JPH0436357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a safety rod device for controlling the combustion of core fuel in a nuclear reactor.

[Technical background of the invention]

Traditionally, nuclear reactors, such as fast breeder reactors (FBR),
In boiling water reactors (BWRs) and pressurized water reactors (PWRs), safety rods are dropped into the reactor core in the event of an earthquake, and this controls the combustion of fuel in the reactor core to ensure reactor safety. There is. Among these fast breeder reactors, there are generally tank-type and loop-type fast breeder reactors, and the tank-type fast breeder reactor is constructed as shown in FIG. That is, it has a large-diameter main vessel 1 and a safety vessel 2 that concentrically surrounds the main vessel 1, and inside the main vessel 1 are built-in equipment such as a core 3, a core upper mechanism 4, a pump 5, a heat exchanger 6, etc. has been done.
In FIG. 1, 7 indicates a roof slab that closes the vessel opening, and 8 indicates a safety rod inserted into the reactor core. The reactor core 3 including the fuel assemblies and control rod guide tubes is supported by a core support mechanism 9 provided at the bottom of the main vessel 1. 10 indicates liquid sodium.

[Problems with background technology]

As mentioned above, the main vessel 1 accommodates the reactor core, various structural members, etc., so the shape and dimensions of the main vessel 1 become large.In order to reduce the weight, the main vessel 1
is made of thin-walled material. In addition, in order to reduce thermal stress under the high temperature conditions peculiar to fast breeder reactors, the main vessel 1 must be made of a thin material.

As described above, the main container 1 has a flexible structure because it is made of a thin material, and responds to large vibrations in the horizontal and vertical directions during an earthquake. moreover,
The support mechanism 9 that supports the core cannot be made sufficiently rigid due to the rigidity of the wall of the main vessel 1, and exhibits a large response in the vertical direction to earthquake input in the vertical direction.

Therefore, the support mechanism 9 may exhibit an acceleration response of 1G or more in the vertical direction, and in this case, there is a risk that the safety rod 8 inserted into the reactor core 3 will fly upwards when an earthquake occurs and cease to operate as a safety rod. There is.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to obtain a safety rod device for a nuclear reactor that, once inserted, has no risk of escaping from the core unless intentionally pulled out.

[Summary of the invention]

In the present invention, a stopper is attached to a safety rod that is inserted into the reactor core and controls the combustion of core fuel, and is applied with an elastic force in a direction away from the circumferential surface of the safety rod, and the safety rod is guided and inserted into the hollow interior of the stopper. - It consists of a safety rod guide tube that guides the direction of withdrawal and the safety rod is detachably held, and when a disturbance occurs, the holding of the safety rod is released and the safety rod is moved with the stopper closed. a safety rod holding means for inserting the safety rod into the safety rod guide tube by gravity; a small diameter portion formed within the safety rod guide tube through which the stopper can pass when the safety rod is inserted; and the safety rod guide. a large-diameter portion formed in the pipe, which restricts the movement of the safety rod in the insertion/extraction direction by engaging the stopper away from the circumferential surface of the safety rod when the safety rod is dropped and inserted to a predetermined position; The configuration includes the following.

[Embodiments of the invention]

As shown in FIG. 2, U-shaped notches 11a are provided on the circumferential surface of the lower end of the safety rod 11 in opposing relationship, and the lower ends of the stoppers 12 are pivoted to the lower ends of these notches 11a, respectively. has been done. Further, between the upper end of the stopper 12 and the upper end of the notch 11a, there is a spring 1 that applies a spring force in the direction of opening the stopper 12.
3 is installed. The stopper 12 is provided with a thick wall portion 12a having a triangular cross section on the surface of the upper end facing the safety rod.

On the other hand, as shown in FIG. 3, the safety rod guide tube 14 is provided with a small diameter portion 20 through which the stopper 12 can pass when the safety rod 11 is inserted. A large-diameter portion 15 is provided at the lower end of the safety rod guide tube 14, and the small-diameter portion 20 has a U-shaped shaft located at both diametrical ends and whose outermost surface coincides with the circumferential surface of the large-diameter portion 15. Directional groove 16
is provided up to the top opening. FIG. 4 shows a part of the reactor core incorporating the safety rod 11 of this embodiment.
That is, the guide tube 14 is supported by the core support plate 17, and the upper end of the safety rod 11 is connected to the safety rod drive mechanism 18.
and is connected via a magnet 19. The safety rod drive mechanism 18 has a function of pulling out the safety rod 11,
It has a function of rotating it around an axis, and constitutes a rotating means in this embodiment.

When an earthquake occurs, the magnet 19 is deenergized and the safety rod 11 is dropped and inserted. Therefore, safety rod 1
1, the stopper 12 at the lower end of the guide tube 14 normally
Since it is placed in a state where it does not face the groove 16 of
The safety rod 11 falls while the stopper 12 is brought into sliding contact with the circumferential surface of the small diameter portion 20 of the guide tube 14 by the spring 13.
When the fall ends, the stopper 12 engages with the stepped portion 15a formed by the large diameter portion 15. When the stopper 12 engages with the stepped portion 15a in this manner, there is no fear that the safety rod 11 will escape from the core even if the core support mechanism makes a large upward response to earthquake motion.

When the safety rod 11 is pulled out after the earthquake, the safety rod 11 is connected to the drive mechanism 18 by the magnet 19, and the safety rod 11 is first rotated to remove the stopper 1.
2 to face the groove 16, and then drawing is performed. After the withdrawal is completed, rotate the safety rod 11 again and close the stopper 1.
2 from the position of the groove 16.

Note that the safety rod 11 is not limited to being inserted by being dropped by gravity as described above, but may be inserted using the pressure of pressurized water in the case of BWR. The shape, number, mounting position, etc. of the stopper 12 can be changed in various ways. Furthermore, this invention is also applicable to BWR and PWR.

〔Effect of the invention〕

As is clear from the above, even if the main vessel and core support mechanism have a flexible structure, there is no risk of the safety rods escaping from the reactor core during an earthquake, which is extremely useful in maintaining the safety of the reactor.

[Brief explanation of drawings]

Fig. 1 is a schematic sectional view of a fast breeder reactor, Fig. 2 is a sectional view of main parts of an embodiment of the present invention, Figs. 3A and B are longitudinal sectional views and cross-sectional views of other main parts, and Fig. 4 1 is a longitudinal cross-sectional view showing a state in which an embodiment of the present invention is incorporated into a reactor core. 11... Safety rod, 12... Stopper, 13... Spring,
14...Safety rod guide tube, 15...Large diameter part, 16...Groove,
19...Magnet (safety rod holding means), 20...Small diameter portion.

Claims (1)

[Scope of Claims] 1. A stopper that is attached to a safety rod that is inserted into the reactor core and controls the combustion of core fuel and that applies an elastic force in a direction away from the circumferential surface of the safety rod, and a stopper that guides the safety rod into its hollow interior. and a safety rod guide tube that guides the direction of insertion and withdrawal, and the safety rod is detachably held, and when a disturbance occurs, the holding of the safety rod is released and the safety rod is removed with the stopper closed. a safety rod holding means for inserting the rod into the safety rod guide tube by gravity; a small diameter portion formed in the safety rod guide tube through which the stopper can pass when inserting the safety rod; The stopper is formed in the rod guide tube, and when the safety rod is dropped and inserted to a predetermined position, the stopper is engaged away from the peripheral surface of the safety rod,
A safety rod device for a nuclear reactor, comprising: a large diameter portion that restricts movement of the safety rod in the insertion/extraction direction;