JPH0556837B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a self-actuating control rod drive mechanism that inserts control rods into a reactor core in order to emergency stop a liquid metal cooled fast reactor or the like in the event of an abnormality. More specifically, we installed an abnormality detection device in the reactor that turns off the electrical contacts by taking advantage of the fact that the internal pressure rises due to temperature rise, which lowers the level of liquid metal. This relates to the control rod drive mechanism to be inserted.

[Prior Art] In general, fast reactors and the like are equipped with control rods that are inserted into the reactor core in the event of an abnormality, in addition to control rods for output control, in order to increase the reliability of reactor shutdown. The control rod drive mechanism that drives these starts operating in response to an external scram signal. Therefore, reliability in the event of an emergency depends on the outside and the scram signal generation mechanism, and the signal transmission path from the occurrence of an abnormality in the reactor to the scram becomes complicated, which poses problems in terms of reactor shutdown responsiveness and reliability.

In order to solve these problems, a configuration has been proposed in which a temperature switch is installed inside the reactor and the control rods are directly driven by the signal from the temperature switch (for example, Japanese Patent Laid-Open No. 127493/1983).
(see publication). Here, the temperature switch used to detect abnormalities inside the reactor is configured to control the contacts on and off using the difference in thermal expansion of multiple dissimilar metals, and transmits the signal to the control rod holding mechanism. configured to do so.

[Problems to be Solved by the Invention] In the above-mentioned prior art, the temperature switch consists of a combination of dissimilar metals in which a tungsten rod is inserted into a stainless steel tube that is immersed in a coolant. The upper end of the tungsten rod is connected to the movable contact. Due to the difference in thermal expansion between the stainless steel tube and the tungsten rod, the upper end of the tungsten rod moves in the vertical direction to bring the movable contact into contact with the fixed contact or to separate it from the fixed contact.

Since the temperature switch is installed near the reactor core, it is affected by irradiation, which poses a problem in terms of reliability. In addition, since the tube is immersed in the coolant, a leak detector must be installed inside the stainless steel tube to detect whether or not the liquid coolant has entered the tube, making it mechanically complex and causing many problems in terms of reliability. .

An object of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a self-actuating control rod drive mechanism that is simple in structure, highly reliable, and fail-safe even if damage occurs. There is a particular thing.

[Means for Solving the Problems] The present invention provides a control rod, a control rod holding mechanism that holds the control rod above the reactor and is electrically releasable, and an in-core abnormality detection device that provides a scram signal to the control rod. This assumes a control rod drive mechanism equipped with

In order to achieve the above object, the present invention includes a detection unit in which a liquid metal is placed in the lower part of a closed container, the upper space is filled with gas, and an electrical contact is incorporated so as to be immersed in the liquid metal; An in-core abnormality detection device is used, which is equipped with a bellows that communicates with the detection part via a conduit and is filled with liquid metal, and the signal from the electrical contact is supplied as a scram signal to the control rod holding mechanism. This is a self-actuated control rod drive mechanism.

[Function] Normally, electrical contacts are immersed in liquid metal and maintain continuity. On the other hand, when an abnormal temperature rise occurs inside the reactor, the pressure of the gas inside the detection section increases, and this increase in internal pressure is absorbed by the expansion of the bellows, which pushes down the liquid metal level inside the detection section. Electrical contacts are exposed. This opens a circuit and transmits a signal to the control rod holding mechanism to release the control rod. The control rods fall due to their own weight and shut down the reactor.

The bellows, which can be affected by irradiation, is drawn out by a conduit and can be installed in a location away from the core where the irradiation level is low, making it less susceptible to irradiation effects.The simple structure also makes it possible to turn the contacts on and off. Clear and extremely reliable as a scrum signal.

In addition, even if damage occurs, the liquid inside can be used as the same as the coolant, so there will be no negative impact.
Furthermore, if it is damaged, the liquid metal will flow out, causing the contacts to open and generate a scram signal, resulting in a fail-safe structure.

[Embodiment] FIG. 1 is an explanatory diagram showing an embodiment of a self-actuated control rod drive mechanism according to the present invention, and FIG. 2 is an explanatory diagram of an in-core abnormality detection device incorporated therein.

A control rod 14 has a handling head 10 made of a magnetic material on the upper part and a neutron absorber 12 inside.
It is located above the lower guide tube 16 in the reactor core and is held by a control rod holding mechanism. The control rod holding mechanism is
It consists of an extension tube 20 inserted through the upper guide tube 18 and an electromagnet 22 attached to the lower end of the extension tube 20. Electric current is supplied from a power source through a cable 24, and the excited electromagnet 22 is connected to the magnetic material handling head. 10 to hold the control rod.
Therefore, by cutting off the current supply to the electromagnet 22, the control rod 14 can be disconnected.

The in-furnace abnormality detection device 30 is provided along the extension pipe 20. As shown in detail in FIG. 2, this in-furnace abnormality detection device 30 includes a liquid metal 34 placed in the lower part of a closed container 32, a gas 36 filled in the upper space, and a pair of electrical contacts 38a. ，
38b is inserted through the liquid metal 34 so as to be immersed therein; a bellows 42 communicating with the sensing part 40 at its lower end; and a conduit 44 connecting the sensing part 40 and the bellows 42. configured. Bellows 42 and conduit 44 are filled with liquid metal.

As can be seen from FIG. 1, the detection section 40 is located at the lower end of the extension tube 20, and the bellows 42 is located far above it in a low-temperature region far away from the core. The contacts 38a and 38b of the detection unit 40 are connected to the electromagnet 2.
The power supply cable 24 is connected in series to the power supply cable 24 to the power supply cable 24.

The operation of this device configured as described above is as follows. When the temperature is within the normal range, the detection unit 40
The pressure of the gas 36 inside is low, and the contacts 38a, 38b
is substantially immersed in the liquid metal 34, so that there is electrical conduction between the contacts. Therefore, cable 2
4, current from a power source can be supplied to the electromagnet 22. Therefore, the magnetic material handling head 10 remains attracted to the electromagnet 22, and the control rod 14 is held suspended above the lower guide tube 16.

When an abnormality occurs in the furnace and the temperature rises, the detection unit 40
The gas 36 expands and the internal pressure increases, trying to push the liquid metal 34 downward. This force is bellows 4
2, the bellows 42 attempts to expand and absorb the pressure change. For this reason, the liquid level of the liquid metal 34 in the detection unit 40 decreases, and eventually the contacts 38a, 3
8b is exposed. This opens a circuit from the power source through cable 24 to electromagnet 22. The electromagnet 22 becomes demagnetized, loses the attraction force of the handling head 10, and releases the control rod 14. As a result, the control rod 14 falls under its own weight, stopping the reactor.

The temperature at which the contacts 38a and 38b open can be easily set by the pressure of the gas 36 and the spring force of the bellows 42. Here, the bellows 42 can be routed and installed in the upper part of the control rod holding mechanism through the conduit 44, that is, in a low-temperature place away from the reactor core, so it is less susceptible to the effects of irradiation and is less affected by the vapor pressure of the liquid metal. It also becomes difficult to accept. Since the on-off operation is performed depending on whether or not the contact is in contact with liquid metal, the operation is clear and extremely reliable as a scram signal. Even if the conduit or bellows were to break and the liquid metal inside leaked out, it would not have a negative effect on the furnace because the same coolant was used, and if it did leak out, the liquid level would drop. Since the contacts are exposed and the circuit opens to generate a scram signal, it is fail-safe and extremely safe.

Although a preferred embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to only such a configuration. In the above embodiment, the handling head 10 is suspended directly by the electromagnet 22, but it may also be configured such that the handling head is gripped by a gripper and the opening/closing operation of the claws of the gripper is controlled by an electromagnet or the like.

[Effects of the Invention] As described above, the present invention provides a furnace that combines a detection unit containing a gas and a liquid metal and equipped with a contact that is immersed in the liquid metal, and a bellows that communicates with the detection unit and is filled with the liquid metal. Because it has an abnormality detection device, the bellows can be installed in a low-temperature location away from the reactor core, so it is less susceptible to irradiation, the contact turns off reliably, and a reliable scram signal can be generated. This has advantages such as ease of setting the temperature that generates the scram signal.

Since the present invention uses the same liquid metal as the coolant, there is no risk of adversely affecting the furnace even if damage occurs, and even if damage occurs, a scram signal will be generated due to the drop in the liquid level due to the outflow of liquid metal. Extremely reliable as it is fail safe.

[Brief explanation of drawings]

FIG. 1 is an explanatory view showing one embodiment of a self-actuating control rod drive mechanism according to the present invention, and FIG. 2 is an explanatory view showing an example of an in-core abnormality detection device used therein. 10... Handling head, 12... Neutron absorber, 14... Control rod, 22... Electromagnet, 30
... In-furnace abnormality detection device, 32 ... Sealed container, 34
...Liquid metal, 36...Gas, 38a, 38b...
...Contact, 40...Detection section, 42...Bellows, 4
4... Conduit.

Claims (1)

[Claims] 1. Equipped with a control rod, a control rod holding mechanism that holds the control rod above the core and can electrically release it, and an in-core abnormality detection device that provides a scram signal to the control rod holding mechanism. In this method, the in-furnace abnormality detection device is installed in such a way that liquid metal is placed in the lower part of the sealed container, gas is filled in the upper space, and the electrical contacts are immersed in the liquid metal and exposed as the liquid level drops when the temperature is abnormal. 1. A self-actuating control rod drive mechanism comprising: a detecting section that is connected to the detecting section; and a bellows that communicates with the detecting section via a conduit and is filled with liquid metal.