Development of a capillary electrophoresis separation of uranium, plutonium and lanthanides coupled with MC-ICPMS for isotope ratio measurements

Precise isotopic and elemental characterization of nuclear spent fuel is a major concern for the validation of the neutronic calculation codes and waste management in the nuclear industry. The conventional protocol for the analysis of nuclear fuel samples uses several purification steps by liquid chromatography. Uranium (U) and plutonium (Pu) and a fraction containing fission products and minor actinides are separated using ion exchange chromatography prior to the isotopic characterization of the U and Pu fractions by multi-collector mass spectrometry techniques. The objective of the work presented is to develop a new analytical approach based on miniaturized separation techniques like capillary and micro-fluidic electrophoresis coupled with a multi collector inductively coupled plasma mass spectrometry (MC-ICPMS) detection for online isotopic ratio measurements. An electrophoretic separation method of U, Pu and fission products with a stacking step was developed using thorium (Th) as a chemical analog for Pu(IV). The separation electrolyte is composed of acetic acid (0.25 M) as complexing agent for the separation and 0.1 M of ammonium salt to realize the stacking step. The instrumentation was adapted to be used in glove box and directly coupled to a MC-ICPMS. The separation of Am, Pu and U was realized with few nL of a spent nuclear fuel solution. The reproducibilities obtained on the isotope ratios were in the order of few per thousand and comparable with those obtained with the conventional analytical protocol. This new protocol will help to reduce the quantities analyzed from μg to ng, the liquid waste volume scale from mL to μL and the sample volumes form μL to nL. (author)