs as β and γ emitters, respectively, to evaluate local radiation effects on cladding corrosion. The tube materials included an early BWR 8 x 8RJ type and a new, more corrosionresistant BWR 9X9-type cladding. Both tubes contained UO2 and Al2O3 pellets and were irradiated under the same conditions in two rigs in the same loop for about 180 days. Nodular corrosion appeared on the 8X8RJ-type tube, while the 9X9-type tube presented only uniform oxide layer. Metallographic and SEM observations revealed that the β and γ emitters enhanced the uniform oxide formation for the 9X9-type tube, while they increased the nodule density for the 8X8RJ type. Computer analyses on neutron flux and β- and γ-ray intensities were conducted for the 8X8RJ-type and 9X9-type test rods. Those results were utilized to comprehensively discuss and to understand the in-pile corrosion behavior.