Comparative tests of the efficiency of sorption-filtering materials for removing radioactive iodine from gaseous emissions

Abstract

Tests of how effectively CH 3 131 I and radioactive iodine are removed from air for the ventillation system of the VVRts reactor are performed. Carbon-fiber materials such as Busofite and fiber materials filled with impregnated OU-A carbon are studied as sorbtion-filtering materials. It is shown that these materials absorb iodine with approximately the same efficiency. The front layer traps I 2 . CH 3 I becomes distributed on several layers of the sorbing assembly. Iodine desorption from Busofite and the fiber material with OU-A is negligible (≤2%) over 114-3000 h. Recommendations are given for the composition of the fiber materials for removing iodine from air.The main components of gas-aerosol emissions from a nuclear power plant are radioactive inert gases, aerosols of radioactive fission products and activated products of corrosion, and volatile compounds of radioactive iodine. The most dangerous radionuclides from the radiation standpoint are 131 I and its volatile compounds [1,2].Filters of the type A-17 and D-23 (FPP and FPA-15 filtering materials) and AUI-1500 iodine adsorbers, equipped with SKT-3I granular activated charcoal, are ordinarily used to remove radioactive aerosols and gaseous forms of iodine from the gas-aerosol media of a nuclear power plant. SKT-3 carbon is impregnated with KI and various amines (TEDA -triethylenediamine, hexamethylenetetramine, and other substances) and/or AgNO 3 . Thermoxide (TiO 2 ), siloxide (SiO 2 ), and zeolites impregnated with AgNO 3 are used to remove iodine from gaseous media at temperatures above 100°C [3][4][5][6][7][8][9]. However, the fiber filtering materials used thus far have drawbacks. In practice, Petryanov filtering fabric based on perchlorovinyl polymer fibers in moist media becomes wet and loses its filtering properties. FPP material does not meet the fire safety and toxicity requirements [10], since it is combustible, and toxic substances are formed when it burns.Analysis of the efficiency of filters and carbon adsorbers, operating in the special ventilation systems of a nuclear power plant, has shown that the systems for removing aerosols and volatile compounds of iodine from steam-air media need to the improved because the removal efficiency is low and does not meet modern requirements [10,11]. The removal efficiency is 93-96% for radioactive aerosols and 28-94% for volatile forms of iodine but in most cases it is 67-83%. The low iodine removal efficiency is due to, among other things, inadequate sorption efficiency for organic forms of iodine sorbed by SKT-3 activated carbon and the possibility that these forms of iodine are not sorbed.

Porous sorbents for the capture of radioactive iodine compounds: a review

“…To increase the iodine adsorption capacities of activated carbons, these materials are impregnated with TEDA with a concentration of usually between 0 and 10 wt%. 6,17,27,57,148,151,156,157 However, a decrease in the accessibility of the surface and pores was observed by Chinn et al 158 and González-García et al 147,157 when the TEDA concentration was increased, which can be explained by the formation of TEDA clusters that blocked the entrances of pores. However, despite this phenomenon, it has been recognized that the presence of TEDA in activated carbons increases their iodine capture capacity (especially for CH 3 I).…”

Adsorption of gaseous radioactive iodine by Ag/13X zeolite at high temperatures

“…Although there are reports for adsorbing radioactive iodine at lower temperatures with high adsorption capacities [25][26][27][28][29], there is a lack till now for adsorbents with good radioiodine adsorption capacities at higher temperature (about 600°C). However, the need of capturing radioactive iodine in the condition of nuclear accidents or in the core is increasing, especially after the nuclear accident at Fukushima, Japan in 2011.…”