HLW repository optimisation including closure (OPTI)
WP Leader: Philipp Herold (BGE, Germany)
Objectives
Develop a mutual understanding and provide recommendations on methodologies and further activities for the design and optimization of specific HLW deep geological repository systems, structures and components (SSCs) and procedures.
Achievements
Workshop No. 1 in January 2025 (Delft), where partners presented their views on optimization and discussed common perspectives.
Workshop No. 2 in June 2025 (Prague), where the draft version of the Green Paper was discussed, summarizing the mutual understanding of optimization and reviewing the status of the case studies.
Contributions to ICS Workshops No. 1 (2025) and 2 (2026), discussing views and key topics related to optimization with civil society representatives.
Dissemination of activities and project results during the SafeND conference (Berlin) and the IGD‑TP Exchange Forum (Prague).
Forward look
The second year, and especially 2026, will be dominated by the publication of the deliverables. By the end of March, the White Paper discussing future key challenges will be published. The impact report for end‑users will follow in May. With the project ending in September, the final report will then be delivered.
In April, a joint workshop, “Optimization: Bridging Science, Strategy and Society”, will be held together with WP ANCHORS.
Description of the WP
As the first repositories move into their construction and operational phases, optimization naturally becomes a central focus of advanced programmes. This need arises from the long‑term nature of repository projects and evolving boundary conditions require continuous adaptation. Such evolving boundary conditions might be the emergence of new waste types, technological progress or operational experience. Optimization cannot be treated as a purely technical exercise. It is a process that must actively involve all stakeholders in a radioactive waste management programme, including civil society. When carried out effectively, optimization strengthens technical performance, economic efficiency, long‑term safety, and the overall flexibility and robustness of the system.
The aim of WP OPTI is to identify a shared understanding of how different actors view optimization. Key questions include:
What drives optimization efforts?
At which stages of a programme is optimization necessary, advisable, or inappropriate?
What key challenges related to optimization are perceived?
The dialogue may lead to a mutual understanding of optimization that reflects the perspectives of the various stakeholder groups. The initiative will also foster networking around best practices for optimization strategies related to safety‑significant components such as engineered barrier systems and deep geological repository processes. The resulting insights will support less advanced programmes as they progress through earlier phases of repository development, facilitating knowledge transfer from more experienced programmes. In addition, the work will help identify research and development needs for specific components and procedures that could benefit from further optimization.
Outcomes
A key outcome of this work will be the development of joint proposals for future activities aimed at improving repository optimization, integrating perspectives from all relevant actors, including civil society. In addition to this overarching result, several more specific outcomes are anticipated.
First, the WP will provide an overview of existing approaches and optimization strategies for specific engineered barrier system (EBS) components and deep geological repository (DGR) processes, such as buffer, backfill, seals, support structures, and emplacement operations. This aligns with SRA topics 5.2.2, 5.1, and 3.3, and is driven by the need for innovation and enhanced implementation safety.
Second, the work will explore opportunities to optimize options and plans related to closure processes, including the development of potential closure or acceptability criteria. This corresponds to SRA 5.1.1 and is motivated by societal engagement considerations as well as implementation safety.
Third, the initiative will foster a shared understanding of the robustness of mechanical structures, such as lining systems, under different environmental conditions, and assess their potential for optimization. This also relates to SRA 5.1.1 and is driven by the broader goal of innovation for optimization.
