Investigation of the pumps which had been tested showed no signs of damage. However, EDF considers that owing to the high level of vibration, the reliability of these pumps cannot be guaranteed for more than about thirty hours in certain accident situations.

According to EDF, only the pumps on the RIS LP and EAS systems in the 900 MWe reactors are affected by this anomaly, as the 1300 MWe reactor pumps are equipped with a device to compensate for thermal expansion of the transmission shaft, while those in the 1450 MWe reactors use a different technology.

In an accident situation such as that described above, if there is a leak from the primary system, and because of the high temperature of the water circulating through the RIS and EAS systems, the anomaly is liable to cause malfunction of the RIS LP and EAS pumps and thus eventually lead to loss of the recirculation function.

The anomaly has no impact on normal operation of the reactors.

EDF informed the ASN that the anomaly could be corrected, in particular by replacing the pump motor upper bearing by a double-thrust bearing which would prevent the motor rotor from lifting under the effect of thermal expansion. EDF aims to carry out these replacements on all 900 MWe reactors before 31 March 2006.

At the ASN's request, the Advisory Committee for nuclear reactors in 2005 examined experience feedback from operation of pressurised water reactors over the period 2000-2002. An initial meeting of the Advisory Committee was given over to examination of generic topics. A second meeting was devoted to analysis of topics concerning plant organisation and operating practices.

Investigation of the incidents listed for the period 2000-2002 highlighted the fact that a large number of the significant events was caused by the periodic test programmes. The ASN asked EDF to initiate actions to remedy the weaknesses identified in the periodic test and restart test preparation and performance processes and to submit a review of the improvements resulting from the action taken.

In addition, nonconformity with the technical operating specifications accounts for more than one-third of the significant safety events. The ASN asked EDF to initiate or continue with proactive steps to reduce the number of events involving these fields, in particular to improve how human and organisational factors are considered in the design of the technical operating specifications, and to analyse and monitor any failures to comply with these specifications.

Review of the risk analysis approach and how it is implemented operationally revealed problems with analysing cross-functional risks involving several professions, as well with involving contractors in the risk analysis process. The ASN asked EDF to improve its handling of these aspects as well as its in-depth analysis of significant safety events in order to identify those factors leading to inadequacies in the risk analyses.

Finally, in experience feedback analysis, the ASN wishes to see greater importance attached to studies concerning lessons learned from events occurring abroad.