Thermal-shock experiments with flawed clad cylinders

Abstract

Abstract In recent years, four thermal-shock experiments with a large (991 mm OD × 1220 mm lenght) thick-walled (152 mm), clad, steel cyclinder, containing both through-clad and subclad flaws, have been conducted to evaluate the effects of cladding on the propagation of flaws in light-water-reactor (LWR) pressure vessels. The thermal shock was achieved by first heating the test cylinder to ∼ 93° C and then applying liquid nitrogen to the inner surface. During the first experiment, one of six equally spaced, 19 mm-deep by 114 mm-long, semielliptical subclad flaws propagated in two initiation-arrest events to a length of ∼ 1100 mm and a maximum depth of 70 mm. There was no breaching of the cladding. Two 20 mm-radius, semicircular, surface flaws were added for the second and third experiments. These flaws did not propagate. For the final experiment, four of the subclad flaws that did not propagate during the first experiment were converted to surface flaws. These flaws propagated extensively in length and depth, bifuracting several times in the length direction, but all propagation was subclad (no breaching of the cladding). The results of these experiments indicate that under the specific test conditions, the cladding was beneficial in reducing the potential for initiation of a subclad flaw and deep propagation of a surface flaw. However, the benefit was not as great as predicted.