Observation and analysis of secondary hydriding behavior of failure fuel rod

During the service of fuel rods in the reactor, the primary break will lead to the secondary hydriding failure of cladding, which is an important factor leading to the serious damage of fuel rods. Post-irradiation examination on the failure fuel rods was carried out at Fuel and Material Examination Facility in China Institute of Atomic Energy. The secondary hydriding behavior of fuel rods was observed and analyzed by the method of metallography in hot cell. The results show that the hydride swelling phenomenon is significant at the position of secondary hydriding failure, the hydride diffuses from the inner side to the outer side of the cladding in stages and forms a 'sun-burst' phenomenon eventually. The temperature of the pellet increases significantly at the position of secondary hydriding failure, which causes pore migration, grain growth of the pellet and columnar crystal growth. Comparing with the intact rods, the thickness of the water side oxide film at the position of secondary hydriding failure increases, but the values is still within the criteria. (authors)