Seismo-acoustic Characteristics of HFIR Cooling Tower Fans and Pumps

Seismic and acoustic characteristics of three cooling tower pumps and four fans at High Flux Isotope Reactor (HFIR) were investigated using data from three targeted experiments on December 6, 2019, June 5, 2020, and February 10–11, 2021. We used spectrograms, power spectral density (PSD), an interactive frequency picking tool, and ground truth information to study seismic and acoustic responses due to the operating of these pumps and fans. By varying operating speed of the fans, we found faster fan speed leads to higher seismic and acoustic energy. A stepwise increase in fan speed leads to a stationspecific stepwise pattern in seismic spectrograms. At each fan speed and for each fan, different impulsive frequencies can be identified using the interactive frequency picker. Seismic responses of two fans operating concurrently are equivalent to the summation of seismic responses of each fan. We can match the acoustic response of fans from one targeted experiment with that from three actual operational cycles of HFIR. Seismic responses of the fans show significant differences at different stations even for the same fan operating at the same speed, though common impulsive frequencies can be found in most cases. Unlike the fans, seismic responses of the cooling tower pumps contain mostly broadband features in the frequency band of 5–50 Hz (or 5–150 Hz for some stations). Clear seismic responses of the three cooling tower pumps were observed at all seismic stations with a maximum distance of 120 m. As expected, seismic energy is higher when the sensor is located closer to the source. We were able to locate the source of pump-related seismic responses using absolute amplitudes of seismic signals. The inferred source location region includes the actual location of the pump, which may be improved with a polarization analysis of seismic signals.