Year
2015
Abstract
This paper describes the design, development and testing of an updated and automated segmented gamma scanner (SGS) for measuring radioactive waste generated at a nuclear power station. The instrument retains the capabilities of the original SGS developed by Parker and Martin at the Los Alamos National Laboratory and now widely used for radioactive waste assay. It also incorporates additional features to improve measurement efficiency and reduce cost. These features include continuous helical scanning of the waste drum, the use of a single lifting pillar to move both the detector and transmission source and a re-designed SGS collimator and both transmission source shield and transmission source shutter mechanisms. Updated motion control electronics, based on the use of a programed logic controller (PLC) have been incorporated to address potential future obsolescence. The SGS employs a 40% high purity Germanium detector with electro-mechanical cooling and state of the art digital spectroscopy counting electronics for gamma ray spectrum data acquisition. Testing of the unit has been performed with both point sources and rod sources, which are traceable to international standards. Typical test drums, each with six distributed re-entrant tubes and with different density matrices, have been employed with the rod sources to validate both the calibration and the measurement performance of the SGS for drums of different density. Benchmarked Monte Carlo MCNP calculations have been performed and the calculation results agree and confirm the replicated measurement results for a variety of drum density configurations.