JPS60158378A - Fast breeder reactor - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an internal structure of a nuclear reactor, and particularly to an internal structure suitable for use in a liquid metal cooled tank type fast reactor.

[Background of the invention]

The structure of a conventional tank-type nuclear reactor is roughly shown in FIG. The coolant (liquid metal sodium here) heated in the core 1 enters the hot plenum 2 and then flows into the intermediate heat exchanger 3 through the inlet window 4, where it heats the secondary sodium to a low temperature and flows into the cold plenum. Enter 5. Thereafter, it is sent to the core 1 again through the high-pressure plenum 7 by the circulation pump 6. Further, the hot plenum 2 has a furnace upper mechanism 8, and a partition wall 9 is provided between the hot plenum 2 and the cold plenum 5 to isolate them. Further, a rectifier lO is installed below the furnace upper mechanism 8. When the reactor scrams for some reason in such a tank-type nuclear reactor, the chain reaction in the reactor core 1 stops and only decay heat is generated, so that the calorific value rapidly decreases to a few percent of the normal value. On the other hand, the circulation pump that drives the coolant is also stopped, but the circulation pump 6 and electric motor 9
Due to the rotational inertia of the core, the core flow rate does not decrease rapidly but gradually. As a result, the coolant temperature at the exit of the core l drops rapidly, and a low flow rate of cold coolant flows out into the hot plenum 2. At this time, since the volume of the coolant existing in the hot plenum 2 is large and the temperature is high, the low flow rate of cold coolant flowing out from the outlet of the core 1 is not sufficiently mixed within the hot plenum 2. That is, in the hot plenum 2, a curse (herein referred to as a stratification phenomenon) occurs in which high-temperature coolant accumulates in the upper part and cold coolant flowing out from the core 1 flows horizontally in the lower part.

When this stratification phenomenon occurs, a large temperature gradient occurs near the boundary between the upper high-temperature coolant and the lower low-temperature coolant, and as this boundary gradually moves upward, structures (e.g. intermediate heat exchanger 3
, circulation pump 6, furnace walls, etc.).

[Purpose of the invention]

An object of the present invention is to provide a means for reducing thermal shock of structures within a hot plenum by effectively exerting a mixing action within the hot plenum during reactor scram.

[Summary of the invention]

The present invention provides means for restricting the flow of coolant flowing out from the reactor core outlet with a plurality of vertical flow paths as a means for eliminating the temperature stratification phenomenon in the hot plenum that occurs during reactor scram. A hot plenum 2 is placed in the flow path.
By providing outflow windows at different heights in the circumferential direction, a mixing effect of the coolant flowing into the hot plenum 2 can be effectively generated during startup/shutdown, normal operation, and reactor scram. This is how it was done.

[Embodiments of the invention]

An embodiment of the present invention will be described using FIGS. 2 and 3. The furnace upper mechanism 8 is the same as the conventional one, but a relatively thin inner cylinder 11 and outer cylinder 12 are arranged outside the furnace upper mechanism. The lower end of the outer cylinder 12 is tightly coupled to the rectifier 10. The inner cylinder 11 is connected to the outer surface of the upper furnace mechanism 8 via a spacer, and its lower end is connected to the outer surface of the upper furnace mechanism 8.
It is near the lower end of . The upper ends of the inner cylinder 1 and the outer cylinder 12 are located below and in the vicinity of a dip plate 13 installed to suppress fluctuations in the liquid level. Outer cylinder 12
The upper end between the inner cylinder 11 and the upper furnace end 8 is open, and the upper end between the inner cylinder 11 and the upper furnace end 8 is closed. FIG. 3 shows the detailed structure of the inner cylinder 11 and outer cylinder 12. A plurality of flow paths partitioned in the vertical direction by a plurality of partition plates 14 are formed in the gap between the inner cylinder 11 and the outer cylinder 12.

The lower end of the partition plate 14 is connected to the rectifier 10.

Further, in these plurality of flow paths, flow paths 16 having windows 15 opened in the outer cylinder 12 and flow paths 17 without windows are arranged alternately in the circumferential direction. Moreover, the window 15 is opened at a position close to the lower end of the outer cylinder 12. A gap is also provided between the inner surface of the inner cylinder 11 and the outer surface of the upper furnace mechanism 8, but since the upper end is closed, the coolant in this gap is stagnant.

The flow condition of the coolant in the flow path configured as described above will be explained below.

The coolant flowing out from the core fuel assembly outlet is flowing through the rectifier f? 1
0 and flows into the space below the furnace upper mechanism 8 surrounded by the outer cylinder 12. Most of the coolant that has flowed in is divided into a plurality of flow paths formed by the inner cylinder 11, outer cylinder 12, and partition plate 14, and ascends through the flow paths. Here, most of the coolant that has flowed into the flow path 16 that has a window below the outside @ 12 flows out into the hot plenum 2 through the window, and most of the coolant stagnates above the window. On the other hand, the coolant that has flowed into the windowless channel 17 in the outer cylinder 12 rises to the upper end of the channel 17 and flows out into the hot plenum 2 from the upper end opening. Furthermore, a part of the coolant that has passed through the rectifier 10 and flowed into the lower space of the upper furnace mechanism 8 surrounded by the outer cylinder 12 rises through the annulus flow path between the inner cylinder 11 and the upper furnace mechanism 8 and flows into the interior. It flows out into the hot plenum 2 from the upper end opening of the cylinder 11 .

During a reactor scram, the coolant at a temperature lower than the coolant temperature in the hot plenum 2 flows out from the fuel outlet.
Since the size of the window 15 provided in the outer cylinder 12 is determined, approximately 1/2 of the cold coolant flowing out from the fuel outlet flows out through the upper end opening of the outer cylinder 12, and the remaining 1/2 coolant flows out from the upper end opening of the outer cylinder 12. Window I5
flows out from. Therefore, since the coolant flowing out from the upper end opening of the outer cylinder 12 has a relatively high density, it flows out in the radial direction and then falls in the vertical direction, forming a flow as roughly shown in FIG. 4. Therefore, even during the reactor scram, mixing within the hot plenum 2 is performed efficiently, thereby preventing temperature stratification. Here, the reason why the window 15 is provided at the lower part of the outer cylinder 12 is to promote mixing in the hot plenum 2 even in reactor operating states other than the reactor scram. That is, in the process of starting up the nuclear reactor and bringing it into the rated state, coolant having a temperature higher than the average temperature in the hot plenum 2 flows out from the fuel assembly outlet. Therefore, if the outer cylinder 12 does not have a window, all of the relatively high-temperature coolant flows out from the upper opening of the outer cylinder 12, and the coolant in the lower part of the hot plenum is not mixed and stagnates.

Further, even during rated operation, the coolant flows out from the upper end opening of the outer cylinder 12 and the lower window 15 at approximately the same flow rate, so mixing within the hot plenum 2 is promoted. In the reactor shutdown process, the coolant at a temperature lower than the average temperature of the coolant in the hot plenum 2 flows out from the fuel assembly outlet, contrary to the start-up process. Therefore, similar to the reactor scram, the relatively dense coolant flows to the upper part of the hot plenum 2, resulting in a mixing effect. This has the effect of shortening the time required to shut down the reactor.

Here, there is an annulus space between the inner cylinder 11, the furnace I:, and the section mechanism 8, in which stagnant coolant exists. Therefore, the heat v due to the sudden change in the temperature of the core fuel outlet coolant
The blow is applied to the inner cylinder 11, outer cylinder 12, and partition plate 14,
Thermal shock of the cutting section mechanism 8 is significantly alleviated. That is, by providing the inner cylinder 11, there is an effect of a thermal shock prevention device for the cutting upper mechanism 8.

FIG. 5 shows another embodiment of the invention.

The structure of the inner cylinder 11 and outer cylinder 12 and how to attach them to the cut-off mechanism are shown in Fig. 3, Part II! Same as example i.

The difference from the embodiment shown in FIG. 3 is that the plurality of flow paths formed by the inner cylinder 11, outer cylinder 12, and partition plate 14 are spiral-shaped. The angle θ between the partition plate 14 and the vertical direction is determined so that a sufficient centrifugal force is generated in the coolant flowing through the partitioned flow path. The coolant flowing out into the outside WJ 2 through the rectifying device 10 rises through the gap between the inner cylinder 11 and the outer cylinder 12 while rotating in a spiral shape according to the spiral flow path.

Most of the coolant that has entered the spiral flow path having the window 15 flows out from the window 15 in the tangential direction of the outer cylinder 12 and in the spiral direction due to centrifugal force, and flows into the hollow 1 to the plenum 2.

On the other hand, the coolant entering the spiral channel without the window 15 is
After rising to the upper end opening of the outer cylinder, it flows out in a tangential direction of the outer cylinder 12 and in a spiral direction. Since a dip plate 13 is provided near the liquid level of the coolant in the phon 1 to plenum 2, the flow direction of the flowing coolant is changed to the horizontal direction, and then the coolant in the hot plenum 2 is mixed with the coolant in the hot plenum 2. While mixing it reaches the window 4 of the intermediate heat exchanger 3. According to this embodiment, in addition to the vertical mixing effect caused by the coolant flowing out of the outer cylinder 12 flowing out from different positions in the vertical direction of the outer cylinder j2, there is also a horizontal mixing effect. This has the effect of promoting three-dimensional mixing of the coolant within the hot plenum.

FIG. 6 shows still another embodiment of the present invention. This embodiment differs from FIG. 3 in that fins 19 are attached to the outer surface of the outer cylinder 12, that the positions and sizes of the windows in the outer cylinder 12 are changed for each DC flow path, and that the partitions The point is that the number of boards has been increased. Since the positions of the windows 15 provided in the plurality of vertical channels are different in the vertical direction, the coolant flows out into the hot plenum 2 from a plurality of different positions in the vertical direction. In addition, the size of the window 15 is determined based on the fact that the friction loss in the vertical flow path and the head position of the coolant in the vertical flow path are different for each vertical flow path. The outflow flow rates are determined to be approximately equal. Furthermore, fins 19 are attached to the outer surface of the outer cylinder 12,
In addition, since a large number of partition plates are provided, for example, when coolant at a lower temperature than the coolant in the hot plenum 2 flows out from the fuel outlet like during a reactor scram, the cooling in the hot plenum 2 The heat retained in the material is transferred to the low-temperature coolant in the vertical flow path via the fins 19 and the partition plate 14. Therefore, the temperature of the coolant in the vertical flow path increases and positive buoyancy is generated, so that the flow velocity of the coolant that has risen to the upper end opening of the outer cylinder 12 increases, promoting mixing within the hot plenum. That is, the fins 19 have the effect of increasing the natural circulation force. In this way, in this embodiment, the outer cylinder 1
The position and size of the windows 15 in the hot plenum 2 are different for each flow path, and the effect of the fins 19 further promotes mixing of the coolant in the hot plenum 2. [Effects of the Invention] According to the present invention Since the mixing effect within the hot plenum can be effectively exhibited, the temperature stratification phenomenon particularly during the reactor scram can be prevented, and the thermal shock of equipment and structural materials within the hot plenum can be greatly alleviated.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the mechanical structure of a conventional tank-type fast reactor, FIG. 2 is a sectional view showing an embodiment of the present invention, and FIG. 3 is a perspective view showing details of an embodiment of the present invention. FIG. 4 is a sectional view showing the effects of one embodiment of the invention, FIG. 5 is a perspective view showing details of another embodiment of the invention, and FIG. 6 is a perspective view showing details of still another embodiment of the invention. FIG. 1...Reactor core, 2...Hot plenum 28...Furnace upper mechanism, 10...℃i flow f! Fitting, 11... Inner cylinder, 12
...Outer cylinder, 1481 Figure Hayabusa 2 Mouth 85 Hayabusa Figure 6

Claims (1)

[Claims] 1. In a nuclear reactor that has a plenum that accommodates the reactor core and coolant, and an upper reactor mechanism above the reactor core, a cylindrical structure is arranged around the outer periphery of the two-part mechanism, and the outer peripheral surface of the upper reactor mechanism is and a plurality of partition plates that vertically divide a gap between the inner surfaces of the cylindrical structure into a plurality of parts, an outer peripheral surface of the furnace upper mechanism, the inner surface of the cylindrical structure, and the partition plates. A fast breeder reactor characterized in that a plurality of flow channels are provided, and an opening through which a coolant flows out is provided at a lower side surface of the cylindrical structure in some or all of the plurality of flow channels.