STRESS-CORROSION CRACKING OF U-0.1-PERCENT-CR IN HUMID HELIUM ATMOSPHERE

Rivets were matched into adapted drilled holes in plates, both made of U-0.1% Cr alloy and were placed in different environments containing dry air and helium and humid air and helium for a variety of exposure times. After opening, the most significant amounts of corrosion produc ts were detected in the specimens that stayed for three years in humid helium (5% RH) environment. Radial cracks, developed in the bore edge , were detected in the specimens. X-ray diffraction patterns of the co rrosion products gave the composition of UH3 and UO2. The microstructu re was examined using fight and electron microscopy techniques. The hy dride phase that was observed, formed mainly beneath the oxide layer a nd penetrated into the metal matrix as needle-like forms. The formatio n of a lower density hydride phase, yielded in a large volume change c ausing the development of high stresses at the rivet-bore interface. T he combination of the high stress and the weakening of the bore edge d ue to the presence of the brittle hydride phase led to radial crack fo rmation around the bore edge.