Experimental study of nuclear workplace aerosol samplers

Abstract

Monitoring radionuclide effluents has historically been recognized as an important operational activity and a mandatory requirement. US DOE facilities generally require that a continuous air monitor (CAM) instrument be installed to provide an alarm for safety purposes, and that a fixed air sampler (AS) be installed to provide emissions quantification information for both compliance and liability functions. It is very important that aerosol losses in the sampling systems be minimal for the Cams to provide prompt and reliable alarms and that FASs yield data that accurately characterize the emissions. Recognizing that the particle sampling characteristics have a significant role in determining the ability of sampler to properly signal an alarm, this study was conducted to characterize the collection efficiency of aerosol sampler systems as affected by variations in particle size and sampler flow rate. The results presented deal with the aerosol sampling aspects of an overall sampling system, which consists of an inlet-elbow, a transport line, and a EL-900 CAM prototype manufactured by EG&G. Results show that only 12% of 10 []m aerodynamic diameter (AD) aerosol particles penetrate through the complete sampling system when it is operated at flow rate of 84.9 L/min in a free stream velocity of 9 m/s. About 88% of the losses occurred on the internal walls of the inlet-elbow probe and about 10% in the transport line. The EL-900 has a cutpoint larger than 20 []m AD and a penetration of 88% for 10 m AD aerosol particles when operated at 84.9 L/min. Deposition of 10 []m AD aerosol particles at the EL-900 take place primarily in the center of the filter, where the counting efficiency of the detector is highest. A FAS has been developed for sampling radionuclide aerosol particles from the workplace. Wind tunnel testing was used to verify sampling performance. When the sampler was oriented at O' over various ranges of free stream velocities, sampling flow rates and particle sizes, the aspiration efficiency of aerosol was typically greater than 95%. The aspiration efficiencies varied from 80% to 106% for 10[]m AD particle over the previously noted range of free stream velocities and inlet orientations.