Key Topic 3: Technical Feasibility and Long-term Performance
This research area involves RD&D activities for demonstrating and optimising technology and construction of a repository and its components. This includes confirmation of a feasible and safe operational phase, as well as ensuring that the specified safety functions will be provided for the required time frame after repository closure. Surface and underground works are included, as well as construction technologies for waste containers, buffer, backfill, plugs and seals. This research area also includes understanding of the repository components long-term behaviour and the maintenance of their safety functions.
The first objective (a) for this research area is to demonstrate, to the level required by national licensing rules, that the technical design requirements based on safety of construction and operations, safety during the post-operational transient phase, and long-term safety after closure can be met in practice by available construction technologies and related working procedures. This includes confirmation of repository components against pre-defined design specifications to determine their state before closure and extends to optimising operations and costs over the lifetime of a repository.
The 2011 IGD-TP Strategic Research Agenda identified six research topics of high importance and urgency, and a further two of low importance and urgency in connection with objective (a):
- Topic 1 (High). Demonstrations of full-scale operations of HLW disposal containers, including industrial-scale fabrication, encapsulation, container handling and emplacement.
- Topic 2 (High). The industrial scale operations for buffer and backfill need to be demonstrated, including the entire production and emplacement chain.
- Topic 3 (High). Construction of main underground facilities, including confirmation of rock properties for final detailed design.
- Topic 4 (High). Repository layout design including operational safety studies and reversibility/ retrievability.
- Topic 5 (High). Pilot demonstrations of repository operations.
- Topic 6 (High). Full-scale demonstrations of plugging and sealing, including construction and installation technologies for plugs and seals, such that all the established performance targets and requirements are met and comply with the safety strategy of the disposal concept.
- Topic 7 (Low). Knowledge compilation on non-destructive testing (NDT) and related requirements on repository components.
- Topic 8 (Low). Knowledge preservation related to retrievability.
The second objective (b) is to demonstrate that the system will provide all the safety functions needed for the system as a whole to fulfil the long-term safety criteria. This requires that the evolution of the engineered components and materials is sufficiently understood for actual repository conditions over the specified time frame.
Due to the relationship between technical design requirements and long-term performance requirements, these requirements must usually be defined iteratively. In this context, robust design may be necessary to account for uncertainties. Each component of the repository needs to fulfil the design criteria based on the specified safety functions of the repository and meet the qualifications defined in the regulations.
The 2011 IGD-TP Strategic Research Agenda identified two research topics of high importance and urgency, five of medium and a further two of low importance and urgency in connection with objective (b):
- Topic 9 (High). Improved understanding of the impact of hydro-geochemical evolution on the long-term performance of bentonite buffer in specific disposal concepts developed for crystalline host rocks. This includes laboratory and modelling studies to improved understanding the impacts on the bentonite buffer long-term safety functions.
- Topic 10 (High). Description of seals and plugs systems and modelling of their long-term behaviour with assessment of the consequences on long-term safety.
- Topic 11 (Medium). Understanding of the evolution of cement-based seals.
- Topic 12 (Medium). The interaction of cement-based sealing and construction materials with clay-based buffer and seals is also of importance.
- Topic 13 (Medium). Continued development of low pH concretes is needed to allow them to replace conventional cements and concretes in some applications.
- Topic 14 (Medium). Laboratory and modelling work on salt backfill to study its long-term behaviour (consolidation, healing, interaction with the surrounding rock, influence of fluids, permeability and porosity).
- Topic 15 (Medium). Investigation of the effects of the iron-bentonite interaction and elevated temperatures (above 100°C) on bentonite buffer material evolution.
- Topic 16 (Low). Sharing of knowledge on container materials behaviour.
- Topic 17 (Low). The emplacement methodology of bentonite directly around waste containers and thereby the influence on thermal effects needs to be optimised.