Preliminary studies of dynamic regimes in the extraction-scrubbing groups of units of the experimental and demonstration center (EDC) using mathematical modeling

Abstract

The plutonium accumulation in the extraction-scrubbing cascade in the course of reprocessing of spent nuclear fuel from water-cooled water-moderated energy reactors (WWER) via the combined flowsheet of the RT-1 plant of Mayak production association and via the flowsheet of the Experimental and Demonstration Center (EDC) of the Mining and Chemical Combine, with transformation of the scrubbing section into a zirconium stripping unit, was compared using a dynamic model of extraction processes. The limiting level by which the productive capacity can be increased without emergencies is ∼15% for RT-1 and 22% for EDC. In the latter case, the accumulation with the potential discharge of a part of Pu into the Zr strip occurs in the third stage of the Zr stripping unit, which is confirmed by rig trials and can be detected in practice by neutron control method because of the absence of Am and Cm. Complete recovery of Zr without its accumulation in the extraction section can be ensured by its coextraction with the Cr(VI) anion fed as a separate small stream. Stopping this stream leads to a reversible decrease in the Zr recovery and to a sharp increase in the entrainment of aqueous microemulsion containing 137Cs. This fact confirms the assumption that the Zr extraction in the cascade in the presence of U and at increased HNO3 concentration has micellar character [without Cr(VI)].