Stress-induced hydride reorientation and cracking in fuel cladding tube

Abstract

The goal of this research was to find out if reorientation can influence cladding failure and determine conditions and possible mechanism of failure. Reorientation tests were done on zircaloy nuclear fuel cladding specimens. Specimens were made having two triangular notches along specimen axis, which are similar to the surface flaw that can form during operation. The loading was applied using pin-loading tension (PLT) loading fixture to give stress proportional to a distance from the specimen front. When loaded, specimen was cooled from 340 °C to 40 °C at a cooling rate 0.25 °C/min., total duration of test was 20 h. After testing, the specimen was examined layer by layer metallographically to determine hydride reorientation under certain stress conditions. In case of a surface flaw reorientation of hydrides takes place perpendicular to the stress direction. It was found that hydride reorientation occurs at a stress range (77 – 89) MPa, for initiation of delayed hydride cracking (DHC) process larger stress is required than for hydride reorientation.