Radiolysis of supercritical water at 400 °C and liquid-like densities near 0.5 g/cm³ — A Monte Carlo calculation

Abstract

Monte Carlo simulations are used to calculate the primary radical yields gðe aq À Þ, g( OH), the sum [gðe aq À Þ + g( OH) + g(H )], and the ratio g(H )/gðe aq À Þ in the low linear energy transfer (LET) radiolysis of supercritical water (SCW) at 400 8C in the high-density, liquid-like region near *0.5 g/cm 3 . Using all the currently available information on the reactivities and diffusion coefficients of the radiation-induced species under these conditions, and assuming the aqueous medium to be a ''continuum'', a good accord is found between our calculations and the available experimental data. In particular, our computed e aq À yields at 60 ps and 1 ns compare very well with recently reported direct time-dependent e aq À yield measurements in SCW (D 2 O) at 400 8C and 0.570 g/cm 3 using picosecond pulse radiolysis experiments.

Technical Readiness and Gaps Analysis of Commercial Optical Materials and Measurement Systems for Advanced Small Modular Reactors

“…Supercritical water, like sub-critical water, undergoes radiolysis to produce oxygen and hydrogen peroxide, which can lead to corrosion within the reactor vessel. H 2 can be added to the reactor coolant to suppress dissociation of water, but the effect is not well understood under supercritical conditions (Meesungnoen et al 2010). The pH environment in SCWRs influences the corrosion potential, rate, and to some extent the mode.…”

Density dependence of the yield of hydrated electrons in the low-LET radiolysis of supercritical water at 400 °C: influence of the geminate recombination of subexcitation-energy electrons prior to thermalization

“…The radiolysis of SCW was modeled using an extended version of our Monte Carlo simulation code called IONLYS-IRT; this program simulates, in a 3D geometrical environment, irradiation of pure liquid water and (dilute) aqueous solutions at ambient 27 and elevated 15,17,28,29 temperatures. In brief, the IONLYS program models, on an event-by-event basis, all of the events of the early ''physical'' and ''physicochemical'' stages 30 in a track development.…”

“…This information is particularly important because preliminary studies suggest, in many cases, a markedly different behavior of the effects of radiation under supercritical water (SCW) conditions compared to what one would have predicted from simplistic extrapolations of values originally obtained at lower temperatures. 6,13,15,[17][18][19] Key examples here include the rate constants of many chemical reactions involved in the radiolysis of water and aqueous solutions that are found to exhibit, at high temperature and pressure, non-Arrhenius behavior. [20][21][22][23][24] Currently, however, only very limited experimental data are available on the radiation chemistry and reaction kinetics of transients under supercritical conditions, 15,17,19,25 and significant gaps in the database remain.…”

“…6,13,15,[17][18][19] Key examples here include the rate constants of many chemical reactions involved in the radiolysis of water and aqueous solutions that are found to exhibit, at high temperature and pressure, non-Arrhenius behavior. [20][21][22][23][24] Currently, however, only very limited experimental data are available on the radiation chemistry and reaction kinetics of transients under supercritical conditions, 15,17,19,25 and significant gaps in the database remain.…”

Generation of Ultrafast Transient Acid Spikes in High-Temperature Water Irradiated With Low Linear Energy Transfer Radiation

“…While the radiation-induced chemistry (radiolytic yields or G values and reaction rates) in water at elevated temperatures (say, up to 350°C) is relatively well documented [9][10][11], there are only very limited experimental data available on supercritical water radiolysis [12][13][14][15]. Direct measurements at elevated temperatures and pressures are difficult, especially beyond the thermodynamic critical point of water (t c = 373.95°C and P c = 22.06 MPa); thus, theoretical modeling and computer simulations are an important route of investigation [3,6,[16][17][18][19][20].…”