DESIGN AND OPERATION OF A WIDE RANGE SEGMENTED GAMMA RAY SCANNING ASSAY INSTRUMENT FOR THE MEASUREMENT OF BOTH LOW AND INTERMEDIATE LEVEL WASTE

摘要

This paper describes the design and operation of a Wide Range Segmented Gamma ray Scanning (WR-SGS) assay instrument for the measurement of both Low and Intermediate Level Waste (LLW and ILW) in 200 and 340 litre drums and other waste containers. The instrument employs a single shielded and collimated high purity germanium (HPGe) detector to quantify the radionuclide content of the waste. A novel feature of the instrument is the use of an automated variable aperture collimator, which allows the vertical segment height to be adjusted. Conventional SGS measurements may be performed where the drum is rotated and measured in vertical segments. Alternatively, faster measurement can be made using continuous helical scanning of the drum as it rotates. Very high activity drums can be measured through the use of the variable aperture collimator. A gamma ray emitting transmission source is used to correct for waste density. In place of a conventional shutter the shielded transmission source is moved to a shielded storage position to eliminate background radiation arising from the transmission source. Using this approach, higher activity transmission sources may be used in order to achieve adequate density corrections for higher density drums. The various features of the WR-SGS make it applicable to the measurement of both very low and very high activity waste drums as well as waste drums with a wide range of density. Results will be presented from a variety of test drum and waste drum measurements.