25th DOE/NRC NUCLEAR AIR CLEANING AND TREATMENT CONFERENCE STACK SAMPLER CALIBRATIONS

Tests were conducted to verify that new air monitoring systems at Hanford air exhaust stacks met the Draft HPS/ANSI N13.1 performance criteria developed for air sampling systems at nuclear facilities.(‘) The standard’s performance criteria address both the suitability of the air sampling probe location and the sample transport to the collection devices. The contaminants in a stack must be well mixed with the airflow at the air sampling probe location so that the extracted sample represents the whole. The sample transport criteria ensure that the contaminants are quantitatively delivered to the collection device. The specific performance criteria are described in the report. The new systems tested provide airborne effluent measurements at the Hanford Site in Richland, Washington. The general design features a probe with a single shrouded sampling nozzle, a sample delivery line, and sample collection system. The collection system includes a filter holder to collect the sample of record and optional radionuclide continuous air monitors. The sample collectors are short-coupled to the stack, and the single sample flow is divided with a splitter. The testing was conducted by the Pacific Northwest National Laboratory using full-size or scale-model stack mockups. Tests of candidate sampling probes were made in a wind tunnel. The results compare the performance of single and multi-nozzle isokinetic probes with single shrouded nozzle probes over a range of particle size and air velocity. The shrouded nozzle probes exhibited superior transmission of sampled particles. The velocity and tracer uniformity tests on the mockups demonstrated the detrimental effects of flow straighteners and misalignment of components. Particle penetration tests showed acceptable results for the short-coupled systems and enabled the identification of problem-causing components. The test program showed that the new monitoring systems meet all of the performance criteria for a range of exhauster configurations. The Department of Energy’s Hanford Site contractors are actively implementing single-point sampling methodology in all new and many existing stack monitoring systems. On December 15, 1989, 40 CFR 61, Subpart I-I, “National Emission Standards for Emissions of Radionuclides Other than Radon from Department of Energy Facilities, “(*) came into effect. This regulation required the use of isokinetic probes, as described in ANSI N13 .1-1969.(3) However, recent research indicates poor performance for isokinetic probes and shows improved performance for probes using a single shrouded nozzle. @) These and other results were the motivation for the U.S. Environmental Protection Agency (EPA) recently to approve a DOE petition that allows an alternative method, which uses of a single shrouded probe in applications that previously required a manifold of several isokinetic probes. (‘) In addition, the draft revision to ANSI N13.1 describes implementation standards for single point sampling.