Short term irradiation behaviour of controlled porosity fuel

BNFL controlled porosity oxide fuel containing 8% porosity in two different size ranges was irradiated to the point where densification was expected to be at its maximum. The conditions used were representative of those in an LWR at a linear rating of 400 w/cm. Stack length changes, density changes and porosity distribution changes were measured and irradiation stability was confirmed. The total porosity changes were compared with those predicted by the HOTROD computer code and quite good agreement was obtained. Significant decreases in porosity less than 1.0 μm were observed but these pores constituted only approximately 0.5% of the pore volume. In the case of the larger pore sized sample, a significant increase in pores in the range 1.0-3.0 μm was noted, but this was not observed in the smaller pore sized sample. No significant changes in the controlled pore content were noted but there was a redistribution of porosity in the region of the pellet affected by columnar grain growth. (Auth.)