European THERFAT project—thermal fatigue evaluation of piping system “Tee”-connections

Abstract

Thermal fatigue is a significant long-term degradation mechanism in nuclear power plants (NPP). In particular, as operating plants become older and life time extension activities are initiated. Operators and regulators need screening criteria to exclude risks of thermal fatigue and methods to determine significant fatigue relevance. In general, the common thermal fatigue issues are well understood and controlled by plant instrumentation at fatigue susceptible locations. However, incidents indicate that certain piping system Tee's are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentations. Therefore, a European project on thermal fatigue evaluation of piping system Tee-connections THERFAT has been initiated. In THERFAT, a collation of existing field experience has been conducted leading to a selection of Tee-connections for further investigations. The load determination covers experimental tests and advanced thermo-hydraulic flow simulations. The integrity evaluation work package comprises stress/fatigue analyses and fracture mechanics assessments supported by targeted verification damage tests. Proposals will be made for improved load thermal fatigue assessment procedures, screening criteria to determine lower non fatigue significant threshold values and for establishing a European methodology on thermal fatigue. THERFAT participants No. Name Organisation Country 1 K.-J. Metzner E.ON Hannover, GER 2 C. Faidy EDF Villeurbanne, F 3 J.-A. Le Duff Framatome-ANP Paris la Défense, F 4 O. Braillard CEA St Paul Lez Durance, F 5 C. Cueto-Felgueroso Tecnatom S.A. Madrid, E 6 I. Varfolomeyev Fraunhofer-Gesellschaft Freiburg, GER 7 J. Solin VTT Espoo, SF 8 M. Schippers Framatome ANP Offenbach, GER 9 L. Stumpfrock MPA Stuttgart, GER 10 K.-F. Nilsson EC-JRC/IAM Petten, NL 11 Y. Hytoenen Fortum Nuclear Services Vantaa, SF 12 J. Seichter Siempelkamp Dresden, GER 13 T. Abbas Cinar London, GB 14 S. Figedy VUJE Trnava, SLK 15 P. Carmena Endesa Generacion Madrid, E 16 L. Cizelj Jozef Stefan Institute Ljubljana, SLO