Expert Group on Integrated Performance Assessment
The management of radioactive wastes and, in particular, the safety assessment
of radioactive waste disposal systems are areas of high priority for the
NEA. The Working Group on Integrated Performance Assessments of Deep Repositories
(IPAG) was set up in 1994 to provide a forum for informed discussion on
the performance assessment (PA) of proposed deep repositories for radioactive
waste. The group has recently ended in the third phase of its work. A
common object of all IPAG studies is the collection of detailed information
from national programmes through a questionnaire; the compilation and
rationalisation of the information into a synthesis; and the identification
of the lessons to be learnt.
Phase I: Feedback from IPAG exercises
In Phase I, the IPAG examined recently completed PA studies from ten
organisations as a practical body of evidence to indicate the current
status of PA and to shed light on what can and should be done in future
studies. The major findings of this phase of the group's work were that
traceability and transparency in the conduct of PAs were essential. 'Traceability'
refers to the unambiguous and complete record of the decisions and assumptions
made, and of the models and data used in arriving at a given set of results.
'Transparency' refers to the PA being clearly reported, so that the audience
can gain a good understanding of what has been done, what the results
are, and why the results are as they are. This is a more subtle, and audience-dependent,
requirement. The difficulty of finding an unambiguous vocabulary for discussion
of these issues was also addressed, along with recommendations for the
essential elements of a safety assessment report. Completed in 1996, the
resulting Lessons Learnt from
Ten Performance Assessment Studies is available free online (pdf,
395 kb).
Phase II: Regulatory experience of IPA reviews
In the second phase, IPAG-2, the goal was to examine the experience of
peer reviews of integrated PAs, and especially reviews performed in support
of regulatory assessment. These were examined from both the implementer
and regulator points of view. Seventeen national organisations participated
in this phase, where each had either carried out or reviewed a recent
integrated PA study. The work, carried out mainly between May 1997 and
October 1998, was focused by means of a questionnaire on the PA and review
process, and examination and discussion of the answers. The final
report (available from the OECD bookshop) makes recommendations and
observations on the conduct of the review, aspects of the safety case,
traceability and transparency, and regulatory guidance.
Phase III: Approaches and arguments for establishing confidence in
safety and the overal results of IPAs
A third phase of the programme has evaluated different approaches and
arguments for establishing technical and stakeholder confidence in the
long-term safety of proposed deep repositories for radioactive waste.
Establishing technical confidence requires the corroboration of both the
disposal concept's intrinsic safety and its long-term performance. These
two elements can be further articulated in the following checklist for
establishing technical confidence in the disposal proposal:
- the
multi-barrier disposal system must be intrinsically robust;
-
disposal system data must be reliable and formally established;.
- a
logical, clear and systematic assessment approach must be implemented
and independently reviewed;
- the
Integrated Performance Assessment (IPA) models employed must predict
measurable parameters and produce intuitive results;
- the
safety case and the IPA analyses must
demonstrate that the assumptions made are representative or conservative,
and set out a clear strategy for handling uncertainty;
- there
must be clear feedback mechanisms on the site's design and its geological
characteristics.
Findings
show that communicating confidence arguments to stakeholders must be done
in a clear and unambiguous way. The arguments need to be both tailored
to the audience and consistent with both the assessment and the safety
case. Different audiences have different information needs, and confidence
has to be demonstrated, not just stated.
The IPAG-3 final
report surveys international experience in achieving these goals.
Twenty organisations from NEA member countries have participated in this
initiative, providing a variety of viewpoints, institutional interests
and national experiences. The report is entitled "Establishing and
Communicating Confidence in the Safety of Deep Geologic Disposal".
Related publications
Establishing
and Communicating Confidence in the Safety of Deep Geologic Disposal
Approaches and Arguments
Confidence among both technical experts and the public in the safety of
deep geologic repositories for radioactive waste is a key element in the
successful development of the repositories. This report presents the approaches
and arguments that are currently used in OECD contries to establish and
communicate confidence in their safety. Link to the OECD bookshop.
Regulatory
Reviews of Assessments of Deep Geologic Repositories - Lessons Learnt
The
goal of the IPAG-2 study was to examine the experience of regulatory reviews
of IPAs, from both the implementer and regulator points of view. Ten implementer
and seven regulatory organisations participated. This report presents
the lessons learnt from their review experiences, and provides recommendations
to aid future regulatory decision making. Link to the OECD bookshop.
Lessons Learnt from Ten Performance
Assessment Studies
Phase-1
of the IPAG study focused on the production, refinement and answering
of a questionnaire on the submitted Performance Assessments, and examination
and discussion of the answers. Document available online in pdf format
- 395 kb.
Related links
E-Mail
Contact: Claudio Pescatore (nea@nea.fr)
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