The isotope separation process used in the plant is based on gaseous diffusion. The plant comprises 1400 cascaded enrichment modules, split into 70 sets of 20 modules grouped in leak-tight rooms.

The gaseous enrichment principle consists in repeatedly diffusing UF6 gases through porous walls called "barriers". These barriers give preferential passage to the uranium isotope 235 contained in the gas, thereby increasing the proportion of this fissile isotope in the UF6 at each passage.

Each enrichment module has a compressor for raising the UF6 gas to the required pressure, an exchanger removing the heat produced by compression and the actual diffuser containing the barriers.

The U235 enriched diffused gas flow is routed to the next higher module. The depleted, non-diffused flow is routed to the lower module. These modules or stages, grouped in four gaseous diffusion plants, constitute the enrichment cascade.

The UF6 is introduced in the middle of the cascade, with the enriched product drawn off at one end and the depleted residue at the other.

Safety review of the plant after twenty years of operation

Following the safety review conducted in 2000, the licensee in 2002 forwarded the dossiers concerning the seismic resistance of the plants. Additional investigations were necessary to determine the seismic behaviour of the U annex building, where the enrichment cascade feed and draw-off operations are carried out, taking account of the seismic movement determined according to the new RFS 2001-01. The investigations show that the seismic resistance of the U annex building needs to be improved and the licensee proposed measures designed on the one hand to reinforce the civil engineering structures and on the other to limit the quantities of radioactive materials present in these buildings. The licensee intends to limit the quantities of liquids present and to apply for the corresponding authorisation in 2006.

The ultracentrifugation process should eventually replace gaseous diffusion. COGEMA has transmitted the safety options dossier for the future ultracentrifugation enrichment units. This dossier was analysed by the ASN and its technical support organisation. The licensee also forwarded the preliminary safety analysis report for the installation which, from 2007, is scheduled to gradually replace the Eurodif plant. Commissioning of the three planned production units will take place from 2007 to 2016.

This planned new plant was the subject of a public debate which ended on 20 October 2004 and led to no opposition to the project. This installation will be covered by a public inquiry in 2005 as part of the authorisation application process.

Review of this project involved the nuclear safety authority visiting nuclear facilities throughout Europe that use the same technology and initiating exchanges with its foreign counterparts concerning the corresponding safety considerations.