Introduction

The key component of a geological repository for high level long lived radioactive waste is the disposal unit (a borehole, a drift, a room or a cell) which contains the waste. The disposal unit design is mainly based on the long term safety requirements to ensure that the radionuclides will be confined or sufficiently delayed in their migration. Nevertheless, this design must also be sufficiently realistic with regard to operational considerations which encompass notably the construction and the waste emplacement processes.

So far, in most international conferences, the attention dedicated to the long term performance tends to imply that this aspect is the main criterion for assessing the feasibility of a deep disposal. However, today the nuclear waste management agencies and research organizations are becoming more and more aware of the importance of the operational considerations.

First of all, it must be demonstrated that the input data taken into account in the long term safety calculations are realistic given the construction processes envisaged.

Secondly, it must also be shown that the waste emplacement process is duly taken into account in the design of the disposal units and that this process can offer a high level of occupational safety particularly in terms of radioprotection.

Thirdly, protecting the people and the environment during the next century is at least as important as protecting them over the long term. Consequently, operational safety should be an integral part of the feasibility demonstration.

In some national concepts reversibility, retrievability and an associated monitoring programme must also be taken into account.

This conference is a first of its kind insofar as it will provide a unique opportunity to demonstrate how the combination of operational and long term safety considerations are intimately linked to the different disposal unit concepts. It is organised within the framework of the ESDRED Project which is part of the European Union's 6th EURATOM Framework Programme for Nuclear Research and Training.