PREPARATION AND PERFORMANCE OF U-10ZR ALLOY NUCLEAR-FUEL USING POWDER-METALLURGY TECHNIQUES

The mechanical interaction between highly radioactive, porous nuclear fuels and their surrounding cladding is a key safety issue. Uranium - 10 wt.% zirconium is an alloy nuclear fuel proposed for use in the new Integral Fast Reactor. The purpose of this study was to prepare unirradiated U-10Zr specimens with simulated porosity by sintering powder specimens in an argon atmosphere with ambient pressure of 500 psi to entrap gas in closed porosity. Two methods for mixing the highly reactive powders and sintering the alloy beyond the point of pore closure have been explored. For the first method, uranium hydride powder (UH3) was mechanically mixed with zirconium hydride powder (ZrH2) and pelletized at 80 Ksi. The hydrides were decomposed to the metals under vacuum as the specimens were heated to the sintering temperature of 1100C. The specimens sintered readily, but the required temperature was very near the alloy solidus temperature. Also, approximately 50% of the zirconium was gettered by C, N, and O impurities to form separate highly stable phases. To reduce the impurity level, a second method was investigated in which acid-washed uranium spherical powder was mechanically mixed with zirconium metal powder and pelletized at 160 Ksi. This method yielded relatively pure specimens with a final density >92%. The hot pressing behavior for the two classes of specimens show clear differences which appears to be due to the presence of the impurity phases.

PREPARATION AND PERFORMANCE OF U-10ZR ALLOY NUCLEAR-FUEL USING POWDER-METALLURGY TECHNIQUES Conference Paper