Characterization of Irradiated Metal Waste from the Pyrometallurgical Treatment of Used EBR-II Fuel

As part of the pyrometallurgical treatment of used Experimental Breeder Reactor-II fuel, a metal waste stream is generated consisting primarily of cladding hulls laden with fission products noble to the electrorefining process. Consolidation by melting at high temperature [1873 K (1600 degrees C)] has been developed to sequester the noble metal fission products (Zr, Mo, Tc, Ru, Rh, Te, and Pd) which remain in the iron-based cladding hulls. Zirconium from the uranium fuel alloy (U-10Zr) is also deposited on the hulls and forms Fe-Zr intermetallics which incorporate the noble metals as well as residual actinides during processing. Hence, Zr has been chosen as the primary indicator for consistency of the metal waste. Recently, the first production-scale metal waste ingot was generated and sampled to monitor Zr content for Fe-Zr intermetallic phase formation and validation of processing conditions. Chemical assay of the metal waste ingot revealed a homogeneous distribution of the noble metal fission products as well as the primary fuel constituents U and Zr. Microstructural characterization of the ingot confirmed the immobilization of the noble metals in the Fe-Zr intermetallic phase

Sintering high tungsten content W-Ni-Fe heavy alloys by microwave radiation

This paper presents a detailed study of microwave (MW) sintering of W-Ni-Fe heavy alloys (WHAs) with tungsten (W) content 90 to 98 mass pct (Ni and Fe mass ratio of 7 to 3) in comparison with conventional (CV) hydrogen sintering. Experimental results show that WHAs were MW sintered to fully dense (≥99 pct of theoretical) when heated to sintering temperatures at a heating rate of 50 K/min to 80 K/min (50 C/min to 80 C/min) and isothermally held for 2 to 10 minutes, with sintering cycle times of only 25 to 35 minutes (excluding the cooling time). The desired microstructures of finer W grains, more matrix phases, and lower W contiguity (in 95W and 98W) were produced compared to the counterparts by CV sintering. Such microstructural features offered the alloys excellent tensile properties: ultimate tensile strengths (UTS) 1080 to 1110 MPa and tensile elongation 22.1 to 26.8 pct in 90 to 95W, and UTS 920 MPa and elongation 11.2 pct in 98W. MW sintering appeared to be more effective in fabricating WHAs with W content ≥95 pct. It was observed that the superior UTS with MW-sintered alloys was mainly due to the fast heating and shortened isothermal holding times. Prolonged sintering led to substantial grain coarsening as a result of faster tungsten grain growth in MW sintering, and consequently deteriorated the tensile properties. The grain growth rate constant K achieved was calculated to be 5.1 μm3/s for MW sintering compared to 2.9 μm3/s for CV sintering. Fast heating and short isothermal holding times are thus suggested for the fabrication of WHAs by MW sintering