Characterization of Surface Contamination in 56 Rooms of a Decommissioned Radiological Laboratory
K.E. Meyer (Canberra Oak Ridge, LLC)
In-situ high-resolution gamma spectroscopy was used to characterize residual radiological contamination on walls, floors, and ceilings in Building 107, a mixed-use (office/laboratory) facility undergoing decommissioning at the AECL Chalk River Laboratories. The spectroscopy system consisted of a Broad Energy Germanium (BEGe) detector, a 50mm-thick lead backshield, sideshield, and collimator, a laptop PC, and spectrum acquisition software. Each measurement was modeled and analyzed using In-Situ Object Counting (ISOCS) mathematical calibration software. During the six week campaign, 253 static measurements were performed in 56 rooms, covering a total surface area of 3,733 m2. Counting times were selected to maintain Minimum Detectable Activities (MDA's) below 1.0 Bq/cm2 for beta/gamma-emitting contaminants of concern (137Cs, 60Co, 235U) and below 0.1 Bq/cm2 for alpha-emitting contaminants of concern (241Am), per AECL Radiation Protection guidelines. The counting time used for most measurements was 30 minutes. 137Cs contamination was detected throughout the facility with concentrations ranging from 0.01 to 13.6 Bq/cm2. 60Co was occasionally detected in concentrations from 0.003 to 0.170 Bq/cm2. 241Am contamination was detected at an average concentration of 0.18 Bq/cm2 in one isolated floor section. The Total Measurement Uncertainty (TMU) for this series of measurements is estimated to be ±30%.