Key Topic 4: Implementation and Optimisation
The future development of reactor, fuel cycle and waste management technologies and policies and the long duration of disposal development (several decades) will inevitably raise opportunities and needs for changes and adaptations in the design, implementation, construction and operation of geological repositories. Some of the future likely trends are already visible and may be reflected in adaptable and flexible designs and implementation schemes.
Construction of a repository will involve successive stages of construction operations with gradual implementation of the various technologies used for the disposal and surface facilities (including a pilot phase or pilot demonstrator(s)). This step-wise implementation allows continuous optimisation, flexibility and adaptation:
- Optimisation concerns technical and economic aspects, but also increases in the robustness of post-closure safety demonstration and/or operational safety.
- Flexibility concerns adapting the repository design and programme over time to address uncertainties that exist at the licensing application stage (e.g. if necessary, defining different design options to allow for inventory uncertainty). The need for flexibility particularly relates to possible variations in waste delivery, reception flows, packaging modes and processes, disposal modes for radioactive waste packages, waste inventory management of current nuclear power plant (increase of operating duration), etc.
- Adaptability concerns the ability of the repository design and programme to adapt over time, for example, to the disposal of waste not provided for in its inventory at the licensing application stage or to modification of requirements or design criteria.
Of course, the importance each WMO places on adaptability and flexibility in their disposal programme depends on their national context (e.g. national policy in terms of reprocessing of spent fuel or not, policies in terms of evolution of the current/future nuclear fleet, etc.) and associated radioactive waste inventory.
The design strategy has to be “optimised”, taking into account the potential benefits of increased adaptability and flexibility versus management of uncertainties in the future, including assessment of the cost impacts of such adaptability and flexibility. This research area deals with the integration of new developments during the lifetime of a geological repository (construction and the operation time up to closure). A licence would be issued for constructing and operating a geological repository on the basis of the available information at the time of the application. However, during the operational lifetime of a geological repository from its construction to its closure, new technologies, new scientific findings or improvements, and changes in the radioactive waste inventory, are likely to occur and can also be considered for the future closure, as well as for any reversibility and retrievability rationale [i].
Adaptation and flexibility will be ongoing throughout the lifetime of the repository from the reference layout, through design (including adaptation to the site), and during construction and operation. This supports the gradual development of a repository that may include a pilot phase or a pilot demonstrator in many design strategies.
The research area aims to ensure that a higher level of safety, or at least the same level as that demonstrated for the initial licence (taking into account the entire waste lifecycle), is achieved through adaptation and flexibility, independent of the new developments or new inputs (such as change of radioactive waste inventory) related to the repository over time.
A geological repository should take account of new developments in order to adapt and to optimise its construction, operation and closure, particularly in concert with feedback from operation. Improving industrial conditions is expected to simplify the work and to improve quality and safety (both during operations and post-closure) and, at the same time, potentially reduce the costs. This holistic approach has to take into consideration the long timescale of repository development, particularly for cost assessment. Therefore, research with these objectives contributes to the second pillar, “Optimise and Industrialise”, of the 2040 Vision.