Radiolysis elevated temperatures

Sunaryo GR, Katsumura Y, Ishigure K (1995) Radiolysis of water at elevated temperatures-III. Simulation of radiolytic products at 25 and 250°C under the irradiation with y rays and fast neutrons. Rad Phys Chem 45 703-714... 

Katsumura Y, Sunaryo G, Hiroishi D, Ishiqure K (1998) Fast neutron radiolysis of water at elevated temperatures relevant to water chemistry. Prog Nucl Energy 32 113-121... 

RADIOLYSIS OF WATER AT ELEVATED TEMPERATURE—RADIATION EFFECT OF COOLANT WATER IN NUCLEAR REACTORS... 

T o grasp the chemical condition of water in the pressure vessel, direct measurement is practically impossible because of high pressure, high temperature, and intense radiation. In order to predict the concentrations of water decomposition products, a computer simulation should be applied. This idea was found in 1960s [1-3]. To perform the simulation, both a set of G-values for water decomposition products and a set of reactions for transient species are necessary. For these two decades, much effort has been made in Sweden, Denmark, United Kingdom, Canada, and Japan to evaluate the G-values and rate constants of the reactions at elevated temperatures up to 300 °C, and now there are practically enough accumulated data. There are several reviews of water radiolysis at elevated temperatures [4-7] and examples of practical application of the radiolysis in reactors [8,9]. 

Common features of water radiolysis at elevated temperatures up to 300°C are summarized as below. 

It is known that more than 30 reactions are needed to reproduce the radiation-induced reactions occurring in pure water. Intensive measurements with a pulse radiolysis method have been done at elevated temperature up to 300°C [25 2], and the temperature dependence of some reactions does not exhibit a straight line but a curved one in Arrhenius plot. These examples are the reactions of the hydrated electron with N2O, NOJ, NO2, phenol, Se04, 8203 , and Mn [33,35], and two examples, egq + NOJ and ejq -i- NOJ, are shown in Fig. 2. The rate constant for the reaction of hydrated electron with NOJ is near diffusion-controlled reaction at room temperature and is increasing with increasing temperature. Above 100°C, the rate does not increase and reaches the maximum at 150°C, and then decreases. Therefore the curve is concave upward in Arrhenius plot. 

Other transient radicals such as (SCN)2 [78], carbonate radical (COj ) [79], Ag and Ag " [80], and benzophenone ketyl and anion radicals [81] have been observed from room temperature to 400°C in supercritical water. The (SCN)2 radical formation in aqueous solution has been widely taken as a standard and useful dosimeter in pulse radiolysis study [82,83], The lifetime of the (SCN)2 radical is longer than 10 psec at room temperature and becomes shorter with increasing temperature. This dosimeter is not useful anymore at elevated temperatures. The absorption spectrum of the (SCN)2 radical again shows a red shift with increasing temperature, but the degree of the shift is not significant as compared with the case of the hydrated electron. It is known that the (SCN) radical is equilibrated with SCN , and precise dynamic equilibration as a function of temperature has been analyzed to reproduce the observation [78],... 

Christensen H, Sehested K (1983) Reaction of hydroxyl radicals with hydrogen at elevated temperatures. Determination of the activation energy. J Phys Chem 87 118-120 Dainton FS, Peterson DB (1962) Forms of H and OH produced in the radiolysis of aqueous systems. Proc R Soc Lond A 267 443-463... 

Baldacchino G, De Waele V, Monard H, Sorgues S, Gobert F, Larbre J-P, Vigneron G, Marignier J-L, Pommeret S, Mostafavi M. (2006) Hydrated electron decay measurements with picosecond pulse radiolysis at elevated temperature up to 350°C. Chem Phys Lett A2A 77-81. 

Miyazaki T, Katsumura Y, Lin M, Muroya Y, Kudo H, Asano M, Yoshida M. (2006) y-Radiolysis of benzophenone aqueous solution at elevated temperatures up to supercritical condition. Radiat Phys Chem 75 218-228. 

Lin M, Katsiuniua Y, He H, Muroya Y, Han Z, Miyazaki T, Kudo H. (2005) Pulse radiolysis of 4,4 -bipyridyl aqueous solutions at elevated temperatures Spectral changes and reaction kinetics up to 400°C. J Phys Chem A 109 2847-2854. 

It was some ten years before any systematic program of pulse radiolysis at high temperature had begun when Christensen and Sehested [75] had available a pulse radiolysis cell that enabled measurements to be made up to 320 °C and 140 bar. This work focused on the radiation chemistry of water at elevated temperatures because of its relevance to the radiation chemistry occurring in the primary cooling circuits of pressurized water reactors used for electricity generation. 

Relevant to water radiolysis in nuclear reactor, G-values of the water decomposition by fast neutrons have been determined by using a fast reactor at elevated temperatures [59]. Since fast neutron radiolysis is equivalent to proton radiolysis because of the recoil proton formation through the elastic collision of fast neutrons with H2O molecules [60], an alternative approach as a model experiment is the ion beam radiolysis with different LET particles from accelerators at elevated temperatures [61]. 

This chapter begins with a brief sununary of the scheme for water radiolysis, followed by a description of the chemical systems used to obtain radiation chemical yields, or G-values, and rate constants at elevated temperatures that are pertinent to this scheme for both high and low LET, in H2O and DjO. Next, there is a section showing how the data can be accommodated in a simple spur difiusion model, and finally Arrhenius parameters for a number of reactions of more general interest are presented and discussed. 

It is known that more than 30 reactions are needed to reproduce the radiation-induced reactions occurring in pure water. Intensive measurements with a pulse radiolysis method have been done at elevated temperature up to 300°C [25-42], and the temperature dependence of some reactions does not exhibit a straight line but a curved one in Arrhenius plot. These examples are the reactions of the hydrated electron with N2O, NOJ, NOJ, phenol. 

Shiraishi, H., Katsumura, Y., Hiroishi, D., Ishigure, K., and Washio, M. 1988. Pulse-radiolysis study on the yield of hydrated electron at elevated temperatures. J. Phys. Chem. 92 3011-3017. 

The y-radiolysis of PMMA at room temperature in an atmosphere of NO as well as photolysis leads to the formation of acylalkylaminoxyl radicals. The evacuation of samples at elevated temperatures gives rise to the appearance of the signal of iminoxyl radicals in the ESR spectrum. As distinct from photolysis, y-radiolysis can stimulate hydrogen-atom detachment from the C-H bonds of macromolecules and, consequently, the formation of primary and secondary macromolecular nitroso compounds takes place in an atmosphere of NO. Such nitroso compounds are rapidly isomerised into oximes [63]. The abstraction of hydrogen atoms from the OH groups of oximes by active free radicals results in the formation of iminoxyl radicals [64]. This viewpoint is confirmed by the observation of ESR spectra of iminoxyl radicals in y-irradiated PMMA and AC in the presence of NO. 

Hexafluorobenzene and perfluoro-naphthalene, -biphenyl, and -a-terphenyl have been shown to retain their moderate radiation stability at elevated temperatures perfluorobiphenyl at 500°C is several orders of magnitude more stable thermally and many times more stable to y-radiation than its hydrocarbon analogue. Hexafluorobenzene is as e ent an electron scavenger as perfluorocyclohexane during y-radiolysis of liquid cyclohexane at room temperature. ... 

T. Miyazaki, Y. Katsumura, et al., Gamma-Radiolysis of Bcaizophenone Aqueous Solution at Elevated Temperatures up to Supercritical Conditirai, Radiation Physics and Chemistry, Vol. 75, 218-228 (2006)... 

Microemulsion-mediated materials synthesis employs three basic methods, as illustrated in Fig. 3 [17]. The microemulsion-plus-trigger method (Fig. 3, method a) is based on a single microemulsion. The fluid system is activated in some way in order to initiate the reactions that eventually lead to particle formation. Pulse radiolysis and laser photolysis have served as triggers for the preparation of nanosize gold particles [41]. In the case of metal oxides, temperature elevation can provide the needed trigger action hydrated metal ions solubilized... 

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