No description available.

No description available.

This thesis concerns the investigation of radioisotopes as indicators for precipitation reactions. As a precipitate forms in the presence of a radioisotope, adsorption may take place on its surface. If this adsorption changes markedly at the stoichiometric point it will be possible to use this variation as an indicator for the reaction.

The purpose of this investigation is to reveal the effects of certain factors affecting adsorption on some specific precipitates. It is hoped that the choice of precipitate types will enable extension of the information gained here to other precipitates similar to those investigated.

The ability of zeolites, particularly clinoptilolite, to immobilise Cs arising as an intermediate level radioactive waste is studied. The zeolites are incorporated into Portland cement blends containing additives such as blast furnace slag, pulverised fuel ash and silica fume, and high alumina cement blends. Desorption of Cs+ from the zeolite by ion-exchange cement pore fluid species, mainly K+, Na+ and Ca is studied and ion-exchange isotherms are presented. The Cs distribution between clinoptilolite and cement pore fluid is studied by X-ray diffractometry (XRD) and by chemical analysis of the pore fluid. Some Cs is released into the pore fluid, mainly by ion-exchange with K. The kinetics and mechanism of the pozzolanic reaction between clinoptilolite and Portland cement is studied at various temperatures, using a selective dissolution method, as well as XRD, thermogravimetric analysis and analytical electron microscopy. A model is developed, whereby long-term predictions of clinoptilolite reactivity can be made. Methods of limiting the pozzolanic reaction to ensure the long-term persistence of clinoptilolite in cement by blending are investigated. Slag cements show lowest reactivity. Leach tests are carried out on cement-clinoptilolite cylinders (45x80mm) using a standard leaching method. These confirm the importance of ion-exchange and chemical reactivity in determining leach rate. Additionally, the effect of factors such as clinoptilolite particle size, Cs -loading level, clinoptilolite-cement ratio, quantity and type of cement additive, curing temperature, curing time, leaching temperature and mercury porosity on leach rate are investigated. An optimal cement-clinoptilolite blend is suggested. A method is described for the measurement of oxidation-reduction potential (Eh) of cement pore fluids extracted under pressure, and of measuring the poising capacity of solid and aqueous phases. OPC is mildly oxidising, whereas slag cements provide a reducing environment due to the presence of S-containing species. The implications of E. and pH in terms of radwaste immobilisation are discussed.

Call number: LD2668 .T4 1959 M87

U migration was studied in order to better understand to processes of safety relevant elements, particularly U. The rock sequence on the site can be analogous to a potential rock overburden of deep geology repositories. A multidisciplinary approach was undertaken in order to identify and characterise U mobilisation/immobilisation processes within sedimentary clayey rocks with organic matter enriched interlayers. Both conventional methods and modern sophisticated spectroscopic methods were combined. Sequential extraction, wet chemical method and even spectroscopic methods proved that U prevailed in the U(IV) form in low-oxidised samples. It moved towards more easily releasable fractions with sample ageing (oxidation). The combination of SE, µ-XRF and µ-XAFS results proved U to be unexpectedly associated with As and P, leading to the presumption that U(VI) from groundwater was reduced to U(IV) on As pyrite. The evaluation of the hydrogeochemical conditions and isotope analyses then brought the results into broader context: Sedimentary organic matter within the sedimentary layers was microbially oxidised, releasing dissolved organic matter and providing H+ in order to dissolve sedimentary inorganic carbonates. SO4 2- could be reduced under reducing groundwater conditions, thus causing FeS2 formation....

Digitized by Kansas Correctional Industries

No description available.

Thesis (Ph.D.) in Physics--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 94-99).