Change in the pH of NaI and methyl alkyl ketone solutions under gamma irradiation
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Change in the pH of NaI and methyl alkyl ketone solutions under gamma irradiation Minsik Kim1 · Sue Young Hong1 · TaeJun Kim1 · Sang‑Hyuk Jung1 · Jei‑Won Yeon1 Received: 14 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The effects of dissolved chemicals such as NaOH, NaI, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) on solution pH after gamma irradiation were investigated. Upon irradiation with 1.6–24 kGy of gamma radiation (0.4–6 kGy h−1), the pH of the NaOH solutions decreased, while the O H− consumption increased with increasing initial solution pH. This was attributed to acid–base neutralization between the OH− in the solutions and the acidic species (HO2· and ·NO2) formed by irradiation. The pH of the acidic NaI solution increased after irradiation with 8 kGy dose (at 2 kGy h−1), which was attributed to I− oxidation by the products of water and air radiolysis. The pH values of the MIBK and MEK solutions decreased from 7 to 4.5 or lower upon irradiation with 40 kGy dose (at 10 kGy h−1), which indicates that the alkyl groups of the ketones do not significantly affect the rates of decomposition by irradiation. The pH of the mixed solution of ketone and NaI was in the range of 6.7–6.9 before irradiation but decreased to 4.5 after irradiation with 40 kGy dose. In the mixed solutions, CH3COR and I− competed with each other to contribute to pH change. Keywords Iodide · Methyl alkyl ketone · pH · Gamma irradiation · Methyl isobutyl ketone · Methyl ethyl ketone
Introduction The behavior of radioactive iodine is an important subject in the field of nuclear safety in view of the severe accidents that have occurred at nuclear power plants. This behavior is because iodine radionuclides are highly radioactive, eas‑ ily vaporized, and well absorbed by the human body [1–7]. Radioactive iodine is generally released as an iodide salt and iodine oxide aerosol from damaged fuels [1–5, 8, 9]. Then, the iodide in the emergency core cooling system dissolves in the coolant and radiolytically oxidizes into I 2. Moreover, under irradiation, I 2 converts into volatile organic iodides such as CH3I by reacting with organic materials such as the paints [10–16] in the containment building. Among the various organic materials, methyl alkyl ketones (CH3CORs) Minsik Kim and Sue Young Hong have contributed equally to this work. * Jei‑Won Yeon [email protected]; [email protected] 1
Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, 989‑111 Daedeok Daero, Yuseong‑gu, Daejeon 305‑353, Republic of Korea
such as methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK) mainly originate from paint thinner trapped in the paint matrix [12–17]. Further, the pH of aqueous solutions is one of the critical factors that affect the equilibria and rates of chemical reac‑ tions since most reactions generally involve H+ or OH− ions. The volatility of I 2 under gamma irradiation depends on the solution pH [1, 2, 4, 5, 11–14, 18–21] since the formation and decomposition reaction
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