Patent Number: 043199593
Section: claims

1. In a boiling water reactor wherein a plurality of fuel assemblies constitute a reactor core and the fuel assemblies are cooled by a two-phase coolant flow which exhibits a density wave oscillation, a method of supervising the stability of said oscillation comprising the steps of determining a thermal power and a coolant flow quantity in each fuel assembly by signals produced by a plurality of in-core neutron flux detectors installed in said reactor core, and by signals regarding such operating conditions of said reactor core as inserted positions of control rods, a total flow quantity of the reactor core and the thermal power of the core determined by the heat balance of a nuclear power plant, judging the stability of said oscillation of each fuel assembly from said thermal power and the coolant flow quantity in said fuel assembly as well as from measured values of such parameters as inlet subcooling of the core and a pressure in a reactor vessel, or determining a stability limit of a selected one from said thermal power of the core or said total flow quantity of the reactor core or parameters described above, and comparing said stability limit with a measured value thereof so as to determine a stability margin. 2. The method according to claim 1, which further comprises the step of identifying a most unstable fuel assembly in said reactor core thereby facilitating the supervision of the whole core. 3. In a boiling water reactor wherein a plurality of fuel assemblies constitute a reactor core and the fuel assemblies are cooled by a two-phase coolant flow which exhibits a density wave oscillation, and a plurality of in-core neutron flux detectors are installed along the flow of said coolant, a method of superivsing the stability of said oscillation comprising the steps of determining a thermal power in each fuel assembly by signals produced by a plurality of said in-core neutron flux detectors, and by signals regarding operating conditions of the reactor, measuring a mutual correlation function of the output signals of said neutron flux detectors installed along the flow of said coolant so as to determine a propagation time of a disturbance in the coolant flow, determining the flow quantity of the coolant in each fuel assembly from said propagation time, judging the stability of said oscillation of each fuel assembly from said thermal power and said coolant flow quantity in said fuel assembly as well as from measured values of such parameters as inlet sub-cooling of the core and a pressure in a reactor vessel or determining a stability limit of a selected one from said thermal power of the core or said total flow quantity of the reactor core or said parameters, and comparing said stability limit with a measured value thereof so as to determine a stability margin. 4. The method according to claim 3, which further comprises the step of identifying a most unstable fuel assembly in said reactor core thereby facilitating the supervision of the whole core. 5. In a boiling water type nuclear reactor having a plurality of fuel channels forming a reactor core, each of said fuel channels being cooled by a quantity of coolant flowing through each channel, a method for supervising channel stability comprising: 6. A method for supervising the channel stability in a reactor core of a nuclear reactor of the type wherein a plurality of fuel channels are provided having coolant flow therethrough comprising: 7. A method for supervising the channel stability in a reactor core of a nuclear reactor of the type wherein a plurality of fuel channels are provided having coolant flow therethrough comprising: