JPS5916676B2 - reactor protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiling water reactor (BWR) protection device.

In order to control output in a nuclear power plant, control rods are inserted into the reactor from the bottom of the reactor, pulled downwards to increase the output, and inserted upwards to decrease the output. I try to control it.

However, in this control rod, the neutron absorbing part and the driving part are not integrated, but are connected by a joint, so it is thought that a mechanical malfunction of this joint part could cause the upper neutron absorber and the lower driving part to separate. It will be done.

In such a case, since the control rod position detector is attached to the lower driving part, it cannot be determined whether the neutron absorber has separated or not.

If the control rod is pulled out in this state, only the neutron absorber remains in the reactor, and the drive device is pulled out.

Therefore, if the neutron absorber falls due to some kind of shock or the like at this time, it may cause a sudden increase in the output of the nuclear reactor.

Here, the schematic structure of a boiling water nuclear reactor will be explained with reference to FIGS. 1 to 4.

That is, in FIG. 1, 1 is a nuclear reactor pressure vessel, and 2 is a nuclear reactor core provided within this reactor pressure vessel 1. In FIG.

Grid plates 3 and 4 are provided at the upper and lower portions of this nuclear reactor core 2, and fuel assemblies 5 are loaded within the reactor core.

Reference numeral 6 denotes a control rod inserted into the reactor core from the lower part of the reactor core 2. This control rod 6 is pulled out through a control rod guide tube 8 by a drive rod of a control rod drive device 7 that penetrates the bottom of the reactor pressure vessel 1. The insertion has been made.

Further, 9 is a reactor water supply pipe for supplying water into the reactor pressure vessel 1, 10 is a jet pump for circulating water in the reactor pressure vessel 1, and this jet pump 10 is supplied with jet pump driving water 11. Driving water is spouted from a jet pump nozzle 12 at the tip.

On the other hand, 13 is a steam separator installed at the water surface in the reactor pressure vessel 1, 14 is a steam dryer installed above this steam separator 13, and the steam dried in this steam dryer 14 is Air is supplied through the main steam delivery pipe 15.

Therefore, in such a BWR, the energy generated by the nuclear fission reaction of the fuel assembly 5 loaded in the reactor core 2 is absorbed by the cooling water 16 flowing from the lower part of the reactor to the upper part in the reactor core, and the cooling water is boiled. Steam is extracted and supplied to a turbine, etc.

The output of the nuclear reactor is controlled by increasing and decreasing the flow rate of cooling water (also a moderator) flowing through the reactor core 2 and by inserting and withdrawing the control rods 6 inserted into the reactor core.

This control rod 6 is a cross-shaped blade that has the function of absorbing neutrons generated by nuclear fission, and if the control rod 6 is inserted deeply into the reactor core, the amount of neutrons generated by nuclear fission absorbed increases, causing a chain reaction. When the number of neutrons used is reduced, the reactor output is suppressed, and the control rod 6 is withdrawn,
Output increases.

FIG. 2 shows the external shape of the control rod 6, in which a stainless steel coating forming a cross-shaped blade 61 is filled with boron carbide, which is a neutron absorber, and a handle 62 is mounted on the top. Joint sockets 63 are provided at the bottom.

When such a control rod 6 is installed in the reactor, it is installed from the upper part of the reactor.

On the other hand, a device 7 for driving the control rod 6 shown in FIG. 2 is driven by water pressure, and is inserted from the bottom of the reactor, and both are connected by a joint.

FIG. 3 shows details of the joint mechanism that connects the control rod 6 and the drive device 7.

That is, in FIG. 3, 64 is a lock nut attached to the shaft end provided in the joint socket 63 of the control rod 6 that is guided by the control rod guide tube 8 and inserted into and withdrawn from the reactor core. This is a lock spring provided around the shaft and restrained by a lock nut 64.

Further, 71 is a housing of the drive device 7 attached to the outer periphery of the joint socket 63, and 72 is a drive body provided within this housing 71. This drive body 72 has a sleeve 73 at its center, and a tip end thereof. It has a joint spud 74 that is inserted into and coupled to the hollow part of the joint socket 63.

FIGS. 4a and 4b are enlarged views of such a control rod joint mechanism, where a shows the state after connection and FIG. 4b shows the state before connection.

In the state before coupling as shown in FIG. 4, the lock release handle 66 is pulled up and the lock nut 64 is pulled up to the state shown.

The number of joint spuds 74 on the drive body 72 of the drive device 7 is 6.
It is divided into individual pieces and contracts in the radial direction.

Therefore, when the lock release handle 66 is released after the joint spud 74 is completely inserted into the joint socket 63, the joint socket 63 and the joint spud 74 are in the state shown in FIG. 4a, and the two are combined and locked. be done.

Furthermore, after the control rod 6 is installed in the reactor, the lock release handle 66 cannot be pulled up, so the sleeve 73 shown in FIG. be.

This becomes necessary when the control rod 6 and the drive device 7 are replaced.

However, with such a joint structure, if the joint comes off, only the drive device 7 shown in FIG. 3 will be pulled out and the control rod 6 will remain in the furnace, resulting in a possible failure 2.

It is conceivable that the control rod 6 may fall downward due to some kind of vibration or the like.

The causes of the joint coming off in this way are (1) the spud 74 was not inserted securely during assembly due to bending, etc.;
(2) The lock release handle 66 remains pulled up; (3) The sleeve 73 is bent and the lock nut 64
Possible reasons include pushing up the amount.

Therefore, in such a case, if the control rod 6 and the drive device 7 are removed and the control rod is pulled out, and as a result, the control rod 6 falls, a failure will occur in which the output will suddenly increase, and the reactor cannot be safely operated. become unable to drive.

Incidentally, a large number of fuel assemblies, control rods, and neutron flux detectors are arranged within the above-mentioned nuclear reactor core.

FIG. 5 is a cross-sectional view of the reactor core and schematically represents such a state.

In FIG. 5, 5 is a fuel assembly, 6 is a control rod, 17a
17b shows an output system neutron detector, 17b shows an intermediate output system neutron detector, and 17C shows a starting output system neutron detector.

In this way, the neutron flux detector is divided into a startup system, an intermediate output system, an output system, etc.

Next, a vertical cross-sectional view of the nuclear reactor core shown in FIG. 6 is shown regarding the positional relationship in the height direction of the core.

In the example shown in this figure, the startup system neutron flux detector 17G has one detector in the height direction and is movable in the height direction.

Further, the intermediate output system neutron flux detector 17b has one detector in the height direction and is movable in the height direction.

Four starting system and intermediate output system neutron flux detectors are arranged in the height direction.

The present invention was developed in view of the above-mentioned circumstances, and its purpose is to determine whether or not the neutron absorber of the control rod has been pulled out from the inside of the reactor, based on the readings of the neutron flux detector inside the reactor. If the connection between the control rod and the drive part becomes separated, this can be notified to the operator through an alarm or a display on the lamp, and furthermore, by preventing the control rod from being pulled out, accidents can be prevented from occurring. It aims to provide a nuclear reactor protection device.

Therefore, in the present invention, we pay attention to the correlation between the readings of the various neutron flux detectors and the position of the control rod, monitor the neutron flux, and predict changes in the neutron flux for a given control rod drive operation. If the predicted value does not change, it is determined that the control rod blade is stuck and the joint is separated, a display is given, and the control rod is prevented from being pulled out or In general, the change in neutron flux for a withdrawal control rod is given as a function of the distance from the withdrawal control rod to the neutron flux detector, and the relationship is as shown in FIG. 7.

Now, the neutron flux detector S is located at a distance R from the withdrawn control rod.
If the neutron flux increase rate after control rod withdrawal is △φ, then it is expressed as △φ−f@.

Neutron flux detectors S1 . . . located at distances R1, R2, . . . Rn from the control rod. S2. ...The neutron flux increase rate in Sn is △φ1. △φ2. ...If △φn, then △
φn=fn(Rn) (1).

Here, the function fn is a function determined by the positional relationship (control rod pattern) of other control rods inserted into the reactor core, and fn-F(Pl, R2, R3,...Pn)...・・・
... expressed as (2).

Here, Pl, R2, R3, . . . Pm are the positions of control rods adjacent to the extracted control rod.

Figure 7 shows R1, R2゜R3 from the pull-out control rod as an example.
The four at a distance of t R4 are neutron flux detectors S1°S2
．． S3. The case for S4 is shown.

Neutron flux detection device S1. S2. S3. The neutron flux increase rate in S4 is △φ1= f 1 (R1), △φ
2-f 2 (R2), △φ3=f3 (R3), △φ
4-f4(R4), and the curve passing through these is Δφ=g(6).

At this time, if the actual neutron flux increase rate △φa is △φa + △φn (3), the actual neutron flux increase rate does not fall within the deviation from the predicted increase rate. , it is determined that the control rod has not come out to the specified position.

An embodiment of the present invention will be described below with reference to FIG.

In addition, regarding the nuclear reactor portion, the same parts as in FIGS. 1 to 6 are given the same symbols, and the explanation thereof will be omitted here.

That is, in FIG. 8, 20 is a control rod position processing device that generates a control rod position signal from the control rod drive device 7;
21 is an amplifier that amplifies the signal from the neutron flux detection device 17; 22 is a control rod position processing device 20; an electronic computer that receives process quantities from the amplifier 21 as input; It consists of a device 24, a storage device 25, and a process output device 26.

Further, 27 is a control console equipped with an operation switch 28 that receives output signals from the process output device 26 of the computer 22 and issues commands for operators to operate the control rods 6; A control rod control device that operates upon receiving commands, output signals from the process output device 26 of the electronic computer 22, and output signals from the control rod position processing device 20, respectively. This is to drive and control the T.

Next, we will discuss its effect.

The operation signal for the control rod 6 is transmitted to the control rod control device 29 by the operator operating the operation switch 28 on the control console 27, and the control rod control device 29 generates a predetermined drive signal.

The drive signal is transmitted to the control rod drive device 29, which drives the control rod 6 to withdraw.

At this time, a control rod position signal is generated by the control rod position processing device 20 and read into the arithmetic and control device 24 via the process input device 23 of the electronic computer 22 .

This position signal, that is, Pl, R2,
. . . From Pm, the function fn is calculated by the arithmetic and control unit 24 according to equation (2), and is then calculated from each neutron flux detector S1. S2. . . . The predicted neutron flux increase rate Δφn at Sn is calculated and calculated according to equation (1) and stored in the storage device 25 of the electronic calculator 22.

By the way, in the reactor core 2, the in-reactor neutron flux increases due to the withdrawal of the control rods 6, but this in-reactor neutron flux signal is amplified by the amplifier 21 and sent to the process input device 23 of the above-mentioned computer 22. Through the arithmetic and control unit 2
4 and further stored in the storage device 25.

Here, the neutron flux data is read before and after the control rod is withdrawn, and the neutron flux increase rate Δφa is calculated and calculated according to the following equation.

Δφa Neutron flux after extraction - Neutron flux before extraction Neutron flux before extraction (4) The above predicted neutron flux increase rate △φn and the actual neutron flux increase rate △φ
a is calculated using equation (3).

If formula 1(3) holds true, the arithmetic processing unit 24 sends a control rod withdrawal prevention signal and a control rod insertion signal to drive and control the control rod drive device 1 via the process output device 26 to drive the control rods 6. Prevent it from being pulled out or make it fully inserted.

Alternatively, the drive device may be driven to the position of the control rod to prevent the control rod from falling, or the control rod may be inserted to a predetermined position and then stopped.

Furthermore, it is also possible to simultaneously output an alarm display signal from the process output device 26 and display an alarm on the control console 27 to inform the operator of the abnormality.

In this way, in this example, we focused on the correlation between the readings of various neutron flux detectors and the drive amount of the control rod, monitored the neutron flux, and predicted the change in neutron flux for a given control rod drive operation. If the predicted value does not change, it is determined that the control rod blade is stuck and the joint is separated, and a display is given to prevent or insert the control rod. As a result, accidents can be prevented from occurring and safe driving can be performed.

Note that the above example concerns a boiling water reactor,
I mentioned the case where the control rods are pulled out from the bottom of the reactor.
It goes without saying that the present invention is not limited to the direction in which the control rods are inserted, and can be applied to nuclear reactors that utilize control rods in which the neutron absorber and the drive device are separated.

In addition, the present invention can be implemented with various modifications without changing the gist thereof.

As described above, according to the present invention, it is determined whether the neutron absorber has been pulled out from inside the reactor based on the readings of the neutron flux detector inside the reactor, and the control rod and its driving part are separated from each other. In such a case, a display is given or the drive of the control rods thereafter is appropriately controlled, thereby providing a reactor protection device that enables safe operation.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the schematic configuration of a boiling water reactor;
The figure is a perspective view showing the outer shape of the control rod, FIG. 3 is a sectional view showing details of the control rod joint mechanism, and FIGS. 4a and 4a. b is an enlarged view of the main part of Fig. 3, a is a diagram showing the state in which the control rod and the driving part are connected, b is a diagram showing the state before joining, and Fig. 5 is a schematic cross-section of the reactor core. FIG. 6 is a curve diagram showing the relationship between the neutron flux increase rate and distance, FIG. 7 is a cross-sectional view of FIG. 5 taken along the line A-A, and FIG. FIG. 1 is a configuration explanatory diagram of a nuclear reactor protection device showing one embodiment. 1...Reactor pressure vessel, 2...Reactor core,
5...Fuel assembly, 6...Control rod, 7
... Drive device, 8 ... Guide tube, 17.
...Neutron flux detection device, 20...Control rod position processing device, 21...Amplifier, 22...
...Electronic computer, 23...Process input device,
24... Arithmetic control device, 25... Storage device, 26... Process output device, 27...
...Control console, 28...Control rod control device.

Claims (1)

[Claims] 1 The neutron absorber of the control rod and the control rod drive device are configured to be connected and separated by a joint mechanism, and the control rod is inserted into and withdrawn from the reactor by the drive device to control the reactor. In the nuclear reactor, the predicted neutron flux increase rate Δφn after control rod withdrawal in each of the neutron flux detectors 81 to Sn, which are arranged at distances R1 to Rn from the control rods, is a function of the distance, Δφn= fn(R
n) and the actual neutron flux increase rate △φ before and after withdrawing the control rod driven by the drive device.
The relationship between the predicted neutron flux increase rate △φn obtained by the first means and the actual neutron flux increase rate △φa obtained by the second means is △φa
+Diameter Δφn (where ε: Tolerable Deviation) or not, and if the third means determines that Δφa +Degree Δφn, the control rod is moved to a predetermined position. and a fourth means for outputting a control rod withdrawal prevention signal or control rod insertion signal to the drive device upon determining that the control rod has not come out, and outputting an alarm display signal to the alarm display unit. A nuclear reactor protection device characterized by: