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Research Papers

# Steady-State Radiolysis of Supercritical Water: Model Predictions and Validation

[+] Author and Article Information
V. Subramanian, J. M. Joseph, H. Subramanian, J. J. Noël

Department of Chemistry,
University of Western Ontario,
London, ON N6A 5B7, Canada

D. A. Guzonas

Chalk River, ON K0J 1J0, Canada

J. C. Wren

Department of Chemistry,
University of Western Ontario,
London, ON N6A 5B7, Canada
e-mail: jcwren@uwo.ca

Manuscript received April 9, 2015; final manuscript received July 13, 2015; published online February 29, 2016. Assoc. Editor: Thomas Schulenberg.

ASME J of Nuclear Rad Sci 2(2), 021021 (Feb 29, 2016) (6 pages) Paper No: NERS-15-1051; doi: 10.1115/1.4031199 History: Received April 09, 2015; Accepted August 05, 2015

## Abstract

Chemical kinetic models are being developed for the $γ$-radiolysis of subcritical and supercritical water (SCW) to estimate the concentrations of radiolytically produced oxidants. Many of the physical properties of water change sharply at the critical point. These properties control the chemical stability and transport behavior of the ions and radicals generated by the radiolysis of SCW. The effects of changes in the solvent properties of water on primary radiolytic processes and the subsequent aqueous reaction kinetics can be quite complicated and are not yet well understood. The approach used in this paper was to adapt an existing liquid water radiolysis model (LRM) that has already been validated for lower temperatures and a water vapor radiolysis model (VRM) validated for higher temperatures, but for lower pressures, to calculate radiolysis product speciation under conditions approaching the supercritical state. The results were then extrapolated to the supercritical regime by doing critical analysis of the input parameters. This exercise found that the vapor-like and liquid-like models make similar predictions under some conditions. This paper presents and discusses the LRM and VRM predictions for the concentrations of molecular radiolysis products, $H2$, $O2$, and $H2O2$ at two different irradiation times, 1 s and 1 hr, as a function of temperature ranging from 25°C to 400°C. The model simulation results are then compared with the concentrations of $H2$, $O2$, and $H2O2$ measured as a function of $γ$-irradiation time at 250°C. Model predictions on the effect of $H2$ addition on the radiolysis product concentrations at 400°C are presented and compared with the experimental results from the Beloyarsk Nuclear Power Plant (NPP).

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## Figures

Fig. 1

Radiolysis product concentrations as a function of temperature predicted by the LRM and VRM after 1 s and 1 hr irradiation at a dose rate of 1000 kGy hr−1. The left panels show the concentrations in M (mol dm−3), whereas the right panels show the concentrations in units of g kg−1 (adopted from Subramanian et al. [21]).

Fig. 2

(a) Concentrations of H2 in the vapor phase and (b) H2O2 in liquid phase measured as a function of irradiation time at 250°C. The symbols represent the experimental data and the lines represent the predictions by the VRM (solid line), the LRM (broken lines) without interfacial mass transfer (without MT), and the LRM (dash dot) with mass transfer (with MT).

Fig. 3

O2 concentration predicted by the models at 250°C. The lines represent the predictions by the VRM (solid line), the LRM (broken lines) without interfacial mass transfer (without MT), and the LRM (dash dot) with mass transfer (with MT). In the experiments, [O2] was below the detection limit, which is indicated as a dotted line.

Fig. 4

Effect of H2 addition on suppression of radiolytic production of O2 and H2O2 predicted by the VRM (solid lines) and the LRM (broken lines). The shaded area enveloped by solid lines represents the range of values over different irradiation periods predicted by the VRM, and symbols represent plant data from Beloyarsk NPP Unit-1 (♦, direct H2 addition and 𝕧, NH3 addition) (adopted from Subramanian et al. [21]).

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