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surface. The coupling between water radiolysis and surface interaction is strongly model dependent.
The transition from radiolytic controlled to chemically controlled dissolution is only represented in
few models and the effect of hydrogen is represented only with many ad-hoc assumptions. The effect
of Fe 2+ and H2, and certain parameters like bromide concentrations on fuel dissolution is experimentally
still rather poorly documented, and models describing this effect are not verified experimentally.
Surface area and porosity evolution is not well considered either in the models. No
mechanistic model for MOX fuel dissolution exists. The work of MICADO is concentrated on UO2
fuel.
The current source term models do not yet include the effect of spent fuel/material interfaces (spent
fuel with bentonite, clay, iron or cement). The experiments of NF-PRO suggest that these near-field
materials have at least a short term effect on the matrix dissolution rate. Compared with the large
database on simple spent fuel/UO2/water systems the obtained data are still scarce and less conclusive.
Future research should study this more in detail, and include coupling effects for realistic flow
conditions.
In the normal evolution scenario of long-term hydrogen generation by container corrosion, unsaturated
conditions may prevail in the vicinity and inside of the disposal container of spent fuel for
tens of thousands of years. It is known that radiolysis of thin water films sorbed on solids under under-saturated
conditions may involve quite different radiolysis behaviour than bulk water irradiation.
NF-PRO has provided new data on the spent fuel behaviour under unsaturated conditions, but
the results are not conclusive and new experiments are necessary to enhance the confidence in the
system understanding for all stages in the evolution scenario.
6. General conclusions
In general, the knowledge of glass and spent fuel dissolution is sufficient to propose source term
parameter values (in general dissolution rates) to performance assessment with a specified level of
conservativeness. Further work should be balanced against the necessary degree of conservativeness.
Hence, the selection of future experimental work should be based on its potential impact on
the overall performance of the system. It is important that close interaction with the other system
components and the integration by performance assessment is continued. This evaluation should be
part of the selection process of future research programmes.
References
[1] Alonso, J. et al., Report Deliverable D-N° 5.1.7, EU NF-PRO Project FI6W-CT-2003-02389
(2006).
[2] Grambow, B. et al., RTDC-1 Synthesis Report, Deliverable D-N° 1.6.3, EU NF-PRO Project
FI6W-CT-2003-02389 (2008).
[3] Poinssot, C. et al. Final report of the European Project Spent Fuel Stability under Repository
Conditions. CEA-R-6093. ISSN 0429-3460 (2005)
[4] Johnson, L. et al., RTDC-5 Synthesis Report, Deliverable D-N° 5.2.3, EU NF-PRO Project
FI6W-CT-2003-02389 (2008).
[5] Arcos, D. et al., RTDC-2 Synthesis Report, Deliverable D-N° 2.6.4, EU NF-PRO Project
FI6W-CT-2003-02389 (2008).
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