Better Shields for Lowering Backgrounds and Decreasing MLDs for Analysis of Pu Bearing Solutions

The Savannah River Site’s FB-line has the requirement to quantitatively measure liquid samples from its processing lines for both operations and MC&A needs. A liquid sample Radionuclide Assay System – Photon (L-RASP) was developed, calibrated, and implemented. Immediately after its implementation, requirements changed from a lower assay limit of 3g/l to 0.1g/l resulting in the development of the Low Level Liquid RASP (L3-RASP). This paper will present the needs for such instrumentation, the solution to the problem of extremely low concentration assays, and the resulting implementation. The need for a lower limit of assay of 0.1 g/l arises from discard limits. Prior to the inception of this instrument, all samples were delivered to SRS’s in-house analytical laboratory for results. This analysis normally required 24 hours. With the use of the L-RASP, results can be obtained in 10’s of minutes rather 10’s of hours. The cost saving to production is evident. The solution to the problem was the development of a tungsten shield/collimator with a cadmium/copper sandwich. The sample chamber was also shielded and moved closer to the detector. The results were better than expected, with Minimum Level of Detections(MLD)s now reaching to 0.005 g/l with an uncertainty of ~5% for a 1000 second assay.