FATIGUE ANALYSIS OF REACTOR COOLANT PUMP IMPELLER FOR 1400 MWE NUCLEAR POWER PLANTS

摘要

The objective of the present paper is to outline the procedure of fatigue assessment involving Computational Fluid Dynamics (CFD) as well as Finite Element Method (FEM) calculations. As application a Reactor Coolant Pump (RCP) impeller for 1400 MWe Nuclear Power Plants is presented. To estimate hydraulic loading conditions including transient flow features, time - dependent CFD computations are performed. To solve the full three-dimensional transient Navier-Stokes-equations, the commercial software package Ansys CFX V.12 is applied. The purpose of the CFD analysis is to calculate the time dependent pressure loading in time and frequency domain on the impeller blades, mainly caused by transient rotor-stator interaction. In case of the investigated Reactor Coolant Pump, the Fourier-Analysis of the blade pressure signal shows that only certain excitation frequencies are of importance. Focussing on the impeller blade, the guide-vane passing frequency as well as its harmonics are dominant. Regarding the FEM calculation, the loading at each location of the blade surface can be determined by average pressure, excitation frequency, pressure amplitude and relative phase angle. Hence the problem is treated as a harmonic problem in the frequency domain. Prior to the harmonic analysis, a modal analysis of the impeller surrounded by water has to be performed in order to determine the natural frequencies. Due to fluid-structure interaction, the obtained natural frequencies are significantly lower than the ones calculated with the impeller being surrounded by air. Based on the mode shapes and natural frequencies coming from the modal analysis, the harmonic analysis is performed for each excitation frequency, using the alternating pressure and phase angle distributions determined by CFD. The fatigue analysis is based on a Haigh diagram which was the output of a research project carried out at the Laboratory for Structural Durability in Darmstadt, Germany. The input for the Haigh diagram is the peak stress intensity resulting from mean pressure distribution and centrifugal forces and the alternating peak stress intensity range, determined using the procedure described above.