Bentonite resaturation

Bradbury, M. H. Baeyens, B. 2002. Pore-water Chemistry in Compacted Resaturated MX-Bentonite Physicochemical Characterisation and Geochemical Modelling. Paul Scherrer Institut, Villigen, Switzerland, PSI Berichl Nr. 02-10, 42... 

The equations of poro-elasticity were solved with the finite element code FRACON. The FRACON code was used to predict the in-situ T-H-M experiment at the FEBEX gallery in Grimsel, Switzerland. The FRACON correctly predicted that the bentonite would resaturate from the rock interface. Near the heater, it also correctly predicted that initial drying will take place, followed by a slow resaturation. The model correctly predicted that at the end of 1000 days of heating, resaturation of the bentonite was still... 

The numerical model ROCMAS was applied to predict coupled THM processes in a bentonite barrier at the FEBEX in situ test. The results indicate that numerical modeling can provide highly reliable predictions for temperature distribution, and reasonably reliable predictions for moisture flow and stress in a bentonite barrier. Moreover, field observations and modeling shows that resaturation of the buffer was controlled by the properties of the bentonite barrier whereas the permeability of the rock was sufficiently high to act as an unrestriced water source. Therefore, the wetting of the bentonite took place uniformly from the rock and was not impacted by the permeability difference between the Lamprophyres dykes and surrounding rock. 

There is a slight impact of TH coupling on the resaturation of the buffer (Figure 7b). In TH and THM simulations, the resaturation of the bentonite buffer is slightly delayed because of thermally induced drying near the canister surface. 

DRYING AND RESATURATION OF THE BENTONITE BARRIER IN A NUCLEAR WASTE REPOSITORY. ANALYSES BASED ON AN ANALYTICAL SOLUTION... 

Abstract The bentonite layer, which surrounds the canisters in a nuclear waste repository deep down in rock, experiences an initial drying and a resaturation from the outer rock side. These complex processes interact and a key question is the degree of initial drying and the time it takes to resaturate the bentonite. It is shown that the highly non-linear coupled equations may, when formulated in a special way, be linearized with a loss of accuracy of some 10% only. The paper presents an analytical solution for the linearized case. The solution involves two key parameters only, a time scale and thermodiffusive parameter a. The largest drying at the canister wall and the resaturation are obtained from a single set of curves with a dimensionless time and a as parameter. 

Abramowitz M. Stegun 1., 1972. Handbook of Mathematical Functions. Dover Publ. N.Y. Carslaw H.S. Jaeger J.C. 1965. Conduction of Heat in Solids. Oxford Sc. Publ., Oxford. Claesson J. 2003. Drying and Resaturation of a Bentonite Annulus. An Analytical Solution. Report, Building Physics, Chalmers, Sweden. Rutqvist J., Noorishad J. Tsang C-F. 1999. Coupled Termohydromechanical Analysis of a Heater Test in Unsaturated Clay and Fractured Rock at the Kamaishi Mine. SKI report 99 50, the Swedish Nuclear Power Inspectorate. 

The release model would, however, probably be very conservative at such times as the inner zone of the bentonite would still be in the process of resaturation. The waste-form would thus not be exposed to liquid water and, in addition, a net flux of water towards the canister would be expected to prevent outwards radionuclide transport. 

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