JPS6319594A - Shielding plug for nuclear reactor vessel - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a shielding plug for a nuclear reactor vessel, particularly a reactor vessel for covering an upper opening of a reactor vessel used in a fast breeder reactor, etc. relating to shielding plugs.

(Prior Art) A reactor vessel of a conventional fast breeder reactor will be explained with reference to FIG. In the figure, the upper opening of the reactor vessel 6 is sealed by a shielding plug consisting of a fixed plug 1 and a rotating plug 2. As shown in FIG. A reactor core 21 is housed in the reactor vessel 6, and a control rod drive machine v422 for controlling the output of the reactor core 21 is provided above the reactor core 21, passing through the rotary plug 2.

Further, liquid sodium 5 is sealed in the reactor vessel 6 so as to submerge the reactor core 21 .

By the way, various plugs are mounted on the fixed plug 1 or the rotating plug 2, and these plugs have various diameters. These various plugs are housed mainly for measuring equipment, and below, the liquid level gauge plug 3 will be explained as an example.

The liquid level gauge plug 3 is mounted on the fixed plug 1. The upper part of the liquid level gauge 4 is supported and housed in the liquid level gauge plug 3, and the lower part of the liquid level gauge 4 protrudes from the lower surface of the liquid level gauge plug 3 to reach the liquid level of the sodium 5 and measure the liquid level. do.

Further, a cooling layer 7 is formed under the fixed plug 1 and the rotating plug 2 to circulate nitrogen gas etc. in order to keep the temperature of the upper plate low, and below that, a plurality of thick stainless steel plates are formed. A radiation shield @8 consisting of etc. is provided. Roughly speaking, a heat shielding layer 9 made of a laminated structure of a large number of thin plates is disposed below the nuclear reactor in order to shield heat rising from inside the reactor. And cooling layer 7. A shielding shell 10 is installed to surround the radiation shielding layer 8 and the heat shielding layer 9.

(Problems to be Solved by the Invention) Among the shielding plugs, for example, the temperature distribution in the axial direction of the level gauge plug 3 is normal temperature (approximately 30°C) on the top surface during reactor operation;
It is known that the temperature reaches about 450° C. on the bottom surface, and large thermal stress occurs at the structural discontinuities of the shielding plug body and various plugs included in the shielding plug. This will be explained in detail below with reference to FIGS. 6 and 7.

The bottom plate 11 of the level gauge plug 3 is attached to the body 12 of the plug 3 by welding 23, as shown in FIG.
It was attached to the body 12 of the plug or to a flange attached to this body 12 by bolting. Therefore, this bottom plate 11 serves as a mold support point for other members, prevents sodium vapor and mist from entering the plug, and supports devices such as liquid level gauges penetrating the plug against horizontal seismic force. It has an important role to play.

Next, when the temperature distribution described above occurs in the operating state of the reactor, the deformation state of the shell 12 and the bottom plate 11 becomes as shown in FIG. 7. In this case, the lower end 16 of the shell is the most This is one of the areas where thermal stress is severe. For this reason, the body portion 12 of the shielding plug body and the body portions of various plugs have been designed to be as thin and flexible as possible to alleviate the thermal stress generated. However, making the body thinner is disadvantageous in terms of strength against mechanical loads such as earthquake resistance, so it is extremely difficult to determine the thickness of the body that reduces both thermal stress and stress due to mechanical loads. Met.

The present invention has been made in view of the above circumstances, and its purpose is to alleviate the thermal stress generated in the structural discontinuities of the plug without impairing the strength of the body of the plug against mechanical loads. .

[Configuration of the Invention (Means for Solving Problems)] In order to achieve the above object, the present invention provides a shielding plug for closing an opening of a reactor vessel, in which various plugs mounted on the shielding plug are cylindrical. It consists of a body section formed in the shape of a shape, and a bottom plate attached to the lower end of the body section, and the bottom plate is configured to be held between an upper support body and a lower support body formed inside the body section. It is characterized by this.

(Function) When the shielding plug is configured as described above, even if the temperature distribution becomes high at the bottom of the plug, the body will not be restrained from deforming by the bottom plate at the bottom end of the body. The stress generated at the lower end is almost zero regardless of the wall thickness of the body.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of one embodiment of the present invention, for example, the third
This is applied to the level gauge plug of the reactor vessel of the fast breeder reactor shown in the figure.

In the figure, in order to keep the temperature of the fixed plug 1 to which the level gauge plug 3 is attached low, a cooling layer 7 for circulating nitrogen gas or the like is disposed below the fixed plug 1. Further, a radiation shielding layer 8 made of a plurality of thick plates made of stainless steel is placed below it, and the radiation shielding layer 8 is roughly
In order to shield the heat rising from inside the reactor,
A heat shielding layer 9 made of a laminated structure of a large number of thin plates is provided. And cooling layer 7. A shielding shell 10 is installed to surround the radiation shielding layer 8 and the heat shielding layer 9.

Further, the bottom plate 11 of the level gauge plug 3 is held between an upper ring 14 of an upper support and a lower ring 13 of a lower support attached to the body 12 of the level gauge plug 3.

The liquid level gauge 4 is attached to penetrate the bottom plate 11.

Next, to explain the operation of this embodiment, when the temperature distribution is such that the lower part of the liquid level gauge plug 3 becomes high temperature, the body part 1
2 and the bottom plate 11 are thermally deformed as shown in FIG. That is, since the body part 12 and the bottom plate 11 are not connected by welding or the like as in the conventional case, the lower end 15 of the body part 15 is not restrained by the bottom plate 11 and can be freely deformed. Furthermore, the deformation of the bottom plate 11 is not restricted by the body 12 at the outer periphery. Moreover, the bottom plate 11 prevents sodium vapor and mist from entering the plug, and serves as an earthquake-resistant support when the liquid level gauge 4 receives horizontal seismic force.

As described above, according to this embodiment, the lower body end 15 of the level gauge plug 3 is not subject to thermal deformation restraints, so the thermal stress on this body lower end 15 becomes extremely small.
Thermal stress on the outer periphery of the bottom plate 11 of the level gauge plug 3 is significantly reduced. Roughly speaking, assuming that an accident occurs in a nuclear reactor and the pressure inside the reactor increases rapidly, the bottom plate 11 of the level gauge plug 3 according to this embodiment will have less stress and strain than the bottom plate of the conventional structure. Since both become larger, a larger amount of energy is absorbed as elastic strain energy (1q), which is effective in preventing other important equipment from being damaged due to a sudden increase in pressure.

FIG. 4 is a vertical sectional view of a lower part of another embodiment of the present invention, and as shown in the figure, the upper support body that holds the bottom plate 11 of the level gauge plug 3 is the shoulder part 23 of the body part 12. , the lower support is a ring 13, and the bottom plate 11 is held between the shoulder 23 of the body 12 and the ring 13.

FIG. 5 is a bottom view of another embodiment of the present invention, in which a plurality of lower support members 17 are arranged inside the body 12 instead of the ring 13 in FIG. 1
1 is held between the shoulder portion 23 of the body portion 12 and the lower support member 17.

[Effects of the Invention] As explained above, according to the present invention, the thermal stress at the lower end of the body of various plugs can be extremely reduced without reducing the mechanical strength of the body. Further, thermal stress on the outer periphery of the plug bottom plate can be significantly reduced, and thermal deformation of the bottom plate can also be reduced. Furthermore, even if the pressure inside the reactor suddenly increases for some reason, the plug bottom plate can absorb a large amount of energy as elastic strain energy, making it extremely effective in preventing damage to important equipment such as the boundary. It is.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a level gauge plug showing an embodiment of the present invention, Fig. 2 is an enlarged view of the lower part of the level indicator plug shown in Fig. 1 deformed due to thermal stress, and Fig. 3 is a main A schematic sectional view of a fast breeder reactor structure to which the invention is applied, FIG. 4 is a partial sectional view of another embodiment of the invention, FIG. 5 is a bottom view of still another embodiment of the invention, and FIG. 6 7 is a sectional view showing a lower groove path of a conventional level gauge plug, and FIG. 7 is a diagram for explaining a state in which the level gauge plug shown in FIG. 6 is deformed due to thermal stress. 1...Fixed plug 2...Rotating plug 3...
Level gauge plug 4...Liquid level gauge 5...Liquid sodium 6...Reactor vessel 7...Cooling distillate 8.
...Radiation shielding layer 9...Heat shielding layer 10...
Shielding body 11...Plug bottom plate 12...Plug body 13...Upper ring 14...Lower ring 1
7... Lower support member 21... Core 22... Control rod drive mechanism 23... Shoulder (8733) Agent Patent attorney Yoshiaki Inomata (and 1 other person) Figure 1 Figure 5 Figure 6 Figure 7

Claims (3)

[Claims] (1) In a shielding plug that closes an opening of a reactor vessel, the various plugs mounted on the shielding plug are composed of a cylindrical body and a bottom plate attached to the lower end of the body; A shielding plug for a nuclear reactor vessel, wherein the bottom plate is configured to be sandwiched between an upper support member and a lower support member formed inside the body. (2) The shielding plug for a nuclear reactor vessel according to claim 1, wherein the upper support is a shoulder of a groove formed in the upper ring or the lower end of the trunk. (3) The shielding plug for a nuclear reactor vessel according to claim 1, wherein the lower support member is a lower ring or a plurality of lower support members.