Sodium-cooled fast reactor modular steam generator shell side flushing system and method

Abstract

The invention provides a sodium-cooled fast reactor modular steam generator shell side flushing system and method, and belongs to the technical field of sodium-cooled fast neutron reactor steam generator shells. The system comprises a sodium filling path formed by a sodium storage tank, a sodium storage tank electromagnetic pump, a superheater and an evaporator which are connected through a pipeline, and a primary sodium discharging path formed by the evaporator, an evaporator low-point sodium discharging valve and a primary accident discharging tank which are connected through a pipeline, the primary accident discharge tank, the primary accident discharge tank sodium filling and discharging valve and the sodium storage tank are connected through a pipeline to form a secondary sodium discharging path. The high reducibility of high-temperature metal sodium is utilized for rust removal, and a contrast test in a laboratory verifies that the rust removal effect is good.

Description

Technical Field

[0001] The invention relates to the technical field of sodium-cooled fast neutron reactor steam generator shells, and in particular to a sodium-cooled fast reactor modular steam generator shell side flushing system and method. Background Art

[0002] The demonstration fast reactor belongs to the sodium-cooled fast neutron breeder reactor in the fourth generation of nuclear power technology. Unlike the current pressurized water reactor, the main heat transfer system adopts a sodium-sodium-water / steam three-circuit design. The secondary main cooling system belongs to the intermediate loop. Its function is to transfer the heat of the sodium in the primary main cooling system to the liquid metal sodium in the secondary main cooling system through the intermediate heat exchanger, and then to the third loop (water / steam) system by the steam generator of this system to provide superheated steam to drive the steam turbine to generate electricity.

[0003] The secondary circuit main cooling system is equipped with two parallel loops, each of which is mainly composed of a sodium circulation pump, a sodium distributor, a sodium buffer tank, eight sets of steam generator modules and related pipes and valves. The steam generator module is the boundary between the sodium (secondary circuit) and the water / steam system (third circuit). Sodium flows on the shell side of the steam generator module, and the water and steam of the third circuit flow on the tube side, and the flow direction is opposite to that of the sodium. The modular design of the steam generator is mainly to deal with heat transfer tube leakage incidents. At the same time, the modular design can improve the sensitivity of sodium-water reaction detection. When the steam generator triggers a large / small sodium-water reaction condition, the accident module can be isolated in time.

[0004] After the steam generator equipment arrives at the project site, it is necessary to conduct an opening inspection before installation. It is found that there is a large area of ​​rust on the inner surface of the shell side of the steam generator module, the outer surface of the heat transfer tube, the tube sheet and other pressure-bearing parts. The traditional wiping and chemical cleaning and rust removal processes cannot be implemented. At the same time, there is no specific description on how to deal with it in the equipment design manual and related literature. If the rust is not treated and the sodium is directly added to the secondary circuit main cooling system, there are the following risks:

[0005] 1. The lower bearing of the sodium circulation pump is a static pressure bearing with a clearance of less than 1mm. Impurities carried by the sodium liquid will enter this area and cause scratches on the bearing surface, resulting in a risk of major equipment damage;

[0006] 2. Rust will cause the sodium blocking temperature in the system to be high, and the secondary circuit main cooling system will be filled with a large amount of sodium, which will prolong the purification time and affect the construction period;

[0007] 3. Rust will cause the sodium blocking temperature in the system to be high, and it is easy to cause blockage in the small branch pipe area of ​​the system during the sodium filling process. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the prior art and provide a shell side flushing system and method for a modular steam generator of a sodium-cooled fast reactor, which can effectively solve the problem of large-area corrosion of the steam generator, while eliminating the risk of damage to major equipment, saving the construction period, and reducing the risk of sodium inlet blockage in the system.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] In one aspect, the present invention provides a shell side flushing system for a modular steam generator of a sodium-cooled fast reactor, comprising:

[0011] A sodium storage tank, a sodium storage tank electromagnetic pump, a superheater, and an evaporator connected by pipelines form a sodium charging path;

[0012] A primary sodium discharge path formed by the evaporator, the evaporator low point sodium discharge valve, and the primary emergency discharge tank connected by pipelines; and

[0013] The secondary sodium discharge path is formed by the primary emergency discharge tank, the primary emergency discharge tank sodium filling and discharge valve, and the sodium storage tank connected by pipelines.

[0014] In some embodiments, the sodium storage tank electromagnetic pump transports the high-temperature metallic sodium in the sodium storage tank to the lower section of the superheater.

[0015] In some embodiments, the superheater and the evaporator are connected via a bridge tube.

[0016] In some embodiments, the superheater is connected to the primary emergency discharge tank via a pipeline, and a superheater low-point sodium discharge valve is provided on the connecting pipeline.

[0017] In some embodiments, a steam generator sodium charging and discharging valve and a superheater inlet regulating valve are provided on the sodium charging path, and the steam generator sodium charging and discharging valve and the superheater inlet regulating valve are arranged between the sodium storage tank electromagnetic pump and the superheater.

[0018] In some embodiments, a third branch is connected between the steam generator sodium charging and discharging valve and the superheater inlet regulating valve, and the third branch is provided with a superheater inlet isolation valve and connected to a sodium distributor.

[0019] In some embodiments, the superheater is connected to the sodium buffer tank via a seventh branch, and a superheater overflow valve is provided on the seventh branch.

[0020] In some embodiments, the evaporator is connected to the sodium buffer tank via a tenth branch, and an evaporator outlet isolation valve is provided on the tenth branch.

[0021] On the other hand, the present invention provides a shell side flushing method for a modular steam generator of a sodium-cooled fast reactor, wherein the metallic sodium required for flushing is heated to 250±10° C., charged into an isolated steam generator module (one steam generator module is composed of one superheater and one evaporator), and soaked and flushed for several hours to remove rust on the surface of the equipment. Thereafter, the dirty sodium flushed in the steam generator module is discharged into a primary accident discharge tank, and precipitated for several hours to allow impurities in the dirty sodium flushed to be stratified, and 90% of the upper layer of dirty sodium flushed is transported back into a sodium storage tank, and circulated and purified using a cold trap.

[0022] The shell side flushing method of a modular steam generator for a sodium-cooled fast reactor specifically comprises the following steps:

[0023] Step 1: Calculate the volume of the steam generator module and the connected pipes within the flushing range, and prepare sodium in the sodium storage tank according to the calculated volume;

[0024] Step 2: Heat the sodium in the sodium storage tank to 250±10℃;

[0025] Step 3: Confirm that the steam generator module and the connected pipelines have completed the vacuum and argon replacement operations, and the gas sampling and analysis are qualified;

[0026] Step 4: Control the covering gas pressure of the steam generator module and the connected pipeline air cavity within the range of 0.04-0.06MPa;

[0027] Step 5: Heat the steam generator module and the connected pipes to 230±10℃;

[0028] Step 6: Open the superheater inlet regulating valve, evaporator overflow valve, and superheater overflow valve; close the steam generator sodium charging and discharging valve, evaporator outlet isolation valve, superheater inlet isolation valve, superheater emergency sodium discharge valve, evaporator emergency sodium discharge valve, evaporator low point sodium discharge valve, and superheater low point sodium discharge valve;

[0029] Step 7: Open the sodium valve at the sodium storage tank outlet and start the sodium storage tank electromagnetic pump;

[0030] Step 8: Open the sodium filling and discharging valve of the steam generator to fill sodium from the sodium storage tank into the steam generator module and the connected pipelines;

[0031] Step 9: After the sodium filling is completed, close the sodium filling and discharging valve of the steam generator and stop the electromagnetic pump of the sodium storage tank;

[0032] Step 10: Sodium soaking and flushing in the steam generator module for 24 hours;

[0033] Step 11: After soaking is completed, open the evaporator low point sodium drain valve and superheater low point sodium drain valve, and drain the steam generator module sodium to the first-level emergency discharge tank;

[0034] Step 12: After the sodium discharge is completed, close the evaporator low point sodium discharge valve and the superheater low point sodium discharge valve;

[0035] Step 13: Flush the dirty sodium precipitate in the first-level accident discharge tank for 24 hours;

[0036] Step 14: After the precipitation is completed, open the sodium filling and discharging valve of the first-level accident discharge tank, and recover the flushing sodium on the upper layer of the first-level accident discharge tank into the sodium storage tank;

[0037] Step 15: After sodium recovery is completed, close the sodium filling and discharging valve of the first-level emergency discharge tank;

[0038] Step 16: The flushed dirty sodium recovered in the sodium storage tank is sent online to the cold trap system for purification;

[0039] Step 17: The dirty sodium recovered from the sodium storage tank has been purified and is qualified after sampling and analysis;

[0040] Step 18: The purified and qualified recovered sodium in the sodium storage tank is used as reserve sodium for the next cycle flushing.

[0041] Compared with the prior art, the shell side flushing system and method of a modular steam generator for a sodium-cooled fast reactor provided by the present invention has the following beneficial effects:

[0042] The invention utilizes the strong reducing property of high temperature metallic sodium to remove rust, and the comparative test in the laboratory verifies the good rust removal effect. The flushing medium of the invention is the same as the coolant for normal operation of the equipment, and the flushing process does not introduce new impurities.

[0043] The present invention solves the problem that the steam generator module of the demonstration fast reactor is easily corroded due to the easy corrosion of the material, resulting in large-scale corrosion on the shell side after being transported to the project site, thereby providing a guarantee for the safe and stable commissioning of subsequent equipment.

[0044] The present invention designs a circulating flushing process of "sodium flushing - sodium recovery - sodium purification - sodium flushing", and the metallic sodium can be recycled, which is economical and environmentally friendly.

[0045] The amount of dirty sodium generated by flushing of the present invention is minimal, which is approximately 1 / 3 of the dirty sodium amount of the entire system flushing, effectively saving the operating time of sodium filling and discharging operations, sodium recovery and purification, sodium transportation, and the like.

[0046] The amount of sodium in the flushing process of the present invention is precisely controllable, thereby strengthening the safety management and control of dangerous chemical metal sodium; by controlling the total flushing sodium amount, it is possible to avoid sodium filling exceeding the flushing boundary range.

[0047] The amount of sodium in the flushing process of the present invention is precisely controllable, which provides accurate prediction of the time for sodium filling and discharging operations, sodium recovery and purification, sodium transportation and the like, and facilitates work arrangements.

[0048] The present invention controls the flushing range within the steam generator module, realizes local flushing of the rusted area, has strong pertinence, and minimizes the flushing range. The present invention controls the flushing range within the steam generator module, avoiding the risk of dirty sodium entering the static pressure bearing of the sodium circulation pump (with a clearance less than 1 mm) and causing scratches on the bearing surface.

[0049] The gas pressure covering the air cavity of the steam generator module of the present invention is appropriate, and there is no need to perform exhaust and gas replenishment operations during the sodium filling and discharge process, which simplifies the operation and reduces the loss of argon gas; at the same time, the outlet pressure of the electromagnetic pump of the sodium storage tank is reduced, which can reduce the operating power of the electromagnetic pump and improve the economy.

[0050] The present invention increases the temperature of metallic sodium by 10-30°C higher than that of equipment and pipelines. When the metallic sodium with a higher temperature flows through, the indications of thermocouples installed on the equipment and pipelines will change rapidly, thereby judging the current sodium filling liquid level, thereby solving the problem of having no liquid level meter during steam generator module flushing and being unable to observe the current sodium filling liquid level.

[0051] The steam generator module of the present invention adopts the method of low-point sodium inlet and bridge pipe overflow for sodium charging, which is beneficial to the exhaust of the equipment during the sodium charging process.

[0052] The present invention adopts a mode of controlling the sodium filling flow rate in sections, reduces the sodium filling flow rate in the tube sheet area of ​​the steam generator module, reduces the thermal shock of the high-temperature metallic sodium on the tube sheet of the steam generator module; increases the sodium filling flow rate in the cylinder area of ​​the steam generator module, improves the sodium feeding efficiency, and saves construction period.

[0053] The present invention adopts the sodium discharge path at the lowest point of the steam generator module, which can fully discharge impurities in the equipment and reduce the residual dirty sodium in flushing.

[0054] Furthermore, the present invention designs a preliminary treatment process of flushing dirty sodium and letting it settle for 24 hours, which saves the time required for the subsequent cold trap sodium purification process.

[0055] Furthermore, the present invention designs a process for recycling 90% of the upper rinse dirt in the tank. Since the impurity capacity of a single cold trap is fixed, it can only be replaced after reaching the upper limit of the capacity. The precipitation treatment process can effectively reduce the impurity content in the recovered sodium and extend the service life of the cold trap. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for the technical description.

[0057] Figure 1 A schematic diagram of a shell side flushing system for a modular steam generator of a sodium-cooled fast reactor provided by the present invention;

[0058] Figure 2 The present invention provides a flow chart of a shell side flushing method for a modular steam generator of a sodium-cooled fast reactor.

[0059] Description of reference numerals:

[0060] 1. Sodium storage tank; 2. Sodium valve at the outlet of the sodium storage tank; 3. Sodium storage tank electromagnetic pump; 4. Steam generator sodium charging and discharging valve; 5. Superheater inlet regulating valve; 6. Superheater; 7. Evaporator; 8. Evaporator outlet isolation valve; 9. Sodium buffer tank; 10. Evaporator overflow valve; 11. Superheater overflow valve; 12. Superheater inlet isolation valve; 13. Sodium distributor; 14. Superheater emergency sodium discharge valve; 15. Evaporator emergency sodium discharge valve; 16. Steam generator accident protection system; 17. Evaporator low point sodium discharge valve; 18. Superheater low point sodium discharge valve; 19. Level 1 accident discharge tank; 20. Level 1 accident discharge tank sodium charging and discharging valve. DETAILED DESCRIPTION

[0061] The following is further explained in detail through specific implementation methods.

[0062] After studying and analyzing the areas of large-scale rust on the steam generator on site, it was confirmed that the material used for the pressure-bearing parts such as the shell, heat transfer tubes, and tube sheets was 2.25Cr1Mo, which is easily oxidized and rusted when exposed to humid air. In view of the reasons for the above analysis, the present invention proposes a shell-side flushing system and method for a modular steam generator of a sodium-cooled fast reactor. The present invention utilizes the strong reducing property of metallic sodium to remove rust, and conducts comparative tests in the laboratory to determine the temperature of metallic sodium and the duration of immersion and flushing.

[0063] The present invention first heats the metallic sodium required for flushing to 250±10°C, fills it into the isolated steam generator module (one steam generator module is composed of one superheater 6 and one evaporator 7), soaks and flushes for 24 hours to remove the rust on the surface of the equipment, then discharges the dirty sodium for flushing in the steam generator module into a first-level emergency discharge tank, settles for 24 hours to allow the impurities in the dirty sodium for flushing to be stratified, takes 90% of the upper layer of dirty sodium for flushing and transports it to a sodium storage tank (referring to sodium storage tank 2), uses a cold trap for circulation purification, and completes the flushing of the steam generator shell side once the sodium sampling analysis is qualified.

[0064] like Figure 1 As shown, the present invention provides a shell side flushing system for a modular steam generator of a sodium-cooled fast reactor, comprising a sodium storage tank 1, a superheater 6, an evaporator 7, a sodium buffer tank 9, a sodium distributor 13, and a primary accident discharge tank 19 connected by pipelines.

[0065] The sodium storage tank 1 is connected to the sodium storage tank electromagnetic pump 3 through a pipeline; the outlet section of the sodium storage tank electromagnetic pump 3 is provided with two branches (i.e., the first branch and the second branch), the first branch is connected to the first-level accident discharge tank sodium charging and discharging valve 20, the first-level accident discharge tank sodium charging and discharging valve 20 is connected to the first-level accident discharge tank 19, and the second branch is connected to the steam generator sodium charging and discharging valve 4; the outlet section of the steam generator sodium charging and discharging valve 4 is provided with two branches (i.e., the third branch and the fourth branch), the third branch is connected to the superheater inlet isolation valve 12 and the sodium distributor 13 in sequence, and the fourth branch is connected to the superheater inlet regulating valve 5; the outlet section of the superheater inlet regulating valve 5 is provided with two branches (i.e., the fifth branch and the sixth branch), the fifth branch is connected to the superheater emergency sodium discharge valve 14 and a set of steam generators in sequence. The sixth branch of the steam generator accident protection system 16 is connected to the superheater 6; the superheater 6 is connected to the evaporator 7 through a bridge tube, one branch of the superheater 6 (the seventh branch) is connected to the sodium buffer tank 9, and another branch of the superheater 6 (the eighth branch) is connected to the first-level accident discharge tank 19; the evaporator 7 is connected to the sodium buffer tank 9 through the tenth branch, and the tenth branch is also provided with an evaporator overflow valve 10; the evaporator 7 is connected to the first-level accident discharge tank 19 through the eleventh branch, and the eleventh branch is also provided with an evaporator low-point sodium discharge valve 17; the evaporator 7 is connected to the sodium buffer tank 9 through the twelfth branch; the evaporator 7 is connected to the steam generator accident protection system 16 (another set) through the thirteenth branch, and the thirteenth branch is provided with an evaporator emergency sodium discharge valve 15.

[0066] The sodium charging path of this system is: the metallic sodium is charged into the sodium storage tank 1, and then passes through the sodium storage tank electromagnetic pump 3 and the superheater 6 to enter the evaporator 7, that is, the sodium storage tank 1 → the sodium storage tank electromagnetic pump 3 → the superheater 6 → the evaporator 7, and the 8 steam generator modules of the same loop are charged with sodium at the same time. The high-temperature metallic sodium in the sodium storage tank 1 is transported to the lower section of the superheater 6 by the sodium storage tank electromagnetic pump 3, and then flows into the evaporator 7 through the bridge pipe between the superheater 6 and the evaporator 7.

[0067] The primary sodium discharge path of this system is: the metallic sodium in the superheater 6 flows out, passes through the superheater low point sodium discharge valve 18 and flows into the first-level accident discharge tank 19; the metallic sodium in the evaporator 7 flows out, passes through the evaporator low point sodium discharge valve 17 and flows into the first-level accident discharge tank 19, that is, superheater 6 → superheater low point sodium discharge valve 18 → first-level accident discharge tank 19, evaporator 7 → evaporator low point sodium discharge valve 17 → first-level accident discharge tank 19, and each module of the steam generator in the same loop discharges sodium at the same time. Open the low point sodium discharge valve of the steam generator module, and discharge the flushing dirty sodium into the first-level accident discharge tank by gravity. It should be noted that there are two sodium discharge paths, one for the evaporator and one for the superheater, and there is metallic sodium in both the evaporator and the superheater that needs to be discharged.

[0068] The secondary sodium discharge path of this system is: the metallic sodium in the first-level accident discharge tank 19 flows out, passes through the first-level accident discharge tank sodium filling and discharging valve 20 and enters the sodium storage tank 1, that is, the first-level accident discharge tank 19 → the first-level accident discharge tank sodium filling and discharging valve 20 → the sodium storage tank 1. Open the first-level accident discharge tank sodium filling and discharging valve 20, and at the same time increase the air cavity pressure in the first-level accident discharge tank 19, and 90% of the upper layer of dirty sodium in the tank is transported back to the sodium storage tank.

[0069] In addition, if Figure 2 As shown, the present invention provides a method for flushing the shell side of a modular steam generator of a sodium-cooled fast reactor, using high-temperature metallic sodium as a flushing medium, and utilizing the strong reducing property of the high-temperature metallic sodium to react with iron oxide to remove large-area rust on the shell side of the steam generator module. The method specifically comprises the following steps:

[0070] Step 1: Calculate the volume of the steam generator module and the connected pipeline within the flushing range, and prepare sodium in the sodium storage tank 1 (the first sodium storage tank) (because the capacity of a sodium storage tank is limited, multiple sodium storage tanks are required to complete the sodium filling and sodium discharge operations, with the same function) according to the volume;

[0071] Step 2: Heat the sodium in the sodium storage tank 1 to 250±10°C;

[0072] Step 3: Confirm that the steam generator module (the steam generator includes 8 steam generator modules) and the connected pipelines have completed the vacuum and argon replacement operations, and the gas sampling and analysis are qualified;

[0073] Step 4: Control the covering gas pressure of the steam generator module and the connected pipeline air cavity within the range of 0.04-0.06MPa;

[0074] Step 5: Heat the steam generator module and the connected pipes to 230±10℃;

[0075] Step 6: Open the superheater inlet regulating valve 5, the evaporator overflow valve 10, and the superheater overflow valve 11; close the steam generator sodium charging and discharging valve 4, the evaporator outlet isolation valve 8, the superheater inlet isolation valve 12, the superheater emergency sodium discharge valve 14, the evaporator emergency sodium discharge valve 15, the evaporator low point sodium discharge valve 17, and the superheater low point sodium discharge valve 18;

[0076] Step 7: Open the sodium valve 2 at the sodium storage tank outlet and start the sodium storage tank electromagnetic pump 3;

[0077] Step 8: Open the steam generator sodium filling and discharging valve 4 to fill the steam generator module and the connected pipeline with sodium from the sodium storage tank 1;

[0078] Step 9: After the sodium filling is completed, the steam generator sodium filling and discharging valve 4 is closed, and the sodium storage tank electromagnetic pump 3 is stopped;

[0079] Step 10: Sodium soaking and flushing in the steam generator module for 24 hours;

[0080] Step 11: After soaking is completed, open the evaporator low point sodium discharge valve 17 and the superheater low point sodium discharge valve 18, and the steam generator module discharges sodium to the first-level emergency discharge tank 19;

[0081] Step 12: After the sodium discharge is completed, close the evaporator low point sodium discharge valve 17 and the superheater low point sodium discharge valve 18;

[0082] Step 13: flush dirty sodium precipitate in the first-level accident discharge tank 19 for 24 hours; This method allows the flushed dirty sodium in the first-level accident discharge tank 19 to settle for 24 hours for preliminary treatment, and the impurities, foreign matter, oxidation products, etc. in the flushed dirty sodium will precipitate into layers.

[0083] Step 14: After the precipitation is completed, the sodium filling and discharging valve 20 of the first-level accident discharge tank is opened, and the flushing sodium in the upper layer of the first-level accident discharge tank 19 is recovered into the sodium storage tank (sodium storage tank 2);

[0084] Step 15: After sodium recovery is completed, the sodium filling and discharging valve 20 of the first-level emergency discharge tank is closed;

[0085] Step 16: The flushed dirty sodium recovered in the sodium storage tank is sent online to the cold trap system for purification;

[0086] Step 17: The dirty sodium recovered from the sodium storage tank has been purified and is qualified after sampling and analysis;

[0087] Step 18: The purified and qualified recovered sodium in the sodium storage tank is used as reserve sodium for the next cycle flushing.

[0088] It can be seen that the sodium charging path of the present method is: sodium storage tank 1 → sodium storage tank electromagnetic pump 3 → superheater 6 → evaporator 7, and each module of the steam generator in the same loop is charged with sodium at the same time. The high-temperature metallic sodium in the sodium storage tank 1 is transported to the lower section of the superheater 6 by the sodium storage tank electromagnetic pump 3, and then flows into the evaporator 7 through the bridge pipe between the superheater 6 and the evaporator 7.

[0089] The sodium filling flow rate of this method adopts a segmented control mode. When the metallic sodium enters the bottom tube plate area of ​​the superheater 6 and the evaporator 7, the sodium filling flow rate is controlled to be 10-15m 3 / h; When the metallic sodium level is 0.5m higher than the bottom tube plate area of ​​superheater 6 and evaporator 7, adjust the electromagnetic pump 3 of the sodium storage tank to control the sodium filling flow rate to 30-40m 3 / h, improving the sodium filling efficiency. It should be noted that regarding the segmented control method, the first section is the bottom tube plate of the superheater 6 and the evaporator 7 and the area 0.5m above, and the second section is the remaining area of ​​the superheater 6 and the evaporator 7; since the first section is the heat-sensitive area of ​​the equipment, in order to reduce the impact and thermal shock of the metallic sodium liquid fluid, the sodium filling flow rate is reduced; the second section is the non-heat-sensitive area of ​​the equipment, and the sodium filling flow rate is increased. Through segmented control, the risk of damage to the heat-sensitive area of ​​the equipment is reduced, and the overall sodium filling time is saved.

[0090] The primary sodium discharge path of this method is: superheater 6 → superheater low point sodium discharge valve 18 → first level accident discharge tank 19, evaporator 7 → evaporator low point sodium discharge valve 17 → first level accident discharge tank 19, and each module of the steam generator in the same loop discharges sodium at the same time. Open the low point sodium discharge valve of the steam generator module, and discharge the flushing dirty sodium into the first level accident discharge tank by gravity. There are two sodium discharge paths, one for the evaporator and one for the superheater, and there is metallic sodium in both the evaporator and the superheater that needs to be discharged.

[0091] The secondary sodium discharge path of this method is: first-level accident discharge tank 19 → first-level accident discharge tank sodium filling and discharge valve 20 → sodium storage tank 1. Open the first-level accident discharge tank sodium filling and discharge valve 20, and at the same time increase the air cavity pressure in the first-level accident discharge tank 19, and transfer 90% of the upper flushing dirty sodium in the tank to the sodium storage tank.

[0092] The metal sodium temperature used in this method is 250±10℃, and the immersion and flushing time is 24 hours. Using test block samples of the same material as the steam generator, rust removal control tests with different metal sodium temperatures and different immersion and flushing times were carried out in the laboratory, and the above temperature and time were finally determined.

[0093] The method of isolating the steam generator module was adopted to carry out targeted flushing of the rusted area. Considering that the materials of other main equipment in the system (sodium buffer tank, sodium distributor, intermediate heat exchanger, sodium valve) are 316 and 316H, and the material of the system sodium-related pipeline is WP316L, which are not easy to rust and the cleanliness is good during on-site inspection, the flushing work is only targeted at the rusted area; at the same time, the isolation design of the steam generator module for sodium-water reaction is used to minimize the flushing range and control the boundary to the steam generator module and the connected pipeline.

[0094] The immersion and rapid discharge flushing method is adopted. The immersion flushing method is to fill the rusted area with high-temperature metallic sodium medium, and soak it for a period of time to allow the iron oxide in the rusted area to react fully with the high-temperature metallic sodium; at the same time, the steam generator is a slender structure (the length is about 11 times and 20 times the diameter), and the rapid discharge of metallic sodium has a flushing effect on the rusted wall surface, reducing the deposition of reaction products.

[0095] The flushing sodium volume of this method is the volume of the steam generator module and the connected pipeline, which can be accurately calculated by the equipment size, and the error can be controlled within 3%. By calculating the flushing sodium volume, it is possible to strengthen the safety control of metallic sodium and carry out the preparation and transportation of metallic sodium in advance.

[0096] Before the sodium filling operation of the method, the pressure of the gas covering the air cavity of the steam generator module is controlled within the range of 0.04-0.06MPa. Before the sodium filling, the steam generator module completes the vacuuming and argon replacement operation through the vacuum argon system, and the gas sampling and analysis are qualified.

[0097] Before the sodium charging operation in this method, the heating temperature of the steam generator module and the connected pipeline is controlled at 230±10°C, which is 10-30°C lower than the metal sodium temperature.

[0098] The method is to transfer the flushing dirty sodium recovered in the sodium storage tank to a cold trap for purification online, and utilize the cold trap to remove impurities such as oxides and hydrides in the sodium until the flushing dirty sodium is qualified for sampling and analysis.

[0099] This method establishes a cyclic flushing path of "sodium flushing - sodium recovery - sodium purification - sodium flushing", and the number of cyclic flushing is 2-3 times, which can be arranged according to the progress of the project schedule.

[0100] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A shell side flushing system for a modular steam generator of a sodium-cooled fast reactor, characterized in that: include: A sodium storage tank (1), a sodium storage tank electromagnetic pump (3), a superheater (6), and an evaporator (7) connected by pipelines form a sodium charging path; A primary sodium discharge path formed by the evaporator (7), the evaporator low point sodium discharge valve (17), and the primary emergency discharge tank (19) connected by pipelines; and A secondary sodium discharge path is formed by the primary emergency discharge tank (19), the primary emergency discharge tank sodium filling and discharge valve (20), and the sodium storage tank (1) connected by pipelines.

2. The shell side flushing system of a modular steam generator for a sodium-cooled fast reactor according to claim 1, characterized in that: The sodium storage tank electromagnetic pump (3) transports the high-temperature metallic sodium in the sodium storage tank (1) to the lower section of the superheater (6).

3. The shell side flushing system of a modular steam generator for a sodium-cooled fast reactor according to claim 2, characterized in that: The superheater (6) and the evaporator (7) are connected via a bridge pipe.

4. The shell side flushing system of a modular steam generator for a sodium-cooled fast reactor according to claim 1, characterized in that: The superheater (6) is connected to the primary emergency discharge tank (19) via a pipeline, and a superheater low-point sodium discharge valve (18) is provided on the connecting pipeline.

5. The shell side flushing system of a modular steam generator for a sodium-cooled fast reactor according to claim 1, characterized in that: The sodium charging path is provided with a steam generator sodium charging and discharging valve (4) and a superheater inlet regulating valve (5); the steam generator sodium charging and discharging valve (4) and the superheater inlet regulating valve (5) are arranged between the sodium storage tank electromagnetic pump (3) and the superheater (6).

6. The shell side flushing system of a modular steam generator for a sodium-cooled fast reactor according to claim 5, characterized in that: A third branch is connected between the steam generator sodium filling and discharging valve (4) and the superheater inlet regulating valve (5), and a superheater inlet isolation valve (12) is provided on the third branch and is connected to a sodium distributor (13).

7. The shell side flushing system of a modular steam generator for a sodium-cooled fast reactor according to claim 1, characterized in that: The superheater (6) is connected to the sodium buffer tank (9) via a seventh branch, and a superheater overflow valve (11) is provided on the seventh branch.

8. The shell side flushing system for modular steam generator of sodium-cooled fast reactor according to claim 1, characterized in that: The evaporator (7) is connected to the sodium buffer tank (9) via a tenth branch line, and an evaporator outlet isolation valve (8) is provided on the tenth branch line.

9. A shell side flushing method for a modular steam generator of a sodium-cooled fast reactor, characterized in that: Heat the metallic sodium required for flushing to 250±10℃, fill it into the isolated steam generator module, soak and flush for several hours to remove the rust on the equipment surface, then discharge the dirty sodium in the steam generator module into the first-level emergency discharge tank, let it settle for several hours to allow the impurities in the dirty sodium to be stratified, take 90% of the upper layer of dirty sodium and transport it to the sodium storage tank, and use a cold trap for circulation purification.

10. The shell side flushing method of a modular steam generator for a sodium-cooled fast reactor according to claim 9, characterized in that: The specific steps include: Step 1: Calculate the volume of the steam generator module and the connected pipes within the flushing range, and prepare sodium in the sodium storage tank according to the calculated volume; Step 2: Heat the sodium in the sodium storage tank to 250±10℃; Step 3: Confirm that the steam generator module and the connected pipelines have completed the vacuum and argon replacement operations, and the gas sampling and analysis are qualified; Step 4: Control the covering gas pressure of the steam generator module and the connected pipeline air cavity within the range of 0.04-0.06MPa; Step 5: Heat the steam generator module and the connected pipes to 230±10℃; Step 6: Open the superheater inlet regulating valve, evaporator overflow valve, and superheater overflow valve; close the steam generator sodium charging and discharging valve, evaporator outlet isolation valve, superheater inlet isolation valve, superheater emergency sodium discharge valve, evaporator emergency sodium discharge valve, evaporator low point sodium discharge valve, and superheater low point sodium discharge valve; Step 7: Open the sodium valve at the sodium storage tank outlet and start the sodium storage tank electromagnetic pump; Step 8: Open the sodium filling and discharging valve of the steam generator to fill sodium from the sodium storage tank into the steam generator module and the connected pipelines; Step 9: After the sodium filling is completed, close the sodium filling and discharging valve of the steam generator and stop the electromagnetic pump of the sodium storage tank; Step 10: Sodium soaking and flushing in the steam generator module for 24 hours; Step 11: After soaking is completed, open the evaporator low point sodium drain valve and superheater low point sodium drain valve, and drain the steam generator module sodium to the first-level emergency discharge tank; Step 12: After the sodium discharge is completed, close the evaporator low point sodium discharge valve and the superheater low point sodium discharge valve; Step 13: Flush the dirty sodium precipitate in the first-level accident discharge tank for 24 hours; Step 14: After the precipitation is completed, open the sodium filling and discharging valve of the first-level accident discharge tank, and recover the flushing sodium on the upper layer of the first-level accident discharge tank into the sodium storage tank; Step 15: After sodium recovery is completed, close the sodium filling and discharging valve of the first-level emergency discharge tank; Step 16: The flushed dirty sodium recovered in the sodium storage tank is sent online to the cold trap system for purification; Step 17: The dirty sodium recovered from the sodium storage tank has been purified and is qualified after sampling and analysis; Step 18: The purified and qualified recovered sodium in the sodium storage tank is used as reserve sodium for the next cycle flushing.

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