[en] A method is described of applying a decontaminating reagent comprising a one-electron reducing agent based on Vsup(II) or Crsup(II) in combination with a complexing agent to the cooling system of a nuclear reactor or to a decontamination facility, which method comprises: (i) maintaining the Vsup(II) or Crsup(II) ion either in solution under an inert atmosphere in a container made of or lined with an inert material or as a solid salt under an inert atmosphere; (ii) preparing a solution of the complexing agent and removing oxygen therefrom; and (iii) mixing the ingredients from steps (i) and (ii) either in situ in the cooling system of the nuclear reactor or in the decontamination facility, or mixing (i) and (ii) prior to application to the cooling system of the nuclear reactor or to the decontamination facility under conditions whereby no substantial decomposition of the so-formed decontamination reagent occurs. (author)

No abstract available

No abstract available

[en] The objective of this project is to develop chemical reagents for the decontamination of nuclear power reactor coolant circuits with particular emphasis on PWR primary coolant circuits. These reagents must be effective at dissolving activated corrosion products, must be compatible with reactor coolant circuit materials and must be manageable in terms of radioactive waste disposal. A fundamental study of metal oxide dissolution has led to the development of low-oxidation-state transition-metal-ion (LOMI) reagents, which dissolve oxides rapidly without affecting the underlying metal. One of these reagents, vanadous picolinate/formate, has been used to decontaminate reactor specimens efficiently. The radiation-stability of this reagent is good, and the released activity can be collected conveniently on ion-exchange resins. Application of these types of reagents to PWR and BWR decontamination is outlined in the report

[en] The paper concerns the LOMI decontamination system, which was developed by the Central Electricity Generating Board for United Kingdom water reactors and is now used in water reactors worldwide. The LOMI process employs reagents which consist of a strong reducing agent based on low oxidation-state transition metal ions which attach and dissolve the iron rich oxide layers bearing radioactive ions on plant surfaces. A description is given of the decontamination of the Winfrith SGHWR with LOMI, and the corrosion testing programme for the LOMI process. Application of LOMI to BWR and PWR subsystems are described, as well as further process development. (UK)

[en] A frequent observation in metal oxidation is the development of subparabolic kinetics, variously described as cubic or quartic. Although a number of detailed mechanisms have been proposed to account for this effect, none seem generally applicable. A model is presented of the oxidation process which is divorced from such restrictions. It is argued that deviations from parabolic behavior occur as a result of the concurrent development of stresses within the oxide. It is shown that the presence of stress fields can influence significantly the rate of transport of vacancy defects within the oxide such that tensile stresses produce positive deviations and compressive stresses, negative deviations from parabolic behavior. The model is applied in detail to Zircaloy-2 oxidation at 773⁰K. It is predicted that the kinetics should be insensitive to the oxygen potential of the environment and this has been confirmed by previous experimental work. 31 refs

[en] Previous studies showed that methane adsorbed on γ-alumina undergoes radiolysis to form chemisorbed precursor species. These decompose when heated to give C₁-C₃ alkane and alkene products together with hydrogen. The present study uses nitric oxide, nitrous oxide, sulphur hexafluoride, oxygen and carbon dioxide as additives to interfere with product formation, and so allows probable structures to be deduced for each precursor. Both alkane and alkene precursors involve alkylaluminium groups which decompose by homolytic fission of the Al-C bond. The alkane precursor has an accessible hydroxide ion from which a hydrogen atom can be extracted during desorption, whereas the alkene precursor does not. (author)

[en] Graphite is used as a bearing and seal material at gas outlet temperatures in CAGRs under which condition it is subject to thermal corrosion. During thermal oxidation in CO₂-based gas mixtures most graphites exhibit an increase in reactivity. However the relation between structure and changes in thermal reactivity has received little attention, particularly in the nuclear context where the major oxidation reactions are radiolytic. The reactivity of a sample of graphite is a function of the amount and nature of the surface accessible to the gas. The variation in reactivity with weight loss therefore reflects changes in surface area and/or surface nature. The development of surface area is governed by changes in pore structure. It could be expected that the surface nature may be a function of material source and preparation. The purpose of this paper is to describe briefly an investigation of the relationship between reactivity, weight loss and structural changes for two Gilso-carbon based graphites. (author)

[en] An earlier study showed that γ-alumina surfaces outgassed above 570 K contain sites involving exposed lattice ions at which methane is chemisorbed during γ-irradiation. When the species so formed are heated they decompose yielding C₁, C₂ and C₃ alkanes and alkanes together with hydrogen. The present study investigates the kinetics of the reactions occurring during irradiation. These reactions are shown to be the activation of surface sites and the dissociative chemisorption of methane, in accord with the mechanism previously suggested. Overall product yields are chiefly determined by the rate at which excited charge carriers reach the surface, the highest rate observed being G(- CH₄) = 2.0 but declining when fewer than approximately 3 x 10¹⁵ m^-2 chemisorption sites remain unoccupied. A kinetic scheme is proposed to account for the variation in yields with methane coverage, radiation dose and dose rate, and specific surface area of the γ-alumina. It is also shown that the individual products formed when the precursors decompose depend on the configuration of the methane chemisorption sites, and so on the origin of the γ-alumina and the outgassing temperature used. Two subsidiary reactions are identified. The first of these resembles normal radiolysis but occurs at sites less accessible to methane. In the second, however, new surface species are formed when irradiation continues after either the methane or the chemisorption sites have been exhausted. These scavenge part of the adsorbed hydrocarbon material. (author)

[en] Ion exchange is a widely used technique for obtaining radionuclides in solid and concentrated form from liquid effluents and process streams. Frequently the high burden of inactive ions present limits the ion exchange capacity for active nuclides, leading to an unnecessarily large bulk of waste resin. The Sequential Ion Exchange process takes advantage of a resin's selectivity to concentrate the radionuclides and reject the inactive ions. In the process the radionuclides are collected in the normal way, but the resin is then regenerated and, after suitable treatment, the radionuclides are reabsorbed on a smaller volume of the selective resin. The process has been developed to remove and concentrate trace quantities of radiocaesium from the Berkeley Nuclear Laboratories spent fuel handling pond. (author)