JPH0262839B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an apparatus for monitoring core performance of a nuclear reactor in a nuclear power plant, such as a boiling water nuclear power plant.

Technical Background of the Invention A nuclear reactor is for extracting and utilizing the thermal energy generated when nuclear fuel absorbs neutrons and undergoes a nuclear fission reaction. Therefore, it is necessary to maintain the integrity of the nuclear fuel during operation of a nuclear reactor, which requires a device for monitoring thermal output, that is, monitoring core performance.

FIG. 1 is a diagram schematically showing a conventional core performance monitoring device. As shown in Fig. 1, the detected values of the in-reactor neutron flux detector (hereinafter referred to as LPRM) 3 installed in the core 2 of the reactor pressure vessel 1 and various locations in the reactor pressure vessel 1 are shown. A core condition data measuring device 4 (represented by one reference numeral 4 in the figure) is installed to obtain data indicating various core conditions such as control rod pattern, coolant flow rate, inlet/outlet temperature, and reactor pressure. The measured value is derived from the outside of the reactor containment vessel 5 and is supplied to the process control computer 7 through the data sampler 6. The process control computer 7 calculates the heat output distribution etc. based on each of the above measured values and displays the results on the display 8.
In this manner, the operator monitors the content displayed on the display 8, that is, the calculation result of the computer 7, and controls the operation of the reactor so that the integrity of the nuclear fuel is always ensured.

Furthermore, the soundness of nuclear fuel is specifically determined by the linear power density (KW/
ft) and the critical power ratio, which is the ratio between the fuel assembly output that transitions from nucleate boiling to transition boiling and the actual fuel assembly output, are each within the range of thermal limit values. It will be judged. The above thermal limit value is
For example, in a fuel assembly with 8 rows and 8 columns, the upper limit linear power density is 13.4 KW/ft, and the lower limit critical power ratio is 1.23. In other words, the linear power density is 13.4KW/ft
The range where the limit output ratio does not exceed 1.23 is the range where soundness can be ensured.

By the way, in a nuclear reactor under normal operation, generally 1
The detected values of the LPRM3 are introduced into the process control computer 7 every time, and the thermal output, linear power density, and critical output ratio are determined as described above. Therefore, the above 1
During hourly monitoring, operation can be controlled so that the linear power density and critical power ratio are within the thermal limit value, but during the period when the above monitoring is not performed, the core flow rate and control rod 10 insertion are controlled. If a change occurs in the temperature, etc., there is a possibility that the linear power density and the critical power ratio may exceed the thermal limit value. Therefore, as shown in FIG. 1, an alarm device 9 is usually provided to issue an alarm when the linear power density and the critical power ratio approach the thermal limit value. This alarm 9
The alarm level is set for the detected value of the LPRM3 so that the detected value of the LPRM3 is constantly monitored and an alarm is issued when the measured value exceeds a certain level.

As shown in FIG. 2, the core 2 has one control rod 10 connected to four fuel assemblies 11a, 11b,
1c and 11d, and the LPRMs 3 are arranged in a predetermined pattern in the gaps of the fuel assembly where the control rods 10 are not inserted.

Problems with the Background Art The conventional device having the above configuration has the following problems to be solved. That is, the above device is used not only to calculate the thermal output, linear power density, and critical power ratio by the process control calculator 7, but also to set the alarm level when the linear power density and critical power ratio approach the respective thermal limit values. In all cases, the detected values of LPRM3 are used as is. Therefore, in order for this core performance monitoring device to operate normally, it is a prerequisite that the LPRM 3 always operates normally. However, in reality, it is impossible to completely eliminate failures in the LPRM 3, and it is also conceivable that the detected value of the LPRM 3 may change significantly due to an abnormality in the signal control system or signal transmission system. For this reason, there was a risk that the conventional monitoring device would malfunction.

Purpose of the Invention The present invention has been made based on the above circumstances, and its purpose is to prevent malfunctions even if a failure occurs in the LPRM or an abnormality occurs in the signal control system or transmission system. There is no risk of
An object of the present invention is to provide a core performance monitoring device for a nuclear power plant that can be expected to operate with extremely high reliability.

Summary of the Invention In order to achieve the above object, the present invention is characterized by the following configuration. That is, the present invention continuously calculates the power distribution in the reactor at the current point in time based on the detection value detected by the LPRM and the data measured by the core state data measuring device, and also uses the power distribution calculation device to calculate the current power distribution in the reactor. The power distribution within the core is calculated at each predetermined time based on the data measured by the core state data measuring device and the built-in physical model, and the ratio of the former calculation result at the same time to the latter calculation result is calculated as the power distribution. Calculate using a ratio calculator.
Then, an abnormality is detected with respect to the output distribution ratio calculated by the above-mentioned output distribution ratio calculator by an abnormality detection means consisting of, for example, a comparator, a judger, etc., and when an abnormality is detected, an abnormality is detected according to the degree of abnormality. The detected value of the LPRM is corrected by a correction means consisting of a corrector, a switch, etc., or replaced with a specified value calculated by an output distribution calculation device.
In this way, an alarm point for the thermal limit value of the reactor is set by the alarm point setter based on the neutron flux measurement value including the correction by correction or substitution and the calculation result of the process control computer. When the measured value of neutron flux exceeds this set alarm point, an alarm is issued by the alarm. In this way, the detection value from LPRM may change significantly,
If it disappears completely, the abnormality will be detected and
After the detected value is corrected, an alarm point is set, and an alarm is issued based on this alarm point.
Therefore, malfunctions due to LPRM failures can be prevented.

Embodiments of the Invention Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals and detailed explanations will be omitted.

The data sampler 21 samples the detected values of the LPRM 3 and the measured values of the core state data measuring device 4 and supplies them to the process control computer 22 . The process control computer 22 continuously calculates the current in-furnace power distribution based on the sampling signals of the two measuring devices supplied from the sampler 21. On the other hand, the measured values from the core state data measuring device 4 sampled by the data sampler 21 are supplied to the power distribution calculation device 23. Output distribution calculation device 2
3 is activated at a predetermined time, for example, at the instruction of a worker or automatically at intervals of no more than two months, and uses the supplied measurement values and a built-in physical model to calculate the three-dimensional nuclear-thermal-hydraulic coupling and calculate the output distribution. Calculate.
As the physical model, in order to improve the responsiveness of the entire apparatus, a model that requires short calculation time even if calculation accuracy is somewhat poor, such as a so-called one-group coarse-lattice diffusion model, is used. When performing power distribution calculations using this one-group/coarse-lattice diffusion model, the fuel assembly that makes up the reactor core 2 is represented by a set of many spatially scattered nodes, and the neutrons at each node are Let the bundle satisfy the equation Σmφm+B _o ² φ _o =0...(1). In the above formula, φ _o
is the neutron flux at node n, Σm is the sum of all nodes adjacent to node n, and B _o ² is the material buckling at node n.

In addition, the in-furnace power distribution is given by a set of power densities at each node, which can be expressed by the following equation: P _o = Σf, _o φ _o ...(2). In the above equation, P _o is the power density at node n, and Σf,n is the fission cross section at node n.

Based on these equations, the output distribution calculation device 23
calculates the in-core power distribution using a well-known calculation method.
And since this calculation can be done in a short time,
Since the LPRM3 measures on-line, the responsiveness of the monitoring device can be increased, and substitute values for the detected values of the LPRM3 can be provided at very short intervals.

The signal indicating the current output distribution calculated by the process control computer 22 and the signal indicating the output distribution calculated at each predetermined time by the output distribution calculation device 23 are the output distribution ratio calculator (hereinafter referred to as PBF calculator). 24.

The PBF calculator 24 calculates the ratio of the calculation result of the process control computer 23 at the same time to the calculation result of the output distribution calculation device 23. That is, the node n calculated by the output distribution calculation device 23
Let PL _o be the output density at node n, and PC _o be the output density at node n calculated at the same time by the process control computer 22, then calculate the ratio S・PBF _o = PC _o /PL _o ...(3) do. The output distribution ratio S·PBF _o calculated by the PBF calculator 24 is given to the PBF storage device 25 on the one hand, and on the other hand
It is applied to the LPRM detected value correction device 26.

The PBF storage device 25 is composed of, for example, a shift register, and is configured to sequentially store outputs from the PBF computer 24 in chronological order, and discard old data that has been in use for several months or more. This is because the value of the output distribution ratio (hereinafter referred to as PBF) changes gradually, so in order to memorize the normal value of PBF,
This is because it is necessary to always use data from several months ago. With such a storage method, the memory of the PBF storage device 25 can be used more effectively. The data accumulated in the past in this way is used as the abnormality judgment standard value for the detection value of LPRM3.
It is given to the LPRM detected value correction device 26. In addition,
The reason why the accumulated data of the PBF storage device 25 is used as the abnormality determination reference value of the LPRM 3 is as follows. That is, since the output distribution calculation device 23 selects a simple physical model with a short calculation time as described above as a built-in physical model, the PBF values should be distributed around 1.0. However, in consideration of the existence of some other fluctuation factors, actual accumulated PBF data is used as the criterion value.

The LPRM detection value correction device 26 compares the output S1 of the PBF calculator 24 with the stored data S2 of the PBF storage device 25, and determines that the LPRM 3 is malfunctioning if there is a significant difference between the two.
Sends signal S3 to LPRM failure indicator 27 and outputs LPRM
In addition to displaying the failure of the output distribution calculation device 2,
The LPRM calculated value calculated in step 3 is called in as a specified value and replaced with the LPRM detected value taken in from the data sampler 21. Also, although the difference between S1 and S2 is not so large,
If it is determined that the LPRM measurement value contains a systematic error, a correction value is determined from the output of the PBF calculator 24, and the LPRM detection value is corrected using this correction value. Then, the modified or replaced signal is given to the LPRM alarm point setter 28 as a setting information signal S4, and then given to the LPRM alarm 29 as a monitored LPRM measurement signal S5. Note that the LPRM detected value correction device 26 specifically includes, for example, as shown within the broken line frame in FIG.
Comparator 31, determiner 32, corrector 33, switch 3
4, an inverter 35, an AND gate 36, an OR gate 37, etc.

The comparator 31 receives the output S1 of the PBF calculator 24.
and the stored data S2 of the PBF storage device 25 to obtain the deviation. The determiner 32 issues a correction command to the corrector 33 when the magnitude of the deviation exceeds a first setting level given to the terminal T and is within a range of a second level greater than the first level. , when the second level is exceeded, a fault signal S3 is given to the LPRM fault indicator 27, an LPRM calculation value call signal is given to the output distribution calculation device 23, and the signal is sent to one input terminal of the AND gate 36 via the inverter 35. In response, an off command is given. The corrector 33 is in the on state (gate open) during steady state.
The data from the data sampler 21, that is, the sampled LPRM detection value, input through the AND gate 36 is taken in, and it is output as it is. The above-mentioned LPRM detection value is corrected using a correction value based on the output S1 of. The switch 34 is called from the output distribution calculation device 23 inputted via the OR gate 37.
LPRM calculation value or output of corrector 33,
It is temporarily given to the LPRM alarm point setter 28 as a setting information signal S4 at intervals of approximately once every hour, and during other periods, it is sent to the LPRM alarm point setter 29 to be monitored.
Give as LPRM measurement signal S.

The LPRM alarm point setter 28 receives a setting information signal S4 given from the LPRM detected value correction device 26,
Based on the linear power density calculation data and limit power calculation data from the process control computer 22, the alarm set point is calculated as follows.

In other words, there is a nearly proportional relationship between the LPRM measurement value and the linear power density. Therefore, when the linear power density is calculated by the process control computer 22, the LPRM measurement value RP1 is the linear power density of the fuel assembly at this time.
When LPD1 (KW/ft) is assumed, a straight line L1 having a proportional relationship as shown in FIG. 4 can be considered. and,
This LPRM measurement value is calculated by the LPRM detection value correction device 26.
The setting information signal S4 is given as a setting information signal S4. The alarm has a linear power density of 13.4 (KW/
ft) is desirable, and
Taking into account the prediction error of LPRM3, it is necessary to take into account a safety factor F1 of 0.8 to 1.0 for the linear power density limit of 13.4 (KW/ft). Therefore, the LPRM alarm point setter 28 calculates the first alarm set point ATS1 for the linear power density using the following equation.

ATS1=(13.4×F1)/LPD1・RP1……(4) Also, the LPRM measurement value and the fuel assembly output are almost proportional to each other. Therefore, if the limit output calculated by the process control computer 22 is BPC, and the corresponding LPRM measurement value is RP2, then a straight line L2 having a proportional relationship as shown in FIG. 5 can be considered. It is desirable to send the alarm before the critical output ratio reaches 1.23, and considering the prediction error of the LPRM corresponding to the critical output BPC, a safety factor F2 of 0.8 to 1.0 is required for the critical output BPC.
You need to think about it. Therefore, the LPRM alarm point setter 28 calculates the second alarm set point ATS2 for the limit output using the following equation.

ATS2=F2/1.23・RP2...(5) In this way, two types of LPRM alarm set points are calculated: one for linear output density and one for limit output ratio, and the one with the smaller value is selected. is memorized. Note that the calculation of the first and second alarm set points is performed every hour when the process control computer 22 calculates the output distribution, and the calculated values are stored as new alarm points until the next calculation is performed. be done.

The LPRM alarm 29 is connected via the switch 34.
It is configured to sequentially compare the LPRM measurement value given from the LPRM detection value correction device 26, for example every minute, with the alarm point given from the LPRM alarm point setter 28, and to issue an alarm when this alarm point is exceeded. .

Since this device is configured as described above,
When the LPRM 3 is operating normally, the LPRM detection value sampled by the data sampler 21 passes through the LPRM detection value correction device 26 as it is, and the setting information signal S is sent to the LPRM alarm point setter 28.
After giving 4, the LPRM alarm 29 is monitored.
Input as LPRM measurement value signal S5. Therefore, an alarm point of a predetermined level is set by the LPRM alarm point setter 28, and this set alarm point
Monitoring of the LPRM measurements is performed, for example, every minute. In this way, when the linear power density or the critical power ratio approaches the thermal limit value, the LPRM alarm 29 immediately issues an alarm. Therefore, the health of the reactor core can be monitored at all times, not only when the linear power density and critical power ratio are calculated hourly by the process control computer 22.

By the way, if some kind of abnormality or failure occurs in the LPRM 3, a difference will occur between the output signal S1 from the PBF computer 24 and the stored data S2 in the PBF storage device 25. This difference is taken as the output of the comparator 31 in the LPRM detected value correction device 26 and input to the determiner 32. If the above difference exceeds the first level, it is determined that a systematic error has occurred in the LPRM 3, and a correction command is given to the corrector 33. Therefore, the data is introduced from the data sampler 21 to the corrector 33 via the AND gate 36.
The LPRM detection value is corrected in the corrector 33 by a predetermined correction coefficient value according to the output S1 of the PBF calculator 24, and then the OR gate 3
7. LPRM alarm point setter 2 via switch 34
It becomes the setting information signal S4 to the LPRM alarm 29 as well as the input signal S5 to the LPRM alarm 29. Therefore, the LPRM measurement value is monitored with the systematic errors removed.

When the output of the comparator 31 exceeds the second level, it is determined that a failure has occurred in the LPRM 3, and a failure display command signal S3 is given from the determination unit 32 to the failure indicator 27, and output distribution calculation is performed. A command to call up the calculated LPRM count value is given to the device 23. At the same time, a low level signal for gate-off command is applied to the input terminal of the AND gate 36 via the inverter 35. Therefore, instead of the LPRM detection value from the data sampler 21, the LPRM calculation value calculated by the output distribution calculation device 23 is sent via the OR gate 37 and the switch 34.
It is given to the LPRM alarm point setter 28 as a setting information signal S4, and is also inputted to the LPRM alarm 29 as a monitored LPRM measurement value. In other words
Replacement of LPRM measurements is performed. Thus
LPRM failure indicator 2 indicates that LPRM3 has failed.
7, so it can be confirmed that this is the case, and the alarm 29 will not issue an alarm based on the abnormality of the LPRM detection value due to the above-mentioned failure.
Note that it is possible that the measured value of LPRM3 changes significantly due to an abnormality in the signal control system or signal transmission system, but even in such a case, the above operation is performed in the same manner.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the embodiment described above, the LPRM detected value correction device 26 includes a comparator 31 and a determiner 3.
2, corrector 33, switch 34, inverter 35,
Although the example uses an AND gate 36 and an OR gate 37, any specific configuration may be used as long as it can perform the same function. It goes without saying that various other modifications can be made without changing the gist of the present invention.

Effects of the Invention According to the present invention, the detected value from LPRM is
If the abnormality changes significantly or disappears completely due to a malfunction, etc., the abnormality is immediately detected, and the above detected value is corrected or replaced, and then an alarm point is set, and based on this alarm point, A warning will be issued. Therefore, even if a failure occurs in the LPRM or an abnormality occurs in the signal control system or signal transmission system, there is no risk of malfunction and extremely reliable operation can be expected in the core of a nuclear power plant. We can provide performance monitoring equipment.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing a conventional core performance monitoring system, Fig. 2 is a partial plan view schematically showing the configuration of a general reactor core, and Figs. Figure 3 is a block diagram showing the configuration, Figure 4 is a diagram showing the relationship between linear power density and LPRM measurement values, and Figure 5 is a diagram showing the relationship between fuel assembly output and LPRM.
FIG. 3 is a diagram showing the relationship with measured values. 1...Reactor pressure vessel, 2...Reactor core, 3...In-reactor neutron flux detector (LPRM), 4...Core state data measuring instrument, 5...Reactor vessel, 21...Data sampler,
22... Process control calculator, 23... Output distribution calculation device, 24... Output distribution ratio (PBF) calculator, 2
5... Output distribution ratio (PBF) storage device, 26...
LPRM detection value correction device, 27...LPRM failure indicator, 28...LPRM alarm point setter, 29...LPRM
alarm.

Claims (1)

[Scope of Claims] 1. An in-core neutron flux detector disposed in the core of a nuclear reactor, a core state data measuring device for measuring data indicating the core state of the reactor, and this core state data measuring device a process control computer that continuously calculates the current in-core power distribution based on the data measured by the in-core neutron flux detector and the detection value detected by the in-core neutron flux detector; and the data measured by the core state data measuring device. a power distribution calculation device that calculates the power distribution in the core at each predetermined time based on a pre-built-in physical model; and a calculation result at the same time calculated by the process control computer with respect to the calculation result of this power distribution calculation device. a power distribution ratio calculator that calculates the ratio; a power distribution ratio storage device that stores the ratio; and a power distribution ratio storage device that stores the ratio; A second level that is set to a value that exceeds the first level and is higher than the first level when an abnormality in the detector is detected and it is determined that a systematic error has occurred in the detected value of the in-core neutron flux. If the in-core neutron flux detected value is corrected by the power distribution ratio output from the power distribution ratio calculator and the abnormal value of the in-reactor neutron flux detector exceeds the second level in the following range: an in-core neutron flux detection value correction device that displays a failure of the in-core neutron flux detector and corrects the in-core neutron flux detected value by replacing it with an in-core neutron flux calculated value obtained by the power distribution calculation device; and a proportional value between the fuel assembly linear power density and limit power ratio calculated at predetermined time intervals by the process control computer and the in-core neutron flux detection value given from the in-core neutron flux detection value correction device at the time of calculation. A first alarm set point and a second alarm set point obtained by converting the alarm set point for the fuel assembly linear power density and critical power ratio obtained by the process control computer into the in-reactor neutron flux measurement value. An alarm point setter that sets the smaller value of A reactor core performance monitoring device for a nuclear power plant, characterized in that it is equipped with an alarm that occasionally issues an alarm. 2. The correction device includes a comparator that compares the output of the output distribution ratio calculator with a value stored in the output distribution ratio storage device to obtain a deviation, and a comparator that detects an abnormality according to the magnitude of the deviation obtained by the comparator. A determiner that makes the determination, and a determination result by this determiner that indicates that the detected value of the in-core neutron flux detector, which is determined to have a systematic error in the detected in-core neutron flux value, exceeds the first level and this a corrector that corrects the detected value of the in-reactor neutron flux detector based on the output of the power distribution ratio calculator when the value is within the range of a second level set to a value higher than the first level; If the detection value of the in-core neutron flux detector exceeds the second level, the determination result is that the in-core neutron flux detector is malfunctioning. 2. The reactor core performance monitoring device for a nuclear power plant according to claim 1, further comprising means for transmitting the specified value calculated by the power distribution calculation device.