JP5980500B2 - Reactor water level gauge - Google Patents

Description

  The present invention relates to a water level meter that measures the level of cooling water in a boiling water reactor, and more particularly to a reactor water level meter that directly measures the water level with a cooling water detector installed in the reactor.

  In a boiling water reactor, the cooling water supplied from the feed water pipe to the reactor is evaporated by the heat generated by the nuclear reaction in the core fuel, and the generated steam is led from the main steam pipe to the turbine, so that the turbine and the generator are Rotate to generate electricity. At this time, a water level that is a boundary between cooling water and steam is formed in the upper part of the core in the nuclear reactor. In the upper part of the core, a steam separator and a steam dryer are arranged to separate the steam and the cooling water, and the water level is monitored and controlled at an appropriate position to ensure the separation performance. Furthermore, in the event of an accident such as loss of cooling water, the water level is monitored and the safety function is activated according to the water level so that the core is not exposed from the cooling water and heat removal is not insufficient.

  Conventionally, the water level in a boiling water reactor is that the pressure from the reference height water column and the pressure corresponding to the water level in the reactor are led to the differential pressure transmitter outside the reactor by instrumentation piping, and output from this differential pressure transmitter. It is measured based on the differential pressure signal. A plurality of types of instrumentation pipes and differential pressure transmitters used for measurement are provided depending on the application. For example, in addition to the normal level water level meter that closely monitors a narrow range in order to keep the cooling water and steam separation performance high, there is a water level meter that covers a wide range to operate the safety function during a transient or accident. is set up.

  On the other hand, from the viewpoint of improving water level measurement responsiveness and ensuring diversity, methods for detecting the reactor water level directly in the reactor have been studied.

  In Patent Document 1, a sheath thermocouple is incorporated in a neutron detection pipe of a boiling water reactor, and a reactor core that detects the position of the water surface by using a temperature difference between the upper and lower surfaces of the water surface is disclosed. A monitoring device is disclosed.

  Patent Document 2 discloses a water level detector in the reactor in which thermocouples are arranged concentrically around a coaxially configured electrothermal heating element and are less susceptible to the magnetic field effect of the current flowing through the electrothermal heating element. ing.

JP 59-112290 A Japanese Patent Laid-Open No. 3-188327

  Measuring the water level in the reactor over the entire range is important to cope with all situations including accidents. It is necessary to prepare the water level measurement at the bottom of the core in case the core is damaged.

  As described above, the invention for directly measuring the water level in the nuclear reactor has been disclosed, but there are the following problems when applied to the measurement of the water level in the lower part of the core of the boiling water reactor. First, it is to avoid adding a through-hole to the bottom of the pressure vessel when placing the water level detector directly in the reactor. In order to measure the water level at the bottom of the core, it is necessary to insert a water level gauge from the bottom of the reactor into the reactor so that it does not interfere with the core and other reactor internal structures. There is. The addition of through holes is undesirable because it increases the possibility of coolant leakage and increases inspection and maintenance of the furnace bottom.

  If the reactor core monitoring device disclosed in Patent Document 1 and the reactor water level detector disclosed in Patent Document 2 are used, the conventional neutron detection pipe can be used, so that a new through hole is not provided. Although the water level detector can be inserted into the reactor, if the reactor water level drops to the lower part of the core, the water level in the neutron detection pipe does not match the water level at the lower part of the core. This is because the neutron detection pipe is inserted into the in-core instrument housing and the in-core instrument guide pipe arranged between the lower end of the core and the bottom of the pressure vessel. This is because the remaining cooling water does not drop from the lower end of the core, and therefore the water level in the neutron detection pipe inserted therein does not drop from the lower end of the core.

  Conventionally, the neutron detection pipe is provided with a through-hole for introducing cooling water, and the neutron detection pipe is filled with cooling water, but the through-hole is provided in the vicinity of the reactor core. The water level inside cannot be matched with the water level below the core. That is, the remaining problem is to provide a mechanism for matching the water level in the neutron detection pipe with the cooling water level when the cooling water level in the reactor drops to the lower part of the core.

  The present invention has been made in view of such problems, and the object of the present invention is to directly adjust the water level at the bottom of the core in the reactor without adding a through-hole to the bottom of the reactor pressure vessel. It is to provide a reactor water level meter that can measure, and in particular, to provide a reactor water level meter that can directly measure the water level even when the water level is low.

In order to achieve the above object, a reactor water level meter according to the present invention is a reactor water level meter for measuring the level of cooling water inside a pressure vessel of a boiling water reactor, and a vessel wall surface is provided at the bottom of the pressure vessel. and penetrating the furnace instrumentation housing and fixed, the neutron detection pipe that stores inserted into the furnace in the instrumentation housing neutron detector, lower than the core the lower end an internal of the neutron detection pipe A plurality of cooling water detectors arranged at a plurality of height positions, and provided in both the in-core instrument housing and the neutron detection pipe at a position below the plurality of height positions where the cooling water detectors are arranged. A coolant stop for sealing a cooling water through-hole, and a lower opening of the neutron detection pipe into which the plurality of cooling water detector cables and the neutron detector signal cable are inserted below the through-hole. and means, wherein the in The child detection pipe is inserted into the in-core instrument housing so as to prevent cooling water from leaking from between the in-core instrument housing, and the through-hole is connected to the neutron detection pipe. It is characterized in that the inside communicates with the inside of the pressure vessel .

  In the reactor water level meter of the present invention configured as described above, a neutron detection pipe is inserted into an in-reactor instrumentation housing that is fixed through the vessel wall surface at the bottom of the reactor pressure vessel. The cooling water level in the pressure vessel can be measured with a plurality of cooling water detectors arranged at a plurality of height positions. In addition, since a through-hole that leads cooling water to both the in-core instrument housing and the neutron detection piping is provided at a position lower than the plurality of height positions where the cooling water detectors are arranged, the cooling water level in the furnace Even when the temperature falls to the lower part of the core, the cooling water is guided through the through-hole, so that the water level in the neutron detection pipe matches the lowered water level in the reactor, and the water level can be measured directly and accurately.

  According to the present invention, even when the water level drops below the core of the boiling water reactor, it becomes possible to detect the reactor water level directly in the reactor, and it is possible to improve the water level measurement response and ensure diversity. Become. In addition, since temperature distribution measurement at the lower part of the core is possible, it can be used for grasping the core state when the core is damaged.

The conceptual diagram which shows the system configuration | structure of 1st Embodiment of the reactor water level meter which concerns on this invention. (A) is a cross-sectional view of the core of FIG. 1, (b) is a detail view of the main part of (a). The principal part longitudinal cross-sectional view of 1st Example of a cooling water detector. The principal part longitudinal cross-sectional view of 2nd Example of a cooling water detector. The principal part longitudinal cross-sectional view of 3rd Example of a cooling water detector. The conceptual diagram which shows the system configuration | structure of 2nd Embodiment of the reactor water level meter which concerns on this invention.

  Hereinafter, a first embodiment of a reactor water level gauge according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a conceptual diagram showing a system configuration of a reactor water level meter according to this embodiment, FIG. 2A is a cross-sectional view of the core of FIG. 1, and FIG. 2B is FIG. FIG.

  1 and 2, the coolant level detector 14 of the reactor water level meter is directly installed inside the reactor pressure vessel 1. The core 2 is surrounded by a shroud 5, and a large number of fuel assemblies (not shown) are installed between the core support plate 7 installed at the lower end of the core and the upper lattice plate 8 installed at the upper end. . A shroud upper lid 6 is attached to the upper portion of the shroud 5, and an air-water separator 3 and a steam dryer 4 for separating cooling water and steam are installed on the upper portion of the shroud upper lid 6.

  FIG. 2 is a horizontal cross-sectional view of the core 2 of FIG. 1, and a large number of fuel assemblies 33 are vertically arranged and supported between the core support plate 7 and the upper lattice plate 8. A large number of fuel rods (not shown) are accommodated in the fuel assembly 33. Inside the core 2, neutron detection pipes 11 are installed in gaps between a number of fuel assemblies 33. In the example of FIG. 2, 43 neutron detection pipes 11 are arranged vertically and horizontally for every four fuel assemblies so as to penetrate the core 2. In order to insert the neutron detection pipe 11, the nuclear reactor pressure vessel 1 is provided with a number of in-core instrument housings 9 that are vertically penetrated and fixed to the bottom vessel wall surface.

  The neutron detection pipe 11 includes an in-core instrument housing 9 welded directly to the lower part of the reactor pressure vessel 1, and an in-core instrument guide attached between the upper in-core instrument housing and the core support board 7. The upper end of the tube 10 is fixed to the upper lattice plate 8. Inside the neutron detection pipe 11, a metal-coated cable 15 containing a neutron detector 12, a scanning neutron detector guide tube 13, and a cooling water detector 14 is stored. The metal-coated cable 15 incorporating the cooling water detector 14 can be inserted into all the neutron detection pipes 11 shown in the figure, but as shown in the example of FIG. 2, the water level distribution in the pressure vessel is considered to some extent. It may be inserted into about 10 so that it can be done.

  In the present embodiment, two cooling water detectors 14a and 14b are arranged inside the left neutron detection pipe 11A, and three cooling water detectors 14c, 14d, 14e is arranged. The right cooling water detector 14c is arranged at the highest position, the left cooling water detector 14a is arranged at the second highest position, and the right cooling water detector 14d is at the third highest position, that is, The left cooling water detector 14b is disposed at the fourth highest position, that is, the second cooling water detector 14b from the bottom, and the right cooling water detector 14e is disposed at the lowest position. The five coolant detectors are arranged at equal intervals. Note that the upper interval can be set appropriately, such as increasing the interval and decreasing the interval downward.

  The neutron detection pipe 11 passes through the lower part of the reactor pressure vessel 1 through the in-core instrumentation guide tube 10 and the in-core instrument housing, and a signal from the neutron detector 12 is transmitted from the lower end of the neutron detection pipe 11. The cable, the end of the scanning neutron detector guide tube 13, and the end of the metal-coated cable 15 are drawn out. A connector 16 is attached to the metal-coated cable 15, one end of the multi-core cable 17 is connected to the connector, and the other end is connected to the signal processing device 21.

  Both the in-core instrument housing 9 and the neutron detection pipe 11 are provided with through-holes 18 and 19 for guiding the cooling water in the lower part of the core at a position lower than the cooling water detector 14. The neutron detection pipe 11 is also provided with a similar through-hole 20 at the upper part of the core. The through hole 18 and the through hole 19 are formed at the same height position from the bottom surface of the reactor pressure vessel 1, and in the example of FIG. 1, the through hole 19 having a diameter larger than the through hole 18 is formed concentrically. . Further, the through holes 18 and 19 of the right neutron detection pipe 11B are formed at lower positions than the through holes 18 and 19 of the left neutron detection pipe 11A because the bottom surface of the container 1 is lower. For this reason, the cooling water 22 in the pressure vessel 1 is guided into the neutron detection pipe 11 through the lower through holes 18 and 19.

Furnace instrumentation housing 9 is formed into a cylindrical shape the upper and lower openings, the inside, neutron detection pipe 11 from above lateral openings so that the are inserted. The lower end portion of the in-core instrument housing 9 is in close contact with the outer periphery of the neutron detection pipe 11 so that water does not leak even if the cooling water 22 enters the housing. Further, a neutron detector 12 and a lead wire, a scanning neutron detector guide tube 13 and a metal-coated cable 15 are inserted into the neutron detection pipe 11 from its lower opening, and sealed with a water stopcock 23, The cooling water 22 does not leak to the outside.

  Next, the operation of the reactor water level meter of this embodiment will be described. The cooling water 22 in the reactor pressure vessel 1 usually covers the core 2 and absorbs heat generated from the core, and a part thereof becomes steam. Steam and cooling water containing steam are separated from steam and cooling water by the steam separator 3 and the steam dryer 4, a water level is formed in the upper part of the core, and the water level is monitored and controlled by a water level gauge for normal operation (not shown). On the other hand, the system of the present embodiment is used when an accident involving core damage occurs and the water level of the cooling water 22 decreases to the lower part of the core.

  According to the present embodiment, even when the water level of the cooling water 22 is lowered to the lower part of the core, the neutrons are formed at the through holes 18 and 19 provided in the in-core instrument housing 9 and the neutron detection pipe 11 and the upper part of the core in the lower part of the core. Due to the through-hole 20 provided in the detection pipe 11, the upper and lower pressures in the pipe are balanced in a state where the water level of the same height as that in the furnace is formed in the neutron detection pipe 11. The cooling water detector 14 installed in the neutron detection pipe 11 detects the presence or absence of cooling water around each detector.

  For example, when there is a water level at the height shown in FIG. 1, since there is no cooling water around the cooling water detector 14a inside the neutron detection pipe 11A, a Low signal is output. On the other hand, since there is cooling water around 14b, a High signal is output. Similarly, the signals output from the coolant detectors 14c, 14d, and 14e inside the neutron detection pipe 11B are Low, Low, and High, respectively. These output signals are transmitted to the signal processing device 21 via the metal-coated cable 15 and the multicore cable 17. The signal processing device 21 stores in advance the installation height of each detector, detects the water level in the reactor from the presence or absence of cooling water at each height, and outputs the result.

  In this embodiment, since the heights of the cooling water detectors 14a, 14b, 14c, 14d, and 14e are changed in the two neutron detection pipes 11A and 11B, it is detected that there is a water level between 14b and 14d. The The signal processing device 21 outputs the height of the midpoint between 14b and 14d as the current water level. Similarly, the number of cooling water detectors 14 installed in one neutron detection pipe 11 by installing a plurality of cooling water detectors 14 at three or more different height positions in three or more neutron detection pipes 11. A more accurate water level gauge can be realized without increasing the value. That is, the accuracy can be improved without being limited by the number of cores of the connector 16 and the multicore cable 17. Moreover, in this embodiment, as shown in FIG. 2, since the cooling water detector 14 is inserted into 10 neutron detection pipes among the 43 neutron detection pipes 11, the reactor core is damaged. In addition, the temperature distribution in the core stock can be measured, and the core state can be accurately grasped.

  FIG. 3 shows a first embodiment of the cooling water detector 14. The metal sheathed cable 15 is filled with a ceramic insulator 24, and cooling water detectors 14A, 14B, and 14C are installed at a plurality of height positions (three locations in FIG. 3). Each of the cooling water detectors 14 </ b> A to 14 </ b> C includes a thermocouple 25 and a metal heat generating portion 26 that is in thermal contact with the thermocouple 25 (electrically insulated). The cooling water detectors 14A to 14C installed at the lower part of the core generate heat by the gamma rays from the core or the like being absorbed by the metal heating part 26. At this time, if the cooling water 22 exists around the cooling water detectors 14 </ b> A to 14 </ b> C, the metal heat generating portion 26 has a temperature close to the cooling water 22. . By comparing these temperatures, the signal processing device 21 separates the temperature when there is cooling water around and the temperature when there is no cooling water, and detects the water level.

  FIG. 4 shows a second embodiment of the cooling water detector 14. In addition to the configuration of FIG. 3, a cooling water detector 14D for measuring a reference temperature is added below the through holes 18 and 19 provided in the in-core instrument housing 9 and the neutron detection pipe 11. Yes. According to the configuration of FIG. 4, even if the reactor water level is lowered to a position lower than the through holes 18 and 19, the inside of the in-core instrument housing 9 and the neutron detection pipe 11 have a high level of the through holes 18 and 19. Cooling water remains. Therefore, the accuracy and reliability of water level detection can be improved by comparing the response of the cooling water detector 14D installed at a position lower than the through holes 18 and 19 with the response of the other cooling water detectors 14A to 14C. .

  For example, as shown in FIG. 3, when all the coolant detectors 14 are located higher than the through holes 18 and 19, when the water level of the reactor falls below the vicinity of the through holes 18 and 19, There is no cooling water around the detectors 14A to 14C, and there is no significant difference in the temperature of the cooling water detectors 14 at a plurality of height positions. In this case, it is difficult to easily determine whether the water level is above or below all of the cooling water detectors 14A to 14C, or whether the detector itself is defective. As a result, discrimination combined with past water level trend data, comparison with temperature at the time when the water level could be clearly discriminated in the past, and the like become necessary, and the discrimination method becomes complicated.

  On the other hand, in the example of FIG. 4, the temperature detected by the cooling water detector 14 </ b> D below the through-holes 18 and 19 is a temperature when there is surely surrounding cooling water. By comparing the temperature of the thermocouples 25 of the cooling water detectors 14A to 14C at the upper part, even when the water level drops below the vicinity of the through holes 18 and 19, the water level can be easily changed. It can be determined that the voltage has dropped below the vicinity.

  FIG. 5 shows a third embodiment of the cooling water detector 14. In addition to the configuration of FIG. 3, a heating wire 27 is added to the cooling water detectors 14 </ b> A to 14 </ b> C in the vicinity of the thermocouple 25. When the water level is detected, a current is applied to the heating wire 27 by a power source built in the signal processing device 21 (not shown) to cause the metal heat generating portion 26 to generate a certain amount of heat. Due to this heat generation, a temperature difference between when the cooling water detectors 14A to 14C are present and when there is no cooling water 22 is detected. Compared with the example of FIG. 3, even when the radiation from the core or the like is small, a temperature difference can be generated stably and the reliability is improved.

  Next, a second embodiment of the reactor water level meter according to the present invention will be described. FIG. 6 is a conceptual diagram showing the system configuration of the reactor water level meter of the present embodiment. Similar to the configuration of the first embodiment shown in FIG. 1, the coolant detector 14 of the reactor water level meter installed in the metal-coated cable 15 is arranged inside the neutron detection pipe 11 installed in the reactor core 2. Are stored together with a neutron detector 12 and a guide tube 13 for a scanning neutron detector. The neutron detection pipe 11 passes through the lower part of the reactor pressure vessel 1 through the in-core instrumentation guide tube 10 and the in-core instrument housing 9, and the end of the metal-coated cable 15 extends from the lower end of the neutron detection pipe 11. The part is pulled out, and the connector 16 is attached to the end. One end of a multi-core cable 17 is connected to the connector 16, and the other end is connected to the signal processing device 21. The in-core instrument housing 9 and the neutron detection pipe 11 are provided with through-holes 18 and 19 for guiding the cooling water in the lower part of the core at a position lower than the cooling water detector 14. The neutron detection pipe 11 is also provided with a similar through-hole 20 at the upper part of the core.

  In the second embodiment, a water level gauge based on a conventional differential pressure signal is added in addition to the above-described configuration. A high pressure side instrumentation pipe 28 is connected to the reactor pressure vessel 1 in a gas phase portion where steam above the core exists, and a water surface of a certain height is formed in the steam condensing tank 29. A pipe connected to the high pressure side of the differential pressure transmitter 31 is attached to the vapor condensing tank 29. Further, a low-pressure instrumentation pipe 30 is connected to the liquid phase portion where the cooling water of the reactor pressure vessel 1 exists, and is led to the low-pressure side of the differential pressure transmitter 31. Here, the low-pressure side instrumentation pipe 30 is the reactor pressure vessel 1 at a position lower than the highest detector (14a in FIG. 6) among the cooling water detectors 14 installed in the metal-coated cable 15. It is connected to the liquid phase part.

  The operation will be described below. In the cooling water 22 in the reactor pressure vessel 1, the water level is usually formed in the upper part of the core, and the water level is monitored by the water level monitoring device 32 using the differential pressure transmitter 31. On the other hand, in the unlikely event that an accident involving core damage occurs and the water level of the cooling water 22 decreases to the lower part of the core, the differential pressure is maintained while the water level is higher than the low-pressure instrumentation pipe 30. Both the water level monitoring using the transmitter 31 and the water level monitoring using the cooling water detector 14 installed in the metal-coated cable 15 are performed. Then, by comparing the water level monitoring results by the two methods with the water level monitoring device 32, the soundness of both water level monitoring is confirmed, and the response of the cooling water detector 14 with and without cooling water in the surroundings is confirmed. Get a reference.

  For example, in the case of the cooling water detector 14 including the thermocouple 25, the metal heating part 26 and the heating wire 27 shown in FIG. 5, the temperature rise or change when the metal heating part 26 is heated by the heating wire 27. The presence or absence of cooling water is determined based on the rate. In this embodiment, since the information on the rising temperature or the rate of change when the presence or absence of cooling water is known using the differential pressure transmitter 31, the cooling water is obtained. The accuracy and reliability of detection of the presence or absence of cooling water using the detector 14 can be improved.

  In the embodiment shown in FIG. 6, one metal-coated cable 15 is inserted into one in-core instrument housing 9, and the coolant level is detected by the three coolant detectors 14 a to 14 c. You may comprise so that the water level of a cooling water may be detected and measured by inserting the metal-coated cable provided with the several cooling water detector in the several in-core instrument housing.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In the above-described embodiment, an example in which the cooling water detector is configured by a metal heat generating portion and a thermocouple has been described. However, the present invention is not limited to this, and a device for detecting other water may be used. Of course.

DESCRIPTION OF SYMBOLS 1 Reactor pressure vessel 2 Core 3 Steam-water separator 4 Steam dryer 5 Shroud 6 Shroud upper lid 7 Core support board 8 Upper lattice board 9 In-core instrument housing 10 In-core instrumentation guide pipe 11 Neutron detection piping 12 Neutron detection 13 Scanning neutron detector guide tube 14, 14a to 14c, 14A to 14D Cooling water detector 15 Metal-coated cable 16 Connector 17 Multi-core cable 18 Through port 19 Through port 20 Through port 21 Signal processing device 22 Cooling water 23 Stop Water faucet 24 Ceramic insulator 25 Thermocouple 26 Metal heating part 27 Heating wire 28 High-pressure side instrumentation pipe 29 Steam condensing tank 30 Low-pressure side instrumentation pipe 31 Differential pressure transmitter 32 Water level monitoring device 33 Fuel assembly

Claims (10)

A reactor water level meter that measures the level of cooling water inside the pressure vessel of a boiling water reactor,
An in-core instrument housing fixed to the bottom of the pressure vessel through the container wall surface, a neutron detection pipe inserted into the in-core instrument housing to store the neutron detector, and the neutron detection pipe A plurality of cooling water detectors disposed at a plurality of height positions below the lower end of the core, and the in-core instrument housing and the neutron at a position below the plurality of height positions at which the cooling water detectors are disposed. A cooling water through-hole provided in both of the detection pipes, a plurality of cooling water detector cables and a neutron detector signal cable inserted below the through-holes in the neutron detection pipe A water stop means for sealing the lower opening,
The neutron detection pipe is inserted into the in-core instrument housing to prevent leakage of cooling water from between the in-core instrument housing,
The reactor water level meter, wherein the through-hole communicates between the inside of the neutron detection pipe and the inside of the pressure vessel.   The reactor water level meter according to claim 1, wherein the plurality of cooling water detectors are fixed at a plurality of height positions of a metal-coated cable inserted into the neutron detection pipe.   An in-core instrumentation guide tube is provided in communication between the upper part of the in-core instrument housing and the core support board, and the neutron detection pipe is provided in the in-core instrument housing and the in-core instrument guide. The reactor water level meter according to claim 1 or 2, wherein the reactor water level meter is inserted into a pipe. The metal-coated cable includes a signal cable having one end connected to the plurality of cooling water detectors and the other end penetrating through the neutron detection pipe and drawn out of the pressure vessel. The reactor water level meter according to claim 2 , wherein the water level signal output from the plurality of cooling water detectors is supplied to a signal processing device. The pressure vessel is provided with a plurality of the furnace instrumentation housing, any one of claims 1 to 4 wherein the neutron detecting piping for being inserted into the plurality of furnace instrumentation housing Reactor water level meter as described in 1.   The reactor water level meter according to claim 5, wherein the plurality of cooling water detectors arranged in the plurality of neutron detection pipes are arranged at different height positions. Cooling water when the cooling water detector different from the cooling water detector is installed below the cooling water through-hole, and there is cooling water inside the in- core instrument housing and the neutron detection pipe The reactor water level meter according to any one of claims 1 to 6, wherein a reference temperature is measured. The reactor water level meter according to any one of claims 1 to 7, wherein the cooling water detector includes a metal heating part and a thermocouple. The reactor water level meter according to any one of claims 1 to 7, wherein the cooling water detector includes a metal heating part, a thermocouple, and a heating wire. The pressure vessel is connected to a gas phase portion inside thereof and connected to a high-pressure side instrumentation pipe for introducing a constant height of cooling water to which vapor or vapor pressure of the gas phase portion is applied, and to a liquid phase portion inside the pressure vessel. The low pressure side instrumentation pipe for guiding the cooling water in the liquid phase part, the differential pressure transmitter for detecting and transmitting the pressure difference between the low pressure side instrumentation pipe and the high pressure side instrumentation pipe, and the output of the differential pressure transmitter A water level monitoring device that converts the signal into a water level signal,
The connection portion of the low-pressure side instrumentation pipe to the pressure vessel is located at a lower height than that at the top of the cooling water detector, and at the height position of the uppermost cooling water detector. reactor water level gauge according cooling water presence to any one of claims 1 to 9, characterized in that detected by the water level monitoring devices.

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