No description available.

No description available.

No description available.

No description available.

A study has been made of the dynamic behaviour of a nuclear fuel reprocessing plant utilising pulsed solvent extraction columns. A flowsheet is presented and the choice of an extraction device is discussed. The plant is described by a series of modules each module representing an item of equipment. Each module consists of a series of differential equations describing the dynamic behaviour of the equipment. The model is written in PMSP, a language developed for dynamic simulation models. The differential equations are solved to predict plant behaviour with time. The dynamic response of the plant to a range of disturbances has been assessed. The interactions between pulsed columns have been demonstrated and illustrated. The importance of auxillary items of equipment to plant performance is demonstrated. Control of the reprocessing plant is considered and the effect of control parameters on performance assessed.

Ion exchange resins have been used for retrieving radiocaesium from aqueous waste streams since the earliest days of the nuclear power industry. The physical and chemical properties of Lewatit DN ion exchange resins encapsulated in silica fume (SF)-blended cement were investigated with the aim of producing a stable solid wasteform for possible future disposal in an underground repository. Expansive reactions involving resin swelling in the high pH pore fluid and Ca(OH)2 formation around the resin particles can be suppressed by the addition of 50-75% SF at w/c ratios of 1.400-1.71. The basis of this suppression is the pozzolanic reaction between Ca(OH)2 and SF which consumes Ca(OH)2 and lowers the pH of the pore fluid to less than 10. The total heat evolution of blended cements is similar to that of a neat Portland cement, demonstrating the exothermic nature of the pozzolanic reaction. The use of high w/c ratios in cements containing 50% SF increases the permeability of the matrix. Porosity measurements indicate that this is due to the high free water content of the paste and the relatively high porosity of SF agglomerates. Elevated curing temperatures (up to 85oC) also increase the permeability as a result of coarsening of the microstructure. Despite the inferior physical immobilisation of caesium in high SF-content cements, leach tests, sorption measurements and pore fluid analysis show that chemical retention of caesium is enhanced by blending, more so in blends containing a permanent excess of SF, due to the formation of highly sorptive silica gel and low ratio C-S-H (Ca/Si as low as 0.80). On the other hand, SF-blended cements are more susceptible to physiochemical degradation in simulated groundwater's containing MgSO4. Chemical attack by MgSO4 converts C-S-H gel and silica gel to a non-cementitious magnesium silicate hydrate (identified as sepiolite) in 50-75% SF pastes, resulting in extensive deterioration of the attacked zone.

In an EPA/DOE meeting in the U.S. in 1986, concerns on quantifying radon availability and the indoor radon concentration were highlighted (Hopke 1986). This work addressed some of their recommendations in a study on radon levels in S.W. England. This thesis presents: i) investigations into the correlation between indoor and soil gas radon concentrations, by the acquisition of new data from S. W. England. ii) investigations into the influence of geology, meteorological variables, spatial and depth variation on the measured radon levels. iii) a propsed protocol for obtaining soil gas measurements, suitable for use as an indication of potential inddor radon concentrations in S.W. England. iv) a discussion of the applicability of existing prediction models and proposals for the parameters to be included in any models applied to S.W. England. Several geological faults in S.W. England were delineated using radon measurements. Jointing was found to create anomalously high levels of [sup]222 Rn in the soil gas. A previous theory on the movement of ground water in convection cells was found to be unsupported. A dependence of both indoor and soil gas radon concentrations on the local geology was observed. Granite produced the highest levels as expected, and the influence of its metamorphic aureole was clearly detected. The increased fracturing of the rock was found to increase radon concentrations. Significant differences in soil gas radon levels were measured between the various sedimentary rock types. The two factors that were identified as chiefly responsible for any perturbation of a soil gas concentration, associated with a particular geology, are its moisture content and the inhomogeneity of soil permeability. Only a very weak correlation was obtained between the overall [sup]222 Rn concentration in soil gas and inside the home. However, for high soil gas concentrations a stronger correlation with the indoor level was observed. Typically the soil gas concentration was between a factor of 10 and 1000 times greater than that indoors. Levels as low as 10 kBq m[sup]-3 in the soil could produce an indoor concentration above the Action Level of 200 Bq m[sup]-3, The magnitude of influence of the various controlling parameters prevented the construction of a simple algorithm to predict the indoor radon concentration from that in the soil gas. However, in some cases, factors were identified that increased the probability that a house was above the Action Level. For a soil gas concentration in excess of 100 kBq m[sup]-3, it was found that over 70% of homes were above the Action Level, if located above and/or constructed from granite.

No description available.

No description available.

The thesis describes the development of analytical procedures for the isolation and measurement of anthropogenic pure beta-emitting radioisotopes in low-level radioactive wastes and environmental samples. The research focussed on three key pure beta-emitting radioisotopes, namely 63Ni, 90Sr and 99Tc. Iron-55, which decays by electron capture, was also investigated. Source preparation and measurement techniques based on liquid scintillation counting were developed and optimised to permit the low-level measurement of all four radioisotopes. In particular, a technique was developed for increasing the amount of stable Fe that may be loaded into scintillant, reducing the limit of detection achievable for 55Fe measurement and increasing the sensitivity of analysis for 55Fe in Fe-rich materials such as sediments and steels. Chemistries for the isolation of the four radioisotopes were studied and optimised. Solvent extraction was chosen for the specificity offered by the technique. In most instances, improvements in separation efficiency were achieved by adsorbing the extractant onto an inert support producing an extraction chromatographic material. Key separation techniques were then combined to produce a sequential separation scheme that permitted a more rapid analysis of the four radioisotopes on a single sample. The sequential separation technique was then optimised for the analysis of 55Fe, 63Ni, 90Sr and 99Tc in both low-level wastes and environmental matrices (mainly sediments). Such separation schemes are crucial to the efficient analysis of samples in limited time spans and are vital when the amount of sample available is restricted. The optimised methods were used to investigate levels of anthropogenic pure beta-emitters in a saltmarsh sediment core collected from the Esk Estuary in Cumbria. Analysis of the four beta emitting radioisotopes was complemented by the analysis of major elements, trace elements and gamma emitting radioisotopes. This information was used to determine the behaviour of the beta emitters following deposition within the saltmarsh environment. Although all four beta emitters were detected in the core, only 90Sr and 99Tc were at sufficiently high levels to permit a more thorough investigation. The combination of geochemica! analysis and radiochemical analysis of this range of radioisotopes with widely varying chemistries has allowed a range of possible pre- and post-depositional processes to be investigated as well as providing data on the levels of previously unmeasured beta emitters in the saltmarsh environment. Such information is essential in assessing the long-term retention and potential re-release of these radioisotopes and their importance in radiological dose assessment. The information also has wider implications to the behaviour of inorganic pollutants in coastal waters.