CN102820067B - Natural circulation heat exchanger for discharging waste heat of supercritical water reactor - Google Patents

Abstract

The invention belongs to the technical field of safety of nuclear power plants, and in particular relates to a natural circulation heat exchanger used for exhausting waste heat of a supercritical water reactor. The supercritical water flows in the hot fluid supercritical water annular channel to form a primary side cycle, and the hot fluid supercritical water annular channel is a narrow-gap annular pipe; the cold fluid water flows in the cold fluid water descending channel, the lower chamber, and the cold fluid water rises The flow in the channel and the top chamber constitutes the secondary side circulation. In the case of normal shutdown or emergency shutdown of supercritical water reactors, supercritical narrow-slit natural circulation heat exchangers are used to discharge waste heat without any external force, which can effectively reduce damage caused by active component failures and human error System failure probability, improve the operational safety of the reactor.

Description

A Natural Circulation Heat Exchanger for Supercritical Water Reactor Waste Heat Discharge

technical field

The invention belongs to the technical field of safety of nuclear power plants, and in particular relates to a natural circulation heat exchanger used for exhausting waste heat of a supercritical water reactor.

Background technique

The SCWR is the only water-cooled reactor among the six Generation IV future reactor types. It adopts a once-through cycle design, and supercritical water is selected as the core coolant without phase change. Reactor core outlet parameters: 25MPa, 500°C, thermal efficiency can reach 45%. The thermal power of a single unit can reach more than 1700MW.

For a supercritical water reactor with a once-through circulation design, the core coolant circuit is directly connected to the steam turbine, feed water heater and other conventional circulation circuits, and there will be more potential risks in operation, and safety must be adhered to and ensured the rules. One of the main issues to ensure the safety of supercritical water reactors is to ensure the conduction of nuclear fuel heat release under any circumstances. Under normal operating conditions, the heat generated by supercritical water reactor nuclear fission and fission product decay is directly taken away by the main coolant through a once-through cycle; when the reactor is shut down, although the nuclear power through the fission mechanism quickly disappears , but the fission fragments produced by fission and the heat released by their decay products in the radioactive decay process still exist, which also need to be exported in time. Except for the loss of water accident, under the emergency shutdown conditions caused by all benchmark accidents, the waste heat removal system can be used to remove the waste heat from the core.

Passive technologies are gradually being introduced into commercially operating nuclear reactor waste heat removal systems. Taking the third-generation AP1000 nuclear power technology as an example, the use of passive natural circulation to discharge waste heat does not require operator actions to mitigate accidents, reducing the possibility of escalation due to human error after an accident occurs. Passive natural circulation is driven by natural force, which improves the reliability of system operation, without the need for active equipment such as circulation pumps and diesel engines, and reduces system failures caused by power failures or mechanical failures. At this stage, no supercritical water reactor demonstration power plant has been built in the world. Research on supercritical water reactors at home and abroad is still in the conceptual design stage, and most of them focus on the internal structure design of the core, the analysis of neutron physical characteristics and thermal characteristics analysis and other fields. However, no relevant research has been conducted on the waste heat removal heat exchange system of supercritical water reactors, including the design of waste heat removal heat exchangers. Supercritical water reactors are similar to Japan's Fukushima nuclear power plant using a direct current cycle. Once an accident occurs and radioactive leakage enters the coolant cycle, it will be brought into steam turbines, feed water heaters and other equipment. At this time, if the original primary circulation loop is used to export the core heat, the radioactive material will diffuse to the outside of the nuclear reactor containment, endangering the safety of the surrounding environment. In addition, the supercritical water reactor coolant flow rate is large, and the temperature rise of the inlet and outlet is large. It can be seen that the key safety issues such as effectively isolating radioactive substances and timely deriving core waste heat are all major problems in the design of supercritical water reactor waste heat removal system.

Contents of the invention

The purpose of the present invention is to avoid the leakage of radioactive substances inside the supercritical water reactor core under accident conditions and ensure that the core waste heat is exported at the first time after the accident, thereby providing a natural circulation for supercritical water reactor waste heat discharge the heat exchanger.

The technical scheme adopted in the present invention is:

The main structure of the heat exchanger is composed of top end cover, shell and lower head from top to bottom;

The upper partition and the lower partition arranged in parallel are arranged on the upper part of the shell; the top chamber is formed between the upper partition and the top end cover; the upper chamber is formed between the upper partition, the lower partition and the shell; the lower partition Below the plate, there are a number of evenly arranged cylinders connected to the upper chamber. The cold fluid water descending channel is formed between the outer wall of the cylinder, the shell and the lower partition, and the lower wall of the cylinder and the lower head. The lower chamber; an inner cylinder that runs through the cylinder and the upper chamber and communicates with the top chamber and the lower chamber is arranged in each cylinder, and a hot fluid supercritical water annular channel is formed between the cylinder and the inner cylinder;

On the top end cover, a cold fluid water outlet communicating with the top chamber is provided; a hot fluid supercritical water inlet communicating with the upper chamber is provided on the shell, and a cold fluid water drop is provided under the lower partition of the shell A cold fluid water inlet connected by channels; on each cylinder, a hot fluid supercritical water outlet connecting the outside world and the inside of the cylinder is arranged.

The cylinders are cylinders or square cylinders, the number is 4-12; the shape of the inner cylinder is the same as that of the cylinder.

The hot fluid supercritical water inlet leads into supercritical water, flows in the hot fluid supercritical water annular channel, and flows out from the hot fluid supercritical water outlet, forming a primary side cycle; the cold fluid water inlet leads into cold flowing water, The fluid water flows in the descending channel, the lower chamber, the cold fluid water ascending channel formed by the inner cylinder, and the top chamber, and flows out from the cold fluid water outlet, forming a secondary side circulation.

Both the primary side circulation and the secondary side circulation are natural circulation, and helium gas is introduced into the circulation loop to enhance the driving of natural circulation.

The gap between the cylinder and the inner cylinder is 10-20mm.

Flange connections are used between the top end cover and the shell, and between the shell and the lower head.

The beneficial effects of the present invention are:

The heat exchanger is a device that uses the density difference of the fluid itself to realize natural circulation heat transfer on both sides. Both primary side circulation and secondary side circulation adopt straight pipe flow, which reduces resistance and enhances natural circulation capacity. And in order to enhance the heat exchange effect between the primary side circulation and the secondary side circulation, a comprehensive heat exchange method of first forward flow and then counter flow is adopted.

The heat exchanger is arranged inside the containment, and when a leak occurs on the supercritical pressure side, the radioactive material is confined in the containment, which is safe and reliable.

Description of drawings

Fig. 1 is a side sectional view of the heat exchanger of the present invention.

Fig. 2 is an A-A cross-sectional top view when the cross-section of the heat exchanger and the inner and outer cylinders are both circular.

Fig. 3 is a top view of section A-A when the cross section of the heat exchanger and the inner and outer cylinders are both square.

Labels in the figure:

1-top end cover, 2-upper partition, 3-hot fluid supercritical water inlet, 4-cold fluid water inlet, 5-housing, 6-cold fluid water ascending channel, 7-flange, 8-bottom seal Head, 9-lower chamber, 10-hot fluid supercritical water outlet, 11-cold fluid water descending channel, 12-hot fluid supercritical water annular channel, 13-lower partition, 14-upper chamber, 15-cold Fluid water outlet, 16-top chamber, 17-cylindrical body, 18-inner cylindrical body.

Detailed ways

The present invention provides a natural circulation heat exchanger used for supercritical water reactor waste heat discharge, and the present invention will be further described with reference to the accompanying drawings and specific implementation below.

The natural circulation heat exchanger of the supercritical water reactor is mainly used to discharge the waste heat of the supercritical water reactor under accident conditions other than breach accidents. After the accident, the main steam valve in front of the steam turbine inlet is closed, and the nuclear power plant will automatically switch to the operation of the natural circulation waste heat discharge system. At this time, the waste heat discharge heat exchanger is put into operation.

The structure of the heat exchanger according to the present invention is shown in Figure 1. Its main structure is composed of a top end cover 1, a shell 5 and a lower head 8 from top to bottom, and the three are connected by flanges, such as connecting shells. Body 5 and flange 7 of lower head 8.

The upper partition 2 and the lower partition 13 arranged in parallel are arranged on the upper part of the housing 5; the top chamber 16 is formed between the upper partition 2 and the top end cover 1; the upper partition 2, the lower partition 13 and the housing 5 The upper chamber 14 is formed between them; a plurality of cylinders 17 evenly arranged and communicated with the upper chamber 14 are arranged under the lower partition 2, and the outer wall of the cylinder 17 forms a cold fluid between the shell 5 and the lower partition 13. The water descending passage 11, the lower chamber 9 is formed between the lower wall of the cylinder body 17 and the lower head 8; in each cylinder body 17, there is provided a penetrating cylinder body 17 and the upper chamber 14, communicating with the top chamber 16 and the lower chamber. The inner cylindrical body 18 of the chamber 9, and the annular passage 12 of hot fluid supercritical water is formed between the cylindrical body 17 and the inner cylindrical body 18 . The cylinder body 17 is a cylinder or a square cylinder, the number is 4, and the shape of the inner cylinder body 18 is the same as that of the cylinder body; the gap between the cylinder body 17 and the inner cylinder body 18 is 10-20mm, and 15mm is taken in this embodiment .

On the top end cover 1, the cold fluid water outlet 15 communicating with the top chamber 16 is set; The cold fluid water inlet 4 communicated with the cold fluid water descending channel 11 is arranged below the 13; on each cylinder 17, a hot fluid supercritical water outlet 10 communicating with the outside world and the inside of the cylinder 17 is arranged.

The flow mode in the heat exchanger is that the supercritical water coming out of the core enters from the thermal fluid supercritical water inlet 3, and fills the upper chamber 14, and then enters the thermal fluid supercritical water annular channel 12, and adopts the downflow mode and After the cold fluid realizes heat exchange, it flows out through the supercritical water outlet 10 of the hot fluid, forming a primary side cycle. Cooling water enters the cold fluid water descending channel 11 through the cold fluid water inlet 4, contacts and exchanges heat with the outside of the hot fluid supercritical water annular channel 12; then the cold fluid water collected in the lower chamber 9 enters the cold fluid water ascending channel 6 , contacting the inner side of the hot fluid supercritical water annular channel 12 for heat exchange. Finally, it enters the top chamber 16 and flows out through the cold fluid water outlet 15, forming a secondary side circulation.

Both the primary side circulation and the secondary side circulation are natural circulation, and helium gas is introduced into the circulation loop to enhance the natural circulation drive.

When the primary side supercritical water enters the heat exchanger, the temperature is about 350°C~500°C, when it flows out of the heat exchanger, the temperature is about 150°C~300°C, the pressure is 20MPa~25MPa, and the flow rate is 1000kg/s~1500kg/s; the secondary side water enters The temperature in the heat exchanger is about 50°C~80°C, the temperature when it flows out of the heat exchanger is about 100°C~250°C, the pressure is 1MPa~5MPa, and the flow rate is 1000kg/s~2000kg/s.

In addition, a backup forced circulation bypass including circulation pumps and valves is also provided on the secondary side of the designed waste heat discharge heat exchanger. When the supercritical water temperature at the hot fluid outlet of the heat exchanger does not meet the requirements, the forced circulation loop is activated by the control system, and the circulation pump is put into the secondary side to promote heat exchange.

Claims (5)

1. for a natural-circulation heat exchanger for supercritical water reactor Residual heat removal, it is characterized in that: its agent structure is from top to bottom made up of top end cover (1), housing (5) and low head (8);

On the top of housing (5), the upper spacer (2) be arranged in parallel and lower clapboard (13) are set; Top chamber (16) is formed between upper spacer (2) and top end cover (1); Upper spacer (2), between lower clapboard (13) and housing (5), form upper chamber (14); Multiple cylindrical shell (17) be communicated with upper chamber (14) that is that be evenly arranged is set in the below of lower clapboard (13), form cold fluid water decline passway (11) between the outer wall of cylindrical shell (17) and housing (5), lower clapboard (13), between the lower wall of cylindrical shell (17) and low head (8), form lower chamber (9); In each cylindrical shell (17), arrange one run through cylindrical shell (17) and upper chamber (14), the inner barrel (18) being communicated with top chamber (16) and lower chamber (9), between cylindrical shell (17) and inner barrel (18), form hot fluid supercritical water circular passage (12);

In top end cover (1), the cold fluid water out (15) be communicated with top chamber (16) is set; Above arrange the hot fluid supercritical water entrance (3) be communicated with upper chamber (14) at housing (5), lower clapboard (13) below in housing (5) arranges the cold fluid water inlet (4) be communicated with cold fluid water decline passway (11); On each cylindrical shell (17), a hot fluid supercritical water being communicated with the external world inner with cylindrical shell (17) is set and exports (10);

Described hot fluid supercritical water entrance (3) passes into supercritical water, flows in hot fluid supercritical water circular passage (12), exports (10) flow out by hot fluid supercritical water, forms primary side circulation; Cold fluid water inlet (4) passes into cold fluid water, flow in cold fluid water decline passway (11), lower chamber (9), the cold fluid water rising passway (6) be made up of inner barrel (18) and top chamber (16), flowed out by cold fluid water out (15), form secondary side circulation.

2. a kind of natural-circulation heat exchanger for supercritical water reactor Residual heat removal according to claim 1, is characterized in that: described cylindrical shell (17) is right cylinder or square body, and quantity is 4-12; The shape of inner barrel (18) is identical with cylindrical shell (17).

3. a kind of natural-circulation heat exchanger for supercritical water reactor Residual heat removal according to claim 1, is characterized in that: described primary side circulation and secondary side circulation are Natural Circulation, and in closed circuit, introduces helium to strengthen Natural Circulation driving.

4. a kind of natural-circulation heat exchanger for supercritical water reactor Residual heat removal according to claim 1, is characterized in that: the gap between described cylindrical shell (17) and inner barrel (18) is 10-20mm.

5. a kind of natural-circulation heat exchanger for supercritical water reactor Residual heat removal according to claim 1, is characterized in that: all adopt Flange joint between described top end cover (1) and housing (5), between housing (5) and low head (8).