<i>In Situ</i> 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 <i>in situ</i> 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 ⁶⁰Co γ-cell, OCl^- was quantified from calibration curves, where concentrations were validated <i>ex situ</i> 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 O₂ ^•- 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 H₂O₂ formation. From these kinetics, it is estimated that <i>g</i> _HOCl ≈ -0.53 μmol J^-1. Beyond validating DPV as an <i>in situ</i> 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.