Electrofibrous prefilters for use in the nuclear industry

High efficiency particulate air (HEPA) filters are used in the nuclear industry to remove radioactive aerosols. Although these HEPA filters are effective and practical devices, they generate a large volume of radioactive waste and are costly to purchase and operate. In an effort to reduce the HEPA's operational cost and volume of radioactive waste, the Department of Energy (DOE) has contracted with LLNL to develop electrofibrous prefilters to extend the service life of HEPA filters. A comprehensive program has been established to conduct theoretical modelling, small-scale laboratory experiments, prototype development and field evaluations of electrofibrous prefilters. The recent prototype development and field evaluations of this program are reviewed. Compared to a conventional fibrous filter, the electrofibrous filter has a much higher efficiency and a greater service life. The higher efficiency results from electrostatic forces that attract particles to the filter fibers. This electrostatic attraction also causes particles to form a less restrictive deposit around the fibers thereby increasing the filter service life. The electrofibrous filters discussed are generated by applying an electric field across a conventional fibrous filter. Prototype electrofibrous filters have been developed for use in glove boxes and ventilation systems. The results from two field evaluations in radioactive glove boxes indicate the electrofibrous prefilter greatly increases the service life of HEPA filters. In addition, these evaluations show that most of the radioactive material can be recovered from the prefilter