Retrievability of the waste package disposed of in Cigéo
Reversibility of disposal throughout its service life is one of the principles guiding the design of Cigéo, the geological disposal facility project for the most hazardous radioactive waste. Gradually defined as from 1991, disposal reversibility was endorsed by Parliament in 2006, then clarified by a new law in 2016. Considering that the disposal facility is to be operated by 5 successive generations, the aim is to avoid freezing its development at the design stage and imprisoning future generations in the decisions taken at the outset.
Reversibility particularly relies upon the retrievability of the waste packages. This is the ability to remove waste packages from a deep geological disposal facility throughout its service life. For Cigéo, this lasts hundreds of years.
OBJECTIVES AND BENEFITS OF RETRIEVABILITY
Retrievability is an integral part of reversibility, offering future generations the possibility to reappraise the disposal of some or all of the waste. Retrievability could have a dual purpose: either the waste packages are temporarily withdrawn from their disposal cell (for tests, checks, etc.), or they are withdrawn in order to be directed to another HLW and ILW-LL waste stream.
HOW IS RETRIEVABILITY GUARANTEED?
Technically, retrievability means withdrawing the waste packages from the disposal cells using the reverse procedure to their installation and in accordance with the same safety and protection objectives.
Retrievability relies upon the Cigéo design and operating principles: robust, sustainable components (the cells do not collapse or hinder the withdrawal of the packages), handling equipment suited to the disposal and to the withdrawal of the waste packages, traceability of the disposed packages and their contents, monitoring and control of the withdrawal conditions, etc. Retrievability also relies upon programs of technological tests. Withdrawal tests were carried out in conditions more difficult than those expected in real-life operational conditions (deformation, corrosion, etc.). Further real-life withdrawal tests will be carried out in the disposal facility prior to its commissioning.
IMPACT OF DISPOSAL FACILITY CLOSURE ON RETRIEVABILITY
At the end of its operation, the repository is intended to be closed to operate safely and passively over the very long term. The cells are plugged, the tunnels backfilled, the disposal areas are closed and sealed if necessary.
Permanent closure, which only a law can decide upon, means sealing and backfilling the access to the surface. The further the closure operations progress, the greater the effort needed to withdraw the waste packages. The operations to close disposal cells or areas can be undertaken throughout the Cigéo operating period. Future generations will be able to decide to anticipate them, in order to progress more rapidly towards passive disposal operation or, on the contrary, delay them until the end of the repository’s service life (around 2150) to preserve easier retrievability.
IMPLICATIONS OF PACKAGE WITHDRAWAL FOR OVERALL WASTE MANAGEMENT
If a firm alternative to deep disposal were to emerge - providing a safety advantage, including in the long term - this would mean taking the decision to withdraw a large number of waste packages from Cigéo. Such a decision would imply:
• The emergence of an alternative sustainable waste management stream, along with the demonstration of its feasibility and safety;
• The licensing and building of all the nuclear installations, structures and equipment needed to operate the alternative sustainable waste management stream;
• The withdrawal of the packages and their dispatch to the alternative stream for its operation.
Owing to Cigéo’s robust, sustainable design, there is no need to take an urgent decision and the necessary time is left to accomplish these operations.
FURTHER DETAILS
Can Andra guarantee the retrievability of the packages in the event of an accident?
Nuclear safety consists of the set of technical provisions and organizational steps taken to prevent accidents or limit their effects.
In the highly unlikely event of a severe event affecting Cigéo operation, the main objective is to return to a safe state. The equipment and provisions used to withdraw the packages are not a factor in the management of these situations. Once the repository has returned to a safe state, the Cigéo disposal facility operator reviews the arrangements to be made to sustain the safety of the facility and restart its operation, if appropriate. In this context, package withdrawal is one of the potential actions, without having to be considered as a systematic solution.
It cannot be guaranteed that the packages would be systematically withdrawn from disposal at a later date, especially if parts of the underground facility were too heavily degraded. However, Cigéo’s safety relies upon design provisions which facilitate the withdrawal operations: strength of the packages, mechanical robustness of the cells, provisions to control fire and explosion risks.
How long would it take to withdraw all the waste packages from Cigéo?
The time needed to withdraw one package is about the same as the time it takes to install it in the facility.
The studies show that by making full use of the capacity of the equipment (which does not work at full capacity during disposal), and by increasing operating rates (3 x 8), groups of packages could be withdrawn in a shorter time than for installation. The Cigéo repository possesses a substantial margin for speeding up possible waste package withdrawal operations.
Is package withdrawal possible beyond the final closure of the disposal facility?
The start of the final closure work around 2150, which only a law can authorize, marks the end of Cigéo’s reversible operation. It does not signify the cancellation of the retrievability enabled by the disposal facility design provisions. However, at that stage, the effort needed to withdraw the packages would be very complex and costly.