William E. Moddeman

Ni3Nb alloy species in oxide surfaces of INCONEL 718

INCONEL 718 has been studied by Auger and X-ray photoelectron spectroscopy to determine the effect on the surface stoichiometry caused by heat treating in argon to 1000 C. Two surface regions are produced, the one closest to the argon-metal oxide interface being rich in O, Ti, Al, and Cr, and the one closest to the alloy being rich in O, Al, and Nb. Profiles show a gradual increase in the Ni and Nb signals as the profiling time increases. It is noted that during the profile, Al remains an oxide, and that the Ni and Nb signals have metal-like character even in the aluminum oxide phase, suggesting that N/sub 3/Nb exists with oxide at the surface. 6 references.

Thermodynamic Prediction of Compositional Phases Confirmed by Transmission Electron Microscopy on Tantalum‐Based Alloy Weldments

Tantalum alloys have been used by the U.S. Department of Energy as structural alloys for radioisotope based thermal to electrical power systems since the 1960s. Tantalum alloys are attractive for high temperature structural applications due to their high melting point, excellent formability, good thermal conductivity, good ductility (even at low temperatures), corrosion resistance, and weldability. Tantalum alloys have demonstrated sufficient high‐temperature toughness to survive prolonged exposure to the radioisotope power‐system working environment. Typically, the fabrication of power systems requires the welding of various components including the structural members made of tantalum alloys. Issues such as thermodynamics, lattice structure, weld pool dynamics, material purity and contamination, and welding atmosphere purity all potentially confound the understanding of the differences between the weldment properties of the different tantalum‐based alloys. The objective of this paper is to outline the th...

Observation of ionic sodium uranate precursors in a laser simulation of the conditions inside the bubble formed in an HCDA of an LMFBR

The conditions inside the bubble formed in a hypothetical core disruptive accident (HCDA) of a liquid-metal fast breeder reactor have been simulated with a LAMMA 500 laser microprobe mass analyzer. Results for Na/sub 2/U/sub 2/O/sub 7/ show that negative diuranate and positive sodium uranate ions are produced. Higher laser powers favor greater fragmentation to U/sup +/, (UO)/sup +/, and (UO/sub 2/)/sup +/. The Na/sub 2/O/UO/sub 2/ results indicate vapor phase reactions result in the formation of positive and negative sodium uranate ion intermediates. Positive hydrogen ions are observed in some spectra. Higher laser energies (higher HCDA temperatures) favor sodium uranate ion formation. These data support the view that sodium uranate ionic precursors are formed in the vapor phase, bubble, of a simulated HCDA reaction. A prior argon-ionexcited secondary ion mass spectroscopy investigation of Na/sub 2/O/UO/sub 2/ and Na/sub 2/U/sub 2/O/sub 7/ showed no sodium uranate species, only the formation of U/sup +/, (UO)/sup +/, and (UO/sub 2/)/sup +/.