Radiation-induced reaction kinetics of Zn2+ with eS− and Cl2˙− in Molten LiCl–KCl eutectic at 400–600 °C

Abstract

Molten chloride salts are currently under consideration as combined coolant and liquid fuel for next-generation molten salt nuclear reactors. Unlike complementary light-water reactor technologies, the radiation science underpinning molten salts is in its infancy, and thus requires a fundamental mechanistic investigation to elucidate the radiation-driven chemistry within molten salt reactors. Here we present an electron pulse radiolysis kinetics study into the behaviour of the primary radiolytic species generated in molten chloride systems, i.e., the solvated electron (e_S⁻) and di-chlorine radical anion (Cl₂˙⁻). We examine the reaction of e_S⁻ with Zn²⁺ from 400–600 °C (E_a = 30.31 ± 0.09 kJ mol⁻¹), and the kinetics and decay mechanisms of Cl₂˙⁻ in molten lithium chloride-potassium chloride (LiCl–KCl) eutectic. In the absence of Zn²⁺, the lifetime of e_S⁻ was found to be dictated by residual impurities in ostensibly “pure” salts, and thus the observed decay is dependent on sample history rather than being an intrinsic property of the salt. The decay of Cl₂˙⁻ is complex, owing to the competition of Cl₂˙⁻ disproportionation with several other chemical pathways, one of which involves reduction by radiolytically-produced Zn⁺ species. Overall, the reported findings demonstrate the richness and complexity of chemistry involving the interactions of ionizing radiation with molten salts.