In order to enhance the availability and performance of reactors in operation, EDF, together with the nuclear fuel manufacturers, is looking for and developing improvements to fuels and fuel management.

Since 1996, extending cycle lengths has been a major factor in optimising reactor fuel and operations. This extension is combined with increased fuel enrichment, but the quantity of energy released nonetheless remains limited to an average of 52 GWd/t per fuel assembly, which is the maximum authorised value. The ASN keeps a close watch to ensure that changes to fuel management methods are accompanied by a reactor safety demonstration based on the scenarios specific to each type of fuel management. When a management change leads EDF to revise an accident study method, prior examination of it is required and it cannot be implemented without the approval of the ASN.

EDF plans to use M5 alloy in place of Zircaloy 4 alloy as the cladding and structural material for the fuel assemblies in all the new types of management. In 2005, the ASN sent EDF a number of preconditions for generalised use of M5 alloy in all nuclear power plants.

MOX-parity

MOX-parity management concerns the twenty 900 MWe reactors authorised to recycle plutonium. It is characterised by a higher burnup fraction of the MOX fuel assemblies as a result of the higher number of irradiation cycles (4 reactor cycles instead of 3) and a change in their initial plutonium content (average of 8.65% instead of 7.1%). The purpose of this latter change is to compensate for the isotopic degradation of the plutonium resulting from reprocessing of fuels for which the burnup fraction was raised and to ensure that MOX fuel offers equivalent energy to UO2 fuel enriched 3.7% with uranium 235. The purpose of this management is also to help control the quantities of plutonium generated by the French nuclear power plants.

In 2005, the ASN continued to investigate the following aspects of this type of management: normal operation, accident studies, incident and accident operating rules, refuelling safety.

GALICE

As of 2006, EDF envisages replacing the existing GEMMES management, operational on the 20 reactors of the 1300 MWe series, with GALICE management. The uranium 235 enrichment of the fuel assemblies would rise from 4% to 4.5%. The maximum fuel burnup fraction would then be 62 GWd/t and refuelling would be hybrid: some assemblies would undergo three cycles and others four.

The average cycle length would still be 18 months, but could eventually be modulated between 15 and 21 months, in order to offer a degree of flexibility when planning refuelling outages.

Preparation of the safety analysis file for this type of management has been postponed by EDF.

ALCADE

ALCADE management is envisaged as of 2007 for the 4 reactors of the N4 series.

In order to extend the operating cycles for these reactors from 12 to 17 months, uranium 235 enrichment of the fuel assemblies would be raised to 4%. The maximum burnup fraction authorised for these assemblies would however remain unchanged at 52 GWd/t.

Analysis of the feasibility file was completed in the summer of 2005. As with GALICE management, it showed that the justifications for a certain number of points related to the nature of the fuel rod cladding material were still inadequate and that the loss of coolant accident (LOCA) study method required further examination.