Demonstration of an Instrument for On-Line Measuring of the Alpha Radiation

The Salt Waste Processing Facility and the Actinide Removal Process at the Savannah River Site will remove alpha emitting radioisotopes from High Level Waste to meet regulatory disposal requirements. The removal occurs prior to removal of the radioactive cesium. Both facility designs currently include verification measurement using conventional wet chemistry approaches remote from the operation. Use of an on-line monitor for this purpose offers the opportunity to shorten process cycle time and thereby increase facility throughput. Personnel from Pacific Northwest National Laboratory designed, built, and functionally tested an on-line monitor, which is capable of measuring the residual transuranic concentrations in processed high-level wastes with a detection limit of 370 Bq/mL (10 nCi/mL) in less than six hours. Personnel from Savannah River National Laboratory assisted in the design and tested the equipment using actual waste. The monitor measures the neutrons produced by the transuranics in the presence of gamma-ray fields up to 1 Sv/h (100 R/h). The optimum design derives in part from Monte Carlo modeling tempered with practical engineering and cost considerations. We demonstrated operation of the monitor in a cell utilizing an actual sample of high-level waste. Results of that demonstration are given, and suggestions for improvements in the next generation system are discussed. Primary findings include the following. The waste used for the demonstration contained entrained organic from a prior solvent extraction demonstration as well as precipitated fine particles. Settling of the solids during the experiments complicates interpretation of the results. The equipment operated without incident. The dynamic response of the equipment exceeded the design requirement suggesting on-line measurements in much less than the requested 6 hours are possible. Until the equipment is tested in a flow through configuration, we can not quantify the response time. In the demonstration that most closely approximated proposed operational conditions, the monitor gave slightly positive bias in results when compared to conventional wet chemistry results, i.e., 76.7 nCi/g versus 61.1 nCi/g. Flushing of the equipment between demonstrations indicated incomplete removal of the residual sample. As much as 5 percent residual contamination occurred in the most representative demonstration. This value does not represent the behavior in actual deployment within a flow-through system that has a high-velocity flush system