JP5291888B2 - Control rod withdrawal monitoring method and control rod withdrawal monitoring system - Google Patents

Description

  The present invention relates to a control rod drawing monitoring method and a control rod drawing monitoring system, and more particularly to a control rod drawing monitoring method and a control rod drawing monitoring system suitable for application to a boiling water reactor.

  A conventional control rod withdrawal monitoring system includes a control rod withdrawal monitoring device and a control rod operation monitoring device. The control rod withdrawal monitoring device may increase the output near the control rod due to excessive withdrawal of the selected control rod, and the thermal margin of the fuel rod, that is, the minimum critical power ratio (MCPR) may be less than the safety critical value. LPRM signal related to the neutron flux in the core detected by a plurality of local power region monitors (hereinafter referred to as “LPRM”) equally distributed in the core, and the core flow rate installed in the reactor The core flow rate signal from the detector and the control rod operation monitoring device (hereinafter referred to as RC & IS or RMCS. In this specification, only RC & IS is described.) Monitor the pull-out operation. When a control rod to be operated is selected, the control rod pull-out monitoring device inputs a position signal of the selected control rod from RC & IS and selects an LPRM signal around the selected control rod for monitoring the control rod. The control rod withdrawal monitoring device calculates a control rod monitoring value (hereinafter referred to as RBM value) used for control rod withdrawal monitoring based on the selected LPRM signal. Further, the control rod withdrawal monitoring device inputs a core flow rate signal that is an output of the core flow rate detector, and a control rod withdrawal prevention set value (hereinafter referred to as RBL value) as a function of the core flow rate based on this signal. calculate. The control rod pull-out monitoring device compares the calculated RBM value with the RBL value using a comparator. If the RBM value increases due to excessive pulling of the control rod due to an operator's erroneous operation, and reaches the RBL value, the control rod pulls the control rod to RC & IS. Outputs a pull-out prevention signal. RC & IS stops the control rod pulling-out operation by the control rod driving device when the control rod pull-out prevention signal is inputted. By stopping the control rod drawing operation, excessive control rod drawing is prevented, so that the fuel rod is kept sound. The control rod pull-out monitoring device has a plurality of RBL values (usually three). The control rod pull-up monitoring device changes the RBL value to a higher level according to the request of the operator or the RBL value setup function of the control rod pull-out monitoring device. It has the function of excluding bar pullout prevention.

  Patent Documents 1 and 2 are prior art documents related to a control rod pull-out monitoring device.

JP 57-136197 A JP 2000-162356 A

  A conventional control rod withdrawal monitoring device has a plurality (usually three) of RBL values with the core flow rate as a variable. These RBL values are set in the vicinity of the rated power of the nuclear reactor and are fixed unless there is a change request from the operator. In the conventional control rod pull-out monitoring device, the RBL value is set in the vicinity of the rated output, so if an excessive control rod pull-out operation due to an erroneous operation by the operator or the like occurs in a state where the reactor power is low Even if there is a margin in the RBM value, the change in the thermal margin increases depending on the state of the fuel assembly in the core. For this reason, it may be considered that some of the fuel rods become thermally severe. Therefore, from the standpoint of fuel rod protection, it is desirable to expand the range of reactor power for monitoring control rod withdrawal when it is required to operate the control rod on the safer side. By extending the range of the reactor power, the inventors have been able to confirm the thermal margin of the fuel rods and monitor the withdrawal of the control rods in any reactor operating range from low power to rated power. I came up with a rod pull-out monitoring system.

  An object of the present invention is to provide a control rod withdrawal monitoring method and a control rod withdrawal monitoring system capable of realizing a control rod withdrawal operation with higher safety in a reactor operation range from a low power state to a rated power state of the reactor. It is to provide.

A feature of the present invention that achieves the above-described object is that a control rod withdrawal monitoring device generates a first control rod withdrawal prevention signal based on a neutron detection signal output from a local output region monitor disposed in a reactor core, The withdrawal monitoring auxiliary device generates a second control rod withdrawal prevention signal when the minimum limit power ratio calculated when the control rod is withdrawn from the core is less than or equal to the minimum limit power ratio set value calculated by the arithmetic unit. rod withdrawal monitoring auxiliary apparatus, and outputs either one of the pull-out blocking signal of the first control rod withdrawal inhibit signal and the second control rod withdrawal inhibit signal input from the control rod withdrawal monitoring device, a control rod drive control apparatus The control rod withdrawal monitoring auxiliary device outputs the control rod based on any one of the withdrawal prevention signals to stop the withdrawal of the control rod ,
When the control rod withdrawal monitoring auxiliary device inputs a control rod operation command and the reactor output is equal to or greater than the reactor power set value, it outputs a minimum limit output ratio calculation command to the calculation device, and the calculation device outputs the minimum limit output. in Rukoto to calculate the minimum critical power ratio when inputting the ratio calculated command.

The present invention can stop pulling out of the control rod when the minimum limit power ratio at the time of pulling out the control rod from the core is equal to or less than the minimum limit power ratio set value. In the operation region of the reactor that reaches the state, it is possible to realize a control rod pulling operation with higher safety. Furthermore, when the control rod withdrawal monitoring auxiliary device inputs a control rod operation command and the reactor output is equal to or greater than the reactor power set value, it outputs a minimum limit power ratio calculation command to the calculation device, and the calculation device is the minimum Since the minimum limit output ratio is calculated when the limit output ratio calculation command is input, the thermal margin can be monitored each time the control rods are pulled out, and the unnecessary thermal monitoring of the core can be avoided. A highly efficient control rod pulling out operation can be realized more rationally.

  ADVANTAGE OF THE INVENTION According to this invention, the extraction operation | movement of a control rod with higher safety | security is realizable in the operation area | region of the reactor from the low power state of a nuclear reactor to a rated power state.

  In the conventional control rod pull-out monitoring device, the RBL value is set in the vicinity of the rated output, so if an excessive control rod pull-out operation due to an erroneous operation by the operator or the like occurs in a state where the reactor power is low Even if there is a margin in the RBM value, the change in the thermal margin increases depending on the state of the fuel assembly in the core. For this reason, it may be considered that some of the fuel rods become thermally severe. The present invention has been made to solve this problem newly found by the inventors.

  Examples of the present invention will be described below.

  A control rod pull-out monitoring system which is a preferred embodiment of the present invention will be described with reference to FIG. A control rod pull-out monitoring system 1 according to this embodiment includes a control rod pull-out monitoring device (hereinafter referred to as RBM) 2, a control rod pull-out monitoring auxiliary device 3, a control rod operation monitoring device (hereinafter referred to as RC & IS) 10, and a control rod driving auxiliary. A board 11 is provided.

  An outline of a boiling water reactor (BWR) to which the control rod withdrawal monitoring system 1 is applied will be described. The nuclear reactor 26 includes a nuclear reactor pressure vessel 27, a core loaded with a plurality of fuel assemblies 28, and a plurality of control rods 29. Four fuel assemblies 28 surround one control rod 29. The core is disposed in the reactor pressure vessel 27, and a control rod 29 is inserted into the core. The control rod 29 is inserted between the adjacent fuel assemblies 28. Each control rod 29 is separately connected to a control rod drive mechanism (hereinafter referred to as CRD) 30. The CRD 30 is installed in a CRD housing (not shown) attached to the bottom of the reactor pressure vessel 27, and performs an operation of inserting the control rod 29 into the core and an operation of extracting the control rod 29 from the core. A plurality of LPRM assemblies 32 including four local output region monitors (hereinafter referred to as LPRMs) 31 arranged in the axial direction of the core interfere with the operation of the control rod 29 between the fuel assemblies 28 in the core. It is placed at a position that does not become necessary. These LPRM assemblies 32 are arranged at positions that are to be subjected to 1/4 rotation in the core. A core flow rate detector 33 is installed in the reactor pressure vessel 27.

  A detailed configuration of the control rod pull-out monitoring auxiliary device 3 will be described with reference to FIG. The control rod withdrawal monitoring auxiliary device 3 includes a first determiner 4, an AND circuit (arithmetic command device) 5, a second determiner (control rod withdrawal prevention signal generator) 6, and an OR circuit 7. In the first determination device 4, each input terminal is connected to the reactor power setting device 38 by the wiring 13, and is connected to an average output region monitor (hereinafter referred to as APRM) 37 by the wiring 14. The reactor power setting device 38 is installed on the operation panel 12. Each output terminal of the first determiner 4 is connected to the input terminal of the AND circuit 5 by the wiring 16 and to the RC & IS 10 by the wiring 23. The other input terminal of the AND circuit 5 is connected to the RC & IS 10 by a wiring 15. The wiring 17 connects the output terminal of the AND circuit 5 and the process computer 8. The input terminal of the second determiner 6 is connected to the process computer 8 by a wiring 18. The display device 9 installed on the operation panel 12 is connected to the wiring 18 by the wiring 19. The two input terminals of the OR circuit 7 are connected to the output terminal of the second determiner 6 by the wiring 20 and to the RBM 2 by the wiring 21. The output terminal of the OR circuit 7 is connected to the RC & IS 10 by a wiring 22.

  The connection state of other components will be described below with reference to FIG. RC & SI 10 is connected to operation panel 12 by wiring 40. The control rod drive auxiliary board 11 is connected to the RC & IS 10 by wiring 25 and is connected to the CRD 30 by wiring 34. The wiring 36 connects the core flow rate detector 33 and the RBM 2. The wirings 35-1 to 35 -n connected to each LPRM 31 one by one are connected to the RBM 2. These wirings 35-1 to 35 -n are connected to the APRM 37 by wirings 39. A wiring 47 connects the RBM 2 and the process computer 8. RBM 2 is connected to operation panel 12 by wiring 24.

  At the start of the BWR, the control rod 29 is pulled out of the core and changes from the subcritical state to the critical state. Thereafter, the reactor power is increased to the rated power through a temperature raising and pressure increasing process in which the control rod 29 is further pulled out. With respect to such pulling of the control rod 29, control rod drawing information of the control rod drawing sequence is sequentially displayed on the display device 9 of the operation panel 12. The extraction information of the control rod 29 includes position information of the control rod 29 to be extracted and information on the extraction amount. Based on the control rod extraction information displayed on the display device 9, the operator inputs, from the operation panel 12, position information and extraction amount information on the core cross section of the control rod 29 to be extracted. By inputting these pieces of information, a control rod operation command 41 for the corresponding control rod 29 is output from the operation panel 12. The control rod operation command 41 is input to the RC & IS 10 via the wiring 40. The RC & IS 10 outputs a control rod withdrawal control command 42 to the control rod drive auxiliary board 11 based on the control rod operation command 41. The extraction signal 43 output from the control rod drive auxiliary board 11 based on the control rod extraction control command 42 drives the CRD 30 that operates the corresponding control rod 29. As a result, the control rod 29 is withdrawn from the core by the designated withdrawal amount (the number of notches). In the process of increasing the reactor power, the reactor power is increased by pulling out the control rod 29. In particular, the output is increased by the four fuel assemblies 28 adjacent to the control rod 29 to be pulled out.

  During the operation of the BWR, cooling water is supplied to the core, and the fuel rods included in the fuel assembly 28 are cooled. The flow rate of cooling water supplied to the core is detected by the core flow rate detector 33. The core flow rate detector 33 that has detected the coolant flow rate outputs a core flow rate signal 45.

  Each LPRM 31 provided in each LPRM assembly 32 arranged in the reactor core detects a neutron flux generated by fission of each fuel material contained in the fuel assembly 28, and this neutron flux detection signal (hereinafter referred to as a neutron flux detection signal). LPRM signal). LPRM signals (neutron detection signals) 44-1 to 44-n output from the respective LPRMs are input to the APRM 37 through the wirings 35-1 to 35-n and 39. The APRM 37 averages the LPRM signals 44-1 to 44-n to obtain the reactor power.

  The operation of the control rod pull-out monitoring system 1 of the present embodiment will be described. When the control rod 29 selected due to an operator's erroneous operation or the like is excessively pulled out and the output increase in the fuel assembly 28 located around the control rod 29 to be pulled out becomes large, the RBM 2 In order to secure a thermal margin, it has a function of preventing the control rod 29 from being pulled out. Therefore, the RBM 2 inputs the LPRM signals 44-1 to 44-n through the wirings 35-1 to 35-n and the core flow rate signal 45 through the wirings 36. The RBM 2 further inputs a control rod operation command 41 through the wiring 24. The RBM 2 uses the LPRM signal output from each LPRM 31 existing in the LPRM assembly 32 located around the control rod 29 to be pulled out in order to monitor the pulling out of the control rod 29. That is, the LPRM signal selection unit (not shown) of the RBM 2 is arranged so that, when the control rod 29 to be pulled out is located at the center of the core, the four LPRM assemblies 32 adjacent to the control rod 29 When the control rod 29 to be extracted is located at the periphery of the core, three or two adjacent to the control rod 29 are output. LPRM signals 44 output from all LPRMs 31 present in the LPRM aggregate 32 are selected from LPRM signals 44-1 to 44-n. The LPRM signal selection unit calculates the RBM value using the input core flow signal 45 and all the selected LPRM signals 44. The RBM value is updated every calculation cycle of the LPRM signal selection unit. When the RBM value reaches the RBL value by the pulling operation of the control rod 29, the RBM 2 outputs a control rod pull-out prevention signal 46 to the control rod pull-out monitoring auxiliary device 3 through the wiring 21. This control rod withdrawal prevention signal 46 is input to the OR circuit 7 of the control rod withdrawal monitoring auxiliary device 3.

  The RBM 2 has a plurality of RBL values (usually three). That is, these are three control rod pull-out prevention setting lines (RB lines), specifically, three lines of a positive RB line A, an intermediate RB line B, and a low RB line C, and each RBL determined by the core flow rate. Value. The operator has a function of changing the RBL value to a higher RBL value in response to an RBL value setup request input from a man-machine interface (hereinafter referred to as MMI) provided on the operation panel 12. Therefore, when the RBM value reaches the RBL value and the control rod 29 is prevented from being pulled out, it is set up to a higher RBL value by a setup request (for example, the intermediate RB line B is set up to the positive RB line A). ) To prevent the control rod 29 from being pulled out. However, the highest RBM value (the RBM value of the positive RB line A) cannot be set up. This RBL setup function is an extended function of RBM2. By monitoring the RBM value and the core flow rate signal 45 by the LPRM signal processing unit of the RBM 2, the RBM 2 can also perform RBL setup by itself without an operator's operation from the MMI. In addition, when the reactor power drops when the control rod 29 is inserted into the core, the RBM 2 monitors the RBM value and the core flow rate signal 45, sets the RBL value itself, and changes the RBL value to the lower RBL value. (For example, the intermediate RB line B can be changed to the low RB line C).

  Since the control rod pull-out monitoring system 1 of the present embodiment includes the control rod pull-out monitoring auxiliary device 3, in addition to the pull-out prevention function of the control rod 39 by comparing the RBM value and the RBL value, the control rod considering MCPR 29 pull-out prevention functions can be added. The pull-out prevention function of the control rod in this embodiment will be specifically described.

The reactor output 48 output from the APRM 37 is input to the first determiner 4 via the wiring 14. A reactor power set value (reactor power P ₀ (for example, 95% reactor power)) 49 set in the reactor power setting device 38 is input to the first determination device 4 via the wiring 13. The first determiner 4 determines whether or not the reactor power 48 is equal to or higher than the reactor power set value 49. The determination signal 50 is output. The reactor power determination signal 50 is input to the AND circuit 5 through the wiring 16. The control rod operation command 41 output from the operation panel 12 is input to the RC & IS 10 via the wiring 40 and input to the AND circuit 5 via the wiring 15. The AND circuit 5 outputs an MCPR calculation command 51 via the wiring 17 when the reactor output determination signal 50 and the control rod operation command 41 are input.

  The process computer 8 obtains the output distribution of the fuel assembly 28 using the input LPRM signals 44-1 to 44-n. When the MCPR calculation command 51 is input, the process computer 28 uses the core management monitoring function (core management monitoring program), and heat such as the output distribution of the fuel assembly, the core flow rate, the subcooling at the core inlet, and the reactor pressure. The MCPR of the core is calculated based on the information on the mechanical parameters. The process computer 8 that has received the MCPR calculation command 51 may calculate the MCPR for each notch operation or step operation (control rod pull-out operation in the minimum unit) of the control rod 29.

  The MCPR calculated value 52 calculated by the process computer 8 is output to the display device 9 via the wiring 19. The operator can confirm the thermal margin of the core by looking at the MCPR calculated value 52 displayed on the display device 9. The MCPR calculated value 52 is also input to the second determiner 6 of the control rod pull-out monitoring auxiliary device 3 via the wiring 18. The second determiner 6 determines whether the input MCPR calculated value 52 is equal to or less than the MCPR set value (for example, OLMCPR). OLMCPR is the operation limit minimum limit output ratio. When the MCPR calculated value 52 is equal to or less than the MCPR set value (for example, OLMCPR), the second determiner 6 outputs a control rod withdrawal prevention signal 53. The control rod withdrawal prevention signal 53 is input to the OR circuit 7. The OR circuit 7 outputs the control rod withdrawal prevention signal 54 when the control rod withdrawal prevention signal 53 or the control rod withdrawal signal 46 is input. The control rod withdrawal prevention signal 54 is input to the RC & IS 10 via the wiring 22. The RC & IS 10 outputs a control rod withdrawal stop request signal 55 to the control rod drive auxiliary board 11 via the wiring 25 based on the control rod withdrawal prevention signal 54. The control rod drive auxiliary board 11 outputs a control rod extraction stop signal 56 based on the control rod extraction stop request signal 55. The control rod withdrawal stop signal 56 stops the drive of the CRD 30 that is performing the withdrawal operation of the control rod 29. That is, the extraction of the corresponding control rod 29 is stopped. The RC & IS 10 is a control rod drive control device that controls the drive of the CRD 30 based on the control rod withdrawal prevention signal 54 and stops the withdrawal operation of the control rod 29.

The first determiner 4 outputs the reactor power determination signal 50, that is, when the reactor output 48 is equal to or higher than the reactor power set value (reactor power P ₀ (for example, 95% reactor power)) 49. Then, a control rod continuous pulling out prevention signal 57 is output. The control rod continuous pull-out signal 57 is input to the RC & IS 10 via the wiring 23. The RC & IS 10 outputs a control rod continuous drawing stop request signal 58 based on the control rod continuous drawing prevention signal 57. The control rod continuous drawing stop request signal 58 is transmitted to the control rod drive auxiliary board 11 via the wiring 25. The control rod drive auxiliary board 11 outputs a continuous extraction stop signal 59 to the CRD 30 via the wiring 34. As a result, the continuous pulling of the control rod 29 is interlocked, and the CRD 30 allows only intermittent pulling by the notch operation or step operation of the control rod 29. This intermittent pulling operation of the control rod 29 by the CRD 30 is stopped when the second determination device 6 outputs the control rod pull-out prevention signal 53.

  In this embodiment, the control rod 29 can be prevented from being pulled out by the control rod withdrawal prevention signal 53 in consideration of MCPR. Therefore, even if the control rod withdrawal prevention signal 46 is not output from the RBM 2, the control rod 29 Pulling out can be prevented. The control rod 29 can be prevented from being pulled out also by the control rod withdrawal prevention signal 46 output from the RBM 2. Therefore, the control rod can be pulled out with higher safety in the operation region of the reactor from the low power state to the rated power state.

  In the present embodiment, when the control rod operation command 41 is output, that is, when the control rod operation command 41 is generated, the MCPR is calculated by the process computer 8, so that the thermal margin is obtained every time the control rod 29 is pulled out. Therefore, it is possible to realize a control rod pulling operation with higher safety in all the operation regions of the nuclear reactor.

In this embodiment, when the reactor output 48 is equal to or higher than the reactor output set value 49 and the control rod operation command 41 is output, MCPR is calculated. Therefore, avoiding unnecessary thermal monitoring of the core. This makes it possible to more reasonably realize the extraction operation of the control rod with high safety. In this embodiment, when the reactor power 48 becomes the reactor power set value (for example, 95% reactor power) 49 or more, In addition, the continuous withdrawal of the control rod 29 that has been withdrawn is stopped, and the control rod 29 can be switched to an intermittent operation of the control rod 29 (for example, a notch operation or a step operation (control rod withdrawal operation in a minimum unit)) ( (Refer to Fig. 3) The change in the thermal margin due to a single control rod operation can be kept to a minimum. By avoiding unnecessary thermal monitoring of the core, the control rod can be pulled out more safely. Realize Can. When the reactor power 48 is less than the reactor power set value, the control rod 29 to be withdrawn is continuously withdrawn.

  In this embodiment, since the control rod pull-out monitoring auxiliary device 3 and the RBM 23 are provided, the operation of the control rod pull-out monitoring auxiliary device 3 can be easily verified using a simulation signal. For this reason, it is possible to save the trouble of verifying the logic of the control rod pull-out monitoring auxiliary device 3. That is, the verification of the operation of the control rod withdrawal monitoring auxiliary device 3 is performed by inputting a simulation signal of the reactor output 48 and a simulation signal of the MCPR calculation value 52, respectively. If the control rod pull-out prevention signal 54 is output from the OR circuit 7 when these simulated signals are input, the control rod pull-out monitoring auxiliary device 3 is in a normal operation state. As described above, in this embodiment, the operation state of the control rod pull-out monitoring auxiliary device 3 can be easily and effectively verified by using the simulation signal.

Other control rod withdrawal monitoring method of the present embodiment, there is the monitoring method of the reactor power to allow at least one notch operation and step operation in pulling a single operation of the control rod 29 in the P ₀ above. Since the operation of the nuclear reactor is performed with a margin of, for example, about 10% in the OLMCPR even in the vicinity of the rated power, the margin is not immediately lost if only the notch operation and the step operation are performed. Therefore, such a control rod pull-out monitoring method is equivalent to operating the control rod while monitoring the MCPR.

  A control rod pull-out monitoring system according to another embodiment of the present invention will be described below. The control rod withdrawal monitoring system of the present embodiment has a configuration in which the first determination unit 4 and the AND circuit 5 are removed from the control rod withdrawal monitoring auxiliary device 3 of the control rod withdrawal monitoring system 1 of the first embodiment. In the control rod pull-out monitoring system of this embodiment, instead of using the first determiner 4 and the AND circuit 5, the control panel 12 and the process computer 8 are connected by wiring, and a certain control rod output from the operation panel 12 is used. A control rod operation command 41 for 29 is input to the process computer 8. Other configurations of the control rod pull-out monitoring system of the present embodiment are the same as those of the control rod pull-out monitoring system 1.

  The process computer 8 calculates the MCPR as in the first embodiment when the control rod operation command 41 is input. The obtained MCPR calculated value 52 is input to the display device 9 and the second determiner 6. Similar to the first embodiment, the second determiner 6 outputs a control rod withdrawal prevention signal 53 when the MCPR calculated value 52 is equal to or less than the MCPR set value (for example, OLMCPR). Similarly to the first embodiment, this embodiment can prevent the control rod 29 from being pulled out when the MCPR is equal to or lower than the set value or when the RBM 2 outputs the control rod pull-out signal 46.

  The present embodiment can obtain effects other than those related to the first determiner 4 and the AND circuit 5 among the effects generated in the first embodiment.

1 is a configuration diagram of a control rod pull-out monitoring system that is a preferred embodiment of the present invention. FIG. It is a detailed block diagram of the control-rod extraction monitoring auxiliary | assistance apparatus shown in FIG. It is explanatory drawing which shows the control-rod extraction monitoring function with respect to the reactor output in the control-rod extraction monitoring system shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Control rod drawing monitoring system, 2 ... Control rod drawing monitoring device, 3 ... Control rod drawing monitoring auxiliary device, 4 ... First judgment device, 5 ... AND circuit, 6 ... Second judgment device, 7 ... OR circuit, 8 ... Process computer, 10 ... Control rod operation monitoring device, 26 ... Reactor, 27 ... Reactor pressure vessel, 28 ... Fuel assembly, 29 ... Control rod, 31 ... LPRM, 32 ... LPRM assembly, 46, 53, 54 ... control rod withdrawal prevention signal, 57 ... control rod continuous withdrawal signal.

Claims (4)

Control rod withdrawal monitoring device generates a first control rod withdrawal inhibit signal on the basis of a neutron detection signal output from the local power range monitor arranged in the furnace center, the control rod withdrawal monitoring auxiliary device, are calculated by the arithmetic unit Further, when the minimum limit power ratio at the time of pulling out the control rod from the core is equal to or less than the minimum limit power ratio set value, a second control rod withdrawal prevention signal is generated, and the control rod withdrawal monitoring auxiliary device outputting any one of the drawing blocking signal of the first control rod withdrawal inhibit signal inputted from the drawing monitoring device and the second control rod withdrawal inhibit signal, the control rod drive control apparatus, the control rod withdrawal monitoring auxiliary Based on the one pull-out prevention signal output from the device, the pull-out of the control rod is stopped ,
When the control rod withdrawal monitoring auxiliary device inputs a control rod operation command and the reactor output is equal to or higher than the reactor power set value, it outputs a minimum limit output ratio calculation command to the calculation device, and the calculation device control rod withdrawal monitoring method characterized that you calculate the minimum critical power ratio when inputting the minimum critical power ratio calculation instruction. The control rod withdrawal monitoring auxiliary device outputs a control rod continuous withdrawal prevention signal when the reactor output is equal to or higher than a reactor power set value, and the control rod drive control device is based on the control rod continuous withdrawal prevention signal. The control rod withdrawal monitoring method according to claim 1, wherein continuous withdrawal of the control rod is stopped and intermittent withdrawal operation of the control rod is performed. A control rod drive mechanism coupled to a control rod withdrawn from the core;
A control rod withdrawal monitoring device that generates a first control rod withdrawal prevention signal based on a neutron detection signal output from a local output region monitor disposed in the core;
An arithmetic unit for calculating the minimum limit output ratio;
The calculated by the calculation unit, generates a second control rod withdrawal inhibit signal when minimum critical power ratio is below the minimum critical power ratio set value at the time of withdrawal of the control rods from the reactor core, the control rod withdrawal monitoring device A control rod withdrawal monitoring auxiliary device that outputs any one of the first control rod withdrawal prevention signal and the second control rod withdrawal prevention signal input from
A control rod drive control device that stops driving of the control rod drive mechanism based on the withdrawal prevention signal output from the control rod withdrawal monitoring auxiliary device, and stops the withdrawal operation of the control rod ;
When the control rod operation command is input and the reactor power is equal to or higher than the reactor power set value, the control rod pull-out monitoring auxiliary device that outputs the minimum limit power ratio calculation command and the minimum limit power ratio calculation command are input. And a control rod pull-out monitoring system, comprising: the arithmetic unit that calculates the minimum limit output ratio . When the reactor power is equal to or higher than the reactor power set value, the control rod withdrawal monitoring auxiliary device that outputs a control rod continuous withdrawal prevention signal, and the continuous withdrawal of the control rod based on the control rod continuous withdrawal prevention signal are stopped. The control rod pull-out monitoring system according to claim 3 , further comprising: the control rod drive control device that controls the control rod drive mechanism so as to perform intermittent pulling operation of the control rod.

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