1. The Safety Case Radioactive Waste and Spent Fuel Management Unit
Sustaining Cradle-to-Grave Control of Radioactive Sources (INT-9182) Meeting on the development, revision and implementation of the safety case and safety assessment Indonesia, 15 – 19 May 2017
The Safety Case
Radioactive Waste and Spent Fuel Management Unit
Department of Nuclear Safety And Security
IAEA

2. The Safety Case
IAEA Safety Requirements include several requirements for a safety case, including quantitative safety assessments
IAEA GSG-3 and SSG-23 give guidance on the safety case, its various components and its uses

3. The Safety Case
The Safety Case is a tool for integrating all information on the disposal system, for managing the development, operation and closure of the disposal facility, and for demonstrating that the Safety Objective and Requirements are fulfilled
The safety case is:
the collection of scientific, technical, administrative and managerial arguments and evidence supporting the safety of a facility
a formal set of documents produced by the operator and reviewed by the regulator

4. Example Safety Case Documentation Structure: UK

5. Example Safety Case Documentation: Finland
The scope and extent of the safety case and safety assessments should reflect the scale of the hazard and the nature of the facility

6. The Safety Case The safety case should:
Describe all safety-relevant aspects of the site, the design of the facility, and the necessary managerial and regulatory controls
Be prepared and updated by the operator at each step in the development of a disposal facility
Be submitted to the regulatory body for review
Be sufficiently detailed and comprehensive to provide the necessary information for the regulatory body and the decisions at each step
Demonstrate the level of protection provided for people and the environment
Provide assurance to the regulatory body and other interested parties that safety requirements will be met

7. The Safety Case and Safety Assessment
Safety assessment is an integral part of the safety case
It provides an understanding of the safety of the facility under normal conditions and for the case of accidents / disturbing events, considering the time frames over which the radioactive waste remains hazardous
It includes a systematic quantification of radiation doses and risks that may arise from the facility for comparison with regulatory (e.g., dose and risk) criteria

8. The Safety Case The facility shall:
Be constructed in accordance with the design in the safety case and analysed in the safety assessment
Be operated in accordance with the conditions of the licence and the safety case
Accept wastes and waste packages disposal which conform to waste acceptance criteria that are consistent with and derived from the safety case

9. Safety Case Components

10. A. Safety Case Context The safety case context comprises:
Regulatory requirements and criteria for the safety case
The particular decision step in the lifecycle of the facility
Key system characteristics
e.g., the nature of the waste and the site
The purpose of the safety assessment
The assessment timeframes (e.g., a few years to perhaps a few decades for a waste store, longer for disposal facilities), philosophy (e.g., conservative, realistic) and end-points (e.g., potential doses to workers, to the public)

11. B. Safety Strategy The safety strategy comprises:
A high-level integrated approach adopted for achieving safe storage or disposal of radioactive waste
An overall management strategy for the activities required in planning, operation, closure and decommissioning of a facility
Should identify the intended safety functions, the timeframes over which they will be available and how degraded performance of a safety function (e.g., a barrier) will be compensated for by another mechanism or component of the system (robustness, defence in depth)

12. C. System Description The system description: Related terms:
Provides information on the system
Demonstrates system understanding
Provides the basis for safety assessment
Helps to determine needs for further system characterisation and facility design work
Related terms:
The system description includes much of what is sometimes called the “assessment basis”

13. C. System Description
The system description should provide information on:
The facility design and why it has been designed that way
The wastes (e.g., origin, quantities and properties, radionuclides)
The engineering (e.g., waste conditioning and packaging, disposal units, engineered barriers, disposal facility cap or cover, drainage)
The extent and properties of any zone disturbed by excavations or construction
The site - e.g., geographical extent and location, geology, tectonic and seismic conditions
The biosphere - e.g., climate and atmosphere, water bodies, human activities, biota, topography

14. D. Safety Assessment
Evaluates some or all of the potential radiological and non-radiological impacts to humans, non-human species and the environment
depends on the situation and regulations
Involves an process of:
Scenario development
Conceptual, mathematical and computer model development
Gathering of data and model parameter values
Safety assessment calculations
Analysis and review of assessment results
Iterative refinement

15. D. Safety Assessment
The ISAM methodology for safety assessment developed under an IAEA Coordinated Research Project (CRP) on disposal
Very similar safety assessment methodology for pre-disposal developed in the SADRWMS Project
Applied in a wide range of countries

16. D. Safety Assessment Scenario development
Scenarios are descriptions of alternative possible events and evolutions of the system
It is common to develop a set of scenarios for consideration in safety assessment as a way of assessing uncertainties
Scenarios can be derived in several ways e.g. by using Safety Functions, Postulated Initiating Events, and/or Features Events and Processes (FEPs)
The assessment should consider all of the things that could influence the system and affect the safety of the facility
It is best practice not to speculate too much on future human behaviour
To make the assessment practical, the number of scenarios should not be too great – the assessment is illustrative

17. D. Safety Assessment Model development
Conceptual, mathematical and computer models
A conceptual model is a set of assumptions concerning the geometry of the system and the chemical, physical, hydrogeological, biological and mechanical behaviour of the system
A mathematical model is a representation of the conceptual model using mathematical equations
Computer model is a software implementation of the mathematical model – it is important to verify that the computer code functions correctly
Model testing should be undertaken to help build confidence that the model is “fit for purpose”
Uncertainties and use of alternative conceptual models

18. D. Safety Assessment Gathering data and model parameter values
Literature and experimental data
Generic and site-specific data
There are always uncertainties and a need for extrapolation
Expert judgement and expert elicitation
Deterministic and probabilistic approaches
Essential to have QA and fully traceable documentation of the parameter values used and why they were selected for the assessment

19. D. Safety Assessment Safety assessment calculations
Traceable, reproducible, QA
Clearly documented data flows and relationships between models
Analysis and review of assessment results
Results from different scenarios
Sensitivity studies
Careful comparisons with regulatory criteria
Uncertainties

20. E. Iteration and Design Optimisation

21. F. Management of Uncertainties
There are always uncertainties and there can be alternative ways of dealing with them e.g:
Gather more experimental data
Use a less conservative modelling approach
Re-design a component of the physical system
Each of the alternatives will have pros and cons e.g. in terms of cost, timescale, likelihood of successfully reducing the uncertainty of concern

22. G. Limits, Controls and Conditions
The safety case should be used to derive appropriate limits, controls and conditions, e.g:
Limits on the total waste inventory, on acceptable concentration levels for specific radionuclides in the waste, and other waste acceptance criteria (WAC)
Controls and conditions on construction and on the manufacture, materials and quality of engineering
Conditions for a monitoring and surveillance programme
WAC
Transport
Disposal
Storage
Treatment
&
Conditioning
General
requirements

23. H. Integration of Safety Arguments
Simply showing that safety assessment results comply with quantitative regulatory criteria is not sufficient  multiple lines of reasoning
Lines of reasoning may include discussion of:
The use of best available techniques
The history of design and optimisation
Waste isolation and containment
Passive safety
Robusness and defence in depth
QA and peer review
Conservatisms in safety assessment
Application of limits, controls and conditions

24. H. Integration of Safety Arguments
In summary, a safety case is required and should be developed and used to:
Integrate and synthesise available information, analyses and assessments
Acknowledge any limitations of currently available information
Guide the next steps in the development and use of the store or disposal system, and highlight the main reasons why this should be allowed
Describe an approach to the management of uncertainty through which any open questions and uncertainties will be addressed

25. Recent Safety Cases
Near-Surface Disposal
Geological Disposal
Borehole Disposal
LLW, UK
L/ILW, Sweden
DSRS, Malaysia
LLW, Belgium
Spent Fuel, Finland
The scope of the Safety Case should follow the Graded Approach