A Neutronic Analysis of Boiling Water Reactor In-Core Detector Noise

The response of boiling water reactor in-core detectors undergoing vibration has been calculated. A neutronic model based on calculating the fission activity at a detector position in a planar multibundle environment was employed. The model used eight energy groups and two-dimensional Cartesian geometry in a discrete-ordinates transport approximation. The in-core detector responses due to various detector displacements were calculated as a function of channel box corner wear with different effective in-channel voids, bypass voids, and instrument tube voids. The calculated noise was found to have a linear dependence on channel box wear. This was corroborated by measurements. An increase in in-channel voids was found to increase the noise, while an increase in bypass and instrument tube voids decreased the noise. The presence of a nearby control blade increased the noise.