The radiation chemistry of iodine is as complex as nitrogen chemistry. Iodine can exist in several stable and unstable chemical forms in aqueous solutions, particularly at very low concentrations similar to those normally observed in reactor coolant. The effect of gamma-ray radiation on the I-131 activity in aqueous solutions was investigated in a laboratory study at ambient temperature.(18) The I-131 activity in the iodide (I) form was found easily oxidized to iodate as a result of high intensity (>105 R/h) gamma-ray irradiation. The chemical yield of was found to vary with water pH, dose rate and concentration. Thermodynamically the primary oxidizing species, OH and HO2 (oxidation potentials are 2.8 and 1.35 V, respectively)(19) are capable of oxidizing all iodine species to and, in the core region, the concentration of OH is expected to be higher than iodine species in the coolant. Thus, the mechanisms may consist of successive oxidation of iodine by OH, with I, IO, HIO, IO2, and HIO2 as possible intermediate species. The reactions may be represented by:

A number of studies on the chemical behavior of radioiodine in the BWR system have been reported.(20) The results of those studies are summarized in Section 8.3.

6.8 REFERENCES

(1) C.C.Lin “An Overview of Radiation Chemistry in Reactor Coolants”, Proc. 2nd. Int. Symp. Environmental Degradation of Materials in Nuclear Power Systems—Water Reactors.” Monterey, California, p. 160, (September 1988).

(2) C.J.Hochanadel, J. Phys. Chem., 56., 587 (1952).

(3) A.O.Allen, et al., J. Phys. Chem., 56., 575 (1952).

(4) See for example, I.G.Draganic and Z.D.Draganic “The Radiation Chemistry of Water” Academic Press, New York (1971).

(5) W.G.Burns and P.B.Moore, “Radiation Enhancement of Zircaloy Corrosion in Boilng Water System. A Study of Simulated Radiation Chemical Kinetics”, Water Chemistry of Nuclear Reactor System 1, BNES, paper 33, 229 (1977); private communication (1991).



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