JPH06242277A - Control rod assembly - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a control rod assembly capable of highly reliably inserting the control rod into the core by increasing the temperature of the coolant. The control rod assembly 2 according to the present invention includes a control rod body 10 that is housed in a guide tube installed in a reactor core so as to be vertically movable.
And an extension rod 17 extending upward from the upper end of the control rod body 10 and a grip portion 18 provided on the upper portion of the extension rod 17.
An extension pipe 11 which engages with the control rod body 10 to suspend the control rod body 10, a bellows 28 which intervenes a spring 30 in a part of the extension pipe 11 and works with the spring 30, and which surrounds the bellows 28, A temperature-sensitive member 29 having a liquid metal 32 that communicates with the inside of the bellows 28, the temperature-sensitive member 29 and the extension pipe 11
And a sealing body disposed below the bellows 28 in a gap formed by the above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod assembly for controlling the output of a fast breeder reactor.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, the core of a fast breeder reactor includes a large number of fuel assemblies 1, a plurality of control rod assemblies 2 inserted between the fuel assemblies 1, and a fuel assembly 1. It is formed by a large number of shields (not shown) provided so as to surround the outermost portion.

The fuel assembly 1 has a large number of fuel pins 3 therein, and is installed at a predetermined position by inserting an entrance nozzle 4 provided at the lower end into an opening of a core support plate 5. Then, the coolant flows from the high pressure plenum 6 formed in the core support plate 5 through the coolant inlet port 7 of the entrance nozzle 4, and then rises between the fuel pins 3 to remove the heat from the fuel assembly 1. It flows upwards.

The control rod assembly 2 is composed of a lower guide pipe 8, an upper guide pipe 9, a control rod body 10 and an extension pipe 11 for engaging and suspending the control rod body 10. The lower guide tube 8 is installed at a predetermined position by inserting the entrance nozzle 12 formed at the lower end into the opening of the core support plate 5. The entrance nozzle 12 is provided with a coolant inlet port 13 that communicates with the high-pressure plenum 6 and a communication hole 14 that communicates with the inside of the lower guide tube 8 that houses the control rod body 10. Further, the control rod main body 10 has a neutron absorber incorporated therein, and at the time of re-insertion, the engaging portion 15 at the lower end is inserted into the dashpot 16 of the lower guide tube 8 for localization. The control rod body 10 is suspended from the extension pipe 11 by grasping the lower end portion of the extension pipe 11 by the grip portion 18 formed on the upper end portion of the extension rod 17 extending upward from the upper end thereof. By vertically moving this extension pipe 11 by a control rod drive mechanism (not shown), the control rod main body 10 is inserted into or pulled out from the core. The heat removal of the control rod body 10 is performed by the coolant that moves up from the high-pressure plenum 6 through the coolant inlet port 13 of the entrance nozzle 12 and the communication hole 14 to the lower guide pipe 8.

A spring 30 is interposed in a part of the extension pipe 11 or the extension rod 17, and a bellows 28 is provided outside the spring 30. A double cylindrical temperature sensitive member 29 is provided so as to surround the outside of the bellows 28, and a liquid metal 32 is enclosed in the temperature sensitive member 29 and the bellows 28.

Here, the portion of the symbol IV in FIG. 3 is enlarged and shown in FIG. In FIG. 4, the bellows 28 that absorbs the movement of the spring 30 is provided with an absorption bellows 34 that does not interlock with the spring 30. Inside the absorption bellows 34 is a vent hole 3 communicating with the inside 9a of the upper guide tube.
6 is bored inside the extension pipe 11 so that the coolant inside the upper guide pipe 9a can be sucked or discharged. The absorption bellows 34 is connected to the extension pipe 1 as the temperature rises when the reactor is started.
In the absorption space 33 formed inside 1, the temperature sensitive member 29
The expansion of the liquid metal 32 inside is absorbed through the communication hole 31. However, the extension pipe 11 is provided with a lid stopper 35 so that the extension is stopped when the extension pipe 11 is displaced by a certain amount. Therefore, when the temperature of the liquid metal 32 rises above the normal time during an abnormality, the liquid metal 3 that cannot be completely absorbed by the absorption bellows 34.
The expansion amount of 2 will be absorbed by the bellows 28. Therefore, the extension pipe 11 that engages with the bellows 28 is pushed, and the control rod body 10 suspended by the extension pipe 11 is inserted into the core. Therefore, it is possible to automatically insert the control rod body 10 into the core when an abnormality occurs.

[0007]

In the conventional control rod assembly described above, during normal operation, the degree of insertion of the control rod body into the core is adjusted by the vertical movement of the extension pipe to adjust the reactor power. Further, when an abnormality such as an abnormal increase in the furnace output or a decrease in the coolant occurs, a scram operation is carried out to urgently insert the control rod body into the core and stop the furnace.

On the other hand, in a fast breeder reactor, an emergency situation is assumed in which the extension pipe cannot be lowered for some reason and the control rod body cannot be inserted into the core in an emergency. Consideration is given to keep it below the critical level. This is because if the control rod body cannot be inserted into the core in a situation where it is necessary, the reactor power may increase excessively, the coolant temperature may rise, and eventually the core may be damaged. .

As shown in FIG. 5, when the control rod main body is in an emergency when it should be inserted urgently, the control rod reactivity is zero in the core due to the Doppler effect and the coolant density effect, that is, the line a higher than the critical value. Positive reactivity develops over time. However, in the conventional control rod assembly,
The extension pipe and the extension rod expand in the axial direction as the coolant temperature rises due to the reactor power rise, and the control rod body is inserted into the core. At this time, a negative reactivity is generated as shown by the line b in FIG. Then, conventionally, the total reactivity obtained by superposing these positive and negative reactivity is kept in the negative reactivity region lower than the criticality as shown by the line c in FIG. 5 to improve the safety of the reactor. Had secured.

However, in the conventional control rod assembly, when the bellows is damaged, liquid metal may leak from the gap between the temperature sensing member and the extension tube through the damaged part of the bellows, and the extension tube may not be pushed down. It was Therefore, there was a possibility that a negative reactivity could not be obtained without the control rod body being inserted into the core at the time of abnormality.

The present invention has been made in view of the above conventional circumstances, and an object thereof is to provide a control rod assembly capable of highly reliably inserting a control rod into a core due to a temperature rise of a coolant. To provide.

[0012]

In order to achieve the above object, in a control rod assembly of the present invention, a control rod main body for accommodating a neutron absorber is housed in a guide tube installed in a core so as to be vertically movable. An extension rod extending upward from the upper end of the control rod body, an extension pipe for suspending the control rod body by engaging with a grip portion provided on the upper portion of the extension rod, and a part of the extension pipe A bellows which encloses a liquid metal inside by interposing a spring between the bellows and expansion and contraction of the spring, and a double-cylindrical temperature-sensing member which surrounds the outside of the bellows and has a liquid metal flowing inside the bellows inside. The present invention provides a control rod assembly including the temperature sensitive member and a sealing body disposed below the bellows in a gap formed by the extension tube.

[0013]

In the control rod assembly having the above-mentioned structure, the bellows and the surrounding thereof are provided with a double-cylindrical temperature sensitive member having a liquid metal therein. The liquid metal in the temperature sensitive member expands in response to the temperature rise of the coolant, and thereby flows into the bellows.

Even if the bellows is broken, the portion surrounded by the temperature sensitive member and the extension rod is sealed by the sealing body installed in the extension pipe, and the extension pipe is pushed down by the expansion of the liquid metal in this portion. The control rod body is inserted into the core. Therefore, even when the bellows is broken, high reliability can be ensured for inserting the control rod into the core due to the temperature rise of the coolant.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the control rod assembly according to the present invention will be described below with reference to FIGS. FIG. 2 is an enlarged vertical cross-sectional view of a portion II in FIG. In FIGS. 1 and 2, the same parts as those in FIGS. 3 and 4 are designated by the same reference numerals, and the description thereof will be omitted.

In the present embodiment, a piston ring 40, which is a sealing body, is provided in the gap between the extension pipe 11 and the temperature sensing member 29 of a double cylinder surrounding the extension pipe 11 and below the position of the bellows 28. . This piston ring 40 is an extension tube 1
It is arranged in a notch portion 11a formed on the outer surface of 1. In this embodiment, the piston ring 40 is arranged on the outer surface of the extension tube 11, but it may be arranged on the inner surface of the temperature sensitive member 29. Further, the surface of the piston ring 40 is preferably surface-treated with stellite or the like in order to prevent fusion with the temperature sensitive member 29.

In the control rod assembly thus constructed, when the temperature of the coolant rises when the plant is abnormal,
Heat is transferred to the liquid metal 32 in the temperature sensitive member 29, and the temperature of the liquid metal 32 rises and expands. Expanded liquid metal 32
Flows into the bellows 28 and the absorption space 33 through the communication hole 31. The liquid metal 32 that has flowed into the absorption space 33 contracts the absorption bellows 34 by expansion and pushes it up, but since the lid stopper 35 is provided in the extension pipe 11, it flows into the absorption space 33 only up to a predetermined capacity. do not do. Therefore, the expansion amount of the liquid metal 32 that cannot be completely absorbed by the absorption bellows 34 is absorbed by the liquid metal 32 flowing into the bellows 28 as the bellows 28 expands. The extension pipe 11 is pushed down by the extension, and the control rod body 10 suspended by the extension pipe 11 is inserted into the core.

At this time, assuming that the bellows 28 is broken, the liquid metal 32 flows out from the bellows 28, but is sealed by the piston ring 40, and the temperature sensitive member 2
The liquid metal 32 does not flow out of the gap between the extension tube 11 and the extension tube 11. Therefore, the extension tube 11 is pushed down by thermal expansion due to the temperature rise of the liquid metal 32 held in the space formed by the temperature sensitive member 29 and the extension tube 11, and the control rod body 10 is inserted into the core.

[0019]

As described above, in the control rod assembly of the present invention, the control rod main body can be inserted into the core with high reliability by utilizing the coolant temperature rise at the time of abnormality.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of a control rod assembly according to the present invention.

FIG. 2 is a partial vertical cross-sectional view showing an enlarged portion II of FIG.

FIG. 3 is a vertical sectional view showing a conventional control rod assembly.

FIG. 4 is a partial vertical cross-sectional view showing a portion IV of FIG. 3 in an enlarged manner.

FIG. 5 is a schematic diagram showing a temporal change in core reactivity when a plant is abnormal.

[Explanation of symbols]

 2 ... Control rod assembly 10 ... Control rod main body 11 ... Extension pipe 17 ... Extension rod 18 ... Grip 28 ... Bellows 29 ... Temperature sensitive member 30 ... Spring 31 ... Communication hole 32 ... Liquid metal 33 ... Absorption space 34 ... Absorption bellows 35 ... Lid stopper 36 ... Vent hole 40 ... Piston ring

Claims (1)

[Claims] 1. A control rod body which is housed in a guide tube installed in a reactor core so as to be able to move up and down and accommodates a neutron absorber therein, an extension rod which extends upward from an upper end of the control rod body, and the extension rod. An extension pipe that engages with a grip portion provided on the upper part of the control rod body to suspend the control rod body; and a bellows in which a spring is interposed in a part of the extension pipe and the liquid metal is sealed inside in cooperation with the expansion and contraction of the spring. A double-cylindrical temperature-sensing member that surrounds the outside of the bellows and has a liquid metal inside that flows into the bellows; and a gap formed by the temperature-sensing member and the extension tube and below the bellows. A control rod assembly comprising: a sealed body provided.