JPS6015039B2 - Reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fast breeder nuclear reactor using liquid metal coolant in which the reactor vessel and outlet nozzle are protected from thermal shock and thermal deformation.

In nuclear reactors that use liquid metal coolant, in order to improve thermal efficiency, the outlet temperature of the coolant flowing out of the nuclear fuel assemblies arranged in the reactor core reaches 500°C to 600°C.

The upper plenum contains the upper core mechanism necessary for in-core instrumentation and an inner cylinder inside the reactor vessel.

The inner cylinder is installed for the purpose of absorbing the destructive energy generated in the reactor core during nuclear runaway through deformation of the inner cylinder, suppressing the deformation of the reactor vessel and pressure propagation to the primary cooling system, and also during transient operation. It sometimes relieves the thermal shock and stress of the main cooling system and outlet nozzle.

The flow hole is designed to allow the coolant to flow through the flow hole to the outlet nozzle when the coolant level is low, such as when replacing fuel.

In the flow in the upper plenum, the coolant leaving the core assembly flows radially and upwardly through the lower part of the upper core mechanism.
Most of this coolant hits the inner surface of the inner cylinder and flows upward.

A part of it passes through a flow hole provided in the abdomen of the inner cylinder, collides with the furnace vessel (or outlet nozzle), and flows out from the outlet nozzle. This coolant passes through a heat exchanger, a circulation pump, etc., and then returns to the coolant inflow side of the furnace vessel. When there is a scram in a nuclear reactor having the above structure, the coolant outlet temperature from the core fuel assembly may change suddenly.

Then, the coolant with a low (high) temperature suddenly flows out directly through the flow hole, and the coolant rises along the inner surface of the inner cylinder.
There are two routes: changing direction at the top of the inner cylinder and descending along the inner surface of the reactor vessel to reach the outlet nozzle, and there is a time lag between these two routes until the coolant reaches the outlet nozzle. . At this time, a steep temperature change occurs near the exit nozzle, creating a portion with a large temperature difference, which may cause thermal shock and thermal deformation, and in the worst case, cracks may occur. The present invention has been made in view of the above circumstances, and by providing a detour flow path such as a rainbow board at the entrance of the flow hole, the coolant flowing out from the nuclear fuel assembly of the reactor core flows directly from the flow hole to the exit nozzle. It is possible to prevent thermal shock and thermal deformation by preventing sudden temperature changes near the exit nozzle and preventing the formation of large temperature differences, thereby providing a nuclear reactor with increased safety. It's about doing.

Embodiments of the present invention will be described below in comparison with the conventional examples shown in FIGS. 1 to 3. FIG. 1 is a schematic cross-sectional side view of a conventional nuclear reactor.

The coolant flows from the inlet nozzle 2 connected to the bottom of the reactor vessel 1, passes through the lower plenum 13, passes through the core fuel assembly 4 and the Plunket fuel assembly 5, changes direction almost at right angles at the lower surface of the upper core mechanism 9, and enters the reactor. It collides with the cylinder 14, flows upward again, makes a U-turn at the top of the inner cylinder 14, and changes direction to the furnace vessel 1.
It descends along the inner surface and flows out from the outlet nozzle 3.

At this time, a portion of the coolant directly flows out from the outlet nozzle 3 through the flow hole 15 provided in the inner cylinder 14. In addition, in the figure, 7 is a control rod, 8 is a reactor internal structure, 10 is a rotating plug,
11 is a dipped plate, and 16 is a reflector.

FIG. 2 shows the calculated temperature distribution after the coolant flow pattern in the upper plenum 12 and the exit temperature of the core fuel assembly 4 suddenly increased by about 100 qo.

FIG. 3 shows temperature changes at points A, B, and C in FIG. 2.

As is clear from Figure 3, the difference between the temperature at point C and point B of the outlet nozzle 3 is about 40 degrees (△T in Figure 3), and this temperature difference continues for about 5 seconds. . At this time, the outlet nozzle 3
This creates a region in the vicinity with a temperature difference of about 40 qo.

This temperature difference then causes thermal shock and thermal deformation in the outlet nozzle 3 or the furnace vessel 1. In the worst case scenario, a crack may occur, leading to an accident where coolant leaks. Therefore, in the present invention, as shown in FIG. 4, by providing a blocking plate 20 at the entrance of the flow hole 15 to form a bypass flow path, the drawbacks of the conventional system are prevented and safety is increased. . In the figure, the mounting plate 21 connects the cutting board 20 to the inner cylinder 14.
It is to be fixed at At this time, the coolant flow pattern is such that the coolant flowing out of the core fuel assembly 4 collides with the two baffle plates and flows upward, so that no coolant flows out forcefully from the flow holes 15.

FIG. 5 shows the temperature changes at points A', B', and ○ in FIG. 4. According to this, the temperature difference (ΔT') between point B' and point O becomes quite small, so thermal stress and thermal deformation due to a large temperature difference near the exit nozzle can be prevented compared to the conventional structure. This can prevent cracks from occurring in the reactor vessel 1 and outlet nozzle 3 of the nuclear reactor, thereby increasing safety. 6th
FIGS. 18A and 18B partially show an example in which a detour flow path such as a rainbow board at the entrance of the flow hole 15 provided in the inner cylinder 14 is arranged.

FIG. 6 shows the jamb board 20 curved into a round shape, and FIGS. 7 and 9 show the jamb board 20 tilted and fixed to the tapered foot 21.

FIG. 8 shows a cutting board with two or more small holes 22. The effect of the present invention can be obtained not only in FIG. 8 but also in other embodiments in which small holes 22 are provided in the jamb board 20. 1st
Figure 0 shows a box-shaped detour passage 23 installed instead of the cutting board.

At this time, a plurality of small holes 24 are provided above and below. 11th
In the figure, the pipe 25 is attached to the inner cylinder 14 at an angle of about 45 degrees.

FIG. 12 shows the use of an elbow nozzle 26 for forming a detour flow path.

FIG. 13 shows a baffle plate 30 whose upper part is attached to the inner circumference of the inner cylinder 14 so that coolant can flow in from the lower part.

FIG. 14 shows a baffle plate 30 that allows the coolant to flow in from above, contrary to FIG. 13.

31 is a drain.

Fig. 15 shows a block board 40 attached by a spring 41,
The flow hole 15 is shown to be opened or closed depending on the magnitude of the dynamic pressure of the coolant.

In other words, when the flow rate of the coolant is large, the coolant collides with the four walls, and the force of the coolant presses the spring to close the flow hole 15. (Fig. 16) On the other hand, when the flow rate of coolant is low, such as during fuel exchange, the spring plate returns to its original position and serves the purpose of the flow hole 15. Figure 17 shows a chisel coupling 43 (one with a fixed maximum opening and can be opened and closed freely)
A rainbow board 42 is attached to perform the same operation as in FIGS. 15 and 16. The flow holes are designed to open due to the gravity of the baffle plate 42 when the dynamic pressure decreases. FIG. 17 shows the flow hole 15 opened, and FIG. 18 shows the flow hole 15 closed.
As explained above, according to the present invention, the coolant flows through the lower part of the upper core mechanism from the flow hole provided in the inner cylinder in order to prevent thermal stress and thermal strain on the outlet nozzle in the reactor vessel and the wall of the reactor vessel. The reason is that a detour flow path such as a flow hole Nijiyama board is provided to prevent the water from directly flowing out from the outlet nozzle.

Therefore, thermal stress and thermal strain are not caused in the outlet nozzle and the wall of the furnace vessel, and since the coolant flows out to the outlet nozzle after being sufficiently mixed, it also contributes to improving thermal efficiency.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining a conventional nuclear reactor, and FIG. 2 is a schematic cross-sectional view for explaining the flow pattern in the upper plenum and the temperature distribution accompanying temperature changes in the core in FIG. Figure 3 shows A of the upper plenum of the furnace in Figure 2.
A curve diagram showing temperature changes at points B and C, FIG. 4 is a schematic sectional view showing a flow pattern in the upper plenum to explain the nuclear reactor according to the present invention, and FIG. 5 is a curve diagram showing temperature changes at points A' in FIG.
, B', a curve diagram showing temperature changes at points 〇, and FIGS. 6 to 18 are partial cross-sectional views showing examples in which the inner cylinder Nijiyama plate is installed in the nuclear reactor according to the present invention, respectively. . 1...Furnace vessel, 2...Inlet nozzle, 3...
... Outlet nozzle, 4 ... Core fuel assembly,
5...Plunket fuel assembly, 6...
・Reflector, 7... Control rod, 6... Core structure, 9... Core upper mechanism, 10...
・Rotating plug, 11...dipped plate,
12... Upper plenum, 13... Lower plenum, 14... Inner cylinder, 15... Flow hole, 20
, 30, 40, 42...Front board, 21...Mounting plate, 23...Box-shaped detour channel, 22, 24,
31...Small hole, 25...Cylinder, 26...
...L-shaped nozzle, 41... Spring, 43...
・Chiyo mating joint. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18

Claims (1)

[Claims] 1. In a fast breeder nuclear reactor using liquid metal coolant, an upper core mechanism and an inner cylinder are provided in the upper brenum inside the reactor vessel, and multiple flow holes are provided on the side of the inner cylinder, and the multiple flow holes are provided on the side of the inner cylinder. A nuclear reactor characterized in that a detour flow path is provided at the entrance of the hole to prevent coolant from directly flowing out from these flow holes.