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THERFAT Report Summary

Project ID: FIKS-CT-2001-00158
Funded under: FP5-EAECTP C
Country: France

Load determination by experimental tests and computational fluid dynamic analyses

The task of the load determination is to detect and quantify the thermal turbulence occurring in the fluid by experiments and by numerical fluid calculations. The determination of the heat transfer coefficient (fluid to wall) is considered to be one crucial point. After a collation of the existing load determination experience thermo-hydraulic tests have been performed to measure the relevant load parameter. In addition, thermo-hydraulic analyses with CFD (Computational Fluid Dynamics)-codes have been carried out to simulate the turbulent fluid behaviour. Generalised guidelines for load determination have been derived from the experimental and numerical results. As an additional sophisticated aspect, the development of virtual sensors based on neural networks and fuzzy logic tools has been included to determine the temperature loads for a selected NPP-PWR-component (the pressurizer surge line).

In experimental tests temperature differences and load cycle frequencies due to the turbulent fluid flow occurring at various mixing Tees have been simulated, illustrated and quantified by experimental approach in small scale Tee-tests models in various positions and configurations. These tests have been performed on plexi-glass models for flow visualization and metal mock-ups for direct measurements of temperature distributions in the fluid and through the wall pipe.

In addition to the experimental tests, numerical thermo-hydraulic calculations (CFD-analyses) have been performed for benchmark cases and for other Tee-configurations. The Benchmark calculations have been performed to determine the turbulent fluid distribution in a 50:50 mm Tee-connection with different CFD-Code approaches in comparison to experimental testing results. The CFD-Code calculations are based on different simulation approaches (Large Eddy-Simulation, Ke-approach or other code methods), which have been applied in THERFAT. Agreement between analytical predictions and experimental results is reasonable. Guidelines for an analytical load assessment that integrate velocity and temperature fields and the calibration of the heat transfer modelling between fluid and wall can be derived from the obtained results. But the CFD-analyses turned out to be very time consuming; even short time history calculations of a few seconds require a tremendous amount of computer time (weeks or even months). Powerful computers are required for the execution of the calculations.

An additional highly sophisticated aspect in the load determination field covers the development of virtual sensors based on neural network and fuzzy logic tools to simulate the dependency of thermal fluctuations on from transient mass flow and temperature distributions of the surge lines in the Vandellos NPP, Spain and the Mochovce NPP, Slovakia. The THERFAT-work comprises the development and training of the virtual sensors, the pilot installation, the online data acquisition of the surge line temperature transients and the evaluation of the results.

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