| I. Materials > The Uranium-Plutonium Chain > Fuel Management in Reactors |
900 MWe Reactors
In 900 MWe PWRs, EDF generally used fuel enriched to 3.25% and unloaded a third of a core each year. Today EDF loads fuel enriched to 3.75% and unloads a quarter of a core each year. But EDF also uses in certain reactors Mox fuel and fuel based on uranium that has been reprocessed and re-enriched.
Classes CP1 and CP2
EDF is using Mox fuel only in 20 of the 28 900 MW reactors of the CP1 and CP2 classes. In these reactors, 30% of the assemblies are Mox; 70% are uranium oxide. The Mox assemblies are composed of plutonium oxide. EDF is authorized to use, on average in each assembly, up to 7.08% plutonium (with 92.92% or more depleted uranium). The percentage of plutonium in individual fuel rods varies according to whether the rods are in the center of the assembly, on the outside, or in an intermediate position. Those closest to the center have the highest percentage of plutonium; those on the outside, the least.
The limit of 7.08% plutonium represents an increase granted by the authorities in 1999. Previously the limit was 5.3%. With this limit, EDF, if it wished to achieve with Mox an energy level equivalent to that of UO2 fuel enriched to 3.25%, could only incorporate into the Mox, plutonium extracted relatively recently from low burn-up fuel. This plutonium contains a higher proportion of fissile isotopes than does old or high burn-up plutonium. Raising the permissible level to 7.08% plutonium allows EDF to use older plutonium and plutonium extracted from fuel irradiated in PWRs and still to achieve the equivalent in energy of standard fuel enriched to 3.25%.
When EDF first loaded Mox into 900 MW PWRs, it combined Mox with standard fuel enriched to 3.25%. Both the Mox and the UO2 fuel were discharged annually, a third of a core at a time.
EDF now uses a hybrid scheme. The Mox fuel stays in the reactor for three cycles; a third of the core is discharged each year. The standard fuel is enriched to 3.7% and remains in the core for four cycles, ie a fourth of a core is discharged annually.
EDF’s short-term goal in regard to management of Mox in 900 MW reactors is authorization to implement what it calls a "Mox/UO2 parity program." It would then discharge one fourth of a core per year of both Mox and UO2 fuel enriched to 3.7% [IPSN 97]. To keep Mox in a reactor for four cycles, EDF would need an authorization to increase the percentage of plutonium to 8.65% [Bataille 98]. The burnup would go to 47,000 MWd/t [NucF 10.ii.97] or to about 50,000 MWd/t [Fraize 98], depending on the information source. As of 1999, EDF is authorized to use a given Mox assembly for only three annual cycles, the average discharge burnup for Mox from EDF’s 900 MW reactors was 37,000 MWd/t, according to Bernard Esteve of EDF [NucF 22.iii.99].
Class CPO
For the CPO series of 900 MW reactors, EDF is seeking authorization to use 4.2%-enriched uranium oxide fuel. The increase in the enrichment would allow an 18-month cycle, with reloads of one third of a core at a time. EDF refers to this program as Cyclades [IPSN 97; NucF 22.iii.99]. DSIN authorized the first loading of Cyclades fuel into Fessenheim 2 in October 2000 [DSIN 00].
Uranium from reprocessing
In 1998 EDF was authorized to increase the enrichment of fuel made from reprocessed uranium from 3.7% to 4.1%. This means that Repu fuel can now be the equivalent of fuel made from fresh UO2 and enriched to 3.7% [NucF 22.iii.99]. The reason that EDF presented for the change was the same that EDF put forward in the request to increase the level of plutonium in Mox--the decrease in the quality of the reprocessed uranium available [DSIN 98].
1300 MWe Reactors
For its 1300 MW reactors, EDF received an authorization in 1999 to use uranium oxide fuel enriched to 4.1%. This fuel will be discharged one third of a core at a time, once every eighteen months. The irradiation level will be on average 52,000 MWd/t. Previously EDF had been authorized to go only to 47,000 MWd/t and the company used fuel enriched to 3.1%, discharged one third of a core at a time, once every twelve months. EDF had loaded 4.1% enriched fuel into 1300 MW plants in 1997 in the hope that DSIN would approve the change before EDF, under the old regulations, would have had to unload it. DSIN did so. The new fuel management program is known as Gemmes.
1400 MWe Reactors
In its 1400 MW reactors, EDF loads UO2 fuel enriched to 3.4% in uranium 235. It discharges this fuel every twelve months, one third of a core at a time.
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