ICONE15-10805 THERMAL FATIGUE IN THE MIXING TEES IMPACTED BY TURBULENT FLOWS AT LARGE GAP OF TEMPERATURE : THE FATHER EXPERIMENT AND THE NUMERICAL SIMULATION

Abstract

Thermal fatigue is one significant long term degradation in the NPP's. The temperature fluctuations induce a reliability reduction of the nuclear components. In France in may 1998, damages were occurred in a mixing tee from the heat removal system (RHRS) in the Civaux Nuclear Power Plant. A wide experimental program produced by AREVA ANP, CEA, and EDF was initiated to study the thermal fatigue phenomena in the mixing tees. A tee mock-up in 304L stainless steel material and geometrically close to the industrial component were designed to submit a severe endurance test impacted by realistic turbulent mixing of two fluids at large gap of temperature. A large facility, called FATHER, was implemented to supply the necessary power for endurance test performing. A second stage was to set measurements in the fluid and in the wall with specific instrumentation (flux meters) to assess the thermal load which leads the potential damages in the inner surface. This paper presents the experiment and the significant results from the endurance and thermal hydraulic tests. The mean and fluctuating temperature are plotted in the mixing area in the wall and in the fluid close to the wall. Helped by inverse method, the wall temperature can be assessed. The heat transfer in the wall, assumed as 1D is qualified and the key parameters which influence the level of temperature fluctuation as the velocity mixture, the flow rate ratio and the difference of temperature are evaluated. At last, to complement the experiment, a numerical analysis using TRIO U code was performed within the large eddy simulation approach for the specific geometry of the FATHER mock up.