Neutron and β/γ Radiolysis of Water up to Supercritical Conditions. 2. SF₆ as a Scavenger for Hydrated Electron

Abstract

SF(6) has been used as a specific scavenger to investigate the beta/gamma radiolysis yield of hydrated electrons in pressurized high temperature sub- and supercritical water. SF(6) is thermally stable in supercritical water, and each scavenging reaction is known to produce six fluoride ions, which can be readily measured using a fluoride-selective electrode. Problems in the application of this method are described, including buildup of acid product and chain reduction of SF(6) in the presence of organic (*)H and (*)OH radical scavengers. Ultimately we find that the combination of SF(6) and phenol in neutral solution gives reliable results in supercritical water, because the protons and fluoride ions remain associated as HF molecules. The beta/gamma yields in supercritical water are similar to previous measurements using N(2)O scavenger.

Density dependence of the “escape” yield of hydrated electrons in the low-LET radiolysis of supercritical water at 400 °C

“…1. As we can see, our computed g(e aq À ) values reproduce fairly well the experimental data of Janik et al 8 and Haygarth and Bartels 9 (black circles and squares). These results suggest strongly that the scavenged e aq À yields reported by these authors may have been measured at times that are close to the spur lifetimes.…”

“…6 Moreover, in addition to the very limited information on the yields of water radiolysis under supercritical conditions, there are also some apparent discrepancies on existing experimental data. For example, a strong difference has been noted in ''scavenging'' experiments between the e aq À ''escape'' yields 7 in low-density SCW measured by Janik et al 8 and Haygarth and Bartels 9 in Notre Dame, U.S.A.…”

“…The hypothesis has been made that the N 2 O and SF 6 scavenging yield data of Bartels and co-workers and the MV 2+ and 4,4 0 -bipyridyl scavenging results from the group of Katsumura in Tokai, Japan, may have been measured at different times. 6,9,12 The present work aims, first, to calculate the ''spur lifetime'' (t s ) in the low-linear energy transfer (LET) radiolysis of SCW (H 2 O) at 400 1C as a function of water density, using a simple picture of energy deposition initially in spurs, followed by diffusion of the species of the spur until a complete spur overlap. Second, it aims to better understand, based on the stochastic modeling of the radiolysis using Monte-Carlo calculations and the values thus found for t s , the differences that have been observed experimentally in the density dependence of the yield of hydrated electrons in irradiated SCW at 400 1C.…”

Hydroxymethyl Radical Self-Recombination in High-Temperature Water

“…Following Klippenstein and Marcus 45 , it should be possible to carry out the integral to sufficient accuracy by way of Monte Carlo integration over the six Euler angles characterizing the approach of the radicals. Equation (11) reduces to…”

First observation of HO˙ reactivity in water under high energy ions at elevated temperature

“…[28][29][30][31][32] We conclude that temperature effects were investigated mainly with low LET radiations and pulse radiolysis since the 1980s 33 and that only recent experiments in reactors start to bring new approaches under combined radiations. 34,35 However temperature and LET have inversed effects on the radiolytic yields of HO . It is therefore expected a competition when LET and T increases, between the acceleration of recombinations in the track and the escape of species with the increase of diffusion.…”