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 Na₂U₂O₇ show that negative diuranate and positive sodium uranate ions are produced. Higher laser powers favor greater fragmentation to U⁺, [UO]⁺, and [UO₂]⁺. The Na₂O/UO₂ 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-ion-excited secondary ion mass spectroscopy investigation of Na₂O/UO₂ and Na₂U₂O₇ showed no sodium uranate species, only the formation of U⁺, [UO]⁺, and [UO₂]⁺.