scholarly journals An approach to modelling the impact of 14C release from reactor graphite in a geological disposal facility

2015 ◽  
Vol 79 (6) ◽  
pp. 1495-1503 ◽  
Author(s):  
Charalampos Doulgeris ◽  
Paul Humphreys ◽  
Simon Rout
Keyword(s):  
Near Field ◽  
Significant Proportion ◽  
Reactor Core ◽  
Microbial Reduction ◽  
Gaseous Species ◽  
Geological Disposal ◽  
Carbon 14 ◽  
Reactor Graphite ◽  
Disposal Facility ◽  
The Impact

AbstractCarbon-14 (C-14) is a key radionuclide in the assessment of a geological disposal facility (GDF) for radioactive waste. In the UK a significant proportion of the national C-14 inventory is associated with reactor-core graphite generated by the decommissioning of the UK's Magnox and AGR reactors.There are a number of uncertainties associated with the fate and transport of C-14 in a post-closure disposal environment that need to be considered when calculating the radiological impacts of C-14-containing wastes. Some of these uncertainties are associated with the distribution of C-14-containing gaseous species such as 14CH4 and 14CO2 between the groundwater and gaseous release pathways. As part of the C14-BIG programme, a modelling framework has been developed to investigate these uncertainties. This framework consists of a biogeochemical near-field evolution model, incorporating a graphite carbon-14 release model, which interfaces with a geosphere/biosphere model. The model highlights the potential impact of the microbial reduction of 14CO2 to 14CH4, through the oxidation of H2, on C-14 transport. The modelling results could be used to inform the possible segregation of reactor graphite from other gasgenerating wastes.

scholarly journals Overview of CAST project

Radiocarbon ◽  
2018 ◽  
Vol 60 (6) ◽  
pp. 1649-1656
Author(s):  
Simon Norris ◽  
Manuel Capouet
Keyword(s):  
Ion Exchange ◽  
Radioactive Waste ◽  
European Commission ◽  
Source Term ◽  
The Other ◽  
Waste Materials ◽  
Special Edition ◽  
Gaseous Species ◽  
Geological Disposal ◽  
Carbon 14

ABSTRACTThe European Commission CAST project (CArbon-14 Source Term) aimed to develop understanding of the potential release mechanisms of carbon-14 (radiocarbon, 14C) from radioactive waste materials under conditions relevant to waste packaging and disposal to underground geological disposal facilities. The project focused on the release of carbon-14 as dissolved and gaseous species from irradiated metals (steels, Zircaloys), from spent ion-exchange materials and from irradiated graphites. This paper provides an overview of the CAST project and its output. It also acts as an introduction and scene-setter to the other papers in this special edition of Radiocarbon.

scholarly journals Microbial Reduction of Fe(III) under Alkaline Conditions Relevant to Geological Disposal

2013 ◽  
Vol 79 (11) ◽  
pp. 3320-3326 ◽  
Author(s):  
Adam J. Williamson ◽  
Katherine Morris ◽  
Sam Shaw ◽  
James M. Byrne ◽  
Christopher Boothman ◽  
...  
Keyword(s):  
Magnetic Circular Dichroism ◽  
Microbial Reduction ◽  
Geological Disposal ◽  
X Ray ◽  
Electron Shuttles ◽  
Disposal Facility ◽  
Transmission Electron ◽  
Alkaline Conditions ◽  
Set Up ◽  
Final Extent

ABSTRACTTo determine whether biologically mediated Fe(III) reduction is possible under alkaline conditions in systems of relevance to geological disposal of radioactive wastes, a series of microcosm experiments was set up using hyperalkaline sediments (pH ∼11.8) surrounding a legacy lime working site in Buxton, United Kingdom. The microcosms were incubated for 28 days and held at pH 10. There was clear evidence for anoxic microbial activity, with consumption of lactate (added as an electron donor) concomitant with the reduction of Fe(III) as ferrihydrite (added as the electron acceptor). The products of microbial Fe(III) reduction were black and magnetic, and a range of analyses, including X-ray diffraction, transmission electron microscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism confirmed the extensive formation of biomagnetite in this system. The addition of soluble exogenous and endogenous electron shuttles such as the humic analogue anthraquinone-2,6-disulfonate and riboflavin increased both the initial rate and the final extent of Fe(III) reduction in comparison to the nonamended experiments. In addition, a soluble humic acid (Aldrich) also increased both the rate and the extent of Fe(III) reduction. These results show that microbial Fe(III) reduction can occur in conditions relevant to a geological disposal facility containing cement-based wasteforms that has evolved into a high pH environment over prolonged periods of time (>100,000 years). The potential impact of such processes on the biogeochemistry of a geological disposal facility is discussed, including possible coupling to the redox conditions and solubility of key radionuclides.

scholarly journals The carbon-14 IPT: an integrated approach to geological disposal of UK wastes containing carbon-14

2015 ◽  
Vol 79 (6) ◽  
pp. 1641-1650 ◽  
Author(s):  
David Lever ◽  
Sarah Vines
Keyword(s):  
Holistic Approach ◽  
Integrated Approach ◽  
Geological Environment ◽  
Geological Disposal ◽  
Carbon 14 ◽  
Disposal Facility ◽  
Working Together ◽  
Integrated Project ◽  
Engineered Barriers ◽  
Design Options

AbstractCarbon-14 is a key radionuclide in the assessment of the safety of a geological disposal facility because of the calculated assessment of the radiological consequences of gaseous carbon-14-bearing species. Radioactive Waste Management Limited has established an Integrated Project Team (IPT) in which partners are working together to develop an holistic approach to carbon-14 management in the disposal system. We have used an 'AND' approach to structure and prioritize our technical work. For a waste stream to be of concern, there has to be a significant inventory, AND carbon-14-bearing gas has to be generated, AND this gas has to be entrained by bulk gas, AND it has to migrate through the engineered barriers, AND it has to migrate through the overlying geological environment (either as gas or in solution), AND there have to be consequences in the biosphere. We are also using this approach to consider alternative treatment, packaging and design options.

scholarly journals Preliminary investigation of 14C migration from RBMK-1500 reactor graphite disposed of in a potential geological repository in crystalline rocks in Lithuania

Radiocarbon ◽  
2018 ◽  
Vol 60 (6) ◽  
pp. 1839-1848
Author(s):  
Dalia Grigaliuniene ◽  
Povilas Poskas ◽  
Raimondas Kilda ◽  
Asta Narkuniene
Keyword(s):  
Nuclear Power ◽  
Near Field ◽  
Preliminary Investigation ◽  
Crystalline Rocks ◽  
Near Surface ◽  
Carbon 14 ◽  
Reactor Graphite ◽  
Irradiated Graphite ◽  
Geological Repository ◽  
Order Of Magnitude

ABSTRACTThere are two units with RBMK-1500 type reactors at the Ignalina Nuclear Power Plant (Ignalina NPP) in Lithuania where graphite was used as a neutron moderator and reflector. These reactors are now being decommissioned, and Lithuania has to find a solution for safe irradiated graphite disposal. It cannot be disposed of in a near surface repository due to large amounts of 14C (radiocarbon, carbon-14); thus, a deep geological repository (DGR) is analyzed as an option. This study had the aim to evaluate 14C migration from the RBMK-1500 irradiated graphite disposed of in a potential DGR in crystalline rocks taking into account the outcomes of the research performed under the collaborative European project CAST (CArbon-14 Source Term) and to identify the potential to reduce the conservatism in the assumptions that was introduced in the lack of data and led in the overestimated 14C migration. The information gathered during the CAST project was used to model 14C transport in the near field by the water pathway and to perform uncertainty analysis. The study demonstrated that more realistic assumptions could reduce the estimated 14C flux from the near field by approximately one order of magnitude in comparison with the previous estimations based on very conservative assumptions.

An overview of near-field evolution research in support of the UK geological disposal programme

2012 ◽  
Vol 76 (8) ◽  
pp. 2995-3001 ◽  
Author(s):  
T. M. Beattie ◽  
S. J. Williams
Keyword(s):  
Radioactive Waste ◽  
Host Rock ◽  
Near Field ◽  
Radioactive Decay ◽  
Geological Disposal ◽  
Nuclear Decommissioning ◽  
Disposal Facility ◽  
Engineered Barriers ◽  
The Uk

AbstractThe near field, together with the containment and isolation provided by the geosphere, contributes to the long-term safety provided by a geological disposal facility (GDF) after closure. The different engineered barriers can prevent or limit the release of radionuclides and their migration to the undisturbed host rock or geosphere and are expected to fulfil their post-closure safety functions for many thousands to hundreds of thousands of years. They will continue to contribute to containment after their eventual degradation when there would no longer be confidence that they would continue to fulfil all of their safety functions in their totality. By that time, significant radioactive decay will have occurred, substantially reducing the hazard associated with the wastes. Therefore, demonstration of long-term safety requires an understanding of the evolution of the engineered barriers and the consequences for the generic safety functions that the different barriers provide. This paper provides an overview of the research of the Nuclear Decommissioning Authority Radioactive Waste Management Directorate into the evolution of the near field of a GDF.

Modelling evolution in the near field of a cementitious repository

2012 ◽  
Vol 76 (8) ◽  
pp. 3055-3069 ◽  
Author(s):  
A. R. Hoch ◽  
G. M. N. Baston ◽  
F. P. Glasser ◽  
F. M. I. Hunter ◽  
V. Smith
Keyword(s):  
Temporal Evolution ◽  
Near Field ◽  
Extended Period ◽  
Model System ◽  
Geological Disposal ◽  
Waste Package ◽  
The United Kingdom ◽  
Disposal Facility ◽  
Local Porosity ◽  
Groundwater Composition

AbstractIn the United Kingdom, disposal of radioactive waste may involve packages of grouted waste being placed in a geological disposal facility (GDF) and surrounded by a cementitious backfill. This paper describes modelling that has been carried out to develop an understanding of the possible spatial and temporal evolution within the GDF.A single waste package is assumed to be filled with an encapsulation grout, placed in an underground vault and surrounded by a cementitious backfill. Groundwater from the host rock flows into the vault and through the backfill. A simplified model system examines the interactions between groundwater, cementitious backfill and grout.In most cases the model predicts a reduction in the backfill porosity due to precipitation and dissolution reactions, particularly at the upstream edge of the vault. The degree to which this occurs depends on the groundwater composition. The model also predicts precipitation and dissolution reactions would occur in the grouts close to their interface with the backfill, reducing the local porosity significantly which may isolate the grouts from the backfill, so that the pH within the grouts would be unchanged over an extended period.

Implication of Medical Treatment for Surgical Strategies in IBD

2019 ◽  
Vol 20 (13) ◽  
pp. 1363-1368
Author(s):  
Krisztina B. Gecse ◽  
Christianne J. Buskens
Keyword(s):  
Nutritional Status ◽  
Medical Treatment ◽  
Significant Proportion ◽  
Timing Of Surgery ◽  
Multidisciplinary Management ◽  
Key Factors ◽  
Surgical Strategies ◽  
Immunosuppressive Medications ◽  
Medical Paradigm ◽  
The Impact

Despite changing medical paradigm, still a significant proportion of patients with IBD require surgery. The patient's general condition, including nutritional status and the use of immunosuppressive medications is of great importance with regard to surgical complications, as well as the choice of optimal surgical strategy. The indication and the timing of surgery are key factors for the multidisciplinary management of IBD patients. The purpose of this review is to provide an overview on the impact of medical treatment on surgical strategies in IBD.

The impact of algorithmic decision-making processes on young people’s well-being (Preprint)

2019 ◽  
Author(s):  
Elvira Perez Vallejos ◽  
Liz Dowthwaite ◽  
Helen Creswich ◽  
Virginia Portillo ◽  
Ansgar Koene ◽  
...  
Keyword(s):  
Young People ◽  
Significant Proportion ◽  
Well Being ◽  
Early Years ◽  
Negative Experiences ◽  
Children And Young People ◽  
Online Platforms ◽  
Internet Users ◽  
Decision Making Processes ◽  
The Impact

BACKGROUND Algorithms rule the online environments and are essential for performing data processing, filtering, personalisation and other tasks. Research has shown that children and young people make up a significant proportion of Internet users, however little attention has been given to their experiences of algorithmically-mediated online platforms, or the impact of them on their mental health and well-being. The algorithms that govern online platforms are often obfuscated by a lack of transparency in their online Terms and Conditions and user agreements. This lack of transparency speaks to the need for protecting the most vulnerable users from potential online harms. OBJECTIVE To capture young people's experiences when being online and perceived impact on their well-being. METHODS In this paper, we draw on qualitative and quantitative data from a total of 260 children and young people who took part in a ‘Youth Jury’ to bring their opinions to the forefront, elicit discussion of their experiences of using online platforms, and perceived psychosocial impact on users. RESULTS The results of the study revealed the young people’s positive as well as negative experiences of using online platforms. Benefits such as being convenient and providing entertainment and personalised search results were identified. However, the data also reveals participants’ concerns for their privacy, safety and trust when online, which can have a significant impact on their well-being. CONCLUSIONS We conclude by making recommendations that online platforms acknowledge and enact on their responsibility to protect the privacy of their young users, recognising the significant developmental milestones that this group experience during these early years, and the impact that technology may have on them. We argue that governments need to incorporate policies that require technologists and others to embed the safeguarding of users’ well-being within the core of the design of Internet products and services to improve the user experiences and psychological well-being of all, but especially those of children and young people. CLINICALTRIAL N/A

The Relationship Between Highly Visual Social Media and Young People’s Mental Health: A Scoping Review (Preprint)

2020 ◽  
Author(s):  
Alanna McCrory
Keyword(s):  
Mental Health ◽  
Social Media ◽  
Young People ◽  
Scoping Review ◽  
Quantitative Methods ◽  
Grey Literature ◽  
Significant Proportion ◽  
Mental Wellbeing ◽  
Published Evidence ◽  
The Impact

UNSTRUCTURED Users of highly visual social media (HVSM), such as Snapchat and Instagram, share their messages through images, rather than relying on words. A significant proportion of people that use these platforms are adolescents. Previous research reveals mixed evidence regarding the impact of online social technologies on this age group’s mental wellbeing, but it is uncertain whether the psychological effects of visual content alone differ from text-driven social media. This scoping review maps existing literature that has published evidence about highly visual social media, specifically its psychological impact on young people. Nine electronic databases and grey literature from 2010 until March 2019 were reviewed for articles describing any aspect of visual social media, young people and their mental health. The screening process retrieved 239 articles. With the application of eligibility criteria, this figure was reduced to 25 articles for analysis. Results indicate a paucity of data that exclusively examines HVSM. The predominance of literature relies on quantitative methods to achieve its objectives. Many findings are inconsistent and lack the richness that qualitative data may provide to explore the reasons for theses mixed findings.

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