2. Engineering Solutions for High Level Nuclear Waste Disposal
Submitting InstitutionCardiff University
Unit of AssessmentCivil and Construction Engineering
Summary Impact TypeEnvironmental
Research Subject Area(s)
Engineering: Resources Engineering and Extractive Metallurgy, Interdisciplinary Engineering
Summary of the impact
Research conducted at the Geoenvironmental Research Centre (GRC),
supported by the European Commission via its EURATOM programme, has been
instrumental in addressing the long standing global problem of high level
nuclear waste disposal. The pioneering development of a sophisticated
coupled thermal/hydraulic/chemical/mechanical model of clay behaviour has
provided new understanding of the performance of engineered barriers
proposed for use in nuclear waste repositories. This has, in an
unprecedented development, directly enabled the design of numerous nuclear
waste repositories to proceed. The repositories in Sweden and Finland are
currently at "Licence application" and "Construction" phases,
respectively. Therefore the impacts claimed during the REF period are:
significant impact on engineering design, leading to
improved environmental conditions; considerable economic
investment and marked impact on public policy and
The behaviour of clay soils, in relation to nuclear waste repositories,
was insufficiently understood prior to Cardiff University's research. Key
research developments since 1993 are outlined below.
Thermo/Hydro/Mechanical (THM) behaviour: The first step in
developing a suitable model of THM behaviour was to extend the GRC's
research on coupled thermo/hydraulic behaviour [3.1] to accommodate soil
deformation [3.2]. This was achieved in collaboration with International
co- workers, notably Professors Alonso and Gens at UPC Barcelona, who were
developing new models of unsaturated soil deformation. This work was
carried out as part of major European Commission funded research, under
the EURATOM programme. This yielded the first approach to simulating
coupled THM behaviour.
Micro/macro behaviour of clays: The GRC's
investigation (1996-2003) into the re-saturation behaviour of clay
barriers in a large-scale, in-situ experiment at Atomic Energy of Canada's
(AECL) underground research laboratory established that neither the
duration nor the pattern of moisture influx could be predicted accurately
using a conventional hydraulic conductivity model. It showed that the
expansion of the microstructure of the bentonite reduced the pore spaces
available for water transport in the macrostructure, as the material,
overall, was constrained from swelling. This in turn was likely to reduce
the material's hydraulic conductivity and was of major significance in the
estimation of repository re-saturation times [3.3]. This work was extended
[3.4] to include heating. Simulation of pre-heating phases demonstrated
that the model could describe the hydraulic regime in the host rock and
isothermal infiltration into the buffer.
Chemical reaction modelling: The above work
demonstrated very clearly the importance of the physico-chemical behaviour
of bentonitic soils. A multicomponent transport formulation was therefore
developed and coupled with a multiphase geochemical reaction model. This
was achieved by coupling the THM and chemical transport model with a
geochemical reaction model (MINTEQA2). The coupled model was applied to
study various aspects of chemical behaviour during the period of heating
and hydration in the buffer [3.5]. Several relevant hydro-geochemical
features were then incorporated between 2007 and 2012, from a theoretical
modelling approach at micro scale to the inclusion of multicomponent
diffusion. The existing THCM model was coupled with an advanced
geochemical model (PHREEQC), which allows high ionic concentrations and
kinetically-controlled geochemical reactions to be simulated [3.6].
Computational Modelling Aspects: A simulation of the
Prototype Repository experiment, undertaken by the Swedish Nuclear Fuel
and Waste Management Co. (SKB), demonstrated that parallel computation is
invaluable because of the complex, highly coupled nature of the problem.
The temperature field was found to be three-dimensional, with the effect
of adjacent canisters' heat output influencing the temperature within
other deposition holes. In addition, the significance of the backfill as a
substantial sink for pore-water was demonstrated, reproducing the
saturation time exhibited experimentally. The geological supply of water
was critical to the hydration rate.
This research, in addition to the wider work of the Centre, has directly
led to the GRC being awarded the 2013 Queen's Anniversary Prize for Higher
and Further Education. Members of the GRC contributing to the research
are: Prof H R Thomas, (Director of GRC in post since
establishment), Dr P J Cleall, Dr S C Seetharam, Dr P J Vardon and
Dr M Sedighi.
References to the research
3.1 Thomas H.R. and Li C.W.L. (1997) An assessment of a
model of heat and moisture transfer in unsaturated soil, Géotechnique,
Vol 47 No 1 pp 113-131, DOI: 10.1680/geot.19220.127.116.11
3.2 Thomas H.R. and He Y. (1998) Modelling the behaviour of
unsaturated soil using an elastoplastic constitutive model,
Géotechnique, Vol 48 No 5 pp 589-603, DOI:
3.3 Thomas H.R., Cleall P.J., Chandler N., Dixon D.
and Mitchell H.P. (2003) Water infiltration into a large scale in-situ
experiment in an underground research laboratory - physical measurements
and numerical simulation, Geotechnique, Vol 53 No 2 pp 207-224,
3.4 Thomas H.R., Cleall P.J., Dixon D. and Mitchell
H.P. (2009) The coupled thermal- hydraulic-mechanical behaviour of a large
scale in-situ heating experiment, Geotechnique, Vol 59 No 4 pp
3.5 Cleall P.J., Seetharam S.C. and Thomas H.R.
(2007) Inclusion of some aspects of chemical behaviour of an unsaturated
soil in thermo/hydro/chemical/mechanical models. II Application and
transport of soluble salts in compacted bentonite, ASCE Journal of
Engineering Mechanics, Vol 133 No 3 pp 348-356, DOI:
3.6 Thomas H.R., Sedighi M. and Vardon P.J.
(2012) Diffusive reactive transport of multicomponent chemicals under
coupled thermal, hydraulic, chemical and mechanical conditions, Journal
of Geotechnical and Geological Engineering, Vol 30 No 4 pp 841-857,
Details of the impact
Route to Impact: Cardiff University's research has been
integral to overcoming major obstacles associated with high level nuclear
waste disposal. Approximately 250 to 300 Ktons of high level nuclear waste
is in temporary storage facilities worldwide. Multinational governments
and international nuclear authorities, such as the International Atomic
Energy Authority (IAEA), have long recognised the necessity for a
permanent disposal solution. The preferred route is deep geological
disposal. Not only does this absolve the necessity for constant
supervision and maintenance, and reduce security risks associated with
ground level storage, but it prohibits future generations from inheriting
a nuclear waste legacy. However, whilst theoretically appropriate, the
technical complexities of achieving this have meant the aim remained
unrealised. The enormous timescale over which high level nuclear waste is
radioactive and deadly to all living organisms (in excess of 100,000
years) poses a huge challenge to governments and international nuclear
authorities to ensure no nuclear releases reach surface level, resulting
in catastrophic health and environmental threats. The computerised model
developed at the Geoenvironmental Research Centre (GRC) provides
innovative predictions of the behaviour and long term durability of
engineered clay barriers (consisting of bentonite) under specific
repository conditions. The research was funded by the EC under their
EURATOM programme, a programme that is part- funded by the EC itself, and
part-funded by European Nuclear Waste Disposal Authorities [5.1]. The work
performed was therefore immediately "captured" by the Waste Disposal
Authorities (for example, in the UK, Sweden, Finland, Spain, Canada and
Germany) and could be deployed in various aspects of the performance
assessment of geological repositories [5.2]. The findings increased
international governments' confidence in the ability to accurately model
and forecast the behaviour of engineered clay barriers. Subsequently,
several countries issued licences and have begun the process of
constructing nuclear waste repositories.
Impact on Engineering Design: Given their inherent
complexity, application of the newly developed THM/THCM models to
repository design can only be achieved via the use of numerical methods of
analysis. In the GRC's case, this yielded the computer program called
COMPASS, which was developed in-house. This program can be used to
simulate the behaviour of a nuclear waste repository over a period of many
years. The main design criteria that can be considered via the use of the
software are in relation to:
- The temperature effects and the borehole spacings required, to ensure
that the maximum specified temperatures are not exceeded.
- The hydraulic effects and the total time for re-saturation of the
repository; this design parameter marks the end phase of the initial
life of a repository.
- The mechanical effects, the swelling pressures and displacements that
are generated as a result of moisture ingress.
- The chemical effects, a repository's response due to changes in the
chemical composition of the pore water.
All of the above are key features in the overall design of a
repository. They are principal elements of a safety assessment and,
consequently, are fundamental factors in a Licence Application. The
software has been accessed and applied (as aforementioned, via the
EURATOM programme) by International Nuclear Waste Disposal Authorities.
Work with SKB, the Swedish Nuclear Fuel and Waste Management Company,
for example, was conducted at a specially built Underground Research
Laboratory (URL), the Aspoe Rock Laboratory, on the island of Aspoe (http://www.skb.se/default____24417.aspx).
During the REF period, work conducted at the URL was used to inform
decisions regarding the site selection for a final repository. The
search had been ongoing for 20 years but was narrowed to two options,
Forsmark and Oskarshamn. The results of the research provided new
insights into the behaviour of the bentonite buffer under a range of
conditions, as described above, and determined the suitability of the
rock at each site. Subsequently, in June 2009, SKB made the decision to
locate the repository at Forsmark. This heralded a landmark event in the
process of achieving a fully operational nuclear waste repository. Based
on the site selection, an application to construct the repository was
submitted to the Swedish Radiation Safety Authority and the
environmental court in March 2011. The Swedish repository at Forsmark is
expected to be filled by 2025 [5.3].
The greatest progress has been made in Finland, where the repository
design is similar to the Swedish concept. Posiva, the Finish nuclear
waste management company (also part of the EURATOM research programmes),
has significantly benefited from Cardiff's unique research. Excavation
and design work at the selected site (Olkiluoto) began in 2004 (http://www.posiva.fi/en/research_development/onkalo).
Between 2008-2013, excavation of the access tunnel to the repository
(named Onkalo) was completed. In February 2012 this reached the target
depth of 455m below ground. In December 2012 the final design plans were
also completed [5.4]. These would not have been possible without Cardiff
University's research, which is cited in official reports describing the
technology employed at Onkalo [5.5]. Posiva have publicly stated that `the
long-term safety of final disposal is, above all, based on carefully
studied, complimentary engineered barriers' [5.6]. The design
plans formed the basis of an application for a full construction
licence, which was submitted to the Radiation and Nuclear Authority of
Finland (STUK) in December 2012. In April 2013, STUK reported a positive
response to initial reviews of the licence application. Activity at
Onkalo is now focused on structural work; the final disposal of nuclear
waste at the repository is scheduled to start in 2020 [5.7].
Global nuclear authorities support for Onkalo is illustrated by
endorsement from the IAEA In August 2012 the Director, General Yukiya
Amanom, visited Onkalo in a two day official visit. He stated that `This
development is good news for Finland and for the world, since
Finland's success as a forerunner in mastering this significant
engineering challenge will offer alternatives for other nations
seeking to sustainably and responsibly manage spent fuel.' [5.8]
Impact on Public Policy and Services: The disposal of
high level nuclear waste is a worldwide problem and the GRC's research
has been taken up on a global scale. In particular, the GRC has been
designated by the IAEA as a "Centre of Excellence/Expertise" [5.9]. In
this context, the GRC is a founder member of the Agency's Underground
Research Facilities Network (URF), dedicated to "building confidence
in the geological disposal of high level nuclear waste". The role
of the network is to deliver training and demonstration activities
related to high level nuclear waste. Training courses and coordinated
research programmes are pursued, with the overall objective of
transferring good practice from countries with developed programmes,
such as in Scandinavia, to those countries that are just beginning to
embark on the difficult task of implementing a geological disposal
option. Virtually all of the countries with a civil nuclear programme
take part. The GRC has participated extensively in these programmes, via
the delivery of training courses and execution of research programmes.
It is claimed that the impact of the work is significant, particularly
in relation to the important issue of capacity building. It is
anticipated that this will help "build confidence" in the geological
disposal programme worldwide. Since 2007 the GRC's Director (Prof H R
Thomas) has served as Chair to the network and in this capacity has also
been instrumental in shaping and guiding policy developments in this
Economic Impact: £200M investment has been made from
2008-2013, by SKB, as a direct consequence of the research. The final
cost of Onkalo is expected to be €3.3B. However this sum is markedly
less than the expense of continuing storage of high level nuclear waste
(at Sellafield in the UK, for example, this amounts to £1.6B per year,
in addition to the cost of cleanup and maintenance work, which is priced
at £67.5B - http://www.nao.org.uk/report/managing-risk-
reduction-at-sellafield/). The activities that the research has
enabled, highlighted by the scale of investment, are a major step
towards a permanent long-term solution to high level nuclear waste
In summary, the research conducted at the GRC has orchestrated a major
development in nuclear waste disposal. The resulting impact has had both
global reach and significance.
Sources to corroborate the impact
Confirms Cardiff's involvement in the ERATOM programme and the
organisations that were subsequently able to use the research.
Confirms the use of the research by the EC and international Nuclear
5.3) Executive Secretary at SKB. Confirms the use and impact of the
research for SKB.
5.4) Senior Adviser at Posiva. Confirms the use and impact of the
research at Posiva.
Relates to the use of the research and impact at Onkalo.
Confirms the use and impact of the research by the Nuclear Waste
Authorities in Finland.
Evidence of the impact of the research regarding the repository in
Evidence of the global impact of the research.
Confirms the GRC is a IAEA Centre of Expertise.
5.10) Executive Secretary at SKB. Confirms the financial investment
made post 2008.