Book Description

Zircaloy-4 fuel sheath specimens 15.2 mm diameter by 0.42 mm wall thickness with beryllium-brazed appendages have been laboratory tested at high temperature with internal gas pressurization and inert gas shielding of the outer surfaces. with sufficient hoop stress at temperatures less than 1073 k cracks, which were due to a beryllium assisted crack penetration mechanism, were found to occur at the appendages. formulae to predict the beryllium penetration and rupture have been derived by westinghouse canada ltd. based on data from direct resistance-heated specimens. the formulae are thought to be able to predict the phenomenon in fuel sheaths with changing temperature/pressure histories. a series of tests was done by canadian general electric to determine the formulae ability to predict the occurrence of beryllium assisted crack penetration in specimens heated indirectly with internal heaters. the tests showed: 1) there is an incubation period before any beryllium assisted crack penetration occurs. 2) at sheath temperatures below approximately equal to 1073 k sheath rupture by excessive mechanical strain will preclude rupture by beryllium assisted crack penetration. 3) the formulae predicted rupture times above and below the braze alloy melting temperature within the previously determined confidence limits. 4) predictions of beryllium assisted crack penetration rupture for specimens with changing temperature/pressure histories were of similar accuracy to predictions of isothermal tests. 5) specimens with an appendage plane of one bearing pad and three spacer pads behaved similarly to the specimens with four spacer pads on which the formulae were based.