| 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 3.7% and unloads a quarter of a core each year (the Garance program introduced in 1994). 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 in only twenty-two of the twenty-eight 900 MW reactors of the CP1 and CP2 classes. In these reactors, 30% of the assemblies may be Mox; 70%, uranium oxide. The Mox assemblies are composed of plutonium oxide. EDF is authorized to use, on average in each assembly, up to 8.65% plutonium. 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 lowest..
The limit of 8.65% plutonium represents an increase granted by the authorities in 2006. Previously the limit was 7.1%. When Mox was first used the limit was 5.3%. With the 5.3% 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 8.65% plutonium allows EDF to use older plutonium and plutonium extracted from fuel irradiated in PWRs and to achieve the equivalent in energy of standard fuel enriched to 3.7%.
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. Now the standard fuel is enriched to 3.7% and both this fuel and the Mox stay in the reactor for four cycles; a quarter of the core is discharged each year. This fuel management program, long a goal of EDF, is known as Mox/UO2 parity or simply Mox parity. Maximum burnup is limited to 52 MWd/t on average per assembly [ASN 2007].
Class CPO
For the CPO series of 900 MW reactors, EDF is authorized to use 4.2%-enriched uranium oxide fuel. This allows 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; ASN 07]. 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 isotopic 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 is discharged one third of a core at a time, once every eighteen months. The irradiation level is on average 52 GWd/t. Previously EDF had been authorized to go to only 47 GWd/t and the company used fuel enriched to 3.1%, discharged one third of a core at a time, once every twelve months. The program using fuel enriched to 4.1% is known as Gemmes.
In 2007 EDF envisaged replacing in 2008 Gemmes with Galice, based on fuel enriched to 4.5% and a maximum burnup of 62 GWd/t. Galice would entail a hybrid refueling plan: some assemblies would remain in the reactor for three cycles and some for four. The average length of a cycle would remain eighteen months, but actual assemblies would remain as few as fifteen months and as many as twenty-one months in the reactor. ASN studied Galice in 2007 [ASN 07].
1450 MWe Reactors
For EDF's 1450 MW reactors, ASN in 2007 authorized the loading of UO2 fuel enriched to 4% in uranium 235. It discharges this fuel every seventeen months. This program is known as Alcade. Previously the maximum enrichment was 3.4% and discharge occurred every twelve months. Maximum burn-up at discharge remains 52 GWd/t. for Alcade as for the previous plan [ASN 07].
--revised December 27, 2008
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