Safety of French reactors in service

The electricity-generating reactors operating in France at the end of the 1990s are all of the type using slightly enriched uranium oxide, possibly mixed with plutonium oxide, moderated and cooled with pressurized light water, the steam driving the turbine being produced in steam generators. They are therefore pressurized water reactors (PWRs).

As explained in other articles (B 3 800 and B 3 810 in particular), the operator is primarily responsible for the safety of his facility. However, he must justify this to the French safety authority, represented by the Direction de la Sûreté des Installations Nucléaires (DSIN). These principles are in line with international recommendations and, in particular, with the International Convention on Safety, ratified by France. Technical analysis of the supporting documentation submitted by operators is carried out by expert bodies, principally the Institut de Protection et de Sûreté Nucléaire (IPSN). This article does not go back over this organization or the authorization procedures described elsewhere, but focuses on more technical aspects.

The safety of nuclear power plants currently in service depends on :

• their original design and the quality of their workmanship;

• ageing installations ;

• improvements made to this design over time;

• operating conditions and, more generally, the safety culture of all those involved and their superiors.

Compliance with the design and operating rules defined for these facilities is intended to ensure a high level of safety.

It is then possible to calculate the probability of core meltdown, an accident likely to cause significant releases into the environment. Thanks to the precautions taken in design, construction and operation, this phenomenon is rare, and experience does not allow us to verify the relevance of the overall result of these calculations.

On the other hand, observation of the operation of a large fleet of nuclear power plants and the incidents and anomalies that occur are indicators of the level of safety. Their actual radiological consequences are usually nil. Analysis of these incidents, some of which may be precursors of more serious situations, enables us to define corrective measures to avoid their recurrence. Man obviously plays an essential role in the prevention, detection and management of these anomalies and incidents. Sometimes, however, he can also provoke them.

Lastly, since safety is not a fixed concept, periodic overall reviews (every 10 years or so) ensure that the original safety level has been achieved and...