Pulse Radiolysis Study on the Estimation of Radiolytic Yields of Water Decomposition Products in High-Temperature and Supercritical Water:  Use of Methyl Viologen as a Scavenger

Abstract

In the present work, methyl viologen (1,1′-dimethyl-4,4′-bipyridinium dichloride) is used as a scavenger to estimate the radiolytic yields of water decomposition products from room temperature to 400 °C by pulse radiolysis method. {G(e aq -) + G(OH) + G(H)} has been studied using a 0.5 mM MV 2+ solution in the presence of 10 mM NaCOOH up to 200 °C and in the presence of 0.2 M ethanol up to 400 °C. The results show that the {G(e aq -) + G(OH) + G(H)} increases with temperature up to 350 °C at 25 MPa, while it depends also on pressure in supercritical conditions. The G(e aq -) was estimated using MV 2+ solutions in the presence of 0.2 M tert-butyl alcohol. The results agree well with the reported data up to around 300 °C at 25 MPa; however, in supercritical conditions a very significant density effect was observed. At a given temperature, G(e aq -) and {G(e aq -) + G(OH) + G(H)} decrease with increasing density while at a fixed density they decrease with increasing temperature.

Neutron and β/γ Radiolysis of Water up to Supercritical Conditions. 1. β/γ Yields for H2, H• Atom, and Hydrated Electron

“…10 It is our conclusion that the G(e aq -) numbers reported by Lin et al 17 are much too large to represent the true e aq -escape yield in low-density supercritical water. On the other hand, as we noted above, our estimate of G(-H 2 O) is not in qualitative disagreement with Lin et al's evaluation of G(radicals), given the difference in scavenging power and the probable density error from presence of 0.2 m ethanol.…”

“…10,17 In this range we have chosen two temperatures to illustrate the effect of density, 380 and 400°C. The flow was kept constant and the density in the sample was adjusted by changing the pressure in the system.…”

“…A number of studies have been published in the last several years with the aim of providing the necessary fundamental information needed to model radiation chemistry in supercritical water. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] Both reaction rates and radiation yields (G-values) for the primary free radicals • OH, H • , and e aq -are required, as well as for the recombination products H 2 and H 2 O 2 . Moreover, in reactor cores radiation is deposited both via γ radiation and energetic neutrons; 24 this paper represents the first in a series that will report G values from both /γ radiation and neutrons using the same detection methodology.…”

An apparatus for the study of high temperature water radiolysis in a nuclear reactor: Calibration of dose in a mixed neutron/gamma radiation field

“…1 In the past few years a number of studies have focused on radiation-induced chemistry in water above 250°C in an effort to accumulate data for accurate modeling of a power reactor environment. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Supercritical water ͑T c Ͼ 374°C, P c Ͼ 220 bars͒ is of particular interest because this is projected as one possible cooling fluid in generation IV nuclear reactors. 19,20 All existing models of pressurized water reactor chemistry in the 300°C range rely upon extrapolation of some critical rate constants and yields.…”

“…3,10 Gamma radiolysis yields of free radicals have also been found to increase dramatically in low density supercritical water. 2,12 Notably lacking in the database thus far are good measurements of the chemistry induced by neutrons. For this reason, an experiment has been designed to measure neutroninduced chemical yields as a function of temperature and pressure at the University of Wisconsin Nuclear Reactor ͑UWNR͒.…”