In Situ Monitoring of Hypochlorite Decay under Radiation Using Differential Pulse Voltammetry

Abstract

Understanding how concentrations of corrosive oxidants evolve under γ-radiation is essential for assessing long-term material performance in nuclear environments. This work integrates in situ differential pulse voltammetry (DPV) with finite-element kinetic modeling to track and interpret the decay of hypochlorite (OCl(-)) in aerated 0.1 M NaCl at pH ∼9.9 under a dose rate of 725 Gy h(-1). Using a three-electrode setup inside a (60)Co γ-cell, OCl(-) was quantified from calibration curves, where concentrations were validated ex situ by UV-vis spectroscopy. For an initial OCl(-) added concentration of 10 mM, both methods showed a decrease to ∼1 mM after 24 h. Kinetic analysis based on a radiolysis/halogen reaction scheme indicates that HOCl consumption is dominated by OH(•) abstraction (∼71%), with a secondary contribution from O(2) (•-) reduction (∼22%) and a minor Cl(-)-mediated pathway (∼7%); contributions from e(-) and H(•) are negligible at the steady state. The added HOCl drives a pronounced rise in OCl(•) that feeds back to lower the steady-state OH(•) level and modulates H(2)O(2) formation. From these kinetics, it is estimated that g (HOCl) ≈ -0.53 μmol J(-1). Beyond validating DPV as an in situ radiation electroanalytical method, the combined measurements and modeling provide a mechanistic basis for OCl(-) transformation in saline waters, establishing a general radiation-electrochemistry platform for time-resolved detection of radiolysis products relevant to nuclear-waste containment.