Detecting ¹³⁷Cs Breakthrough in an Ion Exchange Process

Abstract

Large volumes of liquid wastes that must be stabilized are one of the legacies of the United States nuclear weapons program. Before these liquid wastes currently contained in holding tanks can be solidified/immobilized, it will be necessary to remove certain high specific activity or potentially dangerous long-lived radionuclides. For example, in the case of high-level liquid wastes, it will be necessary to remove most of the ¹³⁷Cs to ensure that the final waste product is in compliance with the radioactivity limits for disposal. Typical high-level liquid wastes contain between 10 and 500 Ci/m³ of ¹³⁷Cs, and disposal limits for the solidified wastes are expected to be on the order of 1 Ci/m³. The current plan is to selectively remove ¹³⁷Cs from the waste feed stream on an ion exchange column. In order to determine the removal efficiency factors of the column, which must be at least a factor of 20, and to determine breakthrough of ¹³⁷Cs when the column has reached its holding capacity for cesium, it is necessary to measure cesium in the eluent in real time with respect to the process response time for diverting the effluent stream from the immobilization stage back to feedstock. This “real time” value is dependent on the system design, particularly with respect to the buffer time between the ion exchange column and the immobilization stage; it could easily be on the order of minutes.