Low LET radiolysis escape yields for reducing radicals and H2 in pressurized high temperature water

Abstract

Low Linear Energy Transfer (LET) radiolysis escape yields (G values) are reported for the sum (G(H) + G(e-) aq) and for G(H 2) in subcritical water up to 350 o C. The scavenger system 1-10 mM acetate/0.001M hydroxide/0.00048M N 2 O was used with simultaneous mass spectroscopic detection of H 2 and N 2 product. Temperature-dependent measurements were carried out with 2.5MeV electrons from a van de Graaff accelerator, while room temperature calibration measurements were done with a 60 Co gamma source. The concentrations and dose range were carefully chosen so that initial spur chemistry is not perturbed and the N 2 product yield corresponds to those reducing radicals that escape recombination in pure water. In comparison with a recent review recommendation of Elliot and Bartels (AECL report 153-127160-450-001, 2009), the measured reducing radical yield is seven percent smaller at room temperature but in fairly good agreement above 150 o C. The H 2 escape yield is in good agreement throughout the temperature range with several previous studies that used much larger radical scavenging rates. Previous analysis of earlier high temperature measurements of G esc (OH) is shown to be flawed, although the actual G values may be nearly correct. The methodology used in the present report greatly reduces the range of possible error and puts the high temperature escape yields for low-LET radiation on a much firmer quantitative foundation than was previously available.

Radioactive Wastes

“…Impact of Radiolysis. Moncoffre et al, (2016) for G (H2) in subcritical water up to 350°C was studied by Sterniczuk et al, (2016). The study showed that measured reducing radical yield is seven percent smaller at room temperature in comparison with a recent review recommendation of Elliot and Bartels.…”

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

“…Although H 2 is a molecular product, g(H 2 ) is observed to continue to increase with temperature, particularly above 200°C. This anomalous increase in g(H 2 ), which is an issue of much debate in the radiation chemistry of high-temperature water, has been discussed at length elsewhere [48][49][50][51][52][53][54][55]. From a theoretical perspective, we have recently performed Monte Carlo track chemistry simulations of the low-LET radiolysis of liquid water over the range 25-350°C [51], incorporating newly measured or re-assessed experimental data.…”

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

“…continuously increase. 56,62 We expect the yield of H 2 to further increase at higher SCWR temperatures. Bartels et al proposed that the spur recombination reactions that produce H 2 are mainly through the channel of R2, R3, and R5.…”