JPS6052398B2 - control rod drive mechanism - Google Patents

Description

Detailed Description of the Invention The present invention relates to a control rod drive mechanism (hereinafter referred to as CRD) that controls nuclear reactions in a nuclear reactor, and in particular to a control rod drive mechanism (hereinafter referred to as CRD) that controls the smooth movement of bellows, which is a main component of the mechanism and forms the pounds inside and outside the reactor. This relates to a mechanism that provides flexible expansion, contraction, and sliding movement, and prevents the bellows from buckling, galling, and damage caused by this.

The pressure inside the reactor must be low for the shaft seal of the sliding part of the CRD in a fast reactor.

(~10 to 9/dG or less), the allowable leakage amount is extremely strict. (~1x10'Acc/sec or less) The temperature of the shaft seal portion is high. (up to 550°C), and the sliding distance and speed are relatively large. (Distance approx./00oT!n)
The maximum elongation speed is ~57rL/sec), and measures such as lubrication are difficult. (Reaction with the inside of the furnace, exposure to radiation, etc.) Structural materials (for example, SUS316L or Inconel 718) with polar groove thickness (■0.1 to 0.4Tm) are joined into a bellows shape (accordion shape) by welding. A welded bellows is used as the shaft seal. In addition, the bellows for CRD is designed to prevent damage in the event of damage (ensuring the safety of nuclear facilities), and in the event of damage, the activation cover gas (Aγ gas) inside the reactor is
In order to prevent radioactive sodium or the same vapor from leaking into the CRD (Ij2ak-ln) and to detect damage to the bellows (due to leakage of internal gas), the internal pressure is (~0.3 to 9/
The internal and external pressure of the bellows is controlled by gas so that it is slightly higher (approximately crlG). Also, even if there is damage, gas will always leak out from the bellows (rare
ut) (leak-in to the reactor). For this reason, a thin plate with a long length (diameter φ120T
The length is about 2000~2500wr for fgR! ! of)
Due to the high internal pressure, the bellows for CRD is in an extremely unstable state compared to B considering the energy balance, and can be said to be in a so-called meandering state. In other words, the bellows causes local buckling due to concentrated deformation due to meandering, and damage such as galling and wear occurs between the bellows and the sliding shaft, resulting in a reduction in the life of the bellows and the scram gate operating mechanism. This is the cause of a significant decline. The present invention has been made in view of the above points, and its first purpose is to alleviate the meandering of the bellows due to high internal pressure without changing the current idea of leaking out the built-in gas when the bellows breaks, and to prevent buckling due to the meandering. The objective is to prevent damage to the bellows caused by this and to enable smooth sliding. The second purpose is to provide smooth sliding during reactor emergency shutdown (CRD).
The objective is to reduce the insertion resistance due to galling of bellows, etc. during scram operation) and to speed up the furnace shutdown operation.
Next, the configuration of the present invention will be explained in detail with reference to the drawings.

Figure 1 is an explanatory diagram of the overall configuration of the CRD, and Figure 2 is an explanatory diagram of the overall configuration of the CRD.
It is a detailed view of the shaft seal part of D. The CRD is roughly divided into a drive unit 1 and a lower mechanism (guide tube 2, extension tube 3, bellows 4, etc.)
and a control rod 5. A plurality of CRDs have sufficient capacity to control the nuclear reaction inside the reactor, and are installed in a plurality of plugs 6, which are the upper lid of the reactor vessel, and drive the control rods 5 through a lower mechanism. The nuclear reaction is controlled by moving the part 1 up and down. Further, a bellows 4 is used as a shaft seal for the sliding part against the cover gas 7 and sodium 8 in the furnace. Now, to further describe the structure of the CRD shaft seal, the CRD shaft seal can be roughly divided into a guide tube 2 fixed to the reactor vessel side, an extension tube 3 which is a movable part, and a bellows 4 which is a shaft seal. It is configured.

The extension tube 3 moves up and down to expand and contract the bellows 4 for nuclear reaction control. On the other hand, as mentioned above, since the gas pressure inside the bellows 4 is higher than the pressure outside, the bellows 4 expands and contracts (the control rod is driven up and down), so that the meandering and buckled portion is formed on the inside surface of the extension tube 3. Or they may come into contact with the inner surface of the guide tube 2 and damage each other. Especially during the scram operation of the CRD, the sliding speed of the extension tube 3 is at a maximum of approximately 57TL,/S.
As a result, the wear of the bellows 4 made of thin material and the welded portion of the same material increases significantly.

Furthermore, there is a high possibility that the bellows, which is a thin shaft seal, will be damaged not only when the material is worn away due to meandering, but also when "galling" or the like occurs due to surrounding environmental conditions.

Therefore, a meandering prevention mechanism 9 for the bellows 4 is installed.
This meandering prevention mechanism 9 has guide rollers (or balls) 10 attached to the CRD bellows at arbitrary intervals and angles to slide in the direction of expansion and contraction of the bellows. Here, in order to limit the sliding direction of the guide roller 10 and prevent the occurrence of twisting, etc., the cross-sectional shape of the guide tube 2 or extension tube 3 is adjusted along the expansion and contraction direction of the bellows 4, as shown in FIG. Change the sliding guide groove 1 of the guide roller (or ball) 10
2a, 12b or the rail mechanism 13 is installed. Next, the operation of the present invention will be explained using FIG. 2.

Under the operation control of the nuclear reactor, the extension tube 3 of the CRD moves up and down in response to force transmitted from the drive section. Therefore, the bellows 4 also expands and contracts as the extension tube 3 moves up and down. On the other hand, as mentioned above, the internal and external pressure of the bellows 4 is a little high, so it is easy to meander due to the expansion and contraction movement. However, the guided roller (or ball) 10 according to the present invention The welded part 11 of the bellows has the function of preventing meandering caused by sliding, and by installing the welded part 11 of the bellows in a position that maintains an appropriate distance from the extension pipe 3 and the guide pipe 2, the welded part 11 of the bellows can be prevented from meandering due to sliding. It becomes possible to prevent damage caused by contact. Furthermore, by attaching guide grooves 12a, 12b and rail mechanism 13 to guide tube 2 or extension tube 3, it becomes possible to limit the sliding direction of guided roller (or ball) 10, and twisting due to sliding of bellows 4. can also be prevented. Furthermore, the present invention has a similar effect even during emergency shutdown of a nuclear reactor (during scram operation). As described above, the installation of these guided rollers (or balls) and guide grooves has the effect of preventing the CRD bellows from meandering due to internal pressure and the buckling that accompanies this. This prevents contact and damage caused by this and enables smooth sliding.

Furthermore, by providing smooth sliding of the bellows, resistance to insertion and withdrawal is reduced, and during emergency reactor shutdown (CR)
This improves the ease of inserting control rods during scram operation (D).

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the overall configuration of the control rod drive mechanism. FIG. 2 is an enlarged partial cross-sectional view of the shaft sealing portion of a control rod drive mechanism according to an embodiment of the present invention, and FIG. 3 shows the shapes of the guide tube and extension tube portion of FIG. Cross-sectional view of the guide tube, b
FIG. 3 is a cross-sectional view of another embodiment of a, and c is a cross-sectional view of an extension tube. 1・
... Drive unit, 2... Guide tube, 3... Extension tube, 4...
・Bellows, 5... Control rod, 9... Meandering prevention mechanism,
10...Roller with guide (or ball), 12a, 12
b. Guide rod, 13... rule mechanism.

Claims (1)

[Scope of Claims] 1. A drive unit that moves the control rod up and down, an extension tube connected to the control rod, and a guide tube installed on the outer periphery of the extension tube.
1. A control rod drive mechanism comprising a bellows forming a boundary between a furnace atmosphere and a drive mechanism, the control rod drive mechanism comprising a guide mechanism capable of moving up and down at arbitrary intervals in the axial direction of the bellows. 2. The control rod drive mechanism according to claim 1, wherein the guide mechanism includes a roller. 3. The control rod drive mechanism according to claim 1, further comprising a guide means in the axial direction of the movable surface of the guide mechanism.