Determining the tube factor of conduits of equipment for aerosol and iodine sampling in the stack of a nuclear power plant

Aerosols and iodine are trapped by fibre filters and mixed-bed filters simultaneously at two points, i.e. at a reference measuring point at the stack, and at the end of a sampling conduit, for subsequent activity measurement. Eighty-eight of such aerosol or iodine filter samples have been examined by gamma spectroscopy after an exposure time 7 days each. In addition, the overall alpha and overall beta activity of the aerosol samples have been measured. The tube factor for gaseous, elemental iodine is determined to be (1.00±0.02), for elemental and organically bound iodine the factor is (1.00±0.03). The tube factor for radioactive aerosols is (2.6±0.1), except for aerosol-borne I-131 and La-140, the relevant factors being (1.3±0.1), and (1.04±0.03). The average tube factor for aerosol-borne radionuclides is (2.5±0.1). Additional examinations have been made on the particle size variation of radioactive aerosols. The largest group with regard to mass and activity is formed by particulates with the size of 0.05 μm - 20 μm in diameter. On the basis of these results, combined with data of sampling systems, - such as length, diameter, and volume flow -, possible losses in aerosol-borne activity are calculated. (orig./HP)