A holdup measurement campaign is in progress at the Oak Ridge Y-12 Plant as part of facilitydeactivation. When holdup measurements confirm that all significant deposits have been removed,the building’s physical security and nuclear criticality controls can be downgraded.In this campaign, holdup measurements are “endpoints-driven”. Process equipment in the facilityhas been divided into several subsystems, each subsystem corresponding to an endpoint in thefacility’s deactivation plan. Holdup in each subsystem is quantified individually; results arereported to the program manager and reviewed for nuclear criticality safety impact.Before making measurements, analysts and process engineers inspect each equipment unit andidentify its boundaries. Photographs and drawings are made. A gamma ray detector/ratemeter isused to identify “hot spots” in the equipment. Ratemeter readings are recorded on the drawings.The equipment is mathematically modeled as a combination of points, lines, and areas using theGeneralized Geometry Holdup model. Bar code labels are attached at appropriate intervals, andquantitative measurements are made. Data are analyzed and preliminary results are calculated. Theresults are assessed and corrections are applied if warranted. Corrections may include finite sourceand self-attenuation corrections and corrections for spectral interferences.Spectral interferences may occur if the uranium has been irradiated in a reactor. Pb-212, acommonly occurring contaminant, emits a gamma ray at 238 keV, which interferes with the 186-keV signal from U-235 in low-resolution spectra. The two gamma rays may be resolved usinghigher-resolution cadmium-zinc-telluride detectors.A typical piece of equipment may require 100 measurement points for proper characterization.Each measurement requires about 50 parameters including calibration, quality control, andgeometric correction factors. Due to the large amount of data, measurement parameters are trackedusing the HMS3 database manager developed at Y-12. HMS3 also computes results, prints reports,and tracks completion status.This paper will discuss the measurement process in detail, and relate field experiences. Spectra willbe displayed illustrating the Pb-212 problem.
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