Effects of Void Migration Process on Fission-Gas Release

抄録

The release rate of fission-gas from UO₂ was continuously measured during irradiation in the Hitachi Training Reactor. The UO₂ specimen was heated electrically in in-core assemblies by tungsten heaters, either arranged axially transversing the specimen (producing radial temperature gradient) or cylindrically outside the specimen (uniform heating). In a case of the axially heated annular UO₂ pellets with radial temperature gradient, the rate of fission-gas release increased with time under constant temperature and flux. This experimental result was explained by considering as fission gas release mechanism a combination of diffusion and pore migration processes. On the other hand, when UO₂ pellets were heated isothermally up to 2, 000°C, the fission-gas release rate could be explained in terms of diffusion process alone. No effect of equiaxial grain growth was observed on the rate of fission-gas release.