1. Safety Case Components and Documentation
David G Bennett
8 April 2014

2. Safety Case Components

3. 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 disposal facility
Key disposal system characteristics
e.g. the nature of the waste and the site
The purpose of the safety assessment
The assessment timeframes
Assessment philosophy (e.g. conservative, realistic)
Assessment end-points (e.g. dose, risk, fluxes, others)

4. Safety Strategy The safety strategy comprises:
The high-level approach for achieving safe disposal
The overall management strategy for the activities required in planning, operation and closure of a disposal facility
The preferred strategy for the management of all radioactive waste is containment and isolation from the accessible biosphere [SSR-5]
The set of intended safety functions
the timeframes over which they will be available
explanation of system robustness and defence in depth

5. System Description The system description: Related terms:
Provides information on the disposal 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” or the “phenomenological basis”
Also closely related to the “site descriptive model”

6. System Description
The system description should provide information on:
The facility design and the reasons for its selection
The “near-field”:
The wastes (e.g., origin, quantities, properties, radionuclide inventory),
The engineering (e.g., waste conditioning and packaging, disposal units, engineered barriers, disposal facility cap, drainage)
The zone disturbed by excavations
The “far-field” - e.g., geology, hydrogeology, geochemistry, tectonic and seismic conditions, erosion rates
The “biosphere” - e.g., climate and atmosphere, water bodies, human activities, biota, surface geology, topography

7. Safety Assessment

8. Limits, Controls and Conditions
The safety case should be used to assist in the establishment of limits, controls and conditions, e.g:
Site-specific limits on the total waste inventory, on acceptable concentration levels for specific radionuclides in the waste, and other waste acceptance criteria (WAC)
Particularly relevant for near-surface disposal facilities
Controls and conditions on repository construction and on the manufacture, materials and quality of engineered barriers and their emplacement
Conditions for a monitoring and surveillance programme

9. Integration of Safety Arguments
Showing that safety assessment results comply with regulatory criteria is not sufficient
Multiple lines of reasoning should be used, including discussion of:
The use of best available techniques
The history of design optimisation
Waste isolation and containment
Passive safety
Robustness and defence in depth
QA and peer review
Conservatisms in safety assessment
Natural (and other) analogue information
Application of limits, controls and conditions

10. Integration of Safety Arguments
In summary, the safety case should:
synthesise the available evidence, arguments and analyses
highlight the principal reasons why planning, development and use of the disposal system should continue
acknowledge any limitations of currently available evidence
describe the approach that will be used to manage any open questions and uncertainties

11. Safety case documentation
Clear
Logical structure
Transparent
Traceable
Should always explain why?
Need to include accurate summary documents
Written for their intended audience(s)