Aqueous phase reactions of iodine

Iodine in water can be present in a number of chemical forms including the familiar iodide ion, r, the volatile form, l2(aq), and the highly oxidised iodate ion, lOs, as well as a munber of transient forms with oxidation states intermediate between those of the more familiar forms. Even under normal conditions, there is some tendency for interconversions among these forms, but the conversion processes can be glacially slow under normal conditions. A radiation field can greatly accelerate the formation of various chemical forms of iodine in water. Products of water radiolysis can oxidise the iodide ion to form molecular iodine following a reaction scheme that is summarily described by  

The production of the key reactant, the hydroxyl radical ( OH), increases with increases in the radiation dose rate to the water. The dose rate to the water depends, of course, on the total amount of fission products and other radionuclides that escape the core and enter the containment. Dose rates to sump waters will vary depending on the type of reactor, the type of accident and with time following an accident. Typical values will be in the range of 1 to 20 kGy hr.  

The molecular iodine in water can disproportionate and other products of water radiolysis can reduce it back to iodide  

These reactions that destroy aqueous, molecular iodine depend strongly on the pH of the solution. The rates of reactions (5) and (7) increase significantly with temperature. Because the of these reactions that destroy l2(aq) and the reactions of iodide with radiolysis products that form l2(aq), a steady state concentration of this volatile form will develop in the solution. 

The equilibrium constant for this process is usually presented in the form of a partition coefficient, H, which is defined as the ratio of the concentration in the aqueous phase to the concentration in the gaseous phase at equilibrium  

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