Investigation On Effect Of Adhesive Water Condition To Wet Modal Response Of Nuclear Coolant Pump Impeller

The dynamic modal response parameter of the impeller of reaction coolant pump that is usually estimated by a computational model limits the mechanical design of reactor coolant pump. Nevertheless, there are complex boundary conditions with the impeller that are difficult to include in the computational model. One of these boundary conditions is the coolant where the impeller is submerged. The effect of the added mass and damping of surrounding fluid can decrease considerably the natural frequencies of the impeller. Another of these boundary conditions is the spiral casing where the impeller works. Boundary conditions of fluid can modify accuracy of measure results by influencing or even changing parameters of modal response. So impact by boundary conditions of fluid cannot be ignored during modal experiment of a RCP impeller.Two research methods in this paper were carried out to solve the problem of complex boundary conditions in which the impeller works. Firstly, the influence of the added mass and damping of water can be clear through the contrast of impeller modal experiment data between dry mode and wet mode. Secondly, in modal experiment, geometric condition of tank’s walls and the distance between the free surface and impeller’s top is similarly equivalent to structure of spiral casing.An experimental investigation in a reduced scale model of the impeller of reactor coolant pump, using modal analysis, was carried out. Several impact tests with the impeller freely suspended in air and in water were carried out. The modal response was measured with piezoelectric acceleration sensors situated in diverse locations of the impeller. Through COINV DASP data acquisition instrument and the software of modal analysis, the natural frequencies, damping ratios, and mode-shapes were acquired.At last, modal experiment of reactor coolant pump impeller has to be proved reliably compared with the data of numerical simulation. After the impeller model was put into ANSYS software, its nature frequency can be calculated by modal analysis module. A numerical simulation using FEM (Finite Elements Model) was done using the same boundary conditions as in the experiment (impeller in air and surrounded by a mass of water).By the contrast of impeller nature frequency of different nodal diameters between numerical simulation and modal experiment, if the coefficient of proportionality reaches the expected error range, reliability of modal experiment can be trusted.