A new approach to performing holdup measurements on glove box exhausts

A new measurement technique has been developed for quantifying plutonium holdup in process glove box exhausts. This technique has been implemented at Rocky Flats with a shielded, collimate bismuth germanate (BGO) gamma-ray detector. Measurements along the duct are made in pairs. The detector is positioned for an upward view of the deposit from two inches below the duct, and for a downward view from two inches above it. When the detector is placed in the bottom assay position, the area of the holdup material is assumed to extend beyond the detector field of view. A model has been developed that relates the deposit width to the ratio of the count rates measured at two positions, above and below the duct. Once a deposit width has been deduced, it is multiplied by the area-source assay result from the bottom measurement to yield a mass-per-unit-length at that duct location. Total plutonium (Pu) mass is then determined by multiplying the duct length by the average of the mass-per-unit-length assays performed along the duct. In this paper the technique's applicability is presented in a comparison of field measurement data to analysis results on material removed from the ducts