LA FATIGUE THERMIQUE DANS LES CENTRALES NUCLEAIRES: ENSEIGNEMENT DU RETOUR D'EXPERIENCE

摘要

Thermal fatigue is a key degradation mechanism in nuclear power plants. Low cycle fatigue seems to be well managed, that is in accordance with field experience. For high cycle fatigue in connection with complex thermo-hydraulic loads, it seems that a large number of uncertainties remain in the different step of the methodology, that is also in accordance with field experience. 3 major situations are encountered: stratification, penetration of vortex and mixing tees for large ΔT. In this paper, after a quick overview of existing design codes, the last case encountered will be used as a generic example to treat globally the problem. In conclusion, a review of R&D actions and code modifications will be done. The paper confirms the multi-disciplinary actions with 2 important concerns: the metallurgical examinations and a need of international approaches of the subject. The paper is focused on piping systems (not to large components like reactor coolant pumps) and firstly pressurised water reactors.