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The study of heat transfer and moisture movement in liquid and vapour phase has attracted the attention of scientists from the beginning of 19th century. The study is very important to many geotechnical and geoenvironmental problems like diurnal heat mass movement in ground, performance assessment of nuclear waste disposal repositories, buried hot pipes, buried high voltage electric cables and landfill liners. Significant experimental and theoretical development has been made in this field but still there is a lack of experimental data available specially for highly swelling clays. The heat transfer and liquid moisture movement theories for clays more or less are very well established but vapour transfer theory is still based upon rigid matrix granular soils. Therefore, this thesis presents an experimental, theoretical and numerical investigation of the heat and moisture movement in unsaturated clays. A new apparatus termed a thermo-hydraulic (TH) cell has been designed, fabricated and calibrated in-house to perform thermal gradient, thermo-hydraulic gradient and isothermo-hydraulic gradient tests on two types of clays namely Speswhite kaolin and MX-80 bentonite. The TH cell is capable of measuring the transient temperature, relative humidity, volume flow rate of incoming water and swelling pressure. It also facilitates the determination of moisture content, dry density and chemical composition (anions and cations concentration) of the soil samples at the end of the tests. In the thermal test, the clay sample is subjected to fixed temperatures of 85 C at the bottom end and 25 C at the top end. In the thermo-hydraulic test, same thermal gradient is used like the thermal test and in addition to this deionised and de-aired water was supplied at the top end under a pressure of 0.6 MPa. In the isothermal test, the clay sample is supplied deionised and de-aired water from the top end under a pressure of 0.6 MPa and the temperature kept at 25 C at both ends of the clay sample. The test results show that there is a cycle of vapour and liquid moisture movement within the clay sample, vapour moves from the hot end to the cold and condense to liquid at the cold end and liquid moisture moves to the hot end. The accumulation of chloride ions near the hot end indicate that liquid moisture moved from the cold end to the hot end. An empirical method has been developed to calculate the vapour fluxes using the variation of chloride ions concentration with time. The vapour fluxes calculated empirically found to be much lower than that determined by existing vapour theories. Therefore, the existing vapour theory has been modified to more closely predict the observed vapour fluxes. The new modified vapour transfer theory has been incorporated in transient finite element code and validated against the experimental work carried out in this study. The numerically simulated results match reasonably with the experimental heat and mass results. Further research is necessary to explore the new vapour theory application to large scale tests.

This thesis describes the modelling of the thermo-hydro-mechanical behaviour of a large-scale experiment, carried out at SKB's underground research laboratory in Aspo, Sweden. The experiment, known as the Prototype Repository Project, was constructed in highly fractured granite rock and is scheduled to last 20 years. Results from the experiment are collected systematically by SKB from the initial rock characterisation to the highly instrumented installed material. The model applied is the thermo-hydro-mechanical model previously developed at the Geoenvironmental Research Centre (GRC). The GRC's current model was extended to successfully accommodate three-dimensional THM behaviour, including the development of a high-performance computing algorithm using both multi-threaded and message-passing programming paradigms to enable simulations to be completed in significantly reduced time. Model simulations have been conducted of both the pre-placement stage of the experiment and the post-placement operational phase. The results of the pre-placement phase have been used to aid the calibration of the simulation and provide confidence in the development of the operational phase simulation. In the pre-placement phase simulation, a pragmatic approach using a combination of an effective continuum model and a number of key discontinuities was employed. A domain of 100 x 100 x 160m was used, discretised into over 550,000 finite-elements. The simulations were able to reproduce three-dimensional highly anisotropic flow conditions shown in the experimental results. The post-placement operational stage was then simulated in three-dimensions using the same rock domain as for the pre-placement analyses, including the buffer material, and discretised into over 920,000 elements. A number of key features, including the anisotropic hydraulic behaviour, were captured. It was concluded that the geological conditions, backfill re-saturation and buffer re-saturation, including the micro-structural effects of the bentonite, are all important to the simulation of a high-level waste repository. Long term simulation results were also presented. A number of aspects were explored using two-dimensional analyses, including the macro/micro- structural interactions of the bentonite buffer. A time-dependant form of the hydraulic conductivity relationship was developed and yielded significantly improved results in long-term analyses. The behaviour of a fracture intersecting a deposition-hole was also investigated highlighting the importance of discrete fractures on hydration behaviour.

Gamma radiation in the environment is mainly due to naturally occurring radionuclides. However, there is also a contribution from anthropogenic radionuclides such as 137Cs which originate from nuclear fission processes. Since 1986, the accident at the Chernobyl power plant has been a significant source of artificial environmental radioactivity. In order to assess the radiological impact of these radionuclides, it is necessary to measure their activities in samples drawn from the environment and in plants and animals including human populations. The whole body counter (WBC) at the University Hospital of Wales in Cardiff makes in vivo measurements of gamma emitting radionuclides using a scanning ring of six large-volume thallium-doped sodium iodide (Nal(Tl)) scintillation detectors. In this work the WBC was upgraded by the addition of two high purity germanium (HPGe) detectors. The performance and suitability of the detection systems were evaluated by comparing the detection limits for Cs. Sensitivities were measured using sources of known activity in a water filled anthropomorphic phantom and theoretical minimum detectable count-rates were estimated from phantom background pulse height spectra. The theoretical minimum detectable activity was about 24 Bq for the combination of six Nal(Tl) detectors whereas for the individual HPGe detectors it was 64 Bq and 65 Bq, despite the much improved energy resolution Activities of 137Cs in the human body between 1993 and 2007 were estimated from the background Nal(Tl) spectra of 813 patients and compared with recent measurements in 14 volunteers. The body burden of Cs in Cardiff patients increased from an average of about 60 Bq in the early and mid 1990s to a maximum of about 100 Bq in 2000. By 2007 it had decreased to about 40 Bq. This latter value was similar to that of Cardiff residents at the time of the Chernobyl accident and to that of the volunteers measured in 2007 (51 Bq). However, it was less than the mean activity of Cardiff residents in 1988 (130 Bq) indicating an overall decrease over a period of about 20 years. The variation in the in vivo activity is probably due to complex inter-relationships between a number of factors such as the removal of deposited 137Cs into the sea by rainfall, individual dietary choices, the imposition and removal of restrictions on foodstuffs from Chernobyl-affected areas and travel to countries that suffered greater initial fall-out than the UK.

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