JP2003270375A - Passive reactor shutdown mechanism - Google Patents

Abstract

(57) [Summary] A passive reactor shutdown mechanism of a light water reactor having a control rod stroke of about 1500 mm or less. SOLUTION: A furnace stop mechanism comprising a cylindrical electromagnet in which the entire stroke of a control rod is accommodated in a magnetic circuit, and two upper and lower magnetic conducting shafts penetrating therethrough and sandwiching a temperature sensing alloy in an adsorption portion. In order to allow natural circulation cooling, it is placed under the reactor operating water level, and if an abnormal event occurs such that the electromagnet part is exposed above the water surface, the temperature of the temperature sensing alloy is raised by the heat of the electromagnet coil. The suction force is reduced, and the lower magnetic pole on which the control rod is suspended can be separated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive reactor shutdown mechanism used as a backup reactor shutdown device for a light water reactor having a control rod drive stroke of about 1500 mm or less in combination with an appropriate drive mechanism. is there.

[0002]

2. Description of the Related Art In an existing nuclear reactor for power generation, when the reactor water level drops due to a pipe breakage accident or the like, a pressure change or water level change is detected by a sensor, and the reactor is connected to a control rod drive mechanism via an electric circuit. A stop signal is sent, the drive shaft disconnection mechanism consisting of the electromagnet and mechanism of the control rod drive device is operated, and the control rod is dropped into the core or inserted, or the valve is opened by the above signal and the accumulated water is stored in The method of sending it to the cylinder and inserting the control rod by water pressure is taken,
Safety is ensured by making sensors and electric circuits multiplicity and diversity.

However, in the future, in the practical application of small furnaces such as installation close to demand areas, in addition to the conventional methods,
There is a need for a simple, passively operated furnace shutdown mechanism. Furthermore, in order to prevent accidents of the control rods popping out, it is also effective in terms of safety to install the control rod drive mechanism in the reactor.

FIG. 7 shows an embodiment of a control rod drive device for a small reactor disclosed in Japanese Patent Laid-Open No. 11-30683, which is a reactor internal type. Reference numeral 51 is a lower magnetic axis, 52 is an upper magnetic axis, and a drive screw is processed. A control rod is attached to a lower portion of 51, an upper portion of 52 is engaged with a ball nut 55, and 55 is directly connected to a rotor 56. A stator 57 is attached to the outside of 56 and together with 56 forms an electric motor 58.

An electromagnet 60 composed of a cylindrical coil 53 and a magnetic flux guide member 54 is attached to the outside of 51 and 52. 60 is longer than the drive stroke S of the control rod.
The separating surface 59 of the and 52 is accommodated in the magnetic field of 60 over the entire area of S. Therefore, when power is supplied to 60, 51 and 52 are adsorbed, and when 58 is rotated in the forward direction, 51 is adsorbed and 52
Is pulled up, the control rod is pulled out, and when 58 is rotated in the reverse direction, the control rod is inserted. Then, when the power supply of 60 is stopped at an arbitrary position of S, 52 to 51 are separated, the control rod is inserted by free fall, and the reactor is emergency stopped.

[0006]

As described above, the control rod drive device of this type has no mechanism or valve in the control rod disconnection portion as compared with the control rod drive device of the existing nuclear reactor for power generation.
Although it is a simple and highly reliable control rod drive device, like the control rod drive device of the current nuclear reactor for power generation, it operates by receiving a signal from an electric circuit and does not have a passive operation function. .

Further, when the water level is lowered due to a pipe breakage or the like, in the worst case, the core cooling function is lost, resulting in a core melting accident. Therefore, the absolute condition is to detect the water level drop immediately and immediately stop the reactor, and there is a demand for equipment that operates passively even if a failure occurs in the electric circuit.

In particular, in the case of a small reactor, in order to secure safety and reduce costs, the filling system may be deleted in order to minimize the piping connected to the nuclear reactor, so that the fluctuation range during operation may be small. Since there is no choice but to deal with large water level gauges, a passive reactor shutdown device is indispensable from the viewpoint of diversity to ensure safety.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a passive shutdown mechanism for a light water nuclear reactor having a control rod stroke of about 1500 mm or less. That is, the present invention is a furnace stop consisting of a tubular electromagnet in which the entire stroke of the control rod is contained in the magnetic circuit, and two upper and lower magnetic conducting shafts that penetrate the electromagnet and sandwich the temperature sensing alloy in the adsorption part. The mechanism is placed under the reactor operating water level so that it can be cooled by natural circulation. When an abnormal event occurs such that the electromagnet part is exposed above the water surface, the temperature of the temperature sensing alloy rises due to the heat of the electromagnet coil. It is a control rod drive mechanism of a nuclear reactor, which is composed of at least reducing the attraction force and separating the lower magnetic pole shaft on which the control rod is suspended.

More specifically, the present invention comprises a control rod separating mechanism composed of two magnetically conductive shafts, an upper and a lower magnetically adsorbed shaft, wherein the upper shaft is the drive shaft of the drive mechanism and the lower shaft is the atomic shaft. The present invention relates to a control rod drive mechanism of a nuclear reactor connected to a reactor control rod, the feature of which is that the attraction surface of the drive shaft has:
A temperature-sensing alloy whose magnetic saturation value decreases at high temperatures is sandwiched, and a mechanism is provided that has a function to passively separate the adsorption surface when the temperature rises abnormally, and a flow path that leads from the coil lower end to the upper end is provided. When the cooling water of this mechanism is cooled by natural circulation by passing the reactor cooling water through it, and the cooling water outlet of this mechanism is located just below the safe water level of the reactor, the water level of the reactor drops below the safe water level. When the cooling outlet is exposed on the water surface, the natural circulation cooling function of the coil is lost, the temperature of the temperature sensing alloy is increased, and the lower shaft is cut off. This is a mechanism that cuts off the magnetism axis and inserts the control rod into the core to passively stop the reactor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Structure of Shutdown Mechanism) FIG. 1 shows an embodiment of a backup reactor shutdown device incorporating a passive reactor shutdown mechanism of the present invention. Reference numeral 1 is a lower magnetic axis, and 2 is an upper magnetic axis. The lower part of 1 is connected to the control rod through the guide tube 3, and 2
Is connected to the drive screw shaft 4 on the upper part of the
The meshing 5 is directly connected to the rotor 6. A stator 7 is attached to the outside of 6 and together with 6 forms an electric motor 8.

An electromagnet 11 composed of a cylindrical coil 9 and a magnetic flux guide member 10 is attached to the outside of 1 and 2. 1
Reference numeral 1 is longer than the drive stroke S of the control rod, and the separation surfaces 12 of 1 and 2 are accommodated in the magnetic field of 11 over the entire area of S. Therefore, when power is supplied to 11, 1 and 2 are adsorbed, in this state, when 8 is rotated normally, 2 is pulled up while 1 is adsorbed, the control rod is pulled out, and when 8 is rotated reversely, the control rod is inserted. Then, when the power supply to 11 is stopped at an arbitrary position of S, 2 to 1 are separated, the control rod is inserted into the core by free fall, and the reactor is stopped urgently. The operation principle up to this point is the same as that of the embodiment disclosed in Japanese Patent Laid-Open No. 11-30683.

A drive mechanism 1 is provided around the upper electric motor 8.
3. Passive reactor shutdown mechanism 14 around the lower electromagnet 11
Then, the present invention relates to 14, in which the temperature-sensitive alloy 15 is incorporated into the upper end of the lower magnetic-conducting shaft 1 or the lower end of the upper magnetic-conducting shaft 2 constituting the magnetic flux guiding member 14 as a path for cooling the coil 9. Multiple lower cooling water holes 1 at the bottom of 10
6-1 and a plurality of upper cooling water holes 16-2 are provided in the upper part, and these reactor shutdown mechanism 14 is processed in the lower part with a plurality of cooling water outlet holes 16-3 serving as outlets of the cooling path. It is connected to the drive mechanism 13 via a guide tube 17 having a length.

FIG. 2 shows the details of the reactor shutdown mechanism 14. Reference numeral 9 denotes a coil bobbin 9-1 made of a non-magnetic material such as Inconel or austenitic stainless steel, and a coil 9-2 wound with an inorganic insulated cable.
And lead wire protection tubes 9-3 and 9- for pulling out the cable
It is composed of a can 9-4 for sealing 1. Further, 1, 2, and 10 are composed of a magnetic material such as martensitic stainless steel.

As the material 15, nickel or a nickel-iron alloy whose magnetic saturation value drops sharply at a temperature exceeding the normal operating temperature of the reactor is used. For example, in the case of a heat supply furnace with a normal operating temperature of 230 ° C., nickel whose magnetic saturation value drops sharply when the temperature exceeds 300 ° C. as shown in FIG. 3 is used.

The coil conductor 9-2 is generally made of copper, but a material having a large electric resistance such as a copper-nickel alloy may be used for the purpose of improving the temperature response of the temperature sensing alloy 15. . As a result, the time from low water level to reactor shutdown can be shortened, so it is applied when a pipe breakage accident with a relatively large diameter is assumed.

4 and 5 show an example in which a control rod drive mechanism incorporating the passive reactor shutdown mechanism of the present invention is incorporated in a small reactor. This furnace is an integrated natural circulation furnace with an output of 100 Mwt, and has no circulation loop, filling system, etc., and minimizes the through piping of the reactor vessel.

In FIG. 4, the left half (a) shows the reactor shutdown state, and the right half (b) shows the reactor operating state. Also, FIG.
Indicates a state in which the passive reactor shutdown mechanism is activated and the reactor is shut down when the reactor water level is abnormally lowered due to leakage such as damage to the piping of the safety valve system.

In FIGS. 4 and 5, reference numeral 21 denotes a reactor vessel, 22
Reference numeral denotes a reactor vessel upper lid, in which a core 23 composed of a nuclear fuel, a core internal structure 24 for supporting the core 23, an upper core mechanism 25 for preventing the core fuel from floating and guiding and controlling the control rod, and steam generation The container 26 is incorporated.

(Operation of Stopping Mechanism) The reactor is controlled by inserting or withdrawing the control rod 27 into or from the core 23.
27 is driven by two types of drive devices with different drive principles in order to ensure safety. One is a main control rod drive device for controlling the output of the nuclear reactor, and the other is a backup reactor stop device according to the present invention. A plurality of units are installed, respectively, and the latter is shown in FIGS. 4 and 5. .

In FIG. 4, 13 is a driving mechanism, 14 is a furnace stopping mechanism, and 12 is a separating part. 28 is the water level before operation,
29 is the water level during operation. As described above, since this furnace does not have a cooling water filling system, the water level changes greatly depending on the operating temperature. However, since the reactor shutdown mechanism 14 is arranged immediately below the water level 28 so that it is always submerged in water when the reactor is in a normal operating state, at the time of reactor startup, all control rods in the post-shutdown system will reach the upper limit. Although pulled out and held at the upper limit during reactor operation, 14 is always in water and cooling is guaranteed.

If the water level drops due to accidents such as breakage of a small-diameter pipe such as a safety valve during operation of the reactor, an abnormal water level is detected by means such as a water level gauge, and the reactor shutdown mechanism 14 is powered off and controlled. Insert rod 27 into the core and shut down the reactor,
Assuming a failure of the detector or the electric circuit of the control system, the water level will further drop, and in the worst case, the core will be damaged. However, as shown in FIG. 5, when the cooling path outlet 14 is lowered to the abnormal water level 30 where it is exposed on the water surface,
Since the natural circulation cooling of 14 is cut off, the internal temperature rises, and the temperature of the temperature sensing alloy 15 also rises, the magnetic flux density for adsorbing the lower magnetic pole 1 and the upper magnetic pole 2 decreases, and 1 is separated. And the reactor shuts down.

[0023]

As described above, the passive reactor shutdown mechanism according to the present invention can passively shut down the reactor before reaching the critical water level without relying on the means for detecting an abnormality. FIG. 6 shows an example of analysis when the reactor output is 100 Mwt, the outlet temperature is 230 ° C., and nickel is used for the temperature sensing alloy 15. If a pipe breakage accident occurs, the water level will drop, and the temperature of the sensing alloy will rise sharply from the abnormal water level, which will cause a sharp drop in the attraction force of the magnetic shaft that suspends the control rod. .
This indicated that the reactor would be shut down well before the critical water level was reached.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a post-reactor shutdown device incorporating a passive reactor shutdown mechanism according to the present invention.

FIG. 2 is a vertical sectional view showing details of a passive reactor shutdown mechanism according to the present invention.

FIG. 3 is a diagram showing a relationship between saturation magnetic flux density of nickel and temperature.

FIG. 4 is a vertical sectional view of a reactor in which a passive reactor shutdown mechanism of the present invention is arranged.

5 is a diagram showing a case where a cooling water outlet hole in FIG. 4 is exposed on the water surface.

FIG. 6 is a diagram showing an analysis example showing an effect of the passive reactor shutdown mechanism of the present invention.

FIG. 7 is a diagram showing a reactor control rod driving device equipped with a conventional reactor shutdown mechanism.

[Explanation of symbols]

1: Lower magnetic axis 2: Upper magnetic axis 3: Guide tube 4: Drive screw shaft 5: Ball nut 6: rotor 7: Stator 9: coil 10: Magnetic flux guide member 12: Separation surface 15: Temperature sensing alloy 16: Cooling water hole 17: Guide tube 23: Core 26: Steam generator 27: Control rod 28: Water level before operation 29: Water level during operation 30: abnormal water level

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsutomu Yoritsuke             4 of 2 Shirane, Shikata, Tokai-mura, Naka-gun, Ibaraki Prefecture               Japan Atomic Energy Research Institute Tokai Research Center (72) Inventor Sho Imayoshi             4 of 2 Shirane, Shikata, Tokai-mura, Naka-gun, Ibaraki Prefecture               Japan Atomic Energy Research Institute Tokai Research Center (72) Inventor Minoru Nishihara             2-21-2 Nishishimbashi, Minato-ku, Tokyo             Ken Co., Ltd. (72) Inventor Norihiro Sakamaki             2-21-2 Nishishimbashi, Minato-ku, Tokyo             Ken Co., Ltd.

Claims (3)

[Claims] 1. A tubular coil for placing the entire driving stroke of a control rod in a magnetic circuit, a magnetic flux guide member arranged outside the tubular coil for guiding magnetic flux, and a magnetic flux guide member arranged on the axial center of the tubular coil.
It is equipped with a control rod separating mechanism consisting of two magnetic upper and lower magnetic shafts that are separated into individual pieces and adsorbed and joined at the adsorption surface.The upper shaft is the drive shaft of the drive mechanism and the lower shaft is the reactor control rod. In the coupled control rod drive device, a temperature sensing alloy whose magnetic saturation value decreases when the temperature becomes high is sandwiched between the adsorption surface of the drive shaft, and when the temperature rises abnormally, the adsorption surface is passively separated. The cooling water outlet of this cooling mechanism is installed by providing a mechanism that cools the heat generation of the coil part by natural circulation by providing a flow path from the lower end of the coil to the upper end and passing the reactor cooling water. Of the temperature-sensing alloy, which is located just below the safety water level of the reactor, and when the water level of the reactor drops below the safe water level, the cooling water outlet is exposed above the water surface, causing the coil to lose its natural circulation cooling function. Up and down By separating the axes, reactor water level low passively disconnecting the upper and lower portions of the conductive magnetic axis, passive reactor shutdown mechanism, characterized in that allowed to shut down the reactor was inserted into the reactor core control rods. 2. The passive reactor shutdown mechanism according to claim 1, wherein the temperature-sensitive alloy is nickel or a nickel-based alloy. 3. The coil material of the passive reactor shutdown mechanism is generally made of a material such as copper having a low electric resistance as a conductor, but if necessary, a material having a high electric resistance obtained by adding nickel or the like to copper. The passive reactor shutdown mechanism according to claim 1, wherein the responsiveness from the low water level to the shutdown of the reactor is enhanced by using.