Calorimetry of In Development Dispersion Nuclear Fuels. THOMAS MCDONALD (Northwestern University Evanston, IL 60208) J. RORY KENNEDY (Idaho National Laboratory, Idaho Falls, ID, 83415)

The Reduced Enrichment for Research and Test Reactors (RERTR) project develops new fuels for the conversion of civilian research and test nuclear reactors from high enriched uranium to low enriched uranium fuels and targets. Fundamental physical properties of new fuels are needed to accurately model how the fuels will behave in and out of a reactor. Using a heat flux differential scanning calorimeter, the enthalpy of reaction and reaction onset temperatures were determined for two uranium-molybdenum-aluminum dispersion type fuel mixtures. The reaction onset temperatures for the two fuels were found to be very similar. However, the enthalpy of reaction was smaller for the fuel containing less uranium. These measurements are one of the many steps necessary to qualify new nuclear fuels for the RERTR program, whose aim is to reduce the threat of nuclear proliferation.

Electrospray Mass Spectrometry of Selected Uranyl Amide Complexes. SIGRID BARKLUND (The College of St. Catherine St. Paul, MN 55105) ANITA GIANOTTO (Idaho National Laboratory, Idaho Falls, ID, 83415)

Uranyl complexes are significant for several reasons: they are necessary for the actinide separations needed to produce fuel for nuclear energy, have untapped catalytic potential, and play a major role in solution phase chemistry influencing movement in the environment and living systems. Amides are important functional groups in both advanced extraction agents and complex biomolecules, so amide interactions with actinides are of interest. The presence of closely spaced d and f orbitals enables formation of multiple, interconverting species, making experimental studies complicated. Coupled with radioactivity and toxicity concerns, this has motivated utilization of computational chemistry (high-level density functional theory (DFT)) for the investigation of actinide-ligand coordination complexes. However, computational efforts have not been verified by experimental data. Here, trapped-ion mass spectrometry is used to evaluate the extent of coordination and ligand binding preference in uranyl ([UO₂]²⁺) complexes. A Finnigan LCQ-Deca XP Plus electrospray ion trap mass spectrometer was used to identify the composition of sprayed [UO₂(anion)(amide)_n]⁺ complexes using collision-induced dissociation. Six amide ligands of increasing nucleophilicity were compared: formamide (F), N-methylformamide (NMF), N,N-dimethylformamide (DMF), acetamide (AA), N-methylacetamide (NMA), and N,N-dimethylacetamide (DMA). Tetraligated [UO₂(NO₃)(F)₃]⁺ adducts underwent extensive substitution of weakly basic MeOH and water, indicating that F is weakly bound. NMF and AA also form [UO₂(anion)(amide)₃]⁺ complexes, but because NMF and AA are stronger nucleophiles, there is little solvent substitution. DMF, a much stronger base, shows almost no solvent substitution in the anion complexes, and forms abundant doubly charged ions, suggesting that it is outcompeting the anions for uranyl coordination sites. These trends continue for NMA and DMA, even stronger nucleophiles. Although no calculations on the uranophilicity of the simple amide ligands exist, it was expected that they would echo the proton affinity values. In the gas phase with all solvent effects removed, the intrinsic order of amide uranophilicity mirrors proton affinity. These conclusions will be compared with those generated using DFT calculations, which are currently underway.