SINGLE-POINT AEROSOL SAMPLING - EVALUATION OF MIXING AND PROBE PERFORMANCE IN A NUCLEAR STACK

Alternative reference methodologies have been developed for sampling o f radionuclides from stacks and ducts, which differ from the methods p reviously required by the United States Environmental Protection Agenc y. These alternative reference methodologies have recently been approv ed by the U.S. EPA for use in lieu of the current standard techniques. The standard EPA methods are prescriptive in selection of sampling lo cations and in design of sampling probes whereas the alternative refer ence methodologies are performance driven. Tests were conducted in a s tack at Los Alamos National Laboratory to demonstrate the efficacy of some aspects of the alternative reference methodologies. Coefficients of variation of velocity, tracer gas, and aerosol particle profiles we re determined at three sampling locations. Results showed that numeric al criteria placed upon the coefficients of variation by the alternati ve reference methodologies were met at sampling stations located 9 and 14 stack diameters from the flow entrance, but not at a location that was 1.5 diameters downstream from the inlet. Experiments were conduct ed to characterize the transmission of 10 mu m aerodynamic diameter li quid aerosol particles through three types of sampling probes. The tra nsmission ratio (ratio of aerosol concentration at the probe exit plan e to the concentration in the free stream) was 107% for a 113 L min(-1 ) (4-cfm) anisokinetic shrouded probe, but only 20% for an isokinetic probe that follows the existing EPA standard requirements. A specially designed isokinetic probe showed a transmission ratio of 63%. The shr ouded probe performance would conform to the alternative reference met hodologies criteria; however, the isokinetic probes would not.