Evaluation of elevated strontium 89/90 analytical responses -- An investigative study

For a one week period, erroneously elevated strontium 89/90 readouts, up to 1,000 fold, were received from extracted process material analyzed using Liquid Scintillation Counting. The samples were extracted from heavy water waste tanks. While laboratory personnel realized that the responses were higher than historically observed, measurement control indicators were within control limits. An effort was launched to determine probable causes. This paper summarizes those efforts taken to answer: (1) Why did the standard fail to signal an out-of-control method? (2) What were the factors that contributed to the elevated readouts? Additionally, the corrective actions implemented to preclude other occurrences are discussed