Immobilization of Am-241, Formed Under Plutonium Metal Conversion, Into Monazite-Type Ceramics

Lanthanum orthophosphate with the monazite structure was proposed on examinations as a suitable matrix for immobilization of future americium-containing liquid wastes, which could be formed in conversion of metallic plutonium into oxide at PA “Mayak.” Specimens of monazite non-active ceramics were fabricated from LaPO4 powders obtained using a thin-film evaporator by either hot-pressing or cold-pressing and sintering at 900–1300 °C. According to electron microprobe analysis (EMPA), scanning electron microscopy (SEM), and X-ray diffraction (XRD), which were used for characterization of produced samples, all specimens did not contain any phase other than the monoclinic monazite phase. Ceramics having the specific activity of Am-241 2.13×107 Bq/g were prepared by only cold-pressing with subsequent sintering at 1300°C during 1 hour. The normalized leach rates of lanthanum and americium in distilled water at 90°C were less than 1.2×10−4 and 2.3 10−4 g/m2×day, respectively.

Phase Analysis of Metallic Plutonium-Containing Fuel Alloys Using Neutron Diffraction

Pulsed neutron powder diffraction studies at IPNS have expanded our understanding of the phases present in Integral Fast Reactor (IFR) metal fuel alloys at temperatures in the range of reactor operating conditions. We report results from the binary alloy (U-10wt.%Zr) and ternary alloys (U-8%Pu-10%Zr) and (U-19%Pu-10%Zr). Determining the role and the location of Zr and Pu in these alloys is considered of fundamental importance for maximizing engineering efficiency.Rietveld profile analysis was utilized to study the phase diagrams. Data were collected at temperatures ranging from 25-650°C. Although the expected U/Pu/Zr phases (α-U, β-U, γ-U, δ-U/Zr/Pu, ζ-U/Pu) were observed in appropriate temperature ranges, there were some unexpected results. Relative amounts of all phases at each temperature were calculated from Rietveld scale factors and inferences were made as to the location of zirconium and plutonium, i.e. amounts in each phase, from site occupancies and absorption characteristics of the phases present. Finally, we were able to identify ZrO and ZrO1-x inclusion phases in the U-Zr alloy present in very small (0.5-1.0%) amounts.