Control rod position indication system

Abstract

The present invention is a system which determines nuclear reactor control rod axial position using a deviation signature database generated from a current or reference signal pattern produced by one or more strings of axially dispersed fixed incore detector sections in the reactor core. The deviation signature database is produced by assuming deviant axial positions for the control rods in the core, calculating expected detector signals for the assumed positions and storing the deviation of expected signals from a calibration reference along with corresponding assumed rod positions. The signature database is periodically updated to take into account changed core conditions. When a change in detector responses is detected the system performs a signature analysis of the deviations in the signature database using the current deviation from the reference to search for the closest match. The change indicates not only the bank or individual rod that has moved but also the direction of movement allowing the search of the database to be circumscribed to the portion associated with the bank or individual rod and direction of movement. The closest match is used to incrementally search for the exact rod position by calculating expected response deviations for each assumed incremental move and comparing the expected response deviation to actual response deviations. If the system searches past the actual position, the last assumed position is output.