1. Intrusion scenarios in radwaste repositories
Jean de Mèredieu
Risk management division / Post closure safety departement
26/09/2012
DMR/SAF/

2. 1 – The French classification of radwaste and Andra’s sites locations
2 – Highlighting a few topics :
French national guidance, safety case and safety functions, time-frames, contamination routes and depth parameter.
3 – Intrusion scenarios in Andra’s safety assessments
4 – Possible uses of intrusion scenarios results
DMR/SAF/
26/09/2012

3. Waste classification and management channels
DMR/SAF/
26/09/2012

4. Andra’s sites locations
DMR/SAF/
26/09/2012

5. Guidance 1/2
French national guidance issued by ASN (Nuclear Safety Autority)
LIL-SL Surface facilities
RFS-I.2 (November 8th 1982, updated June 19th 1984) : safety objectives and design bases of surface facilities for the long term disposal of SL and/or IL radioactive waste of low specific activity,
HIL-LL Deep geological repository Safety Guide
Guide de Sûreté 2008 (formerly RFS-III.2.f) : objectives to be retained in the siting and study phases for the long term disposal of HL and IL-LL waste in deep geological formations in order to ensure safety after the operational phase of the repository.
LL-LL Intermediate depth repository Safety Guide
General safety guidance 2008 : guidances in the prospect of siting for a LL- LL repository.
DMR/SAF/
26/09/2012

6. Guidance 2/2 Elements are given as regards :
the types of intrusion scenarios that have to be analysed :
for the surface facilities : road works within the repository footprint, residential area with permanent inhabitants on the site, “playground” scenario in the residential area.
for the deep repository : the case of a drilling assumed to hit the repository has to be addressed.
the timeframe for a possible intrusion :
300 years after closure in case of the CSFMA surface disposal.
500 years after closure for the deep geological repository.
Regulatory Guidance let Andra free to describe the intrusion scenarios to be assessed with respect to the safety objectives.
DMR/SAF/
26/09/2012

7. Human intrusion within the safety assessment
Position of the intrusion scenarios in the safety case
Strategy - Context
Framework and Safety Strategy
Regulatory framework/reference guidance
Data input – Assessment basis
Waste package characteristics
Site Characteristics
Technological knowledge
Scientific knowledge
Description / design of repository components
Functional analysis (FA)
Operational
Post closure
Operational safety / risk analsyis (RA)
Post closure safety/analysis of uncertainties (QSA)
Normal operation
Incidental /accidental situations
Normal Evolution Scenario
Altered Evolution Scenarios
Impact in normal operation (indicators)
Impact of incidental / accidental scenarios ( indicators)
Impact of normal and altered scenarios (indicators)
Compliance of the safety level with the objectives (function of the stage of the project development)
DMR/SAF/
26/09/2012

8. Safety functions Safety functions
Repository safety functions are defined in order to meet the main fundamental objective : “protect humans and the environment from the dispersion of radionuclides”.
After closure all function are safety functions, they must be fullfiled without any human intervention (“passive function”).
Main after closure functions are (illustration) :
Isolate the waste from human beings activities
Prevent the circulation of water in the repository
Limit the release of radionuclides and toxic chemicals and immobilise them in the repository
Delay and reduce the migration of radionuclides released outside of the repository disposal cells.
As regards human intrusion, the point is “How far the achievement of each safety functions could be degraded by an intrusion event hitting one or more components ?”
DMR/SAF/
26/09/2012

9. Time-frames Multiple timeframes have to be considered :
Radionuclides decay, and possibly appearance through radioactive chains
Waste source-term (packages duration, waste matrix release ...)
Geo-prospective aspects (uplifts, erosion processes, climate …)
Institutional control and record keeping which define the earliest possible date for intrusion.
Duration of the assessment (up to 1 My in the case of deep repository)
(déchets vitrifiés)
Radium bearing waste
HL Waste radiological activity evolution over time
Typical activity for a vitrified waste canister
DMR/SAF/
26/09/2012

10. Possible routes for contamination
Two routes for contamination
Air pathway
External irradiation through direct contact or vicinity with the waste.
Internal irradiation through ingestion and inhalation of contaminated dust or inhalation of radioactive gases (Radon).
Sources : cuttings from drilling, road works, houses construction.
Main contributors : alpha decay radionuclides, radon ...
Water pathway
Through drinking water, livestock watering or irrigation : due to borehole drilling likely to shortcut the geological layers or engineered barriers.
Main contributors : mobile beta-gamma decay radionuclides e.g. Cl-36, I-129 …
Water pathways assessment needs are different : especially in terms of hydrogeological and transport modeling tools.
DMR/SAF/
26/09/2012

11. The depth parameter Intrusion types Timeframes Waste content
Water wells drilling
Road works
Houses construction
Mining
Timeframes
Radionuclides decay rate
Possible site erosion site stability
Source term (packages duration, waste matrix release ...)
Institutional control duration
Waste content
Radionuclides activity and decay rate
Matrix form - primary package
Mobility and sorption of radionuclides
Toxic compounds content
Site and repository design
Host formation with suitable properties (hydraulic conductivity ...)
No valuable resources in the subsoil
Cells design / Dead end design
Depth : Surface / Near surface or intermediate / Deep
Pathways of contamination
Air path (ingestion and inhalation)
Water path (drinking water and other uses)
Depth of repository
DMR/SAF/
26/09/2012

12. Intrusion scenarios for the deep geological repository 1/2
Intrusion scenarios definition
Types of intrusion
Exploratory drilling passing trough the repository and continuing till the under-laying aquifer is reached (assumed target).
Cores are brought to surface.
The drilling is supposed abandoned without any plugging and keeps open.
Time frames
Direct impact to the driller : 500 years (loss of repository memory).
Indirect consequences to the repository performances : continuous evaluation starting at 500 years.
Assumption that all waste packages can be drilled.
Locations of the hitting points in the repository, number of drillings
IL waste tunnel, IL waste package, HL waste package, HL access tunnel ...
One or two drillings at a time.
Consideration is also given to potential indirect consequences of the drilling on other human groups.
The fact of drilling a water well into a contaminated plume outside the repository footprint may rather be considered in the normal evolution scenario, except if the contamination is the consequence of an intrusion.
DMR/SAF/
26/09/2012

13. Intrusion scenarios for the deep geological repository 2/2
The 2009 architecture
IL waste area
IL waste
Sub-zone IL
waste
tunnel
Shafts
Non thermal HL waste area
Main accesses
Division module
Slope access
HL waste cell
Division module
HL waste sub-zone
Thermal
HL waste area
DMR/SAF/
26/09/2012

14. Intrusion scenarios for the near-surface disposals
Types of scenarios
Related with a route of contamination trough the air :
Road works,
Residence building on site,
Playground scenario.
Related with a route of contamination trough ground water :
A water well is dug within the repository footprint.
The intrusion is assumed to take place at the moment and location of maximum impact for each radionuclide.
CSFMA scheme
DMR/SAF/
26/09/2012

15. Use of intrusion scenarios
Even assumed that :
an “non-interesting” site in terms of geological or surface resources has been chosen,
the quantity of valuable material in the repository has been limited as far as possible;
and future actions likely to make location and design records available as long as possible have been promoted,
Intrusion risk can’t be excluded.
Then the main purpose of the analysis is to make sure that an intrusion would not alter the safety functions in a way that would bring impact to an unacceptable level. In addition, intrusion scenarios may be used as a mean to improve and optimize the design in terms of robustness.
If impact is slightly higher than acceptable :
Define waste activity limits (total Bq or specific activity Bq/g) in order to achieve the protection goal (link with Waste Acceptance Criteria)
Bring improvements to the repository design or possibly to the cell filing procedures in order to avoid “hot spots” (link with the design process)
Improve the knowledge in order to reduce the calculation margins due to uncertainties (link with science and experiments)
In any case, feedback is provided for the next safety assessment iteration:
Identify the aspects that deserve improvement,
Evaluate the interest of a better waste caracterisation and classification (if possible) in order to direct some of the waste categories towards better adapted facilities.
DMR/SAF/
26/09/2012

16. DMR/SAF/
26/09/2012