Short Lived Species Produced in Pulse Irradiated Melts of LiF-KF and LiF-NaF-KF Eutectic Mixtures

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

“…6 Subsequently, and to the contrary, several studies reported radiation-induced formation of oxidizing and reducing transients in a variety of alkali metal halide molten salt systems. 7–14 These studies have shown that the absorption of ionizing radiation by molten halide salt systems (represented as M + X − ) initiates production of an energetic excess electron (e − ) and corresponding ‘hole’ (electron vacancy) that localizes on the halide component (X − ) to produce a halide radical (X˙). As in water, the initial energetic e − passes through states of partial or pre-solvation prior to complete solvation (e S − , absorbing in the visible and near-IR), while X˙ rapidly forms an anion-radical dimer with other halide anions (X 2 ˙ − , predominantly absorbing in the UV): 11,15,16 M + X − M + + X˙ + e − ,e − → e pre − → e S − ,X˙ + X − → X 2 ˙ − .The identification and optical characterization of these transient species in molten salt systems is fundamentally significant, as they are analogous to the highly-reactive hydrated electron (e aq − ) and hydroxyl radical (˙OH) produced by water radiolysis, and thus are expected to participate in similar chemical reactivity that may negatively influence MSR performance and durability.…”

“…More recently, Sawamura and coworkers performed nanosecond electron pulse radiolysis experiments on molten lithium chloride-potassium chloride (LiCl–KCl), lithium bromide-potassium bromide (LiBr–KBr), lithium fluoride-potassium fluoride (LiF–KF), and lithium fluoride-sodium fluoride-potassium fluoride (LiF–NaF–KF) systems. 12–14 In each salt system, they observed the absorption band of e S − , with peak absorbances between 500 and 800 nm depending on salt mixture composition and temperature, which decayed via first-order kinetics with lifetimes on the order of hundreds of nanoseconds. In each case, the addition of 50 mM Cd 2+ caused the e S − absorption band to disappear, and the appearance of an additional absorption with a peak around 330 nm that indicated the formation of Cd + .…”

Impact of iodide ions on the speciation of radiolytic transients in molten LiCl–KCl eutectic salt mixtures

“…) by a molten halide salt (M n+ X n À ) leads to the formation of transient excess electrons (e À ) and halide radicals (X ): [3][4][5][6][7][8][9][10][11]13 M n+ X n À e À , X , M (n+1)+ .…”

“…The absorption of ionizing radiation () by a molten halide salt (M n + X n − ) leads to the formation of transient excess electrons (e − ) and halide radicals (X˙): 3–11,13 M n + X n − e − , X˙, M ( n +1)+ .These initial radiolytic species can undergo additional chemistry should they escape geminate/non-geminate recombination:X˙/M ( n +1)+ + e − → X − /M n + .The e − undergoes successive energy transfer events prior to capture and ultimately solvation (e S − )—defined here as a cavity electron coordinated by metal cations (M n + )—or reduction of the metal ion component( s ) of a given halide salt: 3–11,13 e S − + M n + → M ( n −1)+ .On the other hand, the X˙ radical rapidly reacts with a neighboring halide anion (X − ) to yield the corresponding dihalogen radical anion (X 2 ˙ − ), which typically undergoes disproportionation: 3,6,7,13 X 2 ˙ − + X 2 ˙ − → X 3 − + X − ,and its product X 3 − leads to the equilibrium reaction:X 3 − ⇌ X 2 + X − .…”

“…New reactors are required to meet the ever-increasing global energy demand, of which molten salt reactor (MSR) concepts are being championed for their capacity to provide safe, cost-efficient, and sustainable commercial electricity from nuclear fission. 1,2 However, our fundamental understanding of molten salts in radiation environments is limited, [3][4][5][6][7][8][9][10][11][12][13] compared to complementary water-cooled reactor technologies. 14,15 For example, extensive fundamental studies have been done for the radiation-induced fate of fissionproduct iodine in water-cooled reactor environments, 16 owing to government regulations on the health and safety concerns surrounding the uptake of radioiodine by the thyroid gland if it were to be released into the environment.…”