Prediction of rate constants of important chemical reactions in water radiation chemistry in sub and supercritical water – non-equilibrium reactions

Abstract

The rate constants for reactions involved in the radiolysis of water under relevant thermodynamic conditions in supercritical water-cooled reactors are estimated for inputs in simulations of the radiation chemistry in Generation IV nuclear reactors. We have discussed the mechanism of each chemical reaction with a focus on non-equilibrium reactions. We found most of the reactions are activation controlled above the critical point and that the rate constants are not significantly pressure dependent below 300 °C. This work will aid industry with developing chemical control strategies to suppress the concentration of eroding species.

New functional form to describe the temperature dependence of liquid phase reaction rates

“…Subcritical fluids also serve as excellent reaction media for the conversion of biomass to fuels and other valuable chemicals [12,13,14]. In nuclear power plants, subcritical or supercritical water is used as a coolant for a reactor, and a knowledge of the kinetic mechanisms of water radiolysis is essential for designing a safe water-coolant reactor that can suppress the formation of oxidizing species and mitigate corrosion [15,16,17,18].…”

“…The Arrhenius equation assumes a linear relationship between ln 𝑘 and 1∕𝑇 and treats 𝐴 and 𝐸 𝑎 as temperature-independent parameters. While most reactions show the linear dependence, many liquid phase reactions start to exhibit non-Arrhenius behavior as temperature approaches a critical point of a solvent [15,16,20,21,22,18]. Near a critical point, the physicochemical properties of a solvent change dramatically with a slight variation of temperature, and as a result, rapid slowing-down or acceleration of rate constants are observed for many liquid phase reactions at elevated temperatures.…”

Supercritical Water: A Simulation Study to Unravel the Heterogeneity of Its Molecular Structures

“…These radiation fields play a major role in contributing to the formation of various troublesome reactive oxidizing species, including hydroxyl radicals ( • OH), hydrogen peroxide (H 2 O 2 ), oxygen (O 2 , as a decomposition product of H 2 O 2 ), and the superoxide anion/hydroperoxyl radical (O 2 •− /HO 2 • , depending on pH level). These species critically affect the chemical environment, operational efficiency, and aging of the reactor (see, e.g., [ 8 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]), potentially accelerating corrosion processes in in-core materials, particularly fuel cladding. This can lead to fuel failures and the release of fuel fragments and fission products into the coolant, which further affects the transport of radioactive materials out of the core into downstream piping components, increasing radiation exposure to reactor maintenance personnel.…”

“…•− /HO 2 • , depending on pH level). These species critically affect the chemical environment, operational efficiency, and aging of the reactor (see, e.g., [8,[15][16][17][18][19][20][21][22][23]), potentially accelerating corrosion processes in in-core materials, particularly fuel cladding. This can lead to fuel failures and the release of fuel fragments and fission products into the coolant, which further affects the transport of radioactive materials out of the core into downstream piping components, increasing radiation exposure to reactor maintenance personnel.…”

Molecular Dynamics Characterization of Dielectron Hydration in Liquid Water with Unique Double Proton Transfers

“…Radiolysis of aqueous environments is always a traditional and fascinating chemical problem because it has the fundamental interest and applications including interpreting numerous reaction mechanisms in various catalytic or nuclear reactions in aqueous systems. − Ionizing radiation in liquid water could produce major radiolysis products. − Hydrated electron (e – aq ), a unique electron entity and special reactive reductant among them, has been evidenced not only to exhibit some special properties but also to participate in various reactions including hydrogen evolution as initiator or catalyst, thus attracting researchers’ continuous attention for more than half a century. − Great progresses have been made on the structures, energies, spectra, and reactivity of solvated electrons in various media with some documented information. − However, questions on the radiation-induced hydrated electrons and other reactivity in aqueous solution still remain (Section S1 in the Supporting Information (SI)). For example, e – aq was experimentally assumed to connect with hydrogen evolution via a recombined form (e 2 2– aq ) as a hypothetical intermediate in interpreting the anti-Arrhenius behavior of the hydrogen evolution rate in radiolysis of water, − but the underlying mechanisms always lack direct evidence.…”