Automated Analysis of Radionuclides in Nuclear Waste:  Rapid Determination of ⁹⁰Sr by Sequential Injection Analysis

A rapid, automated, microanalytical procedure for the determination of 90 Sr in aged nuclear waste has been developed. It is based on a sequential injection analysis (SIA) system which rapidly separates 90 Sr from 90 Y, 137 Cs, and other radionuclides. The isolated 90 Sr is then detected on-line with a flow-through liquid scintillation counter. The separation is achieved using a sorbent extraction minicolumn containing a resin (EIChrom, Sr-Spec) that selectively binds 90 Sr as a crown ether complex under acidic conditions. The 90 Sr is eluted with water, mixed with liquid scintillation cocktail, and detected in the flow cell of the counter. Sample 90 Sr activity can be quantified from peak areas, giving linear calibration curves. The instrument can also be operated in a stopped-flow mode for longer counting times. Analyses of aged nuclear waste samples from the Hanford site by the SIA method and a manual method were in excellent agreement: correlation coefficient R = 0.994. Sample analysis by the SIA method is complete in less than 40 min. The advantages of the new 90 Sr analyzer include faster analysis, greater precision, reduced labor costs, and reduced secondary waste. Worker safety is improved because solution handling operations are fully automated and contained.