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.

An Integrated Approach to Geological Disposal of UK Wastes Containing Carbon-14

2013 ◽  
Author(s):  
Sarah Vines ◽  
David Lever
Keyword(s):  
Radioactive Waste ◽  
Gas Phase ◽  
Alternative Treatment ◽  
Phase 1 ◽  
Project Team ◽  
Waste Stream ◽  
Second Phase ◽  
Geological Disposal ◽  
Carbon 14 ◽  
Design Options

Carbon-14 is a key radionuclide in the assessment of the safety of a geological disposal facility for radioactive waste because of the calculated assessment of the radiological consequences of gaseous carbon-14 bearing species [i]. It may be that such calculations are based on overly conservative assumptions and that better understanding could lead to considerably reduced assessment of the radiological consequences from these wastes. Alternatively, it may be possible to mitigate the impact of these wastes through alternative treatment, packaging or design options. The Radioactive Waste Management Directorate of the UK’s Nuclear Decommissioning Authority (NDA RWMD) has established an integrated project team in which the partners are working together to develop a holistic approach to carbon-14 management in the disposal system [ii]. For a waste stream containing carbon-14 to be an issue: • There must be a significant inventory of carbon-14 in the waste stream; AND • That waste stream has to generate carbon-14 bearing gas; AND • A bulk gas phase has to entrain the carbon-14 bearing gas: AND • These gases must migrate through the engineered barriers in significant quantities; AND • These gases must migrate through the overlying geological environment (either as a distinct gas phase or as dissolved gas); AND • These gases must interact with materials in the biosphere (i.e. plants) in a manner that leads to significant doses and risks to exposed groups or potentially exposed groups. The project team has developed and used this “AND” approach to structure and prioritise the technical work and break the problem down in a manageable way. We have also used it to develop our approach to considering alternative treatment, packaging and design options. For example, it may be possible to pre-treat some wastes to remove some of the inventory or to segregate other wastes so that they are removed from any bulk gas phase which might facilitate migration through the geosphere. Initially, the project team has undertaken a six month programme of work to examine the current understanding of these aspects and has captured this in the Phase 1 report [ii], in a modelling basis spreadsheet and in scoping assessments, which help us better understand the potential significance of carbon-14. Using the current modelling basis, but ignoring any potential benefits from the geosphere in retarding or preventing gas from reaching the surface, the calculated release of carbon-14 is dominated by: corrosion of irradiated reactive metals (in the operational and early post-closure time frame); corrosion of irradiated stainless steel and leaching of irradiated graphite (in the longer term). The Phase 1 work has shown that there is considerable scope for reducing the calculated radiological consequence for these wastes and a roadmap has been developed for a second Phase of work.

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 14C Exposure from Disposal of Radioactive Waste Compared to14C Exposure from Cosmogenic Origin

Radiocarbon ◽  
2018 ◽  
Vol 60 (6) ◽  
pp. 1911-1923
Author(s):  
Erika A C Neeft
Keyword(s):  
Ion Exchange ◽  
Radioactive Waste ◽  
Metal Oxide ◽  
Release Rate ◽  
Cementitious Materials ◽  
Release Mechanism ◽  
Management Technique ◽  
Chemical Corrosion ◽  
Carbon 14 ◽  
Exchange Resins

ABSTRACTThe potential14C (carbon-14, radiocarbon) flux from disposal of14C containing waste into air is compared with the natural14C emanation rate from soil in order to put the14C hazard potential from disposal of this waste in perspective with the14C exposure from cosmogenic origin. Chemical corrosion of neutron irradiated metals, steel and Zircaloy, is bounded by diffusion of water through a thermodynamically stable metal-oxide layer and dissolution of this metal-oxide in a nuclear plant. Many countries process radioactive waste for disposal using cementitious materials, an acknowledged end-point management technique for this waste. The metal-oxides are also stable when these waste forms are embedded in cementitious materials. The14C release rate from this Zircaloy at these alkaline and reducing conditions is comparable to the natural14C emanation rate from soil into air. Neutron irradiated graphite and spent ion exchange resins are chemically inert and therefore other release mechanisms need to be assumed. Radiolytic corrosion is used to determine the14C release rate from this graphite. Moreover, ion exchange—with ingressing anionic species that have a higher affinity than contained anionic14C—is proposed as a release mechanism for these resins.

Evaluation of dialysis treatment in uremic patients by gel filtration of serum

1990 ◽  
Vol 36 (11) ◽  
pp. 1906-1910 ◽  
Author(s):  
J Osada ◽  
T Gea ◽  
C Sanz ◽  
I Millan ◽  
J Botella
Keyword(s):  
Ion Exchange ◽  
Gel Filtration ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
The Other ◽  
Control Group ◽  
Dialysis Treatment ◽  
Additional Information ◽  
Molecular Masses ◽  
Two Peaks

Abstract A group of substances of molecular masses between 300 and 1500 Da have been found to be toxic metabolites in patients with uremia. We determined the concentration in serum of these molecules in the following groups of patients: two hemodialyzed groups (one with cuprophane and the other with polyacrylonitrile dialyzers), one group treated with continuous ambulatory peritoneal dialysis, one group of nondialyzed azotemic patients, and one control group of healthy persons. Ultrafiltrates of the subjects' sera were fractionated on Sephadex G-15 followed by ion-exchange chromatography. Eluates were monitored by absorbance at 254 and 206 nm. Partially characterized peaks P1 and P2, obtained by gel filtration, correlated with the concentration of creatinine in serum; their concentrations were significantly (P less than 0.01) larger in hemodialyzed groups than in peritoneal dialyzed or in nondialyzed azotemic patients. After ion-exchange chromatography, two peaks (P'5 and P'6) correlated with serum creatinine and also were larger in hemodialyzed patients than in the other groups. Apparently, adequate discrimination is obtained by gel-filtration analysis and further analysis by ion-exchange chromatography does not provide additional information in most of the affected patients.

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