JP2004245666A - Monitor for pulling-out of control rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the higher-power generation operation of a reactor by utilizing a larger safety margin brought by reducing the decrement (ΔMCPR) of the thermal margin of the reactor in an event when a control rod is pulled out mistakenly during the power generation operation of the reactor. <P>SOLUTION: A monitor 1 for the pulling-out of the control rod has the function of producing two-channel (an A line and a B line) signals for monitoring the pulling-out of the control rod by averaging signals from local output range monitor detectors 15a located in a core with average output range monitors 20a to 20f and that of issuing a command 39 to inhibit the control rod from being pulled out by comparing these monitoring signals with a set value. In the monitor 1, a set value for permitting the bypass of the signals for monitoring the pulling-out of the control rod is established for the output of the reactor or an indication corresponding to it. If the indication is lower than the set value for permitting the bypass of the signals, one of the two-channel signals for monitoring the pulling-out of the control rod can be bypassed. If the indication is higher than the set value for permitting the bypass of the signals, signals of all channels are used as those for monitoring the pulling-out of the control rod to prohibit the signals from being bypassed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control rod pull-out monitoring device in a boiling water reactor.
[0002]
[Prior art]
A control rod withdrawal monitoring device (Rod Block Monitor, hereinafter abbreviated as RBM) is a device that prevents withdrawal of a control rod so as to prevent the occurrence of fuel rod breakage even when the control rod is continuously withdrawn due to erroneous operation. is there. The RBM has two channels A and B. Each channel averages detector signals of a local power range monitor (hereinafter abbreviated as LPRM) to generate an RBM indication value, It has a function of comparing the indicated value with the set value and issuing a command to prevent control rod withdrawal.
FIG. 8 is a plan view of a part of the core of a boiling water reactor (hereinafter abbreviated as BWR) viewed from above, and shows the positions of LPRM detector assemblies 10a to 10d. Things. The LPRM detector assemblies 10 a to 10 d are installed in a gap outside the corner of the fuel assembly 11. When the operator selects the control rod 12a as the pull-out control rod, the LPRM detector outputs belonging to the four LPRM detector assemblies 10a to 10d closest to the pull-out control rod 12a are taken into the RBM.
[0003]
FIG. 9 is a schematic diagram showing a method of distributing the output of the LPRM detector to the two-channel RBM. The LPRM detector assembly 10a has four LPRM detectors 15a to 15d in the axial direction. This LPRM detector is a neutron flux detector consisting of a small fission counter. Similarly, the other LPRM detector assemblies 10b to 10da also have four LPRM detectors 15e to 15p, respectively. A total of 16 LPRM detector outputs, eight belonging to the height positions A and C are distributed to the RBM A channel 3a, and eight belonging to the height positions B and D are distributed to the RBM B channel 3b, The RBM averages each of the eight acquired LPRM detector outputs.
A number of LPRM detectors (for example, 172 for a 1,100 MWe-class BWR) are installed in the reactor, and an average power range monitor (hereinafter, abbreviated as APRM) is an averaging operation. To detect the average reactor power level. The RBM inputs the APRM indication value and the LPRM detector indication value, and if the average of the taken LPRM detector indication values is higher than the control rod pullout prevention set level, sends a control rod pullout prevention signal to the control rod drive device. To prevent further withdrawal of the control rod. In addition, among the maximum eight LPRM detectors taken into each channel of the RBM, half of the detector signals can be separated from the use state (hereinafter, referred to as bypass).
[0004]
FIG. 10 is a schematic diagram showing an example of the operating characteristic curve 61 of the nuclear reactor and the control rod withdrawal prevention setting level 60 of the RBM. When the recirculation flow rate is less than 100%, the control rod withdrawal prevention setting level 60 is set as a function of the recirculation flow rate. For example, when the recirculation flow rate is F% (the rated flow rate is 100%), the reactor output or APRM instruction value is G% (the APRM instruction value when the reactor output is 100% is 100%). However, at this time, if the average value of the LPRM detector readings taken by the RBM exceeds P%, a control rod pull-out prevention signal is generated. In the region where the recirculation flow rate exceeds 100%, the control rod withdrawal prevention set level 60 is set to a constant value of 105% output in this example. That is, when the average value of the LPRM detector readings taken by the RBM is 5% or more larger than the APRM reading at the reactor power of 100%, the control rod withdrawal prevention signal is generated.
The RBM can bypass one of the two channels when the reactor power is equal to or higher than the lower limit set value H (for example, 30% output). With this function, even when one of the channels of the RBM fails, the monitoring function can be satisfied, and operations such as maintenance, inspection, adjustment, and calibration of the RBM can be performed even during the operation of the nuclear power plant. When the reactor power is equal to or lower than the lower limit set value H, the RBM is automatically bypassed for both channels. Each channel of the RBM is duplicated so as not to lose the security protection function.
[0005]
[Problems to be solved by the invention]
In the BWR, the thermal margin of the reactor is represented by an index called a critical power ratio (hereinafter, abbreviated as MCPR). The MCPR is defined by the ratio (Pc / P) of the fuel assembly output Pc that causes a boiling transition from nucleate boiling to film boiling or steam cooling to the current fuel assembly output P. Generally, the MCPR at the time of abnormal transient change is smaller than the MCPR at the time of normal operation, and the amount of the decrease is referred to as ΔMCPR. The event with the largest ΔMCPR among some abnormal transient events is called a limiting event, and the heat output during normal operation is designed with a margin (at a low output) by the ΔMCPR at that time.
As one of the abnormal transient change events of the reactor, there is a control rod erroneous withdrawal event during output operation in which the control rod is erroneously and continuously withdrawn during power operation. When this event occurs, the power increase of the whole reactor is small, but the output of the fuel assembly near the pulled out control rod increases remarkably, and the thermal margin of the fuel assembly decreases.
When the control rod pullout monitoring device according to the related art is used, the analysis of the control rod erroneous pullout event during the output operation is performed by bypassing the channel (usually the B channel) which is sensitive to the control rod to be pulled out of the two-channel RBM. The evaluation is performed in the state of Further, the evaluation is performed assuming the most conservative case in which half of the eight LPRM signals taken into the RBM of the A channel with the slow response are bypassed and four LPRM signals with the slow response are used. The ΔMCPR (about 0.13) of the control rod erroneous withdrawal event during the output operation was second to the ΔMCPR (about 0.15) of the load loss event and the feedwater heating loss event which were limiting events.
In recent studies, it has been found that even if a boiling transition from nucleate boiling to steam cooling (called dryout) occurs in the BWR, if it returns to nucleate boiling in a short time, there is no problem with the integrity of the fuel rods. It has been obtained. Based on this knowledge, the review of reactor installation permission criteria for abnormal transient events is underway. If a short dryout is allowed, the loss of load event that returns to nucleate boiling in a short time will not be the limiting event that determines the reactor heat output during normal operation. Also, regarding the feedwater heating loss event, it has been found that ΔMCPR is about 0.08 when the effect of the core power space distribution is evaluated in detail. As a result, it was found that a control rod erroneous withdrawal event during output operation may be a limiting event under a criterion that allows a short dryout.
[0006]
An object of the present invention is to reduce a decrease in thermal margin (ΔMCPR) of a reactor when an erroneous withdrawal of a control rod occurs during a power output operation of a nuclear reactor, and utilize the generated safety margin to reduce nuclear power. The purpose of this is to increase the power of the furnace.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, it is possible to bypass one or more of the RBM signals of a plurality of channels in a region where the reactor power is low, and use a signal of all channels as an RBM signal in a region where the power is high. Ban.
Here, the boundary between the low power region and the high power region of the reactor power is set in the range of 70% to 90% of the rated power.
In the region where the core flow rate or the recirculation flow rate is low, one or more of the RBM signals of a plurality of channels can be bypassed. In the high flow rate region, the signals of all channels are used as RBM signals and bypass is prohibited. It is characterized by the following.
Here, the boundary between the low flow rate region and the high flow rate region of the core flow rate or the recirculation flow rate is set in the range of 60% to 90% of the rated flow rate.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 3 is a configuration diagram of a main circuit of the control rod withdrawal monitoring device according to one embodiment of the present invention.
The LPRM detector 15a installed in the reactor core is a neutron detector using a fission ionization chamber, and the local power area monitor (LPRM) 16a installed in the central control room detects the DC current from the LPRM detector 15a. Amplify and measure neutron flux level. In a BWR of the 1,100 MWe class, there are 100 or more LPRM detectors, but the output signal 36 of the LPRM representing the neutron flux measured by each LPRM detector is arranged such that the arrangement in the radial direction and the height direction is almost equal. In combination, about 20 pieces are distributed to six average output area monitors (APRMs) 20a to 20f. The APRM averages the plurality of acquired LPRM output signals.
The control rod pull-out monitoring device (RBM) 1 is composed of two units (A channel 3a and B channel 3b).
An LPRM output signal 37 corresponding to all the LPRM detectors located at positions A and C in the height direction in FIG. 9 is transmitted to the RBM A channel 3a. Also, three APRM (20a, 20c, 20e) signals 30a, 30c, 30e are fetched, and these signals are averaged to calculate the average power indicated value of the reactor. The flow rate measurement unit A (21a) is connected to the RBM A channel 3a. The flow rate measurement unit A (21a) measures the recirculation flow rate from the recirculation pump flow rate and the core support plate differential pressure, and transmits the recirculation flow rate or the core flow rate 31 to the RBM A channel 3a.
An LPRM output signal 38 corresponding to all the LPRM detectors at the positions B and D in the height direction in FIG. 9 is transmitted to the RBM B channel 3b. Also, three APRM (20b, 20d, 20f) signals 30b, 30d, 30f are fetched, and these signals are averaged to calculate the average power indicated value of the reactor. A flow measurement unit B (21b) is connected to the RBM B channel 3b to transmit the recirculation flow or the core flow 31 to the RBM B channel 3b.
[0009]
Since the following configurations and functions are common to the RBM A channel 3a and the RBM B channel 3b, the following description will be made using the RBM A channel 3a as a representative.
The control rod selection module 22 has a function of selecting a control rod operated by an operator via a man-machine interface (MMI) 23 of the central control panel. The RBM A channel 3a is selected from the control rod selection module 22. Control rod position information 32 is transmitted.
When the operation control rod is selected, the RBM A channel 3a selects LPRM signals (up to eight) at positions A and C in the height direction near the operation control rod based on the operation control rod position information 32. Then, an averaging process is performed in consideration of the LPRM bypass information input from the MMI (23), and an RBM average output of the A channel (hereinafter, referred to as an RBM instruction value) is calculated. Further, the RBM indication value is compared with the APRM average output indication value of channel A, and if the RBM indication value is smaller than the APRM average output indication value, calibration is performed so as to be equal to the APRM average output indication value. When the RBM indication value is larger than the APRM average output indication value, the RBM indication value is used as it is. The RBM A channel 3a outputs an RBM indication value 35a to the MMI (23).
When the operator starts the control rod withdrawal operation, a control rod withdrawal signal 34a is transmitted from the MMI (23) to the RBM A channel 3a. In the RBM A channel 3a, as shown by the solid line 60 in FIG. 10, the relationship between the recirculation flow rate and the control rod withdrawal prevention setting level is set. The RBM A channel 3a calculates a control rod withdrawal inhibition set value for the current recirculation flow rate, compares the control rod withdrawal inhibition set value with the RBM instruction value, and when the RBM instruction value exceeds the control rod withdrawal inhibition set value. , And transmits a control rod pullout prevention signal 39a to the control rod driving device 24.
The control rod driving device 24 stops pulling out the control rod when the control rod withdrawal prevention signal 39 is generated in one or both of the RBM A channel 3a and the RBM B channel 3b.
[0010]
The operator can transmit to the RBM (1) a command to bypass either the RBM A channel 3a or the RBM B channel 3b via the MMI (23) for the purpose of maintenance and inspection. Differently, it has a function to prohibit RBM bypass.
FIG. 1 is a schematic diagram illustrating an example of a permission / prohibition area of the RBM bypass according to the present embodiment. The RBM according to the present embodiment has a region in which RBM bypass is prohibited, a region in which one RBM bypass is allowed by an operator's instruction, and a region in which RBM is automatically bypassed. Is determined. In FIG. 1, as an example, the RBM bypass permission set value 62 is set to 70%, and the set value H for automatically bypassing the RBM is set to 30%.
It is assumed that the operator issues an instruction to bypass the RBM A channel 3a to the RBM (1) via the MMI (23). At this time, the RBM A channel 3a compares the current APRM average output instruction value G with the preset RBM bypass permission setting value 62, and if the APRM average output instruction value G exceeds the RBM bypass permission setting value 62, If not, the RBM indication value is bypassed. When the APRM average output instruction value G exceeds the RBM bypass permission set value 62, the bypass of the RBM A channel 3a is rejected, and the MMI (23) indicates that the RBM A channel 3a cannot be bypassed. If the APRM average output instruction value G exceeds the RBM bypass permission set value 62 due to the control rod withdrawal operation while the RBM A channel 3a is already bypassed, the RBM A channel 3a bypass is released. , MMI (23) indicates that the bypass of RBM A channel 3a has been released.
The operation when the operator issues an instruction to bypass the RBM B channel 3b is the same as that of the RBM A channel 3a.
When the reactor power is equal to or lower than the lower limit set value H, the RBM is automatically bypassed for both channels.
[0011]
Hereinafter, the reason why ΔMCPR of the control rod erroneous withdrawal event during the output operation according to the present embodiment is reduced will be described with reference to FIG.
FIG. 4A is a schematic diagram showing an example of the RBM instruction value 66 of the RBM A channel and the RBM instruction value 67 of the RBM B channel when one of the inserted control rods is gradually pulled out. The initial value of the recirculation flow rate is 100%, and the initial value of the RBM indicated value is equal to the APRM average output indicated value at the time of 100% output. Since the control rods of the BWR are pulled out to the lower part of the core, when all the inserted control rods are pulled out, the neutron flux and the heat output at the upper part of the core rise at first. For this reason, the RBM B channel having a higher LPRM detector position has a larger increase in the indicated value than the RBM A channel, and the RBM indicated value reaches the control rod withdrawal prevention setting value (here, 105%) with a smaller control rod withdrawal amount. I do.
FIG. 4B is a schematic diagram showing the amount of decrease in thermal margin (ΔMCPR) of the fuel assembly at this time. When the control rod withdrawal is stopped when the RBM B channel reaches the control rod withdrawal set value, ΔMCPR is 0.07. When the control rod withdrawal is stopped when the RBM A channel reaches the control rod withdrawal set value, ΔMCPR is used. Was 0.13.
Prior art RBMs can unconditionally bypass one channel of the RBM. In the reactor license evaluation, it is necessary to conservatively consider the bypass of the RBM B channel which has a faster response, so that the ΔMCPR of the control rod mispulling event during the power operation is 0.13 in the above example. On the other hand, in the present embodiment, since the RBM bypass is not recognized in the high output region, ΔMCPR of the control rod erroneous withdrawal event during the output operation is 0.07, and ΔMCPR can be reduced.
The decrease in ΔMCPR of the control rod mispulling event during operation from 0.13 to 0.07 corresponds to a margin of about 5% in terms of reactor power. That is, the minimum value of the thermal margin of the transient event when the reactor initial output is 100% and RBM bypass is prohibited, and the transient value when the reactor initial output is 95% and one RBM bypass is allowed. The minimum value of the thermal margin of the event is almost equal. From this point, it is realistic to set the RBM bypass permission set value to about 90% or less of the reactor power.
[0012]
When the present invention is applied, since the RBM cannot be bypassed in the high-power region, there is a concern that the usability at the time of starting the reactor or at the time of maintenance and inspection is worse than that of the related art. However, there will be described no such concern.
FIG. 5 is a schematic diagram of a reactor output time change 70 at the time of starting the reactor, in which control rod withdrawal is frequently performed and the probability of occurrence of a control rod erroneous withdrawal event is considered to be relatively high. The straight line bc, straight line de, straight line fg, and straight line ij are sections where the control rod is pulled out to increase the reactor power, and the straight line gh and the straight line jk are the recirculation flow rates. In the section where the reactor power is increasing by increasing the number of reactors. The straight line hi is a section where the recirculation flow rate is reduced and the control rod is inserted to reduce the reactor power.
When the reactor power is less than 70%, the reactor power is controlled mainly by control rods. When the reactor power exceeds 60 to 70%, the reactor power is mainly controlled by the recirculation flow rate. It can be seen that when the reactor power reaches 70% or more, the control rod is inserted but the power is reduced, but the control rod is hardly pulled out.
Another opportunity for the control rod withdrawal operation is to replace the control rod insertion pattern at the end of the core cycle to compensate for combustion reactivity. Also at this time, the withdrawal of the control rod is performed after the reactor power is reduced to about 60% or less in consideration of fuel safety.
Therefore, even if the RBM bypass is prohibited in the reactor power region of 70% or more, there is almost no chance of pulling out the control rod with high power, so that the operation of the reactor is the same as the conventional operation and the usability does not deteriorate. .
[0013]
As described above, in the present embodiment, ΔMCPR (about 0.13) of the control rod erroneous withdrawal event during the output operation can be halved, and the control rod erroneous withdrawal event during the output operation allows a short dryout. It is no longer a limiting event under certain criteria. The ΔMCPR of the limiting event at this time is about 0.08, and a thermal margin of about 5 to 6% occurs in terms of the reactor power when compared with the ΔMCPR of the current core (about 0.15). That is, the increased power operation in which the normal reactor power is increased by 5 to 6% becomes possible, and the economic efficiency can be improved.
[0014]
In the above embodiment, the bypass permission set value of the RBM is set to the APRM output. However, the bypass permission set value may be determined based on the recirculation flow rate.
FIG. 2 is a schematic diagram showing an example of another bypass permission set value in the present invention, in which the reactor output and the recirculation flow rate are indicated by a reactor operation characteristic curve 61. In FIG. 2, the bypass permission set value 63 of the RBM is set to the recirculation flow rate of 80%.
For example, it is assumed that the operator issues an instruction to bypass the RBM A channel 3a to the RBM (1) via the MMI (23). At this time, the RBM A channel 3a compares the current recirculation flow rate F with the preset RBM bypass permission set value 63, and if the recirculation flow rate F does not exceed the RBM bypass permission set value 63, Bypasses the RBM indication value. When the recirculation flow rate F exceeds the RBM bypass permission set value 63, the bypass of the RBM A channel 3a is refused, and the fact that the RBM cannot be bypassed is transmitted to the MMI (23). The MMI (23) indicates that the RBM cannot be bypassed for the operator. Further, when the recirculation flow rate exceeds the RBM bypass permission set value 63 by the increase operation of the recirculation flow rate while the RBMA channel 3a is already bypassed, the bypass of the RBM A channel 3a is released, and the MMI ( 23) displays that the bypass of the RBM A channel 3a has been released, and records the time and the like.
The operation when the operator issues an instruction to bypass the RBM B channel 3b is the same as that of the RBM A channel 3a.
When the reactor power is equal to or lower than the lower limit set value H, the RBM is automatically bypassed for both channels.
It is realistic that the RBM bypass permission set value 63 is set in the range of the rated flow ratio 60% to 90%, which is the recirculation flow rate corresponding to the rated output 70% to 90% from the operation characteristic curve 61.
[0015]
In each of the above embodiments, the RBM bypass prohibition determination is performed in each of the RBM channels 3a and 3b, but may be performed at an intermediate stage between the MMI (23) and the RBM (1).
FIG. 6 is a configuration diagram of a main circuit of a control rod pull-out monitoring device according to another embodiment of the present invention. The meanings of the symbols are the same as those in the configuration diagram of the main circuit in FIG.
In the present embodiment, the bypass selection device 25 is installed separately from the RBM (1). The bypass selecting device 25 inputs the APRM average output instruction value 45a from the RBM A channel 3a and the APRM average output instruction value 45b from the RBM B channel 3b. Upon receiving the instruction 43 from the MMI (23) to bypass one channel of the RBM, the bypass selection device 25 compares the APRM average output instruction values 45a and 45b with the RBM bypass permission setting value 62. If the APRM average output instruction values 45a and 45b do not exceed the RBM bypass permission set value 62, the RBM (1) transmits the RBM bypass command 42 to the RBM (1).
On the other hand, when the APRM average output instruction value 45a or 45b exceeds the RBM bypass permission set value 62, the bypass selecting device 25 does not transmit the bypass signal to the RBM (1), and the RBM is transmitted to the MMI (23). Communicate that you cannot bypass. The MMI (23) indicates that the RBM cannot be bypassed for the operator.
Further, the bypass selecting device 25 monitors the APRM average output instruction values 45a and 45b, and when the APRM average output instruction value 45a or 45b exceeds the RBM bypass permission set value 62 while one of the channels is bypassed. , RBM (1) automatically transmit a bypass release signal. Also, the fact that the RBM bypass has been released is transmitted to the MMI (23), and the MMI (23) indicates that the RBM bypass has been released for the operator.
In this embodiment, the bypass permission set value is determined based on the APRM output, but may be determined based on the recirculation flow rate. In that case, the bypass selecting device 25 is configured to take in the recirculation flow rate information 31 from the flow rate measurement unit 21.
An advantage of the present embodiment is that when the present embodiment is applied to an existing BWR, it is not necessary to modify the RBM, and the function of the present embodiment can be realized only by introducing the bypass selection device 25. The modification period can be shortened, and the modification cost can be reduced.
[0016]
In each of the above embodiments, the RBM is configured with two channels, but the present invention can be applied to a control rod pullout monitoring device including three or more channels.
FIG. 7 is a schematic diagram showing an example of a method of distributing an LPRM detector output to an RBM in a BWR using a hexagonal fuel assembly to which the present invention is applied. This reactor has three LPRM detectors in the height direction. When the operator selects one control rod as the extraction control rod, the LPRM detector outputs belonging to the three LPRM detector assemblies 10a to 10c closest to the extraction control rod are taken into the RBM. The RBM is composed of three channels (3a, 3b, 3c), and the LPRM detector outputs at the same height are averaged to obtain an RBM average output.
When the operator issues an instruction to bypass any one channel of the RBM, the RBM compares the current APRM average output instruction value with a preset RBM bypass permission setting value, and if the APRM average output instruction value Does not exceed the RBM bypass permission set value, the RBM instruction value of the designated channel is bypassed. If the APRM average output instruction value exceeds the RBM bypass permission setting value, the RBM channel bypass is rejected, and the MMI indicates that the RBM cannot be bypassed. If the APRM average output instruction value exceeds the RBM bypass permission set value due to a control rod withdrawal operation or the like when one channel of the RBM is already bypassed, the RBM bypass is released, and the RMI is transmitted to the MMI. It indicates that the bypass of was canceled.
As described above, by applying the present invention in which the RBM bypass is prohibited at the RBM bypass permission set value or more, the control rod during the power operation of the reactor is compared with the case where the RBM bypass is unconditionally permitted. The ΔMCPR of a false extraction event can be reduced.
[0017]
In the above embodiment of the present invention, the APRM average output instruction value or the recirculation flow rate, which is the bypass permission setting value of the RBM, is a constant value independent of other parameters, but the APRM average output instruction value is a function of the recirculation flow rate. Alternatively, the recirculation flow rate can be a function of the reactor power (APRM average power indication value).
Further, in the embodiments described above, the control rod pullout monitoring device corresponding to the type of reactor that operates one control rod at a time has been described as an example. However, the present invention provides a gang that pulls out a plurality of control rods at the same time. The present invention can also be applied to a multi-channel control rod pull-out monitoring device corresponding to pull-out.
[0018]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce a decrease (ΔMCPR) in the thermal margin of a nuclear reactor when a control rod erroneous withdrawal event occurs during power operation. As a result, under the reactor installation permission standard that allows short-time dryout, it is possible to reduce the ΔMCPR of abnormal transient events and improve the thermal margin, and to reduce the safety margin generated here. The increased power operation in which the heat output level at the time of normal operation is increased can be used, and an economical reactor having a high specific power can be provided.
In addition, by installing the bypass selection device separately from the control rod pull-out monitoring device (RBM), the remodeling of the RBM is not required, the remodeling period of the existing equipment can be shortened, and the remodeling cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a permission / prohibition area of an RBM bypass according to the present invention.
FIG. 2 is a schematic diagram showing another example of a permission / prohibition area of the RBM bypass according to the present invention.
FIG. 3 is a configuration diagram of a main circuit of a control rod pullout monitoring device according to an embodiment of the present invention.
FIG. 4 is a schematic diagram (a) showing an example of RBM indicated values of the RBM A channel and B channel when all the inserted control rods showing the effect of the present invention are gradually pulled out, and the fuel at this time. Schematic diagram (b) showing the amount of decrease in thermal margin (ΔMCPR) of the aggregate
FIG. 5 is a schematic diagram of a reactor power time change at the time of reactor startup.
FIG. 6 is a configuration diagram of a main circuit of a control rod pull-out monitoring device according to another embodiment of the present invention.
FIG. 7 is a schematic diagram showing a method of distributing an LPRM detector output to three-channel RBMs;
FIG. 8 is a plan view showing a part of the inside of the BWR core showing the position of the LPRM detector assembly as viewed from above.
FIG. 9 is a schematic diagram showing a method of distributing an LPRM detector output to two-channel RBMs;
FIG. 10 is a schematic diagram showing an example of a reactor operating characteristic curve and an RBM control rod withdrawal prevention setting line.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Control rod pull-out monitoring device (RBM), 3a ... RBM (A channel), 3b ... RBM (B channel), 10a-10d ... LPRM detector assembly, 11 ... Fuel assembly, 12a-12d ... Control rod 15a to 15p: LPRM detector, 16a, 16b: Local output area monitor (LPRM), 20a to 20f: Average output area monitor (APRM), 21a, 21b: Flow rate measurement unit, 22: Control rod selection module, 23: Man Machine interface (MMI), 24: Control rod drive, 25: Bypass selector, 30a-30f: APRM output, 31: Recirculation or core flow signal, 32: Selected control rod position information, 34: From MMI to RBM Input signals (control rod withdrawal command, RBM bypass command), 35... Output signals from RBM to MMI ( BM average output signal), 36, 37, 38... LPRM output, 39... Control rod withdrawal prevention signal, 45... APRM average output instruction value, 60... Control rod withdrawal prevention setting line, 61... Operating characteristic curve, 62, 63. RBM bypass permission setting value

Claims (4)

A function of averaging a plurality of local power area monitor detector signals installed in the reactor core to create a control rod removal monitoring signal for two or more channels, and comparing this monitoring signal with a set value to prevent control rod removal In the control rod withdrawal monitoring device having a function of issuing a command, a bypass permission set value of the control rod withdrawal monitoring signal is provided for the reactor output or an index corresponding thereto, and when the index is smaller than the bypass permission set value, One or more of the control rod pull-out monitoring signals of two or more channels can be bypassed. If the index is larger than the bypass permission set value, the signals of all channels are used as control rod pull-out monitoring signals, A control rod pull-out monitoring device characterized in that the control rod is prohibited. 2. The control rod pull-out monitoring device according to claim 1, wherein a value in a range of 70% to 90% of a rated output is set as the bypass permission setting value. A function of averaging a plurality of local power area monitor detector signals installed in the reactor core to create a control rod removal monitoring signal for two or more channels, and comparing this monitoring signal with a set value to prevent control rod removal In the control rod pull-out monitoring device having a function of issuing a command, a bypass permission set value of the control rod pull-out monitoring device is provided for an index corresponding to the core flow rate or the recirculation flow rate, and the index is smaller than the bypass permission set value. One or more of the control rod withdrawal monitoring signals of two or more channels can be bypassed. If the index is larger than the bypass permission set value, the signals of all channels are used as control rod withdrawal monitoring signals. A control rod pullout monitoring device characterized in that a bypass is prohibited. 4. The control rod pullout monitoring device according to claim 3, wherein a value in a range of 60% to 90% of the rated flow rate is set as the bypass permission setting value.

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