JPH09243775A - Connecting device for reactor control rod driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, a highly reliable connecting device by providing the device with a push-up pin formed of a material having specified dimension and thermal expansion coefficient, and a thermosensitive member formed of a magnetic material having a specified curie temperature. SOLUTION: When the operation of a reactor is normal, and the temperature of liquid sodium is within a normal range less than 640 deg.C, a sufficient electromagnetic attractive force is generated on the attractive surface 23a of an electromagnet 11 to surely hold a control rod 5 through a control rod connecting shaft 41. When the temperature becomes 640 deg.C or more, the upper end of a thermal expanding pin 47 is flush with attractive surfaces 27a, 29a, and when the temperature is 680 deg.C, the pin 47 is further expanded to protrude its upper end from the upper surface of a self-fusion preventing hardware 45, pushing up the magnet 11 to extend the clearance between the surface 23a and the surfaces 27a, 29a, whereby magnetic flux leakage is increased to significantly reduce the holding force. Thus, the holding force cannot be supported by the dead weight of the control rod 5 and the connecting shaft 41, and is separated and naturally fallen into the reactor core, whereby the control rod 5 is fully inserted into the core to suppress the nuclear reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor control rod drive device, and more particularly to a detachable connecting device therefor.

[0002]

2. Description of the Related Art Generally, a nuclear reaction in a reactor core is carried out by inserting a reactor control rod having a neutron absorption capability into the reactor core by a control rod driving device placed outside the reactor container, or from the reactor core. It is controlled by pulling it out. Then, in order to protect the safety of the reactor, it is required to immediately insert a reactor control rod (hereinafter abbreviated as control rod) into the core to stop the nuclear reaction when an abnormality occurs. For emergency insertion of the control rod, gravity drop or free fall is used to ensure the reliability of operation.

An outline of the nuclear reactor control device will be described by taking a liquid metal cooling type fast breeder reactor as an example. In FIG. 5, a control rod guide tube 3 having the same outer shape as that of the fuel assembly 1 constituting the core of the nuclear reactor is provided, and the control rod 5 is provided therein so as to be vertically movable. A control rod drive shaft 9 hangs down from the control rod drive device 7 on the upper lid or shield plug of the reactor vessel, and the upper end of the connecting shaft 13 of the control rod 5 is connected to the electromagnet 11 at the lower end thereof. In such a core structure, the coolant, such as liquid sodium 15, rising from below contacts the core fuel 17 in the fuel assembly 1 to flow to a high temperature, and once flows into the coolant introduction pipe 19 in the upper part. After that, it flows out laterally from the flow hole 21 on the side. Such a coolant is guided to, for example, an intermediate heat exchanger (not shown) and exchanges heat with a heat carrier medium to an external heat utilization device. The control rod 5 is adjusted in the vertical position in the core by the control rod drive device 7, is pulled upward from the core, or is inserted into the core to adjust the nuclear reaction or power in the core.

The electromagnet 11 is located in the coolant introducing pipe 19 and is adapted to connect the control rod drive shaft 9 and the control rod 5 in the event of an abnormality in response to the temperature of the heating coolant 15 coming out of the fuel assembly 1. The control rod 5 is released to allow the control rod 5 to freely fall.
The structure of the electromagnet 11 is shown in FIG. 6, and the coil 25 is embedded in the electromagnet iron core 23 fixed to the lower end of the control rod drive shaft 9 to form the electromagnet 11. It connects to the power supply through a lead wire passing through. The electromagnet iron core 23 has a temperature of 20 degrees higher than the normal temperature of the coolant 15.
It is made of pure iron or chromium molybdenum steel, which is a magnetic material having a high Curie point of about 0 ° C. and a high saturation magnetic flux density, and a flat adsorption surface 23a is formed at its lower end. An inner iron core 27 and an outer iron core 29 are arranged at the upper end of the control rod connecting shaft 13 so as to face the electromagnet 11. The inner iron core 27 and the outer iron core 29 are made of the same material as the electromagnet iron core 23, and have flat attracting surfaces 27a and 29a formed at the upper ends thereof. When the electromagnet 11 is actuated, a closed magnetic path 31 shown by the alternate long and short dash line is formed. It is provided. This temperature sensing member 33
Is made of a magnetic alloy having a Curie point higher than the normal temperature of the coolant 15 by about 50 to 150 ° C. and a high saturation magnetic flux density. Self-fusing prevention metal fittings 35, 37 are provided so as to be exposed on the adsorbing surfaces 23a, 27a, 29a, and these are slightly protruding from the adsorbing surfaces 23a, 27a, 29a, and are electromagnet irons in the high temperature coolant 15. The self-bonding of the core 23 with the inner iron core 27 and the outer iron core 29 is prevented.

During operation of the nuclear reactor, a current is applied to the coil 25 of the electromagnet 11 described above, the control rod drive shaft 9 and the control rod connecting shaft 13 are connected as shown in FIG. 6, and the control is performed as shown in FIG. The control rod 5 is moved up and down by the rod drive device 7. However, if the temperature of the coolant 15 exiting the fuel assembly 1 is abnormally increased, the coolant temperature is transmitted to the temperature sensing member 33, the temperature approaches the Curie point, and the saturation magnetic flux density sharply decreases. Therefore, the magnetic flux flowing through the magnetic path 31 is reduced, the holding force of the electromagnet 11 is reduced, the weight of the control rod 5 cannot be supported, and the control rod 5 falls into the control rod guide tube 3. In short, if there is something abnormal and the temperature of the coolant 15 exiting the fuel assembly 1 becomes higher than normal, the holding force of the electromagnet 11 decreases and the control rod 5 is allowed to fall freely into the core.
Suppress nuclear reactions in the core to prevent accidents.

[0006]

The control rod drive shaft-control rod connecting device as described above must never disconnect the control rod in the normal temperature range where the control rod drive shaft and control rod are slightly wide (when disconnection occurs, Another accident may occur.),
And if it deviates from the normal temperature range, it must be disconnected immediately. In the coupling device that detects the abnormal temperature of the coolant by using only the temperature sensing member as described above and releases the operation of the electromagnet, the operation greatly depends on the magnetic characteristics of the material. Range is 550-60
When applied to a practical fast breeder reactor having a temperature of 0 ° C. and a disconnection temperature of 680 ° C., there is a problem in reliability. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a highly reliable temperature sensing and releasing type reactor control rod drive coupling device.

[0007]

In order to solve the above-mentioned problems, according to the present invention, a disconnection is provided between a control rod drive shaft extending from a reactor control rod drive device and a control rod connecting shaft above the control rod. A flexible reactor control rod drive connecting device comprises an electromagnet fixed to the lower end of the control rod drive shaft and having a downward attracting face formed thereon, and an upper end of the control rod connecting shaft facing the downward attracting face of the electromagnet. And an inner iron core and an outer iron core, each of which has an upwardly attracting surface and is combined with the inner iron core and the outer iron core, and is provided at the upper end of the control rod connecting shaft to cooperate with the inner iron core and the outer iron core. A temperature sensing member that works to form a magnetic path that passes through the electromagnet, and a push-up pin that is provided so as to be extendable along the control rod connecting shaft and that appears on the upwardly attracting surface of the inner iron core and the outer iron core. The push-up pin is for the reactor coolant. It is made of a material that has a suitable size and coefficient of thermal expansion such that it projects from the upward adsorption surface and pushes the downward adsorption surface at a predetermined temperature corresponding to an abnormally high temperature deviating above the normal temperature range. The member is made of a magnetic material having a Curie point slightly higher than the predetermined temperature. In general, if the extension pin is formed of an elongated member, it is easy to satisfy the above-mentioned conditions. In this case, the extension pin is held by the buckling prevention ring on the control rod drive shaft, but at least about three pins are arranged at equal circumferential intervals. It is preferable to dispose the control rod around the control rod connecting shaft. Further, when the reactor control rod drive connecting device of the present invention is such that the reactor coolant is such as hot liquid metal sodium, the members in contact therewith are likely to cause self-fusion, the electromagnet On the downward suction surface and the upward suction surface facing it,
Self-fusion prevention members made of non-magnetic material facing each other are embedded respectively, and at least one of the self-fusion prevention members is slightly protruded from each of the attraction surfaces to prevent adverse effects on the magnetic flux in the magnetic path of the electromagnet. It is preferable that the adsorption surfaces are slightly separated.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings, in which the same members as those of the conventional apparatus are designated by the same reference numerals, and the above-mentioned description will be given thereto. The description also applies to this embodiment. First, referring to FIG. 1, an electromagnet 11 is formed by embedding a coil 25 in an electromagnet iron core 23 fixed to the lower end of the control rod drive shaft 9, and the coil 25 is formed through a lead wire passing through the drive shaft 9. Contacting a power source (not shown). The electromagnet iron core 23 is made of chromium molybdenum steel, which is a magnetic material having a Curie point higher than the normal temperature of liquid sodium as a coolant by about 200 ° C. and a high saturation magnetic flux density. The electromagnet iron core 23 may be made of pure iron having similar magnetic characteristics. A flat suction surface 23a is formed downward at the lower end thereof, and a projection for guiding is formed at the center. Under the coil 25, a self-fusing prevention metal fitting 35 made of an annular non-magnetic material is embedded so as to slightly project from the attraction surface 23a.

On the other hand, an inner iron core 27 and an outer iron core 29 surrounding the inner iron core 27 are arranged at the upper end of a control rod connecting shaft 41 attached to the upper end of the control rod 5. The inner iron core 27 and the outer iron core 29 are made of chromium molybdenum steel similar to the electromagnet iron core 23, and have a flat attracting surface 27 on the upper end thereof.
a and 29a are formed upward, that is, facing the downward attracting surface 23a of the electromagnet 11. Surrounding the inner iron core 27 and below the outer iron core 29 is a temperature sensing member 43, the outer surface of which is exposed for contact with liquid sodium flowing outside. The temperature sensing member 43 has a temperature higher than the normal temperature of the liquid sodium as a coolant
It is made of a magnetic alloy having a high Curie point of about 0 to 150 ° C. and a high saturation magnetic flux density. Then, as is apparent from the figure, a self-fusing prevention metal fitting 45 made of an annular non-magnetic material is provided surrounded by the adsorption surfaces 27a and 29a, and it faces the self-fusing protection metal fitting 35. The self-fusing prevention hardware 35, 45 defines a gap of about 0.05 mm between the suction surfaces 27a, 29a and the suction surface 23a when they are in contact with each other as shown in the figure. The gap of this degree does not affect the magnetic flux in the magnetic path, which will be described later. Note that the self-fusing prevention metal parts 35, 45 are not liquid sodium as a coolant, and when there is no concern that the material in contact with another material will cause self-fusing, the structure is simplified and omitted. May be.

Further, on the outer peripheral surface of the small diameter portion of the control rod connecting shaft 41, three axial grooves are formed at equal circumferential intervals, and austenitic stainless steel push-up pins or thermal expansion pins 47 each having a diameter of 3 mm are formed on the grooves. Has been passed through. The lower end of the thermal expansion pin 47 is fixed, while the upper part thereof extends through the large diameter portion of the control rod connecting shaft 41, the through hole formed in the temperature sensing member 43 and the self-fusion prevention member 45. It is shown enlarged in FIG. The length of the thermal expansion pin 47 is approximately 1 meter, which is about 5 with respect to the control rod connecting shaft 41 made of a nickel-based alloy corresponding to Inconel (trademark).
It has an effective thermal expansion coefficient of × 10 ^-6 mm / mm / ° C, and its upper end is the upper surface of the self-fusing prevention metal 45 when the temperature is 640 ° C (the same surface as the adsorption surfaces 27a and 29a). The dimensions are set to be flush with. In other words, in the normal temperature range, the upper end of the thermal expansion pin 47 is below the adsorption surfaces 27a and 29a as shown in FIG. Returning to FIG. 1, the thermal expansion pin 47 is horizontally supported by the buckling deformation preventing ring 49, and does not buckle even if its upper end abuts against the self-fusion preventing metal 35.

In the coupling device 40 having the above-described structure, the temperature of the liquid sodium which is normally operated and flows out from the fuel assembly of the core and contacts the thermal expansion pin 47 and the temperature sensing member 43 is 640 ° C. When in the normal range below, the upper end of the thermal expansion pin 47 is below the upper surface of the self-fusing prevention metal 45 and the adsorption surfaces 27a and 29a, and a closed magnetic path 51 is formed, as shown in FIG. That is, the electromagnet 11
A sufficiently large electromagnetic attraction force is generated on the attraction surface 23a of the above, and the control rod 5 is firmly held via the control rod connecting shaft 41.
On the other hand, when the temperature of the liquid sodium reaches 640 ° C., the upper end of the thermal expansion pin 47, which is relatively expanded due to thermal expansion, becomes flush with the adsorption surfaces 27 a and 29 a, and when it reaches 680 ° C., it is somewhat exaggerated in FIG. As shown, the self-fusing prevention hardware 3
A gap of about 0.20 mm is formed between 5,45. Further, due to the above-mentioned temperature rise, the temperature sensing member 43 approaches the Curie point, the saturation magnetic flux density decreases, and the holding force also decreases. The relationship between such temperature changes and holding force changes is shown in the graph of FIG. In FIG. 4, the solid line shows the change of the holding force according to the present embodiment, and the broken line shows the change of the holding force of the conventional coupling device having no thermal expansion pin. According to the present embodiment, due to the thermal expansion of the thermal expansion pin 47, the upper end thereof protrudes from the upper surface of the self-fusing prevention metal fitting 45, pushes up the electromagnet 11, and expands the gap between the adsorption surface 23a and the adsorption surfaces 27a and 29a. Since the leakage of magnetic flux is increased, the holding force is greatly reduced as compared with the conventional one. In this way, the holding force cannot support the own weight of the control rod 5 and the control rod connecting shaft 41, and is separated and inserted into the core by free fall.
That is, the control rod 5 is fully inserted into the core to suppress the nuclear reaction.

[0012]

As described above, according to the present invention, when the push-up pin that thermally expands in response to the temperature rise of the coolant reaches a predetermined temperature or higher, the electromagnet at the lower end of the control rod drive shaft and the control rod connecting shaft are connected. Since the distance from the upper end is increased and the holding force of the electromagnet is greatly reduced in combination with the decrease in the saturation magnetic flux density of the temperature sensing member, the control rod can be reliably disconnected in the event of an abnormality. Further, in the normal temperature range of the coolant, since the interval is unchanged, a sufficient holding force is obtained, and the control rod is not accidentally disconnected.

[Brief description of drawings]

FIG. 1 is a partially cutaway vertical sectional view showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a partially enlarged view for explaining the operation of the embodiment.

FIG. 3 is a partially enlarged view for explaining the operation of the embodiment.

FIG. 4 is a graph showing a change in holding force according to the above embodiment in comparison with a conventional one.

FIG. 5 is an overall conceptual diagram of an example of a reactor control rod drive system to which the present invention is applied.

FIG. 6 is a conceptual partial cross-sectional view of a conventional device.

[Explanation of symbols]

 7 Control rod drive device 9 Control rod drive shaft 11 Electromagnet 23 Electromagnet Iron core 23a Adsorption surface 27 Inner iron core 27a Adsorption surface 29 Outer iron core 29a Adsorption surface 35 Self-fusing prevention hardware 40 Coupling device 41 Control rod connection shaft 43 Temperature sensing Member 45 Self-fusion prevention hardware 47 Thermal expansion pin 49 Buckling prevention ring

Claims (3)

[Claims] 1. A detachable connecting device provided between a control rod drive shaft extending from a reactor control rod drive device and a control rod connecting shaft above the control rod, the device being fixed to a lower end of the control rod drive shaft. An electromagnet having a downwardly attracting surface formed thereon, and an inner iron core and an outer iron core having an upwardly attracting surface formed at the upper end of the control rod connecting shaft so as to face the downwardly attracting surface of the electromagnet. A temperature sensing member which is provided at an upper end of the control rod connecting shaft in combination with the inner iron core and the outer iron core, and which cooperates with the inner iron core and the outer iron core to form a magnetic path passing through the electromagnet; A push-up pin protruding and retracting from the upward suction surface of the inner iron core and the outer iron core, the push-up pin protruding from the upward suction surface at a predetermined temperature. Size and For a reactor control rod drive, the temperature sensing member is made of a magnetic material having a Curie point at a temperature slightly higher than the predetermined temperature. Coupling device. 2. Self-fusion prevention members facing each other are embedded in the downward suction surface and the upward suction surface, respectively, and at least one of the self-fusion prevention members is slightly separated from both suction surfaces. 2. The coupling device for a reactor control rod driving device according to claim 1, wherein the coupling device projects and a small gap is formed between the suction surfaces. 3. The reactor control rod drive device according to claim 1, wherein the push-up pin is composed of an elongated member and is held on the control rod connecting shaft by a buckling prevention ring. Connecting device.