JPS58156891A - Reactor transient property monitoring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a transient characteristic monitoring device for predicting a low critical power ratio when an abnormal transient phenomenon occurs in a nuclear reactor.

[Technical Background of the Invention] A boiling water nuclear reactor has a reactor core configured by loading a large number of fuel assemblies into a reactor pressure vessel, and output is controlled by inserting and withdrawing control rods into the reactor core. is configured to do so.

In addition, the reactor water in the reactor pressure vessel is heated by the reaction heat in the reactor core, becomes high-temperature, high-pressure steam, and is sent from the main steam pipe to the turbine that drives the generator. Or, if a turbine trip occurs due to a turbine failure, etc., the flow path from the reactor pressure vessel to the turbine is cut off, and a flow path to the water rupture device is formed through a bypass pipe branching from the main steam pipe. The control rod is urgently pushed into -★. At this time, the blocking of the flow path from the reactor pressure vessel to the turbine and the formation of the flow path from the reactor pressure vessel to Taishidake are all controlled by the careful opening and closing operations of the valves, so the opening and closing operations of the masu are During this period, the pressure in the reactor pressure vessel increases, the id contribution coefficient decreases, and positive reactivity is applied, and scram reactivity only begins to take effect after the core neutron pressure has risen rapidly. There is a possibility that an abnormal uneven g phenomenon may occur. Among the four abnormal acupuncture configurations, the MCPR value, which is a picture of fuel health evaluation, becomes especially severe when the pipe inserted in the 8117 world is affected by negative 11fJ interruption or turbine trifle. - Chair valve non-operating failure f, name of the place where it occurred -
It is. In such a case, the pressure in the core suddenly increases *VC, so the core is temporarily reduced to SAM or 11, positive reactivity is applied, and the output increases extremely. Therefore, in order to ensure reactor safety 8:, it is necessary to predict the minimum critical power ratio MCPR that will occur when an abnormal four-way phenomenon occurs. That is, the safety limit MCPR (SLM
The operating limit MCPR (OLM
CPR) and set O with MCPR set like this
It is necessary to monitor it so that it does not fall below LMCPR.

Figure 1 also shows the change in the amount of control rods inserted during each operating cycle of the reactor (from the start of operation to the time of stopping for fuel exchange and the start of the next operation), that is, the burnup (MWD/l).
) and the change in MCPR value during load shedding.As is clear from this figure, the MCPR value closest to the SLMCPR value when a transient phenomenon occurs throughout the operation cycle is when all control rods are This is near the end of the cycle when the state is pulled out. Therefore, transient characteristics are most important near the end of the cycle throughout the entire operating cycle.

Therefore, before the start of each reactor operation cycle, an operation plan is usually created that predicts the change in the amount of control rods inserted throughout the entire operation cycle, and the transient characteristics at the end of the cycle when the operation plan is followed are evaluated. This ensures fuel integrity throughout the driving cycle.

However, in actual operation, the initial operation plan is often changed after the start of operation. In such a case, it is necessary to predict, at a certain point in time, the transient characteristics near the end of the cycle when the changed operation plan is followed.

For this reason, in the past, the MCPR value was monitored as follows to predict the transient characteristics near the end of the cycle (see Japanese Patent Laid-Open No. 56-26287).

In other words, Figure 2 is a characteristic diagram showing the relationship between the control rod insertion ratio (the ratio of the newly inserted amount to the insertion gate at the time of total insertion) (%) and the applied amount of scram reactivity. The Scrum effectiveness index is defined as the integral value of the insertion ratio from 0 to 50 (the shaded area in the figure). Also, the initial MCPR (IMCPR) and the maximum expected change in 5-MCPH when a transient phenomenon occurs! (ΔMCPRm, do. In addition, the scram effect index can be approximated by a function of the axial power distribution of the core immediately before the transient phenomenon occurs, that is, the power distribution in the direction along the axial direction of the fuel rods and the control rod insertion ratio.
Based on the data on the axial power distribution and control rod insertion ratio in the core, a process computer predicts and calculates the scram effect index, and then compares the predicted calculation results with the minimum value S, which serves as a guideline, to monitor MCPR. there were.

[Problems with background technology]

Traditionally, MCPH monitoring uses Scrum effectiveness indicators,
MCPR can be indirectly calculated as ΔMCPR by calculating it approximately 6 as a function of the axial power distribution of the core and the control rod insertion rate just before the transient phenomenon occurs, and monitoring the scram effect index calculated in this way. It's something to monitor, and what's more. The PR value is not determined only by the relationship with the scrum effectiveness index as shown in Figure 2, but is actually influenced to some extent by the void coefficient, so in conventional monitoring that ignores the influence of the void coefficient,
There was a risk that PR predictions would not be made accurately.

In addition, the comparison between the scram effect index and the minimum value S, which is a guideline, is simply that MCPR during current operation is the operating limit MCP.
It merely monitors whether it is greater than R(OLMCPR). Therefore, it was not possible to determine how close the MCPR during current operation was to the safety limit MCPR (SLMCPR), and it was not possible to clearly provide a guideline for safety.

[Purpose of the invention]

The present invention has been made based on the above points, and its purpose is to be able to predict MCPR with high accuracy when a transient phenomenon occurs, and to clearly grasp the safety standard during current operation. An object of the present invention is to provide a device for monitoring transient characteristics of a nuclear reactor.

[Summary of the invention]

The transient characteristics monitoring device for a nuclear reactor according to the present invention includes a process computer into which various signals representing the state of the reactor core are input, and an axial power distribution parameter X and ? of the reactor based on data transferred from the process computer. Calculate the meter b corresponding to the id coefficient, and combine these with the initial minimum limit output ratio IMCPR.
and minimum output predicted change amount ΔMCPR (a: constant) IiV
From the relationship: iCPR, the minimum critical output ratio M when a transient phenomenon occurs
It is equipped with a processing device that predicts CPR and a display device that displays the prediction result by this processing device.

[Embodiments of the invention]

FIG. 4 is a system diagram of the transient characteristic monitoring device, and FIG. 5 is a flowchart showing signal processing in the device.

A reactor pressure vessel 1 of a boiling water reactor is loaded with a large number of fuel assemblies to form a reactor core 2, and control rods 3 are inserted into and withdrawn from the reactor core 2. I am trying to control the output. In addition, 4... in the figure is a control rod drive mechanism that drives the control rods 3....

Various data representing the state of the reactor core, such as the average axial power distribution of the core 2, the reactor water flow rate in the core, the pressure in the core, the core thermal output, and the control rod insertion state, are stored in various instrumentation systems (not shown). ) to the process computer 5 (Fig. 5, ■).

In the figure, reference numeral 6 denotes a processing device, and this processing device 6 receives data such as the average axial power distribution P (Z) and burnup distribution of the core from the data section of the process computer 5 according to instructions from the operator, and The axial power distribution parameter X is calculated using the formula: 9- (where 2 indicates the position in the height direction of the core 2, Zo indicates the upper end position of the core 2, and 0 indicates the lower end position of the core 2). In addition, the axial output distribution parameter X calculated in this way and the MCP predicted when a transient phenomenon occurs
The amount of change in R, that is, the predicted amount of change in the minimum critical output ratio ΔMCP
There is a relationship between R and R as shown in FIG. In addition, this figure 6 shows the transient M when the bypass valve has an inoperable failure during load shedding in a 1.1 million kW class boiling water reactor.
This shows the analysis results of CPR, b(bl +b2+b
3+...) is a gelameter, 1, the axial output distribution parameter X is plotted on the rectangular axis, and ΔMCPR is plotted on the vertical axis. Also, IMCPR=1.24, and from this figure, it can be seen that the following relationship holds true: a is almost constant regardless of the parameter b. It has been confirmed by the solution 10-fold that the relationship between the void coefficient and the parameter b when the number is 1 is a linear relationship of 11 as shown in FIG. Therefore, the void coefficient is calculated based on the core burnup, core average void fraction, and control rod insertion state, and the void coefficient/ceramometer by is calculated from the relationship shown in Figure 6 (Figure 5 (■)). Part 1. Based on the calculated axial power distribution, ceramic X, and void coefficient parameter b that was not calculated above, M CP R@
Prediction is made based on the q-dimensional equation (Fig. 5 ■).

MCPR=IMCPR-ΔMCPR=IMCPR(1-(aX+b)) This predicted MCPR value is a fixed limit value for SLMC
Compare with the PR value (in Figure 5).

8LMCPl (If it is smaller than the value, it is transferred to the display device 7. The display device 7 generates an alarm with a lamp, buzzer, etc. ($5 Figure ■).

Therefore, when an alarm occurs, the operator should take steps to reduce the output.
``Well, I'm going to demand countermeasures to force the MCPR into action.''

Next, if you want to know the transient characteristics near the end of the cycle when the 1 rotation plan is followed at a certain point during reactor operation, use the , the input T from the display device 7 for subsequent operation plans is good.As a result, the processing device 6 calculates the burnup distribution near the end of the cycle (see Figure 5 (4).
)),.

Then, in the processing device 6, the core average axial power distribution P(Z), j? Receive data transfer such as void coefficient and initial MCPI ((IMCPR),
Axial rotation distribution of the core! Lameter X.

(p(z)az-,7,"* P(Z)dZ2iX=-□, /"r(z)az It is calculated from the formula of The id coefficient and zo parameter b are calculated (
Figure 5 ■). Using the 4 parameters of the axial output distribution obtained in this way
is predicted from the relationship MCPR=IMCPR(l-(aX+b)) (Fig. 5 ■). And this prediction MC
The PR value is compared with a certain limit value, i.e., SLMCPR (see FIG. 5), and if the predicted MCPR value is smaller than the SLMCPR value, it is output to the display device 7, which generates an alarm (see FIG. 5). Figure ■).

Therefore, when an alarm occurs, take measures such as reducing the output near the end of the cycle or changing the operation plan leading up to the end of the cycle.
Countermeasures are required to increase the MCPR near the end of the cycle.

According to the transient characteristic monitoring device configured as described above, the IMCPR, axial power distribution/cerameter, void coefficient/cerameter are checked at regular intervals, especially near the end of the driving cycle, and the predicted MCPR at the time of overfatigue is calculated. By doing so, highly accurate predictions can be made and a clear guideline for safety can be given during current operation.

Note that this device is not limited to predictive monitoring when all control rods are nearly fully withdrawn, but also performs predictive monitoring based on the control rod insertion state at that time, even when a considerable amount of control rods are inserted. By setting the constant a to an appropriate value, the above equation can be used to predict the MCPR directivity.

In addition, in the above-mentioned implementation section 1, the following was used as the axial power distribution/ceramometer of the core, but may be used.

〔Effect of the invention〕

As described in detail above, the =13- transient characteristic monitoring device for a nuclear reactor according to the present invention inputs various signals representing the state of the reactor core to the Norocess computer, transfers data from the Norocess computer to the processing device, Based on this data, the processing device calculates the core axial power distribution parameter IMCPR"'X+" From the relationship, the minimum output ratio M when a transient phenomenon occurs
The device is configured to predict CPR and display the prediction result on a display device9. Therefore, in a device configured in this way, the MCPR value during current operation is directly monitored, and moreover, when calculating the MCPR value, Since the effect of the void coefficient is also taken into account, when a transient phenomenon occurs,
The MCPR value can be predicted with high accuracy.

゛Also, the MCPR during current operation is at the safe limit MCPR (SL).
It is possible to judge how close the vehicle is to the MCPR, and it is possible to clearly grasp the standard of safety during current operation. Therefore, the operating limit MCPR (OLM
CPR), SLMCP
It is also possible to use one shift, which is the sum of R and -1.times.1jΔMCPR, as a guide. As a result, M during current operation
The adjustment range of CPR has been expanded, and the operating range has been expanded compared to before, which can also contribute to improving the reactor operating rate.3.

[Brief explanation of drawings]

Figure 1 shows the change in burnup and negative fi during the operating cycle.
Figure 2 shows the relationship between the control rod insertion rate and the scram reactivity application rate, and Figure 3 shows the relationship between the scram ΔMCPR effect index and □MCP□. Figure 4 is a system diagram showing one embodiment of the present invention, Figure 5 is a flowchart of the same embodiment, and Figure 6 is axial output distribution, seven meters, and ΔMCPR.
FIG. 7 is a diagram showing the relationship between the 71-"L decoefficient and the void coefficient parameter. 2...Reactor core, 3...Control rod, 5...Process computer, 6...Processing device, 7...Display device. Applicant's agent Patent attorney Kazuichi Suzue Takehiko 16- ('r'l -s 7 08
d] Evil talent 2 figure 0 50 4
00 ('/,) control) 4-Iri side Gaiga 3 figure 5 figure 4 figure

Claims (2)

[Claims] (1) A process computer that inputs various signals representing the state of the reactor core, and based on the data transferred from this process computer, calculates the core's axial power distribution parameter Ratio IMCPR and minimum limit output ratio predicted change amount ΔMCPR
ΔMCPR = a Characteristics of the transient characteristics monitoring device for nuclear reactors. (2) The reactor transient according to claim (1), wherein the display device issues an alarm when the minimum critical power ratio MCPR predicted by the processing device is smaller than the safety limit MCPR. Characteristic monitoring device.