Structure of a Safety Case (NEA)

The Multibarrier Concept each barrier acting passively in concert with the others to isolate, contain and reduce impacts 2

Image: SKB, Sweden ISOLATE radioactivity from people by deep burial in rock CONTAIN radioactivity for many thousands of years until 99.9% has decayed PROVIDE a stable ‘geological cocoon’ for engineered containment system for hundreds of thousands of years PREVENT any releases reaching people and the environment in harmful concentrations typically, m Objectives of Geological Disposal: provide a passively safe system 3

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Safety function indicators (SKB): Contribution to canister-related safety functions: C1 (red), C2 (green), C3 (blue) or to retardation (yellow)

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Activity of Spent Fuel on a linear scale…… 7

Key phenomena contributing to safety functions v. time Nagra, 2002 but many other factors are also involved; e.g. even after engineered barriers deteriorate, they continue to contribute to containment 8

Six orders of magnitude of radiation dose Logarithmic Scale ! /a risk /a risk Eating a banana ‘Low Concern’ Typical Regulatory Constraint for a GDF ‘Low Concern’ Typical Regulatory Constraint for a GDF 9

Key Features of Favourable Geologic Environments Very low to zero water flow at depth, uncoupled from flow in upper rock formations Very old, stable, reducing groundwater at depth No potential fast pathways from repository to surface Thermally stable rock-water system Rock strength allows construction Diffusion dominated radionuclide movement Ability to disperse gas Tectonic stability Resilience to climate change No significant resource potential (intrusion problem)

11 Additional Scenarios examined by N agra Results for SF/HLW/ILW

Geoscience in Radwaste Disposal Assessment Physical Containment (Corrosion) Physical Containment (Concrete) Solubility Sorbtion Gas Generation & Migration NEAR FIELD ASSESSMENT Groundwater Flow Radionuclide Movement Gas Migration GEOSPHERE ASSESSMENT Rivers & Lakes Soils & Rocks Seas & Estuaries Atmosphere BIOSPHERE ASSESSMENT Human Natural INTRUSION ASSESSMENT MODELS ASSESSMENTS Natural Analogues & Demonstration Experiments Site Investigation Repository Design Waste Characteristics

High-techGeology Pictures courtesy of Nagra

Underground Laboratories: Grimsel, Switzerland 14

Roman Cement: 1700 years Hadrian’s wall, England Wood: 1,500,000 years Dunarobba, Italy Copper: years Nahal Mishmar, Israel Glass: 3350 years: Egypt 15 Analogues iron cement steel copper glass organics Roman Cement: 1700 years Hadrian’s wall, England Roman Iron: 1900 years Inchtuthil, Scotland Wood: 1,500,000 years Dunarobba, Italy Copper: years Nahal Mishmar, Israel Glass: 3350 years: Egypt 15

Natural Analogues of GDFs Cigar Lake Uranium Deposit, Canada 16

Archaeological analogues show that we can deal with this period well Radiological impacts of deep uranium ore bodies suggest limited concern about this period We should not expect to do better than nature at long times…. 17

Nagra EN Fig NOTE: mobile fission products very late releases very low doses shaded area s! Dose vs. Time HLW (selected cases)

Calculated radiological impacts: HLW and spent fuel analyses in 5 countries

What is “robust”?  Repository System  simple geology, physics, chemistry, design  large safety factors  some degree of redundancy  Safety Assessment  well validated models  realistic or conservative models, data  all potentially negative processes analysed  insensitivity to parameter changes

Why is safety analysis feasible?  the laws of natural science which govern key processes do not change with time  the geological database extends over longer timescales than the toxic lifetimes of most wastes  accurate predictions of actual system behaviour are not required; it suffices to provide conservative estimates  precise estimates are not needed; even with some orders of magnitude of residual uncertainty we may be clearly within defined safety goals or limits.

Prerequisites for confidence in repository safety  sound disposal concept (robust)  good engineering / technology  suitable site  convincing safety case (robust models /data)  proper regulatory framework  transparent presentation (at all levels)  competent implementing body  competent regulatory body  proper communication

Stakeholder views on risks

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