The introduction of the Enhanced Actinide Removal Plant (EARP) at Sellafield in 1994 was designed to decontaminate radioactive effluents produced during nuclear fuel reprocessing. Through the action of flocculation with iron, followed by filtration, the effluents are decontaminated before being discharging to sea. The plant has been in successful operation for the past 20 years, and has made a significant difference to the level of radioactivity of the waste. However, little is known about the formed flocs. Particular concern focuses around future changes to the effluent compositions to be processed through EARP. These future feeds will potentially contain significantly less iron, thus potentially impacting upon the flocculation process and the efficiency of the decontamination process. The effluents currently treated contain significant concentrations of iron, stemming from the Magnox fuel reprocessing plant, along with actinides, fission and corrosion products. The flocculation of these acidic radioactive ferric feeds results in the formation of solid iron hydroxide flocs with encapsulated radioactivity. The flocs are then filtered, encapsulated and stored. It is envisioned that by characterising the floc properties, both physically and chemically a greater understanding of EARP can be obtained, ultimately leading to a maintained process efficiency with alternative feed compositions. The effect of a reduction in iron concentration on the chemical and physical properties of the flocs has been studied. The presence of any iron in the mock effluents was found to beneficially increase the contaminant decontamination factors (DF). However, the efficacy of this increase varied between contaminates. The DFs of group I and II metals ranged from 7.10 to 1.19 while lead ranged from 4x105 to 1.60, dependent upon iron concentration. Transition metal and lanthanide contaminants were marginally affected. With the use of agar embedding, the 'liquid form' of the flocs has been retained for two and three dimensional observations. SEM/EDX analysis has allowed for the inspection and chemical characterisation of the flocs while 2D microscope image analysis has allowed for the study of floc size and shape. A range of diameters, 300 - 1500 micro metre were found. Three dimensional X-ray Computer Tomography (3D X-ray CT) conducted at the Manchester X-ray Imaging Facility (MXIF) has led to the physical characterisation and classification of the flocs. Further, by studying the 3D shape it has been possible to classify a floc as a granule, fibre, chip or blade according to the Zingg classification with the majority of formed flocs being classified as granules.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:728030 |
| Date | January 2017 |
| Creators | Foster, Richard |
| Contributors | Sharrad, Clint |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/a-multi-method-approach-towards-the-study-and-characterisation-of-simulated-enhanced-actinide-removal-plant-particulates(31138956-ee33-4ba9-98a4-07b319611f54).html |
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