Abstract: A smart reactivity computer is disclosed that processes signals from multiple neutron detectors to generate values of regional core reactivity that are output to a strip chart recorder. The computer compares the regional reactivity values and, when the values are coincident for a period sufficient to satisfy a statistical fit test to a straight line, indicates to the operator that true core reactivity can be determined. The computer determines control rod worth by first fitting a straight line to the coincident portion of the reactivity values. The computer then determines intersections between the straight line and the reactivity value lines produced when the control rods are moved on both ends of the straight line. The difference between intersections for a single control rod movement line determines control rod worth for that movement.

Abstract: The approach to criticality of a nuclear reactor provided with an artificial neutron source is monitored by two neutron detectors, one which measures the neutron flux in a localized region around the artificial neutron source, and the other located simlarly with respect to the core geometry but removed from the localized region. When the reactor is subcritical, the artificial source dominates and the outputs of the two detectors are noticeably different. As the reactor approaches criticality, the critical mode distribution of neutrons, which is symmetrical with respect to the two detectors, becomes dominant and the detector outputs approach each other in magnitude. The ratio of the output signals therefore, provides an indication of the reactor reactivity state. Either linear or logarithmic ratio signals can be generated, and if desired, either can be compared with an appropriately scaled reference signal representative of a selected reactivity state, such as a multiplication factor of 0.