Optimization in the context of high-level radioactive waste repositories

Optimization can be defined as the process of making a system as good or effective as possible. In the context of radioactive waste management (RWM), continuous improvement and optimization are inherent ambitions of every disposal program. However, the terminology and understanding of optimization vary across programs, countries, and stakeholders. Relevant RWM stakeholders include implementers (waste management organizations), regulators, technical support organizations, research entities, and civil society organizations. These stakeholders exhibit distinct views of optimization, attributable notably to their heterogeneous roles and needs in a RWM program. The EURAD-2 work package OPTI provides a platform for interactions between members from the three EURAD colleges as well as CSOs, on the optimisation of HLW GDFs. These views about optimisation were discussed in a workshop held January 2025. A paper summarizing the conclusions of this workshop was prepared and discussed further. The intention of the contribution is to present the content of the paper and open the discussion to a larger group.

The exchange was centred around the “WHY?”, the “HOW?” and the “WHEN?” there are needs and priorities for optimisation. For instance, views on the possible scope for optimisation at the different phases of a RW disposal programme, the main challenges for optimisation and the best or existing approaches to optimisation were collected during the workshop. Some key observations on optimization emerge. Optimization is relevant for all stages of a repository program and optimisation must be considered holistically. It means that the disposal system has to be optimised as a whole, considering several optimisation processes that take place in parallel, such as the optimisation of the protection (radiological and non-radiological) and the optimisation of the resources required (and therefore the costs). The process of optimisation must be carried out taking account of prevailing circumstances, including the regulatory framework, the status of knowledge and the available resources (e.g. financial). However, the priorities shift over the lifetime of the program. At the start of a disposal programme, the focus of the disposal system optimisation is mainly on optimising the protection. Optimization in earlier stages, e.g. preparation of the safety case and licensing, is an established engineering process ensuring compliance with regulatory requirements and enhancing the overall safety of repository systems. Then, once the safety strategy and safety concept have been optimised and agreed with the regulator, the programme enters its next phases and the focus shifts progressively towards optimising the resources needed to implement the safety strategy and safety concept. At later stages, optimization after licensing or during construction and operation may have a different focus, as safety is already demonstrated (e.g. focus on reduction of conservative assumptions, optimization of the procurement of materials). Thus, various approaches and limits to optimization can be defined at different program stages; the prevailing circumstances of each national program set a frame in which optimization can be done. Furthermore, economical drivers, developments in science and technology, and interactions with the society can outmanoeuvre the optimization process.