JPS5931033B2 - Control rod withdrawal monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a specific plurality of LP'RMs among the local power range monitors (hereinafter referred to as LPRMs) arranged in a line in the core of a nuclear reactor. The present invention relates to a control rod withdrawal monitoring device having a control rod withdrawal prevention monitor (hereinafter referred to as RBM) configured to prevent withdrawal of control rods surrounded by a particular LPRM.

The neutron flux distribution within a large nuclear reactor changes in a very complex manner depending on the operating conditions.

Therefore, when operating a nuclear reactor, it is necessary for safety reasons to accurately monitor such changes and take appropriate measures such as preventing fuel burnout and flattening the power distribution. be.

For this reason, inside the reactor core, as shown in Figure 1,
LPRMIs a, 1b, . . . are arranged in an array, and local power within the reactor core can be detected by these LPRMIs.

Also, for a specific one of these LPRM'l, for example, control rod 2a, LPRM1atlbt1ct
For ldt control rod 2b, LPRM 1 e , 1
f tIgtFurthermore, for control rod 2c, LPRMlh
.

11, the LPRM1 is combined to form an RBM; this RBM selects the extraction position of the control rod 2 and controls the output of the reactor.

This relationship between the control rod withdrawal position and the core output is based on the second
As shown in the figure.

According to Figure 2, as the control rods are withdrawn, the core power increases (
d It rises rapidly, and after the control rod is pulled out about 3/4 of the way, it remains almost flat.

Still, the maximum heat flow east exit rises as the control rod is withdrawn, increasing the control rod to 8ft. The maximum value is reached when the amount is withdrawn, and then it decreases.

Furthermore, the critical heat flux C decreases as the control rod is withdrawn.

Considering the relationship between the core output (a), the maximum heat flow east exit, the critical heat flux, and the control rod withdrawal position, it is necessary to prevent the withdrawal of the control rods before the critical heat flux (c) falls as much as possible.

In consideration of this relationship, Figure 2 shows that when the sum of the core output forces reaches 7, that is, the control rods are set to 4 ft. This shows a case where the control rod is set to prevent withdrawal when the control rod is withdrawn.

Therefore, in order to make the withdrawal of the control rods more convenient as described above, the RBM mentioned above has an important meaning.

By the way, as shown in FIG. 3, the LPRMl constituting the RBM has four detectors A t B +C, D, each of which is arranged at a predetermined interval of C in the vertical direction. , RBM are driven as shown in FIG. Then, a signal is sent from the selected control rod sensing device 11 to the specific control rod drive mechanism 12, and the specific control rod 2 begins to be withdrawn.

By pulling out the control rods 2 in this way, the core 3
The neutron flux within changes, but R for this control rod 2
In order to send only the signals from the specific LPRMs 1.1 . 11 control signals are sent to the LPRM designation device 14, which is adapted to accept control signals of 11.

The specific LPR selected by this LPRM designation device 14
The M1 signal is sent to the control rod withdrawal prevention mechanism 13, and is divided into a channel A+C signal and a channel B+D signal of each LPRM1 by an averaging device 15 therein.

The channel A+C signal and the channel B+D signal are, for example, the channel A+C signal.
It means the sum of the signals from detectors A and C in FIG. 3 divided by the number of detectors A and C and then averaged.

Therefore, the signal of channel B is transmitted to the detector A,
Just replace C with B or D.

Therefore, the signal divided by this averaging device 15 is also transmitted to the prevention signal generator 16 in the control rod withdrawal prevention mechanism 13.
sent to.

On the other hand, a signal from a device 17 for detecting the flow rate of the coolant recirculation pump is sent to a calculation device 18, where a set value for preventing withdrawal of the control rod 2 is calculated.

The signal of this calculating device 18 is then also sent to the blocking signal generating device 16 and compared with the signal from the averaging device 15.

This blocking signal generator 16 is configured to send a signal to the control rod drive mechanism 12, and when the signal from the averaging device 15 is larger than the signal from the calculation device 18, the control rod drive mechanism 12, a signal is issued to prevent the control rod 2 from being withdrawn.

In this case, channels A+C from the averaging device 15
Either one of the signals of 1 channel B+D is calculated by the calculation device 1.
If it is a dog based on the signal from 8, a signal is sent to the control rod drive mechanism 12 to prevent the control rod 2 from being withdrawn.

In addition, the signal of each LPRM1 mentioned above? is sent to the core average power monitor 19, where the core average power is determined from the signals of all LPRMs 1, and this average power is displayed on the indicator 20.

Further, the signals of channels A+C and B+D are also displayed on the indicators 21 and 22, respectively.

By the way, in the calculation device 18, the withdrawal inhibition setting value PB for the reactor recirculation flow rate W is generally expressed as PB=a-W+b.

Here, a and b are constants, and PBlW is a value normalized to a rated value. The values of a and b are determined from the worst response condition of the RBM.

That is, L constituting the RBM of a specific extraction control rod 2
Even if only the two LPRMIs 1, which are farthest from the control rod 2, are operating among the PRMIs 1 and 2, the system is designed to prevent fuel damage from occurring due to a local increase in thermal output. The control rod 2 is determined with reference to FIG. 2 so that the control rod 2 is prevented from being withdrawn at a certain withdrawal position.

In the example shown in FIG. 2, W=1.0 pB
= 1.07, and the worst response condition is 4.
ft, a blocking symbol occurs during withdrawal.

Normally, every precaution is taken to ensure safety so that the RBM will not be configured under such worst-case conditions, but this is done just in case.

Therefore, the greater the number of LPRM1's constituting the RBM, the better the response characteristics will be, and therefore the control rod 2 will be prevented from being withdrawn at a height of 4 ft or less.

The control rod withdrawal prevention signal is used to prevent fuel damage (r
Of course, it is desirable to emit the fuel just before thermal conditions become severe, so as not to compromise the integrity of the fuel.

For this reason, it is desirable to set a and b so that PB is small, and to generate a blocking signal before the control rod 2 is pulled out much.

However, as is clear from Fig. 2, the response characteristics of the RBM to the withdrawal of the control rod 2 are poor in the initial stage of withdrawal of the control rod 2, so in order to shorten the withdrawal length of the control rod 2, PB must be made considerably smaller. There must be.

For example, in a control rod drive mechanism 12 that prevents the control rod 2 from being withdrawn every 0.5 ft.
, in order to generate a blocking signal, a
, b must be determined.

However, if the blocking point is lowered in this way, even when there is no movement of the control rod 2, a slight output fluctuation or noise will generate a blocking signal or activate an alarm, causing alarm.
This will result in a decline in sexuality.

It is easy to understand that when withdrawal of the control rod 2 is started, the possibility of malfunction increases due to transient fluctuations in the neutron flux.

In addition, when the control rod 2 is pulled out halfway and is then continuously pulled out while being monitored by the RBM, the outputs of the detectors A, C, B, and D of the LPRMl will be different for each channel. Therefore, the response characteristics of the RBM due to a local power increase at the position where the control rod 2 has come out are the same as those of the LPRM closest to the position where the power increase occurred.
It is clear that the response characteristic is worse than that of the detector, and therefore a local increase in output cannot be detected accurately.

Furthermore, since the LPRM detector is located only at a specific position in the vertical direction, is it possible to accurately detect a localized increase in output at the beginning of the withdrawal of control rod 2 and continue withdrawal of control rod 2? It is desirable that the configuration be such that it can be immediately determined whether or not it is the case.

The present invention improves the poor response characteristics of the conventional RBM at the initial stage of control rod withdrawal, and accurately senses local power increases no matter where the control rod is withdrawn.
It is an object of the present invention to provide a control rod withdrawal monitoring device that makes it possible to determine whether or not the withdrawal is dangerous at the initial stage of the withdrawal.

The present invention will be explained below with reference to embodiments shown in the drawings.

It should be noted that the present invention improves the LPRM designating device 14 and the control rod withdrawal prevention mechanism 13 in particular from the conventional device explained with reference to FIG. Illustrated and explained.

FIG. 5 shows an embodiment of the present invention, and each LPRM
The output signals of the detectors A, B, C, D of 1.1, . . . are led to a comparator circuit 30.

This comparison circuit 30 selects the higher output of detectors A and C of LPRM1, 1°1.1, which constitute the RBM for a specific control rod (not shown), and the detectors B and D. The one with the higher output is selected from among them.

The maximum values selected by the comparison circuit 30 are each sent to the control rod withdrawal prevention mechanism 13, and depending on the signal, a control rod withdrawal prevention signal is issued to the control rod drive mechanism (not shown).

Specifically, the control rod withdrawal prevention mechanism 13 is
Two channels are formed by the detector output selected by the M designation device 14, and the output signal of each channel and the control rod withdrawal prevention setting output value for the reactor recirculation flow rate W set by the calculation device 18. are independently compared in the prevention signal generating device 16, and if the output of either channel exceeds a set value, a withdrawal prevention signal is generated and transmitted to the control rod drive mechanism 12 to stop the control rod withdrawal operation. .

Therefore, even if the position of the neutron detector that generates the maximum output changes due to the deformation of the output distribution due to control rod withdrawal,
Control rod withdrawal prevention response characteristics do not deteriorate.

According to the above-described configuration, max including max indicating the maximum value
Each indicator (not shown) for the x (AtC) channel and the may (B, D) channel indicates the L value that belongs to each channel.
PRM detector A! : Indicates the maximum value of C or each of B and D.

The response characteristics at this time will be explained with reference to FIGS. 6 to 9 according to the bypass conditions of LPRM1 and 1.1.1.

FIGS. 6 and 7 show LPRMla, 1b, and
It shows the reaction characteristics of 1c and 1d, among which,
Figure 6 shows the response characteristics of detectors A and C of each LPRMI, and Figure 7 shows the response characteristics of detector B of each LPRMI.
, D shows the response characteristics.

Therefore, in FIGS. 6 and 7, the reference numeral 1a indicates the LPRM l a closest to the extraction control rod 2a, and the reference numeral 1b
t1d is LPRMl b which is next closest to LPRMla to the extraction control rod 2a.

1d, and 1c indicates the LPRMIC farthest from the extraction control rod 2a (see FIG. 1).

According to FIG. 6, the response of the detector C shown by the broken line is better than the response of the detector A shown by the solid line, but among them, the response of the LPRM 1a closest to the withdrawn control rod 2a is the best. I understand.

On the other hand, according to FIG. 7, the response of detector B indicated by the broken line is better than the response of detector B indicated by the solid line, but among them, the response of LPRMla closest to the withdrawn control rod 2a is the best. I understand.

Comparing the response characteristics of this embodiment shown in FIGS. 6 and 7 with the response characteristics of the conventional one, first, when there is no bypassed (removed) LPRMI, in the present invention, the LPRMl indicated by the broken line in Figure 6
The response of detector C at point a becomes the response signal of one channel, resulting in a characteristic as shown by curve A in FIG. 8A.

The response signal of the other channel is the LP signal indicated by the broken line in FIG.
This is the output of the detection 5D of RMla, and has a characteristic as shown by the curve in FIG. 9A.

The response signals of these two channels are each independently compared with the maximum allowable output set for the recirculation flow rate, and when the response signal of either channel exceeds the maximum allowable output, the blocking signal generator 16 is activated. (FIG. 4), a control rod withdrawal prevention signal is generated.

As a result, the generation of the pull-out prevention signal is detected by the LPRMla shown in FIG. 7, which exhibits the best response characteristics! It depends on D.

In this case, if the signal transmission processing system from the detector to the blocking signal generator 16 should fail, a withdrawal blocking signal will be generated by the response signal of the other channel, and the characteristics of the other channel will also be changed as shown in FIG. The conventional device shown by the curved line in A also has better response characteristics, so safer driving is possible.

Next, when comparing the present embodiment and the conventional one when the LPRMla closest to the withdrawn control rod 2a is bypassed, one channel of the present embodiment (d is shown by the curve in FIG. 8B). response characteristic, and the other channel is the 9th
The response characteristic is shown by the curve in Figure B.

Of these two channels, the control rod withdrawal prevention signal is output by the channel that exhibits better response characteristics, so it is more effective than the conventional one shown by curve 2 in Figure 8B and curve 0 in Figure 9B. The response characteristics will be improved.

Furthermore, when comparing this embodiment with the conventional one when the LPRMlc farthest from the withdrawn control rod 2a is bypassed, one channel of the present embodiment has a response characteristic shown by curve H in FIG. 8C, The other channel has a response characteristic shown by curve W in FIG. 9C.

Of these two channels, the control rod withdrawal prevention signal is issued by the channel that exhibits better response characteristics, so the control rod pull-out prevention signal is greater than the conventional one as shown by the curve in Figure 8C and the curve force in Figure 9C. The response characteristics will be improved.

Furthermore, LPRMla closest to the extraction control rod 2a,
Comparing this embodiment with the conventional one when the next closest LPRMlb is bypassed, one channel of this embodiment has a response characteristic shown by the curve G in Figure 8, and the other channel has the response characteristic of the 9th channel. In the figure, the response characteristic is shown by curve y.

Since the control rod withdrawal prevention signal is output from the channel that shows better response characteristics among these two channels, the response characteristic is better than that of the conventional one shown by curve 1 in Figure 8 and curve 3 in Figure 9. will improve.

If the control rods 2a are prevented from being withdrawn in each of the bypass states described above, especially when the core output reaches 107, the result will be as shown by thin lines in FIGS. 8A-D and 9A-D, respectively. In fact, the present invention is about 0.0% lower than the conventional one.
When the length is as short as 5 to 1 ft, the control rod 2a can be prevented from being pulled out, allowing safe operation.

Note that, unlike the above-mentioned embodiment, the LP constituting the RBM
The outputs of the RMI detectors A, B, C, and D may be led to an electronic computer, and the maximum values of the detectors A, C, B, and D may be calculated by this computer.

In addition, in the embodiment described above, the LP constituting the RBM
Although the number of RMs is assumed to be four, it may be greater or less than this.

Furthermore, by using all LPRM detector outputs as inputs to the RBM, it is possible to omit the LPRM detector selection circuit based on extraction control rod designation.

Finally, the following table shows a comparison of response characteristics between the above-described embodiment of the present invention and the conventional one.

This table shows that the embodiment of the present invention has better response characteristics than the conventional one, and after withdrawal of the control group,
The withdrawal prevention signal can be generated at a short point in the withdrawal length, and fuel damage and integrity loss due to local power increase can be effectively prevented.

As mentioned above, the control rod withdrawal monitoring device according to the present invention has the following features:
Since the maximum value of the output of each detector of the LPRM constituting the RBM is used as the control rod withdrawal prevention signal, the withdrawal prevention signal can be generated at a short point in the withdrawal length after the control rod is withdrawn. This allows for safer operation of nuclear reactors.

In addition, the instructions from the monitoring device are more linear and rise faster than conventional ones, so they are less susceptible to output fluctuations and noise.

Next, even when the channel is divided into two systems, the difference in response between channels is smaller than in the conventional system, so RB
The instruction of M can be intuitively understood as a change in local output.

Furthermore, the LPR closest to the location where the local output increase occurred
Since the output of M becomes the output of RBM as it is, even when a control rod that is partially pulled out is continuously pulled out, the L
Highly reliable functionality can be expected even when PRM is bypassed.

[Brief explanation of the drawing]

Figure 1 is a plan view showing the arrangement of control rods and LPRM in the reactor core, Figure 2 is a graph showing the correlation between core power, critical thermal flux, and maximum heat flux, and Figure 3 is a diagram showing the control rods and LPRM arrangement in the core. L
An explanatory diagram showing the relationship with PRM, FIG. 4 is an explanatory diagram showing the configuration of a conventional control rod withdrawal monitoring device, and FIG. 5 is an explanatory diagram of main parts showing an embodiment of the control rod withdrawal monitoring device according to the present invention. ,
6 and 7 are graphs showing the effect of the embodiment shown in FIG. 5, FIGS. 8A, B, C, and D, and FIG. 9A. B, C, and D are graphs comparing the effects of the embodiment shown in FIG. 5 and the conventional one shown in FIG. 1-LPRM (in general), 1a, 1b. I C11dt1e, 1ft1gt lh, lj・
LPRM (individually shown), 2... control rod (generally shown), 2a, 2b, 2c... control rod (
(individually shown), A, B, C, D...LPRM
Detector, 12... Control rod drive mechanism, 13... Single stick withdrawal prevention mechanism, 15... Averaging device, 16... Blocking signal generating device, 18... Calculating device, 30... ...Comparison circuit.

Claims (1)

[Scope of Claims] 1. Detectors A arranged in an array in the core of a nuclear reactor and arranged at intervals in the vertical direction from the bottom. Among the plurality of local output area monitors consisting of B, C, and D,
A specific one adjacent to the fuel assembly around the strut rod designated for withdrawal is used as a control rod withdrawal prevention monitor, and withdrawal of the control rod is monitored by output signals from each detector of the local power area monitor. In the control rod withdrawal monitoring device, two of the outputs of the detectors A, B, and C9D are selected from the higher output of A and C and the higher output of B and D. 1. A control device characterized in that two channels are formed and these signals are used as control rod withdrawal prevention signals.