Method for controlling hydrogen content in primary loop of nuclear power unit

Abstract

The present invention relates to a method for controlling hydrogen content in the primary circuit of a nuclear power plant, comprising the following steps: S1. Within a first period before the reactor reaches subcriticality, starting a coolant degassing subsystem to dehydrogenate the primary circuit, and controlling the coolant degassing subsystem to stop operation when the temperature reaches a first preset range; S2. From the first period before the reactor reaches subcriticality until the primary circuit is thermally shut down, controlling the pressurizer of the primary circuit to intermittently purge; S3. From the primary circuit thermal shutdown until the primary circuit is connected to a RIS system, maintaining continuous pressurizer purge and controlling the coolant degassing subsystem to dehydrogenate the primary circuit; S4. After the RIS system is connected until the pressurizer begins purging the chamber, isolating the pressurizer to purge the circuit; S5. From the pressurizer beginning to purging the chamber until the primary circuit temperature reaches a first temperature, starting the coolant degassing subsystem to continuously dehydrogenate the primary circuit. The present invention can continuously reduce the hydrogen content in the primary circuit with high degassing efficiency; it is also easy to control and can reduce the workload of the operator.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear power, and in particular to a method for controlling hydrogen content in a primary circuit of a nuclear power unit. Background Art

[0002] Since the RIS system of the nuclear power unit is an oxygen-containing system, the dissolved H2 in the previous circuit connected to the RIS system needs to maintain a certain concentration to consume the introduced oxygen and ensure that the oxygen content in the first circuit does not exceed the standard. However, the dissolved H2 cannot be too high to avoid increasing the time required for subsequent units to remove hydrogen and meet the prerequisites for oxidation purification.

[0003] The related technology increases the pressure in the control box to raise the liquid level in the control box; then exhausts the gas to the TEG system to reduce the pressure; and then slowly lowers the liquid level to introduce new nitrogen. Because the hydrogen removal capacity of a single operation is limited, the above steps need to be repeated multiple times, and generally the above operations need to be completed manually by the operator. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a convenient and efficient method for controlling the hydrogen content in the primary circuit of a nuclear power unit.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing a method for controlling the hydrogen content in the primary circuit of a nuclear power plant, wherein the nuclear power plant includes a coolant degassing subsystem and an RCV system, wherein the coolant degassing subsystem is used to receive the downstream flow of the RCV system and perform degassing, and the coolant degassing subsystem and the RCV system are respectively connected to the primary circuit; the method for controlling the hydrogen content in the primary circuit of the nuclear power plant includes the following steps:

[0006] S1. Within a first period before the reactor reaches subcriticality, start the coolant degassing subsystem to remove hydrogen from the primary circuit, control the hydrogen content of the primary circuit to be within a first preset range, and control the coolant degassing subsystem to stop operating when the hydrogen content reaches the first preset range;

[0007] S2: From the first moment before the reactor reaches subcriticality to the thermal shutdown of the primary circuit, control the primary circuit's pressurizer to perform intermittent purges; and control the primary circuit's hydrogen content within a second preset range;

[0008] S3. Before the primary circuit is hot-shut down and the RIS system of the primary circuit is connected, the pressurizer is continuously purged and the coolant degassing subsystem is controlled to remove hydrogen from the primary circuit; when the hydrogen content of the primary circuit is within a third preset range, the pressurizer is controlled to stop purging and the coolant degassing subsystem is stopped;

[0009] S4, after the RIS system is connected and before the pressurizer starts to extinguish the gas chamber, the pressurizer purge circuit is isolated and the coolant degassing subsystem remains shut down;

[0010] S5. Control the pressurizer to start extinguishing the gas chamber until the temperature of the first circuit reaches the first temperature, start the coolant degassing subsystem to continuously remove hydrogen from the first circuit, control the hydrogen content of the first circuit to be within a fourth preset range, and prepare the first circuit for oxidation treatment.

[0011] Preferably, the step S1 further comprises controlling the pressurizer to be purged within a first time before the reactor becomes subcritical, so as to remove hydrogen from the primary circuit.

[0012] Preferably, the third preset range is 5 ml / kg to 7 ml / kg.

[0013] Preferably, the fourth preset range is less than or equal to 3 ml / kg.

[0014] Preferably, the step S5 further includes the following steps:

[0015] S6. If the temperature of the first circuit is not higher than the first temperature and the hydrogen content of the first circuit is less than or equal to 3 ml / kg, the coolant degassing subsystem is shut down and the first circuit starts to add chemicals for oxidation treatment.

[0016] Preferably, the step S6 further includes the following steps:

[0017] S7. After the dosing of the first circuit is completed, the coolant degassing subsystem is started again to control the coolant in the first circuit to reach the chemical condition of the first circuit opening.

[0018] Preferably, the dosing operation of the first circuit is controlled to be carried out simultaneously with the heating of the first circuit, and the oxygen content of the first circuit is controlled to be qualified before the temperature of the first circuit is heated to 120°C.

[0019] Preferably, the chemical condition of the first loop opening is 133 Xe<900MBq / t, 131 I<200MBq / t.

[0020] Preferably, the coolant degassing subsystem includes an air compressor, a degassing tower and a heat exchanger assembly; the air compressor is controlled to draw a vacuum on the degassing tower, and the downstream flow is preheated by the heat exchanger assembly and then enters the degassing tower for degassing, and is recycled to the RCV system after degassing.

[0021] Preferably, the coolant degassing subsystem also includes a circulation pump, a heater and a delivery pump; the circulation pump and the heater are connected to the degassing tower, and the degassing tower degases the downstream flow through the circulation pump and the heater, and the downstream flow is recovered to the RCV system through the delivery pump after degassing.

[0022] The implementation of the present invention has the following beneficial effects: the method for controlling the hydrogen content in the primary circuit of a nuclear power unit of the present invention can continuously reduce the hydrogen content in the primary circuit with high degassing efficiency; at the same time, the control is convenient and the workload of the operator can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0024] Figure 1 Schematic diagram of the structure of the coolant degassing subsystem of the present invention;

[0025] Figure 2 The present invention is a flowchart of a method for controlling hydrogen content in a primary circuit of a nuclear power unit. DETAILED DESCRIPTION

[0026] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "back", "up", "down", "left", "right", "longitudinal", "horizontal", "vertical", "horizontal", "top", "bottom", "inside", "outside", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings and are constructed and operated in specific directions. They are only for the convenience of describing the technical solution and do not indicate that the devices or components referred to must have specific directions. Therefore, they should not be understood as limiting the present invention.

[0027] It should also be noted that, unless otherwise clearly specified and limited, terms such as "installed", "connected", "connected", "fixed", and "set" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or there may be one or more intervening elements. The terms "first", "second", "third", etc. are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0028] In the following description, specific details such as particular system structures and techniques are provided for purposes of illustration, not limitation, to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0029] It should be noted that the nuclear power unit in this embodiment includes an RCV system (control chemistry and volume control system) and a RIS system (safety injection system), and the RCV system and RIS system are respectively connected to the primary circuit of the nuclear power unit. The primary circuit maintains hydrogen coverage through the RCV system to ensure a sufficient reducing environment to suppress the radiolytic decomposition of water to produce oxidants. The RIS system integrates the original RIS system and the RRA system (residual heat removal system). Therefore, the RIS-RHR operation mode refers to the RIS system operating in a single-circuit residual heat removal mode. The RIS-RHR operation mode specifically refers to taking water from the hot section of the primary circuit, passing through a low-pressure injection pump, passing through a cooler, and finally returning to the primary circuit from the cold section of the primary circuit, thereby completing the primary circuit temperature control.

[0030] The hydrogen-oxygen reaction formula is 2H2+O2=2H2O. When the RIS-RHR system is connected, it is estimated that there will be about 21m 3 (The pipe volume of a RIS-RHR train is 10.5m 3 When the primary circuit is 180°C, oxygen-enriched water (two columns, A / B, are connected to the primary circuit) enters the primary circuit. The oxygen content in the water is approximately 9 mg / L, and the estimated hydrogen consumption is approximately (9*21*1000 / 32)*2*2 = 22,500 mg. Based on a primary circuit water load of 300 tons, this translates to approximately 0.07875 mg / kg, or 0.07875 / 0.089 = 0.8848 ml / kg (STP). Based on the volume dilution calculation after the RIS-RHR system is connected, the dissolved hydrogen content is approximately affected by 21 / 300 = 7%. According to chemical and radiochemical technical specifications and operational experience, the dissolved hydrogen content in the primary circuit should be maintained above 5 ml / kg (STP) before the RIS-RHR system is connected.

[0031] The nuclear power unit of the present invention comprises a coolant degassing subsystem and an RCV system, wherein the coolant degassing subsystem is used to receive the downflow of the RCV system and perform degassing; Figure 1As shown, in some embodiments, the coolant degassing subsystem includes an air compressor 1, a degassing tower 2, a heat exchanger assembly, a sealing liquid tank 4, a sealing water pump 5, a filter assembly 6, etc.; the air compressor 1 is connected to the heat exchanger assembly and is also connected to the degassing tower 2; in some embodiments, the heat exchanger assembly includes a first heat exchanger 31, a second heat exchanger 32, and a third heat exchanger 33; the filter assembly 6 includes a first filter 61 and a second filter 62. It is understandable that the number of heat exchangers and filters can be adjusted according to actual conditions and is not limited here. One end of the air compressor 1 passes through the sealing liquid tank 4, the sealing water pump 5, the first heat exchanger 31, the first filter 61, and is connected back to the air compressor 1 to form a loop; the other end of the air compressor 1 passes through the second filter 62, the first control valve 71, the second heat exchanger 32, and the third heat exchanger 33 to connect to the degassing tower 2. In this embodiment, water flows down from the RCV system, is preheated by the heat exchanger assembly 6, and then enters the degassing tower 2 for degassing. After passing through the degassing tower 2, the hydrogen content is very low. After degassing, the water is recycled back to the RCV system and finally enters the primary circuit. Furthermore, by controlling the air compressor 1 to draw a vacuum on the degassing tower 2, the boiling point of the coolant in the coolant degassing subsystem is relatively lowered, boiling at approximately 60°C. The negative pressure also facilitates gas diffusion, resulting in effective degassing. In some embodiments, the coolant degassing subsystem further includes a circulating pump 81, a heater 9, and a transfer pump 82; the circulating pump 81 and heater 82 are connected to the degassing tower 2. The degassing tower 2 degases the downflow through the circulating pump 81 and heater 82. After degassing, the downflow is recycled back to the RCV system via the transfer pump 82 and the second control valve 72. The coolant degassing subsystem can continuously reduce the hydrogen content of the primary circuit and has high degassing efficiency. At the same time, the coolant degassing subsystem is started and stopped according to the hydrogen content of the primary circuit, which is easy to control and can reduce the workload of the operator.

[0032] Figure 2 A method for controlling the hydrogen content in the primary circuit of a nuclear power plant according to an embodiment of the present invention is shown. The method for controlling the hydrogen content in the primary circuit of a nuclear power plant comprises the following steps:

[0033] S1. Within the first time before the reactor becomes subcritical, the coolant degassing subsystem is started to remove hydrogen from the primary circuit, and the hydrogen content of the primary circuit is controlled to be within a first preset range. When the first preset range is reached, the coolant degassing subsystem is controlled to stop operation. In some embodiments, in order to further dehydrogenate the primary circuit, a backup means can be started to control the primary circuit pressurizer purge to dehydrogenate the primary circuit together with the coolant degassing subsystem, so that the hydrogen content of the primary circuit reaches the desired value. In some embodiments, the first preset range is 20 to 25 ml / kg; and the hydrogen content is preferably controlled as close to 20 ml / kg as possible. In some embodiments, the first time before the reactor becomes subcritical can be 24 hours before the reactor becomes subcritical.

[0034] S2. From 24 hours before the reactor reaches subcriticality until the primary circuit is thermally shut down, the pressurizer of the primary circuit is controlled to be intermittently purged according to the actual H2 content of the primary circuit; the hydrogen content of the primary circuit is controlled to be within a second preset range; in some embodiments, the second preset range can be 15 to 25 ml / kg, and the hydrogen content is preferably controlled to be close to 15 ml / kg.

[0035] S3. Before the primary circuit is thermally shut down and connected to the RIS system of the primary circuit, start and maintain continuous purging of the pressurizer, and control the coolant degassing subsystem to dehydrogenate the primary circuit; control the RIS system to complete the connection when the primary circuit temperature is the second temperature, and can be controlled to operate in the RIS-RHR mode; the second temperature can be 180°C. When the hydrogen content of the primary circuit is within a third preset range, control the pressurizer to stop purging and the coolant degassing subsystem to stop operating. In some embodiments, the third preset range can be 5ml / kg to 7ml / kg, so the purge can be stopped when the hydrogen content of the primary circuit is close to 6ml / kg. At this time, the hydrogen content of the primary circuit is close to and higher than 5ml / kg.

[0036] After the S4 and RIS systems are connected and before the pressurizer is ready to start extinguishing the gas chamber, isolate the pressurizer purge circuit and keep the coolant degassing subsystem out of service. At this time, the hydrogen content in the primary circuit is controlled at 3-4 ml / kg.

[0037] S5. Control the pressurizer to begin extinguishing the gas chamber until the primary circuit temperature reaches a first temperature. The coolant degassing subsystem is then reactivated to continuously dehydrogenate the primary circuit, and the coolant degassing subsystem flow rate is adjusted based on the RCV system's downstream flow rate to continue dehydrogenating the primary circuit. This maintains the hydrogen content in the primary circuit within a fourth preset range, preparing the primary circuit for oxidation. In some embodiments, the first temperature may be 80°C, and the fourth preset range is less than or equal to 3 ml / kg. At this point, the dissolved hydrogen content in the primary circuit is kept as low as possible, ensuring that the dissolved hydrogen content in the primary circuit does not exceed 3 ml / kg before the primary circuit reaches 80°C. This creates the prerequisite for the subsequent addition of H2O2 to the chemical control platform below 80°C for primary circuit oxidation. During primary circuit maintenance outages, degassing using the coolant degassing subsystem offers advantages over traditional nitrogen purging in the control cabinet, resulting in higher efficiency and improved results, reducing operational processing time.

[0038] In some embodiments, step S5 further includes the following steps:

[0039] S6. When the temperature of one circuit is not higher than 80℃ and the hydrogen content of one circuit is less than or equal to 3ml / kg, stop the coolant degassing subsystem, start adding medicine in one circuit and perform oxidation treatment; start circulating purification in one circuit.

[0040] In some embodiments, step S6 further includes the following steps:

[0041] S7, the first circuit dosing is completed, the coolant degassing subsystem is restarted, and the first circuit purification platform (more than 20 hours time window) is used to control the first circuit coolant to reach the first circuit opening chemical condition. In some embodiments, the first circuit opening chemical condition is 133 Xe<900MBq / t, 131 I<200MBq / t.

[0042] In some embodiments, the chemical dosing window for primary deoxygenation has been optimized for the unit's run-up process. By controlling primary deoxygenation and heating simultaneously, and ensuring that oxygen content meets the required standards before the primary temperature reaches 120°C, this prepares for subsequent steam chamber construction in the primary pressurizer. This eliminates the requirement for oxygen content to meet the required standards before 90°C, saving approximately two hours on the critical path of the overhaul and optimizing the overhaul schedule.

[0043] It is understandable that the above embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, all of which fall within the scope of protection of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should fall within the scope of coverage of the claims of the present invention.

Claims

1. A method for controlling hydrogen content in a primary circuit of a nuclear power unit, characterized in that: The nuclear power unit includes a coolant degassing subsystem and an RCV system, wherein the coolant degassing subsystem is used to receive the downstream flow of the RCV system and perform degassing, and the coolant degassing subsystem and the RCV system are respectively connected to the primary circuit; the method for controlling the hydrogen content in the primary circuit of the nuclear power unit includes the following steps: S1. Within a first period before the reactor reaches subcriticality, start the coolant degassing subsystem to remove hydrogen from the primary circuit, control the hydrogen content of the primary circuit to be within a first preset range, and control the coolant degassing subsystem to stop operating when the hydrogen content reaches the first preset range; S2: From the first moment before the reactor reaches subcriticality to the thermal shutdown of the primary circuit, control the primary circuit's pressurizer to perform intermittent purges; and control the primary circuit's hydrogen content within a second preset range; S3. Before the primary circuit is hot-shut down and the RIS system of the primary circuit is connected, the pressurizer is continuously purged and the coolant degassing subsystem is controlled to remove hydrogen from the primary circuit; when the hydrogen content of the primary circuit is within a third preset range, the pressurizer is controlled to stop purging and the coolant degassing subsystem is stopped; S4, after the RIS system is connected and before the pressurizer starts to extinguish the gas chamber, the pressurizer purge circuit is isolated and the coolant degassing subsystem remains shut down; S5. Control the regulator to start extinguishing the gas chamber until the temperature of the first circuit reaches the first temperature, start the coolant degassing subsystem to continuously dehydrogenate the first circuit, and adjust the processing flow of the coolant degassing subsystem according to the downstream flow of the RCV system to continuously dehydrogenate the first circuit; control the hydrogen content of the first circuit to be within a fourth preset range, and prepare the first circuit for oxidation treatment.

2. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 1, characterized in that: The step S1 further includes controlling the pressurizer to purge within a first time before the reactor becomes subcritical, so as to remove hydrogen from a primary circuit.

3. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 1, characterized in that: The third preset range is 5 ml / kg to 7 ml / kg.

4. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 1, characterized in that: The fourth preset range is less than or equal to 3 ml / kg.

5. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 4, characterized in that: After step S5, the following steps are also included: S6. If the temperature of the first circuit is not higher than the first temperature and the hydrogen content of the first circuit is less than or equal to 3 ml / kg, the coolant degassing subsystem is shut down and the first circuit starts to add chemicals for oxidation treatment.

6. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 5, characterized in that: After step S6, the following steps are also included: S7. After the dosing of the first circuit is completed, the coolant degassing subsystem is started again to control the coolant in the first circuit to reach the chemical condition of the first circuit opening.

7. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 5, characterized in that: The dosing operation of the first circuit is controlled to be carried out simultaneously with the heating of the first circuit, and the oxygen content of the first circuit is controlled to be qualified before the temperature of the first circuit is heated to 120°C.

8. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 6, characterized in that: The chemical conditions for the primary circuit opening are: 133 Xe<900MBq / t, 131 I<200MBq / t.

9. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 1, characterized in that: The coolant degassing subsystem includes an air compressor, a degassing tower and a heat exchanger assembly; the air compressor is controlled to draw a vacuum on the degassing tower, and the downstream flow is preheated by the heat exchanger assembly and then enters the degassing tower for degassing, and is recycled to the RCV system after degassing.

10. The method for controlling hydrogen content in the primary circuit of a nuclear power plant according to claim 9, characterized in that: The coolant degassing subsystem also includes a circulation pump, a heater and a delivery pump; the circulation pump and the heater are connected to the degassing tower, and the degassing tower degases the downstream flow through the circulation pump and the heater. After degassing, the downstream flow is recovered to the RCV system through the delivery pump.

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