Experimental Analysis of Plutonium Product and Raffinate Waste Streams from a PUREX Process on A Low Burn-Up, Fast Neutron Irradiated DUO2 Pellet

Abstract

Experimental investigations of separating actinides (uranium and plutonium) from fission products (FP) were conducted using a modified Plutonium Uranium Recovery by Extraction (PUREX) process. The sample under investigation was a low-burn-up (< 5 GWd/tHM), depleted uranium dioxide (DUO2) sample (~13 mg) irradiated in a fast neutron spectrum in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL).

The objective of the study was to quantify the fission product decontamination factor for PUREX process steps while separating and purifying plutonium. Aliquots of the dissolved neutron-irradiated DUO2 sample containing FPs and near weapons-grade plutonium (~ 89% 239Pu), underwent three modified PUREX decontamination cycles with products (organic and aqueous solutions) from each process step being analyzed via high-resolution gamma spectroscopy.

The purification cycle consisted of tri-n-butyl-phosphate (TBP) and kerosene contacted with the feed solution aliquot to extract actinides (plutonium and uranium primarily) from feed to organic phase and further actinide (plutonium only) back-extraction using ferrous sulfamate. Fission product elements, cesium (by measuring 137Cs) and cerium (by measuring 144Ce) were determined to be the most readily removed elements from the product stream when analyzing a whole plutonium purification cycle. The nuclides that posed the greatest difficulty in removal included zirconium (by measuring 95Zr) and ruthenium (by measuring 106Ru) through the 1st cycle of the purification.

The results of this study could be useful in nuclear forensics analysis in the event of a plutonium smuggling interdiction or reprocessing plant inspection. This is because individual element decontamination factors will aid in nuclear forensics while examining the trace fission product contaminants in the smuggled plutonium.