THE EXTRACTION OF CESIUM AND STRONTIUM FROM ACIDIC HIGH ACTIVITY NUCLEAR WASTE USING A PUREX PROCESS COMPATIBLE ORGANIC EXTRACTANT

Abstract

Purex process compatible organic systems which selectively and reversibly extract cesium and strontium from synthetic mixed fission product solutions containing3M HNO3, have been developed. This advance makes the development of continuous solvent extraction processes for their recovery more likely. The matrix solution from the Purex process consists of tributyl phosphate (TBP) and kerosene. For cesium and strontium recovery a macrocyclic polyether (crown compound) has been developed for each element. When used in conjunction with a liquid cation exchanger in the matrix solution, the crown compounds will extract either alkali metals or alkaline earths from the synthetic mixed fission product solution. The organic cation exchangers used in this research were didodecylnaphthalene sulfonic acid (DNS) and dinonylnaphthalene sulfonic acid (NNS). As was expected both zirconium and ruthenium also tend to be extracted due to the TBP in the matrix solution and to their complex chemistry. The most favorable cesium and strontium complexing solutions have been tested for radiation stability to 107 rad using a 0.4 × 107 rad/hr 60 Co source. The distribution coefficients dropped somewhat but remained above unity. For cesium the comp1exing organic solution is 5vol% (0.10M) NNS, 27vol% TBP and 68vol% kerosene containing 0.05M bis 4,4′,(5′) [l-hydroxy 2-ethylhexyl]benzo 18-crown-6 (Crown XVII). with an aqueous phase containing 0.006M Cs+l in contact with an equal volume of extractant, the Dorg/aq = 1.6 at a temperature of 25−35°C. For strontium the complexing organic solution is 5vol% (0.10M) NNS, 27vol% TBP and 68vol% kerosene containing 0.02M bis 4,4′(5′) (l-hydroxyheptyl)cyclohexo 18-crown-6 (Crown XVI). with an aqueous phase containing 0.003M Sr+2 in contact with an equal volume of extractant, the Dorg/aq 1.98 at a temperature of 25−35°C.