Abstract
Oxidation tests were conducted for zircaloy-2 in steam at temperature ranging from 900 to 1300°C to clarify its oxidation kinetics as a nuclear fuel cladding materials in case of a loss-of-coolant accident.
The influence of maximum temperature and heating rate of the specimen on its oxidation rate in steam was investigated. The changes in mechanical properties of the specimens after oxidation tests are also studied.
The results obtained were summarized as follows:
(1) The weight of the specimen after oxidation in steam increased two times as the time required to reach the maximum temperature increased from 1 to 10 mins.
(2) The kinetics of oxidation of zircaloy-2 in steam were not affected by the difference in the surface condition before test such as chemical polishing or pre-oxidation in steam.
(3) The dominant growth of oxide film on the surface of zircaloy-2 was observed at the initial stage of oxidation in steam. However, the thickness of oxygen-rich solid solution layer under the film increased gradually with the progress of oxidation and the ratio of oxygen in oxide to that in solid solution has a constant value of 8:2.
(4) The breakaway took place only in the specimen subjected to 900°C repeated heating. This penomenon was caused by the local growth of the oxide below a crack of the oxide film resulting from the reheating of the specimen.
(5) The results of bending tests showed that the deflection until fracture of the specimen was smaller for the one heated at a higher temperature even if the weight increase was of the same order of magnitude for both specimens.
(6) It was concluded that the ductility of zircaloy-2 decreased remarkably at a heating temperature in excess of 1100°C for more than 5 min.
