Role of the Safety Case in disposal programmes
Nicolas Solente
Workshop on Regulatory Requirements
to Ensure Safe Disposal of Disused
Sealed Sources for Operators and
Regulators
Amman, JORDAN 7-11 April 2014
Outline of the presentation
•
Objectives of the Safety Case
•
Contents of a Safety Case
•
SC flow diagram
•
The disposal programme planning
•
Safety Functions and Disposal programme
•
The safety case and the site selection
•
The safety case and the initial disposal facility design
•
The safety case and the detailed disposal facility design
•
The Safety case and the scientific and R&D programme
•
The Safety Case and disposal operations
•
Conclusions
Objectives of the Safety Case
Fundamental safety objective of disposal programme:
“to protect people and the environment from harmful effects
of ionizing radiation”
The operator of the facility is responsible for safety,
must
and
• assess the safety of the facility
• demonstrate that the design and operation of the facility
are compliant with the relevant safety requirements
The Safety case (SC), including a Safety Assessment (SA) is
developed to o provide evidence to demonstrate that the
disposal facility will be safe to operate, will remain safe after
its closure and complies with all applicable regulatory
requirements.
Contents of a Safety Case
A typical disposal facility SC will comprise:
• An Operational SC: demonstrates that the construction and
operations of the facility will be safe for the workers, the
public and the environment
• A Long Term, post-closure SC: demonstrates that the
Radionuclides will not present an unacceptable risks in the
future
• Scientific and engineering supporting material:
a
comprehensive collection of evidence providing the basis
and justification for the SA
• Other information (local and national context, managerial
decisions…) supporting decision making
SC flow diagram
The disposal programme planning
Safety Functions and Disposal programme
During the start-up and initial phases, a safety concept is
selected and developed.
The concept relates to specific safety functions,
such as confine
RN, prevent intrusion, isolate from water…. The safety functions are defined to
prevent or reduce the risks, and thus provide the required level of safety.
The safety functions are an important component of the
SA/SC
Simultaneously, a disposal concept is chosen,
deep geological, surface disposal
such as borehole,
The safety functions are fulfilled by the repository system,
subsystems and components.
The safety functions and their implementation in the disposal
system will be a constant link between the disposal programme
and the SC
The safety case and the site selection
The site selection is a complex process that considers many
factors.
A number of those factors are safety related and define some
of the selection criteria,
The site selection criteria are established to eliminate those
sites where some safety functions could not be provided or
would require to consider a different disposal concept
(seismicity, flooding, population…)
Disposal concept and selection criteria are interdependent,
and the availability of the required environment (geology,
hydrogeology, surface water bodies, population) should be a
major contributing factor in the disposal concept selection
The safety case and the initial disposal facility design
1. Conceptual design:
a generic design is selected, with regards to
•
The waste inventory (quantity + RN contents)
•
The available geology (from desktop studies at this stage)
•
The national policy, including RAW management and safety policies
An initial safety case should be performed to validate the
concept selection, using generic/preliminary parameters.
Output: Are the preliminary Waste Acceptance Criteria, issued
from the Preliminary SC consistent with the waste inventory?
The safety case and the detailed disposal facility design
1. Functional analysis  defines all functions of the facility
2. Functions
systems)
attributed
to
components
3. Safety functions attributed
systems/subsystems
to
(systems,
single
or
sub-
multiple
4. Quantitative assessment of the performance of the
repository and its components – identification and
quantification of the uncertainties
5. Verification of the robustness of the systems (defense in
depth, compatibility, interdependencies…)
6. Modification of the systems
7. Back to step
demonstrated
3
until
Performance
and
robustness
Interdependencies & iterations
The design and the decision-making processes are iterative
and shall incorporate safety aspects in most cases. Revisions
in design will trigger modification of the SC, as changes in the
safety strategy, or in the SA (models, uncertainty
management) will trigger modifications of the design
The Safety case and the scientific and R&D programme
A scientific programme is required to provide the parameters
and data needed to model the behavior of the facility in its
environment and evaluate its performance indicators (dose,
RN flow...)
The SC is a demonstration of compliance to safety objectives,
and must be based on undisputable data (geology, corrosion,
cement, waste composition, rad & non-rad…)
The required quality and quantity of data will increase as the
project and the SC progress. Data acquisition will be largely
driven by SA considerations.
Ex: The geological investigations must be designed with a
view on providing data in a quality and a quantity sufficient
to the demonstration of safety and the modelling of the
subsurface. Several survey campaigns may be necessary .
The Safety Case and disposal operations
Waste acceptance Criteria evolutions
• Disposal of new waste streams, new DSRS types require
that their acceptability is verified and, occasionally, that
WAC are modified. The consequences on the safety
assessment of the new conditions (RN, waste form,
chemical composition) must be evaluated, in the
framework of the initial safety case
• The SC must be regularly updated, to reflect the changes to
the facility or the waste, and to take advantage of new
scientific results, international practice, regulations…
Conclusions
The SC controls
programme:
several
aspects
of
any
disposal
• Site selection and facility design are justified for a large
extent by compliance to safety objectives. For a similar
objective of safety, the level of performance required must remain
commensurate with the hazards associated with the waste
• Waste acceptance Criteria are directly related to the
SA/SC
• The acceptable RN inventory is directly related to the
SA/SC
• The management of uncertainties commands the extent
of the scientific/R&D programme
• …