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Rate and speciation of volatile carbon-14 and tritium releases from irradiated graphite

Published online by Cambridge University Press:  05 July 2018

G. M. N. Baston ,
T. A. Marshall ,
R. L. Otlet ,
A. J. Walker ,
I. D. Mather  and
S. J. Williams
G. M. N. Baston*
Affiliation:
AMEC (formerly Serco), B150, Harwell, Didcot, Oxfordshire OX11 0QB, UK
T. A. Marshall
Affiliation:
Research Centre for Radwaste Disposal, School of Earth, Atmospheric and Environmental Science, The University of Manchester, Manchester M13 9PL, UK
R. L. Otlet
Affiliation:
RCD, The Old Stables, East Lockinge, Wantage, Oxfordshire OX12 8QY, UK
A. J. Walker
Affiliation:
RCD, The Old Stables, East Lockinge, Wantage, Oxfordshire OX12 8QY, UK
I. D. Mather
Affiliation:
RCD, The Old Stables, East Lockinge, Wantage, Oxfordshire OX12 8QY, UK
S. J. Williams
Affiliation:
NDA Harwell Office, B587, Curie Avenue, Harwell, Didcot, Oxfordshire OX11 0RH, UK
*
*E-mail: graham.baston@amec.com
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Abstract

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The release and migration of gaseous carbon-14 has been identified as a key issue for geological disposal of intermediate-level radioactive wastes in the UK. A significant fraction of carbon-14 in the UK inventory is in irradiated graphite. This paper describes measurements of gaseous carbon-14 releases from irradiated graphite on immersion in alkaline solution. Apparatus has been developed to discriminate organic and inorganic (14CO/14CO2) species in the gas phase by means of selective oxidation and capture. In the initial experiment, small amounts of gaseous carbon-14 (∼4 Bq) were released from 9 g of crushed graphite within a two-week period. In a long-term experiment, cumulative releases were measured periodically from an intact specimen of graphite over a 14 month period. A small fraction of the graphite carbon-14 inventory was released to the gas phase (∼0.004% as CO/CO2 and ∼0.001% associated with organic compounds). A larger quantity of carbon-14, about 0.1%, was released to the solution phase and was thought to be mainly 14CO2, with some possible organic component. In general, the rate of gaseous carbon-14 release decreased with time. The results suggest a small initial release of relatively labile, accessible carbon-14, with longer term release occurring at a much slower rate. Tritium (T) releases were also measured.

Keywords

graphitecarbon-14tritium
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 8 , December 2012 , pp. 3293 - 3302
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2012] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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