Studies have been carried out investigating the photochemical and photophysical properties of anthracene adsorbed on silica gel. The photochemistry and photo physics of anthracene in solution are well reported and known, hence its choice as a probe for the silica gel surface. UV -visible absorption and fluorescence spectra of anthracene adsorbed on silica gel reveal aggregate formation at very low loadings (1 % of a monolayer) indicating preferential adsorption occurs at some surface sites. Laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene, their production was found to be mono- and multi-photonic respectively. The decays of both these transients were complex and the rates increased with increasing loading. Analysis of the triplet state decay has been carried out by studying the delayed fluorescence which arises from triplet triplet annihilation. Fractal and twodimensional models have been used to describe this bimolecular decay. The coadsorption of anthracene and an electron donor having an oxidation potential below 1.09 V on silica gel causes electron transfer to occur from the electron donor to the anthracene radical cation produced following laser flash photolysis at 355 nm. Studies using a selection of electron donors with varying reduction potentials were carried out. The electron donor transfers an electron to the anthracene radical cation, thus greatly accelerating its rate of decay; for electron donors such as triphenylamine, N,N-dimethylaniline and N,N,N',N'tetramethyl- l,4-phenylenediamine the rise of the donor radical cation is observed as the anthracene cation decays. These systems were studied using fluorescence measurements and laser flash photolysis to study any fluorescence quenching and the rate of decay of both the anthracene triplet and radical cation. A selection of anthracene derivatives adsorbed onto silica gel were also briefly studied to see the effect of substituent group and its position. Symmetrically substituted dialkoxyanthracenes and 9-cyanoanthracene were used. The transient absorption spectra of the 2,3- and 2,6-dialkoxyderivatives and 9-cyanoanthracene revealed spectral similarities with that of unsubstituted anthracene. The spectra of9,10- and I,S-didecyloxyanthracene showed significant differences in the radical cation spectra to those obtained for unsubstituted anthracene.

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The favoured option for disposal of low and intermediate level radioactive waste is burial deep underground. In the safety assessment of deep disposal facilities a possibility which has to be considered is the eventual penetration of the engineered and natural barriers by ground water. Unfortunately humic and fulvic acids, present in most natural waters, can combine with radionuclides to produce metal complexes which are potentially more mobile in the environment than the original radionuclides from which they are formed. Migration of such complexes via groundwater and/or subsequently surface water routes could result in accelerated release of radionuclides to the biosphere. Quantitative knowledge of the extent of possible metal humate and fulvate interactions is therefore of considerable importance. In this study the complexation of Ni, Eu and Ce by humic and fulvic acids present in both ground and surface waters has been investigated. In most studies, to simplify the chemistry involved, humics and fulvics are separated from the water in which they occur before determination of their complexation properties. However, the severe conditions employed in the extraction process could conceivably alter the very properties to be measured. Accordingly the complexation properties of humics and fulvics present in a surface water have been studied both before and after extraction. The major part of this study was undertaken using a High Performance Size Exclusion Chromatographic technique especially developed to facilitate determinations on nonextracted materials. A fluorescence technique was also investigated as a more rapid alternative but was found to be of limited applicability. Complexation parameters were derived using a strong and weak site model. The effects of side reactions, ionic strength, pH, ligand type and nature of the cation were taken into account. With respect to measured stability constants, no major differences between ground and surface waters or extracted and non extracted materials were found. However, measured capacities of humics and fulvics for metals showed some variation according to the nature of the material and the system.

En cas d’accident grave sur un Réacteur à Eau Pressurisée, l’évaluation de la quantité d’iode susceptible d’être rejetée dans l’environnement revêt une grande importance du fait de la radiotoxicité et de la volatilité de cet élément. Ainsi, une connaissance de tous les phénomènes physico-chimiques se produisant est nécessaire. Ce travail s’est focalisé sur la re-vaporisation, jusqu’à 750°C, de dépôts des PFs contenant de l’iode, particulièrement le CsI et l’AgI, depuis la surface du circuit primaire composée d’acier 304L, 316L et Inconel 600 partiellement oxydés. Les résultats ont montré une influence significative de la composition de l’atmosphère sur les quantités et les formes chimiques de césium et d’iode re-vaporisés. Ainsi, sous vapeur d’eau l’iode et le césium se re-vaporisent intégralement depuis la surface métallique, sous forme de CsI. En présence d’air, l’iode est relâché intégralement, sous forme d’I2(g) majoritairement, tandis que le césium est partiellement retenu à la surface sous forme de chromate de césium, résultant de l’interaction entre le césium et l’oxyde de chrome (III) de la couche d’oxyde. L’utilisation de la technique de spectroscopie optique en ligne IBB-CEAS a permis d’établir la cinétique de relâchement d’I2(g), celle-ci présentant deux pics de relâchement, indiquant l’existence de plusieurs mécanismes conduisant à la formation de cette espèce. Un résultat similaire a été observé pour la re-vaporisation d’AgI en présence d’air. Finalement, des calculs à l’équilibre thermodynamique ont été entrepris afin d’identifier les voies réactionnelles principales pouvant conduire à la formation d’I2(g) lors de la re-vaporisation de CsI en présence d’air. / In case of a severe nuclear accident on a Pressurized Water Reactor, radioactive fission products can be released in the environment and represent a hazard for the human. In order to better predict the progress of the accident and the release of fission products with the use of dedicated simulation tools, the knowledge of all physicochemical phenomena is necessary. This research is focused on the re-vaporisation, up to 750°C, of iodine-containing fission products’ deposits, particularly CsI and AgI, from the surface of the primary circuit, composed of partially oxidized 304L, 316L steels and Inconel 600 alloy. The results have revealed a strong influence of the re-vaporisation atmosphere composition on the quantities and the chemical species nature of re-vaporized caesium and iodine. In steam atmosphere, iodine and caesium are released integrally from the surface, mainly as CsI. In presence of air, iodine is released integrally, mainly as I2(g), whereas caesium is partially retained on the surface of the steel as caesium chromate, resulting from the interaction between caesium and chromium (III) oxide present in the oxide layer. The use of an online optical spectroscopic technique such as IBB-CEAS allowed to follow the I2(g) re-vaporisation kinetics. The latter exhibits two release peaks, suggesting several mechanisms leading to I2(g) formation. A similar result has been observed during the re-vaporisation of AgI in presence of air. Finally, thermodynamic equilibrium computations have been performed in order to identify the main reaction pathways leading to the formation of gaseous molecular iodine in presence of air.