ESV Euridice GIE

RESEARCH PROGRAMME | THE PRACLAY PROJECT

The most important parts of the PRACLAY project consist in the extension of the URF HADES (second shaft, connecting gallery), the realisation of the PRACLAY-experiment and the realisation of an on - surface preparation of the PRACLAY _ experiment (the OPHELIE mock-up) The initial aim of the PRACLAY project was to demonstrate the feasibility of the reference design for the deep disposal of heat-emitting high-level vitrified radioactive waste. For that reason the objectives of the PRACLAY project, from which PRACLAY experiment makes part, were originally defined as follows:

Demonstrate the feasibility - from a technical and economical point of view - of digging a gallery similar, except in length, to the contemplated disposal galleries, using industrial techniques that would have to be dealt with for the full-size repository.Het bestuderen en uitvoeren van de kruising tussen de hoofd- en de bergingsgalerijen.

Study and realise the crossing between main and disposal galleries.

Set up and fill in a pilot gallery geometrically identical, except in length, to a disposal gallery for vitrified HLW as considered in the reference architecture. Except for the vitrified waste that will be replaced by electrical heaters, the materials and techniques used should insofar as possible be similar to the planned ones. An on surface mock-up (the OPHELIE mock-up) of this pilot gallery will be realised and operated before realising the pilot gallery.

Confirm and improve our knowledge of the reference architecture and the components of the Engineered Barrier System (EBS).

At present the first aim is already met by the successful realisation of the connecting gallery using an industrial technique. The second aim is partially met by the construction of the crossing between the second shaft and the connecting gallery, but is still to be fully met by the construction of the crossing between the connecting gallery and the PRACLAY gallery and the study of its behaviour under different constraints such as thermal load. The 3rd aim has not been met yet but has been experimentally prepared through the OPHELIE Mock up (on surface). Some parts of the 4th aim have been included in the OPHELIE works.

Recent evolution of thinking, inherent on the stepwise approach of the R&D regarding disposal of radioactive waste has led to a complete review by Ondraf/Niras of the SAFIR II reference design. This review recently led to new basic design that could be used as the reference for the PRACLAY-experiment. However, the establishment of a detailed design for the EBS requires notably the characterisation of each component (if not already performed), their respective interactions and their interactions with the host rock in general and the EDZ in particular. This will require a series of tests going from small and intermediate experiments to larger "mock-up" tests (and their necessary modelling support).

It is clear that this process is stepwise and could take a long time. Therefore it was decided not to use this recent design as the reference design for the PRACLAY-experiment because ONDRAF/NIRAS wishes to keep the choices made as flexible as possible, in order to get the possibility to reorient parts of the design towards another alternative should the need arise on the basis of scientific and technical progress and/or socio-economic aspects and/or regulatory requirements. In this context it is clear that the realisation of a unique large scale demonstration "PRACLAY" experiment as initially planned and specific to one detailed design may not be the most adequate option.

In this framework, 2 options have been considered :

to postpone the whole PRACLAY experiment until a new design has been sufficiently defined to allow an in situ demonstration ;

to redefine - parts of - the experiment to use it as a key support to the current stepwise design development and to focus on confirmation aspects (experimental and modelling) of the feasibility and understanding of some of the EBS elements.

The second option has been withheld as it is in line with the stepwise design development. This option allows in particular to test in situ and at a large scale some issues that are generic to, and key for, all potential designs (i.e. that are design-independent) as the thermal impact on the Boom Clay and its EDZ, the gallery lining and crossing, as well as the efficiency of gallery plugs.

According to (i) the design independence of these issues ; (ii) the importance for he overall confirmation of the performances of the Boom Clay as host formation for HLW and (iii) extended experimental duration needed to ensure representativeness, it was decided to start relevant in situ tests as soon as possible. This means that some less design related aspects will be tested without waiting for the reference design being fully defined.

Therefore NIRAS/ONDRAF decided that the original scope of the PRACLAY experiment, being the demonstration of the reference design for vitrified HLW, should be enlarged to characterization, verification, confirmation and demonstration of relevant elements of the disposal system and their behaviour by means of a combination of small surface and large in situ experiments and that the PRACLAY - experiment should be redifined.