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The calculation of dry particle deposition velocity (Vg) for small particles in field studies is subject to much variability between theoretical and measured values. This work will assess some of the factors which may influence the calculation of Vg. The other key parameter which is used to define the near-surface exchange of material is the resuspension factor (K). The certainty of using a Vg which is representative of small particles typically 1 pm requires clarification. During September 1993-1994, four size-selective air and deposition experiments were carried out at an on-site and off-site sampling location close to the BNFL Sellafield nuclear reprocessing plant in Cumbria UK. Dry and total (wet & dry) particle deposition velocities were determined for ^^^Cs, The dry deposition velocities of naturally-occurring ^Be were also determined and used as a 'marker' for small particle transport processes. Resuspension factors K (m ^) for radiocaesium and Plutonium were also derived. Automated individual particle characterisation (AlP) using scanning electron microscopy coupled to energy-dispersive x-ray analysis (SEM-EDXA) was used to determine the particle size distribution and associated elemental composition of material deposited to Frisbee deposition collectors. Enhanced a-emitting hot-spots from surface soils and material deposited to Frisbee collectors at 1 m above ground level were isolated and characterised for size and shape using nuclear track detector film, LR-115. Dry particle deposition velocities for ^^^Cs, 239+240py and were commonly in excess of 1E-03 m s"^ by more than two orders of magnitude. Total deposition velocities (dry and wet) were even higher with values ranging from 0.2 m s^ -1 ms"^ for both radiocaesium and plutonium. High derived values of dry deposition velocity for radiocaesium and plutonium were to some extent influenced by air sampling artefacts. Air sampling artefacts result in an under-estimation of airborne activity for radioactivity associated with particle diameters >10 pm. The derived values of dry particle deposition velocity for ^Be were consistent with literature values of sub-micron sized particles with evidence of a seasonal spring maximum. Resuspension factors K (m'^) for radiocaesium and plutonium agreed well with literature values of weathered weapons fallout values which ranged from 2E-08 to 5E-11 (m"^) for plutonium and radiocaesium respectively. Differences in dry particle deposition velocities for radiocaesium and plutonium between the on-site and off-site locations varied by no more than a factor of three. Correlations between dry particle deposition velocities for Cs and Pu with wind speed, wind direction and precipitation rates were not found. Size-specific air sampling show that the majority of the plutonium was predominantly associated with the >11 lam aerosol size fraction. The association between activity and large particle size suggest this material was probably attached to large soil-derived particles. Plutonium isotope data indicate this material originated fromthe nuclear weapons programme of the late 1950's-earty 1970's. Radiocaesiumactivities were equally distributed between the < 10 ixm and > 11 ^m aerosol fractions for two out of the four runs. This suggests that historically deposited ''^^Cs and current emissions contributed to measured airborne activities. Enhanced a-emitting hot-spots were isolated from bulk surface soils and in material deposited to Frisbee collectors. Rare particles such as these with atypical activities of Pu may lead to mis-leadingly high deposition fluxes. The calculation of Vg in the field is therefore sensitive to the presence of these particles because they are not representative of the aerosol flux and their size s 50 |im precludes their collection by the Pmio air sampler. The main conclusions of this work indicates the very high values of Vg sometimes measured in the field are strongly influenced by large resuspended soil particles and associated air sampling artefacts. The inclusion of large particles within the deposition flux is confirmed by size selective mass based Vg using scanning electron microscopy

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The mechanisms controlling radiocaesium migration through the peat soil were investigated by considering physico-chemical & biological factors affecting radionuclide adsorption/desorption in the peat soil using the Batch & Column Methods as well as a "Direct Fumigation Extraction Method". The biological factors were investigated under different conditions by variation of the micro-organisms content in the peat soil, the soil solution and leaching conditions. Samples of peat soil were reacted with solutions containing caesium ions, and the effect on caesium-K_d determined. The caesium adsorption/desorption was found to be influenced by concentration of caesium and other cations (NH₄⁺, K⁺ and Ca⁺⁺) and by the pH of the solution. Below pH 3, in presence of calcium and potassium, desorption could occur as the exchangeable sites on microparticles were replaced by other cations. At pH>1, in presence of ammonium, adsorption could occur. The distribution coefficient, K_d value was strongly reduced following the addition of NH₄⁺, K⁺ and Ca⁺⁺ at a fixed pH. NH₄⁺ was found to be more effective in the caesium desorption than the other cations. By increasing the concentration of radiocaesium (>0.2 MBq/100μl) the effect became much less leading eventually to an increase in caesium-K_d values. A decrease in the caesium-K_d was also observed at pH<3 in peat samples. It was found that the caesium adsorption approached to an equilibrium state at pH>3 depending upon caesium concentration in peat solution. Caesium adsorption took 180 days to reach equilibrium state. For the measurement of the release/uptake of radionuclides in the peat soils by the microbial biomass, homogenised wet peat samples were fumigated by chloroform. The influence of the microbial population present in the peat on the environmental mobility of caesium was clearly demonstrated.

The complexity of cementitious matrices and their application in the immobilisation of radioactive waste has led to detailed examination of their ability to condition permeating water to high pH by both experimental and thermodynamic studies. This thesis considers the stability and solubility of pure hydrate phases: Ca(OH)₂; CaO-SiO₂-H₂O gel, Ca:Si = 0.85, 1.1, 1.4, 1.8; 3CaO.Al₂O₃.6H_zO; 3CaO.Al₂O₃.CaSO₄.12H₂O and 3CaO.Al₂O₃.3CaSO₄.32H₂O, and the phase formation and stability within CaO-SiO₂-CaCO₃-H₂O and CaO-Al₂O₃-SiO₂-H₂O compositions aged in saline solutions, up to 1.5M NaCl and 0.05M MgSo₄, at 25°, 55° and 85°C. The two main high pH conditioning phases of cementitious systems are Ca(OH)₂ and C-S-H gel. Sodium chloride enhances the solubility of Ca(OH)₂ and causes a slight reduction in the Ca:Si ratio of C-S-H gels by the progressive leaching of calcium. Silicate polymerisation within C-S-H phases is inhibited by sodium chloride though it is uncertain how this alters the crystallisation kinetics. The pH buffering capacity is maintained when aged in sodium chloride concentrations 0.5, 1.0 and 1.5M at 25°, 55° and 85°C. The stability of calcium sulfoaluminate aged in sodium chloride is greater than of 3CaO.Al₂O₃.6H₂O, which is unstable with respect to 3CaO.Al₂O₃.CaCl₂.10H₂O in NaCl < 0.5M. These phases undergo a progressive phase change to the 3CaO.Al₂O₃.0.5CaSO₄.0.5CaCl₂.10-12H₂O and 3CaO.Al₂O₃.CaCl₂.10H₂O at increasing aqueous Cl:SO₄ ratios. The formation of a limited solid solution region within 3CaO.Al₂O₃.xCaSO₄.l-xCaCl₂.yH₂O: 0.00 ≤ SO₄:Cl ≤ 0.06, was characterised. In magnesium sulfate, 5 - 50m.mol/l, calcium within hydrate phases is progressively replaced by magnesium with formation of Mg(OH)₂, MgO-SiO₂-H₂O gel, 4MgO.Al₂O₃.xH₂O and gypsum. The pH conditioned by the resultant solid assembly decreases to less than that desirable for containment of radioactive waste, to < 9. Consideration of the phase formation and persistence within the CaO-SiO₂-CaCO₃-H₂O and CaO-Al₂O₃-SiO₂-H₂O systems was examined in solutions containing both sodium chloride and magnesium sulfate. The chemical interactions observed were dominated by the replacement of calcium by magnesium within the solid phases with the formation and persistence of mixtures of Mg(OH)₂, MgO-SiO₂-H₂O gel and gypsum. At low Mg:Ca-CO₃ ratios the persistent stability of gehlenite hydrate at 25°C was observed in appropriate samples. The chemistry of the aqueous phase is dependent on the Mg:Ca-CaCO₃ ratio as well as the Ca:Si ratio. At high Mg:Ca-CaCO₃ ratios the high pH conditioning properties are destroyed and buffering occurs at a value below pH 9.

Following the Chernobyl accident in 1986, a range of countermeasures has been developed to reduce the transfer of 137Cs from soil to plant and from the plant into grazing animals. One such countermeasure is the application of potassium to the soil. However, little is known of any side-effects such an application may have on the ecosystem, the longevity of the application and the effectiveness in a range of soil types. An application of potash (KCl) was made to four organic upland soils in Cumbria. England at two application rates of 100 and 200 kg K ha-1 in June 1997 and at a single site in June 1998. Following application. a range of parameters within the ecosystem were recorded, through the collection of monthly samples of sail, vegetation and water samples over a period of fifteen months. The results indicate that the application was effective for at least one year following application, that a lag phase existed between potash application and any effect within each ecosystem and that the duration of this phase was site specific. The results also showed that the countermeasure was effective at all sites and there was little apparent difference between the two application rates. The parameters measured which included soil pH, plant biomass, changes in Cu, K, Mg, Mn and Ca concentrations within the soil and vegetation indicated only a relatively small effect of the application on the ecosystem as a whole. The application can be considered as a viable option for reducing the transfer of 137Cs from soil to plant. The study also shows that the effectiveness of the application is dependent on the measurement used. i.e. concentration ratios, Tag values or a total flux approach. It is argued that the flux approach is the most appropriate basis for comparing the effectiveness of potash as a countermeasure between several sites.

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