EDF is continuing several experimental programmes aimed at improving both fuel safety and performance levels. The avenues for improvement explored are numerous and concern both the composition and shape of the metal parts of the assembly (clad, skeleton assembly, nozzles, etc.) and the fuel pellet matrix.

M5 alloy fuel cladding

In 2005, the ASN authorised burnup of a load of AFA3GLrAA fuel (clad and structure made of M5 alloy) in several reactors (Cattenom 3, Nogent 2 and Civaux 2).

A certain number of questions concerning the loss of coolant accident, pellet-clad interaction and the impact of M5 on the fuel cycle will require answers from EDF before this type of assembly can be deployed for general use.

Westinghouse RFA fuel loads

Westinghouse RFA type assemblies are characterised by technologies for holding the rods in their skeleton assembly which are different from those used by Framatome. In 2005, the ASN authorised the introduction of new RFA fuel loads in six 900 MWe reactors. The four reactors already authorised in the past introduced their second refuelling load.

Rod Cluster Control assembly drop time

Since 2002, fuel assemblies with a reinforced structure (see above) have gradually been introduced into the reactors by the licensee, in order to limit irradiation induced deformation and improve the overall RCC assembly drop time. Based on this favourable experience feedback, the ASN in 2004 relaxed the requirements concerning measurement of the RCC assembly drop time during the cycle.

This favourable trend continued and in 2005, the ASN authorised the licensee to load fuel under RCC assemblies during their final irradiation cycle and put an end to the obligation to carry out RCC assembly drop time tests during the course of the cycle. Requirements concerning RCC drop time tests at the end of the cycle and the particular fuel assembly deformation measurements are for their part maintained for all reactors in order to consolidate experience feedback.

Refuelling operations, during which end of life fuel assemblies are replaced by new assemblies, take place with the reactor shutdown and vessel open. Refuelling requires underwater handling of fuel assemblies between the fuel building pit and that in the reactor building, so that they can be positioned in the reactor vessel in accordance with predetermined reloading sequences.

Since the loading incident at Dampierre in 2001, EDF has gradually implemented measures designed to improve the organisation and monitoring of handling operations and licensee criticality risk training.

Implementation of the initial measures was not in itself enough to prevent further positioning errors involving a few assemblies, so in 2004 the ASN once again asked EDF to bolster its provisions for preventing fuel assembly positioning errors in the reactor.

At the beginning of 2005, EDF took additional steps, in particular to ensure that each fuel assembly is pre-positioned at the correct location in the reactor before it is actually reloaded. Furthermore, the organisation of the teams in charge of fuel handling was modified in order to further reinforce the checks on correct performance of the fuel reloading operations. Finally, surveillance of criticality risk control was redefined in order to anticipate the risk of primary coolant dilution during fuel handling operations in the reactor.

These measures meant that the fuel handling operations performed in 2005 were more reliable.