Steady-state [gamma]-radiolysis of aqueous 2-butanone (MEK) and its effect on aqueous iodine volatility in containment
Driver, Paul A.
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In the event of a loss-of-coolant accident (LOCA) in a water cooled reactor, a break in the primary cooling circuit followed by fuel failure could release a significant fraction of the core inventory of radioactive iodine into containment. Non-volatile aqueous iodide may be converted into volatile I$\sb2$ and subsequently released into the environment. This process has been shown to be affected by the radiolytic breakdown of dissolved organic compounds that may be present in containment. In this study, the effect of a model organic compound, 2-butanone (methylethylketone, MEK), on iodine chemistry was investigated. In this work, MEK was $\gamma$-irradiated in aqueous solutions and the formation of decay products were followed by a various analytical methods (HPLC, GC, GC/MS and MS) to establish a decay profile. For aerated solutions, MEK degradation produced products, of continually decreasing size. In contrast, in non-aerated solutions where hydroxyl radical was not scavenged evidence of dimerization was observed. Under aerated conditions the main pathway for radiolysis is the abstraction of a hydrogen atom by hydroxyl radical attack to give MEK radical which undergoes reaction with dissolved oxygen, producing an organic peroxide. This species recombines to form a tetroxide intermediate that subsequently dissociates to form carbonyl compounds. Based on this understanding and literature data, a hypothetical decay pathway for the breakdown of MEK under aerated conditions was postulated and used to create a computer model of MEK decay. (Abstract shortened by UMI.)