JPS63259495A - Advanced reactor stop mechanism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a new type of reactor shutdown mechanism, and particularly to a new type of reactor shutdown mechanism suitable for preventing the occurrence of ATWS (transient fluctuation without scram).

[Conventional technology]

Figure 9 is a block diagram schematically showing the back-up reactor shutdown Ia structure shown in Japanese Patent Application Laid-Open No. 56-7093.
is a cross-sectional view, and FIG. 3(b) is a partial cross-sectional view showing the operating state. The control rod 1 is supported at its upper part 5 in the upper space within the guide tube 4 by a holding device consisting of a magnetic body 6 and a magnet 8 provided in the guide head 7 . As the material for the magnetic body 6 or magnet 8, a magnetic material whose temperature is the operating temperature of the backup reactor shutdown mechanism, which is set to an appropriate margin higher than the design coolant temperature of the yX subreactor, is used. When the coolant temperature rises due to a coolant accident or a coolant accident and reaches this operating temperature, the supporting force of the control rod 1 due to magnetic force decreases rapidly, and the control rod 1 is inserted into the reactor core 2 under its own weight. Note that 3 is a support plate, 9 is a control rod head, and 10 is an absorption pin.

According to such conventional technology, gJ, which occurs directly in the reactor core without going through the reactor scram signal,
The control rod can be inserted by catching the object.

[Problem that the invention seeks to solve]

In rationalizing new types of reactors, such as fast breeder reactors, HC
There is an international trend toward treating DA (hypothetical core collapse accident) as a non-design basis event. There are several accident sequences that lead to HCDA, but ATWS is the most important sequence among them. For this reason.

As a method of preventing the occurrence of ATWS, it is considered to improve the reliability of the nuclear reactor shutdown system and reduce the probability of ATWS occurrence to a negligible value.

However, almost all scram relay failures were discovered during periodic inspections at the Kahl reactor in West Germany (1
975), Brown's Ferry, USA
The failure of half of the control rod insertions in Unit s Ferry (1980) and failure of the trip circuit breaker during tripping in Unit 1 (Salon) (1983) have occurred, and these are caused by redundancy. This is a type of common cause failure in which devices with similar conditions fail at the same time due to the same cause.

As a method to prevent such common cause failures and improve the reliability of the reactor shutdown system, we have developed a method to prevent such common cause failures and improve the reliability of the reactor shutdown system. 5ASS (self-actuated reactor shutdown mechanism) is being considered as a method of inserting control rods in order to capture the increase in JM slave reactor output. Types of 5ASS include those that use a Curie point of a magnetic material and those that use fluid pressure to capture the rise in sodium temperature at the outlet of the reactor core when an abnormality occurs, but these are basically Both of these methods are effective in cases where the coolant temperature rises due to an abnormality, which is detected and the control rod falls in time.

However, like TOP (reactivity insertion type event),
This method is not very effective when the reactor power increases first and the coolant temperature increases relatively slowly by 1 m.

An object of the present invention is to provide a new type of reactor shutdown mechanism that can shut down the reactor by dropping a control rod in direct response to an increase in output, that is, an increase in neutron flux.

[Means for solving problems]

The above purpose is to hold the control rods by activating an electromagnet using a control rod holding power source that uses uranium metal as a fuse, which has a relatively low melting point that has sufficient margin compared to the coolant temperature during normal operation and during an accident. death.

In response to a reactivity insertion type event, the above-mentioned fuse reacts to the increase in output due to reactivity insertion and melts, thereby cutting off the holding power and causing the control rod to fall. Secondly, an electromagnet is connected to the middle of the cable that connects the coil of this W1 magnet and the control rod holding power source.As the number of neutron threads increases, nuclear fission increases, the temperature rises, and the metal uranium melts. A plurality of fuses are provided corresponding to each operation mode, and a switching means is provided for switching each of the electromagnets and each of the fuses according to the operation mode and connecting them to the control rod holding power source,
By melting the fuse, the control rod is held 1'! ! This is achieved by shutting down the reactor by cutting off the power source and dropping the control rod. Third, uranium hexafluoride gas is sealed in a ceramic case as a fuse,
A fuse is connected that is mechanically blown out when this uranium hexafluoride undergoes nuclear fission and its temperature rises, causing a sudden increase in gas volume, and the rupture of this fuse shuts off the control rod holding source. This was achieved by dropping the control rod to shut down the reactor.

[Effect]

The basic function of the present invention is that when the power reaches the level at which the control rod must be inserted, the metallic uranium fuse melts due to increased nuclear fission of uranium, or the uranium hexafluoride gas inside the case undergoes nuclear fission. The temperature rises and the gas volume rapidly increases, blowing out the fuse, cutting off the power supply that holds the control rod, and causing the control rod to fall.

In reality, in plant operation, there are various operation modes, so the control rod holding power supply system is configured with the above-mentioned fuses that are set accordingly.
Assuming that there are three operating modes, a control rod holding power supply system consisting of three fuses is prepared. That is, fuse A has a melting point in output region A, and fuse B has a melting point in output region A.
has a melting point in exit region B, and fuse C has a melting point in exit region C.
It shall have a melting point of .

When the control rod is held by the control rod holding power supply system as described above and all the fuses are melted, all the holding power is cut off in the exit region C and the control rod falls. Furthermore, if the control rod is configured with fuses A and B, all the holding power sources are cut off in the output area B and the control rod falls.

In this way, by changing the control rod holding power supply system by changing the combination of fuses, it is possible to change the setting output corresponding to each operation mode.

〔Example〕

The present invention will be explained in detail below with reference to the embodiments shown in FIGS. 1 to 3 and 5 to 8, and FIG. 4.

FIG. 1 is a schematic diagram showing an embodiment of the new type reactor shutdown mechanism of the present invention. In FIG. 1, 11 is a control rod assembly; 12 is a control rod assembly;
1 is a connecting pipe, 13 is a magnetic material, 14 is an electromagnet, 15 is a control rod holding power cable, 16 is a control rod holding power cable 15
A fuse made of uranium metal provided in the middle of the guide tube 17 is a guide tube.

FIG. 2 is a perspective view showing an embodiment of the control rod assembly 11 shown in FIG. 1, and shows the control rod assembly 11 in a fast breeder reactor. The control rod assembly 11 is composed of control rod elements 19 containing absorbent pellets 18, as shown in FIG. 2(b), and control rod elements 19, as shown in FIG. 2(a). The protective tube 20 includes a guide tube 17 that serves as a passage through which the protective tube 20 is inserted into the reactor core. When the control rod assembly 11 is in plant operation, the protective tube 20 is pulled up to the upper part of the reactor core by the connecting tube 12. When the plant is shut down, the protection tube 20 is designed to fall into the reactor core. Hereinafter, the protection tube 20 will be read as the control rod 20.

FIG. 3 is a sectional view showing an example of details of the main part of FIG. 1. As shown in FIG. 3, a fuse 16 made of metal uranium is provided in the middle of the cable 15 that supplies the control rod holding ltg (not shown), and the electromagnet 14 connected to the cable 15 is connected to the middle of the connecting pipe 12. In an abnormal situation, when the metallic uranium constituting the fuse 16 increases in response to an increase in reactor power (increase in neutrons), nuclear fission increases in response to an increase in neutrons, the temperature rises, and the fuse 16 melts. , the control rod holding power supply is cut off, the electromagnet 14 loses its magnetic force, the lower connecting pipe 12 is cut off, and the control rod 20
falls into the reactor core and is inserted.

Here, in order to particularly facilitate the temperature rise of the fuse 16, the fuse 16 is positioned at a position where it is easily sensitive to the neutron flux. Details of the construction of fuse 16 are shown in FIG. 3 and are covered with ceramic 21.

A suction plate 22 provided at the top of the connecting pipe 12 is connected to each electromagnet 14.
The coil 23 of the electromagnet 14 is wound around each of the magnetic bodies 24 to 26 in a ladder shape, and the magnetic flux generated by the electromagnet 14 attracts the attraction plate 22 at the top of the connecting pipe 12. .

In fact, when a reaction-insertion type event occurs in the core of a fast breeder reactor (e.g., controlled erroneous withdrawal, bubble passage, etc.), the reactor power increases and the fuel temperature, coolant temperature, and molten area ratio increase. It rises as shown in Figure 4. In this event, first, the reactor power increases, and the coolant flow becomes insufficient relative to this, and the coolant temperature increases with a slight time delay. in this way,
It is thought that there is a possibility that HCDA may occur due to the injection of positive reactivity into the reactor core.

However, according to the embodiment of the present invention, the fuse 16 made of metallic uranium is melted by reacting directly and immediately to the increase in reactor power by nuclear fission of metallic uranium, thereby reducing the control rod holding power supply. The reactor is shut down, the control rods 20 are shut down, the reactor is shut down, and the event ends safely. Additionally, if a flow rate reduction event occurs in the reactor core (for example, loss of ffi source, stuck pump shaft, etc.),
first.

As the coolant temperature rises and positive reactivity is injected into the reactor core, large-scale voids will occur where the coolant boils. The event can be brought to an end.

Next, a method for controlling the output of dropping the control rod 20 in accordance with the operation mode and an outline of the control system will be described.

Taking into consideration the operation mode, the output (thermal output base) for dropping the control rod 20 is 60% overpower (mode A), 70%
The case where excessive output (mode B) and 150% excessive output (mode C) are set will be described.

In this case, the corresponding output setting is made by adjusting the shape of the metal uranium used as the fuse 16 or the thickness of the ceramic 21 as the sheath material.

3rd stage: Fuse A (corresponds to 60% overpower) 2nd stage: Fuse B (corresponds to 70% overpower) 1st stage: Fuse C (corresponds to 150% overpower) . Here, the electromagnet 14 is energized as shown below in accordance with each operation mode.

Mode C: Energizing only the coil 23 wound around the magnetic material 24 Modero: Energizing the coil 23 wound around the magnetic materials 24 and 25 Mode C: Energizing the coil 23 wound around the magnetic materials 24 to 26 As described above, The energization state of the electromagnet 14 is ensured in accordance with each operation mode.

If the reactor output exceeds 60% in mode A, the fuse 16 connected to the coil 23 of the magnetic body 24 and installed in the middle of the cable 15 will melt, causing the control rod holding power source to melt. is cut off, the electromagnet 14 loses its magnetic force, and the suction plate 22 is no longer attracted, so the control rod 20 falls.

In Mode B, when the reactor output reaches 70% overpower, the fuse 16 of the cable 15 connected to the coil 23 of the magnetic material 24, 25 melts, the control rod holding power is cut off, and the electromagnet 14 The control rod 20 loses its magnetic force and falls.

In mode C, when the 1M sub-reactor output reaches 150% overpower, the fuse 16 of the cable 15 connected to the coils 23 of the magnetic bodies 24 to 26 melts, the control rod holding power is cut off, and the electromagnet 14 loses its magnetic force and the control rod 20 falls.

As described above, one embodiment of the system for controlling the energization state of the electromagnet 14 according to the operation mode is shown in FIG. 5. The entire system is composed of the control device 30 that generates the operation mode signal, the circuit breaker 31, etc. It is.

In the state of operation mode A, the control device 30 outputs the signal 32 of operation mode A. When this signal 32 is output, a wipeout (Iilipe out) circuit 33 blocks other operation mode signals.

f! ! Only the circuit breaker 31 of the magnet energization signal A34 is energized, only the power circuit breaker 36 of the electromagnet A35 of the electromagnet 14 is energized, and only the electromagnet A35 has magnetic force.

In operation mode B, the control device t! ! A signal 37 of operation mode B is output from 30, and the wipeout circuit 33
The other operation mode signals are cut off, and only the circuit breaker 31 of the electromagnet energization signal 838 is energized, and the electromagnet 14
Power circuit breaker 36 for electromagnet A35 and electromagnet B39.
40 becomes energized, and electromagnet A35.40 becomes energized. ff! Magnet B3
9 has magnetic force.

In operation mode C, the signal 41 of operation mode C is output in the same way, and the circuit breaker 31 of the electromagnet energization signal C42 is output.
Only energized state, electromagnetic, a, electromagnetic 35
．． Electromagnet B39 and electromagnet C43 have magnetic force.

By using the above control system, the energization state of the electromagnet 14 can be controlled according to the operation mode. In this case, the pregnant use 16 is inserted at the position shown in FIG.

Next, regarding other embodiments of the electromagnet 14, FIG. 6(a),
Explain (b) with a smile. Figure 6(a) is Figure 6(b)
It is AA, il sectional view of a front view.

The embodiment shown in FIG. 6 is characterized in that the electromagnets 14 are arranged horizontally. The suction portion 27 provided on the lower connecting pipe 12 and in contact with the nine suction plates 22 is made of a ferromagnetic material. According to the electromagnet 14 according to this embodiment, the magnetic flux increases as the reactivity of the magnetic bodies 24, 25, 26 arranged in the horizontal direction is inserted into the reactor core. Then, when the metallic uranium forming the fuse 16 shown in FIG. 1 is melted, the control rod holding power source is cut off and the control rod 20 can be properly inserted into the reactor core. Note that in order to change the way the control rods 20 are inserted in accordance with the operating mode, the control system shown in FIG. 5 is used, as in the case described above.

Next, FIG. 7 (
This will be explained using a) and (b). FIG. 7(a) is a front view taken along line A-A in FIG. 7(b), and the embodiment shown in FIG. 7 is characterized by being constructed with independent electromagnets 14.

As shown in FIG. 7, an electromagnet 14 composed of a magnetic body 13 and a coil, each having a fuse 16, is oriented approximately 6 mm in the axial direction.
The electromagnets 14 are provided at an angle of 0 degrees, and each electromagnet 14 independently secures a suction portion 27 with respect to the lower connecting pipe 12. According to the embodiment shown in FIG. 7, when reactivity is inserted in the reactor core, the metal uranium fuse 16 provided in the middle of the control rod holding power cable 15 melts, thereby cutting off the control rod holding power. When the electromagnet 14 loses its magnetic force, the control rod 20 is inserted into the reactor core. However, it is possible to control the control rod insertion output in accordance with the operation mode by using the control system shown in FIG.

Next, another embodiment of the fuse 16 will be described using FIG. 8. The fuses 16 of the devices described so far all utilize melting caused by the temperature rise due to nuclear fission of uranium metal, but in Fig. 8, the fuse 16 is one filled with uranium hexafluoride gas (UFe). When an event associated with reactivity insertion occurs, this uranium hexafluoride undergoes nuclear fission, and the gas volume rapidly increases due to the temperature rise, causing the fuse 50 to undergo mechanical load (
This is to blow it away using pressure (pressure) and cut off the current.

In FIG. 8, 28 is a case made of ceramic, and uranium hexafluoride gas 29 is sealed inside the case 28.

15 is a control rod holding power cable.

By using the device described above, when a reactivity insertion type event or a flow rate reduction type event occurs in the reactor core,
The control rods 20 can be inserted into the reactor core appropriately according to the operation mode of the plant.

Generation of HCDA can be suppressed. In addition, if there is an error in the manufacturing of the fuse 16, the fuse 16
This can be achieved by adjusting the thickness of the ceramic 21 that serves as the sheath to Ws, which is advantageous in manufacturing the metallic uranium fuse 16.

〔Effect of the invention〕

According to the present invention described above, when an abnormality (especially a reactivity insertion type abnormality) occurs in the reactor core, the temperature of the metallic uranium used as a fuse will rise due to the increase in reactor power and it will melt or Alternatively, the gas volume of the hexagonal uranium gas in the case increases rapidly and blows out the fuse, causing the power to hold the control rods to be cut off and the control rods to lose their supporting force, causing the control rods to be inserted into the reactor core due to their own weight. At this time, since the set output can be changed depending on the operation mode, it is possible to prevent the occurrence of ATWS over all operation modes of the plant.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the new reactor shutdown mechanism of the present invention, FIG. 2 is a perspective view showing an embodiment of the control rod assembly of FIG. 1, and FIG. FIG. 4 is a diagram showing temporal changes in fuel temperature, coolant temperature, and molten area ratio in a reactivity insertion type event;
Figure 5 is a system diagram showing one embodiment of the control system that controls the energization state of the electromagnet according to the operation mode, Figure 6 is a configuration diagram showing another embodiment of the electromagnet shown in Figure 1, and Figure 7 is A configuration diagram showing another embodiment of the electromagnet shown in FIG. 1, and FIG.
FIG. 9 is a block diagram showing another embodiment of the fuse shown in the figure, and FIG. 9 is a block diagram schematically showing a conventional back-up reactor shutdown mechanism. 11... Control rod assembly, 12... Connecting pipe, 13...
・Magnetic material, 14... Electromagnet, 15... Control rod holding power cable, 16... Fuse, 17... Guide tube,
20... Protection tube (control rod), 21... Ceramic,
22... Suction plate, 23... Coil, 24-26...
・Magnetic material, 28... Case, 29... Uranium hexafluoride, 30... Control device, 31... Circuit breaker, 33...
・Wipeout circuit, 35°39.43...electromagnet,
36, 40.44...Power circuit breaker, 50...l use.

Claims (1)

[Scope of Claims] 1. In a device in which a connecting tube at the top of a control rod housed in a guide tube so as to be freely raised and lowered is supported by an electromagnet, a cable connecting a coil of the electromagnet and a control rod holding power source is provided. A fuse made of metallic uranium, which melts as nuclear fission increases as the number of neutrons increases and the temperature rises, is connected along the way, and when the fuse melts, the power supply for holding the control rod is cut off, and the control rod is dropped. A new type of reactor shutdown mechanism characterized by a configuration that performs reactor shutdown. 2. The new type reactor shutdown mechanism according to claim 1, wherein the fuse made of metallic uranium is covered with ceramic on the outside and has a capacity corresponding to the operating mode. 3. In a device in which a connecting tube at the top of a control rod housed in a guide tube so that it can be raised and lowered is supported by an electromagnet, a cable connecting the electromagnet, the coil of the electromagnet, and the control rod holding power source is A plurality of fuses made of metallic uranium, which melt due to increased nuclear fission as the number of connected neutrons increases, are provided to correspond to each operation mode, and each electromagnet and each fuse are connected to each operation mode. The reactor is characterized in that it is equipped with a switching means that switches to connect to the control rod holding power source according to the fuse, and when the fuse melts, the control rod holding power source is cut off and the control rod is dropped to shut down the reactor. A new type of reactor shutdown mechanism. 4. In a device in which the upper connecting tube of the control rod housed in the guide tube so as to be able to rise and fall is supported by an electromagnet, a case made of ceramic is provided in the middle of the cable connecting the coil of the electromagnet and the control rod holding power source. A fuse is connected that is mechanically blown out when the uranium hexafluoride undergoes nuclear fission and the temperature rises, causing a sudden increase in the gas volume. A new type of reactor shutdown mechanism characterized by a mechanism that shuts down the reactor by cutting off the rod holding power supply and dropping the control rod.