JPH03128488A - Nuclear reactor emergency stopping device - Google Patents

Abstract

PURPOSE:To improve the reliability of an emergency stopping function and to easily introduce the device in an existent plant by operating an emergency stop valve which is provided later even by an independent detector and a logic circuit, and stopping a nuclear reactor in emergency. CONSTITUTION:The device is provided with the detector 14 independent of a detector 1 and detection signals as to parameters of high reactor pressure and low reactor water level which become extremely severe to handle in case of a failure in scramming are inputted to a substitute control rod insertion logic circuit 15 independent of a scram logic circuit 2 to generate a substitute control rod insertion signal S2 completely independent of a scram signal S1; and the existent emergency valve 13 which is provided afterward is put in operation to discharge air from a scram air header 11, and the control rod is inserted in emergency. Consequently, the scram logic circuit 2 and detector 1 are made redundant and diversed, so the reliability of the emergency stopping device due to them is improved greatly. Further, the device can be introduced in the existent plant only by providing the relatively inexpensive logic circuit and detector additionally.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a nuclear reactor emergency shutdown device for emergency shutdown of a nuclear reactor.

(Prior technology) A nuclear reactor emergency shutdown system automatically inserts all control rods (scram) to protect the reactor when a situation that may impair the safety of the reactor occurs or is expected to occur. It has the function to

Hereinafter, a conventional nuclear reactor emergency shutdown system will be explained with reference to the schematic diagram of FIG. 2.

Although Figure 2 only shows the control rod drive mechanism and its emergency stop device for one control rod in a nuclear reactor, in reality, multiple control rods are installed, and multiple control rods are used to improve reliability. Redundancy is being implemented.

In general, the occurrence or prediction of the occurrence of a situation that may impair the safety of a nuclear reactor is determined based on whether or not an important parameter regarding the safety of a nuclear reactor exceeds a certain set value. This important parameter is constantly monitored by the detector 1. The detection signal of the detector 1 is sent to a scram logic circuit 2 to determine whether a scram operation is necessary, and if a scram operation is necessary, a scram signal S1 is generated.

First, the emergency insertion operation of the control rod will be explained.

The scram inlet valve 4 and the scram outlet valve 5 of the water pressure control unit 3 are closed during normal operation, but during scram, the scram inlet valve 4 opens and high-pressure drive water flows from the accumulator 6 to the cylinder section 8 of the control rod drive mechanism 7. At the same time, the scram outlet valve 5 opens and the drive water in the cylinder upper part 9 of the control rod drive mechanism 7 is discharged into the scram discharge container 10. Therefore, the control rod drive mechanism 7 is inserted into the reactor from the bottom to the top. The hydraulic control unit 3 and control rod drive mechanism 7 are provided for each control rod.

Next, the opening/closing control of the scram population valve 4 and the scram outlet valve 5 will be explained.

The scram population valve 46 and scram outlet valve 5 are pneumatically operated and are designed to open upon loss of air pressure. Instrument air is normally supplied to the scram air header 11, and this air pressure keeps the scram population valve 4 and the scram outlet valve 5 closed.

As described above, when a scram signal @S1 occurs, the scram pilot valve 12 unique to each control rod operates to shut off the instrument air supply side and open the exhaust side.
As the air in the scram air header 11 is vented, air pressure is lost, the scram population valve 4 and the scram outlet valve 5 open, the control rod drive mechanism operates and the control rod is emergency inserted.

Roughly speaking, a backup emergency stop valve 13 common to all control rods is provided independently of the scram pilot valve 12, and this backup emergency stop valve 13 also exhausts the scram air header 11 in response to the scram signal S1. , can perform Scrum operations.

As explained above, the nuclear reactor emergency shutdown device uses the scram signal S1 to exhaust the air in the scram air header 11, thereby emergencyly inserting the control rods and stopping the nuclear fission reaction in the reactor.

On the other hand, as mentioned above, the reactor emergency shutdown system is used to urgently insert all control rods (scram) in order to protect the reactor in a situation where the safety of the reactor may be compromised. If the reactor emergency shutdown system loses its function, the accident progresses so quickly that operators do not have time to use other systems to bring the accident under control and ensure safety. There is. If such a situation were to occur, the safety of the nuclear reactor could not be maintained and a major accident could occur.

For this reason, reactor emergency shutdown equipment is highly multiplexed.

The system is designed to be redundant and highly reliable, and although the probability of such an event occurring is very small, when considering the effects of a failure, it is not necessarily the case that it occurs due to other causes. There is also a possibility that the risks may no longer be negligible compared to the risks involved.

The most likely cause of failure that will lead to loss of functionality of this reactor emergency shutdown device is a failure of the scram logic circuit 2.
Next is the failure of the detector 1. Therefore, in order to further improve the reliability of the reactor emergency shutdown function, it is necessary to provide a logic circuit and a detector completely independent of the scram logic circuit 2 or the detector 1.

As such equipment, alternative control rod insertion systems are being developed in the United States and other countries. As mentioned above, the detector 14, which is completely independent of the reactor emergency shutdown system, is used to detect parameters that would be extremely difficult to deal with for the safety of the reactor in the event of a scram failure.
An alternate control rod insertion logic circuit 15 is provided. Then, regarding the parameters that have a very severe effect on the safety of the reactor, the alternative control rod insertion logic circuit 15 generates an alternative control rod insertion signal S2, thereby creating an independent control rod insertion signal S2 that has the same function as the backup emergency stop valve 13. Alternative control rod insertion valve 16
Scram air header 1
This is to improve reliability for emergency insertion of control rods.

(Problem to be solved by the invention) By the way, in addition to the reactor emergency shutdown device as mentioned above,
Equipping Zara with an alternative control rod insertion system is very effective in improving the reliability of emergency control rod insertion, but this alternative control rod insertion system can be fed back to existing plants and added to the plant. If so, there are the following problems.

In other words, when adding a control rod insertion system to an existing plant, plant modification work is required to add an alternative control rod insertion valve 16 to the scram air header 11, which requires considerable cost. It becomes necessary.

However, the main factor contributing to the loss of functionality of the reactor emergency shutdown system is not the failure of the backup emergency stop valve 13 but the failure of the scram logic circuit 2 and the detector 1, and the addition of this alternative control rod insertion valve 16. The problem was that construction was difficult and expensive, but it did not significantly improve reliability.

The present invention has been made in view of the above circumstances, and its purpose is to provide a nuclear reactor emergency shutdown device that can significantly improve the reliability of the nuclear reactor emergency shutdown function and can be easily introduced into existing plants. There is a particular thing.

[Structure of the Invention] (Means and Effects for Solving the Problems) In order to achieve the above object, the present invention provides a detector for detecting parameters of a nuclear reactor and a detection signal obtained from the detector. A logic circuit that generates an emergency stop signal for the reactor, and the emergency stop signal operates an exhaust valve specific to each control rod and a backup emergency stop valve common to all control rods to exhaust air from the air header. In a nuclear reactor emergency shutdown device that urgently stops a nuclear reactor by urgently inserting a rod, a detector independent of the above-mentioned detector and a logic circuit independent of the above-mentioned logic circuit are provided, and this independent detector and logic circuit The present invention is also characterized in that the backup emergency stop valve is operated to bring the reactor to an emergency stop.

According to the reactor emergency shutdown system of the present invention, by simply adding a relatively inexpensive alternative control rod insertion logic circuit and a detector that monitors the input signal thereto, the reliability of the reactor emergency shutdown system in an existing plant can be improved. It is possible to greatly improve the performance through inexpensive and simple construction.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention, and the same components as those of the conventional example shown in FIG. 2 already explained are given the same reference numerals and explained.

First, the emergency insertion operation of the control rod will be explained.

The scram population valve 4 and scram exit valve 5 of the water pressure control unit 3 are closed during normal operation, but during scram, the scram inlet valve 4 opens, and high-pressure drive water is supplied from the accumulator 6 to the cylinder section 8 of the control rod drive mechanism 7. At the same time, the scram outlet valve 5 opens, and the drive water in the cylinder upper part 9 of the control rod drive mechanism 7 is discharged into the scram discharge container 10. Therefore, the control rod drive mechanism 7 is inserted into the reactor from the bottom to the top. The hydraulic control unit 3 and control rod drive mechanism 7 are provided for each control rod.

Next, the opening/closing control of the scram population valve 4 and the scram outlet valve 5 will be explained.

The scram population valve 4 and the scram outlet valve 5 are pneumatically operated and are designed to open upon loss of air pressure. Instrument air is normally supplied to the scram air header 11, and this air pressure keeps the scram population valve 4 and the scram outlet valve 5 closed.

As described above, when the scram signal S1 is generated, the scram pilot valve 12 specific to each control rod operates to shut off the instrument air supply side and open the exhaust side,
As the air in the scram air header 11 is exhausted, air pressure is lost, the scram population valve 4 and the scram exit valve 5 open, the control rod drive mechanism operates, and the control rod is emergency inserted.

Roughly speaking, a backup emergency stop valve 13 common to all control rods is provided independently of the scram pilot valve 12, and this backup emergency stop valve 13 also exhausts the scram air header 11 in response to the scram signal S1. , can perform Scrum operations.

The emergency insertion operation of the control rods and the opening/closing control of the scram artificial valve 4 and the scram outlet valve 5 described above are the same as in the conventional example. In this embodiment, a detector 14 independent from the conventional detector 1 is provided, and detection signals regarding parameters such as high reactor pressure and low reactor water level, which would be extremely difficult to deal with in the event of a scram failure, are transmitted to the scram. The signal is input to an alternative control rod insertion logic circuit 15 that is independent of the logic circuit 2, generates an alternative control rod insertion signal S2 that is completely independent of the scram signal S1, and operates the existing standby emergency stop valve 13 to prevent scram air.・It is configured to exhaust the header 11 and perform emergency insertion of control rods.

In the case of this embodiment, the scram logic circuit 2 and the detector 1, which contributed the most to failures in conventional reactor emergency shutdown systems, are made redundant and diversified, so the reliability of the reactor emergency shutdown system due to these is made redundant and diversified. Sexuality is greatly improved. Furthermore, since there is no need to install an alternative control rod insertion valve or modify the complicated and expensive scram air header 11, it can be introduced into an existing plant by simply adding relatively inexpensive logic circuits and detectors. It becomes possible.

In addition, in this embodiment, the case where the detector 14 is installed independently from the existing detector 1 has been explained, but if the existing detector 1 is used as this detector 14, it is possible to reduce the cost and reduce the risk of reactor emergency in an existing plant. It becomes possible to improve the reliability of the stopping device.

Note that the detector 14 does not necessarily need to be installed for all the scrum parameters, and may be installed only for the parameters for which it is extremely difficult to deal with a scrum failure as described above.

[Effects of the Invention] As explained above, according to the present invention, the reliability of the nuclear reactor emergency shutdown system, in which it is extremely difficult to alleviate the effects in the event of loss of function, can be greatly improved. This makes it possible to further improve the safety of nuclear reactors. In general, it can be relatively easily introduced not only into new plants but also into existing plants.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a nuclear reactor emergency shutdown system according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a conventional nuclear reactor emergency shutdown system. 1.14...Detector, 2...Scram logic circuit 3...Water pressure control unit, 4...Scram population valve 5...Scram outlet valve, 6...Accumulator 7...Control rod Drive mechanism, 8... cylinder part 9...
・Cylinder top, 10...Scrum discharge container 11...
・Scram air header 12...Scram pilot valve 13...Backup emergency stop valve 15...Alternative control rod insertion logic circuit 16...Alternative control rod insertion valve (8733) Agent Patent attorney Sho Inomata Akira (idiot)
1 person) Figure 1

Claims (1)

[Claims] a detector for detecting reactor parameters; a logic circuit for generating an emergency stop signal for the reactor based on the detection signal obtained from the detector; In a reactor emergency shutdown system that operates a backup emergency stop valve common to all control rods and exhausts the air in the air header to urgently insert control rods and shut down the reactor, a detection system independent of the detector described above is used. A nuclear reactor emergency shutdown system, characterized in that a logic circuit is provided that is independent of the reactor and the logic circuit, and the independent logic circuit also operates the backup emergency stop valve to bring the reactor to an emergency shutdown.