Euradwaste '08 - EU Bookshop - Europa
Euradwaste '08 - EU Bookshop - Europa Euradwaste '08 - EU Bookshop - Europa
under isothermal conditions. If the existence of a threshold hydraulic gradient will hinder the full saturation of the barrier is still open question. The laboratory, the mock-up and the in situ tests results have proven that the thermal gradient delays saturation and that it has a major effect on water distribution inside the bentonite. To explain this observation, several physical processes have been tested, among which the thermo-osmosis effects. The inclusion of this process in the model improves the predictions of saturation in the hotter areas but not near the hydration front. The mock-up and the in situ tests have provided long-term (up to 10 years) data bases on the evolution of the thermal, hydraulic and mechanical parameters of the clay barrier, information that is still very limited for judging the long-term performance of the clay barrier due to its slow evolution. Also, a data base on water intake and distribution inside the clay for different periods of time, as well as on porosity and geochemical changes has been obtained for several laboratory tests. The state of the bentonite after 7.6 years of being submitted to barrier conditions is known: no mineralogical modifications have been observed and the swelling capacity has not been altered. The effect of temperature on HM properties is better known and has been quantified for several boundary conditions. Trends of behaviour and factors affecting have been revealed: the swelling capacity decreases with temperature only when the bentonite is compacted at high densities and the overload is high; the permeability increases with temperature approximately in the proportion expected by water viscosity changes. New developments have been made that have significantly improved the capabilities of the THM formulation used in the analyses. The new developments have been proposed based on strong physical basis. Therefore, the better description of the clay behaviour obtained using the new mathematical formulation is not due to the simple fitting of experimental data, but it is the results of the development of a more complete and reliable formulation. One successful gas migration test has been performed in the Lasgit setup. The buffer in the Lasgit experiment is very close to full saturation, but still quite far from stress equilibrium. Therefore, all results so far should be taken with some caution. However, the work has demonstrated that it is possible to construct and operate a full scale gas migration experiment. The obtained results also indicate that the previous understanding of the gas migration process remains valid when the assumptions are tested in a relevant scale. Observations from Lasgit include: The hydraulic testing of the buffer material pre-gas injection indicates a hydraulic conductivity of ~7·10 �14 m/s, which is comparable to values obtained from laboratory scale experiments. The same hydraulic behaviour is observed post-gas injection, which indicates that no permanent conductive channels are formed in the bentonite during the gas injection. In the gas injection test, gas entry pressure was ~800 kPa, which is much lower than what is observed in laboratory scale experiments (the most likely reason for this is that the clay is not in stress equilibrium). The peak gas pressure in the gas injection test was 5.7 MPa, which is slightly above the total stress in the Lasgit experiment. This could indicate that the gas pressures in the repository would remain at reasonable levels. However, no firm conclusions should be drawn at this stage. Lasgit is planned to operate for many years in the future and more gas injection tests will hopefully give a better understanding of the gas migration process in bentonite. 200
The investigations performed in NF-PRO on salt backfills have lead to a better understanding of the mechanical and hydraulic behaviour of the materials especially in the range of low permeability. Different constitutive laws have been tested and it was found that the Zhang model is appropriate for describing salt bricks. Use of the Spiers model requires some more experimental work. It was found that highly compacted crushed salt differs in its hydraulic properties from naturally grown rock salt, even at comparable porosities. While rock salt is practically tight, the compacted samples always showed a measurable permeability. It seems to be the case that a network of connected pores remains present even in highly compacted salt grit, while it does not exist in natural rock salt. The compaction behaviour highly depends on the moisture content of the backfill material. This is a well-known fact, but the investigations have contributed to enhancing the understanding of this phenomenon and quantifying it, especially at low porosities between 1% and 10%. Bentonite as an additive to crushed salt backfill is a possibility to enhance the compactibility since it acts as some kind of lubricant between the salt grains. Additionally, the permeability of the material mixture is reduced in comparison with pure crushed salt at the same state of porosity. 6. Acknowledgements This project has been co-funded by the European Commission and performed as part of the sixth Euratom Framework Programme for nuclear research and training activities (2002-2006) under contract FI6W-CT-2003-02389. References [1] Huertas F., Villar M. V., Garcia-Siñeriz J. L., Sellin P., Stührenberg D., Alheid H-J., (2007) Thermo-hydro-mechanical (geochemical) processes in the engineered barrier system European Commission EUR ##### EN. [2] Johnson L., Alonso J., Plas F., Pellegrini D., Bildstein O., Van Geet M., Becker D., Sellin P., Cormenzana J.L., Nordman , H., Lehikoinen J., Sillen X., Weetjens E., Schnier H., Vokal A., Hodgkinson, D., Serres C., Norris S, Amme M., BauerA C., Mathieu G., Hautojärvi A (2008) Understanding and Physical and Numerical Modelling of the Key Processes in the Near-Field and their Coupling for Different Host Rocks and Repository Strategies European Commission EUR ##### EN. [3] ENRESA (1997). Evaluación del comportamiento y de la seguridad de un almacenamiento geológico profundo en granito. Publicación técnica 6/97. Madrid. 179 pp. [4] Zhang, X, Grupa, J, 2006:‘NF-Pro deliverable 3.5.7 Compaction behaviour and permeability of low porosity compacted salt grit (dry and wet)’ NRG 21146/06.77412, 15.12.2000. 201
- Page 166 and 167: 5. Conclusions The HLW arising from
- Page 168 and 169: 152
- Page 170 and 171: tinides (MA) are destined for geolo
- Page 172 and 173: [3] Enrique González: Head of Nucl
- Page 174 and 175: 158
- Page 176 and 177: 160
- Page 178 and 179: erage level of funding of research
- Page 180 and 181: Prior to NF-PRO, the question wheth
- Page 182 and 183: nant exchangeable cation. This chan
- Page 184 and 185: eal concentration gradient in sampl
- Page 186 and 187: access shafts, providing higher per
- Page 188 and 189: 172
- Page 190 and 191: in the European coordinated action
- Page 192 and 193: proved, with amongst others the det
- Page 194 and 195: 4. Discussion Tests with dissolved
- Page 196 and 197: though with a slow rate. The data i
- Page 198 and 199: surface. The coupling between water
- Page 200 and 201: nuclear waste within the near-field
- Page 202 and 203: tion of the column [2]. Moreover, t
- Page 204 and 205: case, the iron diffusion front in t
- Page 206 and 207: 5.1 Sorption As an example of the t
- Page 208 and 209: corrosion; up-scaling of clay alter
- Page 210 and 211: Bentonite barriers are very importa
- Page 212 and 213: To determine the impact of temperat
- Page 214 and 215: in the underground laboratory in Gr
- Page 218 and 219: 202
- Page 220 and 221: Zones around such openings which ex
- Page 222 and 223: layout of cells developed by ENPC w
- Page 224 and 225: ) a) e) d) f) d) e) f) c) Figure 3.
- Page 226 and 227: EDZ removal by additional excavatio
- Page 228 and 229: [7] Wenk H.-R., Voltolini, M., Mazu
- Page 230 and 231: that provided by various national s
- Page 232 and 233: system robustness, rather than as s
- Page 234 and 235: Regarding diffusion studies perform
- Page 236 and 237: 7. EDZ characterization and evoluti
- Page 238 and 239: [4] Alonso, J. et al. 2004: Bentoni
- Page 240 and 241: There has been a significant change
- Page 242 and 243: 226
- Page 244 and 245: 228
- Page 246 and 247: 2. Methodology ESDRED has been focu
- Page 248 and 249: Figure 3: Reduced scale mock-up aft
- Page 250 and 251: Figure 8: Demonstration of emplacem
- Page 252 and 253: The various reports produced by the
- Page 254 and 255: 238
- Page 256 and 257: 2. Methodology In general, the work
- Page 258 and 259: limitations of the selected press.
- Page 260 and 261: Figure 3.2.1 Schematic representati
- Page 262 and 263: which was relatively homogeneous in
- Page 264 and 265: Figure 3.3.1 Emplacement of SF-Cani
The investigations performed in NF-PRO on salt backfills have lead to a better understanding of the<br />
mechanical and hydraulic behaviour of the materials especially in the range of low permeability.<br />
Different constitutive laws have been tested and it was found that the Zhang model is appropriate<br />
for describing salt bricks. Use of the Spiers model requires some more experimental work.<br />
It was found that highly compacted crushed salt differs in its hydraulic properties from naturally<br />
grown rock salt, even at comparable porosities. While rock salt is practically tight, the compacted<br />
samples always showed a measurable permeability. It seems to be the case that a network of connected<br />
pores remains present even in highly compacted salt grit, while it does not exist in natural<br />
rock salt.<br />
The compaction behaviour highly depends on the moisture content of the backfill material. This is a<br />
well-known fact, but the investigations have contributed to enhancing the understanding of this<br />
phenomenon and quantifying it, especially at low porosities between 1% and 10%.<br />
Bentonite as an additive to crushed salt backfill is a possibility to enhance the compactibility since<br />
it acts as some kind of lubricant between the salt grains. Additionally, the permeability of the material<br />
mixture is reduced in comparison with pure crushed salt at the same state of porosity.<br />
6. Acknowledgements<br />
This project has been co-funded by the European Commission and performed as part of the sixth<br />
Euratom Framework Programme for nuclear research and training activities (2002-2006) under contract<br />
FI6W-CT-2003-02389.<br />
References<br />
[1] Huertas F., Villar M. V., Garcia-Siñeriz J. L., Sellin P., Stührenberg D., Alheid H-J., (2007)<br />
Thermo-hydro-mechanical (geochemical) processes in the engineered barrier system European<br />
Commission <strong>EU</strong>R ##### EN.<br />
[2] Johnson L., Alonso J., Plas F., Pellegrini D., Bildstein O., Van Geet M., Becker D., Sellin P.,<br />
Cormenzana J.L., Nordman , H., Lehikoinen J., Sillen X., Weetjens E., Schnier H., Vokal A.,<br />
Hodgkinson, D., Serres C., Norris S, Amme M., BauerA C., Mathieu G., Hautojärvi A (2008)<br />
Understanding and Physical and Numerical Modelling of the Key Processes in the Near-Field<br />
and their Coupling for Different Host Rocks and Repository Strategies European Commission<br />
<strong>EU</strong>R ##### EN.<br />
[3] ENRESA (1997). Evaluación del comportamiento y de la seguridad de un almacenamiento<br />
geológico profundo en granito. Publicación técnica 6/97. Madrid. 179 pp.<br />
[4] Zhang, X, Grupa, J, 2006:‘NF-Pro deliverable 3.5.7 Compaction behaviour and permeability<br />
of low porosity compacted salt grit (dry and wet)’ NRG 21146/06.77412, 15.12.2000.<br />
201
Change language