JP2508549B2 - Vibration absorption mechanism of self-actuated reactor shutdown mechanism - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-actuating nuclear reactor shutdown mechanism for holding a control rod by an electromagnet and automatically disconnecting the control rod when the coolant temperature rises abnormally to emergency stop the reactor. It is about improvement.

More specifically, the vibration absorption of the self-actuated reactor shutdown mechanism for preventing the control rod from swaying and accidentally falling due to hydrodynamic vibration due to the flow of the coolant, vibration during an earthquake, etc. It is related to the mechanism.

[0003]

2. Description of the Related Art In a conventional control rod drive mechanism in a nuclear reactor, since the control rod is mechanically held by a gripper, even if the control rod sways due to an earthquake or hydrodynamic vibration, the control rod will be erroneously moved. It is never dropped into the core. On the other hand, a Curie point electromagnet, which incorporates a magnetic material with a Curie point in the magnetic circuit, is installed in the coolant inside the reactor vessel, and the Curie point electromagnet holds the control rod by adsorption. Has also been proposed in the past. According to such a self-actuated reactor shutdown mechanism, when the coolant temperature rises abnormally, the magnetic circuit of the Curie point electromagnet is cut off, and the holding force of the electromagnet is reduced without turning off the power of the electromagnet to control. The rod can be automatically disconnected and dropped into the core, shutting down the reactor.

However, in the self-actuated reactor shutdown mechanism, since the control rod is directly adsorbed and held by the electromagnet through the armature, the control rod is laterally swayed by the flow force of the coolant, vibration of the flow force or vibration during an earthquake. Then, when a bending moment is applied, the force to open the adsorption surface of the electromagnet acts,
Even if the electromagnet has a sufficient holding force in a static state, it is extremely likely that the control rod is accidentally dropped. Therefore, in the self-actuated reactor shutdown mechanism, it is desirable to install a vibration absorbing mechanism to prevent the bending moment due to the rolling of the control rod from being transmitted to the attracting surface of the electromagnet.

Some of the vibration absorbing mechanisms proposed so far employ a spherical sliding bearing system as shown in FIG. In the illustrated self-actuating reactor shutdown mechanism, during normal operation of the reactor, the armature 1 with the control rod 2 attached to the lower end is electromagnetically attracted to the Curie point electromagnet 4 at the attracting surface 3, When the temperature of the coolant is abnormally increased and a part of the electromagnetic circuit of the electromagnet 4 is cut off, the armature 1 is separated from the adsorption surface 3 and falls into the core together with the control rod 2. The vibration absorbing mechanism by the spherical sliding bearing system in this furnace stopping mechanism has a structure in which a spherical surface 6 is formed on the control rod upper end connecting portion 5 and the spherical surface 6 is held by a concave bearing 8 formed on the side surface of the armature lower end connecting portion 7. have.

[0006]

In the case of the vibration absorbing mechanism based on the spherical sliding bearing system described above, the spherical surface 6 and the bearing 8 are used.
Since the entire surface of them touches and slides, it is desirable to apply a lubricating oil to the sliding surface to reduce the friction resistance, but it is difficult to use the lubricating oil in high temperature sodium. Sodium itself can be expected to have some lubricating effect, but basically it is the slip of the spherical surface 6 and it is unavoidable that the friction resistance during sliding becomes large, and a large bending moment acts on the electromagnet attracting surface 3. There is a high risk of accidentally dropping the control rod 2.

Further, in the case of the spherical sliding structure, the gap between the spherical surface 6 and the bearing 8 is very small, on the order of a few microns, so that when scratches due to wear occur on the spherical surface 6, the frictional resistance becomes remarkably large, and as a vibration absorbing mechanism. It is likely that the effect will be lost. Further, when the temperature changes, there is a difference in thermal expansion between the spherical surface and the bearing, so that it is difficult to secure an appropriate gap, and there is a drawback that reliability is poor in long-term use.

Therefore, the present invention has a smaller frictional resistance than the vibration absorbing mechanism of the spherical sliding bearing system described above, and has a highly reliable vibration absorbing performance even for long-term use in a high temperature environment in a nuclear reactor. The purpose of the present invention is to provide an improved vibration absorbing mechanism in a self-operating reactor shutdown mechanism that can be maintained.

[0009]

That is, the vibration absorbing mechanism of the self-actuating nuclear reactor shutdown mechanism according to the present invention is installed at the lower end of the control rod drive mechanism 10 when referring to the embodiment shown in FIG. A control rod holding electromagnet 14, an armature 11 attracted and held by the electromagnet, and a control rod 12 connected to the armature are installed between the armature 11 and the control rod 12 of a self-actuating reactor shutdown mechanism. In the vibration absorbing mechanism described above, the connecting portion 30 attached to the upper end of the control rod is suspended from the connecting portion 20 attached to the lower end of the armature via the spherical rolling contact joint including the spherical surface 31 and the spherical seat 21 that receives the spherical surface 31. It is characterized by that.

[0010]

When the control rod 12 rolls, the spherical surface 31 and the spherical seat 21 in the spherical rolling contact joint installed between the armature 11 and the control rod 12 make rolling contact with each other, and this joint portion Only the suspended control rod 12 makes a pendulum motion. Therefore, the bending moment due to the rolling of the control rod 12 is not transmitted to the armature 11 and further to the attraction surface 13 with the electromagnet 14,
As a result, the vibration received by the control rod can be effectively absorbed.

Compared with the spherical sliding bearing system shown in FIG. 7, in particular, the spherical rolling contact system of the present invention has an extremely small frictional resistance during operation, so that the vibration absorbing effect is further improved and at the time of high temperature environment. Spherical surface 3
Even if there is a difference in thermal expansion between 1 and the spherical seat 21, the vibration absorbing effect is not impaired.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 2 showing a schematic view of the essential parts of the vibration absorbing mechanism of the present invention shown in the embodiment of FIG. 1 and FIG. 3 showing a section taken along line XX of FIG. The present invention will be described in more detail.

The vibration absorbing mechanism of the present invention is installed between the armature 11 and the control rod 12 of the self-actuated reactor shutdown mechanism using the Curie point electromagnet. The connecting portion 20 attached to the lower end of the armature is composed of a spherical seat 21, a spherical seat mounting bracket 22 for embedding and fixing the spherical seat, and a connecting bracket 23 for connecting the spherical seat mounting bracket to the armature. On the other hand, the connecting portion 30 attached to the upper end of the control rod includes a steel ball 31, a ball fixing fitting 32 for embedding and fixing the steel ball, and a connecting fitting 33 for attaching the ball fixing fitting in a fitting structure and connecting with the control rod 12. Composed of and. The armature lower end connecting portion 20 and the control rod upper end connecting portion 30 are combined in such a manner that the steel ball 31 of the control rod upper end connecting portion 30 is placed on the concave surface of the spherical seat 21 of the armature lower end connecting portion 20. Thus, the control rod 12 is suspended below the armature 11 via the spherical rolling contact joint composed of the spherical surface 31 and the spherical seat 21, and the components of the control rod upper end connecting portion 30 and the total load of the control rod 12 are spherical. It will hang on the seat 21.

Under such a condition, for example, when a lateral load is applied to the control rod upper end connecting portion 30 side to cause lateral vibration, the steel ball 31 rolls into contact with the concave portion of the spherical seat 21, as shown in FIG. While performing a pendulum motion, a bending moment due to rolling is applied to the attraction surface 13 of the armature 11 and the electromagnet 14.
(See FIG. 1) to prevent the control rod 12 from falling and malfunctioning.

The vibration absorbing mechanism of the present invention utilizes spherical rolling contact, and in order to reduce the frictional resistance of rolling contact, the difference between the curvature of the concave surface of the spherical seat 21 and the steel ball 31 is increased. Is preferred. However, spherical seat 2
If it is close to a flat surface in order to make the curvature of the concave surface of 1 large,
The stability of the counterpart steel ball 31 will be impaired, and if the steel ball 31 is made smaller, the concentrated load will increase and a problem in strength will occur. In general, these strengths (stresses) determine the curvature so as to be within the allowable stress obtained from the Hertzian stress. The calculation results for the relationship between these curvatures and strengths are shown below.

The steel ball 31 has a radius of 9 mm (diameter 18 mm), the spherical seat 21 has a radius of 11 mm, and both members are made of stellite # 6 which is a material excellent in high temperature strength. Considering only the strength, the larger the diameter of the steel ball 31 is, the more advantageous it is. However, since the maximum diameter of the entire vibration absorbing mechanism needs to be about 50 mm, the radius of the steel ball is set to 9 mm. Under such a shape, the results of the following "Hertz surface pressure calculation formula" and "Evaluation method of the maximum allowable surface for wear prevention in general steel gears"
(Masayoshi Ishibashi, "Prevention of Fatigue and Destruction of Metals", published by Yokendo), was evaluated for strength problems.

Hertzian surface pressure calculation formula: q ₀ = 0.388 × {P × E ² × (R ₂ −R ₁ ) ² / (R ₁
² −R ₂ ² )} ^1/3 where q ₀ : maximum surface pressure generated at the center of the contact surface (kg / mm ² ) E: longitudinal elastic modulus (kg / mm ² ) R ₁ , R ₂ : sphere radius ( mm) P: Concentrated load (kg).

Calculation result of Hertz surface pressure (of Stellite # 6
E: 1.44 × 10 ⁴ , P: 80 kg) at data of 600 ℃ is q ₀
= 73.4 kg / mm ² . On the other hand, the maximum allowable surface pressure is 86.52 kg / mm ² (Stellite # 6 Brinell hardness: 30
9 is 0.28 times), which satisfies this. Therefore, it is understood that the above-described structure of the vibration absorbing mechanism of the present invention can be manufactured within a range where there is no problem in strength.

Considering the fact that the steel ball 31 is used in a high temperature environment, the above-mentioned stellite material can be preferably used, but in addition, Inconel 718 material and ceramic (Al ₂
Materials such as O ₃ and SiC) can also be used. A similar material can be used for the spherical seat 21 that contacts the steel ball. In the illustrated embodiment, a steel ball 31 having a spherical shape is used as the ball fixing fitting 3.
Although the spherical surface is formed by the structure embedded in 2, the steel ball 31
It may be manufactured by a single member in which the and the ball fixing metal fitting 32 are integrated.

In the illustrated embodiment, the upper end 32a of the ball fixing member 32 has a convex surface structure. This is because the armature 11 including the vibration absorbing mechanism and the control rod 12 are separated from the electromagnet 14 (see FIG. 1). This is to ensure that the adsorbing surface 13 of the electromagnet and the armature 11 is brought into smooth contact when the electromagnet 14 is again adsorbed and held by the electromagnet 14 and then pulled up. That is, as shown in FIG. 5, when the armature 11 is separated from the electromagnet, the contact between the steel ball 31 and the spherical seat 21 is released, and the lower end surface 23a of the connecting fitting 23 contacts the upper end surface 32a of the ball fixing fitting. At this time, if the upper end surface 32a of the ball fixing member is formed in a convex shape as shown in FIG. 5, even when the electromagnet is slightly inclined and descends without being kept horizontal with the attraction surface 13 of the armature,
Since the lower end surface 23a of the connecting fitting 23 can freely move, the attraction surface 13 between the electromagnet and the armature 11 is in a sufficiently close contact state, and the control rod 12 can be reliably pulled up.

In the illustrated embodiment, the spherical seat 21 is attached to the armature lower end connecting portion 20 side and the steel ball 31 is attached to the control rod upper end connecting portion 30 side. Are the same. That is, as shown in FIG. 6, the steel ball 41 is attached to the armature lower end connecting portion 20 side.
It is also possible to construct a spherical rolling contact joint by providing a spherical seat 51 on the control rod upper end connecting portion 30 side and placing the spherical seat 51 on the upper surface of the steel ball 41.

[0022]

As can be seen from the above, the vibration absorbing mechanism of the present invention has the control rod upper end connecting portion at the armature lower end connecting portion via the spherical rolling contact joint constituted by the spherical surface and the spherical seat receiving the spherical surface. Since it is configured to be suspended and engaged, it is possible to prevent the bending moment due to the lateral load received by the control rod due to an earthquake or hydrodynamic vibration of the coolant from being transmitted to the electromagnet attraction surface.

In particular, compared with the spherical sliding type shown in FIG. 7, the spherical rolling type vibration absorbing mechanism of the present invention has extremely small frictional resistance during operation and is more reliable against malfunction. Become. In the structure of the spherical slip system shown in FIG. 7, since the spherical surface and the bearing are formed with a very small gap of several microns, it is extremely difficult to maintain an appropriate gap under an environment where the temperature changes. Further, when scratches due to wear occur, the frictional resistance increases rapidly because the gap is small, and there is a high possibility that the effect of the vibration absorbing mechanism will be lost. On the other hand, in the structure of the spherical rolling system of the present invention, the problems of gap and sliding friction with respect to temperature change can be avoided, its function can be maintained for long-term use in a high temperature environment in the furnace, and its reliability is high. high.

By installing the vibration absorbing mechanism of the present invention having such a function and high reliability in the self-actuating reactor shutdown mechanism, the control rod can be controlled by the vibration of the disturbance even if there is no abnormality in the reactor. It can be prevented from accidentally falling,
The function of the self-actuated reactor shutdown mechanism, which is the original function of the reactor coolant, is that the electromagnet loses its holding force due to the abnormal temperature rise of the reactor coolant and the control rod is inserted into the core to shut down the reactor. In addition, since the control rod can be prevented from being accidentally dropped, the reliability of the self-actuating reactor shutdown mechanism can be improved, and it is also possible to prevent a decrease in the operating rate of the plant.

[Brief description of drawings]

FIG. 1 is a partially cutaway explanatory view showing an embodiment of a vibration absorbing mechanism of the present invention.

FIG. 2 is an explanatory view schematically showing a main part of the vibration absorbing mechanism shown in the embodiment of FIG.

FIG. 3 is a sectional view taken along line XX of FIG.

FIG. 4 is an explanatory diagram showing a state in which the control rod is laterally shaken in FIG. 2;

FIG. 5 is an explanatory view showing the positional relationship of each component when re-adsorbing the once separated armature to the electromagnet in the embodiment of FIG.

FIG. 6 is an explanatory view showing another embodiment of the vibration absorbing mechanism of the present invention.

FIG. 7 is a partially cutaway explanatory view showing a vibration absorbing mechanism of a spherical slip system different from the present invention. 10 ... Control rod drive mechanism, 11 ... Armature, 12
... control rod, 13 ... adsorption surface, 14 ... electromagnet, 20 ... armature lower end connecting portion 21, 51 ... spherical seat, 30 ...
Control rod upper end connecting portion, 31, 41 ... Spherical surface (steel ball).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayoshi 圷 1-6-1, Otemachi, Chiyoda-ku, Tokyo Inside Japan Atomic Power Company (72) Yoshinobu Okabe 1-6-1, Otemachi, Chiyoda-ku, Tokyo No. Japan Atomic Power Company (72) Inventor Toshiya Nozawa 1-6-1, Otemachi, Chiyoda-ku, Tokyo Japan Atomic Power Company (56) Reference JP-A-63-289487 (JP, A) JP Flat 2-245695 (JP, A)

Claims (3)

(57) [Claims] 1. A self-actuating reactor shutdown mechanism comprising a control rod holding electromagnet installed at a lower end of a control rod drive mechanism, an armature attracted and held by the electromagnet, and a control rod connected to the armature. In the vibration absorbing mechanism installed between the armature and the control rod, it was attached to the upper end of the control rod through a spherical rolling contact joint composed of a spherical surface and a spherical seat receiving the same, at the connecting part attached to the lower end of the armature. A vibration absorbing mechanism for a self-actuated reactor shutdown mechanism characterized by suspending a connecting portion. 2. The vibration absorbing mechanism according to claim 1, wherein a spherical seat is attached to the armature lower end connecting portion and a spherical surface is attached to the control rod upper end connecting portion. 3. The vibration absorbing mechanism according to claim 1, wherein a spherical surface is attached to the armature lower end connecting portion and a spherical seat is attached to the control rod upper end connecting portion.