The Belgian Agency for Radioactive Waste and En-riched Fissile Materials, ONDRAF/NIRAS, proposes to develop a geological disposal facility for the long term management of category B waste and category C waste. Without any preconceived opinion regarding the site location, ONDRAF/NIRAS developed a reference design of a geological disposal facility in a clay formation. The facility consists of two shafts and underground galleries that can be allocated to the shaft and support zones and two wings with connecting access galleries, and branch-ing disposal galleries. The facility for waste disposal package (DWP) production and a buffer/interim storage facility will be erected near to the waste transport shaft at the surface. Long-lived, low- and intermediate level waste (B waste) will be conditioned in concrete mono-liths and high-level waste (C waste) in so-called super-containers (SC).

The DWPs will be transported on trolleys of a hybrid rail-wheel configuration using battery driven locomo-tives. After the emplacement of a specified number of DWPs a formwork will be installed and voids will be backfilled. It is foreseen to mix the backfill at the surface and to pump the material through a pipeline distribution system.

An insufficient performance of backfill processes and/or emplacement rates that are significantly smaller than the production rate of the DWPs would cause inter-ruptions in DWP production. The total operational phase of the facilities would be extended and associated costs increased. The relation between DWP production rate and emplacement rate is therefore of great im-portance. To investigate the general feasibility of the planned operation and to identify bottlenecks, areas for optimization etc., DBE TECHNOLOGY GmbH carried out simulations of the future operation. The simulation mod-el considers all relevant boundary conditions, e.g. the disposal facility design, the planned transport and back-fill techniques, and strategic decisions of ONDRAF/NIRAS relating to the operation of the facili-ties. For example, one scenario considered to start the emplacement of the DWPs in the rearmost parts of the emplacement fields, and to carry out the construction of the plugs at the entrance of the disposal galleries, and the backfilling of the access galleries after backfilling of all disposal galleries.

According to the results of the simulations, at the beginning of the disposal operation the production rate will marginally exceed the rate of emplacement due to the longer transport routes. Consequently, the buffer is filled up with monoliths, however, this does not lead to a reduction of DWP production. Before the capacity of the buffer storage is exceeded, the decrease of transport distances and times with disposal operations advancing towards the shaft leads to an increased emplacement rate. The buffer stock is reduced and all new monoliths can be emplaced according to the DWP production rate.

Failures of the emplacement and backfilling tech-nique do not have significant effects for emplacement, because the buffer facility has a sufficient capacity. In addition, a variety of operational measures can be real-ized to raise the speed of emplacement and backfilling after resumption of the works, e.g. a temporary change from single shift to two shift operation. Consequently, there seems to be little risk that the average emplacement rate will fall back behind the DWP production rates and cause an extension of the total disposal operation peri-od. According to the simulations, the emplacement of the monoliths will last slightly less than 13 years.

The construction of the plugs and a final seal is still at the planning stage and no safe statements can be made to the time period of their implementation. Howev-er, a little more than 400 work days (~1.6 calendar years) can be estimated for the backfilling of the access galler-ies and their connecting galleries of the B waste field, if the works in the access galleries can be carried out sim-ultaneously.

After closure of the B waste field, the second wing of the disposal facility will be constructed and the super-containers will be emplaced in analogy to the B waste monoliths. Further simulation studies will examine the effects of the major differences between the planned operation of the B waste part of the disposal facility and its C waste part.