RU2794150C1 - Hydrogenation system for pressured water reactor and corresponding method - Google Patents

Abstract

FIELD: water-containing reactor.

SUBSTANCE: invention relates to a reactor (2) with pressurized water, as well as to a method for operating a reactor with pressurized water. The reactor uses a system (14) for monitoring the chemical water state of the reactor, containing a selection line (18) in the direction of the flow of the coolant of the primary circuit of the reactor, a high-pressure injection pump (32) with a given pressure at the outlet and an injection line (34) leading to the first circuit (4) of the reactor coolant. Moreover, the system (14) for controlling the chemical water state of the reactor also contains a hydrogenation system (16) with a hydrogen source (36) and a hydrogen supply line (38). A high-pressure feed pump (40) is located in the feed line (38) to provide a gas pressure that is higher than the outlet pressure of the pressure pump (32), with the feed line (38) leading to the pressure line (34).

EFFECT: efficient and fast supply of hydrogen to the primary reactor coolant circuit, with the ability to supply a precisely defined amount of hydrogen in a certain time.

8 cl, 4 dwg

Description

The present invention relates to a pressurized water reactor comprising a primary reactor coolant loop, an associated water chemistry control system, and an associated hydrogenation system. The invention also relates to a corresponding method for operating a pressurized water reactor.

The pressurized water reactor comprises a first reactor coolant loop within which the primary reactor coolant circulates at high pressure. The water chemistry control system (CVCS) is hydraulically connected to the primary reactor coolant circuit. The CVCS contains a low pressure section that typically provides an entry or injection point for various fluids into the primary coolant of the reactor. In particular, it may be necessary to inject hydrogen into the reactor primary loop in order to, for example, bind dissolved oxygen.

EP 0 852 800 B1 describes a pressurized water reactor according to the preamble of paragraph 1 of the claims. In the described system, the hydrogen supply line exits to the low pressure section of the CVCS upstream of the high pressure discharge pump (i.e. on its suction side), thereby realizing a low pressure hydrogen supply (typical operating pressure: 3 bar).

In addition, wet chemistry systems exist for pumping hydrazine or hydrogen peroxide into low pressure lines.

The disadvantages of these approaches are usually associated with the limitation of the hydrogen supply rate. The feeding process is temporarily inert, and its effect is delayed in time. In addition, liquid chemical solutions may be toxic, malignant, corrosive, and/or generally harmful to the environment and personnel, and may not provide free hydrogen.

Therefore, the object underlying the present invention is to provide a pressurized water reactor with a hydrogenation system and an associated method of operation that are suitable for efficiently and rapidly supplying hydrogen to the primary coolant of the reactor. The device and associated process must be robust and resistant to disturbances. A modular and compact design is desirable.

In accordance with the invention, these problems are solved using a pressurized water reactor according to paragraph 1 of the claims. The corresponding method of operation is described in paragraph 7 of the claims.

Therefore, the key feature is that a high pressure feed pump is installed in the hydrogen gas feed line to provide a feed pressure higher than the outlet pressure (or outlet pressure) of the pressure pump for the primary coolant, and that the feed line exits into the pressure line, that is, at an injection point downstream of the pressure pump.

A proposed technical modification of the general approach is to create an active high pressure inlet instead of a passive inlet into the low pressure section of the system.

This design is based on the need to have a hydrogen supply system capable of supplying a precisely defined amount of hydrogen in a certain amount of time. In modern designs, the amount of hydrogen gas in the volume control tank (VCT) or in the gas separator depends on the plant design. In both cases, the maximum working pressure of the respective parts of the system varies from 1 to 4 bar (higher in the case of transients). For high pressure hydrogen supply in accordance with the present invention, the injection point is downstream of the high pressure positive displacement pumps. From a physics point of view, the advantage of introducing hydrogen is diffusion at a certain pressure for a certain time through a certain surface, while the pressure is about 40 times higher than for a low pressure injection.

Instead of passive mechanisms (eg, injection at a hydrogenation station or nebulizer in a VCT), it is preferable to use a reciprocating compressor to pressurize the gas in the pipeline to allow injection downstream of the high pressure positive displacement pumps.

The pressure control at the outlet of a reciprocating compressor must be limited by the operating conditions in the discharge line. Thanks to this design, the rate of the diffusion process is greatly increased due to the high pressure. Gas bubbles will be injected directly into the injection stream, where the hydrogen solubility is ~50 times higher than in the low pressure section of the system. This also makes it easier to control the hydrogenation process (ie, the waiting time for the control action is shorter).

Another advantage of the design is that nitrogen contamination will not occur to the same extent as in the case of low pressure injection through the hydrogenation station (with VCT connected and nitrogen purged). This limits the formation of C14 in the core, thereby limiting the amount of radioactive deposits.

In terms of time and cost, the important point is to reduce the time spent during start-up waiting for the increase in hydrogen concentration to reach 100% power mode.

The design can also be easily duplicated (provide redundancy) at any point to ensure high availability.

Thus, the present invention uses a high pressure feed pump, preferably a reciprocating compressor or a diaphragm compressor, to introduce hydrogen at any suitable CVCS location downstream of the pressure pump (which may be of any suitable type). This concept can also be formulated as backpressure-independent hydrogenation of the primary reactor coolant due to the generally lower primary reactor pressure compared to the feed pump and pressure pump discharge pressures.

It should be recalled that the proposed high pressure inlet with an inlet point located downstream of the pressure pump (typical outlet pressure 185 bar) provides, among other things, the following advantages:

- in addition to pipelines, there are no cavities containing gaseous hydrogen;

- hence less risk of explosion due to improved detection/prevention of leaks;

- hydrogen control with shorter response time;

- higher possible and more stable concentrations of hydrogen in the primary circuit of the reactor due to resistance to disturbances;

- inerting the VCT into the CVCS with nitrogen is no longer required;

- modular design.

The disadvantages are the need for a high pressure feed pump in the gas supply line and high hydrogen pressure in the supply line.

In a preferred embodiment of the invention, a check valve is located in the section of the supply line between the supply pump and the point of entry into the discharge line.

Preferably, the gas supply line comprises a double-walled pipe with a vacuum gap between the inner wall and the outer wall, the leak detection system being designed to monitor the pressure within the gap and, preferably, to isolate the leaking section of the pipeline.

In another preferred embodiment of the invention, the hydrogenation system comprises a control system with a hydrogen sensor that measures the hydrogen content of the primary reactor coolant in the injection line downstream of the injection point, the control system being configured to close the check valve if said measured hydrogen content is not corresponds to the set rate of hydrogen supply to the hydrogenation system.

In yet another preferred embodiment of the invention, the hydrogenation system comprises a control system with a hydrogen sensor that measures the hydrogen content of the primary reactor coolant in the extraction line, the control system being designed to control the hydrogen supply rate by setting the feed pump power based on the difference between said measured hydrogen content and a predetermined value of said hydrogen content.

Next, with reference to the accompanying drawings, examples of embodiments of the invention are discussed.

In FIG. 1 shows a schematic overview of a pressurized water reactor;

in fig. 2 - scheme of pipelines and instrumentation of the hydrogenation system connected to the control system of the water-chemistry regime of the pressurized water reactor;

in fig. 3 - block diagram of the corresponding control and measuring functions;

in fig. 4 is a leak detection system on a double wall pipe or tank for use in the system shown in FIG. 2.

As shown in FIG. 1, a pressurized water reactor (PWR) 2 comprises a first reactor coolant loop 4 through which the primary reactor coolant passes. The first reactor coolant circuit 4 comprises a nuclear reactor pressure vessel (RPV) 6, a blower 8, a steam generator 10 and a reactor coolant circulation pump (RCP) 12 . The steam generator 10 provides a thermal connection to the second reactor coolant loop. The volume, chemistry, and other physical properties of the circulating primary reactor coolant can be controlled by a reactor water chemistry control system (CVCS) 14 that is fluidly coupled to the primary reactor coolant loop 4. This is shown schematically in FIG. 1.

In FIG. 2 shows a simplified piping and instrumentation (P&ID) diagram of a hydrogenation system 16 connected to a PWR 2 CVCS 14 in a nuclear power plant (NPP). As explained above, the CVCS 14 is fluidly coupled to the first reactor coolant loop 4 of the PWR 2 to continuously withdraw the primary reactor coolant stream from the first reactor coolant loop 4, process it chemically and/or physically, and reinject it into the first reactor coolant loop 4 after said processing. Processing is typically performed at low pressure (eg 4 barg) compared to the high pressure in the primary reactor coolant loop 4 (eg 185 barg) during operation.

Through the withdrawal line 18, abbreviated as withdrawal, the flow of the coolant of the primary circuit of the low pressure reactor passes after depressurization by means of a pressure reducer (not shown here). To remove heat from the primary coolant flow of the reactor, a heat exchanger 20 is installed in the extraction line 18, through which the cooling medium passes (see the next paragraph). Downstream of the heat exchanger 20, the low pressure, low temperature reactor primary coolant passes through the main line 22 of the CVCS 14 and may be chemically and/or physically treated. The main line 22 can be considered as the downstream section of the line 18 selection. For example, if necessary, a boric acid supply line and/or a demineralized water supply line (not shown here) can be connected to the main line 22 to introduce boric acid and/or demineralized water into the primary reactor coolant stream. In addition, there is a tank 24 volume control (VCT), communicating with the main line 22 CVCS 14 and designed to work as a compensation tank. In addition, a fluid outlet line 28 may be connected to the VCT 24, for example, to facilitate the removal of gaseous wastes or in general for degassing.

Downstream of tee connection 30 to VCT 24 is a high pressure booster pump 32 connected to main line 22 to bring the pressure of the flowing primary reactor coolant back to a level corresponding to the first reactor coolant circuit 4 (for example, 185 barg), and reintroduce or inject it into said circuit or loop through the subsequent injection line 34. More specifically, in the example shown, there are two high pressure injection pumps 32 connected in parallel for redundancy. In addition, there is a heat exchanger 20 through which the heating medium passes and which is located in the discharge line 34 to increase the temperature of the coolant of the primary circuit of the reactor before entering the first circuit 4 of the reactor coolant. Preferably, the hot incoming primary reactor coolant passing through the withdrawal line 18 acts as a heating medium so that regenerative heating and cooling is achieved.

To facilitate the introduction of hydrogen (H ₂ ) into the primary coolant passing through the CVCS 14, a hydrogenation system 16 is provided in communication with the CVCS 14. In accordance with the invention, the hydrogenation system 16 is designed to introduce high pressure hydrogen into the high pressure primary coolant stream. reactor, passing through the injection line 34. For this, there is a supply 36 of hydrogen or a source of hydrogen, in particular an electrolytic cell or a hydrogen cylinder, providing hydrogen supply at low or medium pressure, for example 40 barg. The hydrogen (gas) supply line 38 extends from the hydrogen source 36 to the injection line 34, with the injection point located downstream of the injection pump(s) 32. A high pressure supply pump 40 is located in the supply line 38 to provide supply pressure, which slightly exceeds the outlet pressure of the discharge pump(s) 32 and thus exceeds the pressure prevailing in the discharge line 34.

In the preferred embodiment of the invention, there is an optional bypass line that bypasses the feed pump 40 and preferably leads to the exhaust system in case the check valve 44 is a solenoid valve and the feed pump diaphragm compressor 40 needs some time to prevent an increase pressure in the gas supply line 38 is higher than necessary and/or to prevent unnecessary pressure transients in the supply pump 40.

The connection between the supply line 38 and the discharge line 34, preferably a simple tee 42 or pipe, is preferably located on the section of the discharge line 34 located between the discharge pump(s) 32 and the heat exchanger 20. Check valve 44 located in the line 38 between feed pump 40 and tee 42, allows supply line 38 to be shut off regardless of the state of supply pump 40, thereby disconnecting hydrogenation system 16 from CVCS 14 and shutting off the flow of hydrogen to pressure line 34 if desired or required.

The feed pump 40 is preferably a reciprocating compressor or a diaphragm compressor, compressor 70 for short, preferably with a variable speed motor. This means that the pumping power and hence the hydrogen supply rate can be adjusted. The hydrogen feed rate is controlled by the pumping power by means of an appropriate control system 46 (see FIG. 3 and description below). Alternatively, based on compressor technology, a solution can be provided for control, comprising a control valve in the flow line 38 and additional devices. The control system 46 also regulates or controls the check valve 44. Therefore, the feed pump 40 and the check valve 44 can be considered as the executive objects of the hydrogenation system 16. A suitable control scheme will be described in more detail below.

Preferably, the connection from the low pressure hydrogen distribution to the feed pump 40 will be made adjacent to the tee connection 42 to the discharge line 34 in order to shorten the length of the high pressure piping. The connection is preferably located outside the reactor building to allow maintenance and reduce qualification requirements. In existing systems, there is no need for additional changes to the injection line 34, with the exception of the tee connection 42 to connect the gas supply line 38.

Downtime can be reduced by using a second (standby) compressor, allowing maintenance of the second discharge circuit while the plant is operating at full capacity. While currently VCT 24 can be easily used in any atmosphere, it can also be used as a degassing agent without affecting hydrogenation.

Sensory input to the control system 46 is provided by a number of hydrogen concentration sensors, abbreviated as hydrogen sensors or H ₂ sensors.

The first hydrogen sensor 48 is configured to measure the content or concentration of hydrogen in the low pressure, low temperature reactor primary coolant stream in the withdrawal line 18 or subsequent main line ₂₂ of the CVCS 14. selection." In the example shown, the measuring point is downstream of the heat exchanger 20 and upstream of the tee connection 30 with VCT 24. For practical reasons, measurements are preferably made in the main flow bypass. In other words, there is a short branch 50 running parallel to the main line 22, with the bypass inlet 52 and outlet 54 provided by tee connections so that the primary reactor coolant flow is diverted from the main flow and then recombined with it. The hydrogen sensor 48 is located either directly in said branch 50 or in a secondary branch.

The second hydrogen sensor 56 is designed to measure the hydrogen content or concentration in the high pressure but preferably low temperature primary reactor coolant stream within the injection line 34 downstream of the entry point of the hydrogenation system 16 (i.e. tee 42). It is also referred to as the discharge line sensor or "H ₂ discharge line sensor". In the example shown, the measurement point is upstream of the heat exchanger 20. Like the first hydrogen sensor 48, the second hydrogen sensor 56 may be located in a bypass from the main stream. That is, there may be a branch 58 extending from the injection line 34, so that the second hydrogen sensor 56 is located in the specified branch 58 or in the secondary branch. As shown in FIG. 2, branch 58 may lead to a low pressure section of main line 22 or to branch 50 with first hydrogen sensor 48, with its outlet preferably located downstream of first hydrogen sensor 48. In this way, a reverse flow of sampling is realized from the high pressure section to the low pressure section of the CVCS 14. A pressure reducing valve (not explicitly shown here) in the return flow line 60 compensates for different pressure levels.

Description of instrumentation functions and control concepts

The scheme of instrumentation and automation (KIPiA), presented in Fig. 3 shows the simplified logic that must be integrated to control the hydrogenation system 16. The equipment (in particular, sensors, valves, compressors) can also be integrated into own I&C stations or can be supplied with stand-alone I&C as a black box. The circuit input contains the H ₂ concentration setpoint and as many component feedback signals as required by the station operator. The I&C itself will be based on standard I&C components, so it will be easy to integrate into any existing I&C structure. Additional components, such as an electrolyzer as a source of hydrogen, can also be realized in a black box upon request.

measurements

As discussed above, there are preferably two real-time hydrogen metering devices, one connected to the extraction line 18 (including the subsequent main line 22) and the second to the injection line 34. The extraction line meter is located in the low pressure/temperature section of the CVCS 14 to physically simplify the interface for real-time measurement. Preferably, measurements are made in the bypass from the main stream. For reasons of availability at each location in injection line 34 and/or withdrawal line 18, hydrogen sensors 48, 56 may be implemented two or three times with simple voting logic providing, for example, a 1-of-2 or 2-of-3 signal.

Executive mechanisms

As discussed above, there are essentially two actuators in the design of the hydrogenation station. A reciprocating or diaphragm compressor 70 which is used as a feed pump 40 to pressurize hydrogen into the main pressure line 34 of the CVCS 14, and a check valve 44 located downstream of the compressor 70 and designed to serve as isolation functions for either normal operation or for limitation functions. Depending on the compressor technology, an additional control valve in the gas supply line 38 may be necessary or useful.

Control

The management of the hydrogenation system 16 is based on the measurement of hydrogen in the extraction line 18 . The hydrogen concentration in the withdrawal line 18 is essentially the same as in the primary reactor coolant circuit 4, provided that the main primary pumps (i.e. the reactor coolant pumps 12) are operating and therefore the primary reactor coolant circuit 4 is in a homogenized state. .

The setpoint (referred to as "Setpoint" in the diagram) of the hydrogenation system 16 is set by the operator as a constant and together with the concentration of H ₂ in the line 18 selection (H ₂ in the selection), the adjustable deviation is obtained by subtracting the concentration of H ₂ in the line 18 selection from setpoint (in fact, the setpoint is the target value in the main primary circuit). The PID controller 66 adjusts the reactivity of the control with variable gain control based on the difference between the setpoint and the hydrogen concentration measured in the extraction line 18 . The higher the deviation between the setpoint and the concentration of H ₂ in the line 18 selection, the more reactive the controller will be due to gain, which increases in proportion to the deviation.

The (speed-controlled) compressor 70 of the feed pump 40 is controlled by the PID controller 66. It is turned off by a pair of different signals, such as: closed check valve 44, sensor errors, reactor coolant pump (RCP) low pressure, or a high H ₂ signal. Check valve 44 operates in a similar manner.

The signal from the PID controller 66 to the compressor 70 is delayed to start the regulation compared to the check valve 44 open signal. In order not to have a continuous active control loop, the check valve 44 opens only in the event of a certain minimum control deviation. If regulation indicates that this step is not necessary, the limit can be set to 0.

Restrictions

In general, there is a "Maximum Concentration Reached" signal and a "Minimum Concentration Reached" signal, both of which are generated based on the measured hydrogen concentration in the extraction line 18 . To make the circuit more reliable in case the CVCS 14 sections are not working, it is also possible to receive an external signal from the sampling system.

The hydrogen sensor 48 in the extraction line 18 acts as an operating safety device to initiate hydrogenation in the event of post-load operation or other types of hydrogen concentration disturbances in the main primary system, or to terminate hydrogenation as soon as it is technically determined that concentration limits have been reached.

The hydrogen sensor 56 in the injection line 34 is used to check the possibility of input. If the concentration in the discharge line 34 does not increase within a predetermined time, despite the operation of the compressor 70, then the compressor 70 is turned off (for example, in the event of a supply line shutdown).

Operational safety

To ensure the necessary safety of the hydrogen-containing pipeline, it is preferable to use double-walled pipes 80 with a leak control system 82 for the supply line 38, in particular its high pressure section, located downstream of the supply pump 40. A schematic example is shown in FIG. 4. Under normal operating conditions, the space (gap) between inner wall 84 and outer wall 86 will be kept under vacuum by means of a small vacuum pump 90. should be detected by the appropriate pressure gauge 88, an alarm will be triggered allowing automatic action to be taken to isolate the pipe (wired signal from pressure gauge 88 and feed pump is preferred). In the event of such an alarm, the automatic action would include directly stopping the inlet reciprocating compressor 70, thereby limiting the amount of hydrogen in the double wall portion of the pipe.

List of reference positions

2 pressurized water reactor (PWR)

4 primary reactor coolant circuit

6 nuclear reactor pressure vessel (RPV)

8 supercharger

10 steam generator

12 reactor coolant pump (RCP)

14 reactor water chemistry control system (CVCS)

16 hydrogenation system

18 selection line

20 heat exchanger

22 main line

24 volume control tank (VCT)

26 liquid supply line

28 liquid outlet line

30 tee connection

32 pressure pump

34 injection line

36 source of hydrogen

38 gas supply line

40 feed pump

42 tee connection

44 stop valve

46 control system

48 hydrogen sensor

50 branch

52 input

54 exit

56 hydrogen sensor

58 branch

60 return line

66 PID controller

70 compressor

80 double wall pipe

82 leak control system

84 inner wall

86 outer wall

88 gauge

90 vacuum pump.

Claims (12)

1. Reactor (2) with water under pressure, containing the first loop (4) of the reactor coolant, through which the coolant of the first loop of the reactor flows during operation, and also containing the system (14) for controlling the water-chemistry mode of the reactor for the coolant of the first loop of the reactor, moreover, in the direction of the flow of the coolant of the first circuit of the reactor, the system (14) for monitoring the water-chemical regime of the reactor contains a line (18) of selection, a pressure pump (32) of high pressure with a given pressure at the outlet and an injection line (34) leading to the first circuit (4 ) reactor coolant, while the system (14) for monitoring the water-chemical regime of the reactor additionally contains a hydrogenation system (16) with a hydrogen source (36) and a hydrogen supply line (38), characterized in that a high-pressure supply pump (40) is located in the hydrogen supply line (38) to provide a gas pressure that is higher than the pressure at the outlet of the pressure pump (32), while the hydrogen supply line (38) goes into the discharge line ( 34), moreover, a heat exchanger (20) is located in the discharge line (34), designed to pass a heating medium through it, to increase the temperature of the coolant of the primary reactor circuit before entering the first circuit (4) of the reactor coolant, the connection between the hydrogen supply line (38) and the discharge line (34) is located in the section of the discharge line (34) located between the discharge pump (32) and the heat exchanger (20). 2. Pressurized water reactor (2) according to claim 1, wherein the feed pump (40) comprises a compressor. 3. Pressurized water reactor (2) according to claim 2, wherein the compressor is a reciprocating compressor or a diaphragm compressor. 4. Reactor (2) with pressurized water according to any one of paragraphs. 1-3, in which the shut-off valve (44) is located in the section of the supply line (38) between the supply pump (40) and the point of entry into the discharge line (34). 5. Pressurized water reactor (2) according to claim 4, wherein the hydrogen supply line (38) comprises a double wall tube (80) with a vacuum gap between the inner wall (84) and the outer wall (86), wherein the system leak detection is configured to monitor the pressure in the specified gap. 6. Pressurized water reactor (2) according to claim 4 or 5, which contains a control system (46) with a hydrogen sensor (56) that is configured to measure the hydrogen content in the primary coolant of the reactor in the injection line (34) below downstream from the injection point, wherein the control system (46) is configured to close the check valve (44) if said measured hydrogen content does not match the set hydrogen supply rate provided by the hydrogenation system (16). 7. Reactor (2) with pressurized water according to any one of paragraphs. 1-6, which contains a control system (46) with a hydrogen sensor (48), which is configured to measure the hydrogen content in the primary reactor coolant in the extraction line (18), while the control system (46) is configured to control the feed rate hydrogen by setting the power of the feed pump (40) based on the difference between said measured hydrogen content and the set value of said hydrogen content. 8. A method of operating a pressurized water reactor (2), wherein the pressurized water reactor (2) comprises a first reactor coolant loop (4) through which the reactor primary coolant flows during operation, as well as a water pressure control system (14). - the chemical regime of the reactor for the coolant of the primary circuit of the reactor, and in the direction of the flow of the coolant of the primary circuit of the reactor, the system (14) for monitoring the water-chemical regime of the reactor contains a line (18) of selection, a pressure pump (32) of high pressure with a given outlet pressure and a discharge line (34) leading to the primary circuit (4) of the reactor coolant, and in the discharge line (34) there is a heat exchanger (20) designed to pass the heating medium through it to increase the temperature of the coolant of the primary circuit of the reactor before entering the first circuit (4) reactor coolant, wherein the connection between the hydrogen supply line (38) and the discharge line (34) is located in the section of the discharge line (34) located between the injection pump (32) and the heat exchanger (20), moreover, the method includes the step of bringing the hydrogen pressure to a value above the pressure at the outlet of the pressure pump (32), and then introducing pressurized hydrogen into the primary coolant of the reactor through the injection line (34).

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