Abstract
Neptunium (Np) possesses a rich and unique chemistry that often diverges from other actinide elements yet remains relatively underexplored compared with the other light actinides. A resurgence of interest in Np has been spurred by the application of 237Np for plutonium-238 (238Pu) production for use in radioisotope thermoelectric generators (RTGs), necessitating evaluation of Np chemical reactions and materials. The work presented here studied the thermal decomposition of neptunyl ammonium nitrate (NH4NpVIO2(NO3)3) for synthesis of neptunium dioxide (NpO2), which is the target material used for production of 238Pu. Additionally, structural characterization of the intermediate solid Np pentoxide (Np2O5) was performed. Advanced solid-state characterization techniques, including simultaneous thermal analysis (STA), powder X-ray diffraction (pXRD), Raman spectroscopy, and density functional theory (DFT) modeling have been combined to study the reaction pathways. Analysis revealed that NH4NpVIO2(NO3)3 thermally decomposes to a proposed neptunyl nitrate intermediate, followed by Np2O5 and finally NpO2, all within the temperature range of 150 °C-600 °C. Further characterization of the pentoxide intermediate provided the first Raman spectra of pure-phase Np2O5 and associated DFT modeling confirmed Raman peak assignments for this phase. These findings provide mechanistic information to advance production of the critical radioisotope 238Pu and advance the state of knowledge on Np materials chemistry using modern characterization techniques.
| Original language | English |
|---|---|
| Pages (from-to) | 5915-5925 |
| Number of pages | 11 |
| Journal | Inorganic Chemistry Frontiers |
| Volume | 12 |
| Issue number | 19 |
| DOIs | |
| State | Published - Sep 23 2025 |
Funding
This work was supported by the Pu Supply Program at the US Department of Energy's Oak Ridge National Laboratory with funding provided by the Science Mission Directorate of the National Aeronautics and Space Administration and administered by the US Department of Energy, Office of Nuclear Energy, under contract DEAC05-00OR22725. The authors wish to thank Cory Dryman, John Dyer, Kaara Patton, Curt Porter, and Joseph Renfro for their assistance in preparation and sampling of the Np stock used in these experiments. This work was supported by the 238Pu Supply Program at the US Department of Energy's Oak Ridge National Laboratory with funding provided by the Science Mission Directorate of the National Aeronautics and Space Administration and administered by the US Department of Energy, Office of Nuclear Energy, under contract DEAC05-00OR22725. The authors wish to thank Cory Dryman, John Dyer, Kaara Patton, Curt Porter, and Joseph Renfro for their assistance in preparation and sampling of the 237Np stock used in these experiments. This manuscript has been authored by UT-Battelle LLC under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( https://energy.gov/downloads/doepublic-access-plan ).