IMPLICATIONS OF NEW RADIOBIOLOGICAL INSIGHTS
FOR THE LONG TERM MANAGEMENT OF HIGH LEVEL
RADIOACTIVE WASTE
Keith Baverstock,
Department of Environmental Science, University of Kuopio, PL 1627 70211 KUOPIO,
Finland. keith.baverstock@uku.fi
ABSTRACT
The IAEA has laid down nine principles of radioactive waste management [1], the
first of which covers the protection of human health and demands that radioactive
waste will be managed in such a way as to provide an acceptable level of
protection. The fourth principle demands that future generations are protected in
terms of the level of predicted impacts at the same level of protection as applies
today. Recent developments in the understanding of the effects of ionising
radiation, particularly at low doses and especially for some of the radiation
qualities that characterise long lived components of radioactive waste, suggest that
there may have been an underestimation of the predicted impact on health of future
generations should radioactive waste products reach the biosphere. This could
undermine the existing management framework upon which radiological
protection is based and may lead to violation of the fourth principle.
This paper addresses, from an “in principle” perspective, the issues that new
radiobiological evidence and recent developments in biology and genetics have
raised in the context of determining radiological risk from internal contamination.
Special emphasis is placed on radiation qualities, low energy beta particles, Auger
electrons and alpha particles, which characterise the nuclides that are associated
with long-lived radioactive decay processes. While absorbed tissue dose remains
a guide to one aspect of the risks incurred by exposure (called herein type A risk),
evidence is accumulating that other cellular processes may contribute to additional
risk (type B risk). These processes are the induction of genomic instability and the
bystander effect. Risk assessment in these cases cannot readily and convincingly
be based on absorbed tissue dose and require addressing at the levels of the
individual cell and the specific track structural features of the different radiation
qualities. A potential framework for assessing type B risk is proposed.
It is concluded that there is no basis to assume other than that the linear no
threshold (LNT) hypothesis will apply to risks (types A and B) from exposure to
environmental radioactivity deriving from leakage of buried radioactive wastes.
Keywords: radiation risk, internal emitters, radioactive waste, radiobiology,
epigenetics
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1. SCOPE AND BACKGROUND
This paper considers the assessment of radiological risk that may arise in the event of
leakage in the long term management of high level radioactive wastes. The wastes
include spent fuel and that which arises after reprocessing of spent fuel, namely high
level liquid wastes. Spent fuel as it is discharged as fuel rods from the reactor at the
end of the fuel’s working life already has a level of containment in the fuel rod casing
and is to a large degree insoluble. On the other hand the reprocessing of spent fuel
results in a liquid waste which first has to be converted to an insoluble form, usually
a glass.
The radioactivity contained in high level nuclear wastes is extremely long lived,
with half lives in excess of hundreds of thousands of years. In countries where long-
term management strategies for such waste are being considered the only solutions
regarded as viable are some form of geological disposal/management. This is also the
solution that has been recommended, albeit rather guardedly, for the UK’s legacy of
high level waste by the Committee on Radioactive Waste Management (CoRWM) [2].
Ideally the radioactivity would be packaged and placed such that it is isolated from the
environment and thus the biosphere, over time-scales of the order of 100,000 to 1
million years. In practice of course no guarantees of such containment can be given. It
seems reasonable to assume that containment and isolation can be effective over
periods of thousands of years. Beyond those timescales the confidence that can be
placed in preventing escape of radioactivity and its emergence into the biosphere will
decline. The risk of penetration of the biosphere can be minimised, but not eliminated,
by selecting a suitable geology. Discharges from the repository could enter the
biosphere either in water or in the form of a gas, which eventually is metabolised by
vegetation. Thus, in the period beyond ten thousand years hence the possibility that
there will be population exposures from geologically contained waste has to be
addressed. The key issue are:
• how can these risks be quantified, and
• what would be an acceptable risk.
This paper addresses in part the first of these issues; the second issue is socio-political
in character and is not addressed.
2. DEVELOPMENTS IN RADIOBIOLOGY
Traditionally radiation risk is assessed in relation to the dose (energy per unit mass) of
radiation absorbed by the body or in the case of partial body irradiation, absorbed by
specific tissues. This risk is best understood in the context of exposure of the whole
body to externally generated penetrating radiation, i.e., gamma rays. In this context
there are several direct measurements from epidemiological studies of exposed
populations, most notably the survivors of the atomic bombings in Japan (JBS). Where
exposure is to high doses (>~0.1 Gy) at high dose-rate, this risk is generally accepted
to be of the order of 10%/Gy for the lifetime fatal cancer risk with an additional
smaller risk for hereditary diseases. However, in the contexts of radioactive wastes
released as a result of either mid-life or end of life containment failure, the dose-rate
will be very low and the types of radiation concerned may be very different from high
498 Energy & Environment · Vol. 19, No. 3+4, 2008