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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.

Carbon filters--adsorbers are used in the third and fourth power-generating units of the second phase of the Leningrad nuclear power plant for catching gaseous and aerosol forms of radioactive iodine. They are installed in VTs-4 and -8 ventilation systems, where air enters from the space below the equipment and enclosures of the bottom water pipes, blowoff from the stub of the unloading-loading machine and the tank for emptying it, as well as cases with nonhermetic fuel assemblies. The airflow into ventilation systems equals 2300-8300 m3/h or, on the average, 6000 m3/h [I]. Iodine filters are installed three to four filters in parallel. The temperature of the filtered air equals 60-70~ and the relative humidity equals 90% (at 20 ~ The AUI-1500 carbon iodine absorber has the following characteristics: capacity (with velocity in the free cross section 0.4 m/sec) 1500 m3/h, height of the adsorption layer 40 cm, carbon mass 200 kg, absorber resistance 2.35-2.55 kPa, working temperature <60~ and dimensions 131.5 x 115 x 81.25 cm. Impregnated SKT-3I activated carbon is used as the adsorbent. The rated efficiency of radioiodine removal equals 98-99% [2]. However, this carbon is not produced commercially. For this reason, prior to August 1996 in the case of the fourth power-generating unit and up to now in the case of the third power-generating unit, AUI-1500 filters were filled with nonimpregnated SKT-3 carbon with the following characteristics [3]: bulk density 0.472 g/cm 3, apparent density (no voids) 0.75 g/cm 3, specific surface area 1100 m2/g, and fractional composition 3.6-1 mm (97%).In designs, the iodine carbon absorbers must meet several requirements. The adsorber must work in the entire temperature and humidity interval characteristic for normal operation and operation during an accident. Ordinarily, the maximum relative humidity is taken to be 98 %. The most important criterion is the duration of the contact (ratio of carbon volume to volume velocity of the flow or the height of the fill to the linear velocity), which should equal 1 sec and longer but not shorter than 0.5 sec. The purification efficiency increases with contact duration [4].The possibility of carbon dust being carried out of the filter imposes an upper limit on the velocity of the gas: the average gas velocity should not exceed 0.6 m/sec. The mass of the carbon fill must be calculated for absorption of iodine in all of its chemical forms. Furthermore, the geometry and dynamic resistance of the fill (the layer must be at least 30-cm high), the exposure dose from radionuclides accumulated in the filter, the ease of replacing carbon in the filter, and the possibility of leakage must all be taken into account.The efficiency of radioiodine absorption in carbon filters in VTs-4 and -8 ventilation systems was determined at the Leningrad nuclear power plant in 1993-1995 (Table 1). The 131,133I concentration in air was measured by the standard method by a team from the OOT and TB Office. The 131'133I removal factor calculated from the ratio K = Cin/Cou...

In the designs of new units for nuclear power plants (of the type NP-500. NP-600) ensure safety in the event of accidents on the basis of passive heat removal from the hermetically sealed zone by providing for an accident pond. The heat removal system is also intended to keep radioactive products, including iodine, within the containment vessel.Up to 99% of the iodine in the coolant of a VVI~R reactor is in the form of an iodide. In the presence of the oxygen in the air the iodide ion is oxidized to molecular iodine and the iodate (IO3-). "II~e ratio of the fotm~, of iodine and the coefficient of its distribution between the aqueous and vapor-gas phases depend on the pH. the reduction-oxidation potential of the medium, the concentration, and the temperature. It is assumed that during accidents the ratio of the forms of iodine in the vapor-gas phase is 10% aerosol form and 90% volatile forms (I2, CH31), including 1% of CH3I.One possible passive method of binding volatile forms of iodine and keeping them in the containment vessel is for polymer coatings to absorb them. Experimental data [1][2][3] indicate that molecular iodine can be absorbed by some types of protective paint coatings, but no systematic studies have been made of the laws governing the absorption of volatile forms of iodine by different kinds of paint coatings.In this article we report the results of a study on the absorption of volatile forms of iodine, 12 and CH3I, from the gas phase by organosilicate and epoxy coatings used in the projects for new units of nuclear power plants.Methodology, The studies were done with:--OS-51-03 organosilicate coatings (technical specification TU 84-725-88) based on a composition consisting of a suspension of pigments, silicates, and metal oxides in a toluene solution of polyorganosiloxane. The hardeners used were tetrabutoxytitanium (TBT) or boron-containing polyorganosilazanes (MFSN-V). which were introduced into the composition at the rate of 0.2-0.3 mass % and 1-2 mass %, respectively; --epoxy coatings based on the enamels I~P-525 (TU 6-10-1790-80) and I~P-574 (TU 6-10-1640-84), which are a suspension of pigments in a solution of epoxy resin (I~-41 and 1~-44) in a mixture of organic solvents with additions of plasticizers and melamine-formaldehyde resin. Polyethylene polyamine, added to the composition at the rate of to I0 mass %, served as the hardening agent.The paint compositions were applied to the specimens in 1 to 3 coats, each coat being dried in air and heated to 100-120~ for 3-8 11. Both sides of the specimen were painted, with the coating covering an area of i0 cm 2.Absorption of iodine from the gas phase by the painted specimens was studied under static and dynamic conditions. In the first case the we used an air-filled container which was constantly saturated with iodine vapor at the given temperature, i.e., under isothermal and isobaric conditions; in the second case we used an arrangement that allowed a constant iodine vapor pressure to be maintained in an air stream. The arrangement included a co...

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