JPH0458196A - Control rod driving mechanism for fast reactor - Google Patents

Abstract

PURPOSE:To improve safety by making pressurized gas to flow in a metal reservoire where low melting point metal is stored and disconnecting a control rod with the pressure of gas passed through the low melting point metal in the metal reservoire. CONSTITUTION:The metal reservoire 35 is applied with the pressurized gas. when the nuclear reactor is in normal operation, the low melting point metal 34 is solid, so the pressurized gas which flows in from an intake pipe 36 is stopped. If abnormality is caused, the low melting point metal 34 is fused to become liquid, so the pressurized gas passes through the low melting point metal 34 to flow in a cylinder 39 from a hole formed at the upper part of the metal reservoire 35, thereby pressing down a piston 38. consequently, a finger rod 20 falls and a latch finger 21 operates to insert the control rod into the reactor core. Thus, the abnormality of the nuclear reactor is detected artificially and physically from outside when caused and the control rod is inserted into the reactor core in safety to stop the nuclear reactor.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a control rod drive mechanism for a fast breeder reactor.

(Prior art) In general, power control and reactor shutdown in nuclear reactors, especially fast breeder reactors that use liquid metals such as sodium as coolants, are performed by installing control rods containing a neutron-absorbing substance such as boron or tantalum in the core support plate. This is done by inserting the fuel assemblies between a plurality of fuel assemblies.

That is, the reactivity of the nuclear reactor is controlled by moving a control rod up and down within a guide tube fixed to a core support plate parallel to the longitudinal direction of the fuel assembly. This control requires that the device that drives the control rods be stable and highly reliable.

The conventional control rod drive mechanism is a rotating control rod drive mechanism that is installed at the top of the reactor vessel that houses the fuel assembly, and is installed in a part of a shielding plug that isolates the atmosphere inside the reactor vessel and closes the top opening of the reactor vessel. A control rod drive mechanism having a drive part fixed on the plug, and an extension tube provided to pass through the rotating plug and reach above the core region to connect the drive part and the control rods. and a control panel that is installed in the central control room and generates electrical signals for driving the drive section automatically or manually. Normally, the output control of the drive unit and the operation for shutting down the furnace are performed by electro-mechanical means.

An example of a conventional control rod drive device is shown in FIGS. 5 and 6.

The liquid level of the coolant 1 in the reactor is at the position shown in the figure.

The drive housing 2 is fixed to the rotary plug 3 and is connected to an upper guide tube 4 passing through the rotary plug 3. A motor 5 is provided at the top of the drive unit housing 2 , and the motor 5 is electrically connected to a control panel 7 by a cable 6 . A screw 8 is concentrically coupled to the rotating shaft of the motor 5, and a pole nut 9 is threaded onto the screw 8. The pole nut 9 is connected to a pair of load cells 11 via a plate 10, and the load cell 11 is connected to a hollow disc-shaped plate 12.
is combined with An electromagnet 13 and a tube 1 are provided on the bottom surface of the plate 12.
4 are combined. The lower part of the cylinder I4 is a hollow disc-shaped plate I
5, and its lower part is connected to an outer extension tube 16. The outer extension tube 16 passes through the rotary plug 3 and extends above a lower guide tube 18 provided in the core I7. The distal end of the outer extension tube 16 is formed with a plurality of leaf spring-shaped latch fingers 2I to constitute a latch mechanism together with the finger rod 2o connected to the distal end of the inner extension tube 19.

On the other hand, an armature 22 is provided at the lower end of the electromagnet 13 that is electrically connected to the control panel 7 and is magnetically detachable. The extension pipe 19 and the outer extension pipe I6 are
It has a heavy tubular shape and penetrates the corresponding position of the rotating plug 3,
Its tip is a finger rod 20 that engages with a latch finger 21.

In the gap between the upper guide tube 4 and the outer extension tube 16, a biological shield 23 is fixed to the top of the upper guide tube 4 at a position corresponding to the rotary plug 3. The lower end of the biological shield 23 and the upper end of the bellows 24 are airtightly connected, and the lower end of the bellows 24 is connected to the outer extension tube 1.
6 and is hermetically connected to a hollow plate 25 installed at an appropriate position. In addition, the inner extension pipe 19 and the outer extension pipe 16
A bellows 26 is provided at each appropriate location, both ends of which are hermetically joined.

An acceleration spring 28 is coupled to the stepped portion 27 of the outer extension tube 16, and the acceleration spring 28 has a coil spring shape on the outer side of the outer extension tube 16 and extends downward, with its lower end touching the top of the acceleration tube 29. ing.

The acceleration tube 29 is provided outside the outer extension tube I6, its lower end is in contact with the handling head 31 of the control rod 30, and its upper end is provided with a tapered dash ram 32.

Further, a dashbot 33 having a tapered inner diameter is installed near the lower end of the upper guide tube 4.

The control rabbit 30 has a structure in which a plurality of absorption pins containing a neutron absorption material are bundled and housed in a protection tube. control rod 3
0 and the lower guide tube J8.

Next, an example of the operation of the conventional control rod drive device will be described.

During normal operation, as shown in FIG. 5, the handling head 31 of the control rod 30 is engaged with the shoulder of the latch finger 21, and the outer extension tube 16 and the control rod 30 are connected. The inner surface of the latch finger 21 is the finger rod 2.
It is constrained by 0. At this time, armature 22
is attracted to and in contact with the electromagnet 13 by magnetic force.

Further, the acceleration spring 28 is in a compressed state, with its upper end being restrained by the stepped portion 27 of the outer extension tube 14, and its lower end being restrained by the acceleration tube head which is restrained by the acceleration spring 28 of the control rod 3°.

To adjust the output of the reactor core in this state, the control panel 7 is manually operated and a forward or reverse rotation signal is transmitted to the motor 5 to cause the motor 5 to rotate. This rotational motion is converted into vertical motion by the screw 8 and the pole nut 9, whereby the control rod 3o is pulled out or inserted, and output adjustment is achieved.

Now, if an abnormal condition occurs in the plant due to some reason, such as a failure such as a decrease in coolant flow rate, a rise in coolant temperature, or an increase in core neutron flux, the failure will be detected and measured by multiple sensors installed inside the reactor. A signal is generated by the system and transmitted to the control panel 7. The control panel 7 generates a scram command signal automatically or according to an operator's operation using a preset logic circuit, and stops energizing the electromagnet 13. An electrical sequence is constructed so that this operation can normally be performed simultaneously for a plurality of reactor shutdown devices installed in a nuclear reactor.

FIG. 6 shows the control rod when it is in a scram. When the electromagnet 13 is deenergized, the armature 22 is separated and falls into the tube 14 by the gap between it and the plate-shaped portion 15 at the lower end. Along with this, the inner extension tube 19 falls entirely, so the finger rod 20 falls and releases the restraint of the latch finger 21. The latch finger 21 is then pinched inward by the restoring force of the leaf spring and disengages from the handling head 31 of the control rod 30.

The control rod 30 rapidly falls through the lower guide tube 18 under the force of gravity and the spring force of the acceleration spring 28 transmitted to the acceleration tube 29 .

Further, when the dash ram 32 installed at the upper end of the acceleration pipe 29 enters the dash pot 33 installed inside the upper guide pipe 4, the acceleration force of the acceleration pipe 29 is relaxed by the fluid pressure of the coolant and the acceleration pipe 29 remains as it is. Supported by dashbot 33.

Through the above steps, the scram operation of the control rods is achieved.

The bellows 24 and the bellows 26 are used for the purpose of allowing the outer extension tube 16 and the inner extension tube 19 to move in the axial direction and isolating the atmosphere within the furnace vessel.

Further, the load cell 11 is used for the purpose of confirming the healthy operation of the control rod drive mechanism.

(Problem to be Solved) As mentioned above, in conventional nuclear reactor operation, the state inside the reactor is monitored by displaying it on a measurement system using a plurality of sensors installed inside the reactor.

In the event of an abnormality, a scram signal generated from the measurement system is sent to the control panel and the control rods are inserted into the reactor core either automatically or by operators manually operating the control panel 7 according to the measurement system display. . However, if a control rod cannot be inserted into the reactor core due to a failure in the measurement system including sensors, the control panel, or the control rod drive mechanism, or if a human operation error occurs, appropriate measures for abnormal core output may be delayed. Or there are tasks that are not done.

The present invention was made in order to solve the above problems, and an object of the present invention is to provide a fast reactor control rod drive mechanism suitable for improving safety.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized in that a rotating plug is provided in a part of a shielding plug that closes an opening at the upper end of a reactor vessel housing a reactor core, and a rotary plug that penetrates the rotating plug is provided. An outer extension tube is provided so as to reach above the core region and connect with a control rod in the core region, and an inner extension tube that is separated by electromagnetic action is provided within the outer extension tube, and the inner extension tube is separated by electromagnetic action. In a fast reactor control rod drive mechanism, a finger rod is connected to the end of the outer extension tube, and a latch finger is connected to the end of the outer extension tube, and the control rod is gripped by the latch finger. A metal reservoir is provided to contain metal,
An inflow pipe for pressurized gas to flow into the metal reservoir and an exhaust pipe for the pressurized gas are provided, and a latch mechanism is provided for disconnecting the control rod by the gas pressure that has passed through the low melting point metal in the metal reservoir. It is characterized by:

(for production) The metal reservoir is pressurized by pressurized gas.

During normal operation of a nuclear reactor, low melting point metals are in a solidified state;
The pressurized gas flowing in from the inflow pipe is stopped.

When an abnormality occurs, the low melting point metal melts and liquefies, so the pressurized gas passes through the low melting point metal, flows into the cylinder through a hole provided above the metal reservoir, and pushes down the piston. This causes the finger rod to fall, actuate the latch fingers, and insert the control rod into the reactor core. The pressurized gas inside the cylinder is exhausted to the outside from the exhaust port.

In this way, in the event of an abnormality, it is possible to physically detect an abnormality in the reactor and safely insert the control rods into the reactor core to shut down the reactor without manually operating from the outside.

(Example) A first example of a control rod drive mechanism for a fast reactor according to the present invention will be described with reference to FIGS. 1 and 2.

In addition, in the present invention, the conventional control rod drive mechanism is improved so that the scram operation of the control rod drive mechanism is performed mechanically by the flow of gas, so only the main parts are shown in FIGS. 1 and 2. ing.

Figures 1 and 2 show a conventional control rod drive mechanism.
The latch mechanism for connecting control rods, which is the part where the present invention is incorporated, is shown in an enlarged view, with FIG. 1 showing the present invention before its operation and FIG. 2 after its operation. Further, in the drawings, parts having the same functions as those of conventional component equipment are designated by the same reference numerals, and explanations of overlapping parts are omitted.

A cylindrical metal reservoir 35 is installed inside the finger rod 20 shown in FIGS. 5 and 6, which serves as a reservoir for a low melting point metal 34 having a melting point of 550° C. to 650° C. A pressurized gas inlet pipe 36 having a length from the inner upper part of the metal reservoir 35 to a position where the low melting point metal 34 is immersed is installed in the center. A vent hole 37 is provided in the upper part of the metal reservoir 35.

A finger rod 20 having an upper portion shaped like a piston 38 is installed on the outside of the metal reservoir 35 to enable vertical movement, and the outside of the piston 38 is a cylinder 39.

The lower part of the cylinder 39 has a shape suitable for accommodating the spring 40, and the spring 40 exerts an upward force to push up the finger rod 20 in order to keep the finger rod 20 in a fixed position. .

Further, a bellows 41 is used to isolate the inner envelope of the spring 40 and a part of the cylinder from intrusion of the coolant.

An exhaust pipe 42 is installed at the top of the cylinder 39,
Although not shown, the exhaust pipe 42 extends above the control rod drive mechanism, passes through the rotary plug 3, is routed out of the reactor, and is connected to a valve 43.

Next, an example of the operation of this embodiment will be explained.

During normal operation of the nuclear reactor shown in FIG. 1, gas pressure is always applied to the inlet pipe 36 from outside the reactor through the inner extension pipe 19, and the direction and flow of pressurization are shown by arrows.

The low melting point metal 34 in the metal reservoir 35 is in a solid state at the reactor temperature (550° C.) during normal operation, and the loaded gas is stopped at the upper surface of the low melting point metal 34 in the inlet pipe 36. Be in a state of being. Note that the valve 43 is normally closed.

Adjustment of the core output during operation is performed in this state,
In addition, the control rod 30 can be disconnected from the inner extension tube 19 as before.
Drop the entire unit, close the latch finger 20, and then close the control rod 2.
0 can be separated.

Figure 2 shows the operating state of the present invention when the control rods cannot be separated due to the fall of the inner extension tube 19 due to some kind of failure during the abnormal core output.
As the temperature of the coolant 7 rises, the temperature of the coolant 1 passing through the inside of the lower guide pipe 18 installed in the reactor and the reactor core I7 also rises, and is discharged to the upper part of the reactor core 17.

Since the latch fingers 21 and the finger rods 20 are located directly above the reactor core 17, heat is transferred to the internal low melting point metal 34 and melts it, and the gas that is normally stopped is transferred to the low melting point metal 34. The latch finger 20 closes and the control rod 20 is separated from the handling head 31. and falls into the lower guide tube 18, stopping the reactor core 17.

To return after operation, after the core 17 temperature has decreased and the low melting point metal 34 has solidified, the valve 43 is opened to exhaust the gas in the cylinder 39 and the finger rod 20 is returned to its normal position. Low melting point metals 34 include antimony (melting point 630°C), duralumin (melting point 570°C), etc. Also, considering the thermal conductivity that affects operating time, it is possible to select an alloy that has a melting point at the required operating temperature using multiple metals. Methods such as manufacturing and using it may also be considered.

In the first embodiment, since the control rod coupling mechanism of the control rod drive mechanism is operated directly by mechanical operation, electrical troubles from the control panel 7 to the control rod drive mechanism and mechanical problems of the drive section of the control rod drive mechanism are avoided. Even if any trouble should occur, the control rods can be inserted into the reactor core without being affected.

Next, a second embodiment of the present invention will be explained with reference to FIGS. 3 and 4.

The installation position is the same as that of the first embodiment, and the first
Parts having the same functions as those in the embodiment are designated by the same reference numerals.

FIG. 3 is an enlarged vertical sectional view showing the present invention before operation, and FIG. 4 after operation.

Inside the finger rod 20 shown in FIGS. 3 and 4, a metal reservoir 35a that serves as a reservoir for the low melting point metal 34 is installed, and an inflow pipe 36a is installed in the center of the metal reservoir 35a. An exhaust pipe 42 is provided above the metal reservoir 35a.
After the pressure switch 44 is connected and pulled out of the furnace,
It is connected to the valve 43 via.

During normal reactor operation, the output is adjusted by performing the same operation as in the first embodiment.

Next, an example of the operation of this embodiment will be explained.

The basic operation is the same as the first embodiment, but
The gas that has melted and passed through the low melting point metal 34 is transferred to the pressure switch 4.
4 and operate it.

The contact point of the pressure switch 44 is the electromagnet 13 of the control rod drive mechanism.
is coupled in series to the operating circuit.

When the pressure switch 44 shown in FIG. 3 is not loaded with gas, the contacts of the pressure switch 44 are in the ON state. Therefore, if the pressure switch 44 is not loaded with gas pressure, the operating circuit of the electromagnet 13 is not affected and normal operation can be performed.

When the reactor output is abnormal, gas pressure is transmitted to the pressure switch 44 as shown in FIG. 4, and the operating circuit for the electromagnet 13 demagnetizes the electromagnet 13 and disconnects the control rods regardless of the operation of the control panel 7. . To return after operation, the valve 43 is released as in the first embodiment.

In the second embodiment, since there is no mechanical movement compared to the first embodiment, the structure can be simplified.

[Effects of the Invention] According to the present invention, even if there is a failure of equipment such as the measurement system, control panel, control rod drive mechanism, human operation error, delay in response, etc. in the event of abnormal core output, it is possible to prevent damage from external sources. It is possible to detect an abnormality in the output of the reactor core, disconnect the control rods, and insert them into the reactor core without requiring any operations. It is highly safe because it has the ability to return to its normal state when the reactor core output returns to normal and operate again and again.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing the state before functional operation of the first embodiment of the fast reactor control drive mechanism according to the present invention, FIG. 2 is a longitudinal cross-sectional view showing the state after operation, and FIG. 4 is a longitudinal sectional view showing the second embodiment of the present invention before its functional operation, FIG. 4 is a longitudinal sectional view showing the same state after the operation, and FIG. 5 is a drawing showing the control rod connection of the conventional control rod drive mechanism. FIG. 6 is a vertical cross-sectional view showing a state in which the control rods are separated and inserted into the reactor core. Extension tube, 2G... finger rod, 21... latch finger, 30... control rod, 31... handling head, 34... low melting point metal, 35... metal reservoir,
36...Inflow pipe, 37...Vent hole, 38...Piston, 39...Cylinder, 40...Spring, 4
1...Bellows. 42...Exhaust pipe, 43...Valve, 44...Pressure switch. (8733) Agent: Yoshiaki Inomata, patent attorney (and others)
1 person) 1... Coolant, 3... Rotating plug, 4...
・Upper guide pipe, 16...Outer extension tube, 17...Reactor core, 19...Inner Teikoku No. 2 Fig. Half 3 χ Kaya 4 Fig.

Claims (1)

[Claims] A rotating plug is provided in a part of a shielding plug that closes an upper end opening of a reactor vessel housing a reactor core, and extends through the rotating plug to reach above the core region and is coupled to a control rod in the core region. An outer extension tube is provided within the outer extension tube, and an inner extension tube that moves toward and away from the outer extension tube by electromagnetic action is provided, and a finger rod is connected to the distal end of the inner extension tube. In a control rod drive mechanism for a fast reactor in which a latch finger is connected to the latch finger and the control rod is gripped by the latch finger, a metal reservoir containing a low melting point metal is provided in the inner extension tube, and a pressurized gas is introduced into the metal reservoir. A high-speed vehicle comprising an inflow pipe for inflow and an exhaust pipe for pressurized gas, and a latch mechanism for disconnecting the control rod by the pressure of the gas that has passed through the low melting point metal in the metal reservoir. Control rod drive mechanism for reactors.