TITLE:
The Significance of Carbon 14 in Graphite Reactor Components at End of Generation
AUTHORS:
Martin Metcalfe, Athanasia Tzelepi
KEYWORDS:
Intermediate Level Waste, Nuclear Reactor Graphite Components
JOURNAL NAME:
Journal of Environmental Protection,
Vol.10 No.2,
January
24,
2019
ABSTRACT: It is
estimated that there are at least 250,000 tonnes of irradiated graphite
worldwide that will require eventual disposal. This graphite arises from a
number of sources, but principally comprises moderator and structural materials
for experimental reactors, production reactors, commercial power reactors and
fuel assemblies. In the UK, a significant proportion of its irradiated graphite
is classified as Intermediate Level Waste. Such waste is not heat generating
but has a radioactive content exceeding 4 GBq per tonne alpha or 12 GBq per
tonne beta/gamma activity. While the classification of waste is not consistent
across states and proposals by individual states for the management of their
graphite waste vary considerably, a common interest is the nature and distribution
of its radioactive content. The radionuclides in irradiated graphite presenting
the most significant long-term hazard are Carbon 14 (C-14) and Chlorine 36
(Cl-36) with half-lives of 5730 and 301,000 years respectively. For a better understanding of the way in which C-14 is
produced, its distribution within irradiated graphite and realistic
quantification of activity can potentially lead to improved characterization to validate its status within
current or future waste classifications, segregation to reduce Intermediate
Level Waste volumes, or treatment to reduce activity enabling re-classification
as Low Level Waste. This paper reviews all these issues and then focuses on the
significance of C-14. Some findings from a National Nuclear Laboratory study of
C-14 levels in carbonaceous deposits and the underlying Magnox reactor graphite
are presented to illustrate the need for thorough characterization of the waste
material. These results are discussed in the context of aqueous leaching of
C-14 from irradiated graphite and potential treatment options to minimize
aqueous release. The paper concludes with some broader observations on the
significance of C-14 in nuclear reactor graphite components and how these
issues should be considered when preparing the lifetime management of new
nuclear plant.