Radionuclide 131I is used as a reference nuclide for monitoring of gas-aerosol emissions. Under the normal operating modes, 131I radionuclide release does not exceed admissible values, however, during conduction of some activities in the plant premises it can exceed admissible levels that can be potentially dangerous for personnel because of high toxicity of the iodine. In case of accident, the population can also be exposed to risk of radiation. The situation is complicated by imperfection of equipment used for monitoring of iodine radionuclide content in the air at nuclear plants. The variety of iodine radionuclide forms that include an aerosol component - molecular iodine (I2) and iodine organic compounds (iodide methyl (CH3I), primarly) is also an issue. The sorption extraction of iodine radionuclides from gaseous atmosphere is used both for cleaning and iodine content control and is basically single option nowadays. The activated carbon or coals, impregnated with iodide potassium, elemental iodine, silver nitrate, triethylenediamine, etc. are widely used for sorption of iodine radionuclides. However, the coal flammability does not allow to apply such sorbents at temperatures over 150 ° C. Mineral sorbents for iodine capturing are being developed for more than one decade, however, the creation of an effective, cheap and long-life sorbent is still not solved. Important aspect of this problem is the selectivity of iodine extraction to inert radioactive gases.
NITI has developed the Siloxide sorbent used for capturing the volatile iodine radionuclides in gaseous atmosphere. Siloxide is not flammable and does not emit volatile toxic components within operating temperature range. The coefficient of iodine selectivity to 133Xe is 2∙105. The sorbent was tested in laboratory and industrial researches for different types of nuclear power plants. The monitor for determination of volume activity of iodine radionuclides in gaseous atmosphere of NPP has been developed: range of measurements is (10-5 – 105) Bq/l with air flow rate of 30 l/min and sorbent volume of 100 cm3. Time of iodine radionuclides release is from 0.1 to 1000 hours. The URAN-10-BGG - monitor for extracting and detecting the iodine radionuclides in the gaseous atmosphere - comprises of Siloxide-based sorption element and scintillation gamma sensor (BDEG type) hooused within uniform lead protection. The monitor has a simple design, sharp selectivity and capability to extract all forms of iodine radionuclide in gaseous atmosphere. The most significant advantage of Siloxide is that it does not occlude inert radioactive gases and is effective even at 100% of humidity. This methodical and hardware solution is applied at NITI reactor research facility, in JSC «SSC RIAR», FSUE "Zavod Medradiopreparat" and on a number of the NPP.