Biogeochemical controls on the corrosion and fate of depleted uranium

Depleted uranium (DU) is a by-product of the nuclear fuel industry and is used in anti-tank penetrators due to its high density, self-sharpening and pyrophoric properties. Military activities have left a legacy of DU waste in terrestrial and marine environments and presently there are no clean up procedures in place. In order to understand the fate of this DU, long term (500 days) microcosm experiments simulating key environments have been carried out for the first time to investigate the mechanisms and rates of DU corrosion as a function of the biogeochemical and environmental conditions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Influence of pH, competing ions, and salinity on the sorption of strontium and cobalt onto biogenic hydroxyapatite

Anthropogenic radionuclides contaminate a range of environments as a result of nuclear activities, for example, leakage from waste storage tanks/ponds (e.g. Hanford, USA or Sellafield sites, UK) or as a result of large scale nuclear accidents (e.g. Chernobyl, Ukraine or Fukushima, Japan). One of the most widely applied remediation techniques for contaminated waters is the use of sorbent materials (e.g. zeolites and apatites). However, a key problem at nuclear contaminated sites is the remediation of radionuclides from complex chemical environments. In this study, biogenic hydroxyapatite (BHAP) produced by Serratia sp. bacteria was investigated for its potential to remediate surrogate radionuclides (Sr2+ and Co2+) from environmentally relevant waters by varying pH, salinity and the type and concentration of cations present. The sorption capacity of the BHAP for both Sr2+ and Co2+ was higher than for a synthetically produced hydroxyapatite (HAP) in the solutions tested. BHAP also compared favorably against a natural zeolite (as used in industrial decontamination) for Sr 2+ and Co 2+ uptake from saline waters. Results confirm that hydroxyapatite minerals of high surface area and amorphous calcium phosphate content, typical for biogenic sources, are suitable restoration or reactive barrier materials for the remediation of complex contaminated environments or wastewaters

Rock fracture grouting with microbially induced carbonate precipitation

Microbially induced carbonate precipitation has been proposed for soil stabilization, soil strengthening and permeability reduction as an alternative to traditional cement and chemical grouts. In this paper we evaluate the grouting of fine aperture rock fractures with calcium carbonate, precipitated through urea hydrolysis, by the bacteria Sporosarcina pasteurii. Calcium carbonate was precipitated within a small-scale and a near field-scale (3.1 m2) artificial fracture consisting of a rough rock lower surfaces and clear polycarbonate upper surfaces. The spatial distribution of the calcium carbonate precipitation was imaged using time-lapse photography and the influence on flow pathways revealed from tracer transport imaging. In the large-scale experiment, hydraulic aperture was reduced from 276 μm to 22 μm, corresponding to a transmissivity reduction of 1.71x10-5 m2/s to 8.75x10-9 m2/s, over a period of 12 days under constantly flowing conditions. With a modified injection strategy a similar three orders of magnitude reduction in transmissivity was achieved over a period of three days. Calcium carbonate precipitated over the entire artificial fracture with strong adhesion to both upper and lower surfaces and precipitation was controlled to prevent clogging of the injection well by manipulating the injection fluid velocity. These experiments demonstrate that microbially induced carbonate precipitation can successfully be used to grout a fracture under constantly flowing conditions and may be a viable alternative to cement based grouts when a high level of hydraulic sealing is required and chemical grouts when a more durable grout is required

Pathways of radioactive substances in the environment

The release and transport of radionuclides in the environment is a subject of great public concern. The primary sources of radionuclides in the environment are nuclear weapons testing and production, and the processes associated with the nuclear fuel cycle. Whilst nuclear weapons tests have been the main source of atmospheric contamination, resulting in global, low-level contamination, sites associated with weapon production and the nuclear fuel cycle can have localised high levels of contamination, and the spread of this contamination via aquatic pathways represents a significant environmental problem. Migration in the atmosphere will depend on the nature of the radioactive material and the prevailing meteorological conditions. Within surface water and groundwater environments, transport will be controlled by physical processes such as advection and the biogeochemical conditions in the system. In systems with significant flow, advection will be the dominant transport process, but as hydraulic conductivity decreases, chemical processes and conditions become increasingly important in controlling radionuclide migration. Factors such as solution phase chemistry (e.g. ionic strength and ligand concentrations), Eh and the nature of mineral phases in the system have a critical effect on radionuclide speciation, controlling partitioning between solution and solid phases and hence migration. Understanding the complex interplay between these parameters is essential for predicting radionuclide behaviour and migration in the environment