Retaining capacity of 131 I gas effluents on activated carbon

In order to ensure environmental protection filters with active coal carbon designed for ventilation equipment are currently used in nuclear units in which radioactive iodine or chemical combinations has been produced and/or utilized. Hence, all radioactive working boxes in our department, were provided with active carbon based filter ventilation equipment. Since these filters are being purchased in large quantities, stored for many years and used when needed, it is advisable to assess their quality and efficiency via an analysis prior to their use. The quality parameter of a filter with active carbon is 'adsorption efficiency' which is defined as: Er = 100 RF/R0 where RF and R0 are final and initial counting rates (or activities) of the filters. Another way of expressing the quality of the filter is the 'decontamination factor' defined as: FD = R0/(R0-RF), where (R0-RF) is the counting rate after the passing of air through the filter. The relation between Er and FD will be: Er = 100 (1-1/FD); Experimental installation consists of the following components: filter for air purification; thermostat; air humidifier; air dryer; air-radioactive iodine mixer; generator of methyl radioiodide; column with impregnated active carbon disposed in six separated layers by perforated teflon disks; safety ensuring column filled with active carbon impregnated and disposed in three layers; thermometers, humidly meters, ratemeters; a chain of gamma spectrometry for activity measurement of active carbon samples. The generator of methyl radioiodide has been produced by using the reaction between potassium iodide and dimethyl sulfate: 2131 I- + (CH3)2SO42- → 2131 I CH3 + SO42-. Decontamination or retaining factors increased up to 99,99% were observed from these experiments. (authors)