High cycle thermal fatigue due to the mixing of hot and
cold fluids may initiate cracking in pipes of safety related
circuits. A method has been developed to identify such
fluid mixing zones subjected to potential thermal fatigue
damage. This method is based on a loading model and a
mechanical model that depend on the main characteristics
of the mixing zone and on the material properties. It is
supported by a large experimental program. This method
has been applied to all the mixing zones of safety related
circuits of the EDF pressurised water reactors, allowing
to identify sensitive zones and to apply an appropriate
inspection program that ensures the control of the risk due
to this damage mechanism.