B. Key phenomena potentially relevant to repository evolution (NTB 24-10)
The key phenomena that are potentially relevant to the evolution and performance of the repository system are considered in the performance assessment including those phenomena that have the potential to lead to deviations from expected repository performance.
These phenomena are identified in NAB 24‑20 Rev. 1 (Nagra 2024m), which synthesises Nagra’s understanding of the initial state and expected post-closure evolution of the repository. As noted in Section 4.5, this understanding has developed iteratively over many years, with each iteration peer-reviewed and informed by Nagra's extensive R&D programme. The key phenomena identified in NAB 24‑20 Rev. 1 (Nagra 2024m), their relevance to system evolution and performance, their potential to lead to performance deviations are listed in Tab. B‑1 where the sections of the performance assessment synthesis NAB 24‑20 Rev. 1 (Nagra 2024u) indicate where these phenomena are addressed.
Tab. B‑1:Key phenomena potentially relevant to repository evolution
|
Key processes and/or phenomena potentially relevant to repository evolution |
Relevance to evolution and performance (analysed in PA) |
Potential performance deviations |
Addressed in: | |
|---|---|---|---|---|
|
Brittle fracturing, shear failure and reactivation of pre-existing features in the drift and cavern near field (EDZ formation) |
Table 5-1 of NAB 24-20 Rev. 1 (Nagra 2024m) |
EDZ formation/hydro-mechanical evolution |
No potential for performance deviations identified |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
|
Unloading of the rock and consequent changes in volumetric strain and pore pressure |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
EDZ development due to pore pressure recovery as soon as tunnel support is emplaced |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
Loading of the lining and convergence of the rock external to the lining as soon as the pore pressure recovers |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
Onset of EDZ formation (L/ILW) |
Table 6-2 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
Swelling of buffer and possible re-compaction of EDZ (after degradation of rock support) |
Table 7-1 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Not explicitly included |
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|
Thermal heave and subsequent settlement. |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Desaturation of the EDZ during active ventilation and cooling of the drifts and caverns |
Table 5-1 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Thermal and hydraulic evolution and repository-generated gas |
Gas- or thermally-induced faulting or fault re-activation |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
|
Initial heating of the bentonite buffer and redistribution of moisture due to heating (local drying close to canister, and diffusive and convective transport of water vapour possible |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Resaturation of the (L/ILW) EDZ and self-sealing: self-sealing as water reaches any open fractures but also development of (or changes in) the EDZ due to loading, pressure recovery and resaturation (loss of apparent cohesion |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Onset of (HLW) EDZ and buffer saturation |
Table 6-1 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Self-sealing of EDZ due to saturation |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
Temperature increases in buffer, EDZ and host rock due to thermal output from canister |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Gas generation and pressure build-up due to anaerobic corrosion of metals |
Table 6-2 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Partial decrease in oxygen partial pressure |
Not explicitly included but conservatively accounted for in the calculations |
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|
Temperature peaks in EDZ and host rock due to reducing power output from canister. Cooling of buffer and EDZ with reduction in thermal stresses |
Table 7-1 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Ongoing saturation of the EDZ and buffer. Self-sealing of EDZ due to resaturation |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Saturation of the deep geological repository (including ongoing gas production) |
Chapter 6 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Corrosion of steel waste disposed of in MOSAIK containers |
Chapter 6 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
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|
Cement-clay interactions and loss of anion-accessible porosity and thus permeability at the interfaces |
Table 6-2 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Chemical evolution of L/ILW near field Evolution of sealing performance |
No potential for performance deviations identified |
Included in Chapter 4 of NTB 24-22 Rev. 1 (Nagra 2024u) / total system analysis |
|
Internal degradation of cement-based elements |
Chapter 6 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
External degradation of concrete elements: presence of water under partially saturated conditions |
Chapter 6 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
Canister breaching |
Table 7-2 of NAB 24-20 Rev. 1 (Nagra 2024m) |
Breaching of HLW canisters and subsequent evolution of canister interior |
No potential for performance deviations identified |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
|
Bentonite porewater enters the canister |
Not explicitly included but conservatively accounted for in the calculations |
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Release of radionuclides |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
Short-term modulation of fluvial incision by glacial/interglacial cycles |
Chapter 10 (Nagra 2024m) |
Geological evolution |
No potential for performance deviations identified |
Not included but conservatively accounted for in the calculations |
|
Occurrence of permafrost |
Not included but conservatively accounted for in the calculations |
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|
Long-term rock uplift, fluvial incision and remaining overburden |
Faulting or fault reactivation due to earthquakes; extreme erosion |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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|
The expected glacial scenario and deep glacial erosion |
Not included |
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Earthquakes and faulting |
Included in Chapter 3 of NTB 24-22 Rev. 1 (Nagra 2024u) / assessment by component |
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