JPS5933866B2 - Control rod withdrawal monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control rod withdrawal monitoring device with improved response characteristics in a boiling water nuclear reactor.

A boiling water reactor is provided with a control rod withdrawal monitoring device in order to monitor an increase in output caused by control rod withdrawal during power operation.

In order to increase the output, when a control rod is selected, a plurality of fixed in-reactor neutron detectors (hereinafter referred to as LP) are placed around the selected control rod.
RM) is selected, the average value of the signal from that LPRM is taken, and when that value exceeds the average value before withdrawal by a predetermined value, a control rod withdrawal prevention signal is sent to prevent control rod withdrawal. It is equipped with a function to suppress the increase in output to below a predetermined level.

FIG. 1 is a diagram showing an example of the arrangement of T and PI (M) in a conventional device.

As is clear from this figure, 16 LPFtMs, that is, fixed type in-core neutron detectors, indicated by circles 2 and triangles 3 are arranged around the extraction control rod 1.

This LPRM is divided into two systems, for example, A system and B system, and eight LPRMs are assigned to each system.

The A and B systems have different signal strength-control rod withdrawal position characteristics, as shown in FIGS. 2a and 2b, respectively.

When all the LP RMs are normal and both the A and B systems are operating, the response of both systems is fast, as shown by the solid lines in Figure 2 a and b.

If a perpendicular line is drawn from the intersection of this solid characteristic curve and a preset withdrawal prevention level straight line, the control rod withdrawal positions al and bl can be obtained.

Therefore, the control rod withdrawal prevention signal described above is sent from the system that reaches the above-mentioned intersection earlier among the two systems.

If the A system responds quickly, control rod withdrawal is prevented at the al position, and if the B system responds quickly, the control rod withdrawal is prevented at the bl position.

By the way, there are variations in the output of the LPRM as the control rods are withdrawn.

This variation includes some that are undesirable from the viewpoint of preventing control rod withdrawal.

For example, an output that is extremely larger or smaller than the average value due to a malfunction or the like may cause the control rod to be erroneously pulled out.

Therefore, LPR, which is undesirable from the viewpoint of preventing control rod withdrawal,
Bypassing or disabling M, the preferred LPR
A control rod withdrawal prevention signal is output based only on the output signal from M.

Therefore, in some cases, either system A or system B may be completely bypassed.

This is what is meant by the A system bypass or B system bypass described in Table 1.

When the system is bypassed, the response of the system is worse than when it is normal, ie, when there is no bypass.

Furthermore, among the LPRMs in the system, in FIG. 1, if LPRM 2 or 3, which is close to the extraction control rod 1 and shows a good response, is bypassed, the response will be poor.

This case is called worst-case bypass.

Table 1 shows the pull-out prevention position in various cases. In this table, m1s(alt')1) or m1n(a2.b2) is the smaller value of a, )bt. , or a2jb2, whichever is smaller.

The characteristic curves shown by dotted lines in FIGS. 2a and 2b show the characteristics of each group at the worst bypass.

As can be seen from FIG. 2, in the worst-case bypass, the control rod withdrawal position moves to a2 for system A and to b2 for system B, resulting in a considerably worse response state than in normal conditions.

In this way, in conventional devices, each group as well as a specific LPR
When M is bypassed, the response deteriorates, and an improvement has been desired.

Further, in a nuclear reactor where high safety is required, the deterioration of response due to the bypass as described above is undesirable because it narrows the safety margin.

The present invention has been made to eliminate the above-mentioned drawbacks, and is intended to provide a system in which one of the two systems or a specific fixed reactor neutron detector (LPRM), or both one system and each LPRM, are bypassed. It is an object of the present invention to provide a control rod withdrawal monitoring device that exhibits response characteristics even when the control rod is withdrawn.

Hereinafter, the present invention will be explained with reference to an embodiment shown in FIG. 3 and subsequent figures.

FIG. 3 shows a control rod drive system of a boiling water reactor using the control rod withdrawal monitoring device 4 of the present invention.

Inside the reactor core 5 shown in FIG. 3, there are control rods 1 as shown in FIG.
3 is stored.

The control rods 1 are pulled out and inserted by a control rod drive mechanism 6 provided below the reactor core 5.

This control rod drive mechanism 6 is controlled by a control rod control device 7.

This control rod control device 7 inputs a control rod operation signal S1 and a control rod withdrawal prevention signal S2, and outputs a control rod drive signal S3 and a control rod selection signal S4.

The control rod drive signal S3 is sent to the control rod drive mechanism 6,
The control rod selection signal S4 is sent to the control rod withdrawal monitoring device 4.

The control rod withdrawal monitoring device 4 inputs the LPRM signal S5 and outputs the control rod withdrawal prevention signal S2 to the control rod control device 7.

FIG. 4 shows in detail the configuration of the control rod withdrawal monitoring device 4 of the present invention shown in FIG. 3. As shown in FIG.

In FIG. 4, the LPRM selection circuit 8 selects the LPR, M2 around the withdrawn control rod 1 in response to the control rod selection signal S4.
and 3, and the selected L P RM signal S5
is the average circuit 9a of A system and B system.

Send to 9b.

This A-system and B-system average circuit 9a. In 9b, the input L
The PRM signals are each averaged and the average signal is sent to the gain adjustment circuit 10atlOb.

In the gain adjustment circuits 10a and 10b, an APRM signal S from an average output monitor (APRM) (not shown) is used.
A, SB and the signals from the average circuits 9a, 9b are compared, and the average circuit 9a is compared with the signals from the APRM signals SA, SB.
, 9b becomes large, the average circuit 9
Adjust the gain of the outputs of a and 9b.

The gain adjustment circuit 10a. The signal from 10b is sent to signal conditioning circuits 11a and Ilb.

The signal adjustment circuits 11a and llb include the circuit 10a,
In addition to the output from the bypass circuit 10b, a signal from the bypass number determination circuit 12 is also input.

The bypass number determination circuit 12 determines the number of bypassed LPRMs among the selected LPRMs based on a signal provided from the LPRM selection circuit 8.

Note that the circuit 12 receives channel bypass signals S6. from the A system and B system. When S7 arrives, it is determined that all LPRMs in that system are bypassed.

The bypass number signal S8 from the bypass number determining circuit 12. Based on S9, the signal adjustment circuits 11a and 11b are set to adjust the output as follows.

In other words, each output of the averaging circuits 9a and 9b adjusted by the four gain adjustment circuits 10a and 10b is x, the number of LPRMs is N1, of which the number of bypassed LPEs (n is the number of M), and the average before control rod withdrawal is circuit 9a, 9+)
When R is the limit increase rate of the output of the circuits 9a and 9b which should send out the control rod withdrawal prevention signals S2a and S2b, the signal adjustment circuit 11a.

Is the output y from 11b? is set to be.

It is assumed that the above-mentioned limit increase rate R is set to 5% in this embodiment.

Signals from the signal adjustment circuits 11a and 11b are sent to determination circuits 13a and 13b.

These determination circuits 13a and 13b are the signal adjustment circuit 11a.
.

When the signals ya and yb from 11b become larger than the control rod withdrawal prevention signal set value, which is set to (1+R) times the output X of the average circuit 9a t 9b before control rod withdrawal, the control rod withdrawal prevention signal S2a , S2b is output.

In this device configured as described above, a predetermined control rod is selected during output operation, and the control rod control device 7 in FIG.
When the control rod operation signal S1 is input to the control rod selection signal S4, the control rod selection signal S4 is sent to the LPRM selection circuit 8 of the control rod withdrawal monitoring device 4.

Then, the LPRM selection circuit 8 selects a necessary LPRM, that is, a fixed in-reactor neutron detector (LPRM) 2.3 based on the control rod selection signal s4, and sends its output signal to the averaging circuits 9a and 9b.

For example, if 16 LPRMs are arranged around the selected extraction control rod 1 as shown in Fig. 1, they are divided into groups of A system and B system with 8 signals each. The signal is averaged by an average circuit 9a of each system.

Send to 9b.

Further, a part of the output signal of the LPRM selection circuit 8 is also sent to the bypass number determination circuit 12 to select the selected LPRM.
It is determined how many of them are bypassed.

The signals sent to the averaging circuits 9a and 9b are each averaged and then sent to the gain adjustment circuit 10a.

10b, it is adjusted to be larger than the APRM signals SA and SB.

This adjusted average signal is transmitted to signal conditioning circuits lla and 11b.
, the output is adjusted according to the number of LPRMs being bypassed.

For example, if one system is bypassed and the other system's
If four of the LPRMs are bypassed and the signals from the averaging circuits 9a and 9'b are set to 100, then the following equation is obtained.

Furthermore, if all 16 LPRMs are bypassed, then the following equation holds true.

The thus adjusted signal is used in the determination circuit 13a.

13b, it is compared with the control rod withdrawal prevention signal output set value, and when the adjustment signal exceeds the above set value,
Control rod withdrawal prevention signals S2a and S2b are output to prevent control rod withdrawal.

Note that when all 16 LPRMs are bypassed, the set value 105 is always reached as described above, so a control rod withdrawal prevention signal is output.

FIGS. 5a and 5b show response characteristic curves for system A and system B when using the apparatus of the present invention.

In the figure, A is when LPRM is normal, LPRM is the worst bypass and there is no system bypass, C is when LPFtM is normal and one system is bypassed, and 2 is when LPRM is worst bypass and one system is bypassed. It shows each characteristic of .

Therefore, when the LPFtM or the system, or the LPRM and the system are both bypassed, the control rod withdrawal prevention positions are as shown in Table 2.

As is clear from this table, in a normal case, extraction is prevented at the same position m1n(al, 1)1) as in the conventional device.

Further, when the system is normal and the LPRM is in the worst case bypass, the position of m1n(a2.1)2) in the conventional device becomes mtnc a37 b3), and is pulled out at a position almost unchanged from normal.

When one system is bypassed and the LPRM of the other system is normal, in conventional equipment, when the A system is bypassed, it is drawn out at BL, and when the B system is bypassed, it is pulled out at AL. However, in the device of the present invention, when the A system is bypassed, it is pulled out at b4, and when the B system is bypassed, it is pulled out at a4, showing a better response than in normal times.

When one system is bypassed and the other system's LPRM is bypassed in the worst case, in the conventional device, when the A system is bypassed, it is pulled out at b2, and when the B system is bypassed, it is pulled out at a2. However, in the device of the present invention, when the A system is bypassed, it is pulled out at 1]5, and when the B system is bypassed, it is pulled out at a5, showing a better response than normal.

In the above embodiment, the output y (yatyb) of the signal adjustment circuits 11a and 11b was set to y=xX(1+aH), but it may be set to y=x+xO−R,y.

However, XO is the signal level of the average circuits 9a and 9b before extraction.

Of course, it is also possible to adjust the response by simply changing R.

In this embodiment, the output signals of the averaging circuits 9a j 9b are
Although increased by bypassing the PRM, the average circuit 9a
, 9b are left as they are, and the control rod withdrawal prevention signal output set value is decreased in accordance with the number of bypassed LPRs, M, to obtain the same effect.

As described in detail above, the device of the present invention determines the number of bypassed fixed in-reactor neutron detectors (LPRM) using a bypass number determination circuit, and determines the number of bypasses determined by the bypass number determination circuit. Basically, the output signal of the averaging circuit that averages the signals from the LPRMs is amplified by a factor of (1 + RN) by the signal conditioning circuit, so the more LPRMs are bypassed, the more difficult the signal conditioning becomes. The output of the average circuit is amplified by the circuit, and L
No response degradation occurs due to the PRM being bypassed.

Furthermore, in the device of the present invention, even if a control rod is accidentally withdrawn during power operation and many LPRMs are bypassed, the control rod is always prevented from being withdrawn at an early position, thereby preventing an increase in output. However, since the worst-case scenario such as fuel damage can be avoided, this not only improves the response of the control rod withdrawal monitoring device, but also increases the reliability and safety of boiling water reactors.

[Brief explanation of drawings]

Fig. 1 is a layout diagram of a withdrawn control rod and a fixed in-core neutron detector, Fig. 2 alb is a signal strength-control rod withdrawn position characteristic diagram of the conventional device, and Figs. 3 to 5 alb are diagrams of the present invention. FIG. 3 is a diagram showing the control rod 1 drive system of a boiling water reactor to which the present invention is applied, and FIG. 4 is a diagram showing the configuration of the control rod withdrawal monitoring device of the present invention. FIG. 5 alb is a signal strength-control rod withdrawal position characteristic diagram of the device of the present invention. 1... Control rod withdrawal control rod, 2, 3... Fixed type in-reactor neutron detector (LPRM), 4... Control rod withdrawal monitoring device, 5...・Reactor core, 8...L
PRM selection circuit, 9a. 9b...Average circuit, 10a, lOb...
・Gain adjustment circuit, 11 atllb... Signal adjustment circuit, 12... Bypass number determination circuit, 13
a + 13b...Judgment circuit.

Claims (1)

[Claims] 1. In a boiling water reactor, a bypass number determination circuit that determines the number of bypassed fixed in-reactor neutron detectors (LPRM), and a bypass number determination circuit that determines the number of fixed in-reactor neutron detectors (LPRM) that are bypassed, and a The control rod is characterized by comprising a signal adjustment circuit that increases the average value of the signal from the LPRM at a predetermined power increase rate, and means for preventing a control rod withdrawal operation when the output of this circuit exceeds a predetermined level. control rod withdrawal monitoring device. 2 The signal conditioning circuit sets the number of LPRMs used to N,
The number of LPRMs to be bypassed is n1. When the critical increase rate of the above average output signal that should prevent control rod withdrawal with respect to the value of the detection average signal before control rod withdrawal is R, the detection average signal is multiplied by (1+R-i). A control rod withdrawal monitoring device according to claim 1, wherein the control rod withdrawal monitoring device is characterized in that: 3 The signal conditioning circuit sets the number of LPRMs used to N,
When the number of LPIIs (M) to be bypassed is n, and the value of the detected average signal before control rod withdrawal is xO, 0X-R is added to the detected average signal once. A control rod withdrawal monitoring device according to scope 1.