Key Topic 1: Post-closure Safety Case

Overview

A post-closure safety case is a document, or suite of documents, submitted to relevant national regulators in order to obtain a licence for a specific nuclear waste disposal facility, that demonstrates how the proposed facility complies with the long-term safety requirements defined by national authorities.  In addition to national requirements, the safety case should also consider recommendations made by international organisations such as the International Atomic Energy Association (IAEA) and the Nuclear Energy Agency by OECD (OECD/NEA), and internationally-accepted good practice.

The safety case should be simple to understand and robust, providing clear arguments based on sound scientific and technological principles, research and safety assessments.  A post-closure safety case must be able to describe the evolution of the disposal facility in a way that can be seen as a reasonable representation of what might happen and that also gives a clear indication of uncertainties in the description.

A safety case is based on state-of-the-art RD&D in relevant disciplines. The long-term performance of the facility depends on both the natural geological environment and the man-made (engineered) technical barriers.  For some IGD-TP member organisations, the safety case is closely linked to the environmental impact assessment and to social perception issues, so the safety case should be shaped to meet the needs of the regulators as well as other relevant stakeholders.

The regulatory requirements become progressively more focused as decision-making throughout the licensing process proceeds, requiring more focused RD&D in specific areas.  As long as safety assessments are carried out, there is a need for RD&D to update the existing knowledge base. Continuous feedback from the safety assessments to improve and optimise the facility design and monitoring is also important.

Therefore, research in this area aims to consider how consistent safety cases across the different waste management programmes can be developed, how safety assessment concepts and models can be developed and refined, and how sensitivity  and uncertainty treatment can be improved.

Objective

The general objectives of IGD-TP post-closure safety case research are to:

  • Develop a broad view of the basis for long-term safety assessments and thereby the scope and contents of safety cases relevant for all participants of the IGD-TP.
  • Develop and refine concepts and models for improving long-term safety assessments.
  • Improve the treatment of sensitivities and uncertainties.
  • Further improve fruitful dialogue with the authorities.

The 2011 IGD-TP Strategic Research Agenda identified two research topics of high importance and urgency, and a third of medium importance and urgency:

  • Topic 1 (High). Increase confidence in, and testing and further refinement of, the tools used in safety assessments (concepts, scenario definition and computer codes).  A focus of IGD-TP work is the testing of various material interaction models used in performance assessment.
  • Topic 2 (High). Improve safety case communication, including on the short-term safety of construction and operations, the transient phase and long-term safety.  A particular IGD-TP focus is in the area of efficient peer review and related QA processes.  The normal routes by which scientific and technical results are assessed and accepted or corrected by the expert community are slow, but the review processes can be enhanced by creating new channels and practices for peer review among the participants of the IGD-TP.   
  • Topic 3 (Medium). Increase confidence in and further refinement of sensitivity and uncertainty methods.  A broad view should be developed within the IGD-TP on the main principles for analysis of sensitivities and uncertainties, with joint working groups to further improve understanding and treatment of these issues in the safety case.