Euradwaste '08 - EU Bookshop - Europa

one study, the compartment structures should be identical, or at least as similar as possible, in order
to allow a comparison of the results. Since performance indicators are not based on a safety statement
they do not require any reference value and their use is more flexible. Performance indicators
are very important for the understanding of the modelled processes and they can be used for optimising
the repository system. Finally not every applied performance indicator may be used in the
safety case, but most of them give valuable arguments for increasing the confidence in the safety of
a repository system.
With respect to the work concerning safety and performance indicators several test cases have been
defined and applied to host rocks such as clay and rock salt, for which the use of safety and performance
indicators has hardly been investigated in detail yet. The general approach is based on the
SPIN methodology. Preliminary results suggest that this methodology works well for all kinds of
host rock. Some new indicators have been identified, which are tested within PAMINA with results
still pending. It is evident, that performance indicators give a good insight to the functioning of the
system. In this context it was observed that performance indicators applied to specific radionuclides
are useful for identifying influential processes. Finally it is noted that performance indicators are
dependent on repository systems and host rocks.
4. RTDC4
In RTD component 4 several benchmark exercises are carried out, in which quantitative comparisons
are made of approaches that, on the one hand, rely on simplifying assumptions and models,
and on the other hand, on complex models that take into account a more complete process conceptualization
in space and time. The main objective is to evaluate the added value of using more complex
and more realistic modelling approaches not yet fully accounted for in PA. This RTD component
comprises of three work packages.
The first work package focuses on processes which determine the evolution of the near field of a
repository in salt as host rock. One aspect being investigated is the convergence process of rock
salt, which determines the advective flow of radionuclides in case of a repository completely filled
with solution. For several test cases results are compared from different approaches to model this
complex process which depends on many parameters. Also the brine intrusion process into a backfilled
drift and the radionuclide transport by density driven exchange are investigated for salt as
host rock.
Specific benchmarks have been set up to study the reactive transport of radionuclides for clay as
host rock. One exercise investigates Cs migration, considering all competitive effects on sorption
processes. Both empirical and thermodynamic models are defined for geochemical modelling. Another
exercise focuses on heavy elements behaviour with regard to sorption and precipitation processes.
Also, benchmarks are carried out for sensitivity analysis on “Kd” and “solubility limit” models
/ geochemical transport with respect to radionuclide migration in the near field. In case of granite
as host rock benchmark calculations using the reactive transport code CORE and GoldSim as PA
code aim to draw conclusions on the usefulness and the need of implementing fully reactive transport
in PA models instead of the Kd and solubility limit approach commonly used in PA.
The second work package is to investigate the usefulness of codes dealing with geometric complex
representations of the geosphere in comparison to coarse or simplified 1D representations often
used in PA codes for modelling the transport behaviour of radionuclides in the far field. Part of this
work is described in the following for a repository located in rock salt. Typically, the water in the
aquifer that is in contact with the cap rock of the salt dome is highly saline, while other aquifers at
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