Spent fuel and vitrified waste from power generating PWR reactors are the main sources of radioactive materials requiring interim storage as a matter of priority due to their very high activity. However, other sources and materials also exist, and interim storage is therefore used for many different types of waste, pending treatment and conditioning or a decision concerning their future disposal.
Beginning with highly radioactive materials, there is spent fuel from now-decommissioned first-generation reactors, reactors operated by national defence and research agencies and prototype reactors such as Superphenix. All these materials have taken a different route to that of spent fuel from current PWR reactors, which makes up the bulk of the total.
Spent fuel from first-generation graphite-gas reactors was the first to be processed, yielding vitrified waste stored in Marcoule. All the waste produced by this obsolete nuclear process must be managed.
Irradiated fuel produced by propulsion reactors in aircraft carriers and nuclear submarines, as well as fuel from the old heavy water plant in Brennilis, has not been reprocessed. It is held in interim dry storage in a bunker at the Cadarache site. The CASCAD bunker was commissioned in June 1990, with a design life of 50 years, making it a medium-term storage facility.
The 115 tonnes of irradiated fuel from Superphenix, of which the French share accounts for 75 tonnes, were placed in a cooling pool in a workshop at the Creys Malville facility, which EDF is licensed to operate for 30 years. The fate of this fuel is being considered in parallel to that of the irradiated MOX fuel assemblies currently stored underwater in La Hague.
The long-term future of these high-level materials – in terms of reprocessing, transmutation and geological disposal – is also the subject of research conducted in the light of legislation passed in 1991 and 2006.
Next on the radioactivity scale comes intermediate-level waste (ILW-LL), which under the terms of the aforementioned legislation, is destined for geological disposal. The conditioning adopted for this waste has also evolved to reflect advances in reprocessing techniques. A variety of interim storage arrangements exist accordingly.
The technique consisting in shearing spent fuel cladding and end caps into small pieces in order to compact them is recent. The share of end caps and hulls not sheared and conditions is still in underwater storage in La Hague, whereas conditioned waste (CSD-C) is stored in a compacted container storage building (Entrepôt de Colis Compactés - ECC). Until 1995, these sections were conditioned in drums filled with cement and then stacked. Liquid effluent treatment stations also produce waste that is considered to be ILW-LL and as such must be stored in Marcoule and La Hague.
Lastly, various interim storage arrangements for low-level long-lived waste (LLW-LL) have been adopted while research is conducted to determine its final destination. This is the case, for example, of legacy graphite waste from natural uranium-graphite-gas (UNGG) reactors, which were shut down several years ago and are in the process of being dismantled. Most of these graphite liners are being held in interim storage in La Hague.