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]+.