Six different fastened joints representing the various combinations of materials in contact with Zircaloy in the Light Water Breeder Reactor (LWBR) were tested in 520/sup 0/F water for 60 days to determine the out-of-pile hydriding tendencies of the Zircaloy components in the joints. No evidence of massive, accelerated hydriding was found in this test although other testing has shown that local hydriding can occur in one of the fasteners. The same six fastener designs were tested in 600/sup 0/F water for 60 days to assess their load retention capability (thermal relaxation). The measured relaxation of these fasteners confirmed the predicted values for the conditions of the test.