JPS6015598A - Heat exchanger for direct core cooling system - 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 (Technical Field of the Invention) The present invention is for use in a direct core cooling system for a fast breeder reactor, which has a function of removing decay heat from the core through natural circulation within the reactor vessel after reactor shutdown. Regarding heat exchangers.

[Technical Background of the Invention] In general, in a loop-type fast breeder reactor with a liquid metal cooling system, decay heat from the core is removed after the reactor is shut down by operating the Ponymotor of the main circulation pump in the main-primary cooling system. This is done by forcing the circulation of However, in the event of a total power loss or multiple leaks in the main and secondary cooling piping systems, the operation of the Boni motor in the main and secondary cooling systems may become impossible, and the cold air 1j in the reactor vessel may become inoperable. It is possible that the liquid level of the reactor drops below the outlet nozzle position of the reactor vessel and entrains the cover gas into the main cooling system loop, causing the loop circulation heat removal function to be lost. Even in such cases, in order to maintain the integrity of the core fuel elements and remove decay heat, we have proposed a direct core cooling system in which a heat exchanger is loaded directly into the secondary coolant inside the reactor vessel. has been done.

This direct core cooling system heat exchanger has the function of using this device to remove heat from the high-temperature coolant that has flowed from the reactor to the upper plenum C after the reactor is shut down, and uses the natural circulation force within the reactor vessel as the driving force. We are using.

[Problems in the background art] By the way, the recently proposed direct core cooling system heat exchanger has a heat exchanger that is located below the normal operating liquid level (NSL) in the reactor vessel and slightly below the lower end of the reactor vessel outlet nozzle. The lower two levels are equipped with inlet openings for guiding the high-temperature coolant inside the reactor vessel, allowing for low-temperature cooling after heat exchange near the top of the Nida core components or in the mid-plenum region on the sides of the core. It is constructed with an exit opening for the material to flow out.

As mentioned above, the reason why the inlet openings were installed at two levels is to provide a decay heat removal function in the case of heat removal from the main secondary cooling system onward, such as in the case of a total power loss accident, and to This is based on two types of hypothetical accidents in which heat removal is lost in the main-subcooling system due to multiple leakage accidents, etc. In other words, inside the furnace vessel
In the former case, the liquid level of the coolant is the liquid level during normal operation (N
s L), and in the latter case, in order to prevent the liquid level from dropping due to piping leakage or reaching the lower end of the furnace vessel outlet nozzle, each pipe is provided to ensure a natural circulation flow path within the furnace vessel. It is being

However, in a direct core cooling heat exchanger that has openings at the two levels mentioned above, especially when the reactor vessel liquid level drops and flows below the lower end of the reactor vessel outlet nozzle, as in the case of multiple pipe leaks, this heat Since the liquid level in the inner tube #i of the secondary heat transfer tube in the exchanger also falls to the same level as the furnace vessel liquid level, there is a drawback that the heat transfer area decreases in proportion to this.

In addition, in this direct core cooling system heat exchanger that utilizes the natural circulation force of the reactor vessel, the water head difference between the center of the core, which is the heat generation center, and the heat transfer center in the heat exchanger, which is the heat removal center, is
Since it decreases as the liquid level decreases, there is a drawback that the natural circulation heat removal capacity decreases significantly at that rate.

[Object of the Invention] The object of the present invention was to eliminate the above-mentioned drawbacks, and the decay heat removal function in the reactor vessel after the reactor is shut down can be sufficiently impaired by the natural circulation force within the reactor, and in particular, Even for a hypothetical event in which the liquid level of the cold 11 material in the reactor vessel falls below the lower end of the main and secondary cooling system outlet nozzle, the liquid level in the reactor vessel is the same as when it is at the liquid level during normal operation. The purpose of the present invention is to provide a direct 1x core cooling system heat exchanger that has a heat removal function of approximately 100%.

[Summary of the Invention] The direct core cooling system heat exchanger according to the present invention provides a direct core cooling system heat exchanger that penetrates a shielding plug that closes an upper opening of the reactor vessel into the high-temperature upper plenum coolant in the reactor vessel housing the reactor core. An inlet window through which high-temperature primary coolant flows is located slightly below the vicinity of the lower end of the outlet pipe of the furnace vessel, and the coolant flowing through the inlet window flows through the annulus between the outer pipe and the inner pipe. The liquid is guided to an upper header located at a height near the normal liquid level of the reactor vessel, and then descended from the upper header through the inner tube containing the secondary cooling system heat transfer tube group. It is characterized by a flow path configured to remove heat from the primary coolant and allow the low-temperature coolant to flow out from an exit window provided at the bottom of the chamber.

In the heat exchanger according to the present invention, even if the liquid level in the furnace vessel were to cut the lower end of the outlet pipe, the heat exchanger would always be filled with the primary coolant due to the Xybon effect, and the secondary heat exchanger tube would The heat removal area by group is the same as in the case of normal liquid level, and the natural circulation flow rate in the furnace vessel is much more ensured than in the conventional example, so the in-furnace decay heat heat removal function is It will be possible to sufficiently cause illness while ensuring the integrity of the reactor fuel.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 1 indicates a reactor vessel of a loop type fast breeder reactor.
An inlet pipe 2 of the J material is connected to the side surface slightly above the center, and an outlet pipe 3 of the primary coolant is connected to the side surface slightly above the center. Further, the upper end opening of the furnace vessel 1 is closed with a shielding plug 4 . A reactor core 5 in which a large number of fuel assemblies are arranged in an array is provided slightly below the center of the reactor vessel 1, and a blanket 6 is provided to enclose the outer periphery of the reactor core 5. A low pressure plenum 7 and a high pressure plenum 8 are provided below the core 5 and the blanket 6 and are supported by the lower surface of the core lower support plate 9. The core lower support plate 9 is connected to the inner surface of the reactor vessel 1 and mainly supports the reactor core 5 and blanket 6. A heat shield 10 is provided between the upper side surface of the blanket 6 and the inner surface of the furnace vessel 1. Above the core 5, a core upper machine 4i411 passing through the shielding plug 4 is disposed. An inner cylinder 12 is installed upright on the heat shield 10 , and an inner cylinder upper flap 1 is provided on the side surface of the inner cylinder 12 slightly below the liquid level 13 of the primary cooled lJI material housed in the furnace vessel 1 . ''-hole 14A is provided, and an inner cylinder lower flow hole 14A is provided on the surface where the heat shield 10 is located, that is, near the top of the core component. B is set up.

Roughly between the inner surface of the furnace vessel 1 and the interior 12, a heat exchanger 15 having a length that penetrates the shield plug 4 and extends to the heat shield 1o is provided.

The heat exchanger 15 is connected to the inlet window 1 as shown in an enlarged view in FIG.
6 on the lower side surface and an outlet window 24 on the bottom surface; It consists of an inlet pipe 21A and an outlet pipe 21B for the secondary coolant, and a group of secondary cooling system heat transfer tubes wound around the inlet pipe 21A and the outlet pipe 21B. An upper header 18 formed by a partition wall 25 is located above the outer tube 19.
and a lower header 23 formed by a support 26 that supports the lower end of the inner tube 20 on the inner wall of the outer tube 19.

Here, the upper header 18 is located slightly below the normal liquid level NsL of the primary coolant in the furnace vessel 1, and the inlet window 16 is located slightly below the liquid level 13 of the coolant in the outlet pipe connected to the furnace vessel 1. It is provided at a position directly opposite to the position of the upper flow hole 14A of the inner cylinder.

The flow of the primary coolant inside the heat exchanger 15 is such that the high-temperature primary coolant flows in through the inlet window 16, rises along the outer surface of the inner cylinder 20 as shown by the arrow, and enters the inner cylinder from the upper end of the inner cylinder 20. Cylinder 20
It follows a path that descends along the inner surface of the window and flows out from the exit window 24. As it descends through the inner cylinder 20, it exchanges heat with the secondary coolant and flows as shown by the arrow, resulting in natural circulation.

However, in the heat exchanger with the above configuration, when the main and secondary cooling iJI system piping is multiplexed, or when piping breakage is combined with other various failures, the liquid level 13 in the furnace vessel will be lower than the lower end of the outlet piping 3. The decay heat removal function of the main cooling system is lost. Therefore, the counterflow m in the reactor vessel becomes zero flow rate when the liquid level cuts the outlet pipe 3, but after a while, the area of the core 5 with a high calorific value cools down! Natural circulation within the reactor occurs due to the significant temperature difference between the I, fl and the coolant in the low-injection region 1 of the blanket 6 around the reactor core. The flow of coolant in this natural circulation within the furnace is shown in the direction of the arrow in FIG.

That is, the high-temperature coolant flowing out from the outlet of the core 5 rises to the liquid level 13, expands in the system direction, passes through the inner cylinder upper flow hole 14A, and passes through the inlet window 16 of the heat exchanger 15. and then into the outer tube 19 as shown in FIG.
and the inner tube 20 to reach the upper header 18, descend from the upper header 18 inside the inner tube 20 having the secondary heat transfer tube group 22, and pass through the lower header 23. and flows out through the outlet window 24 at the bottom of the heat exchanger.

At this time, the coolant flowing out from the outlet window 24 is transferred to the heat exchanger tube group 22.
Because the temperature is lowered to a sufficiently low temperature by heat removal from
B, flows back from the top to the bottom of the low heat generation area 6 around the core, via the low pressure plenum 7 and the high pressure plenum 8,
A circulation flow path is formed that flows into the reactor core 5 again.

[Effects of the Invention] In the present invention, since the artificial window 16 of the direct core cooling system heat exchanger 15 is located at the lower part near the lower end of the outlet pipe 3, the inside of the heat exchanger 15 is always filled with primary coolant by the siphon. Therefore, the heat removal area of the secondary heat exchanger tube group 22 is the same as that at the normal liquid level (NSL). Furthermore, the height difference between the core heat generation center position and the heat exchanger heat transfer center position, which is the natural circulation driving force due to the above-mentioned flow path formation, is usually about 1 (N
Since this is the same as in the case of s L), a natural circulation heat removal flow rate sufficient to ensure the integrity of the core fuel elements can always be stably obtained.

10,000, the normal liquid level (Ns L) Heat exchanger 1 using high-temperature cooling of the upper furnace plenum near the surface
Due to the heat transfer of -C through the outer tube 19 of 5, the temperature is increased by ``-minR'', so 1! Compared to the proposed heat exchanger 414j with a frontage window at the top, the heat removal function does not deteriorate significantly.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining one embodiment of the present invention. FIG. 1 is a vertical cross-sectional view showing the reactor structure of a loop fast breeder reactor, and FIG. FIG. 2 is a longitudinal sectional view showing a heat exchanger for a core cooling system. 1... Reactor vessel 2... Inlet piping 3... Outlet piping 4... Shielding plug 5... Reactor core 6... Planks 1 to 7... Low pressure plenum 8... High pressure plenum 9 ... Core lower support plate 10 ... Heat shield 11 ... Core upper mechanism 12 ...
・Inner cylinder 13...Furnace vessel liquid level 14A...Inner cylinder upper flow ball 14-B...Inner cylinder lower flow hole 15...Direct core cooling system heat exchanger 16...Inlet window 17.・Annuals Club 18...
Upper header 19...Outer tube 20...Inner tube 21A...Secondary cooling inlet pipe 21 [3...Secondary coolant outlet pipe 22...Secondary cooling system heat transfer tube group 23... ...Lower header 24...Exit L1 window 25...Partition wall 26...Support application agent Patent attorney Kikuchi Gobu

Claims (1)

[Claims] A secondary cooling pipe is installed in the outer pipe of the loop-type high-speed Jj'i breeder reactor, which penetrates the shielding plug into the reactor vessel and extends to the vicinity of the top of the core components, and is provided between the reactor vessel and the inner part. It has an inner tube containing a group of heat transfer tubes, and the annulus formed by the outer tube and the inner tube is lowered inside the upper inner tube to cool the second layer. In the direct core cooling system heat exchanger J3 that exchanges heat with II 4A, an inlet window through which primary coolant flows into the outer tube is provided slightly to one side from the lower end of the outlet pipe connected to the reactor vessel, This direct reactor core is characterized by having an exit L1 window for outflowing the next cooling FJ tank at the bottom of the outer tube, and an upper header on the outer side located at the height of the normal liquid level in the reactor vessel. Heat exchanger for cooling system.