JP7802571B2 - Decay heat removal system heat exchanger structure for fast reactors - Google Patents

Description

The present invention relates to a heat exchanger structure for a decay heat removal system in a fast reactor.

A conventionally known penetration-type direct core cooling system heat exchanger structure in the decay heat removal system of a fast reactor comprises an inner shell, an outer shell, and a gas supply means, and prevents coolant from flowing into the inner shell by supplying inert gas from the gas supply means between the inner shell and the outer shell. The penetration-type direct core cooling system heat exchanger is arranged to penetrate the partition plate inside the main vessel of the fast reactor.

Japanese Patent Application Publication No. 178391/1983

In the above-mentioned Patent Document 1, the space between the inner shell and the partition plate is sealed using a mechanical seal structure, which makes it difficult to ensure a seal between the inner shell and the partition plate, and there is also the problem that thermal deformation of the heat exchanger can cause interference between the heat exchanger and the partition plate, resulting in damage.

The present invention was made in consideration of these points, and its purpose is to provide a through-type direct core cooling system heat exchanger structure that ensures sealing between the heat exchanger and the partition plate and reduces the occurrence of damage caused by thermal deformation of the main vessel and heat exchanger.

To achieve the above-mentioned objective, the through-type direct core cooling system heat exchanger structure of the present invention comprises a cylindrical inner shell that penetrates a partition plate that separates the interior of the main vessel into an upper plenum and a lower plenum, the inner shell having an entrance window that opens in the upper plenum and an exit window that opens in the lower plenum; an outer shell that is disposed in the upper plenum and surrounds a portion of the inner shell; and a cylindrical outer shell that penetrates the partition plate, surrounds the inner shell from the upper plenum to the lower plenum, and has a portion of its upper end extending into the annular space between the inner shell and the outer shell, thereby forming an outer circumferential surface and a front circumferential surface. The system is equipped with a standpipe that forms a first flow path through which coolant flows between the standpipe and the outer shell, and a second flow path that connects the upper plenum and the lower plenum between the inner circumferential surface and the inner shell, and a gas supply mechanism that changes the amount of gas supplied between the inner shell and the outer shell to switch between a blocked state in which the coolant liquid level is below the upper end of the standpipe and above the lower end of the outer shell, thereby blocking communication between the first flow path and the second flow path, and a connected state in which the coolant liquid level exceeds the upper end of the standpipe, thereby connecting the first flow path and the second flow path.

The standpipe may be positioned so that its upper end is below the entrance window.

The outer peripheral surface of the standpipe may be fixed to the partition plate along its entire periphery, and the standpipe may not be in contact with the inner body.

The inner body, the outer body, and the standpipe may all be cylindrical members, and the first flow path and the second flow path may be formed in an annular shape.

The present invention provides a through-type direct core cooling system heat exchanger structure that ensures sealing between the heat exchanger and the partition plate and reduces damage caused by thermal deformation of the main vessel and heat exchanger.

FIG. 1 is a cross-sectional view showing the basic configuration of a fast reactor. 1 is a schematic diagram showing an example of a fast reactor viewed from above. 1 is a cross-sectional view schematically showing the peripheral structure of a penetration-type direct core cooling system heat exchanger structure of a fast reactor. FIG. FIG. 2 is a cross-sectional view schematically showing a state in which a through-type direct core cooling system heat exchanger structure is in use. FIG. 5 is an enlarged view showing a part of FIG. 4 .

(Configuration of fast reactor)
The configuration of a fast reactor according to one embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing the basic configuration of the fast reactor 1. Fig. 2 is a schematic view showing an example of the fast reactor 1 as viewed from above. Fig. 3 is a cross-sectional view showing a schematic view of the peripheral structure of a through-type direct core cooling system heat exchanger structure 70 of the fast reactor 1. Fig. 1 is a cross-sectional view taken along line A-A in Fig. 2, and Fig. 3 is a cross-sectional view taken along line B-B. Arrows in Fig. 1 indicate the flow of sodium, which is a coolant.

The fast reactor 1 is, for example, a tank-type fast reactor that extracts energy by sustaining a controlled nuclear fission chain reaction using, for example, uranium or plutonium as fuel. The fast reactor 1 mainly comprises a main vessel 10, a core 20, a core barrel 30, a core upper structure 40, an intermediate heat exchanger 50, a pump 60, a through-type direct core cooling system heat exchanger structure 70, and a direct core cooling system heat exchanger 90.

The main vessel 10 is, for example, cylindrical with a bottom and a diameter of approximately 15 to 20 meters. The main vessel 10 contains the reactor core 20, core barrel 30, reactor core upper structure 40, intermediate heat exchanger 50, pump 60, through-type direct core cooling system heat exchanger structure 70, direct core cooling system heat exchanger 90, and sodium, which is the primary system coolant.

A roof slab 11, which functions as a lid, is provided on top of the main vessel 10. A partition plate 13 is provided inside the main vessel 10. The partition plate 13 is, for example, a circular member, and is arranged horizontally to separate the interior of the main vessel 10 into an upper plenum and a lower plenum. The upper plenum and lower plenum are connected to each other via the core barrel 30, intermediate heat exchanger 50, pump 60, and other components. As a result, by operating the pump 60, as described below, coolant circulates between the upper and lower plenums.

Specifically, the partition plate 13 may be a member with a thickness of approximately 30 mm to 50 mm, for example. The partition plate 13 may also be formed by joining multiple plate-shaped members together.

The core 20 is a structural component that includes fuel assemblies and control rod assemblies (neither of which are shown). The core vessel 30 is a vessel that houses the core 20 and is located in the center of the fast reactor 1. The core upper structure 40 is a structural component that houses various measuring devices such as a control rod drive mechanism, thermometers, and fuel damage detectors (neither of which are shown), and is located above the core 20, for example.

The intermediate heat exchanger 50 is cylindrical and arranged vertically so as to penetrate the roof slab 11 and the partition plate 13. The intermediate heat exchanger 50 has an inlet window 51 located in the upper plenum and an outlet window 52 located in the lower plenum. The inlet window 51 is an opening through which high-temperature coolant in the upper plenum flows in. The outlet window 52 is an opening through which coolant that has passed through the interior of the intermediate heat exchanger 50 flows out into the lower plenum. The inlet window 51 is located below the liquid level L of the coolant.

The primary system coolant, whose temperature has risen due to heat from the reactor core 20, is cooled by heat exchange with the secondary system coolant (not shown) inside the intermediate heat exchanger 50.

As shown in FIG. 1, a cylindrical pipe member 55 is provided where the intermediate heat exchanger 50 passes through the partition plate 13, and the intermediate heat exchanger 50 extends through the inside of the pipe member 55 from the upper plenum to the lower plenum. As an example, a mechanical seal structure 55a is provided between the pipe member 55 and the intermediate heat exchanger 50 to separate the upper plenum and the lower plenum.

The pump 60 is a mechanism for circulating the coolant and extends vertically, penetrating the roof slab 11 and the partition plate 13. The pump 60 pumps the coolant into the core tank 30 through piping 61 installed in the lower plenum.

The coolant pumped into the core barrel 30 receives heat from the core 20 in the core barrel 30 and is heated to, for example, about 550°C. The coolant then flows upward inside the core barrel 30 and into the upper plenum. The coolant that has flowed into the upper plenum flows into the intermediate heat exchanger 50 through the inlet window 51 of the intermediate heat exchanger 50, where it is cooled to, for example, about 400°C, before flowing downward through the intermediate heat exchanger 50 and out through the outlet window 52.

The coolant that flows out of the outlet window 52 and into the lower plenum is sucked in by the pump 60, and as described above, is pumped back into the core barrel 30 by the action of the pump 60. In this way, the coolant cools the core 20 while circulating within the main vessel 10.

Note that while Figure 2 shows the specific arrangement of the intermediate heat exchanger 50, pump 60, through-type direct core cooling system heat exchanger structure 70, and direct core cooling system heat exchanger 90, the number and arrangement positions of these components may be changed as appropriate depending on the specifications of the fast reactor 1. The direct core cooling system heat exchanger 90 is a conventionally known direct core cooling system heat exchanger, and therefore a detailed description thereof will be omitted.

(Regarding the through-type direct core cooling system heat exchanger structure 70)
The through-type direct core cooling system heat exchanger structure 70 is an auxiliary cooling structure of the thermal dissipation system, and does not operate during normal operation of the fast reactor 1, but operates to cool the core inside the main vessel 10 in the event of, for example, an abnormal transient change or an accident.

As shown in Figure 3, the through-type direct core cooling system heat exchanger structure 70 comprises an inner shell 71, an outer shell 73, a standpipe 75, and a gas supply mechanism 77. Similar to the intermediate heat exchanger 50, the through-type direct core cooling system heat exchanger structure 70 cools the reactor core by exchanging heat between the primary system coolant inside the main vessel 10 and the secondary system coolant outside the main vessel 10.

The inner body 71 is a cylindrical member arranged vertically so as to penetrate the roof slab 11 and the partition plate 13. As an example, the inner body 71 is a cylinder with closed upper and lower ends. The inner body 71 is fixed to the main vessel 10, for example, by being joined to the roof slab 11. The outer peripheral surface of the inner body 71 is formed with an inlet window 71a that opens into the upper plenum and an outlet window 71b that opens into the lower plenum. A flow path (not shown) through which the secondary system coolant flows is formed inside the inner body 71, and the primary system coolant that flows into the inner body 71 is cooled by heat exchange with the secondary system coolant.

The outer body 73 is a member that forms a space between the inner body 71 and the outer body 73 to which gas is supplied from the gas supply mechanism 77. The outer body 73 is disposed in the upper plenum and has a cylindrical shape that surrounds a portion of the inner body 71. As an example, the outer body 73 is a cylindrical member with a diameter larger than that of the inner body 71, and is connected to the roof slab 11. The outer body 73 is disposed, for example, coaxially with the inner body 71. The outer body 73 extends vertically so that its lower end is located below the entrance window 71a of the inner body 71.

The standpipe 75 has a cylindrical shape and surrounds a portion of the inner body 71. The standpipe 75 is a cylindrical member having a diameter, for example, larger than that of the inner body 71 and smaller than that of the outer body 73. As an example, the standpipe 75 is arranged coaxially with the inner body 71 and the outer body 73. Specifically, the standpipe 75 is arranged to penetrate the partition plate 13 and surrounds a portion of the inner body 71 from the upper plenum to the lower plenum of the main vessel 10.

As an example, the standpipe 75 is arranged so that it does not come into contact with the inner body 71. The diameter of the standpipe 75 is determined appropriately, taking into consideration, for example, the amount of deformation of the inner body 71 due to thermal stress and the ease of removal of the through-type direct core cooling system heat exchanger from the main vessel 10.

It is preferable that the standpipe 75 is configured so that it does not come into contact with the inner body 71, but the standpipe 75 and the inner body 71 may be partially connected while maintaining a gap between them.

As an example, the standpipe 75 is connected to the partition plate 13. Specifically, the standpipe 75 has its outer peripheral surface fixed to the partition plate 13 along its entire circumference. More specifically, the outer peripheral surface of the standpipe 75 is fixed to the partition plate 13 in such a manner that no gaps are formed between the standpipe 75 and the partition plate 13 through which coolant can pass. The outer peripheral surface of the standpipe 75 and the partition plate 13 may be fixed by welding, for example.

By fixing the entire outer periphery of the standpipe 75 to the partition plate 13, coolant is prevented from flowing from the upper plenum to the lower plenum between the standpipe 75 and the partition plate 13. This means that the occurrence of a bypass flow in which coolant flows from the upper plenum to the lower plenum other than through the intermediate heat exchanger 50 is suppressed, and this configuration makes it possible to prevent a reduction in cooling efficiency due to a bypass flow.

As shown in Figure 3, the standpipe 75 is positioned so that a portion of its upper end extends into the annular space between the inner body 71 and the outer body 73. In other words, the standpipe 75 is positioned between the inner body 71 and the outer body 73 so that its upper end is inserted between the inner body 71 and the outer body 73.

A first flow path Pa through which the coolant flows is formed between the outer peripheral surface of the standpipe 75 and the outer body 73. The first flow path Pa may, for example, be an annular flow path with a constant width in the circumferential direction. A second flow path Pb that connects the upper plenum and the lower plenum is formed between the inner peripheral surface of the standpipe 75 and the inner body 71. The second flow path Pb may, for example, be an annular flow path with a constant width in the circumferential direction, similar to the first flow path Pa.

The standpipe 75 is positioned so that its upper end is below the entrance window 71a of the inner body 71. Specifically, the upper end of the standpipe 75 is preferably located below the top of the entrance window 71a, and more preferably at the same height as or below the bottom of the entrance window 71a. The reason why such a configuration is preferable will be explained later in conjunction with the explanation of the operation of the through-type direct core cooling system heat exchanger structure 70.

(Regarding the gas supply mechanism 77)
3, the gas supply mechanism 77 includes a gas supply source 78, a gas flow path 79, a first valve 80a, a second valve 80b, a first gas supply member 81a, a second gas supply member 81b, and a control device 82. The first valve 80a and the second valve 80b may be manually operated by an operator to switch between open and closed states, but the following example illustrates a configuration in which the opening and closing are controlled by the control device 82.

The gas supply source 78 pumps inert gas into the main vessel 10 at a predetermined pressure. The gas flow path 79 has a first flow path 79a extending from the gas supply source 78, a second flow path 79b branching off from the first flow path 79a, and a third flow path 79c branching off from the first flow path 79a. A first valve 80a is provided in the first flow path 79a. The second flow path 79b is a flow path connected to the first gas supply member 81a. The third flow path 79c is a flow path connected to the second gas supply member 81b, and a second valve 80b is provided in the third flow path 79c.

As an example, the first valve 80a and the second valve 80b are valves having a drive unit (not shown) that switches the open/closed state of the valve based on a control signal from the control device 82. Specifically, the first valve 80a and the second valve 80b may be valves in which the flow rate of gas passing through the valve is changed by changing the valve opening.

The control device 82 controls the operation of the first valve 80a, the second valve 80b, and the gas supply source 78. The control device 82 is configured to receive a signal indicating an abnormality in the fast reactor 1 from a detection device (not shown) that detects an abnormality in the fast reactor 1. The control device 82 sends a control signal to each of the first valve 80a and the second valve 80b to open or close the valve. The control device 82 also sends a control signal to the gas supply source 78 to start or stop the supply of inert gas. The control signal may include a command value for the gas flow rate.

For example, when the control device 82 is not receiving a signal indicating an abnormality in the fast reactor 1, it opens the first valve 80a to open the gas flow path 79. Meanwhile, the second valve 80b is closed. The control device 82 also operates the gas supply source 78 to supply inert gas from the gas supply source 78 into the main vessel 10. As a result, between the inner body 71 and the outer body 73, the inert gas supplied via the first gas supply member 81a pushes the coolant liquid level L1 below the inlet window 71a of the inner body 71. Outside the outer body 73, the coolant liquid level L is located above the inlet window 51 of the intermediate heat exchanger 50.

When the control device 82 receives a signal indicating an abnormality in the fast reactor 1, it, for example, closes the first valve 80a and stops the supply of inert gas from the gas supply source 78. This stops the supply of inert gas between the inner body 71 and the outer body 73. Furthermore, by opening the second valve 80b, the coolant liquid level L1 between the inner body 71 and the outer body 73 gradually rises to a height above the inlet window 71a of the inner body 71.

(Operation of the through-type direct core cooling system heat exchanger structure 70)
The operation of the penetration-type direct core cooling system heat exchanger structure 70 configured as described above will be described below. Figure 4 is a cross-sectional view showing the penetration-type direct core cooling system heat exchanger structure 70 in use. Like Figure 3, Figure 4 is a cross-sectional view taken along line B-B in Figure 2. Figure 5 is an enlarged view showing a portion of Figure 4.

During normal operation of the fast reactor 1, the through-type direct core cooling system heat exchanger structure 70 does not operate. The control device 82 sends control signals to the first valve 80a and the gas supply source 78, opening the first valve 80a to open the gas flow path 79 and causing the gas supply source 78 to begin supplying inert gas. The second valve 80b is closed. The gas supply source 78 supplies inert gas between the inner body 71 and the outer body 73 so that the coolant liquid level L1 in the space between the inner body 71 and the outer body 73 is located below the upper end of the standpipe 75 and above the lower end of the outer body 73, as shown in Figure 3.

This state is a blocked state in which communication between the first flow path Pa and the second flow path Pb is blocked by gas supplied from the gas supply mechanism 77. Specifically, the gas supplied between the inner body 71 and the outer body 73 pushes the liquid level L1 below the upper end of the standpipe 75, thereby blocking communication between the first flow path Pa and the second flow path Pb. Because communication between the first flow path Pa and the second flow path Pb is blocked, the coolant in the upper plenum does not flow into the lower plenum as a bypass flow.

On the other hand, the standpipe 75 is fixed to the partition plate 13, for example by welding, so that coolant from the upper plenum does not flow into the lower plenum as a bypass flow through the gap between the standpipe 75 and the partition plate 13.

When the through-type direct core cooling system heat exchanger structure 70 is operated, the amount of gas supplied from the gas supply mechanism 77 is reduced or the supply of gas from the gas supply mechanism 77 is stopped. In this embodiment, as an example, when the control device 82 receives a signal indicating an abnormality in the fast reactor 1 from a detection device (not shown), the control device 82 closes the first valve 80a and stops the supply of inert gas from the gas supply source 78. This stops the supply of inert gas between the inner body 71 and the outer body 73. Furthermore, by opening the second valve 80b, the height of the coolant liquid level L1 rises to a position above the upper end of the standpipe 75, as shown in FIG. 4. Specifically, for example, the height of the coolant liquid level L1 rises above the inlet window 71a.

In this state, the first flow path Pa and the second flow path Pb are connected, and as shown by the arrows in Figure 5, the coolant from the upper blenum flows through the first flow path Pa into the space between the inner body 71 and the outer body 73, and then flows into the inner body 71 through the inlet window 71a, where it is cooled by the through-type direct core cooling system heat exchanger structure 70.

(Action and effect)
As described above, in the through-type direct core cooling system heat exchanger structure 70 of this embodiment, the standpipe 75 is disposed between the inner body 71 and the outer body 73, the first flow path Pa is formed between the inner body 71 and the standpipe 75, and the second flow path Pb is formed between the standpipe 75 and the outer body 73. The gas supply mechanism 77 changes the amount of gas supplied between the inner body 71 and the outer body 73 to change the height of the coolant liquid surface L1 in the space between the inner body 71 and the outer body 73, and switches the first flow path Pa and the second flow path Pb between a connected state and a disconnected state.

In conventional configurations without a standpipe 75, in order to prevent bypass flow from flowing from the upper plenum to the lower plenum around the inner body 71, it was necessary to provide a mechanical seal structure, for example, between the outer periphery of the inner body 71 and the inner periphery of a tubular member fixed to the partition plate 13.

However, in a fast reactor 1, the through-type direct core cooling system heat exchanger structure 70 is subject to thermal deformation, and therefore the mechanical seal structure must be able to absorb the thermal deformation of the through-type direct core cooling system heat exchanger structure 70. If the thermal deformation cannot be absorbed, there is a possibility that the through-type direct core cooling system heat exchanger structure 70 or the partition plate 13 may be damaged. Furthermore, since it is anticipated that the through-type direct core cooling system heat exchanger structure 70 will be removed from the roof slab 11 for maintenance, the mechanical seal structure must be able to accommodate the removal of the through-type direct core cooling system heat exchanger structure 70. For these reasons, mechanical seal structures have problems such as a complex structure and difficulty in ensuring sufficient sealing due to thermal deformation of the through-type direct core cooling system heat exchanger structure 70.

In contrast, with the configuration of this embodiment, no mechanical seal is provided between the standpipe 75 and the inner body 71, and the inert gas supplied between the inner body 71 and the outer body 73 presses down the liquid level L1, blocking communication between the first flow path Pa and the second flow path Pb, i.e., the communication between the upper plenum and the lower plenum. This effectively prevents coolant from flowing from the upper plenum into the lower plenum.

Furthermore, if the upper end of the standpipe 75 is positioned below the inlet window 71a of the inner body 71, as shown in Figure 5, there is an advantage in that coolant can easily flow from the second flow path Pb toward the inlet window 71a when the through-type direct core cooling system heat exchanger structure 70 is in operation.

Furthermore, since the standpipe 75 is not in contact with the inner body 71, even if the inner body 71 is thermally deformed to the extent that it does not come into contact with the standpipe 75, no force is applied from the inner body 71 to the standpipe 75. This prevents damage to the through-type direct core cooling system heat exchanger structure 70 or the partition plate 13.

Furthermore, if the inner shell 71, outer shell 73, and standpipe 75 are all cylindrical members and the first flow path Pa and second flow path Pb are formed in an annular shape, the flow of coolant becomes uniform in the circumferential direction of the through-type direct core cooling system heat exchanger structure 70, allowing the coolant to flow smoothly.

It should be noted that it is not necessary for all of the through-type direct core cooling system heat exchanger structures 70 in the fast reactor 1 to have the configuration described above; it is sufficient that at least one through-type direct core cooling system heat exchanger structure 70 has the configuration described above. While the above describes the through-type direct core cooling system heat exchanger structure 70, the through-type direct core cooling system heat exchanger structure of the present invention may also be applied to other types of heat exchangers.

The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and alterations are possible within the spirit of the invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of new embodiments resulting from the combination will also have the effects of the original embodiments.

1 Fast reactor 10 Main vessel 11 Roof slab 13 Partition plate 20 Core 30 Core barrel 40 Core upper structure 50 Intermediate heat exchanger 51 Inlet window 52 Outlet window 55 Pipe member 55a Seal structure 60 Pump 61 Piping 70 Penetrating type direct core cooling system heat exchanger structure 71 Inner body 71a Inlet window 71b Outlet window 73 Outer body 75 Standpipe 77 Gas supply mechanism 78 Gas supply source 79 Gas flow path 79a First flow path 79b Second flow path 79c Third flow path 80a First valve 80b Second valve 81a First gas supply member 81b Second gas supply member 82 Control device 90 Direct core cooling system heat exchanger L Liquid level L1 Liquid level Pa First flow path Pb Second flow path

Claims (3)

a cylindrical inner shell that penetrates a partition plate that divides the interior of the main vessel into an upper plenum and a lower plenum, the inner shell having an inlet window that opens into the upper plenum and an outlet window that opens into the lower plenum;
an outer shell disposed in the upper plenum and surrounding a portion of the inner shell;
a standpipe formed in a cylindrical shape, penetrating the partition plate and surrounding the inner shell from the upper plenum to the lower plenum, with a portion of its upper end extending to the annular space between the inner shell and the outer shell, thereby forming a first flow path through which coolant flows between the outer shell's outer peripheral surface and the standpipe, and a second flow path between the inner shell's inner peripheral surface and the inner shell, which connects the upper plenum and the lower plenum;
a gas supply mechanism that switches between a blocking state in which the liquid level of the coolant is located below the upper end of the standpipe and above the lower end of the outer shell, thereby blocking communication between the first flow path and the second flow path, and a communicating state in which the liquid level of the coolant exceeds the upper end of the standpipe, thereby connecting the first flow path and the second flow path, by changing the amount of gas supplied between the inner shell and the outer shell;
Equipped with
the outer circumferential surface of the stand pipe is fixed to the partition plate along the entire periphery, and the stand pipe is not in contact with the inner shell;
Penetrating type direct core cooling system heat exchanger structure. The standpipe is arranged so that the upper end of the standpipe is lower than the entrance window.
The through-type direct core cooling system heat exchanger structure according to claim 1 . the inner shell, the outer shell, and the standpipe are all cylindrical members, and the first flow path and the second flow path are formed in an annular shape.
3. The through-type direct core cooling system heat exchanger structure according to claim 1 or 2 .