Postirradiation heating tests have demonstrated that irradiated uranium silicide fuel undergoes rapid and gross swelling at temperatures above 900°C. At these temperatures the fission-gas pressure in irradiation-induced pores will exceed the self-restraint of the fuel, and the pores will swell to satisfy the temperature and pressure conditions. The amount of swelling increases with both temperature and burnup, but external pressure helps restrain swelling. Fast heating rates increase the amount of swelling.