Interaction of Hydrogen Peroxide With Carbon Steel and Magnetite
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Interaction of Hydrogen Peroxide With Carbon Steel and Magnetite Javier Gimenez1, Ignasi Casas1, Rosa Sureda 1, Joan de Pablo1,2 1 Chemical Engineering Department, Universitat Politecnica de Catalunya, 08028 Barcelona, Spain 2 Environmental Technology Area, CTM-Centre Tecnologic, Av. Bases de Manresa 1, 08240 Manresa, Spain ABSTRACT Hydrogen peroxide is considered as one of the main oxidants formed due to the radiolysis of water. In a spent nuclear fuel repository, it is necessary to establish the interaction of hydrogen peroxide with the elements constituting the repository. The objective of this work is to study the consumption of hydrogen peroxide via reaction with the elements of the canister. In this sense, two different series of experiments were conducted, with iron steel an magnetite, respectively. Each series consisted on three different experiments that contained a coupon of the solid and different hydrogen peroxide concentrations (10-4 mol·dm-3, 10-5 mol·dm-3 and 10-6 mol·dm-3). Hydrogen concentration in solution was measured at different intervals of time by means of chemiluminescence. At the end of the experiments, the coupons were studied by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) in order to determine the possible secondary solid phases formed on the coupons. In both series of experiments, a decrease of the hydrogen peroxide concentration in solution with time was observed. The determined consumption rates increased with hydrogen peroxide concentration and were higher in steel than in magnetite. The reaction orders relative to hydrogen peroxide concentration were very close to the unity on both solids. The study of the carbon steel coupons by SEM at the end of the experiments showed that they were more attacked at higher hydrogen peroxide concentrations. On the other hand, the XRD measurements in the steel coupons showed that lepidocrocite (γ-FeO(OH)), and magnetite (Fe3O4) were formed on the coupon as iron secondary solid phases.
INTRODUCTION The performance assessment of the spent nuclear fuel (SF) in a high-level nuclear waste repository requires knowledge of the processes that might influence its behaviour on a time-scale up to millions of years. Under anoxic or reducing conditions, the processes that affect the dissolution of UO2, the main SF component (~95%), are: (1) radiolysis of water by the α, β, and γ radiation emitted by the SF, which creates both reducing and oxidizing species in solution, (2) oxidation of the fuel surface by the oxidants produced in the radiolysis of water, (3) dissolution of the U(VI) formed on the SF surface by complexing ligands present in groundwater, and (4) precipitation of U(VI) secondary phases [1-3]. The main molecular-oxidizing species formed as products of water radiolysis are oxygen and hydrogen peroxide [4-6]. Experiments under anoxic conditions point to H2O2 as the main oxidizing species for the fuel surface [7]. Consequently, the interaction of hydrogen peroxide with the SF is an important process in the near-field. However, hydroge
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