Euradwaste '08 - EU Bookshop - Europa

From the panel discussion several possible issues for future research emerged:
- General issue: The host rock specificity must be taken into account in the definition of projects.
Commonalities are negligible.
1- Sorption on crystalline rock and, although less important, on overburden of salt formations,
2- In depth interpretation of existing data, above all from FUNMIG,
3- Geochemical in-situ experiments, micro analytics,
4- Isotopic dilution and exchange,
5- Competition of diffusing species,
6- Retardation processes for iodine and selenium,
7- Mineral reactions and nuclides.
Below is an elaboration on topic 1, 2, 3, 4, 6 and 7. Topic 2 intersects with several of the other
above listed topics and is also relevant to the outcome of the other FP6 IP's.
1. Sorption of radionuclides in crystalline rock
The transport of radionuclides with non-negligible sorption in the far-field of crystalline rock is
strongly dependent on the magnitude of process causing the retention. The present situation is that
sorption data (Kd values) scatter over several orders of magnitude. This broad range of sorption
data reflect on one hand operational differences from underlying experiments, and on the other hand
differences in the composition of the mobile phase and the composition and properties of the stationary
phase. Attempt to relate the differences in sorption values to such variations in the system
properties, however, have not yet given acceptable results. As a consequence, evaluation strategies
are applied in order to select data.
The data selection strategies chosen vary, depending on the objectives, such as selecting values that
are sufficiently conservative for a specific purpose, between the probably most representative ones
and the most representative ones of the set of data available. This may be a necessary intermediate
step in order to proceed with development of the Safety Assessment as part of the disposal Safety
Case (SC). Moving towards a more advanced stage of the disposal SC, however, data should be
used providing for a justified case. Such a justified case needs to build on demonstration of an acceptable
level of process understanding in order to ensure that the data used (i) are void of unacceptable
experimental artefacts, (ii) actually represent the assumed system, and (iii) can be used for
reliable predictions for up-scaling with respect to time and size. The latter is especially important
because the SC builds on a system evolution with changing conditions. Any prediction into the future
will rest on prediction also of the retention behaviour under the different conditions that will be
found in different repository evolution phases. Consequently, even a very elaborate determination
of the best values for the present conditions will not solve the problem of future system evolution.
The salt-dome overburden may also be investigated, however, with less emphasis than that on the
crystalline far-field. In the past, a very broad set of sorption data has been generated for salt-dome
overburden. The problem with these data is comparable with that of crystalline rock, namely difficulties
with justified and trustworthy evaluation, extrapolation and application of the data. Studying
few such systems will also support development, testing and comparison of analytical methods and
evaluation approaches.
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