Leak-before-break in French nuclear power plants

Practical applications of the leak-before-break concept at the present stage are quite limited in French nuclear power plants. However, discussions with safety authorities have included leak-before-break arguments for the different types of reactors: pressurized water reactors (PWRs), liquid metal fast-breeder reactors (LMFBRs) and gas graphite reactors (GGRs).

At present, the fracture mechanics part of the studies are complete for the following components:

• —pipes in GGRs;

• —primary and auxiliary lines in PWRs;

• —steam-generator tubes in PWRs;

• —pipes and main vessels in LMFBRs.

The different approaches are consistent but some specific problems have to be taken into account, depending on the plant, such as creep regime, thin shell components, in-service inspection or the issue of design safety.

A large research and development program, realized in different cooperative agreements (national or international), completes the general approaches. It comprises different topics, such as material properties, elastoplastic fracture mechanics, leak-area determination and leak-detection devices.

Although practical applications are limited at present, EDF, in conjunction with Framatome, Novatome and CEA, will define a complete validated methodology to be used on a variety of cases.