Extremely low level waste gamma-scanner and its characters

It is necessary in reactor dismantling that a large amount of radioactive solid waste arising should be reasonably treated and disposed according to the radioactive level of them. An extremely low level waste γ-scanner has been developed for the purpose of efficiently classifing and confirming the extremely low level radioactive solid waste by γ-ray spectrometry. The system which consists of a scanning mechanism of waste container, a couple of HPGe detectors and multichannel analyzers, and a minicomputer system, can measure automatically radioactivity for each nuclide in the wastes such as concrete in the three types of container. Detection efficiency calibration factors of this system are to be decided for each container by functions of γ-ray energy and effective density of waste in the container. A verification test with radioactive standard containers showed that the calibration factors gave precision within 10-percent for typical radionuclides in the homogeneous specimen. The minimum detectable limit of radioactivity concentration of this system is about 7.5 x 10-3 Bq/g for 60Co in 200 l drum container in measuring time of 600 seconds regardless of their density. This system can classify about 1,000 kg of the waste an hour. (author)