RU2761108C1 - Passive heat discharge system of the reactor plant - Google Patents

Abstract

FIELD: nuclear energy.

SUBSTANCE: invention relates to the field of nuclear energy and is a passive system designed to remove heat from the reactor and the steam generator when the power supply is cut off, including emergency sources, both in normal and emergency modes of operation without electricity consumption. The system includes a once-through steam generator with a steam branch, shut-off and non-return valves installed on pipelines, a jet apparatus, a heat exchanger connected by a supply pipeline to the outlet of a steam-water jet apparatus, and a discharge pipeline to the inlet of the latter. A starting tank is installed with the possibility of placing in it a supply of water under pressure and in a volume that ensures that the pipelines of the system and its devices are filled with water in the initial and/or emergency modes of operation. In the path for introducing the cooling medium from the starting tank into the steam-water jet apparatus, two non-return valves are installed in parallel and oppositely directed, one of which is made of a magnetic type with a structurally specified hysteresis to ensure the operation of the system in an emergency mode.

EFFECT: invention improves the efficiency and reliability of the passive heat removal system in the process of cooling down a nuclear power plant in an extreme situation.

2 cl, 1 dwg

Description

The passive heat removal system of a reactor plant belongs to the field of nuclear power and is a passive system designed to remove heat from the reactor and the steam generator in the event of a power outage, including emergency sources, both in normal and emergency operation without power consumption.

A system is known according to the patent RU No. 150816 dated 06/03/2014, which contains a direct-flow steam generator, the steam and water branches of which are connected to the water storage tank, the upper part of which is connected with a supply pipeline to the heat exchanger, the steam branch is connected to the water storage tank below the water volume level, and on the inlet section of the pipeline, a jet pump is installed, which is connected at the inlet with the water storage tank, and at the outlet with the heat exchanger, which is connected with a discharge pipeline equipped with a check valve, to the bottom of the water storage tank, in addition, the jet pump is connected at the inlet with an additional branch to the discharge a pipeline located between the check valve and the lower part of the water storage tank, and a starting tank equipped with a starting valve is connected between the outlet of the jet pump and the heat exchanger.

The disadvantage of this system is that the opening of the shut-off and start valves must occur simultaneously, because if the start valve opens later, then it is not known after what period of time or by what signal. But with the simultaneous opening of these valves, water is first displaced from the water seal into the water storage tank, and only then the hot steam-water mixture enters and the water storage tank and its steam volume begin to warm up.

In addition, it is known that jet pumps have a limited range of operating parameters and are switched off with a significant decrease in steam flow and pressure. Meanwhile, in the emergency heat removal system, as the power of the residual heat release decreases, the steam capacity of the steam generator and the steam pressure significantly decrease. This causes the jet pump to stop working. However, since the starting tank during the first start-up and long-term operation thereafter will be completely filled with water, the secondary start of circulation in the system after the increase in steam pressure and emergency heat removal will be impossible.

The closest technical solution is an emergency heat removal system according to RU patent No. 2732857 dated 09.23.2020.

The passive heat removal system contains a direct-flow steam generator, the steam branch of which is equipped with a shut-off valve, is connected to a steam-water injector, and the water branch, also equipped with a shut-off valve, is connected to the lower part of the water storage tank, the water storage tank, located above the direct-flow steam generator, the upper part of which is connected an additional branch with a steam branch, and the lower part is divided by a partition into two sections, a water storage section connected to a water branch and a stable water level section, which are combined in the upper part of the water storage tank volume, a steam-water injector located at the level of the upper edge of the tank partition water supply, a heat exchanger connected by an inlet pipeline equipped with a check valve with the outlet of a steam-water injector, and a outlet pipeline with an inlet of a steam-water injector, a starting tank located above the steam-water injector and connected by a supply line with a section of the supply pipeline heat exchange The line between the steam-water injector and the non-return valve and the outlet branch with the inlet branch of the water storage tank.

The disadvantage of this system is that the cooling medium in the starting tank is under low pressure, as a result of which there is a possibility of dehumidification of the steam generator, the amount of water in which at the time of cooldown can be arbitrary, therefore, an intermediate water storage tank is installed in the system. In addition, the spatial location of the starting tank depends on the height of the steam generator.

The technical result of the proposed device is to increase the efficiency and reliability of the passive heat removal system in the process of cooling a nuclear power plant in an extreme situation by optimizing the design and ensuring the autonomy of the system using only the internal energy of the steam of the system itself.

The technical result is achieved by the fact that the proposed system contains:

- a steam generator, the steam branch of which is equipped with two shut-off valves, one of which is non-returnable, is connected to the steam-water jet apparatus, and the water one, also with two shut-off valves installed on it, is connected to the inlet branch of the heat exchanger;

- a starting tank, which by two supply branches, with one shut-off valve installed on each of them, is connected to the high-pressure gas system and to the make-up system, and the outlet branch, with two parallel non-return valves installed on it, one of which is made of magnetic , connected to the outlet branch of the steam-water jet apparatus having a non-return valve;

- a heat exchanger connected by the inlet branch to the outlet branch of the steam-water jet apparatus, and by the outlet branch connected to the inlet of the steam-water jet apparatus.

In this case, the volume of water in the starting tank is under an excess pressure in relation to the steam generator, sufficient for its initial filling with water. The initial volume of water in the starting tank must be greater than the volume of the connected steam generator by the amount necessary to prevent the ingress of high pressure gases into the steam-water jet apparatus and the main pipelines of the system.

The level of the cooling medium in the starting tank is not maintained, it is dynamic, since the starting tank operates in the volumetric expansion compensator mode, but not continuous, but periodic, and, which is very important, the location of the starting tank is not structurally related to the place where the steam generator is installed.

The pressure of the air cushion in the launch tank, created by high-pressure gases, is 15 MPa, which is sufficient to displace water from the launch tank and fill the steam generator when the emergency protection is triggered with the standard load of the nuclear reactor.

In the path for introducing the cooling medium from the starting tank into the steam-water jet apparatus, two non-return valves are installed in parallel and oppositely directed, one of which is magnetic with a structurally specified hysteresis to ensure the operation of the system in an emergency capacity or slightly more than the pressure in the system due to the pressure drop across one of them during cooldown with a steam-water jet apparatus, or slightly less by the value of the constructive drop in the opening of the other valve before restarting the emergency cooldown system.

The shut-off valves installed on the steam and water branches of the steam generator work to disconnect the system from the steam generator and, when they are opened in emergency and normal situations, ensure the simultaneous start of the steam-water jet apparatus and the beginning of water circulation through the heat exchanger without the need to warm up the system.

The proposed system of passive heat removal from the reactor plant ensures stable circulation of the coolant through the steam generator without the use of external energy sources for an unlimited time.

A feature of this system is the use of a magnetic non-return valve, which has a structurally incorporated pressure drop for opening, that is, when a predetermined pressure drop across the valve is reached, it opens to the maximum throughput, and closes, when the differential decreases to a certain value, the valve closes completely. The difference between the opening and closing pressure differences determines the design hysteresis of the valve. The fact is that the thermal processes occurring at the second stage of cooldown are slow current, and the flow rate of the coolant in the start-up tank may not be sufficient for the independent start-up of a steam-water jet apparatus (PVSA), therefore, to intensify the start-up, it is necessary to introduce some imbalance or some instability into the system , caused, for example, by the delay in opening of the installed magnetic non-return valve with a structurally incorporated hysteresis. In the case of a spring-loaded valve, the flow rate increases slowly with increasing pressure drop. The characteristic of the magnetic valve has the opposite character - the maximum force corresponds to the locked state, when the valve is detached from the seat, the magnetic interaction decreases sharply, causing an "avalanche" opening of the valve, thereby intensifying the flow of the cooling medium through the PVSA and making it easier to start.

In contrast to systems with natural circulation in passive heat removal systems, in this case, the relative position of the system elements in the gravity field does not matter, since it is not required to ensure the maximum driving pressure of the cooling medium.

The system also has redundant shut-off valves, which meets the safety requirements of the unit.

The proposed technical solution is presented on:

FIG. 1 is a diagram of a passive heat removal system.

The system is designed for a power of 7% of the nominal power of the installation and combines a steam generator 1, shut-off valves 2, a steam-water jet apparatus 3, a starting tank 4, a water-water heat exchanger 5, redundant shut-off valves 6, non-return valves 7, 8, and 9, magnetic non-return valve 10.

The passive heat removal system works as follows. In the initial state, valves 2 are closed, tank 4 is partially filled with water, and the initial volume in the starting tank should exceed the volume of water when filling a completely empty steam generator by the volume of water required to prevent the ingress of high-pressure gases into the jet apparatus and the circuit line. The pressure in the container is determined by the pressure of the gas cushion and is about 15 MPa. Due to the location of the container 4 above the connecting pipelines of the circuit, these pipelines, the heat exchanger 5 and the jet apparatus 3 are filled with water, which remained after carrying out hydraulic tests when checking the operability of all systems when the installation was put into operation. The system is always in a ready state.

At the signal of emergency protection of the steam generator 1, valves 6 cut off the steam generator from the turbine unit (STU) and at the same time valves 2 open and the system is connected to the steam generator 1. Valve 8 is closed and water from tank 4 flows through open non-return valves 9 and 7 partially into the heat exchanger, from the outlet which is then fed to the jet apparatus, partially through valve 2 through the feed pipeline, into the steam generator 1. The steam generator is filled with cold water and the pressure in the system is equalized, while the pressure in the starting tank and the rest of the circuit is also the same, and the water level in the starting tank will correspond to the initial level minus the amount of water entering the steam generator. There is no differential across valve 10.

The first stage of the cooldown process ends after filling the steam generator and equalizing the pressure in the system. The water level in the starting tank 4 corresponds to the initial level in the tank minus the amount of water supplied to the steam generator 1. The differential on the magnetic non-return valve 10 is negative, the non-return valve 9 is closed due to the pressure drop.

Due to the heat transfer from the coolant of the main loop of the reactor plant, the water temperature in the steam generator 1 increases, and its boiling begins. The non-return valve 8 opens, and the steam-water mixture from the steam generator 1 flows through the steam-water jet apparatus 3 and the open magnetic non-return valve 10 into the starting tank 4. At the same time, the water through the valve 7, the heat exchanger 5 is directed to the inlet nozzle of the steam-water jet apparatus 3. Gradually, the moisture of the mixture decreases, those. at the exit from the steam generator 1, the amount of moisture decreases, and the amount of steam becomes larger, the steam-water jet apparatus 3 starts up and the second stage of cooling begins, which will continue until the steam generator 1 is completely filled with cold (cooled) water. At the same time, initially, after starting the steam-water jet apparatus 3, the level in the starting tank 4 may increase if the pressure difference across the steam generator 1 is greater than the pressure difference required to open the magnetic non-return valve 10. Extraction of steam from the steam generator 1 for condensation in the circuit and feeding the steam generator 1 with cold water will reduce the pressure in the system. In this case, through the valve 9, the starting container 4 will "return" water to the system.

If the steam-water jet apparatus 3 stops and the circulation stops, then the restarting process will be repeated at a lower pressure in the circuit, but with the same structurally specified differential on the magnetic non-return valve 10. In this case, water is pumped through the steam generator 1 and through the heat exchanger 5 with a steam-water jet apparatus 3, and the starting capacity 4 acts as a volume compensator.

If the energy supplied from the primary circuit coolant is insufficient for the complete evaporation of the incoming water from the system, the steam generator 1 is gradually filled with water, and when it is completely filled, the circulation in the cooling system stops.

The final state of the system is that steam generator 1 is completely filled with water, the reactor is cold, all heat release is compensated by heat losses to the environment, there is no circulation, a minimum water level remains in the starting tank 4, which does not allow air to enter the system mains.

Claims (2)

1. The system of passive heat removal from the reactor plant, including a straight-through steam generator with a steam branch, shut-off and non-return valves installed on pipelines, a jet apparatus, a heat exchanger connected by a supply pipeline to the outlet of a steam-water jet apparatus, and by a discharge pipeline to the inlet of the latter, a starting capacity that differs the fact that the starting tank is made with the possibility of placing in it a supply of water under pressure and in a volume that ensures that the pipelines of the system and its devices are filled with water in the initial and / or emergency modes of operation, are installed in parallel in the path of entering the cooling medium from the starting tank into the steam-water jet apparatus and oppositely directed two non-return valves, one of which is made of a magnetic type with a structurally specified hysteresis to ensure the operation of the system in emergency mode. 2. The system according to claim 1, characterized in that the elements of the system in the gravity field are structurally located regardless of their location relative to each other.

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