Patent Number: 
Section: claims

1. A reactor state monitoring apparatus comprising:a pressure vessel;a biological shielding wall at least partially surrounding the pressure vessel;a containment vessel surrounding the biological shielding wall;a first radiation measuring device configured to detect and measure a gamma radiation dose in an atmosphere which is located in between the containment vessel and the biological shielding wall;a second radiation measuring device configured to detect and measure a gamma radiation dose in between the pressure vessel and the biological shielding wall;a third radiation measuring device located in between the pressure vessel and the biological shielding wall and configured to detect and measure a gamma radiation dose of a fuel contained in the pressure vessel;a dosage/water level diagram storage memory configured to store a dosage/water level diagram indicating a relation between measurement values of the second radiation measuring device and water levels corresponding to water amounts of a cooling water in the pressure vessel; anda water amount evaluation device configured to:calculate a difference between the gamma radiation dose measured by the first radiation measuring device and the gamma radiation dose measured by the third radiation measuring device as a corrected fuel radiation dose, thenread out the dosage/water level diagram from the dosage/water level diagram storage memory, thencorrect the read dosage/water level diagram with use of the corrected fuel radiation dose, and thenacquire a water level of the cooling water corresponding to the radiation dose measured by the second radiation measuring device based on the corrected dosage/water level diagram as a water level evaluation value. 2. The reactor state monitoring apparatus according to claim 1, wherein the second radiation measuring device is configured to detect the radiation at least above an upper end of the fuel, and the third radiation measuring device is configured to detect a radiation dose at least below a lower end of the fuel. 3. The reactor state monitoring apparatus according to claim 1, wherein the second radiation measuring device and the third radiation measuring device are configured to detect a gamma-ray dose of 511 keV or more. 4. The reactor state monitoring apparatus according to claim 1, further comprising:a thermocouple water gauge provided inside the pressure vessel and having a heater;an operating state/output relation storage memory configured to store a correspondence table in which outputs of the thermocouple water gauge detected by the thermocouple water gauge based on radiation or heat of the heater are each made to correspond to a relation between operating states of the reactor and the water levels, and in which outputs of the second radiation measuring device are made to correspond to a relation between the operating states of the reactor and the water levels; anda state estimation device configured to evaluate an operating state of the reactor based on the correspondence table read out from the operating state/output relation storage memory, an output of the thermocouple water gauge, and an output of the second radiation measuring device. 5. The reactor state monitoring apparatus according to claim 4, wherein the thermocouple water gauge is provided in a plurality of places along a vertical direction of the pressure vessel, and the state estimation device configured to estimate a height-direction range of a gas-liquid two-phase flow in the pressure vessel based on a plurality of outputs of the thermocouple water gauges and the water level evaluation value. 6. The reactor state monitoring apparatus according to claim 1, further comprising:a thermocouple water gauge provided in the pressure vessel and configured to detect a water level in the pressure vessel; anda state estimation device configured to estimate a position of the fuel based on the water level detected by the thermocouple water gauge and an output ratio of the second radiation measuring device and the third radiation measuring device,wherein the second radiation measuring device is configured to detect the radiation at least above an upper end of the fuel, and the third radiation measuring device is configured to detect a radiation dose at least below a lower end of the fuel. 7. The reactor state monitoring apparatus according to claim 1, further comprising:a thermocouple water gauge provided in the pressure vessel and configured to detect a water level in the pressure vessel;a first storage memory configured to store an output of the thermocouple water gauge;a second storage memory configured to store the water level evaluation value; anda state estimation device configured to estimate a reactor state based on history information on the reactor states stored in the first storage memory and the second storage memory. 8. The reactor state monitoring apparatus according to claim 7, wherein the reactor state is at least one of a state whether the fuel is melted or not, and a state whether the thermocouple water gauge is broken down or not. 9. The reactor state monitoring apparatus according to claim 1,wherein the second radiation measuring device is configured to detect the radiation at least above an upper end of the fuel, and the third radiation measuring device is configured to detect a radiation dose at least below a lower end of the fuel, andwherein the second radiation measuring device and the third radiation measuring device are configured to detect a gamma-ray dose of 511 keV or more. 10. The reactor state monitoring apparatus according to claim 9, further comprising:a thermocouple water gauge provided inside the pressure vessel and having a heater;an operating state/output relation storage memory configured to store a correspondence table in which outputs of the thermocouple water gauge detected by the thermocouple water gauge based on radiation or heat of the heater are each made to correspond to a relation between operating states of the reactor and the water levels, and in which outputs of the second radiation measuring device are made to correspond to a relation between the operating states of the reactor and the water levels; anda state estimation device configured to evaluate an operating state of the reactor based on the correspondence table read out from the operating state/output relation storage memory, an output of the thermocouple water gauge, and an output of the second radiation measuring device. 11. The reactor state monitoring apparatus according to claim 1, further comprising:a thermocouple water gauge provided inside the pressure vessel and having a heater;an operating state/output relation storage memory configured to store a correspondence table in which outputs of the thermocouple water gauge detected by the thermocouple water gauge based on radiation or heat of the heater are each made to correspond to a relation between operating states of the reactor and the water levels, and in which outputs of the second radiation measuring device are made to correspond to a relation between the operating states of the reactor and the water levels; anda state estimation device configured to evaluate an operating state of the reactor based on the correspondence table read out from the operating state/output relation storage memory, an output of the thermocouple water gauge, and an output of the second radiation measuring device,wherein the second radiation measuring device is configured to detect the radiation at least above an upper end of the fuel, and the third radiation measuring device is configured to detect a radiation dose at least below a lower end of the fuel. 12. The reactor state monitoring apparatus according to claim 1, further comprising:a thermocouple water gauge provided inside the pressure vessel and having a heater;an operating state/output relation storage memory configured to store a correspondence table in which outputs of the thermocouple water gauge detected by the thermocouple water gauge based on radiation or heat of the heater are each made to correspond to a relation between operating states of the reactor and the water levels, and in which outputs of the second radiation measuring device are made to correspond to a relation between the operating states of the reactor and the water levels; anda state estimation device configured to evaluate an operating state of the reactor based on the correspondence table read out from the operating state/output relation storage memory, an output of the thermocouple water gauge, and an output of the second radiation measuring device,wherein the second radiation measuring device and the third radiation measuring device are configured to detect a gamma-ray dose of 511 keV or more.