Used nuclear fuel (SNF) contains almost one-third of the periodic table. A selective separation of the long-lived actinides (An) from the fission products of intermediate life-time (90Sr, 137Cs, 99Tc, and 131I), and the relatively shorter lived lanthanides (Ln) reduces both the amount and radiotoxicity of the waste. Nonetheless, a fundamental understanding of the thermodynamic properties of complex formation and speciation in solvent extraction systems is needed for the development of advanced spent nuclear fuel reprocessing systems. In this work, methods have been developed using electrospray ionization – mass spectrometry (ESI-MS) to characterize the speciation of U and Pu with tributyl phosphate (TBP) and dibutyl phosphate (DBP) as would be found in the PUREX process. The polarity of the ionization source was altered to observe both positive and negative gas phase ions. U and Pu complexed to TBP resulted in complexes that could be observed as positive ions, but no negative ion species were observed. In contract, U and Pu complexed to DBP could be observed as both positive and negative ions. Using the relative abundance of ions observed in the gas phase, apparent stability constants were calculated to enable comparison of the gas phase species to known solution species. The protocols developed in these studies help determine fundamental actinide complexation chemistry in solvent extraction systems, and demonstrate the potential of ESI-MS for process control monitoring in spent nuclear fuel reprocessing facilities.

Determining speciation of U and Pu in spent nuclear fuel via electrospray ionization mass spectrometry

252nd National Meeting (2016)

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