The Degradation of Cellulose in the Near Field of a Radioactive Waste Repository

1993 ◽  
Vol 333 ◽  
Author(s):  
B.F. Greenfield ◽  
M.H. Hurdus ◽  
N.J. Pilkington ◽  
M.W. Spindler ◽  
S.J. Williams
Keyword(s):  
Degradation Products ◽  
Cellulose Degradation ◽  
Near Field ◽  
Research Programme ◽  
Water Soluble ◽  
Anaerobic Conditions ◽  
Factors Affecting ◽  
Deep Underground ◽  
The Uk ◽  
Assessment Research

ABSTRACTUK Nirex Ltd is seeking to develop a deep underground repository for the disposal of solid low- and intermediate-level radioactive wastes in the UK. The Nirex Safety Assessment Research Programme (NSARP) comprises scientific research to support the post-closure performance assessment of the repository. One of the investigations carried out by AEA Technology under the NSARP is the investigation of the formation of water-soluble complexants from the degradation of the solid organic polymers and cellulosic materials present in such wastes. The influence of these complexants on the solubility and sorption of a number of radionuclides is also being investigated by a combination of experimental measurements and thermodynamic modelling. Under the alkaline, anaerobic conditions representative of the near field of the repository, cellulose has previously been shown to degrade to yield soluble products which enhance the solubilities and reduce the sorption of several radionuclides. As part of this investigation, cellulose was chemically degraded under conditions similar to those expected in the near field and the leachate analysed. Separation of the products by HPLC gave direct identification of 2-C-(hydroxymethyl)-3-deoxy-D-erythro-pentonic (isosaccharinic) acid as one of the degradation products. More tentative assignments were made for glycolic, formic, lactic and acetic acids. A comparison was made with the degradation products suggested in the literature. The possible mechanisms and extent of cellulose degradation are discussed, as well as the factors affecting its degradation in the near field. The sorption of plutonium on to cement from a leachate produced under alkaline, anaerobic conditions is reported.

The Effects of the Degradation of Organic Materials in the Near Field of a Radioactive Waste Repository

1991 ◽  
Vol 257 ◽  
Author(s):  
B.F. Greenfield ◽  
A.D. Moreton ◽  
M.W. Spindler ◽  
S.J. Williams ◽  
D.R. Woodwark
Keyword(s):  
Organic Materials ◽  
Degradation Products ◽  
Near Field ◽  
Water Soluble ◽  
Hydroxyl Groups ◽  
Modelling Studies ◽  
Deep Underground ◽  
Exchange Resins ◽  
The Uk ◽  
Isosaccharinic Acid

ABSTRACTUK Nirex Ltd are seeking to develop a deep underground repository for the disposal of solid ILW and LLW in the UK. The formation of water-soluble complexants from the degradation of the solid organic polymers and cellulosic materials present in such wastes may influence the solubility and sorption properties of a number of radioelements. A number of materials have been chemically degraded under alkaline, anaerobic conditions representative of the near field of the repository. Measurements of plutonium solubility in the leachates obtained show that the degradation of cellulose is of particular concern; the effects on the solubility can be several orders of magnitude greater than those of other organic materials. Products formed from the degradation of ion-exchange resins were found to have little effect. Solubilities of a number of other radioelements in aerobically degraded cellulose leachates are also given. The effect of reducing the ratio of celluloseto cement in the degradation experiments results in a decrease in plutonium solubility in the corresponding leachate. Several of the likely degradation products of cellulose have been individually synthesised including isosaccharinic acid, a key degradation product of cellulose. Enhanced plutonium solubilities have been measured in 10-3M solutions of these compounds. Sorption of plutonium onto cement from leachates obtained by the degradation of 10% cellulose in cement is reduced by about two orders of magnitude. Interaction with cement removes significant concentrations of complexants from solution. Thermodynamic modelling studies show that hydroxyl groups present in the compounds which result from the alkaline degradation of cellulose can strongly complex with plutonium.

The Sorption of Niobium, Tin, Iodine and Chlorine onto Nirex Reference Vault Backfill

1993 ◽  
Vol 333 ◽  
Author(s):  
S. Baker ◽  
R. McCrohon ◽  
P. Oliver ◽  
N.J. Pilkington
Keyword(s):  
Temperature Dependence ◽  
Performance Assessment ◽  
Safety Assessment ◽  
Scientific Research ◽  
Research Programme ◽  
Intermediate Level ◽  
Sorption Method ◽  
Deep Underground ◽  
The Uk ◽  
Assessment Research

ABSTRACTUK Nirex Ltd is proposing to develop a deep underground repository for the disposal of solid low- and intermediate-level radioactive wastes in the UK, and is currently investigating Sellafield in Cumbria as a possible site. The Nirex Safety Assessment Research Programme (NSARP) comprises scientific research to support the post-closure performance assessment of the repository. One of the investigations carried out by AEA Technology under the NSARP is the study of the sorption of radionuclides onto the backfill. Sorption is one of the key parameters determining the rate of release of radionuclides from the repository. The radionuclides present in the waste include 94Nb, 126Sn, 129I and 36Cl. This paper reports the measurement of the sorption of niobium, tin, iodine and chlorine onto the Nirex reference vault backfill at 20±5°C by the batch sorption method. The temperature dependence of tin sorption was investigated by carrying out additional experiments at 77±5°C. Experiments on niobium solubility and sorption were carried out under saline conditions to reflect the nature of the groundwater at Sellafield. Sorption coefficients (Rd) for niobium are within the range measured in other work, whereas for tin the results are a factor of ten lower than literature values. For iodine and chlorine, the results are consistent with the literature; they also show an increase in Rd with decreasing initial inventory. The Rd values for niobium and tin are significantly higher than those for chlorine and iodine.

The Identification and Degradation of Isosaccharinic Acid, a Cellulose Degradation Product

1994 ◽  
Vol 353 ◽  
Author(s):  
B. F. Greenfield ◽  
G. J. Holtom ◽  
M. H. Hurdus ◽  
N. O’Kelly ◽  
N.J. Pilkington ◽  
...  
Keyword(s):  
High Performance ◽  
Degradation Products ◽  
Cellulose Degradation ◽  
Near Field ◽  
Experimental Studies ◽  
Water Soluble ◽  
Chemical Degradation ◽  
Alkaline Conditions ◽  
Isosaccharinic Acid ◽  
Microbial Action

AbstractNirex is seeking to develop a deep underground repository for the disposal of solid intermediate-level and low-level radioactive wastes (ILW and LLW) in the UK. One possible influence on the behaviour of radionuclides is the formation of water-soluble complexants by the degradation of the solid organic polymers that will be present in the wastes. The degradation products of cellulose have been shown to increase the solubility of plutonium and other radionuclides and to reduce sorption onto near-field and far-field materials. Degradation of cellulose under anaerobic alkaline conditions produces a range of organic acids. In this paper 2-C-(hydroxymethyl)-3-deoxy-D-pentonic acid (isosaccharinic acid, ISA) is identified by High Performance Liquid Chromatography as a significant component of cellulose leachates. A combination of fractionation of cellulose leachates and plutonium solubility determinations shows that ISA is responsible for the majority of the enhancement of plutonium solubility observed in such leachates. Further degradation of ISA by chemical or microbial action may lessen the effect of degraded cellulose leachates. Experimental studies on the chemical degradation of this compound under alkaline conditions suggest that the presence of oxygen is required. Microbial degradation studies show that the plutonium solubility in solutions of ISA is reduced by their exposure to microbial action.

Sorption of radionuclides to a cementitious backfill material under near-field conditions

2012 ◽  
Vol 76 (8) ◽  
pp. 3401-3410 ◽  
Author(s):  
M. Felipe-Sotelo ◽  
J. Hinchliff ◽  
N. Evans ◽  
P. Warwick ◽  
D. Read
Keyword(s):  
Organic Compounds ◽  
Degradation Products ◽  
Cellulose Degradation ◽  
Near Field ◽  
Organic Ligand ◽  
Sorption Isotherms ◽  
Field Conditions ◽  
Sorption Behaviour ◽  
Backfill Material ◽  
Order Of Magnitude

AbstractThe sorption behaviour of I−, Cs+, Ni2+, Eu3+, Th4+ and UO2+2on NRVB (Nirex reference vault backfill) a possible vault backfill, at pH 12.8 was studied. Sorption isotherms generated were compared to results obtained in the presence of cellulose degradation products (CDP). Whereas Cs was not affected by the presence of the organic compounds, a notable reduction in the sorption of Th and Eu to cement was observed. The results also indicated limited removal of Ni from solution (with or without an organic ligand) by sorption, the concentration in solution seemingly being determined solely by solubility processes. In the case of uranium, the presence of CDP increased the sorption to cement by almost one order of magnitude. Further studies into the uptake of CDP by cement are being undertaken to identify the mechanism(s) responsible.

The Effect of Cellulose Degradation Products on the Solubility and Sorption of Pu and Am in Alkaline-Plume-Affected and in Unaffected Boom Clay

2003 ◽  
Vol 807 ◽  
Author(s):  
F. Rorif ◽  
E. Valcke ◽  
M. A. Glaus
Keyword(s):  
Radioactive Waste ◽  
Water Sorption ◽  
Degradation Products ◽  
Cellulose Degradation ◽  
Potential Effect ◽  
Water Soluble ◽  
Boom Clay ◽  
Effect Of Water ◽  
Isosaccharinic Acid

ABSTRACTThe potential effect of water-soluble degradation products (DPs) formed from cellulose-containing cemented radioactive waste on the behaviour of Pu(IV) and Am(III) in Alkaline-Plume-Affected (APA) and in unaffected Boom clay was assessed. After solubility measurements in APA Real Clay Water, sorption experiments of Pu(IV) and Am(III) onto APA Boom clay were performed in the presence or not of DPs or pure α-isosaccharinic acid (α-ISA). Moreover, the sorption of α-ISA onto the unaffected clay was studied.

The effect of cellulose degradation products on thorium sorption onto hematite: studies of a model ternary system

2012 ◽  
Vol 76 (8) ◽  
pp. 3381-3390 ◽  
Author(s):  
G. M. N. Baston ◽  
M. M. Cowper ◽  
T. G. Heath ◽  
T. A. Marshall ◽  
S. W. Swanton
Keyword(s):  
Degradation Products ◽  
Cellulose Degradation ◽  
Near Field ◽  
Principal Component ◽  
High Concentration ◽  
Sorption System ◽  
Model Predictions ◽  
The Impact ◽  
Isosaccharinic Acid ◽  
Good Agreement

AbstractCellulose degradation products (CDPs) can complex with radioelements causing solubility enhancement and sorption reduction, effects which are detrimental to the containment of radionuclides in the near field of a geological disposal facility and surrounding geosphere. Isosaccharinic acid (ISA) is the principal component of CDPs formed under the alkaline anaerobic conditions of a cement-based near field and appears to be largely responsible for the impact of CDPs on radionuclide solubility and sorption under near-field conditions. However, the situation appears to be more complicated under near-neutral pH geosphere conditions.A combined experimental and modelling study was undertaken to compare the impact of a CDP leachate to ISA in a simple model ternary sorption system consisting of hematite as a single mineral substrate, thorium as the radioelement and ISA or a CDP leachate as the complexant. Thorium sorbs strongly to hematite. A triple layer model for thorium sorption to hematite was refined to fit to the experimental data in the absence of ISA or CDP leachate; the effect of ISA on thorium sorption was then predicted.In the presence of CDP leachate, a significant reduction in thorium sorption was observed from pH 6 to 12 in good agreement with model predictions based on a high concentration of ISA. However, only a limited impact of ISA on thorium sorption was observed at pH 6 to 12, in contrast to predictions. The effects of ISA could be accounted for by assuming the formation of a ternary thorium–ISA–surface complex. The model has yet to be extended to the more complex CDP systems. Differences in the thorium speciation in solution due to the formation of a ternary calcium–thorium–ISA complex in the CDP leachate, which is absent from solutions with ISA only, provides the most likely explanation for the differences observed experimentally.

scholarly journals Identifying Risk Factors Affecting the Usage of Digital and Social Media: A Preliminary Qualitative Study in the Dental Profession and Dental Education

2021 ◽  
Vol 9 (5) ◽  
pp. 53
Author(s):  
Rayan Sharka ◽  
Jonathan P. San Diego ◽  
Melanie Nasseripour ◽  
Avijit Banerjee
Keyword(s):  
Risk Factors ◽  
Qualitative Study ◽  
Perceived Risk ◽  
Dental Education ◽  
Dental Students ◽  
General Context ◽  
Structured Interviews ◽  
Factors Affecting ◽  
The Uk ◽  
Dental Professionals

Aims: This study aimed to identify the risk factors of using DSM to provide an insight into the inherent implications this has on dental professionals in practice and trainee professionals’ education. Materials and methods: Twenty-one participants (10 dental professionals and 11 undergraduate and postgraduate dental students) participated in this qualitative study using semi-structured interviews in a dental school in the UK. The interviews were analysed and categorised into themes, some of which were identified from previous literature (e.g., privacy and psychological risks) and others emerged from the data (e.g., deceptive and misleading information). Results: The thematic analysis of interview transcripts identified nine perceived risk themes. Three themes were associated with the use of DSM in the general context, and six themes were related to the use of DSM in professional and education context. Conclusions: This study provided evidence to understand the risk factors of using DSM in dental education and the profession, but the magnitude of these risks on the uptake and usefulness of DSM needs to be assessed.

scholarly journals Factors affecting consultant attitudes to undertaking undergraduate medical student teaching in the UK: a systematic review

BMJ Open ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. e042653
Author(s):  
Isobel Marion Harris ◽  
Heather McNeilly ◽  
Hani Benamer ◽  
Derek J Ward ◽  
Alice J Sitch ◽  
...  
Keyword(s):  
Systematic Review ◽  
Medical Students ◽  
Student Teaching ◽  
Data Extraction ◽  
Undergraduate Medical Students ◽  
Systematic Review Methodology ◽  
Factors Affecting ◽  
Persistent Problem ◽  
Medical Student Teaching ◽  
The Uk

ObjectiveThis systematic review aimed to explore consultant attitudes towards teaching undergraduate medical students in the UK.DesignSystematic review.MethodologyStandard systematic review methodology was followed. MEDLINE, EMBASE and OpenGrey were searched from inception to August 2019 to identify studies exploring senior doctors’ attitudes towards teaching undergraduate medical students. Two reviewers independently carried out key methodological steps including study screening/selection, quality assessment and data extraction. A narrative synthesis was undertaken.ResultsFive studies were included in the review dating 2003–2015. Two studies used questionnaires, and three used focus groups/semistructured interviews. Key findings identified across all studies were consultants generally found teaching undergraduate medical students enjoyable, and consultants identified time constraints as a barrier to teaching. Other findings were consultants feeling there was a lack of recognition for time spent teaching, and a lack of training/guidance regarding teaching students.ConclusionsThis is the first systematic review to explore senior hospital doctors’ attitudes towards teaching undergraduate medical students. Despite these five studies spanning 12 years, the same attitudes and issues regarding teaching are identified by all, suggesting lack of time particularly is a persistent problem regarding consultant-based teaching. An anecdotal impression is that consultants are no longer as enthusiastic about teaching as they once were, but it is evident over the 12 years of these studies that enjoyment levels, and presumably enthusiasm, have not changed significantly.

Factors affecting coagulation: fibrinolysis in chronic subdural fluid collections

1983 ◽  
Vol 58 (2) ◽  
pp. 242-245 ◽  
Author(s):  
Bryce Weir ◽  
Philip Gordon
Keyword(s):  
Degradation Products ◽  
Hemoglobin Content ◽  
Fibrin Degradation Product ◽  
Content Type ◽  
Factors Affecting ◽  
Fibrin Degradation Products ◽  
Subdural Hematomas ◽  
Increased Risk ◽  
Fluid Collections ◽  
Fine Print

✓ Plasminogen, alpha2-antiplasmin, fibrinogen, fibrin degradation products (FDP's), and hemoglobin were measured in the supernatant fluid of 25 chronic subdural hematomas and five chronic subdural hygromas. The 30 patients underwent pre- and postoperative computerized tomography. The hematomas were characterized by low fibrinogen and high fibrin degradation product concentrations. The hemoglobin content varied directly with the alpha2-antiplasmin, and inversely with the plasminogen. Four patients underwent reoperation for recurrences. The initial fluid from these cases was characterized by relatively high plasminogen and low alpha2-antiplasmin. The hygromas had no hemoglobin, and low fibrinogen, high FDP's, low alpha2-antiplasmin, and variable plasminogen levels. It is possible that those cases having the greatest capacity to produce plasmin (high plasminogen and low alpha2-antiplasmin) can produce more FDP's which in turn causes more rebleeding and an increased risk of reaccumulation of chronic subdural hematomas.

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