JPH0850189A - Nuclear reactor stopping device - Google Patents

Abstract

PURPOSE:To provide a magnetic circuit having a sharp changing characteristic to the temperature change of holding force by installing a magnetic bridge to a part of the magnetic circuit provided on the connecting part between a control element and a control rod driving mechanism. CONSTITUTION:An electromagnet 8 formed of a magnet iron core 4 formed from a magnetic material and a coil 2 is mounted on the lower end of a driving extending shaft 1 vertically moved by a control rod driving mechanism. On the other hand, an armature 9 formed of an iron core material 6 and a temperature sensing alloy 5 is mounted on the upper end of a connecting shaft 10 for suspending a control element. When the temperature of a reactor core is raised by any cause, and the temperature of the temperature sensing alloy 5 reaches near the Curie temperature, the magnetic resistance of the magnetic path passing the armature 9 is increased, and the magnetic resistance of the magnetic path passing the magnetic bridge 7 is reduced. A magnetic path 11 never passing a gap 21 is thus formed. The magnetic flux passing the armature 9 is then minimized to reduce the holding force of the electromagnet 8, and the control element is fallen to stop the nuclear reactor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor stop device or a reactor control device for a liquid metal cooled fast breeder reactor.

[0002]

2. Description of the Related Art FIG. 4 shows a liquid metal cooled fast breeder reactor of known structure. The reactor includes a core 13 containing a plurality of fuel elements 12.

The heat generated by the furnace is regulated by a series of control rods 15 which are raised and lowered relative to the core 13 by a control rod drive mechanism 20 in the core superstructure 14.

The reactor core 13 is housed in a container 16, and the entire reactor is contained in a primary container 17.

Liquid metal coolant 18 is typically atmospheric pressure sodium.

The furnace of FIG. 4 is cooled by the flow of liquid metal coolant 18 circulating through the main circulation pump.

The liquid metal coolant 18 flows in from the lower part of the fuel element 12, then the liquid metal coolant 18 flows upward through the core 13, and the heat generated by the fission reaction in the core 13 causes the liquid metal coolant 18 to flow. Be transmitted to.

In order to control the power level, the reactor structure shown in FIG. 4 has a sensor for electrically detecting the occurrence of a temperature rise accident in the reactor, the control rod drive mechanism operates, and the control rod 15
Has a structure for moving in and out of the core 13.

In the case of the system in which the occurrence of an accident is detected by the sensor as described above, a detection delay time occurs from the occurrence of the accident to the insertion of the control rod as shown in FIG. Even in the conventional reactor structure as shown in Fig. 4, it is considered that the reliability of the reactor shutdown system is sufficiently high, but in order to further improve the reliability of the reactor shutdown system, it is different from the conventional type. It is very effective to use this type of reactor shutdown mechanism together.

A system has been devised in which a magnetic circuit incorporating a temperature-sensing alloy is provided at the connecting portion between the control rod drive structure and the control element accommodating the neutron absorber, and the control element is suspended by the attraction force thereof.

This is a system disclosed in, for example, Japanese Patent Laid-Open No. 59-50389.

FIG. 7 shows this known example.

The armature 9 has a double columnar shape which is divided into an inner portion and an outer portion, and the temperature sensing alloy 5 is annularly inserted into a gap 19 between them and is fixed to the armature 9 by a pin.

The Curie point of this temperature sensing alloy 5 is the magnetic path 1.
The Curie point is lower than that of the iron core material of the electromagnet 8 forming 1 and is higher than the normal operating temperature of the nuclear reactor of 500 ° C. to 550 ° C., for example, around 700 ° C.

Therefore, the iron core material is supposed to have a high Curie point and a high magnetic flux density in order to hold the control element with a sufficient coercive force.

The temperature-sensing alloy 5 is formed so that its center diameter is substantially the same as that of the coil 2, and its height, that is, its axial length is such that the surface area of its side surface is sufficiently larger than the magnetic path cross-sectional area of the iron core 4. Is being done.

According to such a self-actuating type reactor shutdown device, as shown in FIG. 6, the reactor shutdown operation is directly performed in response to the occurrence of the accident, so that higher reliability is secured.

However, in the conventional example, the change characteristic of the holding force with respect to temperature from the false fall prevention temperature to the separation temperature is
Since it depends almost on the temperature characteristics of the temperature-sensitive alloy, when implementing this conventional example, it is necessary to have an alloy that meets the required characteristics, and it is costly and time-consuming to develop the temperature-sensitive alloy. Met.

[0019]

According to the conventional example, since the temperature characteristic of the coercive force depends on the temperature characteristic of the saturation magnetization of the temperature sensing alloy in order to secure the responsiveness to the temperature change of the coolant, It was necessary to develop or select a temperature-sensing alloy that meets the holding power requirements each time.

An object of the present invention is to provide a magnetic circuit having a steep change characteristic of a holding force with respect to a temperature change, and
The change characteristic of the holding force with respect to temperature change does not depend only on the characteristic of the temperature-sensitive alloy, and it is an object to be able to arbitrarily set the change characteristic of the holding force with respect to temperature change while utilizing the characteristic of the temperature-sensitive alloy. .

[0021]

By mounting a magnetic bridge on a part of the magnetic circuit, the temperature of the temperature sensing alloy itself can be satisfied, or even if the temperature change characteristic of the saturation magnetization of the temperature sensing alloy itself is somewhat gentle, the false fall prevention temperature can be improved. While maintaining the following holding force, the holding force between the erroneous fall prevention temperature and the separation temperature can be sharply reduced, and the design margin can be improved.

[0022]

By providing the magnetic bridge, the temperature change of the coercive force of the entire magnetic circuit becomes large, the design margin of the temperature sensing alloy is widened, and the realistic design is possible, and at the same time, the selection range of the temperature sensing alloy is widened. .

The operation of the present invention will be described with reference to FIGS.

Now, the temperature of the coolant rises due to the occurrence of an accident, and, for example, the requirement that the coolant does not boil is as shown in FIG.

In order to safely shut down the reactor, the temperature sensing alloy must react with respect to the coolant boiling time T1 by the time T2 in consideration of the insertion delay time ΔT of the control element.

At this time, the temperature of the temperature sensing alloy is θ ₂ which is slightly lower than θ ₁ because the coolant temperature is θ ₁ but there is a slight temperature response delay.

FIG. 9 shows the relationship between temperature and holding force at this time.

Since it should not fall accidentally during normal operation,
At the assumed coolant temperature, that is, the erroneous fall prevention temperature θ ₀ , a holding force equal to or greater than the necessary holding force set with a margin in the weight of the control rod to be suspended is required.

If the temperature of the coolant rises due to some accident, the magnetic resistance of the temperature-sensing alloy increases, and the attracting force of the electromagnet decreases as the temperature rises.

The case of the present invention B, in which the temperature change rate of the holding force is relatively rapid as compared to the conventional case A in which the temperature change rate of the holding force is relatively gentle, has a holding force at the false fall prevention temperature θ ₀ . The rate of change of the holding force at the cutting temperature θ ₂ is large, and the latitude of the magnetic path design is widened, or the selection range of the temperature sensing alloy is widened.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In this embodiment, a magnet iron core 4 made of a magnetic material and an electromagnet 8 composed of a coil 2 are attached to the lower end of the drive extension shaft 1 which is vertically moved by the control element drive mechanism.

On the other hand, an iron core material 6 and an armature 9 made of a temperature sensing alloy 5 are attached to the upper end of a connecting shaft 10 for suspending the control elements.

Since the temperature-sensing alloy 5 is attached to the outside of the armature 9, it directly contacts the coolant flowing outside the structure and can respond quickly to changes in the temperature of the coolant. In addition, a fin structure may be provided outside the armature 9 so as to respond faster to changes in the temperature of the coolant.

FIG. 1 shows the magnetic path at a temperature below the false drop prevention temperature.

The gap 22 of the magnetic bridge is usually larger than the gap 21, and the magnetic resistance of the magnetic path passing through the magnetic bridge 7 is the same as that of the temperature sensing alloy 5 at the false fall prevention temperature θ ₀ with a margin for the temperature during normal operation. Since it is larger than the magnetic resistance on the side of the amateur 7 including the magnetic path, the magnetic path is formed as shown in FIG.

In this case, the magnetic resistance of the magnetic path 11 in the magnetic circuit composed of the electromagnet 8 and the armature 9 is the sum of the magnetic resistances of the iron core material 6 and the temperature sensing alloy 5.

Here, the electromagnet can suspend the armature 9 and below by a force proportional to the square of the magnetic flux in the gap 21.

FIG. 2 shows a magnetic path when the core temperature rises for some reason in the embodiment of FIG.

When the temperature of the temperature sensing alloy 5 reaches near the Curie point, the magnetic resistance of the magnetic path passing through the armature 5 increases and becomes large, and passes through the magnetic bridge 7 having a relatively small change rate of the magnetic resistance with respect to temperature change. The magnetic resistance of the magnetic path is smaller than that of the magnetic path.

Therefore, the magnetic path 11 which does not pass through the gap 21 is formed.

Then, the magnetic flux of the magnetic circuit passing through the armature becomes small, so that the holding force of the electromagnet decreases in proportion to the square of the magnetic flux, the control element cannot be held, the control element is dropped, and the reactor is stopped.

FIG. 3 shows a magnetic circuit of the embodiment shown in FIGS. 1 and 2.

Here, the holding force F [N] of this magnetic circuit is
It is shown by the following formula.

[0045]

FIG.

Here, Φg: amount of magnetic flux in the gap 21 [Wb] Sg: cross-sectional area of the gap 21 [m ² ] μg: permeability of the gap 21 [−] In FIG. 3, Rm includes the temperature sensing alloy 5. The magnetic resistance Rg of the armature 9 part is the magnetic resistance Rc of the gap 21, the magnetic resistance Rb of the electromagnet 8 part is the magnetic resistance of the magnetic bridge 7 and the gap 22 of the magnetic bridge.

Further, NI is a magnetomotive force [AT] generated by the coil 2, Φg is a magnetic flux amount [Wb] in the gap 21,
Φb is the magnetic flux amount [Wb] of the magnetic bridge 7 and the gap 22 of the magnetic bridge, and Φo is the magnetic flux amount [Wb] of the electromagnet 8 portion.

In FIG. 3, the magnetic flux amount Φ in the gap 21 portion
g is represented by the equation (2).

[0049]

[Equation 2]

Of the magnetic resistances Rc, Rm, Rg, and Rb of each part, Rm has a greater rate of change with temperature than others.

Due to this characteristic, the magnetic flux amount Φg in the gap portion
However, even if the temperature is the same, the amount of magnetic flux in the gap portion can be arbitrarily set by adjusting the length, the cross-sectional area, the material, etc. and appropriately setting the magnetic resistances Rc, Rm, Rg, Rb of the respective portions. Can be set.

It is assumed that Rb> Rg is set.

In this case, the magnetic path is as shown in FIG. 1 at the erroneous fall prevention temperature with a margin for the normal operating temperature. At this time, the order of magnetic resistance is

[0054]

## EQU00003 ## Rb> Rg> Rm> Rc (3)

[0055]

Or Rb> (Rg = Rm)> Rc (4)

[0056]

## EQU00005 ## Alternatively, since the temperature sensing alloy 5 satisfying Rb> Rm = Rg> Rc (5) is used, the equation (2) becomes the following equation.

[0057]

(Equation 6)

Next, at the separation temperature at which the magnetic path is as shown in FIG.

[0059]

(7) Rm> Rg> Rb> Rc (7)

[0060]

Or Rm = Rg> Rb> Rc (8)

[0061]

[Equation 9] Or, since it can be considered that Rg> Rm> Rb> Rc (9), the equation (2) becomes the following equation.

The magnetic flux when the magnetic bridge 7 is not used is

[0063]

[Equation 10]

The magnetic flux when the magnetic bridge 7 is used is

[0065]

[Equation 11]

Therefore, the rate of decrease of the amount of magnetic flux at the separation temperature increases by Φgo / Φg.

Here,

[0068]

[Equation 12]

Example The magnetic path shown by the magnetic path 11 in FIG. 1 is a magnetic path up to the false fall prevention temperature and has a magnetic resistance represented by the equation (6).

EXAMPLE The magnetic path 11 in FIG. 2 shows the magnetic path at the separation temperature, and as shown by the equation (12), since the magnetic bridge 7 is provided, the magnetic resistance on the side of the amateur 9 is large. Most of the magnetic flux concentrates on the magnetic bridge side.

As a result, the magnetic flux Φg of the gap portion of the present invention provided with the magnetic bridge is smaller than the magnetic flux Φgo of the gap portion when the magnetic bridge is not provided by the ratio shown in the equation (12).

As a result, the holding force can be sharply reduced by the ratio of the square of the magnetic flux ratio as shown in the equation (1), and the latitude of the magnetic path design is widened and the selection range of the temperature sensing alloy is widened.

FIGS. 10 to 12 are modifications of the embodiment of the present invention.

FIG. 10 shows a modification of FIG. 1 in which a magnetic bridge is provided in a part of the coil case. In this case, there is an effect that the temperature change of the magnetic characteristics can be drastically changed without adding a new component as a magnetic bridge.

The magnetic path 11 in FIG. 10 shows the magnetic path at the separation temperature.

As in the embodiment of FIG. 2, since the main magnetic path does not pass through the gap 21, the holding force at the cutting temperature can be sharply reduced.

FIG. 11 shows a modification of FIG. 1 in which the magnetic bridge is made of a material different from the iron core material.

In this case, the iron core material is, for example, 2-1 / 4 Cr.
-1Mo or 9Cr-1Mo, which has a relatively high strength at high temperature, is used, and pure iron, cobalt, cobalt alloy, etc., which are relatively excellent in terms of magnetic resistance, are installed in a magnetic bridge that does not require relatively high strength. .

As a result, the magnetic resistance at the separation temperature, which is relatively high, is

[0080]

Equation 13 Rb >> Rm> Rg> Rc (13)

[0081]

Or Rb >> Rm = Rg> Rc (14)

[0082]

## EQU15 ## Alternatively, Rb >> Rg = Rm> Rc (15), which makes it possible to provide a device that further rapidly changes the holding force with temperature as compared with the embodiment of FIG.

FIG. 12 shows a modification of FIG. 1 in which the temperature sensing alloy 5 is the same as the iron core material 6.

In this case, by using only one material for the amateur 9 part, the manufacturability is greatly improved by eliminating the joint between the iron core material 6 and the temperature sensing alloy in the amateur 9 part.

Of course, it is the same as in FIG. 1 that a slit or the like is provided on the outside of the armature portion so as to respond to the temperature change of the coolant in a short time.

[0086]

According to the present invention, the main magnetic path passes through the armature side when the temperature is low and the main magnetic path passes through the magnetic bridge side when the temperature is high against the temperature change of the coolant. The amount of magnetic flux in the gap can be changed at a rate of change equal to or higher than the temperature change of the magnetic resistance of the temperature sensing alloy.

Further, since the coercive force characteristic can also be provided with a reactor shutdown device which can be arbitrarily set by adjusting the magnetic path length, the magnetic path cross-sectional area, and the material of each part, the coolant temperature rises for some reason. It is possible to shut down the reactor voluntarily, swiftly, and reliably in response to an event.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an electromagnet section in which a magnetic path is recorded at an erroneous drop prevention temperature or less according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of an electromagnet part in which a magnetic path is entered when an abnormal temperature rise occurs according to an embodiment of the heat retaining invention.

FIG. 3 is an equivalent magnetic circuit diagram of the electromagnet section of the present invention.

FIG. 4 is a conceptual diagram of the interior of a conventionally known fast breeder reactor in a vertical cross section.

FIG. 5 is an operation stroke diagram of a control rod at the time of an accident according to a conventional example.

FIG. 6 is an operation process diagram of a control rod at the time of an accident according to the embodiment of the present invention.

FIG. 7 is a vertical cross-sectional view of an electromagnet portion according to a conventional example.

FIG. 8 is a graph showing time-lapse characteristics due to an increase in false fall prevention temperature between a coolant temperature and a temperature sensing alloy temperature.

FIG. 9 is a graph showing the characteristics of the holding force of the electromagnet due to temperature changes.

10 is a longitudinal sectional view of an electromagnet portion according to a modification of FIG. 1 in which a magnetic bridge is provided in a part of a coil case, which is an embodiment of the present invention.

11 is a longitudinal sectional view of an electromagnet portion according to a modification of FIG. 1 in which the magnetic bridge is made of a material different from the iron core material, which is an embodiment of the present invention.

FIG. 12 is a vertical cross-sectional view of an electromagnet portion according to an example of the present invention, in which a temperature-sensitive alloy is the same as an iron core material.

[Explanation of symbols]

1 ... Drive extension shaft, 2 ... Coil, 3 ... Coil case, 4 ...
Iron core, 5 ... Temperature sensing alloy, 6 ... Iron core material, 7 ... Magnetic bridge, 8 ... Electromagnet, 9 ... Amateur, 10 ... Connecting shaft, 11
... magnetic path, 12 ... fuel element, 13 ... core, 14 ... core upper structure, 15 ... control rod, 16 ... container, 17 ... primary container, 1
8 ... Coolant, 19 ... Gap, 20 ... Control rod drive structure, 21
... Gap, 22 ... Gap of magnetic bridge.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Ishikawa 2-9-1, Aise-cho, Hitachi City, Ibaraki Hitachi Equipment Engineering Co., Ltd. (72) Hidehiro Aono 3-1-1, Saicho-cho, Hitachi City, Ibaraki No. Stock Company Hitachi Ltd.Hitachi factory

Claims (4)

[Claims] 1. A nuclear reactor facility in which a control element containing a neutron absorber is connected to a control rod drive mechanism to reduce the output level of the reactor by the neutron absorber, and the control element is connected to the control rod drive mechanism. A reactor output control apparatus for suspending the control element by a suction force of a magnetic circuit provided in a portion thereof, wherein a magnetic bridge is attached to a part of the magnetic circuit. 2. The nuclear reactor shutdown device according to claim 1, wherein the magnetic bridge installed in a part of the magnetic circuit is a part of a coil case of the electromagnet coil. 3. The reactor shutdown device according to claim 1, wherein the magnetic bridge installed in a part of the magnetic circuit is made of a material different from the electromagnet iron core material. 4. The temperature sensing alloy mounted on a part of the magnetic circuit is made of the same material as the iron core material.
Reactor shutdown device according to.