Passive waste heat removal system through straight flow type steam generator and filling method thereof

Abstract

The invention relates to a passive waste heat removal system through a steam generator, which is suitable for nuclear reactors with heavy liquid metal coolants. The system comprises a straight-flow steam generator; the cooling heat exchanger is positioned in the groove of the passive residual heat removal system and above the steam generator; the steam separator is positioned above the steam generator but is lower than the cooling heat exchanger; the pipeline is used for supplying steam to the steam separator; a duct discharging condensate water from the cooling heat exchanger to the steam separator; the quick stop valves are arranged on a steam outlet pipeline and a water supply pipeline of the steam generator; and means for discharging heat of condensation from the cooling heat exchanger to the final heat sink. A pressure direct-acting type cut-off adjusting device is installed on a pipeline for discharging condensate water from a cooling heat exchanger, and the device can be converted into a closed state through water supply pressure or electromagnet acting force in an energy mode under normal operation. In order to fill a working medium into a steam generator of the passive residual heat removal system, a steam supply valve is opened to supply steam to a secondary loop of a dry steam generator, and the steam pressure exceeds saturation pressure corresponding to a specific value above the melting temperature of a heavy liquid metal coolant; the saturation pressure exceeds the saturation pressure corresponding to the temperature of the heavy liquid metal coolant provided by the heating system, but is lower than the opening pressure of the valve of the cut-off adjusting device. And when the water level in the steam separator reaches a set value, the steam supply valve is closed. The method has the technical effects that the operation safety of the nuclear reactor and the efficiency of a passive waste heat removal system are improved without an external power supply, and meanwhile, the solidification possibility of the heavy liquid metal coolant when the waste heat power is reduced is eliminated.

Description

Technical Field

[0001] The present invention relates to the field of nuclear energy and in particular to ensuring the safety of nuclear reactors with heavy liquid metal coolants, including under blackout conditions, using a guaranteed residual heat removal system. More particularly, the present invention relates to a passive cooling system or a passive residual heat removal system for nuclear reactors with heavy liquid metal coolants, the principle of which is to use a steam generator operating in once-through mode. Background Art

[0002] In all currently operating third generation nuclear power plants, pump operation is required to remove waste heat to the final heat sink (external reservoirs, water towers, jet cooling pools). In this case, this is achieved using a multi-channel safety system that includes a diesel generator with a reliable power supply system, thus ensuring the supply of electrical energy required for the operation of the cooling water pumps.

[0003] At the same time, the Fukushima Gen3 NPP-1 accident and early safety analysis showed that when there is a complete power outage, all safety systems are likely to fail due to common causes. Therefore, in order to ensure safety, Gen3 NPPs need to be equipped with a passive waste heat removal system that can operate without electricity.

[0004] Russian Federation Patent RU2050025 discloses a nuclear reactor emergency cooling system, including a reactor, a circulation pipeline, a steam generator with a tube bundle, a feed pipeline of an electric feed pump, a steam pipeline with a quick shut-off valve and a safety valve, an emergency heat exhaust pipe, a cooling tank with a surface condenser, a bubbling device, an overflow pipeline and a cooling circuit, a drainage pipeline, and an emergency valve with a passive control device. In the event of a complete power failure, the system uses passive cooling to urgently exhaust heat from the nuclear reactor, wherein the steam is started through a condenser located in the cooling tank. The passive control device opens the emergency valve and then opens the condenser. The passive control device will only start when the nuclear reactor is completely powered off. In order to prevent the emergency valve from opening when it is powered on, its control device is provided with an auxiliary element to prevent it from opening.

[0005] Russian Federation Patent RU2646859 discloses a passive waste heat removal system, comprising a heat exchange heater and a heat exchange cooler interconnected by a lifting branch pipe, and a storage tank connected to the downcomer by a pipeline. The system is also provided with a non-condensable gas collection container, which is connected to the downcomer between the heat exchange cooler and the storage tank. A check valve is provided between the storage tank and the non-condensable gas collection container, and a control valve is provided between the check valve and the heat exchange cooler. In the event of a coolant loss accident, the technical solution can improve the reliability of the passive waste heat removal system and the safety of the nuclear reactor.

[0006] In order to improve operational reliability, Russian Federation Patent RU2713747 discloses a passive waste heat removal system, comprising a circulation loop, the loop comprising a steam generator with a steam container and a water volume, the steam container and the water volume are connected through a cooling medium supply pipe and a discharge pipe, the cooling medium supply pipe and the discharge pipe are provided with an active-passive stop valve, and an air heat exchanger. The passive waste heat removal system also includes a thermoelectric generator, a gas collector connected to the air heat exchanger via a cooling medium supply pipe, a Dewar container, and a circulation pump connected to the cooling medium discharge pipe led out of the air heat exchanger.

[0007] Russian Federation Patent RU2740786 discloses a passive waste heat removal system, including a steam generator, a steam-water ejector, a heat exchanger, a storage tank and a start-up tank, wherein the steam generator is provided with a steam branch and a water branch; the heat exchanger is arranged below the steam generator and is cooled by a final heat sink; the storage tank is arranged above the steam generator, connected to the steam generator via a water branch with a shut-off valve, connected to the supply pipe of the heat exchanger via a supply branch, and its top container is connected to the steam branch of the steam generator by an auxiliary branch; and the start-up tank is arranged above the steam-water ejector, and its top is connected to the supply pipe of the heat exchanger. The water branch of the steam generator is connected to the side of the storage tank, and its horizontal position corresponds to the horizontal position of the steam-water ejector, and at the position where the steam branch is connected to the inlet of the steam-water ejector, the auxiliary branch of the storage tank is connected to the steam branch of the steam generator. The invention improves the reliability and duration of waste heat removal, as well as the operational safety of the nuclear reactor, and the waste heat enters the steam generator in a passive mode after passing through the heat exchanger, without time limit and without the need for external energy.

[0008] A passive waste heat removal system is also disclosed, which was developed for a VVER-1200 reactor (AES-2006) used in the Novovoronezh and Leningrad nuclear power plant projects (hereinafter referred to as "NVNPP-2" and "LNPP-2", respectively). In both cases, cooling is performed by means of a steam generator, when the water in the steam generator boils, the steam formed therein condenses in a cooling heat exchanger, and the condensed water formed enters the water volume of the steam generator under the effect of gravity.

[0009] For NVNPP-2, the cooling heat exchanger of the passive waste heat removal system behind the protective shell is cooled in the annular enclosure by natural circulation of the atmosphere (see: "Russian Nuclear Power" No. 4, April 2008, pp. 20-27). In this case, there is no time limit for the non-interference period.

[0010] For LNPP-2, the steam is condensed by an emergency cooling heat exchanger immersed in an emergency heat removal tank, which is located in the annular enclosure behind the protective shell (see: "Russian Nuclear Power" No. 4, April 2008, pp. 28-33). The condensed steam is discharged through the evaporation of water in the emergency heat removal tank, and the steam is discharged to the atmosphere. In this case, due to the limited water capacity of the emergency heat removal tank, the non-interference period is time-limited.

[0011] Since the presence of water in the steam generator is a necessary condition for the passive waste heat removal system to operate through the steam generator, the standby quick shut-off valve discharges steam from the steam generator and supplies water to it. The quick shut-off valve will only be activated when the water supply to the steam generator is stopped or the energy unit is powered off.

[0012] At the same time, the above-mentioned disclosed technical solution can only be used in a nuclear reactor device with water coolant in the primary circuit. Since the waste heat removal power decreases during the cooling process, the water boiling / steam condensation temperature is still 100°C at atmospheric pressure, which is significantly higher than the water solidification and freezing temperature, thereby preventing equipment damage.

[0013] This technical solution shall not be used in reactor devices with heavy liquid metal coolant in the primary circuit. This is because, during the cooling process, when the steam pressure drops and the water boiling temperature drops below the melting (solidification) temperature of the heavy liquid metal coolant, the waste heat removal power decreases and the heavy liquid metal coolant may solidify in the steam generator. This will in turn cause the heavy liquid metal coolant to stop circulating and dissipating heat.

[0014] Heavy liquid metal coolants are lead-bismuth alloys composed of various compositions with different bismuth contents, and their melting / solidification temperatures mainly depend on the bismuth content. For the eutectic alloy with a bismuth content of 56.5%, the melting temperature is the lowest, at 123.5°C; when the bismuth content is reduced to 40%, 30% and 20%, the melting temperature rises to 180°C, 230°C and 270°C respectively; for pure lead, the melting temperature is 327°C (see: Handbook of Lead and Lead-Bi Eutectic Alloys: Properties, Material Compatibility, Thermal Hydraulics and Technology, 2015 edition, Nuclear Energy Agency of the Organization for Economic Cooperation and Development (OECD NEA), No. 7268, Nuclear Energy). At atmospheric pressure, these temperatures exceed the boiling / steam condensation temperature of water (100°C). The reduction in the bismuth content of the heavy liquid metal coolant also leads to a decrease in its value, but in this case, increasing the melting temperature of the heavy liquid metal coolant will complicate operation, and this mode will also increase the possibility of solidification of the heavy liquid metal coolant when normal operating conditions are disrupted.

[0015] For the above reasons, the passive residual heat removal system for the European Lead-cooled Demonstration Fast Reactor (ALFRED) (see: "European Lead-cooled Commercial Fast Reactor (ELFR) and Lead-cooled Demonstration Fast Reactor (ALFRED)", Alessandro Alemberti, Luigi Mansani, Monica Frogheri and Ansaldo Nucleare, Italy, "Heavy Liquid Metal Coolants in Nuclear Technology (HLMT-2013)" Proceedings of the 4th International Conference, Obninsk, September 23-26, 2013, Conference Proceedings, Volume 1 (of 2 volumes), page 92, State Scientific Center of the Russian Federation - Leipunsky Institute of Physics and Power Engineering (SSC RF-IPPE), Obninsk, 2014, ISBN 978-5-906512-39-0 (Volume 1)) can cause the lead heavy liquid metal coolant in the steam generator to solidify and stop the residual heat removal.

[0016] In order to prevent the heavy liquid metal coolant from solidifying in the steam generator and to ensure that the steam condensation pressure in the cooling heat exchanger does not fall below the required value when the residual heat removal power decreases, the condensation temperature should be lower than the melting temperature of the heavy liquid metal coolant. In addition, to achieve the above objectives and to prevent thermal shock to the steam generator tube sheet, when the passive residual heat removal system of the once-through steam generator switches from standby mode to operating mode, if there is no circulation in the loop from the steam generator to the cooling heat exchanger, it is necessary to prevent condensate from entering the steam generator from the cooling heat exchanger. To prevent these adverse effects, appropriate technical solutions should be adopted in combination with the operating mode of the once-through steam generator.

[0017] In addition, when there is no heat generation in the reactor core and the secondary circuit of the reactor plant is in a dry state, in order to enable the passive residual heat removal system of the once-through steam generator to enter the operating mode, an appropriate amount of water must be added to prevent the heavy liquid metal coolant in the steam generator from solidifying.

[0018] Therefore, there is currently a problem of developing a passive residual heat removal system for a once-through steam generator, taking into account the characteristics of the operating mode of the once-through steam generator. The operation should be applicable to a reactor plant with a heavy liquid metal coolant. At the same time, when the input power decreases, especially when the steam condensation surface in the cooling heat exchanger is detected to decrease, the temperature of the condensate at the outlet of the cooling heat exchanger should be prevented from decreasing.

[0019] The technical effect of the present invention is to improve the operational safety of a nuclear reactor with a heavy liquid metal coolant and a once-through steam generator and the efficiency of the passive residual heat removal system in the absence of an external power source. Summary of the Invention

[0020] In order to solve the problems faced and achieve the above technical effects, it is proposed to set a steam separator below the tank of the passive waste heat removal system but above the steam generator, and to set a cooling heat exchanger below the water level in the tank. The cooling heat exchanger operates as a steam condenser. The steam separator is used to separate the steam-water mixture produced by the nuclear reactor in the cooling mode. The superheated steam produced by the steam generator enters the cooling mode through the pipeline. When the nuclear reactor is powered off and the quick shut-off valves on the steam pipeline and the water supply pipeline are closed, the steam (steam-water mixture) will enter the steam separator along the exhaust pipeline. In view of the transient process during the emergency shutdown of the reactor, including the final rate of reactor power reduction and the waste heat removal power, the rated (maximum) power of the cooling heat exchanger is determined. The power value does not exceed 10% of the rated power.

[0021] After the passive waste heat removal system is in operation, the steam generator switches to the steam-water mixture generation mode. The loop circulation is realized by natural convection, and the loop includes the steam generator, the steam separator, the downcomer pipe section containing the boiler water from the steam separator, and the upcomer pipe section containing the steam-water mixture entering the steam separator. In this case, in order to operate the above loop and close the quick stop valve at the same time, the valve on the pipe section between the steam separator and the water supply pipe after the quick stop valve should be opened.

[0022] In this case, the steam separated from the top of the steam separator will enter the top inlet of the cooling heat exchanger. A cut-off regulating device is installed on the condensate discharge pipeline from the steam generator to the cooling heat exchanger for discharging condensate, and its working mechanism (valve) moves, for example, under the action of a force difference, and the force is formed by the steam pressure and the spring in the cut-off regulating device. The spring force is adjusted in the following way: when the steam pressure drops below a set value, which varies depending on the bismuth content and the solidification temperature of the heavy liquid metal coolant, the valve of the cut-off regulating device is completely closed, and the condensate fills the entire shell or tube side of the cooling heat exchanger. Subsequently, the steam condenses and the heat removal stops, and the waste heat removal power without the need to organize the heat removal is achieved. When the waste heat removal power is reached, it is necessary to switch to another mode-heat maintenance mode, which can start the reactor external heating system and perform drying or other required measures on the steam generator.

[0023] When the residual heat removal power in the reactor is at an intermediate level, the condensed water in the cooling heat exchanger partially fills the shell side or the tube side, so that the remaining heat exchange surface can condense the incoming steam and ensure the required output power level while maintaining the steam pressure setting value and the corresponding saturation temperature, which exceeds the solidification temperature setting value of the heavy liquid metal coolant, thereby preventing the heavy liquid metal coolant from solidifying during the cooling process. In this case, in the steam generator loop, a mobile boost is formed due to the difference between the water cavity on the downlink section of the loop and the steam-water mixture cavity on the uplink section of the loop, and under the action of the mobile boost, the steam separator generates a natural circulation.

[0024] In order to ensure the stability of transient processes, it is preferred that the water level in the steam separator does not change significantly during operation. The initial (prepared for operation) water volume in the steam separator should be greater than the sum of the water volume in the cooling heat exchanger with the downcomer and the capacity of the upcomer from the steam generator to the steam separator. The reserved water capacity can cope with the most unfavorable operating conditions of the entire system, that is, the cooling heat exchanger operates at the highest production efficiency in the cooling mode and the steam generator operates at the power generation level in the direct current mode. The second extreme case is that the cooling heat exchanger operates at the minimum power, at which time it is full of water, the evaporation is the lowest, and the steam content of the upcomer from the steam generator to the steam separator is the lowest. In addition, in the first case, the stored and condensed water must not exceed a certain part of the steam separator (for example, half the capacity); in the second case, the water level must not be lower than the drain pipe of the cooling heat exchanger.

[0025] The condensed water after the cut-off regulating device is mixed with the separated water to form boiler water. The boiler water enters the water supply pipe and the inlet of the steam generator from the bottom of the steam separator along the pipeline (with a cut-off valve that opens after power failure).

[0026] Since the shut-off valve on the water supply pipe from the steam separator to the steam generator is closed in standby mode (energy operation mode of the nuclear reactor), the steam in the steam separator will condense due to the heat loss of the insulation. Since the steam separator is connected to the superheated steam pipe through the pipe, the pressure in the steam separator will be close to the pressure of the superheated steam. Condensation will occur at the same pressure, and the temperature of the condensed water will be equal to the saturation temperature at the pressure of the superheated steam. The heat loss of the steam separator will cause the incoming superheated steam to condense continuously, so the heat loss power will be equal to the product of the condensed water flow rate and the enthalpy difference between the superheated steam and water in the steam separator. Considering the limited nature of the heat loss, the condensed water flow rate will not exceed 1%, which is an acceptable value. At the same time, the free capacity of the steam separator and the pipe will continuously decrease and gradually cool down until it drops to the ambient temperature. This may cause thermal shock when the passive waste heat removal system starts to operate and the heavy liquid metal coolant in the steam generator freezes. In order to prevent these adverse conditions, in standby mode, the water temperature in the steam separator should be higher than the solidification temperature of the heavy liquid metal coolant. Furthermore, in order to keep the passive waste heat removal system in standby mode and ready to switch to cooling mode, a set water level should be maintained in the steam separator.

[0027] In order to achieve the above purpose, it is proposed to discharge the condensed water accumulated in the steam separator through an overflow pipe provided in the steam separator in the standby mode, and the overflow pipe is provided with a top opening at a desired water level. The overflow pipe is sealed at the bottom of the steam separator, and its bottom end is connected to a condensed water drainer. The condensed water discharged from the condensed water drainer flows into a condensed water supply pipe through a pipe with a stop valve, for example, into a high-pressure heater.

[0028] In order to prevent the water temperature in the steam separator from dropping, a heat exchanger is provided at a position below the water level of the overflow pipe, through which the supply water flows out. The heat exchanger can ensure that the water temperature in the steam separator is close to the water temperature of the supply water, so that no thermal shock occurs when the supply water is disconnected and switched to the water supply mode from the steam separator to the steam generator.

[0029] Thus, two technical problems are solved at the same time: ensuring the required water level in the steam separator and ensuring the water temperature in standby mode.

[0030] Specifically, the passive waste heat removal system through the steam generator according to the present invention is mainly used for nuclear reactors with heavy liquid metal coolants, including: a direct-flow steam generator, a steam separator and a pipeline connecting the direct-flow steam generator and the steam separator, the steam separator is equipped with a heat exchanger heated by supply water and is arranged below the water level of the overflow pipe; a cooling heat exchanger, located above the steam separator, for condensing steam; a pipeline for supplying steam from the steam separator to the cooling heat exchanger; a pipeline for discharging condensed water from the steam outlet pipeline to the steam separator; a quick shut-off valve, located in the pipeline for discharging steam from the steam generator on and on a water supply pipe for supplying water to the steam generator; a water supply pipe for supplying water to the steam generator; a condensate heat removal device, which is used to discharge condensation heat from the cooling heat exchanger to a final heat sink, for example, to a tank of a passive waste heat removal system located above the steam separator; a stop valve, which is located on a boiler water supply pipe of a water supply pipe from the steam separator to the steam generator; and an overflow heat exchange pipe, which is located in the steam separator, has an open top end above the water level when the steam separator is in standby mode, and is connected to, for example, a condensate drainer at an outlet of the steam separator.

[0031] The condensate level in the cooling heat exchanger determines its production efficiency and waste heat removal power. Therefore, a direct-acting pressure cut-off regulator is installed on the pipe that discharges the condensate from the cooling heat exchanger to adjust the flow of the condensate according to the pressure in the circuit. The cooling heat exchanger has a variable production efficiency in terms of steam condensation rate, and accordingly, the steam generator also has a variable production efficiency in terms of input power, because the condensate level can be maintained in the cooling heat exchanger, which can completely or partially close the heat exchange surface that condenses the steam.

[0032] The pressure direct-acting cut-off adjustment device, together with the cooling heat exchanger with output power (based on the condensate water level) feedback, forms a heat rejection device regulator based on the pressure in the system, which is based on the passive principle. In this case, the cut-off adjustment device can also enter the closed state by providing water supply pressure through a dedicated pipeline and / or by forcibly moving the valve stem by using an electromagnet, so that reducing the water supply pressure or disconnecting the electromagnet will cause the cut-off adjustment device to enter the state of a pressure regulator.

[0033] When programming algorithms for safe control of reactor installations, the above characteristics of the cut-off regulating devices can be taken into account for the most dangerous initiating events, such as power failure or water supply failure.

[0034] The passive waste heat removal system through the steam generator according to the present invention can only operate when there is a sufficient volume of water in the steam generator. Therefore, a spare quick shut-off valve is installed on the pipe for discharging steam from the steam generator and on the water supply pipe for supplying water to the steam generator. The same shut-off valve is installed on the nuclear reactor of the VVER nuclear power plant. Under normal operating conditions, the passive waste heat removal system through the steam generator is in standby mode. Under the action of the water pressure of the water supply pump and / or the electromagnet, the valve of the shut-off regulating device may be forced to close, so that the shut-off valve located on the water supply pipe from the steam separator is closed. In all modes, the condensate drainer only discharges excess water and prevents steam from being discharged from the steam separator above the overflow pipe.

[0035] In cooling mode, when the steam generator is disconnected from the turbine system by pipe fittings, the steam in the steam separator enters the cooling heat exchanger, and the condensed water formed in the cooling heat exchanger enters the tank at the bottom of the steam separator through the cut-off regulating device, where it mixes with the separated water, the saturation temperature of which is significantly higher than the solidification temperature of the heavy liquid metal coolant, and enters from the steam generator inlet in the form of boiler water. This prevents thermal shock to the steam generator tube sheet when the passive waste heat removal system is put into operation.

[0036] The production efficiency of the steam generator is related to the condensate level in it. At the highest condensate level and when the heat exchange surface is completely submerged, the output power of the cooling heat exchanger is the lowest, which is mainly determined by the level of heat losses. When the condensate level is below the level of the heat exchange surface, the production efficiency of the cooling heat exchanger is the highest.

[0037] The water chamber and the valve stem of the cut-off regulating device are hydraulically and mechanically connected by a bellows assembly with an adjusting spring. The cut-off regulating device can be operated in a passive mode because when the steam pressure rises, the force acting on the valve of the cut-off regulating device is greater than the force of the adjusting spring, causing the valve stem to move and the valve to open.

[0038] The tank of the passive waste heat removal system can use a special steel container or the volume of a corresponding process room of the reactor building, the walls and bottom partitions of which are lined with water-corrosion-resistant stainless steel metal.

[0039] A cooling water heat exchanger may also be provided in the tank of the passive waste heat removal system, and the cooling water heat exchanger may actively cool the reactor without being connected to a turbine device.

[0040] The present invention also provides a method for filling a working medium into a passive waste heat removal system through a steam generator, which solves the problems faced and can achieve the above technical effects. According to the method, when the temperature is higher than the melting temperature of the heavy liquid metal coolant, the steam supply valve of the secondary circuit with the dry steam generator is opened, and steam is supplied at a supply pressure exceeding the saturation pressure setting value, for example, steam is supplied from the startup boiler room, and the saturation pressure corresponds to the temperature of the heavy liquid metal coolant provided by the heating system. At the same time, the steam pressure should be lower than the opening pressure of the valve of the cut-off regulating device. When the water level in the steam separator reaches the set value according to the water level indicator, or when the temperature of the condensate discharge pipe of the condensate discharger rises to the steam saturation temperature at the secondary circuit pressure, the steam supply valve is closed. In this case, the water in the tank of the passive waste heat removal system has a significantly lower temperature, the cooling heat exchanger is cooled by the water in the tank, and the heat loss of the steam separator is significantly lower than the heat exchange of the cooling heat exchanger, so the water in the cooling heat exchanger is condensed first. Therefore, the condensed water first fills the cooling heat exchanger and then fills the water volume in the steam separator. When the turbine unit is cold, water from the condensate drain is discharged through the cooler to the process condenser.

[0041] The invention will be explained in more detail below with reference to the accompanying drawings, which show possible embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram showing a passive waste heat removal system through a steam generator according to the present invention is shown;

[0043] Figure 2a An embodiment of a cut-off regulating device in a start-up mode is shown;

[0044] Figure 2b An embodiment of a cut-off regulating device in energy mode is shown;

[0045] Figure 2c An embodiment of a cut-off adjustment device in cooling mode is shown;

[0046] Figure 2d An embodiment of a cutoff adjustment device with a pulse tube in cooling mode is shown;

[0047] Figure 3 A schematic diagram (plan view) of a tank showing a passive waste heat removal system in the form of a fuel storage tank; and

[0048] Figure 4 A schematic diagram (longitudinal section) of a tank showing a passive waste heat removal system in the form of a fuel storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The following reference numerals are used to indicate the elements:

[0051] 1 – Steam generator (ПГ)

[0052] 2 – Steam Separator

[0053] 3-Cooling heat exchanger (TP)

[0054] 4 – Slot for the passive waste heat removal system (СПOT)

[0055] 5 – Superheated steam pipe

[0056] 6-Condensate discharge pipe for cooling heat exchanger

[0057] 7-Quick shut-off valve (БЗΟК)

[0058] 8 – Pipeline supplying steam from the steam separator to the cooling heat exchanger

[0059] 9 – Boiler water heating heat exchanger

[0060] 10 – Stop valve

[0061] 11 – Separator overflow pipe

[0062] 12 – Condensate drain

[0063] 13 – Water supply pipe for steam separator

[0064] 14 – Condensate drain pipe for condensate drain

[0065] 15 – Pipe for introducing superheated steam into the separator

[0066] 16 – Water supply pipeline

[0067] 17-Overvoltage protection device

[0068] 18-Cut-off adjustment device (UZP)

[0069] 19 – Electric Drive

[0070] 20 – Valve stem

[0071] 21 – Spring

[0072] 22 – Bellows

[0073] 23 – Valve

[0074] 24 – Water Cavity

[0075] 25 – Channel

[0076] 26 – Pulse Tube

[0077] 27–Flow direction of water supply pipes

[0078] 28 – Flow direction from cooling heat exchanger (TP)

[0079] 29 – Pipeline for supplying steam from the startup boiler room (ПΡК)

[0080] 30 – Check valve and stop valve for steam supply from the startup boiler room (IPK)

[0081] 31-Cooling water heat exchanger (TOB)

[0082] 32 – Metal lining DETAILED DESCRIPTION

[0083] The passive waste heat removal system by a once-through steam generator according to the invention is mainly used in nuclear reactors with heavy liquid metal coolants, such as Figure 1 shown.

[0084] In general, the passive waste heat removal system through the once-through steam generator includes: a steam generator 1 operating in once-through mode; a steam separator 2; a superheated steam pipe 5; a water supply pipe 16; a cooling heat exchanger 3, located above the steam separator 2 in the tank 4 of the passive waste heat removal system; a pipe 8 for supplying steam from the steam separator to the cooling heat exchanger 3; a condensate discharge pipe 6 for discharging condensate from the cooling heat exchanger 3 to the steam separator 2; and a quick shut-off valve 7, located on the superheated steam discharge pipe 5 from the steam generator 1 and the water supply pipe 16 for supplying water to the steam generator 1. In this case, a pressure direct-acting shut-off regulating device 18 is installed on the condensate discharge pipe 6, and the shut-off regulating device can enter the closed state under normal operating conditions and in the energy mode by means of the water supply pressure or mechanical action of the valve stem (for example, using an electromagnet). For the secondary circuit of overpressure protection, an overpressure protection device 17 must be provided, and its composition is usually specified by safety standards and specifications.

[0085] When the steam generator 1 is operated in the once-through mode, superheated steam is generated in the steam generator 1 under the heat supply from the primary circuit coolant and enters the turbine device. At this time, the stop valve 10 on the water supply pipe 13 from the steam separator is closed. The feed water heats the boiler water in the steam separator 2 through the heat exchanger 9 in the steam separator 2 until its temperature is close to the feed water temperature. However, not all the feed water flow is used to heat the boiler water, but only a part of it. In this case, part of the feed water enters the main water supply pipe, flows along the bypass pipe to the heat exchanger, and then merges with the main water flow and flows to the steam generator 1. Part of the superheated steam enters the steam separator 2 along the pipe 15, where it is condensed to compensate for the heat loss of the steam separator 2. When the condensate water level exceeds the water level of the overflow pipe 11, the excess condensate flows to the condensate drain 12 located below the steam separator 2, and the condensate flows from here along the pipe 14 to the steam turbine system. If the overflow pipe 11 and the pipe connecting the overflow pipe 1 to the condensate drain 12 become dry, the condensate drain 12 ensures that the pipe 14 in which it is installed is closed. In cooling mode, when the steam generator 1 is disconnected from the turbine system by means of the quick shut-off valve 7, the shut-off valve 10 is opened, the steam in the steam separator 2 enters the cooling heat exchanger 3, which is immersed in the water in the tank 4 of the passive waste heat removal system, and the condensate formed in the cooling heat exchanger 3 passes through the pipe 6 and the shut-off regulating device 18 into the water volume at the bottom of the steam separator 2, where it mixes with the separated water, the saturation temperature of which is significantly higher than the melting temperature of the heavy liquid metal coolant, and then the mixed water enters the inlet of the steam generator 1 along the boiler water pipe 13. This prevents thermal shock to the tube sheet of the steam generator 1.

[0086] In the steam separator 2 , water is separated from the steam-water mixture and flows into the bottom of the steam separator 2 under the action of gravity, while the dry saturated steam enters the cooling heat exchanger 3 .

[0087] Figure 1 The solid arrows in the figure indicate the coolant flow direction when the nuclear reactor is operating normally, and the dashed arrows indicate the coolant flow direction after the passive residual heat removal system is put into operation. The crossed dashed arrows indicate that there is no coolant flow when the passive residual heat removal system is put into operation.

[0088] The embodiment of the cut-off adjustment device 18 and its operating mode are shown in Figure 2a , Figure 2b , Figure 2c and Figure 2d .

[0089] In startup mode ( Figure 2a), when the turbine unit is disconnected by the quick shut-off valve 7, the electric drive 19 moves the valve stem 20 to a position corresponding to the adjustment of the spring 21 and the bellows 22 to a set steam pressure, which is different for heavy liquid metal coolants with different melting temperatures. The position of the valve 23 of the shut-off regulating device is determined by the pressure in the water chamber 24, which is transmitted to the bellows 22 via the pipe 25. In this case, when the waste heat removal power is low, the valve 23 is completely closed ( Figure 2b ), when the maximum design power of the passive waste heat removal system is reached, the valve is fully opened ( Figure 2c According to a preferred but non-mandatory implementation example of the passive waste heat removal system through the steam generator, when the water supply pump is running, the cut-off regulating device 18 can be closed by the water supply pressure transmitted by the pulse tube 26, such as Figure 2d As shown. The valve 23 can also be moved down to the closed position by the action of a specially designed electromagnet (not shown in the figure). In this case, it is very important from a safety point of view to activate the valve 23 of the cut-off regulating device by an active command to de-energize the electromagnet, or to passively activate the valve in the event of a power failure.

[0090] When the reactor power is higher than the highest design power in the passive residual heat removal system and the standby turbine unit, the turbine unit is disconnected from the reactor unit through the quick shut-off valve 7, and the electric drive 19 moves the valve stem 20 to the following position: the position ensures that the steam pressure rises to a value that can start the power supply. Subsequently, the quick shut-off valve 7 is opened, and steam enters the turbine unit (not shown in the figure) and is discharged into the condenser of the turbine unit. When the reactor power level reaches a value that the turbine generator can withstand the load, the steam is stopped from being discharged to the condenser, and steam that meets the required parameters is delivered to the turbine.

[0091] In energy mode (standby mode), the valve 23 is in the state of being powered by the spring 21 and by the pulse tube 26 ( Figure 2d ) is closed under the action of the water supply pump pressure transmitted, or the valve is closed under the action of the above-mentioned spring and the force transmitted from the electromagnet to the valve stem 20.

[0092] In cooling mode ( Figure 2c ), the valve stem 20 is located at a position corresponding to adjusting the spring 21 and the bellows 22 to the steam pressure, which ensures that the valve 23 is fully open, and the valve position corresponds to the design power of the passive waste heat removal system through the steam generator. When the waste heat removal power decreases, the valve 23 is completely closed. For heavy liquid metal coolants with different melting temperatures, the steam pressure is also different. The position of the valve 23 is determined by the difference between the spring force of the spring 21 and the pressure in the water chamber 24, which is transmitted to the bellows 22 via the channel 25 (and the gap between the cut-off adjustment device 18 and the valve stem 20).

[0093] Figure 2a , 2b The arrow 27 in 2c and 2d indicates the direction of the pipe 6 for discharging condensed water from the cooling heat exchanger, and the arrow 28 indicates the flow direction from the cut-off adjustment device 18.

[0094] The passive waste heat removal system through the steam generator according to the present invention operates in the following manner.

[0095] When the water supply pump stops, the quick shut-off valve 7 is closed; the water pressure of the valve that closes the shut-off regulating device 18 drops, or a command is issued to cut off the power to the valve solenoid, the valve of the shut-off regulating device 18 is fully opened, the shut-off valve 10 is opened, and the passive waste heat removal system starts to operate.

[0096] As the waste heat removal power decreases, the steam pressure decreases accordingly. In this case, under the action of the spring 21, the valve 23 is partially closed to ensure that the steam pressure exceeds the opening / closing pressure of the valve 23. The smaller the excess value, the less the flow of condensed water. As the flow of the valve 23 decreases, the water level of the condensed water in the cooling heat exchanger 3 increases. In this case, the contact surface area between the steam and the heat exchange surface of the cooling heat exchanger 3 decreases, resulting in a slowdown in the condensation rate of the steam released from the steam separator 2, thereby slowing down the decrease in the steam pressure and water boiling temperature in the steam generator 1, preventing the solidification temperature of the heavy liquid metal coolant from approaching.

[0097] During the cooling process, when the residual heat removal power decreases and the steam pressure decreases accordingly and is lower than the set value, the valve 23 is completely closed. In this case, the heating system of the reactor device should be started. The heating system maintains the heavy liquid metal coolant in a liquid state when the residual heat removal power is low.

[0098] The water chamber 24 is hydraulically and mechanically connected to the valve stem 20 by the spring 21 and the bellows 22, and the cut-off regulating device 18 can operate in a passive mode, because when the steam pressure drops, the waste heat removal power drops, and the force acting on the valve 23 is lower than the force of the spring 21, causing the valve stem 20 to move and the valve 23 to close. Subsequently, the water level in the cooling heat exchanger 3 rises, and the performance of the cooling heat exchanger 3 decreases. According to the waste heat removal power and the condensed water temperature in the corresponding cooling circuit, the passive pressure regulation principle is passively realized to prevent the temperature from dropping below the melting temperature set value of the heavy liquid metal coolant.

[0099] It is also possible to use the passive waste heat removal system trough 4 (similar to LNPP-2) or the atmosphere (similar to NVNPP-2) as the final heat sink. Using the atmosphere as the final heat sink ensures that the non-intervention time is unlimited. However, due to the low efficiency of air heat removal, the large house space required and the large amount of metal consumption of heat exchange equipment, the project cost of this solution is relatively expensive.

[0100] When there is no heat generation in the reactor core and the secondary circuit of the reactor plant is in a dry state, the following method is adopted to make the passive residual heat removal system passing through the steam generator enter the working mode, while preventing the solidification of the heavy liquid metal coolant in the reactor plant with a once-through steam generator.

[0101] The heated heavy liquid metal coolant enters the secondary circuit of the dry steam generator 1 from the primary circuit of the reactor plant heating system, and supplies steam to the secondary circuit. For example, it is supplied through the check valve and stop valve 30 for supplying steam from the startup boiler room, via the pipeline 29 for supplying steam from the startup boiler room, as Figure 1 shown by the arrow in.

[0102] The pressure of the steam discharged from the startup boiler room should exceed the set value of the saturation pressure of the heavy liquid metal coolant, and the saturation pressure corresponds to the temperature of the heavy liquid metal coolant provided by the heating system. At the same time, the steam pressure should be lower than the opening pressure of the valve 23. The incoming steam is gradually condensed, and the water level in the water chamber of the secondary circuit gradually rises. When the water level in the steam separator 2 reaches the design value, the supply of steam is stopped. For example, the design value is set by the water level indicator or determined according to the temperature of the condensed water discharged from the condensate discharger 12.

[0103] In addition to the cooling heat exchanger 3, a cooling water heat exchanger 31 can also be provided in the water volume of the tank 4 of the passive residual heat removal system. In the normal operation mode of a conventional self-cooling reactor, the cooling water heat exchanger can also use the passive residual heat removal system passing through the steam generator without using a turbine device.

[0104] The tank 4 of the passive residual heat removal system can be made of a separate metal structure.

[0105] The tank 4 of the passive residual heat removal system can also be in the form of a reinforced concrete pool ( Figure 3 and 4 ), and the reinforced concrete pool belongs to the process room of the reactor building and is located at the same elevation as the reactor plant building, just like when the tank 4 of the passive residual heat removal system is made of a separate metal structure. The tank 4 of such a passive residual heat removal system is similar to the spent fuel assembly storage pool and has a metal lining 32. Due to the more effective use of the house space, such a technical solution improves the compactness of the passive residual heat removal system and also increases the water capacity of the tank 4 of the passive residual heat removal system, extending the non-intervention time.

[0106] Therefore, the present invention improves the operational safety of the nuclear reactor and the efficiency of the passive residual heat removal system when there is no external power supply.

Claims

1. A passive residual heat removal system through a steam generator, mainly used for nuclear reactors with heavy liquid metal coolant, comprising: a once-through steam generator; a tank of the passive residual heat removal system, located above the steam generator and having a free water level; a cooling heat exchanger, located below the water level in the tank of the passive residual heat removal system; a pipe connecting from the tank of the passive residual heat removal system to the atmosphere for discharging steam; a cooling water heat exchanger, located below the water level in the tank of the passive residual heat removal system, for transferring the condensation heat of the steam in the cooling heat exchanger to the ultimate heat sink; and quick closing valves, located on the steam outlet pipe of the steam generator and the water supply pipe of the steam generator, wherein, a steam separator is provided at a position below the tank of the passive residual heat removal system but above the steam generator to supply steam from the top of the steam separator to the top of the cooling heat exchanger through a pipe, a branch is led out from the steam outlet pipe of the steam generator to conduct steam to the steam separator, a pressure direct-acting stop and regulating device is installed on the condensate discharge pipe of the cooling heat exchanger, the condensate discharge pipe after the stop and regulating device is connected to the lower part of the steam separator, the lower part of the steam separator is connected to the water supply pipe through a pipe with a stop valve, an overflow pipe is provided in the water volume of the steam separator, the overflow pipe is sealed at the bottom of the separator, the top opening of the overflow pipe is located at the water level of the steam separator in the standby mode, and the bottom of the overflow pipe is connected to a condensate discharger, and a heat exchanger is provided in the steam separator at a position lower than the condensate discharger, and the water supply flows through the heat exchanger.

2. The system according to claim 1, wherein, the stop and regulating device includes a spring and a device for adjusting the spring force, and the device ensures that the stop and regulating device is in a closed state under normal operating conditions through the water supply pressure and / or a solenoid valve.

3. The system according to claim 2, wherein, the stop and regulating device hydraulically and mechanically connects the water chamber and the valve stem of the stop and regulating device by using a bellows assembly with a spring to operate in the passive mode, so that when the steam pressure rises, the force acting on the valve of the stop and regulating device is greater than the spring force, causing the valve stem to move and the valve to open.

4. The system according to claim 1, wherein, the tank of the passive residual heat removal system uses the volume of the corresponding process chamber of the reactor building, and the walls and bottom partitions of the process chamber have a stainless steel metal lining resistant to water corrosion.

5. The system according to any one of claims 1 to 3, wherein, the stop and regulating device is designed to be able to turn the valve of the stop and regulating device into a fully closed state under normal operating conditions and in the energy mode through the water supply pressure, and when the water supply stops, turn the valve of the stop and regulating device into a mode of regulating the flow rate and system pressure of the stop and regulating device.

6. The system according to any one of claims 2 to 5, wherein, The cut-off regulating device comprises at least one bellows, which separates the valve stem of the cut-off regulating device from the outside, and the spring applies force to the valve stem of the cut-off regulating device through the end element of the bellows, and the spring force is selected so that the valve of the cut-off regulating device opens when the pressure exceeds a preset value.

7. A system according to any one of claims 2 to 6, It is characterized in that The device for adjusting the spring force is used to change the opening pressure.

8. A system according to any one of claims 2 to 7, It is characterized in that The cut-off adjusting device has an inner cavity, which is defined by a housing of the cut-off adjusting device and a bellows that applies force to the valve stem of the cut-off adjusting device. The inner cavity is connected to the water supply pipe. When there is pressure in the water supply pipe, the water supply pressure is transmitted to the inner cavity, so that the bellows is compressed, the valve stem of the cut-off adjusting device moves, and the valve is closed.

9. The system according to any one of claims 2 to 8, It is characterized in that The cut-off regulating device is equipped with a valve stem driven by an electromagnet, and the electromagnet is used to keep the valve stem of the cut-off regulating device in a closed state. When the electromagnet is powered off, the holding force from the electromagnet is released.

10. A method for filling a working medium into a passive waste heat removal system through a steam generator according to any one of claims 1 to 9, It is characterized in that The steam supply valve is opened to supply steam to the secondary circuit with the dry steam generator. The steam pressure exceeds the saturation pressure corresponding to a specific value above the melting temperature of the heavy liquid metal coolant. The saturation pressure exceeds the saturation pressure corresponding to the temperature of the heavy liquid metal coolant provided by the heating system, but is lower than the opening pressure of the valve of the cut-off regulating device. When the water level in the steam separator reaches the set value, the steam supply valve is closed.

11. The method according to claim 10, It is characterized in that The condensation of the steam is carried out in the tubes of the cooling heat exchanger, and the cooling heat exchanger is cooled by the external environment outside the tubes.

12. The method according to claim 11, It is characterized in that The condensation of the steam is carried out on the outer surface of the tubes of the cooling heat exchanger, and a cooling medium is supplied into the tubes.

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