Absorption of molecular forms of iodine from the gaseous phase by protective paint coatings

Abstract

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...

Interaction of water with epoxy.

“…The absorption varied with the partial pressure to the power 0.59. This contrasts with the linear dependence found by Aleksandrov et al [1996] for the absorption of iodine by epoxy paints. Sukawa et al [1987] found that nylon would absorb about 1.7 grams of molecular iodine per gram of nylon from a 0.1 M aqueous solution.…”