JPS58150891A - Control rod drive 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 The present invention relates to a control rod drive mechanism for a nuclear reactor, and in particular, a gripper for connecting, separating, and holding control rods has finger claws made of a shape memory alloy. This invention relates to a control rod drive mechanism that can spontaneously scram even without external commands in response to overheating during an accident.

The control rod drive mechanism of the conventional example (in the case of FBR) of the present invention is shown in FIGS. 1, 82, and 3. FIG. 1 shows the overall framework of the control rod drive mechanism, and FIG. 2 shows the gripper section 3 is a detailed view of FIG. 2, and FIG. 3 is an AA view of FIG.

The control rod drive mechanism 1 is installed on the upper surface of the shielding plug 2 of the nuclear reactor, and includes therein a drive mechanism for a drive shaft 3 (described later) and a camshaft-mounted drive mechanism (described later). A drive shaft 3 connectable to a control rod 5 is provided to be movable up and down, has a gripper finger claw 6 at its lower end, and is inserted through a drive shaft guide tube 7 fixedly installed in an opening of the shielding prada 2. .

A nine cam shaft 4 is inserted through the drive shaft 3 and is provided so as to be movable up and down.
has a cam portion 8tA at its lower end that opens and closes the gripper finger claw 6. 6 to spinning gripper fingers,
311 (2, 4, 6, etc. depending on the case).

The spoon-shaped finger claws 6a (with 1) are arranged in the shape of a tulip bud, resulting in a nine structure. When the cam portion 8 of the camshaft 4 is pushed into the finger 61, each finger 6 is pushed outward and the cam portion 8 is pushed open.
When protrudes from each lie/galo 1, each lie/galo a closes. The drive mechanism of the drive shaft 3 is as follows:
A drive motor 9, a ball screw shaft 11 connected to the motor 9 via a gear train 1o, a ball screw nut 12 screwed onto the screw shaft 11 and capable of moving up and down, and connected to the ball screw nut 12, It also comprises an electromagnet 13 capable of attracting an armature 14' integrated with the drive shaft 3.

Therefore, if the ball screw nut 12 is moved up and down by the rotation of the drive motor 9, the drive shaft 3, which is attracted to the electromagnet 13, can be moved up and down along the drive shaft guide tube 7. The drive mechanism for the camshaft 4 includes a camshaft drive motor 1.
5. A ball screw shaft 17 that is connected to the motor 15 via a gear train 16, a ball screw nut 18 that is screwed onto the screw shaft 17 and can move up and down, and a camshaft that is connected to the ball screw nut 18. It consists of a camshaft operating flange 2° connected to a rod 19. Control rod guide tube 2 installed in the reactor core 21
A control rod receiver 23 is housed inside the control rod receiver 2 . This control rod receiver 23 has a control rod main body (not shown) tF at the bottom thereof.
! Il! It's hanging. Also, on the top of the control rod receiver 23,
An opening into which the gripper fingers 6 can be inserted is provided, and a self-portion with which each finger claw 61 of the gripper eye/gallo comes into contact is formed on the inner wall of the opening.

Next, the operation of connecting and holding the control rod 5 will be explained. The cam part 8 of the camshaft 4 is made to protrude from the gripper finger 6, and the drive shaft 3 and the camshaft 4 are lowered with the round shape 1, that is, the gripper finger 6 in the closed original state, and the lower end of the drive shaft 3 is attached to the control rod holder 23. touch the top edge of the At this time, the gripper fingers 6 are located at the opening of the control rod receiver 23. Thereafter, the cam shaft 4 is slightly raised by the elastic force of a spring 240 provided on the upper inner circumferential surface, and the cam portion 8t is pushed into the gripper finger 6, and each finger claw 6at of the gripper finger 6 is expanded. . As a result, each finger 6 is pressed against the inner wall of the control rod holder 23. That is, the control rod 5 is coupled to the drive shaft 3 via the control rod holder 23,
It is held within the reactor core 21.

When it is necessary to disconnect the control rods 5 during the preparatory stage of refueling work, first lower the drive shaft 3 and the cam shaft attachment to near the lower stroke limit using the motor 9, and then remove the control rods 5 from the core fuel assembly. It is stored in the section 21. Thereafter, the camshaft 4 is lowered slightly to cause the cam portion 8t to protrude from the gripper fingers 6. As a result, each finger pawl 6a closes and the gripper fingers 6 and the control rod holder 23 are disconnected from each other. That is, the connection between the drive shaft 3 and the +ttt control salary control is released. The above-mentioned connection and disconnection between the control shaft 5 and the drive 3 are confirmed by a limit switch (not shown) that detects the relative displacement between the drive shaft 3 and the camshaft 4 and a load signal from the load cell 25. Good job, friend.

In the case of a conventional control rod drive mechanism O, scram starting is basically done by demagnetizing the electromagnet 13, or by separating and inserting the drive shaft 3 and control rod 5 below the armature 14 as one body, as in the example shown above. The principle was to open the gripper fingers 6 and insert the control rod 5 alone. Therefore, despite the requirement for nine configurations of two independent systems with different principles for the wage control WA structure of a nuclear reactor, strict compliance from the point of view of scram start-up is not a priority. Therefore, in the conventional type, if the drive shaft or camshaft sticks in the drive mechanism at the top of the shielding plug or in the drive mechanism, the principle and structure may be affected even if two control rod drive mechanisms are installed. Since these systems are similar, there is a drawback that there is a possibility that scram insertion will not be possible in both systems in the event of an accident due to a common mode failure.

An object of the present invention is to provide a method for solving the above-mentioned problems in the prior art, in which the gripper automatically disconnects the control rods without being operated by the upper drive mechanism when an overheating state occurs during a nuclear reactor accident, and controls the control rods. An object of the present invention is to provide a control rod drive mechanism for a nuclear reactor in which gripper finger claws are made of a shape memory alloy so as to enable scram operation by rod insertion.

Even if a shape memory alloy is plastically deformed by applying an external force, when heated above a certain temperature, the martensitic phase reversely transforms into a high temperature phase and returns to its original shape as if it had memorized the deformed shape. return. By applying this material property to the opening and closing operations of the gripper fingers, the control rods were held in place during normal conditions, and the fingers were closed in the high-temperature conditions of an accident, allowing the control rods to be detached spontaneously. A heater is built into the gripper for opening and closing the gripper when the furnace is periodically stopped during fuel exchange and maintenance, and the gripper can be disconnected at any time by local heating even when the ambient temperature is cold.

Embodiments of the present invention will be described based on FIGS. 1, 4, and 5. Fig. 1 is an overall framework diagram of the control rod drive mechanism, showing the configuration of an embodiment of the present invention excluding the gripper W; Fig. 4 is a detailed view of the gripper portion of the present invention;
The arrow view and FIG. 4 show the mouse undergoing reverse transformation to the high-temperature phase, and the gripper finger claw 26a comes into contact with the stirring of the inner wall of the upper opening of the control rod holder 23, and the control rod 5 is connected and held by the drive shaft 3. When reverse transformation occurs under high temperature, the gripper finger claw 26a becomes a bud, and the same type 26M becomes a control rod receiver t.
Break down a and start the scrum insertion movement of the control @ stick alone. When the claw 261 is retracted, the inner surface of the claw presses against the tip 31a of the sheath-type pressure sensitive element having the center body at the tip 31a.
It is possible to detect when the gripper is disconnected and to detect the start of a scram.

(As a backup, it is also possible to change the load cell's load notes.) At the time of fuel exchange, when the maintenance special ambient temperature is considerably lower than the reverse transformation point of the material, the gripper disconnection operation is performed from above through the amt- installed on the CRD drive shaft 3. Built-in OMI guided stainless steel T# sheath tube
Gripper case z7 at the tip of drive shaft 3 via the cable
The internal heater (MI cable) K is electrically heated to locally heat the shape memory alloy gripper finger claws 261￥r, and to cause reverse transformation, the local heating is effective.
Depending on the requirements, a heat insulating layer 32 such as a selank coating is provided on the outer shape of the gripper case.

Examples of shape memory alloys that can be used in the present invention include palladium 5
0gm-1 titanium 50g (reverse transformation point 400-5
50t), Ve-Mn alloy (reverse transformation point: 240 to 340°C), although the reverse transformation point is slightly lower.

The driving mechanism of the improving part is as shown in FIG. 1, and its structure and functions are as described in the conventional example.

According to the present invention, when scram insertion of control rods by the upper mechanism of the control rod drive mechanism becomes impossible, 4, when the reactor reaches a heated state to the reverse transformation point of the clipper finger pawl 31a,
The gripper can spontaneously detach the control rods and insert them in a scram, ensuring reactor shutdown functions based on two independent system principles, greatly improving the reliability of the reactor itself. In addition, the structure of the drive mechanism on the shielding plug 2, the camshaft 4 that passes through the drive shaft 3t, etc., which were required to open and close the gripper in the conventional example, is not required in the present invention, and the number of parts can be greatly reduced. This can greatly contribute to improving the reliability of the control rod drive mechanism.

According to the present invention, it is possible to provide a combination of two independent nuclear reactor systems and reactor shutdown systems with different principles, which could not be adequately supported in the conventional embodiments.

By eliminating the movable structure as the drive section for the control rod gripper operation, the number of parts can be greatly reduced, and the reliability of the control rod drive mechanism can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of the control rod drive mechanism. FIG. 2 is a detailed view of the gripper portion of the conventional example, FIG. 3 is a view taken along the arrow A-A in FIG. 2, FIG. 4 is a detailed view of the gripper portion of the embodiment of the present invention, and FIG. FIG. 4 is a view taken along arrows 0A-A. 26.268...Gripper finger claw (made of shape memory alloy), 28...Gripper case interior MI cable, i
Figure 11

Claims (1)

[Claims] 1. A nuclear reactor characterized in that in a control rod drive mechanism, a gripper for connecting, separating, and holding the control rods together is composed of finger pawls made of a shape memory alloy and a locally overheating sheath heater for the same nails. control rod drive mechanism. 2. In claim 1, if the reactor becomes abnormally high temperature due to an accident during power operation of the reactor, the finger claws are deformed due to martensitic transformation of the material, and the control rods are separated. A control rod drive mechanism for a nuclear reactor, which is characterized by being able to perform an emergency shutdown function for a nuclear reactor. 3.1! #Pestrel In claim 1, when the control rods need to be connected or disconnected at any time, such as in preparation for a reactor fuel change or in cleaning up after the completion of a fuel change operation, the above-mentioned heater is energized and heated. The feature is that the finger claws are reversely transformed, the control rod is separated, the electricity is cut off, the finger claws are cooled by natural cooling, etc., and the finger claws return to their original state of gripping the control rod. A control rod drive mechanism for a nuclear reactor. 4. #Claim 1 In claim 1, when the control rod is scrammed, the separation operation causes a detector such as a pressure-sensitive element installed inside the gripper claw to undergo reverse transformation and deform, causing the gripper finger to deform. A control rod drive mechanism for a nuclear reactor, characterized in that it can be quickly detected by being pressed against the inner surface of a claw.