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Research Papers

Radiolysis of Supercritical Water at 400°C: A Sensitivity Study of the Density Dependence of the Yield of Hydrated Electrons on the (eaq+eaq) Reaction Rate Constant

[+] Author and Article Information
Sunuchakan Sanguanmith

Department of Nuclear Medicine and Radiobiology,
Université de Sherbrooke,
3001, 12e Avenue Nord, Sherbrooke, QC J1H 5N4, Canada
e-mail: sunuchakan.sanguanmith@USherbrooke.ca

Jintana Meesungnoen

Department of Nuclear Medicine and Radiobiology,
Université de Sherbrooke,
3001, 12e Avenue Nord, Sherbrooke, QC J1H 5N4, Canada
e-mail: jintana.meesungnoen@USherbrooke.ca

David A. Guzonas

Canadian Nuclear Laboratories, Reactor Chemistry and Corrosion,
20 Forest Avenue, Deep River, ON K0J 1P0, Canada
e-mail: david.guzonas@cnl.ca

Craig R. Stuart

Canadian Nuclear Laboratories, Reactor Chemistry and Corrosion,
20 Forest Avenue, Deep River, ON K0J 1P0, Canada
e-mail: craig.stuart@cnl.ca

Jean-Paul Jay-Gerin

Department of Nuclear Medicine and Radiobiology,
Université de Sherbrooke,
3001, 12e Avenue Nord, Sherbrooke, QC J1H 5N4, Canada
e-mail: jean-paul.jay-gerin@USherbrooke.ca

1Corresponding author.

Manuscript received March 28, 2015; final manuscript received July 1, 2015; published online February 29, 2016. Assoc. Editor: Thomas Schulenberg.

ASME J of Nuclear Rad Sci 2(2), 021014 (Feb 29, 2016) (5 pages) Paper No: NERS-15-1035; doi: 10.1115/1.4031013 History: Received March 28, 2015; Accepted July 07, 2015

The temperature dependence of the rate constant (k) of the bimolecular reaction of two hydrated electrons (eaq) measured in alkaline water exhibits an abrupt drop between 150°C and 200°C; above 250°C, it is too small to be measured reliably. Although this result is well established, the applicability of this sudden drop in k(eaq+eaq)) above 150°C to neutral or slightly acidic solution, as recommended by some authors, still remains uncertain. In fact, the recent work suggested that in near-neutral water the abrupt change in k above 150°C does not occur and that k should increase, rather than decrease, at temperatures greater than 150°C with roughly the same Arrhenius dependence of the data below 150°C. In view of this uncertainty of k, Monte Carlo simulations were used in this study to examine the sensitivity of the density dependence of the yield of eaq in the low–linear energy transfer (LET) radiolysis of supercritical water (H2O) at 400°C on variations in the temperature dependence of k. Two different values of the eaq self-reaction rate constant at 400°C were used: one was based on the temperature dependence of k above 150°C as measured in alkaline water (4.2×108  M1s1), and the other was based on an Arrhenius extrapolation of the values below 150°C (2.5×1011  M1s1). In both cases, the density dependences of our calculated eaq yields at 60  ps and 1 ns were found to compare fairly well with the available picosecond pulse radiolysis experimental data (for D2O) for the entire water density range studied (0.150.6  g/cm3). Only a small effect of k on the variation of G(eaq)) as a function of density at 60 ps and 1 ns could be observed. In conclusion, our present calculations did not allow us to unambiguously confirm (or deny) the applicability of the predicted sudden drop of k(eaq+eaq) at 150°C in near-neutral water.

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Figures

Grahic Jump Location
Fig. 2

Density dependence of G(eaq−) (in molecule per 100 eV) in SCW at 400°C measured directly by picosecond pulse radiolysis experiments (in D2O) [28,29] at ∼60  ps (○) and 1 ns (▪) (estimated uncertainty of ±10%). The solid and dashed lines show our Monte Carlo simulated results in supercritical H2O when k(eaq−+eaq−)=2.5×1011 M−1 s−1 was used at ∼60  ps and 1 ns, respectively. The dash-dot and dash-double-dotted lines show our corresponding calculated eaq− yields when k(eaq−+eaq−)=4.2×108  M−1 s−1 was used at ∼60  ps and 1 ns, respectively. For conversion into SI units (mol/J), 1 molecule per 100  eV≈0.10364  μmol/J.

Grahic Jump Location
Fig. 1

Rate constant for the self-reaction of two hydrated electrons as a function of temperature. The solid line (denoted ka) shows the (eaq−+eaq−) reaction rate constant that was obtained by using an Arrhenius extrapolation procedure above 150°C as proposed by Elliot [18], Stuart et al. [19], and Hatomoto et al. [26]. The dashed line (denoted kb) shows the (eaq−+eaq−) reaction rate constant that was measured by Bartels and coworkers [20,27] (▪) under alkaline conditions. Note that kb was assumed to remain constant between 275°C and 400°C.

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