Neale Hunt Manager, Used Fuel Safety Assessment NWMO

The Safety Case

The Safety Case

Purpose: To present a high level overview of the safety case

Agenda: 1. How is Safety Achieved? 2. Conventional Health and Safety 3. Transportation Safety 4. Preclosure (Operations) Safety 5. Postclosure Safety 6. Monitoring and Oversight 7. Summary

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1.0 How is Safety Achieved?

Focus of safety related activities is on protection of the public, the workers and the environment

Safety is achieved by a combination of:

• Favourable host rock and site • Repository depth • Robust design • Durable wasteform • Trained staff and proper equipment • Monitoring and oversight

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Safety through Design and Operation:

• Similar to any mine or large industrial facility • Use of proven excavation techniques • Wide rock pillars for good rock support • Appropriate equipment • Good ventilation • Minimize combustibles • Training • Safe work practices, etc

Considerable Canadian and international experience exists in managing conventional safety issues

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2.0 Conventional Health and Safety

Safety Achieved by the Container:

• Stainless steel with impact limiter • Weighs 29.5 tonnes empty • Certified by the CNSC • Designed to meet international standards • Testing involves free-drop test, puncture test,

a burn test and an immersion test

Considerable international experience in the transportation of used nuclear fuel extending over a 50 year period

There has never been an accident that has resulted in radioactivity escaping its container

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3.0 Transportation Safety

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4.0 Preclosure Safety (Operations)

Considerable Canadian and international experience in radioactive materials handling

Safety through Design and Operating Procedures

• Used fuel is a solid material - not reactive, not combustible • Used fuel is maintained under dry conditions with low temperatures

- air cooling is sufficient • Fuel handling operations occur inside specially designed rooms with thick concrete

walls for shielding • Fuel is removed from the transport container and placed in the long-term container • Long-term container is sealed, placed inside a shielded conveyance for transport

and moved underground • Fuel handling areas are maintained below atmospheric pressure • Ventilation systems are filtered and monitored • Etc.

4.0 Preclosure Safety – Safety Assessment

Preclosure Safety Assessment Purpose is to demonstrate that the facility can be operated safely

• Addresses: • Normal Operation • Abnormal Occurrences • Accidents

• Normal Operations - Examples: • Workers:

• Occupational dose due to working in close proximity to radioactive materials • Managed by shielding and by distance, workers are directly monitored

• Public: • Very small releases can occur during handling of damaged fuel bundles • Managed mostly through controlled ventilation system and filters • Doses to people estimated for comparison against acceptance criteria • Estimates are so low as to be almost negligible

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4.0 Preclosure Safety – Safety Assessment (cont’d)

Abnormal Occurrences and Accidents - Examples: • Event Identification:

• Events identified via a formal process – Failure Modes and Effects Analysis (FMEA) • Identifies such things as loss of power, breakdown of equipment, crane failures,

dropping of bundles, dropping of container, fire • Also considers external events such as earthquakes, severe storms

• Event Consequence Assessment: • Potential events categorized according

to frequency • Bounding events analysed with

computer models • Potential impacts to workers and public

estimated and compared to criteria • Identifies mitigation measures if appropriate

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4.0 Preclosure Safety – Safety Assessment (cont’d)

Example – Flood Hazard Assessment • Site location would be selected considering the potential for flooding based on

drainage area and flood patterns • Site would have a drainage system with capacity for design-basis storm

• But.....“What if” the design-basis storm is exceeded? • Typically addressed through:

• Consideration of a “Probable Maximum Precipitation” (PMP), which represents the maximum capacity of a storm to supply water, and by

• Considering response of nearby rivers to flooding • E.g. - site specific PMP may be 380 mm over 1 hr (depending on site)

• Hurricane Hazel dropped up to 285 mm rain over 48 hrs

• Shaft collars to underground would be set above any potential flood level to ensure repository did not flood

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5.0 Postclosure Safety

Safety Achieved by Design and Geology

Robust Design: • Multiple barriers (used fuel, container, seals,

rock) • Materials with demonstrated long-life

capability • Designed to work with the geology

Geology: • Deep location • Large volume of low permeability rock • Record of low seismicity • Evidence that rocks are ancient and have

survived multiple glaciations • Evidence that groundwater in rocks is old

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5.0 Postclosure Safety - Multiple Barriers

Design - Combination of Engineered and Natural Barriers

Multiple Barrier System

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5.0 Postclosure Safety - Multiple Barriers (cont’d)

Barrier 1: The Fuel Pellet

• High density durable ceramic • Very low solubility so takes millions of

years to dissolve if submerged in water • Most radionuclides are trapped where

they are formed, in the middle of uranium oxide pellet

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5.0 Postclosure Safety - Multiple Barriers (cont’d)

Barrier 2: The Zircaloy Fuel Sheath

• Used fuel pellets are held in sealed tubes made of Zircaloy (zirconium, tin, iron and chromium )

• Zircaloy is a strong, corrosion-resistant metal

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5.0 Postclosure Safety - Multiple Barriers (cont’d)

• Robust and long-lived • Steel inner shell • Copper outer shell

• Inner shell for strength (hydrostatic pressure, bentonite swelling pressure and future glaciations)

• Outer shell for corrosion protection of the inner shell

• Copper is one of three common stable metals found naturally (others are silver and gold)

Barrier 3: Used Fuel Container

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5.0 Postclosure Safety - Multiple Barriers (cont’d)

• Bentonite is a naturally occurring mineral • Formed from volcanic ash deposited in a sea and modified by geological

process about 100 million years ago • Many industrial uses (e.g., pet litter, drilling fluid, foundry forms, sealants) • Can absorb 10x its weight in water and can swell to 16x its initial size

Barrier 4: Bentonite Clay Based Sealing Materials

• Durable, with ability to self seal • Expanded bentonite provides

an impermeable seal to water

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5.0 Postclosure Safety - Multiple Barriers (cont’d)

• Used fuel containers will be surrounded by bentonite clay

• Underground rooms will be backfilled with bentonite-based materials

• These materials minimize the movement of water through the repository

• If a container fails, chemical properties of the clay make it difficult for radionuclides to travel, greatly slowing their release rate

Barrier 4: Bentonite Clay Based Sealing Materials (cont’d)

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5.0 Postclosure Safety - Multiple Barriers (cont’d)

• Host rock forms a natural barrier • Conditions deep underground promote long

container life • Protects the repository from natural surface

events and human activities • If a container fails, chemical properties of

the geosphere can make it difficult for radionuclides to travel, greatly slowing their release rate

Barrier 5: The Geosphere

5.0 Postclosure Safety - Geosynthesis

Geosynthesis • Detailed study of the geosphere to:

• Understand its past history, its current state and its future evolution • Provides evidence on key processes

• Examples of study areas: • Rock strength • Groundwater age • Mapping and understanding fractures • Rock stability • Seismicity • Glaciation • Barrier function

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Postclosure Safety Assessment Purpose is to provide a quantitative estimate of the ability of the repository to isolate and contain the waste after the repository is sealed and closed

Uses computer models of the repository, the surrounding host rock and the biosphere

Addresses: • Radiological and non-radiological hazards • Effects on people and the environment

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5.0 Postclosure Safety – Safety Assessment

Status

• Presently no assessment for a specific Canadian site • Preliminary Canadian safety case studies for hypothetical sites:

Crystalline Rock: • AECL EIS and Second Case Study (1992 and 1994) • OPG Third Case Study (2004) • NWMO Fourth Case Study (2012) • NWMO Sixth Case Study (underway)

Sedimentary Rock : • NWMO Fifth Case Study (2013) • NWMO Seventh Case Study (for 2016)

• These allow us to identify important features for long-term safety

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5.0 Postclosure Safety – Safety Assessment (cont’d)

Postclosure Safety Assessment does not try to predict the future, but looks at the consequences of a range of scenarios:

Normal Evolution Scenario • Likely evolution of site, repository and containers • Includes earthquakes and glaciation • Assumes a small number of containers are

placed in the repository with undetected defects

Disruptive Event Scenarios • Unlikely and “what if” events • These scenarios check the robustness of the specific site and repository design • Inadvertent human intrusion into repository • Range of situations where container is compromised

(e.g. all containers fail, degraded seals, undetected fault)

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5.0 Postclosure Safety - Safety Assessment (cont’d)

5.0 Postclosure Safety - Safety Assessment (cont’d)

Some Key Assumptions: • People in the future are similar to people of today • Protect future people to the same degree that we would protect ourselves • People in the future unknowingly live on the site • People in the future behave plausibly, with characteristics that maximize exposure: • Assume a self-sufficient farm family

• Living on top of the repository • Growing all their food on top of the repository • Water from deep local well

• If we can show that this hypothetical family is safe, then real families that live further away would be safer

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5.0 Postclosure Safety - Safety Assessment (cont’d)

Timescale: • Considers a 1 million year timeframe because this period covers key processes,

including: • The initial large decrease in used fuel radioactivity within the first 1000 years • The subsequent slow decrease in used fuel radioactivity to the level of that in an

equivalent amount of natural uranium • Future glaciation, assuming first glacial cycle in about 60,000 years • The potential for container failure, and • Is sufficient to determine the maximum impact

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5.0 Postclosure Safety - Safety Assessment (cont’d)

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Radioactivity of Used CANDU Fuel (220 MWh/kgU)

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Some Modelling Illustrations:

5.0 Postclosure Safety - Safety Assessment (cont’d)

Surface and Subsurface Model around Hypothetical Repository

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Some Modelling Illustrations:

5.0 Postclosure Safety - Safety Assessment (cont’d)

3D Model of Repository Room, Tunnel Seals and Three Containers (In-floor Placement Concept)

5.0 Postclosure Safety - Safety Assessment (cont’d)

Sample Results – Normal Evolution (Crystalline Rock)

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5.0 Postclosure Safety – R&D

The Design and Safety Case is Supported by an Extensive R&D Program

Purpose: • For optimization and proof testing • To enhance scientific understanding of processes that may influence safety • To maintain awareness of technology advancements

Achieved by:

• Tests and experiments performed in Canada over many years at a number of universities and private companies

• International collaborations with a number of countries (e.g., Sweden, Belgium, Switzerland, Germany) to share costs and knowledge

• International meetings to share experiences and knowledge

• Conferences

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5.0 Postclosure Safety – Natural Analogues

Postclosure Safety is Supported by Natural Analogues: • These are natural features that exist under conditions or processes occurring

over long periods of time that are similar to those expected in some part of a deep geological repository

• They build confidence that the system will perform as expected

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5.0 Postclosure Safety – Natural Analogues (cont’d)

Cigar Lake (Canada) • Uranium ore deposit

surrounded by clay at a depth of 430 m

• Has remained intact and isolated from the surface environment for over 1.3 billion years

Repository Natural Analogue

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5.0 Postclosure Safety – Natural Analogues (cont’d)

Geosphere Natural Analogue

Oklo (Gabon)

• Naturally occurring fission reactions took place in uranium ore body about 2 billion years ago

• Active over a period of one million years

• Studies show most of the fission product and actinide material has remained in the vicinity of the ‘reactor’

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5.0 Postclosure Safety – Natural Analogues (cont’d)

Copper Natural Analogue

England

• Natural copper plates • Quartz/clay matrix • Reducing conditions • ~1 mm corrosion • ~200 million years old

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5.0 Postclosure Safety – Natural Analogues (cont’d)

Bentonite Clay Natural Analogue

• Sequoia-like trees in Dunarobba forest (Italy) buried in clay for 1½ million years • They are still made of wood and have not decomposed

6.0 Monitoring and Oversight

Safety is independently checked by the regulator: • Construction and operation is only permitted under a licence granted by the CNSC,

the independent federal regulator • Formal CNSC process for licensing (submissions, hearings, intervenors, etc.) • Ongoing CNSC review and oversight for the duration of the project

Project would be monitored continuously from before construction, through operations, and after closure:

• Monitoring by NWMO to demonstrate compliance with licence conditions • Independent verification by CNSC

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7.0 Summary

Safety is achieved by a combination of: Robust design Favourable host rock conditions Repository depth Trained staff and proper equipment Use of international experience Monitoring and oversight

Safety assessment provides a quantitative evaluation of how these contribute to protecting public, workers and environment. The safety case documents all the reasons behind the conclusion that a repository at a particular site will be safe.