Radiolytic

Qin L, Tripathi G N R and Schuler R H 1987 Radiolytic oxidation of 1,2,4-benzenetriol an application of time-resolved resonance Raman spectroscopy to kinetic studies of reaction intermediates J. Chem. Phys. 

Accordingly, the exterior surface is much more reactive than planar analogues, and is comparable to those of electron deficient polyolefins. This, in turn, rationalizes the high reactivity of the fullerene core towards photolytically and radiolytically generated carbon- and heteroatomic-centred radicals and also other neutral or ionic species [8]. The interior, in contrast, is shown to be practically inert [9]. Despite these surface related effects, the... 

The BWR water chemistry parameters are given in Table 4 (19). Originally, no additives were made to feedwater—condensate or the primary water. The radiolytic decomposition of the fluid produced varying concentrations of O2 in the reactor vessel, ranging from about 200 ppb O2 in the reactor recirculation water to about 20 ppm O2 in the steam. Stoichiometric amounts of hydrogen were also produced, ie, 2 mL for each mL of O2. Feedwater O2 was about 30 ppb, hence the radiolytic decomposition of the water was a primary factor in determining the behavior of materials in the primary system and feedwater systems. 

A mathematical model of the operating characteristics of a modem HLW storage tank has been developed (60). This model correlates experimental data for the rate of radiolytic destmction of nitric acid, the rate of hydrogen generation owing to radiolysis of water, and cooling coil heat transfer. These are all functions of nitric acid concentration and air-lift circulator operation. 

Many tracer chemicals are inherently unstable even as the unlabeled forms. Susceptibility of a chemical to hydrolysis, oxidation, photolysis, and microbiological degradation needs to be evaluated when designing suitable storage conditions for the labeled compound. Eactors that reduce radiolytic degradation, such as dispersal in solution, are apt to increase chemical degradation or instability. 

MetaHacarborane dicarboUide complexes are generaUy more robust than the corresponding cyclopentadiene complexes. The bis-dicarboUide sandwich complexes of general formula [M(C2Bg)H )2] , where M is Fe ", Co ", and exhibit great thermal, chemical, redox, and radiolytic stabUity. 

The simplest description of the reaction responsible for the radiolytic oxidation of graphite is ... 

Radiolytic oxidation alters most of the important properties of graphite, including strength, elastic modulus, work of fracture, thermal conductivity, permeability, and diffusivity but does not affect the thermal expansion coefficient or Poisson s ratio. The effects of radiolytic oxidation on the properties of a wide range of graphites have been studied in the U.K. [7,73,74] where it was found that, to a first approximation, they can be described by similar relationships ... 

It is well known that for a given weight loss, thermal oxidation of graphite causes a larger reduction in strength and elastic modulus than radiolytic oxidation. Pickup et al. [78] showed the decrement in dynamic elastic modulus, E, due to thermal oxidation fitted an exponential relationship ... 

Radiolytic oxidation is important to the design and operation of reactors because it adversely affects key graphite properties and, by removing moderator material, may bring about the need for increased fuel enrichment. As mentioned earlier, an inhibitor (methane) is added to the coolant to reduce radiolytic oxidation to acceptable levels. However, access of the inhibitor to the inner portions of the moderator brick must be assured. Two approaches have been adopted in the AGRs to provide this access. Vertical methane access holes are provided in the fuel bricks and in the later stations, Heysham II and Tomess, a pressure drop from outside to inside the brick was established to cause an enhanced flow through the brick. The amount of inhibitor added must be restricted, however, because the carbon inhibition reaction product deposits on the fuel pin and restricts heat transfer to the coolant, thus reducing reactor efficiency. 

In support of the development of graphite moderated reactors, an enormous amount of research has been conducted on the effects of neutron irradiation and radiolytic oxidation on the structure and properties of graphites. The essential mechanisms of these phenomena are understood and the years of research have translated into engineering codes and design practices for the safe design, construction and operation of gas-cooled reactors. 

Kelly, B.T., The radiolytic corrosion of advanced gas-coolcd reactor graphite. Progress in Nucl. Energy, 1985, 16(1), 73 96. 

Kelly, B.T., The effect of radiolytic oxidation on the graphite moderator brick strength in advanced gas-cooled reactors, Nucl. Energy, 1984, 24(3), 265 272. 

Birch, M., Schofield, P., Brocklehurst, J.E., Kelly, B.T., Harper, A. and Prior, H., The combined effects of fast neutron damage and radiolytic oxidation on the physical... 

Burchcll, T.D., Pickup, I.M., McEnancy, B. and Cooke, R.G., The relationship between microstructure and the reduction of clastic modulus in thermally and radiolytically corroded nuclear graphites, Carbon, 1986, 24, 545 549. 

The monoxides SeO and TeO have transient existence in flames but can not be isolated as stable solids. PoO has been obtained as a black, easily oxidized solid by the spontaneous radiolytic decomposition of the sulfoxide P0SO3. 

These hydroperoxide groups undergo radiolytic cleavage during irradiation of the aqueous polymer monomer mixture. 

Packer and Richardson (1975) and Packer et al. (1980) made use of the fact that electrons can be generated in water by y-radiation from a 60Co source (Scheme 8-29) to induce a free radical chain reaction between diazonium ions and alcohols, aldehydes, or formate ion. It has to be emphasized that the radiolytically formed solvated electron in Scheme 8-29 is only a part of the initiation steps (Scheme 8-30) by which an aryl radical is formed. The aryl radical initiates the propagation steps shown in Scheme 8-31. Here the alcohol, aldehyde, or formate ion (RH2) is the reducing agent (i.e., the electron donor) for the main reaction. The process is a hydro-de-diazoniation. 

The involvement of the diazenyl radical as an intermediate in radiolytic dediazoni-ations was demonstrated by Becker s group (Brede et al., 1979), when they identified a tetraazadiene (Ar — N2 — N2 — Ar) among the products. Substituent effects in the radiolytically induced reduction have the same sign, but are larger (p = 0.55, Packer et al., 1980) than those for the electrochemical process. 

As an alternative to electrochemical or radiolytic initiation, homolytic dediazoniation reaction products can be obtained photolytically. The organic chemistry of such photolyses of arenediazonium salts will be discussed with regard to mechanisms, products, and applications in Section 10.13. In the present section photochemical investigations are only considered from the standpoint that the photolytic generation of aryldiazenyl radicals became the most effective method for investigating the mechanisms of all types of homolytic dediazoniations —thermal and photolytic —in particular for elucidating the structure and the dissociation of the diazenyl radicals. 

Mossbauer spectra may also be used to study radiolytic decompositions [330],... 

The high values of E generally characteristic of the decomposition reactions of metal oxyhalides are widely interpreted as evidence that the initial step in anion breakdown is the rupture of the X—O bond and that the energy barrier to this reaction is not very sensitive to the properties of the cation present. Information of use in the formulation of reaction mechanisms has been obtained from radiolytic studies of oxyhalogen salts [887-889],... 

Transition state theory is presented with an emphasis on solution reactions and the Marcus approach. Indeed, to allow for this, I have largely eliminated the small amount of material on gas-phase reactions that appeared in the First Edition. Several treatments have been expanded, including linear free-energy relations, NMR line broadening, and pulse radiolytic and flash photolytic methods for picosecond and femtosecond transients. 

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