A leak quantification method using sulfur hexafluoride as tracer gas.

Abstract

Filter holders and continuous air monitors are used extensively in the nuclear industry. It is important to minimize leakage in these devices, and, in recognition of this consideration, a limit on leakage for sampling systems is specified in; however, the protocol given in the standard is really germane to measurement of significant leakage, e.g., several percent of the sampling flow rate. In the present study, we developed a technique for quantifying leakage and used that approach to measure the sealing integrity of a continuous air monitor and two kinds of filter holders. The methodology involves use of sulfur hexafluoride as a tracer gas with the device being tested operated under dynamic flow conditions. The leak rates in these devices were determined in the pressure range from 2.49 kPa (10 inches H2O) vacuum to 2.49 kPa (10 inches H2O) pressure at a flow rate of 56.6 L min-1 (2 cfm). For the two filter holders, the leak rates were less than 0.007% of the nominal flow rate. The leak rate in the continuous air monitors was less than 0.2% of the nominal flow rate. These values are well within the limit prescribed in the ANSI standard, which is 5% of the nominal flow rate. We suggest that the limit listed in the ANSI standard should be reconsidered as lower values can be achieved, and the methodology presented herein can be used to quantify lower leakage values in sample collectors and analyzers.