JPS623917B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control rod drive mechanism for a fast breeder reactor,
In particular, it relates to a control rod drive mechanism with improved sealing bellows forming a boundary.

The control rod drive mechanism includes a structural part that forms a boundary between the inside of the reactor and a control rod operating mechanism part arranged in the reactor core to control the reactivity of the nuclear reactor. This drive mechanism must be capable of scramming a predetermined number of times during its life, and must also ensure the integrity of the mechanism itself. This scram condition requires a short scram time of less than one second from the start to the end of control rod insertion, and the operating range of this drive part is as large as approximately 1000 mm, making it extremely difficult to use as a part that forms the boundary with the reactor. It can be said that the conditions are harsh.

By the way, welded bellows have conventionally been used as parts that form this boundary, but since these bellows are made for structures that deform under near-static conditions, they are capable of rapid deformation such as during a scram. If used under such conditions, localized concentrated deformation may occur due to dynamic response, and fatigue failure may occur due to repeated deformation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a seal bellows that deforms as uniformly as possible even under rapid deformation conditions such as scram conditions, and has a sufficient margin for the required life.

Hereinafter, the control rod drive mechanism of the present invention will be explained in detail with reference to the drawings of one embodiment.

The control rod drive mechanism includes a drive section 1 as shown in FIG.
and a lower mechanism 2, and a plurality of them are implanted in the upper lid 3 of the reactor vessel. Of these, the drive unit 1 has an elongated cylindrical housing 4 that stands up on the upper lid 3, and a drive motor 5 is housed in the top of the housing 4. The output shaft of the drive motor 5 is supported by a ball bearing 6 and connected to a lead screw 7.
extends vertically downward, and its lower end is inserted into the finger support cylinder.

On the other hand, a screw nut 9 is screwed onto the lead screw 7.
An electromagnet 21 is integrally attached to the. The electromagnet 21 is moved up and down by the rotation of the drive motor 5, and the up and down movement of the electromagnet 21 is caused by the guide protrusion of the screw nut 9 engaging the guide groove on the inner circumferential wall of the housing 4. Guided without rotation.

The armature 22 is placed on the upper end of the finger support cylinder 8, while the lower end of the finger support cylinder 8 grips the outer extension rod 12 and the inner extension rod 13 via a latch mechanism 10. There is. The electromagnet 21 has an electromagnet 2
A scram lock bolt 23 for screwing together the drive unit 1 and the armature 22 is attached, and is rotated by an operating rod 24 inserted from the upper end of the drive unit 1.

Further, the lower mechanism 2 has a guide tube 11 that is inserted into the upper cover 3 of the reactor vessel and hangs down from the upper cover into the reactor vessel, and the upper end of the guide tube 11 is fitted into the housing 4. ing. The guide tube 11 incorporates an outer extension rod 12 and an inner extension rod 13 so as to be slidable in the vertical direction. Above outer extension rod 1
A pair of grippers 14 are swingably supported at the lower end of the reactor 2, and the grippers 14 fixedly support a control rod 15 inserted into the reactor core. Note that bellows 16 and 17 are interposed between the guide tube 11 and the outer extension rod 12 and between the extension rods 12 and 13, respectively, to prevent radioactive gas or steam from entering the housing 4. It forms a boundary that prevents leakage.

FIGS. 2 and 3 are detailed views in which the present invention is applied to a stroke bellows which is also affected by dynamic effects. These bellows were designed to compensate for their shortcomings based on the results of analyzing the dynamic deformation behavior of the bellows structure in consideration of scram conditions. That is, the present invention prevents damage due to dynamic phenomena by making the spring constant near the lower end of the bellows portion receiving a load larger than the spring constant of other parts. In FIG. 2, a bellows 31 is used in which the inner diameter of the lower part (the part that constantly carries the load) increases toward the lower part to increase the spring constant. The broken line in FIG. 2 is the inner diameter of the conventional bellows. In FIG. 3, the upper bellows absorbs the deformation, and the lower part is a molded bellows 32 with a large spring constant. As a modified example of Fig. 2, which has the effect of softening the dynamic effect and extending the life, there is a method in which the outer diameter decreases toward the bottom, and a method in which the lower part of the bellows is composed of two or three plates. It is also possible to use a material for the lower part that is stronger than the upper part.

Next, the operation of the control rod drive mechanism will be described.

During normal operation, the electromagnet 21 is energized with the scram lock bolt 23 unscrewed during shim operation to adjust the reactivity of the reactor. As shown in FIG. 1, the rotational movement of the drive motor 5 is converted into the vertical movement of the electromagnet 21 by the lead screw 7, and furthermore, the vertical movement of the electromagnet 21 is converted by the armature 22 and the finger support cylinder 8. , the latch mechanism 10, and the outer extension rod 12 to the control rod 15, causing the control rod 15 to move up and down. The shim operation is performed in this manner.

Further, during scram, the electromagnet 21 is demagnetized. By demagnetizing the electromagnet 21, the armature 22 is separated from the electromagnet 21, and the finger support cylinder 8 and both extension rods 1 are thereby separated.
2, 13 and the control rod 15 are dropped together,
A scrum operation is performed.

At this time, the bellows 16 extends 1100mm downward,
When a conventional bellows is installed, the deformation of the bellows is concentrated only in the lower part. This deformation behavior is repeated during scramming, causing fatigue failure. However, when the bellows of the present invention is installed, the strong spring constant of the lower part transmits the force to the upper part, resulting in a static deformation state or a state close to it, and the integrity of the bellows is guaranteed. In other words, the deformation state changes from the deformation curve a to the deformation curve b shown in FIG.

As explained above, the control rod drive mechanism of the present invention equipped with a bellows that can sufficiently withstand dynamic deformation behavior is
Local deformation of the bellows during scram is reduced and the boundary function retention life of the bellows portion is improved.
Furthermore, the meandering of the bellows is eliminated and the scram characteristics are improved. This increases the reliability of the control rod drive mechanism.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing one embodiment of the control rod drive mechanism of the present invention, FIG. 2 is an explanatory diagram showing the bellows portion of FIG. 1, and FIG. 3 is a diagram showing another embodiment of the control rod drive mechanism of FIG. The explanatory diagram shown in FIG. 4 is a conceptual diagram showing the deformation behavior when the bellows of the present invention is used. 5... Drive motor, 9... Screw nut, 1
2... Outer extension rod, 13... Inner extension rod, 16, 17... Bellows, 31... Bellows with increased spring constant,
32... Molded bellows with a large spring constant.

Claims (1)

[Claims] 1. A housing installed upright on the upper lid of a container housing a nuclear reactor core, a drive motor installed in this housing, a drive section movable by the rotation of this drive motor, and a drive section connected to this drive section. In a control rod drive mechanism comprising an interlockable rod member and a bellows part which is extendably provided between the rod member and the upper cover and maintains airtightness between the rod member and the upper cover, the bellows part is a control rod drive mechanism characterized by making the spring constant near the lower end larger than the spring constant of other parts.