Examination of T-111 clad uranium nitride fuel pins irradiated up to 13,000 hours at a clad temperature of 990 C

The examination of 27 fuel pins irradiated in the Plum Brook reactor facility is described. Curtailment of NASA sponsored nuclear programs prevented a complete examination of all pins. Nevertheless, results include fuel pin integrity, clad ductility, clad strain, fission gas release, fuel burnup, fuel swelling, neutron fluence, metallography, and instrumentation reliability. Twenty-two fuel pins were tested for fission gas leaks; 13 pins leaked with two having visible cracks. Fuel swelling appeared to be primarily burnup dependent for burnup values up to 2 at. %. Maximum burnup reached in these tests was 2.34 at. %. In general, the fuel pellets did not crack or crumble and fuel metallography remained unchanged. The amount of fission gas released from the fuel was low, generally less than 0.5%. The maximum amount released was 2%. No incompatibilities between fuel, liner, and clad were evident.