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A Multi Method Approach Towards the Study and Characterisation of Simulated Enhanced Actinide Removal Plant Particulates

Foster, Richard

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

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 μm 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.

Bibliographic metadata

Type of resource:
Content type:
Administered thesis
Form of thesis:
Traditional
Type of submission:
Doctoral level ETD - final
Thesis title:
A Multi Method Approach Towards the Study and Characterisation of Simulated Enhanced Actinide Removal Plant Particulates
Degree type:
Doctor of Philosophy
Degree programme:
PhD Chemical Engineering & Analytical Science (42 month)
Publication date:
2016-11-20T22:39:30
Institution:
The University of Manchester
Location:
Manchester, UK
Total pages:
180
Abstract:
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 μm 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.
Additional digital content not deposited electronically:
N/A
Non-digital content not deposited electronically:
N/A
Keyword(s):
Thesis main supervisor(s):
Thesis co-supervisor(s):
Degree grantor:
Language:
en

Institutional metadata

University researcher(s):
Academic department(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:305689
Created by:
Foster, Richard
Created:
20th November, 2016, 22:39:31
Last modified by:
Foster, Richard
Last modified:
1st December, 2017, 09:09:28

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