Modelling the radiolytic corrosion of a-doped UO
2
and spent nuclear
fuel
Nazhen Liu
a
, Zack Qin
a
, James J. No
€
el
a, b, *
, David W. Shoesmith
a, b, **
a
Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
b
Surface Science Western, The University of Western Ontario, London, Ontario, N6G 0J3, Canada
highlights
A model is adapted to simulate the corrosion rates measured on a-doped UO
2
.
Simulated corrosion rates are in good agreement with the published rates.
The corrosion rate is determined by the radiolytic production rate of H
2
O
2
.
The accumulation of O
2
leads to an increase in corrosion rate in a closed system.
The corrosion rate decreases to a negligible level by including H
2
effect.
article info
Article history:
Received 7 March 2017
Received in revised form
26 May 2017
Accepted 6 July 2017
Available online 8 July 2017
Keywords:
a-Doped UO
2
Spent nuclear fuel
Waste disposal
Modelling
abstract
A model previously developed to predict the corrosion rate of spent fuel (UO
2
) inside a failed waste
container has been adapted to simulate the rates measured on a wide range of a-doped UO
2
and spent
fuel specimens. This simulation confirms the validity of the model and demonstrates that the steady-
state corrosion rate is controlled by the radiolytic production of H
2
O
2
(which has been shown to be
the primary oxidant driving fuel corrosion), irrespective of the reactivity of the UO
2
matrix. The model
was then used to determine the consequences of corrosion inside a failed container resealed by steel
corrosion products. The possible accumulation of O
2
, produced by H
2
O
2
decomposition, was found to
accelerate the corrosion rate in a closed system. However, the simultaneous accumulation of radiolytic
H
2
, which is activated as a reductant on the noble metal (ε) particles in the spent fuel, rapidly overcame
this acceleration leading to the eventual suppression of the corrosion rate to insignificant values. Cal-
culations also showed that, while the radiation dose rate, the H
2
O
2
decomposition ratio, and the surface
coverage of ε particles all influenced the short term corrosion rate, the influence of the radiolytically
produced H
2
was the overwhelming influence in reducing the rate to negligible level (i.e.,
<10
20
mol m
2
s
1
).
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
If nuclear energy is to play an important role in alleviating the
risk of global climate change, it must be demonstrated that the high
level waste can be safely disposed of. The approved approach for
the long-term management of used nuclear fuel in Canada is
disposal in a deep geologic repository (DGR) [1,2]. As accepted
internationally, the repository concept is based on multiple barriers
including the fuel bundles, durable metal containers, a clay buffer
and seals around the container, and a deep geologic formation [3].A
key barrier is the corrosion-resistant container which is expected to
isolate the used fuel for a very long time [4,5]. However, it is judi-
cious to examine the consequences of container failure and the
exposure of used fuel bundles to groundwater. In the anoxic con-
ditions anticipated in a DGR, H
2
O radiolysis resulting from the ra-
diation fields associated with the used fuel within a failed container
will be the only source of oxidants. The radiolysis product, H
2
O
2
,
has been shown to be the primary oxidant driving fuel corrosion
[6,7]. Oxidation of fuel (U
IV
) will produce the oxidized form (U
VI
)
* Corresponding author. Department of Chemistry, The University of Western
Ontario, London, Ontario, N6A 5B7, Canada.
** Corresponding author. Department of Chemistry, The University of Western
Ontario, London, Ontario, N6A 5B7, Canada.
E-mail addresses: jjnoel@uwo.ca (J.J. No€ el), dwshoesm@uwo.ca
(D.W. Shoesmith).
Contents lists available at ScienceDirect
Journal of Nuclear Materials
journal homepage: www.elsevier.com/locate/jnucmat
http://dx.doi.org/10.1016/j.jnucmat.2017.07.011
0022-3115/© 2017 Elsevier B.V. All rights reserved.
Journal of Nuclear Materials 494 (2017) 87e94