JPH02257094A - Nuclear reactor shutdown device - Google Patents

Abstract

PURPOSE:To continuously monitor the position of a control rod by setting the position of a magnet in such a manner as to operate a reed switch in the continued scram state of a nuclear reactor and not to operate the reed switch at times exclusive of the continued scram time. CONSTITUTION:A throttle 54 is eventually held in the position relatively conversely higher by as much as the shortened component of a guide tube 56 than an ordinary position in the continued scram state of the reactor. As a result, the magnet 52 hung by a ribbon 51 is held at the same level as the level of the reed switch 53 and the reed switch 53 continuously detects the magnetism from the magnet 52, thus continuously emitting the signal which means that the control rod is held in the scram position. The position of the control rod is continuously monitored in this way in the event of the reactor scram.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention provides a system in which the control rods inserted into the reactor core are 100%
The present invention relates to a nuclear reactor shutdown device that is characterized by being able to reliably confirm that it is in the inserted position.

(Conventional technology) Nuclear power plants are equipped with a reactor shutdown device to urgently stop the nuclear reaction in the reactor in case of abnormal transient changes during operation, an accident, or an earthquake. . This reactor shutdown system generally removes neutrons within the reactor core by immediately fully inserting control rods containing a neutron absorbing material such as boron into the reactor core (hereinafter, this operation of the control rods is referred to as a scram). It has the ability to absorb and stop the chain reaction of nuclear reactions. In the case of boiling water reactors, a hydraulic system is generally used as a driving source for rapidly inserting control rods. On the other hand, during normal operation of a nuclear reactor, it is necessary to appropriately control the amount of nuclear reaction in the reactor, and for this purpose, the control rods are must be slowly moved in and out of the reactor. As described above, reactor shutdown equipment is required to have different functions, such as rapidly inserting control rods into the reactor core in the event of an abnormality, and conversely moving the control rods in and out as slowly as possible during normal operation. To solve this problem, in conventional boiling water reactors, the control rod drive hydraulic system is used as effectively as possible, but the control rods are driven slowly and within a minute range during normal operation. However, a method using only a hydraulic system naturally had its limitations.

This is because hydraulic systems are inherently suitable for rapidly applying water pressure to control rods and rapidly inserting them. In contrast, in recent years, a combined electric and hydraulic reactor shutdown system (Fine Motjon) has been developed as a method suitable for finely controlling control rods during normal operation of a nuclear reactor.
It will be abbreviated as FMCRD below by taking the initials of Control Rod Drive. ) has been proposed. However, this FMCHD has a complex structure, and due to installation space issues, it is difficult to install the control rod position detectors that were installed in conventional reactor shutdown equipment with a separate hydraulic system inside the FMCHD. Become. This control rod position detection function is used to ensure that the control rods are successfully inserted in an emergency situation in the event of an abnormality in the reactor, and that the control rods remain within the reactor and that the nuclear reaction in the reactor is stopped. This is an important item that is essential for safety. Therefore, the above FMCRD is also designed to have a control rod position detector installed outside the FMCRD so that it can be confirmed that the control rod has been successfully inserted once.

A conventional example of FMCHD will be explained below based on the drawings.

In FIG. 1, when the nuclear reactor is in normal operation, the ball screw 2 is rotated by the drive motor 1, and the hollow piston 3 is connected to the upper part of the hollow piston 3 by being pushed up or pulled out. The control rods 4 are indirectly moved in and out of the reactor core 6, which occupies the most important part of the reactor pressure vessel 5. On the other hand, in the event of an abnormality in which some kind of disturbance is applied to the reactor that exceeds normal operation, the hydraulic system 7 is activated, and the hollow screws 1-3 are pushed up at once by the force of water pressure, and the control rods 4 are rapidly pushed into the core 6. inserted. At this time, the hollow piston 3 came off the receiving part (not shown) of the ball screw 2 and rose rapidly, but after about 2 minutes, the receiving part of the ball screw 2 rose due to the rotation of the drive motor 1 and moved to the upper part. It catches up to the position of the hollow piston 3 and supports the hollow piston from below again. Main equipment for driving the control rod 4 such as the ball screw 2 and the hollow piston 3 is housed in a control rod drive housing 8 (hereinafter abbreviated as CRD housing), and the CRD housing 8 and the core 6
are connected via a control rod guide tube 9. The control rods 4 are designed to be guided smoothly into the core 6 at all times through the control rod guide tube 9.

FIG. 2 is an enlarged view showing the main parts of the conventional example of FMCRD shown in FIG. 1 in more detail. In FIG. 2, the hollow piston 3 is in the lower position and the reactor is in normal operating condition. In this case, the hollow piston 3 is supported from below by a ball screw 2 (not shown) and maintains this position. The left and right positions of the hollow piston 3 are held by a guide 22 that is in contact with it through a guide roller 21 and a throttle 24 that is in contact with it through a guide roller 23. The throttle 24 and the guide 22
The throttle 24 is in contact with the guide tube 26 via a disk spring 25, and the throttle 24 maintains its position by placing its lower end on the upper end of the guide tube 26. The guide 22 is fixed to the CHD housing 8 at its upper end, and the throttle 24 can move upward by pushing up the disc spring 25. A latch 2 is attached to the lower end of the super empty piston 3.
7 is provided, and when the hollow piston 3 moves upward and the latch 27 reaches the position of the latch receiver 28 provided in the guide tube 26, the latch 27 is moved to the latch receiver by the force of the spring 29. 28 to hold the hollow piston 3 (see Fig. 4).

A guide roller 30 is provided on the outside of the latch 27,
This allows for smooth movement with the guide tube 26. Furthermore, a magnet 32 is connected to the lower end of the throttle 24 via a ribbon 31. A reed switch 33 is provided several centimeters (referred to as distance A) above the magnet 32 and outside the CRD housing 8, and a signal is generated when the magnet 32 reaches the height of the reed switch 33. It looks like this.

FIG. 3 shows a state diagram in which the control rod is in the uppermost position during scram of the FMCRD shown in FIG. 2. The hollow piston 3 has reached the highest position due to the driving pressure of the hydraulic system 7. At this time, the hollow piston 3 forcibly pushes up the throttle 24, and the disc spring 25 is in the most compressed state.

On the other hand, as the throttle 24 is forcibly pushed up, the magnet 32 connected to the lower end of the throttle 24 via the ribbon 31 moves upward and reaches the position of the reed switch 33. It has been reached. As a result, the reed switch 33 detects the magnetism emitted from the magnet 1 to 32 and issues a signal indicating that the control rods have been reliably scrammed, thereby informing the nuclear power plant operator. However, the position of the hollow piston 3 shown in FIG. 3 shows a momentary momentary state when the reactor is scrammed, and the hollow piston 3 immediately descends due to the reaction of colliding with the throttle 24. Start.

Figure 4 shows that after the hollow piston 3 shown in Figure 3 has descended,
Fig. 2 shows a state diagram held in a Scrum continuation state position. In the scram position, the hollow screws 1 to 3 are located several centimeters below the highest position shown in FIG. 3, and the latch 27 fits into the latch receiver 28 to hold the hollow piston. Along with this, the disc spring 2
Due to the force of 5, the throttle 24 has also come down several centimeters and is now held by the guide tube 26. Due to this, the design is such that the compressive load of the disc spring 25 is not indirectly transmitted to the latch 27. Thereby, the hollow piston 3 is held in the scram position by the latch 27 without receiving unnecessary loads (loads from the disc spring 25 and the throttle 24).

(Problem to be Solved by the Invention) However, in the above-described configuration, the magnet 32 moves downward again by several centimeters (referred to as distance B: distance B = distance A < (moving distance of the hollow piston 3)) like the throttle 24. As a result, the reed switch 33 becomes unable to emit a signal. This may cause operators to be unable to confirm whether the reactor is reliably scrammed. By the way, in the event of a nuclear reactor emergency, one of the most important jobs for reactor operators is to ensure that the reactor is scrammed and maintained in a safe condition. The mental stress on operators when it is difficult to be certain that the reactor is maintained in a safe condition is extremely high, and this can make it difficult for operators to perform other important safety maintenance operations during emergencies. Many experts have pointed out that this may be a factor that could lead to errors.

An object of the present invention is to improve the above-mentioned defects of the conventional FMCRD and to obtain an FMCHD that can continuously monitor the position of control rods when a nuclear reactor is scrammed.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, the position of the magnet during the reactor scram continuation state is within a range that activates the reed switch, and furthermore, when the reactor scram is not in the continuous state, To provide a nuclear reactor shutdown device in which the magnet 1- is outside the range of operating a reed switch.

(Function) In the reactor shutdown device configured as described above, the reed switch is operated only when the reactor scram continues, so the position of the control rod can be continuously monitored when the reactor scrams.

(Example) An example of the present invention will be described below based on the drawings. As shown in FIG. 5, the present invention includes a guide tube 56 whose upper end portion is shorter than that of the conventional FMCRD, and a magnet 52 and reed switch 53 (or a reed switch 53 that is installed relatively downward by that amount). Shortened ribbon 51
(In short, the magnet and reed switch are installed with a dead distance C apart), the Scott 1-rule 54 which is longer and moved downward, the disc spring 55 which is longer than the conventional one, and all other parts are the conventional FMCHD. and similar components.

Next, the operation of the present invention will be explained based on FIGS. 5 and 6. When the nuclear reactor is in normal operation, the FMCRD of the present invention is in the state shown in FIG.

When some kind of abnormal disturbance occurs in the reactor and the reactor becomes in an emergency state, the water pressure system is immediately automatically activated and water pressure is applied in a direction to push the hollow piston 3 upward. hollow piston 3
In response, the control rods (not shown) are rapidly inserted into the reactor core (not shown). Once the hollow piston 3 reaches the highest position in this upward movement (this state is not shown), the throttle 5 is immediately
4 and the disc spring 55, it turns downward. FIG. 6 shows a state in which the latch 27 is stuck in the latch receiver 28 by the force of the spring 29 during the downward movement of the hollow piston 3, and is then fixedly held in the scram position (this state is referred to as the reactor scram continuation state). (called time). In this state, the throttle 54 is held at a relatively higher position than the normal position shown in FIG. 5 by the length of the guide tube 56 that is shorter. As a result, the magnet 52 suspended by the ribbon 51 is held at the same level as the reed switch 53, and the reed switch 53 is held at the same level as the reed switch 53.
The switch 53 will continuously detect the magnetic field from the magnet 52 and will continuously emit a signal indicating that the control rod is held in the scram position.

The FMCRD of the present invention having the above-described effects provides the following effects. If some disturbance is applied to the reactor during normal operation, control rods are urgently inserted toward the reactor core (scram) to bring the reactor to a safe state.
The nuclear reaction in the reactor is stopped. In the event of a reactor scram, it is essential for operators to be able to confirm that the control rods are securely retained within the reactor core at all times to ensure that subsequent emergency operations can be carried out reliably. Although conventional FMCRDs have excellent performance in controlling reactor reactivity under normal conditions, they do not have the ability to continuously monitor the position of control rods when the reactor scrams. As a result, there was a risk that the operator would be subjected to unreasonable mental stress, which could lead to errors in emergency operations. The FMCRD according to the present invention can continuously monitor the position of control rods even when the reactor is scrammed, so operators can always be sure that the nuclear reaction in the reactor has stopped and is maintained in a safe state. Can be confirmed. Therefore, operators can perform the subsequent cooling and depressurization operations of the reactor in a calm state without suffering undue mental stress, and can prevent an emergency situation from occurring at a nuclear power plant. This has the effect of significantly reducing the possibility that operators will commit human error when doing so.

Next, another embodiment of the present invention will be described based on the drawings. FIG. 7 is a schematic configuration diagram showing another embodiment of the FMCRD according to the present invention. In this embodiment, a pilot 71 is newly provided, and the magnet 7 is connected from this via the ribbon 31.
Hang 2. Pilot 71 is guide tube 76
By changing the thickness of the tip in a step-like manner, it is always held slightly below the tip. (Instead of changing the thickness of the tip into a step shape, it is also possible to install a protrusion for holding the guide.) Conversely, the throttle 24 is held at the tip of the guide tube 76 as in the conventional FMCRD. A spring 81 may be provided between the pilot 71 and the throttle 24 so that the pilot 71 is always forcibly pushed down during normal operation.

FIG. 8 shows a situation in which the FMCRD of this embodiment is in a scram state. Pilot 71 is a hollow screw l-
The magnet 7 is held in a higher position than its original state by the ribbon 3, and the magnet 7 is thereby suspended via the ribbon 31.
2 is also held at the same level as reed switch 73, so that reed switch 73 detects the magnetism of magnet 72 and continuously signals that the control rod is in the scram position. Even when the hollow screw 1-3 is in the scram position, according to this embodiment, the slot 1-
Since the lever 24 is held by the tip of the guide tube 76, the load from the throttle 24 and disc spring 25 is applied to the guide tube 76 and not to the hollow screws 1 to 3 or the latch 27. Therefore, according to this embodiment, compared to the conventional FMCRD, there is no need to increase the mechanical strength of the hollow piston 3, latch 27, etc.

〔Effect of the invention〕

Thus, the reactor shutdown system according to the present invention can continuously monitor the position of the control rods when the reactor is scrammed.

[Brief explanation of drawings]

Figure 1 shows the conventional combined electric and hydraulic reactor shutdown system (F
Fig. 2 is a diagram showing the general state of the conventional FMCRD (MCRD); Fig. 3 shows the state of the conventional FMCRD when the hollow piston reaches its highest position during scram operation. The current state diagram, Figure 4 is the conventional FM
Figure 5 is a state diagram of the reactor shutdown system according to the present invention during scram; Figure 6 is a state diagram of the reactor shutdown system according to the present invention during scram; Figure 7 is the state diagram of the reactor shutdown system according to the present invention during scram. FIG. 8 is a state diagram of another embodiment of the nuclear reactor shutdown system according to the present invention during a scram. 1... Drive motor 2... Ball screw 3...
Hollow piston 4...Control rod 5...Reactor pressure vessel 6...Reactor core 7...Hydraulic system 8...Control rod drive mechanism housing 9...Control rod guide tube 21.23...
・Guide roller 22...Guide 24.5
4... Throttle 25, 55... Belleville spring 26.
76...Guide tube 27...Latch
28...Latch receiver 29...Spring 30
... Guide rollers 31, 51 ... Ribbon 32
．． 52.72...Magnet 33, 53.73...
Reed switch 71...Pilot 81...Spring agent Patent attorney Nori Ken Chika Yudo Daishimaru Ken "

Claims (1)

[Claims] a control rod drive mechanism housing; a guide tube provided in the control rod drive mechanism housing and having a latch receiver at the top; a throttle provided above the guide tube and having a first guide roller inside; A guide connected to the upper side via a disc spring and having a second guide roller inside, and a third guide roller at the lower end supported on the sides by the second guide roller of this guide and the first guide roller of the throttle. a hollow piston having a latch having a guide roller, and a hollow piston whose lower end is laterally supported by a guide tube by this third guide roller;
In a reactor shutdown device that has a switch and a magnet that sends a control rod position signal to the reed switch, the position of the magnet is activated when the reactor scram is continuing, and when the reactor scram is not continuing, the reed switch is activated. A nuclear reactor shutdown device characterized by setting a switch in a range in which it is not activated.