The Effect of UO₂ Density on Fission Product Gas Release and Sheath Expansion

The effect of UO₂ density on fission product gas release and sheath expansion has been determined in an irradiation experiment in which the performance of fuel elements with densities between 10.42 and 10.74 g/cm³ was compared at ∫λdθ values of 39 and 42 W/cm. Diametral sheath strain was less for the lower density elements, but fission product gas release and the extent of grain growth were greater as the density decreased. A correlation between the extent of grain growth in the UO₂ and the fractional gas release was found to exist in this test and to apply to a large number of other irradiations; it is suggested that this relationship may be causal and that the fractional gas release is not solely a function of temperature.