COMBINED EFFECTS OF RADIATION-DAMAGE AND HYDRIDES ON THE DUCTILITY OFZIRCALOY-2

Interest remains high regarding the effects of zirconium hydride preci pitates on the ductility of reactor Zircaloy components, particularly in irradiated material. Previous studies have reported that ductility reductions are much greater at room temperature compared to reactor co mponent temperatures. It is often concluded that the effects of irradi ation dominate the ductility reduction observed in test specimens, alt hough there is no consensus as to whether hydriding effects are additi ve. Many of the tests reported in the literature are difficult to inte rpret due to variations in test specimen geometry and material history . In this paper, we present the results of an experimental program aim ed at clearly describing the combined effects of irradiation and hydri ding on ductility parameters under conditions of a realistic test spec imen design and well characterized hydride content, distribution and o rientation. Experiments were conducted at 295 and 605 K, respectively on Zircaloy-2 tubing segments containing 10-800 ppm hydrogen and neutr on fluences between 0-9 x 10(25) n m(-2) (E > 1 MeV). Tests utilized t he well proven localized ductility specimen which applies plane strain tension in the hoop direction of the tubing segment. In all cases, hy drides were also oriented in the hoop or circumferential direction and were uniformly distributed across the tubing wall. Results indicate t hat at 605 K, the ductility of irradiated material was almost independ ent of hydride content, retaining above 4% uniform elongation and 25% reduction in an area for the highest fluences and hydrogen contents. E ven at 295 K, measurable ductility was retained for irradiated materia l with up to 600 ppm hydrogen. In the paper, results of fractographic analyses and strain rate are also discussed. We conclude that at react or component operating temperatures. radiation damage controls the duc tility of Zircaloy-2 for conditions of these tests up to hydride level s of at least 800 ppm, and probably much higher. At room temperature t he effect of hydride content and radiation damage appear to be additiv e. (C) 1998 Elsevier Science S.A. All rights reserved.