JPH05341083A - Nuclear reactor output monitoring device - Google Patents

Abstract

PURPOSE:To provide a nuclear reactor output monitoring device which can certainly monitor the output vibrating phenomenon, etc., in a nuclear reactor and can enhance the safety and the rate of service time. CONSTITUTION:A nuclear reactor output monitoring device includes a calculator 6, which sets automatically the optimum weighting factor and the smoothening length according to the core state at the time and determines a smoothening signal in conformity to the neutron flux sensing system signal, a database 11 which sores the optimum judging criterion for the operating condition, and a judging means 10 which compares the smoothening signal with the judging criterion and emits a judgement signal. The output variation is monitored while the output vibrating phenomenon, spike-form output rise phenomenon, etc., are discriminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor power monitoring device used for core power monitoring of a boiling water reactor.

[0002]

2. Description of the Related Art Power output during boiling water reactor (BWR) operation (operation mode) is averaged by averaging several hundreds of local power range monitor (LPRM) signals arranged in the core to several channels. The output area monitor (APRM) signal is used. An upper limit is given to the average power range monitor system from the viewpoint of preventing damage to the fuel cladding, and if the upper limit is exceeded, the reactor will scram by inserting all control rods into the core at the same time. To be done. This upper limit value is set to, for example, 120% of the rated value during normal rated operation, and during the output increase transient, the average neutron flux corresponding to the heat flux is automatically set along the flow control curve. In some plants, the scram set point has been changed so that it outputs a scrum signal when the average power range monitor signal exceeds its set value. Usually, if the upper limit value is exceeded in two or more of the average power range monitor systems having a plurality of channels (for example, four channels), the core is scrammed.

The average power range monitor high scrum, when operated alone, is operated only at the average power range monitor signal level regardless of the type of event. For example, if the event is an output oscillation phenomenon due to core instability, it is presumed that the oscillation phenomenon occurs long before the power rising scrum set point is reached. That is, if the output signal is detected before reaching the scrum set point, careless scrum can be avoided by taking the output signal suppressing measure instead of the scrum. From such a point of view, as an output vibration suppressing measure, an operation called selective control rod insertion (SRI), which partially reduces the output by inserting a preselected small number suppressing rod, is also considered. However, in this case, the position is to avoid an operating region where the core becomes unstable. For example, in the improved BWR, when two or more recirculation pumps trip at the same time,
When the operating point enters such an unstable region, the system operates the SRI. Therefore, in addition to this position, a system that detects and responds to the instability of the core and the output vibration is conceivable.

As such an approach, a method of monitoring the stability of the core by statistically processing the time series data online and obtaining the spelltle or impulse response, and the neutron flux response in a region within the core (that Monitoring methods have been proposed, such as determining (by averaging the local power domain monitor signals within a domain) and comparing the response to a preset level. However, these approaches are based on stability measures, and are not symmetrical with respect to other output fluctuation phenomena.

[0005]

As described above, in the monitoring device that monitors the average output area monitor signal and activates the scrum signal when the abnormal output rises, the present situation is that the output other than the scrum before the output reaches the scrum setting level. However, there is a problem that the scram malfunction due to a false signal cannot be avoided.

In view of the above points, the present invention has an object to obtain a reactor output monitoring device capable of reliably monitoring output vibration phenomena and the like, and improving safety and availability. To do.

[0007]

According to the present invention, there is provided an arithmetic unit for automatically setting an optimum weighting coefficient and a smoothing length according to a core state at that time and obtaining a smoothing signal from a neutron flux detection system signal. , Which has a database for storing the optimum judgment criterion for the operating condition and a judgment means for comparing the smoothed signal with the judgment criterion and outputting the judgment signal to discriminate the output vibration phenomenon, the spike-like output increase phenomenon, etc. It is characterized in that the output fluctuation is monitored.

[0008]

[Operation] The optimum weighting factor and smoothing length are automatically adjusted at that time in response to low flow rate / high output operation state where output oscillation phenomenon is likely to occur or rated operation when output oscillation phenomenon hardly occurs. Since a smoothed signal of the neutron flux is set and the output fluctuation is monitored by this, unnecessary scrum can be avoided, and stability and availability can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a block diagram of a reactor output monitoring apparatus according to the present invention. Multiple neutron detectors 2 in the core 1
Exists, from which each local output area monitor signal 3 is taken as an analog signal. They are collected in the adder 4 and are evenly averaged about every 20 signals to become the average output area monitor signal 5. By monitoring this average power range monitor signal, this signal is typically used to determine the average power range monitor high scrum. The average output area monitor signal 5 is digitized by using the A / D converter 6. The digitized average output area monitor signal is converted into a smoothed signal in the calculator 7. The smoothing requires the weighting factor and the information of one step before, but these are stored in the memory 8 and are sequentially updated. Further, the smoothing requires a vibration period and a smoothing length, and these settings are made by using the information of the state monitoring device 9 and extracting the information from the memory 8. However, the smooth length and vibration cycle are updated only when the operating point is changed or a transient event such as pump trip occurs.

The smoothed signal obtained by the arithmetic unit 7 is input to the comparison arithmetic unit 10 together with the average output area monitor actual signal which has passed only the A / D converter 6 and the output is monitored. At this time, the judgment standard is stored in the database 11, the optimum judgment standard for the operating state is set based on the information of the state monitor 9, and the judgment signal 12 is issued by comparing the judgment standard with the smoothing signal. ..

By the way, the smoothed signal S (n) is obtained from the average output area monitor signal by the following operation.
That is, the average output area monitor signal x at time t
From (t), digitization is performed at the sampling interval Δt, and the average output area monitor signal x (n) at the discretization time t _n = nΔt is obtained. Then, the following new signal S (n) is obtained from the average output area monitor signal x (n) thus digitized.

[0012] Here, W _i is a weighting coefficient and satisfies the following condition.

[0013] That is, the expression (1) shows that N discrete signals are smoothed (filtered). The smoothed signal S (n) is sequentially calculated at every sampling interval nΔt. That, S (n + 1) = a S (n) -w1x (n- N + 1) + w N x (n + 1) (3), and one step before the smoothed signal S (n), N steps before discretization signal If only x (n−N + 1) is stored in the memory, the smoothed signal S (n + 1) at a new step
Is calculated.

The problem here is how to set the smoothing length N and the weighting factor w _i . Therefore, when the output signal phenomenon is mainly monitored, an important vibration parameter is a vibration cycle, and a typical value of the cycle is 2 to 3 seconds. Therefore,
Assuming that the oscillation period is T _O (seconds), the number M _s of time-series signals sampled during this period is given by M _s = TO / Δt (4). It is considered that 1 ≦ N ≦ M _S (5). Therefore, it is necessary to give the vibration period T _O. Since the output oscillation period mainly depends on the core flow rate and the core heat output, it can be given as a function relating to the operating point with good accuracy. That is, T _O = function (heat output, flow rate) (6) Especially, stability is a problem in the vicinity of the maximum output point of natural circulation that is settled after the pump trip. Seeking,
Set.

The oscillation period is given, if the time series data number M _s is set in the oscillation cycle, is set as follows smoothness Kacho of N.

N = M _s / M _p (7) Here, N _p is the oscillation period division number that determines the smoothing length.

Next, the setting method of the weighting factor w _i complies with the following criteria. That is, from the restriction of the equation (2), "w _N =
1 "is the same as the conventional average output range monitor signal,
Increasing the weighting factor around w _N makes it easier to monitor fast responses. On the contrary, a large smoothing length is adopted,
By setting the weighting factors averagely, it becomes easy to monitor a relatively slow response such as a vibration phenomenon. Therefore, the weighting factor is set so that the transient response, which is more problematic at the operating point, can be easily monitored.

First, since the main purpose of the output monitoring apparatus is to detect and suppress the output vibration phenomenon, an example of monitoring from the viewpoint of the output vibration phenomenon will be described. The output oscillation phenomenon is likely to occur at low flow rate / high output state, and there is almost no possibility of occurring at the rated state, which can be ignored. Even in the low flow rate / high output state, it is considered that the vibration is most likely to occur at the natural circulation maximum output point, which corresponds to the settling level when the recirculation pump is tripped. In such a state, there is a large margin with respect to the limit value of the linear power density, and rather there is a problem that the heat removal capacity is deteriorated due to the boiling transition phenomenon accompanying the flow vibration. Therefore, in this state, the spike-like output increase and the output oscillation phenomenon are distinguished,
Ignore the former as long as there is a margin in linear power density, and scram at the normal average power range monitor high scrum set point level. Regarding the latter, the vibration phenomenon suppressing operation, that is, the selection control rod insertion is performed before the boiling transition occurs.

In order to detect the output oscillation and ignore the spike-like output increase (erroneous signal) depending on the average output area monitor high scrum set point level, the weighting coefficient and the smoothing length are set as follows. Since the weighting coefficient determines the output vibration based on the integral amount, the weighting coefficient is set to the same value. That is,
w _i = 1 / N. Regarding the smoothed length, if it is too short, it becomes difficult to distinguish between vibration and spike-like fluctuation. On the other hand, if it is too long, it becomes difficult to detect because it is too blunted due to vibration or spike-like fluctuation. Spike-like fluctuations do not last as vibrations like the response at the time of an earthquake except those caused by erroneous signals, but since fluctuations last for several seconds, they are considered in the same category as the output vibration phenomenon. Therefore, if it is an erroneous signal, it is considered that it lasts only a few steps at most.
Therefore, if the continuous step of the false signal is M, the scrum setting level P _S , the SRI setting level is P _R , and the operation output is P _O , the smoothing signal does not reach the SRI set point, depending on the scram level of the spike fluctuation. condition is,

{(N−M) P _O + MP _S } / N _P = 1 + M / N (P _S / P _O −1) ≦ P _R / P _O (8) If the ratio of the scrum level to the maximum output level of the natural environment is about 2 to 3, and the SRI set point is (1 + a) times the operation output, the relationship of (M / N) from equation (8) is (1 to 2) Since M / N ≦ a (9), the minimum smoothing length is (1 / a) to (2
/ A). Therefore, in order to set the smoothed length, the SRI set point must be determined.

The SRI set point is set according to the following procedure. If the output vibration is approximated by a sine function of period T and amplitude f, the smoothed signal is given by the following equation.

[0022] _{P O (1 + fN P /} π · sinπ / N P · sin (t)) (10) Therefore, the maximum value of the smoothed signal oscillation amplitude f is
From the equation (10), fN _p / π · sin π / N _P (11) From this, when the maximum value of the smoothed signal exceeds the equation (11), the real signal is a vibration phenomenon with the amplitude f or more. Conceivable. Therefore, the expression (11) is adopted as a in the expression (9). (9) Substituting expression (11), since _{2πM / fM S ≦ sin (π} / N P) (12) the oscillation period is about 2 to 3 seconds, by setting the sampling interval to the number 10 milliseconds For example, M _s is typically around 100. f takes a value of about 0.1 in consideration of the thermal margin due to output vibration. If M is 1 to 2, (1
The left side of equation (2) has a value of about 0.63. From now on, N
The maximum value of _p is about 4.6. However, according to the equation (11), the sensitivity of the smoothed signal is a monotonically increasing function of N _p , so if a too small value is selected for N _p , the detection sensitivity will decrease. Therefore, it is considered that the optimum value of N _P is about 4. That is, it is optimal to smooth the vibration in about 1/4 cycle.

Hereinafter, the smoothing length is set to 1/4 of the vibration period.

FIG. 2 shows an actual example of output vibration monitoring. Output 50% rating, cycle 2 seconds, maximum amplitude about 8% / rating (16
% / Initial value) is an example of monitoring the vibration phenomenon in the present invention. Assuming that the smoothed length is 1/4 cycle (0.5 seconds) and the vibration detection amplitude is 10% / initial value, the SRI set point is 54.5% rated from the equation (11). From FIG. 2, the smoothed signal according to the present invention exceeds the SRI set point at about 18 seconds, and by activating the SRI at this point, vibration is suppressed. FIG. 3 shows an example of monitoring when a spike-shaped erroneous signal occurs. The false signal itself far exceeds the SRI set point, but does not reach the average power region high scrum and the smoothed signal is below the SRI set point, so neither scrum nor SRI is activated.

Next, an example of monitoring during rated operation will be shown. At the time of rated operation, it is considered that the output oscillation phenomenon does not occur because the core flow rate is sufficiently secured. Transient anomalous events during rated operation are almost always scrammed other than neutron flux high scrum. Therefore, at the time of rating, the smoothing signal of the present invention is set to the conventional neutron flux high scrum level, and the normal neutron flux high scrum level is set to be higher than the conventional level, so that an erroneous signal and an earthquake with an intensity lower than the scrum level are generated. Occasionally avoid high neutron flux high scrum.

In the rated operation, the thermal margin is smaller than that in the natural circulation, and the detection of the output vibration does not have to be taken into consideration. Therefore, by changing the setting of the weighting coefficient, a signal suitable for the above-mentioned purpose is used. That is, during rated operation, more emphasis is placed on detection of instantaneous signals than on integral signals. Specifically, the weighting factor defined by the equation (2) is set to be larger as the observation real time is closer. For example, in equation (2), w
_{If N} = 0.5, then in the equation (8), if P _R is the smoothed signal scrum set point and P _S is the neutron flux high scrum set point, then (P _S −P _O ) ≦ 2 (P _R − P _O ) (13), the neutron flux high scrum set point can be set to twice the height of the smoothed signal scrum set point. That is, if the smoothed signal scrum level is set to 120%, which is the same rating as the conventional neutron flux high scrum set point, the neutron flux high scrum set point of the present invention can be set to 140%, and unnecessary neutrons in the meantime can be set. You can avoid a high bunch of scrum. An example of monitoring at this time is shown in FIG. The average output range monitor signal is lower than the scrum level set to twice the conventional level,
Although higher than the conventional scrum level, the smoothed signal is lower than the conventional scrum level (smoothed signal scrum level), so in this case it is considered an erroneous signal and the scrum is not activated. The output increase is suppressed by the high neutron flux high scrum when the water supply heating is lost, but the output increase is slow at the same time, so the smoothed signal has almost the same response as the actual signal. It operates almost the same as the high neutron flux high scrum.

Next, the detection method during an earthquake will be described. At the time of an earthquake, if the acceleration is above the set value, the scram is scrambled, but if the set value is below the set value and the average power range monitor response is above the neutron flux high scrum level, scram is avoided as follows. First, FIG. 5 shows a response example of the average output area monitor actual signal and the smoothed signal at the time of an earthquake. The output response shows the maximum response within a few seconds to a few seconds after the earthquake occurred,
Moreover, since the peak width is relatively large, there is not much difference between the actual signal response and the smoothed signal response. Therefore, when the accelerometer detects an earthquake below the scrum level, the smoothed signal high scrum level is raised to the actual signal scrum level and held at that level for several tens of seconds. If no new earthquake is detected, the smoothed signal high scrum level is returned to the original value. By performing such an operation, it is possible to avoid the seismic scrum between the smoothed signal high scrum level and the neutron flux high scrum level (for example, 120 to 140% / rated) as in the case of an erroneous signal.

[0028]

As described above, the present invention is suitable for a low flow rate / high output operation state in which an output vibration phenomenon is likely to occur or a rated operation in which an output oscillation phenomenon hardly occurs, and is optimal at that time. The weighting coefficient and smoothing length are automatically set to obtain the smoothed signal of the neutron flux, and the output fluctuation is monitored by this, so as long as there is a margin in the line power density, the spike-like power increase is ignored, Alternatively, regarding the output vibration phenomenon, it is possible to perform an operation of suppressing the vibration phenomenon such as insertion of the selective control rod before the boiling transition occurs, and it is possible to prevent the generation of unnecessary scrum and prevent the generation of unnecessary scrum. Therefore, it is possible to improve the safety of the nuclear reactor and improve the operation rate.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a reactor output monitoring device of the present invention.

FIG. 2 is a diagram showing an example of monitoring during output vibration.

FIG. 3 is a diagram showing an example of erroneous signal avoidance in a natural circulation state.

FIG. 4 is a diagram showing an example of erroneous signal avoidance during rated operation.

FIG. 5 is a diagram showing an example of core output response during an earthquake.

[Explanation of symbols]

 1 core 2 neutron detector 3 local output area monitor 4 adder 5 average output area monitor 7 arithmetic unit 8 memory 9 state monitoring device 10 comparison arithmetic unit 11 database 12 judgment signal

Claims (1)

[Claims] 1. An arithmetic unit for automatically setting an optimum weighting coefficient and a smoothing length according to the core state at that time to obtain a smoothing signal from a neutron flux detection system signal, and an optimum judgment criterion for an operating state. And a determination means for outputting a determination signal by comparing the smoothed signal with a determination reference, and monitoring output fluctuation by differentiating an output vibration phenomenon, a spike-like output increase phenomenon, etc. Reactor output monitoring device characterized by.