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o Strongly sorbing radionuclides incl. compatibility of diffusivities with batch sorption
measurements,
o Evaluation of field diffusion experiments,
The structure and surfaces of compacted clays,
The evaluation of natural tracer measurement and up-scaling,
The influence of carbonate and natural organic matter on the sorption of safety relevant radionuclides,
incl. actinides, on clay minerals,
The retention behaviour of the relatively mobile and therefore often dose relevant Selenium,
namely its interaction with pyrite and the sorption on clay minerals incl. the dependence on redox
conditions, compaction degree of sorbing clay and the presence of natural organic matter.
Correspondingly, particularly important topics for crystalline host rocks are
Colloids, incl. bentonite particles from the backfill and humics, and their interaction with radionuclides,
Modelling the up-scaling of reactive transport in heterogeneous fractured systems.
Since hermetical enclosure properties are attributed to the rock salt formation the overburden, to
which work within FUNMIG is focussed on, is considered as supplemental barrier. Migration processes
are therefore of lower relevance.
3.2 Super-FEPS
For clay-rich host rocks the individual FEPs, to which FUNMIG tasks were mapped, were collected
in Super-FEPs. The translation into the FEPCAT terminology showed that virtually all tasks originating
from RTDC 1, 2 and 3 could be mapped onto the FEP group concerning transport mechanisms
(FEPCAT no. A1) and the FEP group concerning retardation mechanisms (FEPCAT no. A2).
Figure 2 depicts the two FEP groups or Super-FEPs . Concerning diffusion related FEPs the two
groups overlap; the group “retardation mechanisms” includes in addition to diffusion related FEPs
also sorption related FEPs according to the broad FEPCAT definition which comprises sorption and
dissolution / precipitation of solids and solid solutions. A few FUNMIG tasks were mapped to FEPs
outside the above mentioned Super-FEPS (cf. Figure 2).
The corresponding parameters typically used in safety assessment are sorption coefficient, solubility,
effective diffusion coefficient and accessible porosity as depicted in Figure 2.
The synthesis is carried out for all three host rock types and is complemented and illustrated by sensitivity
analyses carried out in context with recent safety cases for various European disposal programmes
[6].
4. Discussion
As stated in the introduction of the present paper an interaction between the involved groups is essential
to develop a safety case successfully. In FUNMIG the dialogue between the “supplier
group”, the scientists, and the “customer group”, the performance assessors, was required. In establishing
a co-work between representatives of European Waste Management Organisations as performance
assessors and the Integration Monitoring group (IMG) launched for this purpose, this
challenge was successfully met. The IMG members as representatives of the scientists communicated
the outcome of the research performed within FUNMIG to the performance assessors on one
hand and transmitted the PA feedback to the scientists on the other hand.
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