Technical Justification for Using the Presence of Cs-137 Identified in Whole Body Counts as a Flag for Undertaking In Vitro Analysis of Sr-90/Y-90 at the INL

S. McCord¹; B. Anderson²; P. Ruhter²; and R.R. Brey¹ (¹Idaho State University - Dept. of Physics/Health Physics Program; ²Idaho National Laboratory)

It has been argued that if the ratio of Sr-90/Y-90 to Cs-137 in contamination is well characterized and less than 5 to 1, then Sr-90/Y-90 urine analysis need not be performed except if Cs-137 is detected during a whole body count. The argument is based upon three assertions: 1. Experience has indicated that rarely, if ever, has there been an uptake of strictly Sr-90/Y-90 in the absence of Cs-137 at the INL. 2. The composition of radioactive contamination at most of the INL facilities is best described as mixtures of different radionuclides varying as a function of the chemical and physical processes inherit at each facility. 2. Ratios of the various radionuclides comprising the radioactive contamination at the INL facilities may be well characterized. With a 2.0-nCi 137Cs MDA, and limiting protocol application to a less than 10 to 1 ratio, there would not be an opportunity to miss a significant (> 100 mrem CEDE) Sr-90/Y-90 exposure even if the bioassay occurred 1-year post bolus intake. We verify these assertions and conclude that the protocol is technically justified. Cs-137 may serve as an indicator of Sr-90/Y-90 contamination if bioassays are performed within 20 days of intake.

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