In the core of a boiling water nuclear reactor, local power range monitor strings typically including four vertically spaced monitoring sites are modified. Each monitoring site includes a conventional local power range detector in which fissionable material exposed to thermal neutron radiation produces fission fragments, ionizes a gas and produces a current between the anode and cathode. In the improvement herein, each conventional local power range detector is provided with one or two adjacent gamma thermometers; each gamma thermometer including an interior mass to be heated by gamma radiation, a thermocouple for measuring the heated mass and a reference thermocouple connected in series. Both the conventional local power range detector and the gamma thermometer(s) are all geometrically arranged in a string with individual connecting cables leading to external connectors, one for each detector and gamma thermometer. When the sring is inserted into the core and the reactor operated at a steady state, the gamma thermometers can be utilized to calibrate the local power range detectors in conjunction with a convetional reactor heat balance. By the expedient of referencing the gamma flux to the output of the heat balance, calibration of the local power range monitors occurs over their useful in-service life.
A nuclear reactor instrumentation system including a plurality of in core nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core. The income nuclear instrumentation assemblies each include a fixed type neutron detector assembly having a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly having a plurality of fixed type gamma ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors. A power range detector signal processing device is operatively connected to the fixed type neutron detector assemblies through signal cables. A gamma thermometer signal processing device is operatively connected to the fixed type gamma thermometer assembly of the in core nuclear instrumentation assembly through a signal cable.
To stabilize boiling water reactors against neutron flux oscillations caused by thermal-hydraulic instabilities, random core-wide reactivity perturbations are induced in the reactor either to suppress the onset of asymmetric (regional) mode oscillations or, in response to the detection of asymmetric mode oscillations, to stabilize the reactor in a symmetric (core-wide) oscillation mode. The reactivity perturbations are produced by effecting random changes in dome pressure, core flow or coolant enthalpy.
A plurality of neutron flux sensors (44,46,48,50) and a corresponding plurality of gamma flux sensors (62,64,66,68) are distributed throughout axial zones (24,26,28,30) of the core (14) at the same or closely proximate locations. A steady state comparison, or bias, between the signals of a given neutron/gamma sensor pair are monitored (314, 316), and a divergence (or convergence) can readily be detected through simple signal filtering, to detect a shift in the bias. The pattern of significant convergence and divergence throughout the core, is indicative of the thermal hydraulic stability of the core.
A nuclear reactor instrumentation system including a plurality of incore nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core. The incore nuclear instrumentation assemblies each include a fixed type neutron detector having a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly having a plurality of fixed type gamma ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors. A power range detector signal processing device operatively connected to the fixed type neutron detector assemblies through signal cables. A gamma thermometer signal processing device is operatively connected to the fixed type gamma thermometer assembly of the incore nuclear instrumentation assembly through a signal cable.
A method and an apparatus are used for determining the neutron flux density of a neutron-emitting source, in particular a reactor core of a nuclear power facility. In the method, a first measurement signal and a second measurement signal, which differ from one another and are each monotonally dependent on the neutron flux density, are used to form a wide-range signal that depends uniquely on the neutron flux density. The wide-range signal is defined region-by-region, the wide-range signal is equated to the first measurement signal in a region where the values of the neutron flux density n are lower, n<n.sub.1, is equated to the second measurement signal in a region where the values of the neutron flux density are higher, n>n.sub.2, and is equated to a monotonal function of both measurement signals in an overlapping region located in between.
