Device and method for monitoring leakage of heat transfer tube of lead-bismuth reactor steam generator

Abstract

The invention belongs to nuclear reactor steam generator heat transfer tube leakage monitoring, and particularly relates to a lead bismuth reactor steam generator heat transfer tube leakage monitoring device and method. In the invention, the interior of a reactor core is divided into an upper part and a lower part, the lower part is provided with a fuel rod, the fuel rod is immersed in a lead-bismuth alloy coolant, the lower part is a covering space, the interior is covering gas, a steam generator is communicated with the lower part of the reactor core to form a loop, the interior of the steam generator is a water loop, and the water loop is connected with a steam turbine. The turbine provides driving force through the generator; the high-temperature lead-bismuth alloy enters the steam generator, water in the water loop absorbs heat and is converted into steam, and the steam is cooled through the steam turbine; and the covering space is connected with the Po210 filter membrane through a pipeline to form a loop. According to the invention, the activity level and humidity of Po-210 in the covering gas are measured, the leakage of the heat transfer tube of the steam generator is rapidly identified through the measurement result, and a basis is provided for the subsequent safe operation of a reactor.

Description

Technical Field

[0001] This invention pertains to the monitoring of leaks in heat transfer tubes of nuclear reactor steam generators, specifically relating to a monitoring device and method for leaks in heat transfer tubes of lead-bismuth reactor steam generators. Background Technology

[0002] In lead-bismuth alloy reactors, Bi-209 is activated by neutrons to generate Bi-210, which then decays to produce Po-210. Po-210 is a radioactive nuclide unique to lead-bismuth reactors, an alpha emitter, and is extremely toxic with a strong ionizing ability. Po-210 can be ingested through inhalation, accidental ingestion, or skin contact, leading to internal contamination, poisoning, or acute radiation sickness. During the operation of lead-bismuth reactors, Po-210 must be confined within the reactor coolant system to minimize leakage of both the lead-bismuth coolant and Po-210.

[0003] In lead-bismuth reactors, a covering gas is typically installed above the coolant inside the vessel. The main functions of the covering gas include: inert gas protection, preventing air (oxygen, water vapor) from contacting the high-temperature lead-bismuth and avoiding oxidation or the generation of corrosive impurities; controlling oxygen concentration, by adjusting the oxygen partial pressure in the covering gas, the dissolved oxygen concentration in liquid lead-bismuth can be controlled, thereby inhibiting the corrosion of structural materials; and pressure regulation and safety buffering, the covering gas system can maintain the pressure stability of the reactor's primary loop system and provide buffer space under thermal expansion or transient conditions, preventing pressure fluctuations from causing mechanical stress to the equipment.

[0004] The steam generator is a key heat transfer device in the lead-bismuth cooled fast neutron reactor. It uses liquid lead-bismuth alloy (LBE) as the primary coolant and water as the secondary coolant. The steam generator facilitates heat exchange between the primary and secondary loops, converting water in the secondary loop into steam. As part of the primary loop system boundary, the steam generator also contains radioactive materials from the primary coolant. If a leak occurs in the steam generator, radioactive materials from the primary loop could leak into the secondary loop and further release into the environment. Therefore, it is necessary to implement measures to monitor steam generator leaks.

[0005] Leakage monitoring of heat transfer tubes in water-cooled reactor steam generators is primarily conducted by measuring the radioactivity in the secondary loop medium, including N-16 in the secondary loop steam, radioactivity in the wastewater, and radioactivity in the condenser exhaust. The radiation sources in the coolant system of a lead-bismuth reactor differ significantly from those in a water-cooled reactor. Furthermore, the pressure on the secondary side of the steam generator in a lead-bismuth reactor is significantly higher than that on the primary side. If a minor leak occurs, in the initial stage, water on the secondary side will leak into the lead-bismuth on the primary side, which is distinctly different from the leakage in a water-cooled reactor. Therefore, the methods used for monitoring heat transfer tube leaks in water-cooled reactor steam generators cannot be applied to monitor leaks in the heat transfer tubes of a lead-bismuth reactor steam generator.

[0006] Therefore, it is necessary to explore a monitoring method suitable for heat transfer tube leaks in lead-bismuth reactor steam generators, so that leaks in the steam generator can be detected as early as possible, thus supporting the safe operation of the reactor. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a monitoring device and method for leaks in the heat transfer tubes of a lead-bismuth reactor steam generator. The device measures the activity level and humidity of Po-210 in the covering gas, and quickly identifies leaks in the heat transfer tubes of the steam generator based on the measurement results, thus providing a basis for the safe operation of the reactor in the future.

[0008] The technical solution adopted in this invention is as follows:

[0009] A monitoring device for heat transfer tube leakage in a lead-bismuth reactor steam generator includes a reactor core, a steam generator, a turbine, a generator, and a gas humidity monitor. The reactor core is divided into upper and lower parts. The lower part contains fuel rods immersed in a lead-bismuth alloy coolant. The lower part is a covered space containing a covered gas. The steam generator is connected to the lower part of the reactor core to form a loop. The steam generator contains a water loop connected to the turbine, which is driven by the generator. High-temperature lead-bismuth alloy enters the steam generator, and the water in the water loop absorbs heat and is converted into steam, which is then cooled by the turbine. The covered space is connected to a Po210 filter membrane via pipes to form a loop.

[0010] The Po210 filter membrane is equipped with a gas humidity monitor and a gas pump at both ends, and the Po210 filter membrane is used in conjunction with an alpha activity detector.

[0011] A first valve is provided between the Po210 filter membrane and the gas humidity monitor, and a second valve is provided between the Po210 filter membrane and the gas pump.

[0012] A method for monitoring leakage in the heat transfer tubes of a lead-bismuth reactor steam generator includes the following steps:

[0013] Step 1: Determine the warning value for leakage in the heat transfer tubes of the steam generator;

[0014] Step 2: Gas sampling within the covered space;

[0015] Step 3: Gas measurement.

[0016] Step 1 includes the following steps:

[0017] Determine the generation of Po-210 in lead-bismuth coolant;

[0018] Determine the chemical speciation and distribution of Po-210 in the lead-bismuth coolant system during normal operation;

[0019] Determine the chemical morphology and distribution of Po-210 after a leak in the heat transfer tube of a steam generator.

[0020] The determination of the generation of Po-210 in the lead-bismuth coolant:

[0021] When lead-bismuth alloys are used as reactor coolants, Bi-209 in the alloy is activated by neutrons to generate Bi-210, which then decays to produce Po-210.

[0022]

[0023] Chemical speciation and distribution of Po-210 in the lead-bismuth coolant system during normal operation:

[0024] During lead-bismuth reactor operation, under normal oxygen-controlled conditions in the primary loop system, the chemical form of Po in lead-bismuth is mainly PbPo. PbPo has very low volatility, and Po-210 is mainly present in lead-bismuth, with only trace amounts of Po-210 entering the cover gas space.

[0025] Chemical speciation and distribution of Po-210 after leakage in the heat transfer tubes of the steam generator:

[0026] After a minor leak occurred in the heat transfer tube of the steam generator in the lead-bismuth reactor, water on the secondary side of the steam generator leaked into the lead-bismuth on the primary side under pressure and migrated with the lead-bismuth flow.

[0027] At high temperatures, the leaked water undergoes a chemical reaction with PbPo in lead and bismuth to form volatile Po.

[0028] Volatile Po enters the covering gas through lead and bismuth, resulting in a significant increase in the content of Po-210 in the covering gas;

[0029] Considering the changes in operating temperature, flow rate, and oxygen control conditions, a Po-210 activity of 1.0E10Bq was selected as the early warning value for leakage in the heat transfer tubes of the steam generator.

[0030] Step 2 specifically involves:

[0031] During reactor operation, the first valve, the second valve, and the gas pump of the sampling loop are opened sequentially at regular intervals. A certain amount of cover gas is extracted each time. The sampling gas flows through the Po-210 filter membrane, and the Po-210 in the sampling gas is retained on the filter membrane. During the sampling process, the humidity of the gas is measured using a gas humidity monitor. After the sampling is completed, the loop gas pump, the first valve, and the second valve are closed sequentially.

[0032] Step 3 specifically involves: using an α activity detector to measure the activity level of Po-210 in the Po-210 filter membrane; if the activity of Po-210 is found to be higher than 1.0E10Bq, it indicates that there is a leak in the heat transfer tube of the steam generator; if the humidity measured by the gas humidity monitor is also too high, it further indicates a leak in the heat transfer tube of the steam generator.

[0033] The beneficial effects of this invention are:

[0034] The present invention provides a monitoring device and method for leak detection of heat transfer tubes in a lead-bismuth reactor steam generator. The device can sample and measure the activity of Po-210 in the cover gas during reactor operation and determine whether there is a leak in the heat transfer tubes of the reactor steam generator by monitoring the humidity of the cover gas. Attached Figure Description

[0035] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in describing the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments recorded in the present invention. Those skilled in the art can derive other drawings from the following drawings without any creative effort.

[0036] Figure 1 A schematic diagram of a monitoring device for leaks in the heat transfer tubes of a lead-bismuth reactor steam generator, provided by the present invention.

[0037] In the diagram: 1-Covering gas, 2-Gas humidity monitor, 3-First valve, 4-Po-210 filter membrane, 5-Alpha activity detector, 6-Gas pump, 7-Second valve, 8-Core, 9-Steam generator, 10-Steam turbine, 11-Generator. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., refer to the orientation or positional relationship shown in the accompanying drawings, and are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or a connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] like Figure 1 As shown, the present invention provides a monitoring device for heat transfer tube leakage in a lead-bismuth reactor steam generator, comprising a reactor core 8, a steam generator 9, a steam turbine 10, a generator 11, a gas humidity monitor 2, a Po210 filter membrane 4, an alpha activity detector 5, and a gas pump 6. The reactor core 8 is divided into upper and lower parts. The lower part is equipped with fuel rods immersed in lead-bismuth alloy coolant. The lower part is a covered space containing a covered gas 1. The steam generator 9 is connected to the lower part of the reactor core 8 to form a loop. The steam generator 9 contains a water loop connected to the steam turbine 10. The steam turbine 10 is driven by the generator 11. High-temperature lead-bismuth alloy enters the steam generator 9, and the water in the water loop absorbs heat and is converted into steam, which is then cooled by the steam turbine 10. The covered space is connected to the Po210 filter membrane 4 through a pipe to form a loop. The Po210 filter membrane 4 is equipped with a gas humidity monitor 2 and a gas pump 6 at both ends. The Po210 filter membrane 4 is used in conjunction with the alpha activity detector 5.

[0042] A first valve 3 is provided between the Po210 filter membrane 4 and the gas humidity monitor 2, and a second valve 7 is provided between the Po210 filter membrane 4 and the gas pump 6.

[0043] The present invention provides a method for monitoring leakage in the heat transfer tubes of a lead-bismuth reactor steam generator, comprising the following steps:

[0044] Step 1: Determine the warning value for leakage in the heat transfer tubes of the steam generator.

[0045] Before the steam generator heat transfer tubes leaked, the coolant system was in an oxygen-controlled state with extremely low water or water vapor content. The lead-bismuth alloy was used as the reactor coolant. Bi-209 in the alloy was activated by neutrons to generate Bi-210, which then decayed to produce Po-210. Po-210 accumulated in the lead-bismuth, reaching a total activity of approximately 1.0E17 Bq at equilibrium. The chemical form of Po in lead-bismuth was primarily PbPo, with only trace amounts entering the cover gas space. The total activity of Po-210 entering the cover gas was 2.0E7 Bq.

[0046] After the heat transfer tube of the steam generator leaks, the water pressure on the secondary side is significantly higher than that on the primary side. Therefore, in the initial stage of the leak, the water on the secondary side will leak into the lead and bismuth on the primary side. After the water on the secondary side leaks into the primary side, it will migrate through the core with the lead and bismuth. Since the temperature on the primary side is significantly higher than that on the secondary side, the water will quickly turn into water vapor and migrate into the cover gas, resulting in higher humidity in the cover gas.

[0047] 1) Generation of Po-210 in lead-bismuth coolant

[0048] When lead-bismuth alloy is used as a reactor coolant, Bi-209 in it is activated by neutrons to generate Bi-210, which then decays to produce Po-210. The reaction chain is shown in the following formula.

[0049]

[0050] 2) Chemical speciation and distribution of Po-210 in the lead-bismuth coolant system during normal operation

[0051] During lead-bismuth reactor operation, under normal oxygen-controlled conditions, the chemical form of Po in lead-bismuth is mainly PbPo (99.8% of polonium exists in lead-bismuth as PbPo, and the remaining 0.2% is elemental Po). PbPo has very low volatility, so Po-210 mainly exists in lead-bismuth, and only trace amounts of Po-210 enter the cover gas space.

[0052] 3) Chemical morphology and distribution of Po-210 after leakage in the heat transfer tubes of the steam generator

[0053] After a minor leak occurred in the heat transfer tube of the steam generator in the lead-bismuth reactor, water on the secondary side of the steam generator leaked into the lead-bismuth on the primary side under pressure and migrated with the lead-bismuth flow.

[0054] At high temperatures, the leaked water undergoes a chemical reaction with PbPo in lead and bismuth to form volatile Po.

[0055] Volatile Po enters the covering gas through lead and bismuth, resulting in a significant increase in the content of Po-210 in the covering gas.

[0056] Leaks in the heat transfer tubes of the steam generator lead to a significant increase in the activity of Po-210 in the cover gas. Therefore, changes in the activity of Po-210 in the cover gas can be used to monitor leaks in the steam generator of the lead-bismuth reactor.

[0057] Assuming a leakage rate of 1 g / s, the leaked water would reach 3.6 kg in 1 hour. Assuming that only 0.001% of the leaked water reacts with PbPo, approximately 0.4 g of Po-210 would be converted into volatile Po-210 and enter the covering gas, increasing the Po-210 content in the covering gas to 7.0 E13 Bq.

[0058] Therefore, leakage of the heat transfer tubes in a lead-bismuth steam generator will lead to a significant increase in the Po-210 activity in the covering gas. Based on the normal Po-210 activity of the covering gas before the leakage of the heat transfer tubes in the steam generator, and considering changes in operating temperature, flow rate, and oxygen control conditions, a Po-210 activity of 1.0E10Bq can be selected as the warning value for leakage of the heat transfer tubes in the steam generator.

[0059] Step 2: Gas sampling within the covered space

[0060] During reactor operation, the sampling loop valve 3, valve 7, and gas pump 6 are periodically opened sequentially. A certain amount of cover gas 1 is extracted each time. The sampling gas flows through the Po-210 filter membrane 4, and the Po-210 in the sampling gas is retained on the filter membrane 4. During the sampling process, the humidity of the gas is measured using a gas humidity monitor 2. After sampling is completed, the loop gas pump 6, valve 3, and valve 7 are closed sequentially.

[0061] Step 3, Gas Measurement

[0062] The activity level of Po-210 in the Po-210 filter membrane 4 is measured using an alpha activity detector 5. If a significant increase in the activity of Po-210 is found (above 1.0E10Bq), it indicates a leak in the heat transfer tube of the steam generator. If the humidity measured by the gas humidity monitor 2 is also high, it can further characterize the leak in the heat transfer tube of the steam generator.

[0063] While those skilled in the art will recognize that the present invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and therefore all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0064] Furthermore, it should be understood that although the present invention is described according to embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A monitoring device for leaks in the heat transfer tubes of a lead-bismuth reactor steam generator, characterized in that, The reactor includes a reactor core (8), a steam generator (9), a steam turbine (10), a generator (11), and a gas humidity monitor (2). The reactor core (8) is divided into upper and lower parts. The lower part is equipped with fuel rods, which are immersed in lead-bismuth alloy coolant. The lower part is a covered space, which contains covered gas (1). The steam generator (9) is connected to the lower part of the reactor core (8) to form a loop. The steam generator (9) has a water loop inside, which is connected to the steam turbine (10). The steam turbine (10) provides driving force through the generator (11). The high-temperature lead-bismuth alloy enters the steam generator (9), and the water in the water loop absorbs heat and is converted into steam, which is cooled by the steam turbine (10). The covered space is connected to the Po210 filter membrane (4) through a pipeline to form a loop.

2. The monitoring device for leaks in the heat transfer tubes of a lead-bismuth reactor steam generator according to claim 1, characterized in that, The Po210 filter membrane (4) is equipped with a gas humidity monitor (2) and a gas pump (6) at both ends, and the Po210 filter membrane (4) is used in conjunction with an α activity detector (5).

3. The monitoring device for leaks in the heat transfer tubes of a lead-bismuth reactor steam generator according to claim 2, characterized in that, A first valve (3) is provided between the Po210 filter membrane (4) and the gas humidity monitor (2), and a second valve (7) is provided between the Po210 filter membrane (4) and the gas pump (6).

4. A method for monitoring leakage in the heat transfer tubes of a lead-bismuth reactor steam generator according to claim 3, characterized in that, Includes the following steps: Step 1: Determine the warning value for leakage in the heat transfer tubes of the steam generator; Step 2: Gas sampling within the covered space; Step 3: Gas measurement.

5. The method according to claim 4, characterized in that, Step 1 includes the following steps: The generation of Po-210 in lead-bismuth coolant was determined; Determine the chemical speciation and distribution of Po-210 in the lead-bismuth coolant system during normal operation; Determine the chemical morphology and distribution of Po-210 after a leak in the heat transfer tube of a steam generator.

6. The method according to claim 5, characterized in that, The determination of the generation of Po-210 in the lead-bismuth coolant: When lead-bismuth alloys are used as reactor coolants, Bi-209 in the alloy is activated by neutrons to generate Bi-210, which then decays to produce Po-210.

7. The method according to claim 6, characterized in that, Chemical speciation and distribution of Po-210 in the lead-bismuth coolant system during normal operation: During lead-bismuth reactor operation, under normal oxygen-controlled conditions in the primary loop system, the chemical form of Po in lead-bismuth is mainly PbPo. PbPo has very low volatility, and Po-210 is mainly present in lead-bismuth, with only trace amounts of Po-210 entering the cover gas space.

8. The method according to claim 7, characterized in that, Chemical speciation and distribution of Po-210 after leakage in the heat transfer tubes of the steam generator: After a minor leak occurred in the heat transfer tube of the steam generator in the lead-bismuth reactor, water on the secondary side of the steam generator leaked into the lead-bismuth on the primary side under pressure and migrated with the lead-bismuth flow. At high temperatures, the leaked water undergoes a chemical reaction with PbPo in lead and bismuth to form volatile Po. Volatile Po enters the covering gas through lead and bismuth, resulting in a significant increase in the content of Po-210 in the covering gas; Considering the changes in operating temperature, flow rate, and oxygen control conditions, a Po-210 activity of 1.0E10Bq was selected as the early warning value for leakage in the heat transfer tubes of the steam generator.

9. The method according to claim 8, characterized in that, Step 2 specifically involves: During reactor operation, the sampling loop first valve (3), second valve (7) and gas pump (6) are opened in sequence periodically; a certain amount of cover gas (1) is extracted each time, and the sampling gas flows through the Po-210 filter membrane (4). The Po-210 in the sampling gas remains on the filter membrane (4). During the sampling process, the humidity of the gas is measured by a gas humidity monitor (2). After the sampling is completed, the loop gas pump (6), first valve (3) and second valve (7) are closed in sequence.

10. The method according to claim 9, characterized in that, Step 3 specifically involves: using an α activity detector (5) to measure the activity level of Po-210 in the Po-210 filter membrane (4). If the activity of Po-210 is found to be higher than 1.0E10Bq, it indicates that there is a leak in the heat transfer tube of the steam generator. If the humidity measured by the gas humidity monitor (2) is also too high, it further indicates that there is a leak in the heat transfer tube of the steam generator.

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