Benchmarking of deformation and vibration measurement techniques for nuclear fuel pins

Understanding the mechanical interactions between the coolant and the core structure in nuclear reactors helps to determine the lifetime, health or optimal design of the reactor core. The flow of the coolant produces vibrations in the reactor core containing the fuel assemblies that consists of a matrix of fuel pins. We report on an evaluation of the performance of different vibration measurement techniques considered for measuring the flow induced vibrations on a fuel pin mock-up. These techniques include a laser Doppler vibrometer (LDV), a grid method (GRID), fiber Bragg grating sensors (FBGs), electrical strain gages and two types of accelerometers. In this paper we first show the practical aspects of the validation experiments before proceeding with the influence of the techniques on the pin dynamics. Finally we compare the signal-to-noise ratio (SNR) and the level of determination of the response signal of the sensors for low amplitudes and low frequencies. We conclude that for our setup the optical techniques and MEMS-type accelerometer prove to offer superior performance. Considering the space constraints, we believe that the fiber Bragg gratings are the best candidate for vibration monitoring in nuclear reactor core mock-ups.