Year
2001
Abstract
The term “holdup” refers to the accumulation of nuclear material inside the processing equipment of nuclear facilities. Process holdup material can accumulate on internal surfaces of pipes, tanks, ducts, furnaces, gloveboxes, and other equipment. It is important to measure holdup material because of the high economic value of nuclear material, the need to ensure radiation safety and criticality safety, and the need to safeguard against theft or diversion [1]. Measurement of nuclear material process holdup in a facility generally requires use of a portable, collimated gamma-ray detector. Either a sodium iodide or high purity germanium detector is used, depending on energy resolution requirements. A collimator, usually made of lead, surrounds all but the front face of the detector and is rigidly fixed with respect to the detector to form a detector-collimator assembly. The collimator is used to limit the field of view of the detector so that gamma radiation from the intended source can be measured in the presence of background radiation from other sources. This detector-collimator assembly can be calibrated for the various holdup measurement geometries for which it will be used[2]. The suitability of a detector-collimator assembly to a particular application is determined by the detector-collimator assembly characteristics and the layout and accessibility of the equipment in which the hold up radioisotopic material is located. A collimator of appropriate design is a tool necessary for making accurate holdup measurements.