Advances in time-dependent Monte Carlo simulations for void velocity determination using neutron noise techniques

Abstract

Neutron noise measurements for estimating void velocity in a void-containing water flow where spherical bubbles move upward are simulated using a continuous energy Monte Carlo method. The method is newly equipped with a function for handling time-varying locations of void bubbles. In the simulations, time-series data of neutron counts in axially-placed detectors are obtained. The data are subsequently processed to yield the cross-correlation function (CCF), cross-power spectral density (CPSD), and auto power spectral density (APSD). The void velocities are estimated from the maximum CCF, slope of the phase of the CPSD as a function of frequency, and dip frequency of the APSD. These three methods yield a constant void velocity estimation. The simulations demonstrate that the noise techniques are insensitive to a void flow that contains smaller bubbles.