JPH0219792A - Upper mechanism of reactor core - Google Patents

Abstract

PURPOSE:To maintain thermal stress below a correct value even if a temperature of a coolant is varied suddenly by providing an outer drum on the outside peripheral part of a drum and providing plural flow holes for penetrating the drum on the upper and the lower parts of the drum. CONSTITUTION:This mechanism 25 contains a control rod driving device therein, and has a drum 37 for penetrating a free liquid level 40 of a cover gas and a coolant 14. In this state, when a temperature of the coolant 14 is varied suddenly at the time of tripping a nuclear reactor, the coolant 14 of an annular part 52 of the inside of an outer drum 38 is brought to temperature fall a little later than that of the outside, as well, and a temperature difference is generated between this coolant and that of the inside of the drum 37. By flow holes 50, 51 of the upper and the lower parts of this drum 37, these coolants 14 are allowed to communicate with each other, therefore, a natural convection is generated. In such a way, the quantity of the coolant 14 of the annular part 52 is sufficiently smaller than that of the inside and a difference of the heat capacity is also large, and the coolant 14 which scarcely causes a temperature fall for many hours flows out of the hole 50. Accordingly, a variation of a temperature distribution in the vicinity of the liquid level 40 of the drum 37 becomes slow, and generated thermal stress is also reduced.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention provides a fast breeder reactor core in which coolant flowing out from the core flows outside the shell instead of flowing directly into the interior of the shell. Regarding the upper mechanism.

(Prior art) The upper core mechanism of a fast breeder reactor consists of control rods, control rod drive mechanism,
It is equipped with a control rod guide tube, instrumentation well, rectifier, etc.

As shown in FIG. 5, the rectifier 33 is connected to the core upper mechanism 25
The other equipment mentioned above is housed inside the body 37.

(Problem to be solved by the invention) When the coolant temperature changes suddenly during a reactor trip,
Although the temperature of the coolant 14 outside the core upper mechanism 25 drops rapidly, the temperature of the coolant inside does not follow the temperature of the outside coolant and is maintained at a high temperature.

(See Figure 4).

Further, the temperature of the upper part of the core upper mechanism 25 located in the cooling plug 17 and the cover gas 16 is maintained at the temperature before the reactor trip due to its large heat capacity and heat insulation properties.

Therefore, a temperature difference occurs in the coolant inside and outside the shell 37, and at the same time, a large temperature gradient also occurs in the axial direction.

Due to these plate thicknesses and axial temperature gradients, the coolant 14
Because excessive thermal stress occurs near the free liquid level 40 of the reactor, conventional measures have been required such as structural measures such as installing a thermal resistor and restricting the operating mode of the reactor.

In addition, the liquid-contacted parts of the flow straightener 33 and the lower end of the shell 37 near the core 19 were required to have a structure such as a flexible joint so that they would be able to withstand even more severe temperature changes than those near the free liquid level 40.

This invention was made in consideration of the above facts,
It is an object of the present invention to provide an upper core mechanism for a fast breeder reactor that can maintain thermal stress below an appropriate value even if the temperature of the coolant changes suddenly.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides an upper core mechanism for a fast breeder reactor having a shell containing a control rod drive mechanism, etc., which has an outer shell on the outer periphery for the above purpose, and has an upper and a lower part of the shell. It is equipped with a plurality of flow holes that pass through the body.

(Function) Therefore, in the upper core mechanism of the fast breeder reactor according to the present invention, when the temperature of the external coolant suddenly drops, the coolant in the outer shell and the annulus of the shell is also cooled, creating a downward flow, which occurs in the lower part. It flows into the river through the flow hole.

On the other hand, high-temperature coolant flows from the upper flow hole to the annulus section, reducing the thickness of the shell and the temperature gradient in the axial direction.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a core upper mechanism 2 of a fast breeder reactor according to the present invention.
5 is a side view showing a broken part of the main part of one embodiment in No. 5;
The figure is a sectional view showing a fast breeder reactor to which the embodiment of FIG. 1 is applied.

As shown in FIG. 2, a fast breeder reactor 13 generally uses liquid metal such as liquid sodium as a coolant 14. This coolant 14 is filled into the reactor vessel 15 .

The upper end of this reactor vessel 15 is closed by a shield plug 17, and a reactor core 19 is accommodated within the reactor vessel 15.

A coolant 14 such as liquid sodium is configured such that a coolant population 21 in the lower part of the reactor vessel 15 flows into the reactor vessel 15, flows upward in the reactor core 19, is heated, and flows out from a coolant outlet 23.

A core upper mechanism 25 is attached to the shield plug 17 .

This core upper mechanism 25 includes control rods, a control rod drive mechanism 27,
A shell 37 containing the control rod inner tube 29 and the instrumentation wafer 31
penetrates the free liquid surface 40 of the coolant 14. A rectifier 33 is attached to the lower part of the shell 37 to divert the coolant flowing out from the core and guide it to the upper plenum 41 of the reactor.

On the other hand, an outer body 38 is attached to the annulus portion 5 on the outer periphery of the first cavity 37.
M3 is installed as a heat shield plate for the shell 37.
At the same time, a coolant 1 is added inside to alleviate the temperature change applied to 7.
The boundary is formed so that 4 does not easily flow in.

When the coolant temperature changes suddenly during a reactor trip, etc., the temperature of the coolant 14 outside the upper core mechanism 25 changes suddenly, but the coolant temperature inside the shell 37 changes due to the temperature of the coolant outside the core upper mechanism 25. It does not follow the temperature, and a significant temperature difference occurs between the inside and outside of the upper core structure.

To show this transient state in detail, as shown in FIG. The temperature of the coolant also drops with a little delay, creating a temperature difference between the coolant and the coolant inside the shell 37.

Since these coolants are in communication with each other through the flow holes 50 and 51 in the upper and lower parts of the body, the coolant in the annulus part 52, which was stagnant when there was no temperature difference, flows downward and flows from the flow hole 51 in the lower part to the part 37. Due to the difference in specific gravity, the high temperature coolant inside 15i37 is pushed upwards and accumulates at the bottom.

On the other hand, the coolant in the cylinder 37 that has been pushed up flows out from the upper flow hole 50 to the annulus portion 52.

Due to the occurrence of this natural convection, the temperature distribution becomes as follows.

As shown in FIG. 4, the amount of coolant in the annulus section 52 is sufficiently small compared to the amount of coolant inside, so there is a large difference in heat capacity, and the temperature does not drop for a long time from the upper flow hole 50. The remaining coolant flows out, the temperature distribution near the liquid surface of the shell 37 changes slowly, and the generated thermal stress is also reduced.

The coolant, which was at a high temperature near the liquid level in the upper part, is cooled down while descending through the annulus section 52 and becomes low-humidity, and flows into the shell 37 from the flow hole 51 in the lower part, so the temperature rapidly drops near the reactor core and becomes low temperature. The lower outer surface of the trunk 37 and the trunk 3
Since the temperature difference inside 7 is reduced, the thermal stress in this part is also reduced.

〔Effect of the invention〕

As described above, according to the upper core mechanism of a fast breeder reactor according to the present invention, the outer shell, the annulus portion of the shell, and the coolant of the shell are communicated through the upper and lower flow holes, and sudden changes such as when the reactor trips, etc. Natural convection occurs when the temperature changes, reducing the temperature difference between the inside and outside of the circle and alleviating thermal stress.

This reduction effect, that is, the strength of natural convection is proportional to the severity of the temperature drop of the external coolant, no external operation is required, and the structure is simple, making it possible to apply the present invention. This has great effects, such as simply adding flow holes to the conventional structure.

In particular, if a temperature difference occurs, the effect of alleviating thermal stress is always changed, which greatly contributes to improving reliability.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the main parts of an embodiment of the upper core mechanism of a fast breeder reactor according to the present invention, Fig. 2 is a sectional view showing a fast breeder reactor to which the embodiment is applied, 13...Fast breeder
25... Core upper mechanism 37-1. torso
38... Outer body 50... Upper flow home
51... Lower Flow Home 52... Annulus Department Agent Patent Attorney Nori Chika Ken Yudo Daishimaru Ken Figure 1 Figure 2

Claims (1)

[Claims] In the upper core mechanism of a fast breeder reactor, which has a shell that houses the control rod drive mechanism etc. and penetrates the cover gas and the free liquid surface of the coolant, the shell has the coolant stagnant inside, and the outer part of the shell passes through the annulus. An upper core mechanism comprising an outer shell installed in the upper core and a plurality of flow holes in the upper and lower parts of the shell.