Speaker
Description
One of the ways for diminishing risks during storage and burial of Purex-process HLW, which are arising from high heat evolution by -emitting 90Sr & 137Cs, is recovery of long-lived TPE radio-nuclides, especially 241+243Am, which could be recycled in NFC by inclusion in the fuel for fast reac-tors. Commercial TPE partitioning in Russia has been carried out and developed using fluorinated diluents, such as metanitrobenzotrifluoride (F-3) [1]. They are recognized now as corrosion activa-tors at HLW evaporation due to their destruction products generated by radiolysis and hydrolysis. So, the progress in TPE partitioning is connected with the use of non-halogenated diluents.
The goal of this work was TPE and RE partitioning by solvent extraction with dropping of Cs & Sr to raffinate in the frames of the joint extraction cycle of Modified Purex-process using the sin-gle TBP solution in paraffine diluent as a solvent. The influence of component concentration on the effectiveness of 241Am & 154Eu extraction by 30% and by 50% TBP in hydrocarbon fraction C13 from nitric acid solutions in the presence of salting-out reagents (ammonium, aluminum and iron ni-trates with nitrate-ion concentration up to 6 mol/L) has been investigated in the course of laboratory scale experiments.
The parameters of the above combined process have been optimized computer simulation us-ing the model developed in KRI. It has been shown that 50% TBP in hydrocarbon diluent is the limiting composition of the single solvent for the Modified Purex-process. It is the maximum TBP concentration in the 1st extraction cycle which does not lead to the phase inversion and to increase of U backwash specific volume. At the same time, it is the minimum one for efficient TPE recovery from evaporated HLW raffinate of the 1st cycle in the presence of salting-out reagent, which could further form a matrix for HLW immobilization.
Rig trials on TPE and RE recovery from real bottoms solution after evaporation of HL raffi-nate generated in WWER-1000 fuel reprocessing have been carried out in the hot cells using mixer-settler units. The flowsheet has included TPE&RE extraction, solvent product scrubbing, backwash-ing and solvent regeneration. The HLW feed has been adjusted by metallic iron dissolving in the feed solution up to salt concentration 1 mol/L for both decrease of acidity and forming of the salt-ing-out agent. TPE and RE were recovered by 99.98% and further backwashed by weak nitric acid solution with decontamination factor from 137Cs up to 7500. The patent application has been filed.
The further investigations would be devoted to TPE and RE partitioning, their concentration during backwashing and to testing of the single-solvent hybrid extraction cycle.
