A control system and method for activating corrosion product source terms in a nuclear power plant

Abstract

The present invention belongs to the field of activated corrosion product control in nuclear power plants, and specifically relates to a control system and method for controlling activated corrosion product sources in nuclear power plants. The system comprises: a reactor, a primary coolant purification system, a primary coolant purification system, a boric acid storage water tank, a spent fuel pool purification system, a spent fuel pool, a main pump, and a charging pump; the reactor is circulated into the primary coolant purification system via the main pump; the reactor is connected to the primary coolant purification system via the charging pump to establish a charging and discharging operation; the boric acid storage water tank is connected to the spent fuel pool purification system to form a circulation loop for purifying activated corrosion products; and the spent fuel pool is connected to the spent fuel pool purification system to form a circulation loop for purifying activated corrosion products. The present invention can effectively reduce the content of activated corrosion products in the primary coolant system and their deposition on the surfaces of major equipment, reduce the radiation dose field level during unit maintenance, and reduce the exposure dose to workers in radioactive environments.

Description

Technical Field

[0001] The present invention belongs to the field of activated corrosion product control in nuclear power plants, and in particular relates to a control system and method for a source term of activated corrosion products in nuclear power plants. Background Art

[0002] Corrosion products generated during nuclear power plant reactor power operation are easily deposited in high-temperature irradiated areas of the reactor (such as the fuel cladding surface) as the coolant flows. After absorbing neutrons, they are activated and transformed into activated corrosion products. Under normal operating conditions, activated corrosion products contribute over 80%-90% of the radiation dose outside the core. Therefore, activated corrosion products are widely used to assess and characterize the radiation dose field during overhauls and the corrosion of primary circuit system equipment. Among activated corrosion products, the majority of the dose comes from Co-60 and Co-58, with others primarily from nuclides such as Sb-124 and Ag-110m. During unit shutdown, changes in water chemistry (pH, temperature, and oxygen content), as well as heat flux and pressure, can lead to concentrated release of activated corrosion products into the primary circuit coolant. These products can deposit on equipment surfaces and in areas of slow water flow, forming radiation hotspots and posing a health hazard to maintenance and operating personnel.

[0003] During overhaul, most PWR units add hydrogen peroxide when the primary circuit is cooled to 80°C, maintaining the dissolved oxygen concentration in the primary circuit above 5 mg / L. This changes the water chemistry in the primary circuit from a reducing to an oxidizing environment, allowing the activated corrosion products to be rapidly released into the coolant. The main pump is used to force circulation and remove them through the purification system. During the overhaul shutdown and cooling process, VVER units do not add hydrogen peroxide. Instead, they only use the primary circuit purification system to remove radioactivity at a high flow rate. The purification time is uncertain, and the activated corrosion products are released into the coolant at a slow rate, with a late peak. After the primary circuit liquid level drops, the main pump stops, and the primary circuit purification system exits. The purification system has a short effective time for removing radioactive nuclides. During the overhaul, as the primary circuit is drained and the liquid level rises and falls, the activated corrosion products flow along with the coolant to various systems in the primary circuit.

[0004] In order to reduce the source term of activated corrosion products in nuclear power plants and lower the radiation dose to personnel, the VVER unit of Tianwan Nuclear Power Station needs to establish a control method for the source term of activated corrosion products while ensuring that all water quality indicators are qualified. Summary of the Invention

[0005] The purpose of the present invention is to provide a control system and method for the activated corrosion product source term in a nuclear power plant, which can effectively reduce the content of activated corrosion products in the main system of the primary circuit and reduce their deposition on the surface of major equipment, thereby reducing the radiation dose field level during unit maintenance and reducing the exposure dose of workers in a radioactive environment.

[0006] Technical solution to achieve the purpose of the present invention:

[0007] A control system for an activated corrosion product source term in a nuclear power plant comprises: a reactor, a primary coolant purification system, a primary purification system, a boric acid storage water tank, a spent fuel pool purification system, a spent fuel pool, a main pump, and a charging pump; the reactor is circulated into the primary coolant purification system via the main pump; the reactor is connected to the primary purification system via the charging pump to establish a charging and discharging operation; the boric acid storage water tank is connected to the spent fuel pool purification system to form a circulation loop for purifying activated corrosion products; and the spent fuel pool is connected to the spent fuel pool purification system to form a circulation loop for purifying activated corrosion products.

[0008] The spent fuel pool is connected to the reactor, and the spent fuel pool and the reactor are purified by the spent fuel pool purification system.

[0009] Two boric acid storage tanks are connected in parallel, and each boric acid storage tank is connected to the spent fuel pool purification system to form a circulation loop to purify activated corrosion products.

[0010] A method for controlling a source term of activated corrosion products in a nuclear power plant, the method comprising:

[0011] Step 1: Activate corrosion product control before shutdown;

[0012] Step 2: Control of activated corrosion products during shutdown phase;

[0013] Step 3: Control of activated corrosion products after shutdown;

[0014] Step 4: Activate corrosion product control after startup.

[0015] The step 1 comprises:

[0016] Step (1.1): Two months before the shutdown, use the spent fuel pool purification system to purify the radioactivity of the boric acid storage tank;

[0017] Step (1.2), before the safety passage is repaired, a boric acid water tank-safety passage-boric acid water tank cycle is established to jointly flush the activated corrosion products deposited in the safety passage, and the boric acid water tank is purified after the flushing is completed;

[0018] Step (1.3): One week before the shutdown, use the spent fuel pool purification system to purify the radioactivity in the spent fuel pool;

[0019] Step (1.4): Flush the spare series of the primary coolant purification system one day before shutdown and analyze the anions and TOC; after the flushing is qualified, close the outlet valve of the spare series and keep the inlet valve open.

[0020] The step 2 includes:

[0021] In step (2.1), when the unit power is reduced to 40%, the ammonia addition in the primary circuit is stopped;

[0022] Step (2.2): When the unit enters the boron injection phase at the minimum monitorable power level, the standby series of the primary coolant purification system is put into operation, and the purification system is maintained at the maximum flow rate that can be achieved to jointly purify the primary circuit, and the radioactivity of the primary circuit and after the bed is regularly tracked;

[0023] Step (2.3), during the cooling phase of the unit, the primary coolant purification system is maintained at the maximum flow rate that can be achieved for combined purification until the main pump stops operating, and the primary circuit and post-bed radioactivity are tracked regularly;

[0024] Step (2.4): After the unit is naturally oxidized, a charging pump is used to establish a primary circuit charging and discharging condition, and the primary circuit purification system is continuously put into operation for combined purification at the maximum flow rate that can be achieved, and the time is maintained for more than 25 hours.

[0025] The step 3 comprises:

[0026] Step (3.1): After the unit enters the refueling cold shutdown, the reactor primary circuit is connected to the spent fuel pool. During the refueling process, the spent fuel pool purification system is continuously operated to purify the spent fuel pool and reactor radioactivity until the refueling is completed.

[0027] In step (3.2), during the maintenance cold shutdown of the unit after unloading, a boric acid storage water tank-spent fuel pool purification system-spent fuel pool combined purification system is established to activate corrosion products to reduce radiation dose, according to the operation window.

[0028] The step 4 comprises:

[0029] After the unit cover is closed and before hydrazine is added to the primary circuit for deoxidation, the upper charging pump is used to establish the upper charging and lower draining conditions as soon as possible. Before the activated corrosion products are converted into colloidal state, they are removed by the primary circuit coolant purification system to reduce the impurity ions introduced during the overhaul process and the probability of their deposition and activation in the core irradiation area.

[0030] In step (4.2), during the overhaul of the unit, the radioactivity of the boric acid storage water tank receiving drainage from various systems in the primary circuit and the spent fuel pool will increase due to fuel operation. The spent fuel pool purification system will continue to be used to control the radioactivity of the boric acid storage water tank and the spent fuel pool to achieve the radioactivity target.

[0031] The beneficial technical effects of the present invention are:

[0032] 1. This invention investigates the material properties of the main equipment of the VVER unit and the characteristics of activated corrosion products, and studies the migration mechanism of activated corrosion products under the natural oxidation shutdown condition of the unit;

[0033] 2. The present invention independently studies the purification efficiency of nuclear-grade resins for major nuclides, accurately controls the time for commissioning and purification of each resin bed, and ensures the progress of the overhaul;

[0034] 3. The present invention controls the timing of stopping ammonia addition to ensure that the time for the primary coolant purification system to effectively remove activated corrosion products is maximized;

[0035] 4. The present invention establishes the upper filling and lower discharge working conditions for the first time after natural oxidation during shutdown and before adding hydrazine for deoxidation during startup (detailed description is provided), and implements a circuit activation corrosion product purification;

[0036] 5. Through the study of the properties of various nuclides, the present invention has found that under low pH conditions, the activated corrosion products Sb-122 / 124 are released in advance, and the large particles of oxide film are removed through the bed by mechanical interception after falling off;

[0037] 6. The present invention optimizes the operation process of the primary purification system, maximizes the utilization of the remaining resin capacity of the purification bed, and efficiently removes activated corrosion products. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a diagram of the transfer mechanism of activated corrosion products in the primary circuit system during the overhaul outage;

[0039] Figure 2 This is the process flow chart of the activated corrosion product source control system in a nuclear power plant.

[0040] In the figure: 11- non-irradiated pipe wall; 12- spent fuel pool; 13- primary coolant purification system; 14- large particle sedimentation; 15- primary coolant; 16- irradiated pipe wall;

[0041] 1- Reactor; 2- Primary coolant purification system; 3- Primary purification system; 4- Boric acid storage tank; 5- Spent fuel pool purification system; 6- Spent fuel pool; 7- Main pump; 8- Charging pump. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0043] 1. Characteristics and properties of activated corrosion products of VVER units

[0044] 1.1Material of main equipment in the primary circuit of VVER unit

[0045] Units 1-4 of the Tianwan Nuclear Power Plant use a pressurized water reactor (PWR) model of the Russian VVER-1000 reactor. Compared to other PWR units, they are equipped with four horizontal steam generators (SGs). The heat transfer tubes with the largest contact area with the primary coolant are made of austenitic stainless steel, not nickel-based alloys. The materials of the main equipment are shown in Table 1:

[0046] Table 1 Main equipment materials

[0047]

[0048] 1.2 Composition of main activated corrosion products during VVER unit overhaul

[0049] During the overhaul of the VVER units, a statistical analysis of activated corrosion products in the primary coolant circuit was conducted, as shown in Tables 2 and 3. The primary circuit equipment of Unit 3 was contaminated with Ag-110m. The composition of activated corrosion products in the main circuits of Units 1, 2, and 4 during the overhauls was similar, but the main circuit system of Unit 3 was contaminated with silver, a more unique situation. Tables 2 and 3 show that when the VVER units were not contaminated with silver, the largest proportions of activated corrosion products in the main circuit during the overhaul were Sb-122 / 124 and Co-58. For the units contaminated with silver, Ag-110m accounted for the highest proportion of coolant, followed by Co-58 and Sb-122 / 124.

[0050] Table 2 Proportion of activated corrosion products in the main circuit during the overhaul of VVER units (OT212 overhaul)

[0051]

[0052] Table 3 Proportion of activated corrosion products in the main circuit during the overhaul of VVER units (OT301 overhaul)

[0053]

[0054] 2. Study on purification efficiency of activated corrosion products

[0055] 2.1 Introduction to the primary circuit purification system

[0056] During overhauls, high-activity corrosion activation product sources diffuse into and deposit in low-temperature areas of primary loop auxiliary systems (such as chemical and volume control system downflow lines and waste heat extraction channels) through water dumping and replacement in the primary loop, increasing local dose rates. Control of activated corrosion products in the primary loop relies primarily on a resin bed purification system, primarily consisting of the primary coolant purification system and the spent fuel pool purification system.

[0057] 1) Primary coolant purification system

[0058] The primary coolant purification system, KBE, is installed on the main pump bypass to remove dissolved ionic impurities, radioactive fission products, and corrosion products from the primary coolant, ensuring that the primary water chemistry meets the technical specifications. It consists of a KBE10 and a KBE50 connected in parallel. KBE10 consists of a cation bed, KBE10AT001 (saturated with potassium ammonia), and an anion bed, KBE10AT002 (saturated with boron), connected in series. The mixed bed, KBE50AT001, is located in a separate system. During normal operation, KBE10 is in continuous operation, while KBE50 is on standby.

[0059] 2) Spent fuel pool purification system

[0060] The spent fuel pool purification system features two mechanical beds, FAL30AT001 and FAL30AT002, for purifying mechanical impurities in the spent fuel pool. A cation bed, FAL30AT003, and an anion bed, FAL30AT004, purify the water in the spent fuel pool and the boron water storage tank. When the purification system is in operation, the two mechanical beds are used, one in operation and one in standby. The operating mode is one mechanical bed + one cation bed + one anion bed, purifying the water.

[0061] 2.2 Study on purification efficiency of main activated corrosion products

[0062] The purification efficiency η of radioactive nuclides represents the purification ability of the resin to nuclides. The calculation formula is as follows:

[0063] η = (activity before purification - activity after purification) / activity before purification

[0064] 2.2.1 Study on the efficiency of purification of nuclides using resin bed in primary purification system

[0065] Table 4 Purification efficiency of cationic resin for Ag-110m

[0066]

[0067] Table 5. Purification efficiency of cationic resin on Co-58

[0068]

[0069] Table 6 Anion resin purification efficiency of Sb-124

[0070]

[0071] 2.2.2 Study on the Efficiency of Resin Beds in the FAL Spent Fuel Pool Purification System for Nuclides

[0072] Table 7 Purification efficiency of nuclear grade cationic resin for ionic Ag-110m

[0073]

[0074] Table 8: Purification efficiency of nuclear grade cationic resin on Co-58

[0075]

[0076]

[0077] Table 9 Statistics on the purification efficiency of nuclear grade anion resin for Sb-124

[0078]

[0079] From the statistical data in the table, it can be seen that the purification efficiency of the cationic resin for Co-58 in the ionic state is close to 100%, and it is easy to be removed; after the natural oxidation of the first circuit, the water chemical conditions of the first circuit are transformed into acidic oxidation, Sb-124 is transformed into anionic form, which is easily removed by the anion bed, and Ag-110m is transformed into cationic form, and the purification efficiency of the cationic resin is above 94%.

[0080] 3. Study on the migration mechanism of activated corrosion products during overhaul shutdown

[0081] a) After the overhaul begins, the neutron flux of the VVER unit is negligible and the generation rate of activated corrosion products becomes zero when the power is reduced to the minimum monitorable power level and in all subsequent states.

[0082] b) After the primary water chemical condition turns acidic, the solubility of the sediment deposited on the pipe wall surface increases. In order to maximize the time for the primary coolant purification system to effectively remove activated corrosion products in an acidic environment, after reducing the power to 40%, stop adding ammonia to the primary circuit. After the minimum monitorable power level, the primary circuit de-alkali bed is put into operation at a large flow rate to remove the total alkali metals in the primary circuit, which can further reduce the pH of the coolant and advance the release of activated corrosion products until the main pump stops operating. At this time, the primary circuit nuclides such as Co-58 / 60 mostly exist in ionic state, and Sb-124 and Ag-110m mostly exist in colloidal or elemental state, which can provide an important basis for the flow distribution ratio when the cationic bed and mixed bed are put into operation.

[0083] c) As the main circuit temperature decreases, large particles of activated corrosion products flow through the steam generator heat transfer tubes and main pipelines, and are deposited due to hydraulic and gravity effects. The outer deposits and oxide layers of nickel ferrite and cobalt ferrite begin to dissolve. When the temperature drops to between 150-180°C, the solubility of iron oxide reaches its peak, and Sb-122 / 124 begins to rise before other nuclides. Then the reactor continues to cool down to a cold state.

[0084] d) After boron is injected into the primary circuit, the water chemical environment changes from weakly alkaline reducing to acidic reducing, and the activated corrosion products deposited in the irradiated area of the core begin to dissolve. After the unit starts to cool down, the solubility of the activated corrosion products changes due to the change in temperature. At 150-180℃, the activated corrosion products attached to the surface of large particles of nickel ferrite, ferrosoferric oxide, etc. dissolve into the coolant.

[0085] e) Before the reactor cover is opened, the VVER unit uses nitrogen purge to remove hydrogen from the primary circuit. The water chemistry of the primary circuit will gradually change to an oxidizing environment, and the release rate of activated corrosion products will further increase. The activated corrosion products in the main circuit coolant will not reach a peak until 1-2 days after the reactor cover is opened.

[0086] f) After the reactor purge is completed, the unit enters the maintenance cold shutdown state. The primary circuit undergoes natural oxidation and gradually becomes oxidizing. In addition, the pH is below 4.7, and the oxides deposited on the tube wall surface begin to fall off on a large scale. A large number of activated corrosion products such as Co-58 / 60, Sb-122 / 124, Ag-110m and other nuclides gradually transform from elemental or colloidal forms to ionic forms, and the activity of nuclides in the coolant gradually increases to a peak value.

[0087] g) As the liquid level in the primary circuit rises and falls, after the unit enters a cold shutdown for refueling, the reactor pit is connected to the spent fuel pool. Due to the dilution effect, the activity of nuclides in the primary circuit coolant decreases by 1-2 orders of magnitude.

[0088] like Figure 1 As shown in FIG, the transfer mechanism of activated corrosion products in the primary circuit system during the overhaul outage includes the release of activated corrosion products attached to the irradiated area tube wall 6, such as the fuel cladding, into the primary circuit coolant 5. The activated corrosion products in the primary circuit coolant 5 are deposited on the non-irradiated area tube wall 1, such as the steam generator heat transfer tube, main pipeline and safety passage as the coolant circulates, forming radiation hotspots. At the same time, the activated corrosion products will also be redeposited on the irradiated area tube wall 6 and the non-irradiated area tube wall 1. As the primary circuit coolant purification system 3 purifies and removes 3 and large particles are settled 4, the activated corrosion products are reduced. After the refueling starts, the primary circuit coolant 5 is connected to the spent fuel pool 2, and the activated corrosion products are transferred.

[0089] like Figure 2 As shown, the present invention provides a control system for the activated corrosion product source term of a nuclear power plant, comprising: a reactor 1, a primary coolant purification system 2, a primary purification system 3, a boric acid storage tank 4, a spent fuel pool purification system 5, a spent fuel pool 6, a main pump 7, and a charging pump 8.

[0090] Reactor 1 is circulated into a primary coolant purification system 2 via a main pump 7; reactor 1 is connected to the primary coolant purification system 3 via a charging pump 8 to establish a charging and discharging operation; two boric acid storage tanks 4 are connected in parallel, and each boric acid storage tank 4 is connected to a spent fuel pool purification system 5 to form a circulation loop for purifying activated corrosion products; a spent fuel pool 6 is connected to the spent fuel pool purification system 5 to form a circulation loop for purifying activated corrosion products; the spent fuel pool 6 is connected to the reactor 1, and the spent fuel pool 6 and the reactor 1 are purified by the spent fuel pool purification system 5.

[0091] The coolant in the reactor 1 is circulated through a main pump 7 and brought into a primary coolant purification system 2 for purification. After natural oxidation, a charging pump 8 establishes an upward charging and downward discharge operation, and the coolant is purified by a primary purification system 3. Before overhaul, activated corrosion products in the boric acid storage tank 4 and the spent fuel pool 6 are purified by a spent fuel pool purification system 5. During the refueling and cold shutdown phase, the reactor 1 is connected to the spent fuel pool 6, and the spent fuel pool purification system 5 is continuously used to purify the activated corrosion products.

[0092] The present invention provides a method for controlling the source term of activated corrosion products in a nuclear power plant, which specifically includes the following steps:

[0093] Step 1: Activate corrosion product control before shutdown

[0094] Step (1.1): Two months before the shutdown, use the spent fuel pool purification system 5 to purify the radioactivity of the boric acid storage tank 4. The purification target value is total γ < 5.0E5Bq / m 3 ;

[0095] Step (1.2), before the safety channel is repaired, a boric acid water tank-safety channel-boric acid water tank cycle is established to jointly flush the activated corrosion products deposited in the safety channel. After the flushing is completed, the boric acid water tank is purified. The purification target value is total γ <5.0E5Bq / m 3 ;

[0096] Step (1.3): One week before the shutdown, use the spent fuel pool purification system 5 to purify the radioactivity of the spent fuel pool 6. The purification target value is total γ < 1.0E6Bq / m 3 ;

[0097] Step (1.4): One day before shutdown, flush the standby system of primary coolant purification system 2 and analyze for anions and TOC. After the flush is qualified, close the outlet valve of the standby system and keep the inlet valve open.

[0098] Step 2: Control of activated corrosion products during shutdown

[0099] In step (2.1), when the unit power is reduced to 40%, the ammonia addition in the primary circuit is stopped.

[0100] Step (2.2): When the unit enters the boron injection phase at the minimum monitorable power level, put the standby series of the primary coolant purification system 2 into operation and maintain the maximum flow rate achieved by purification system 2 for combined purification of the primary circuit (recommended values: 9±1 kg / s for the standby series and 4±1 kg / s for the other series). Regularly monitor the radioactivity in the primary circuit and after the bed.

[0101] Step (2.3), during the unit cooling phase, the primary coolant purification system 2 is maintained at the maximum flow rate that can be achieved for combined purification until the main pump 7 stops operating, and the primary circuit and post-bed radioactivity are tracked regularly.

[0102] Step (2.4): After the unit is naturally oxidized, the charging pump 8 is used to establish a primary circuit charging and discharging condition, and the primary circuit purification system 3 is continuously put into operation for combined purification at the maximum flow rate that can be achieved, and the time is maintained for more than 25 hours.

[0103] Step 3: Post-Shutdown Activated Corrosion Product Control

[0104] Step (3.1): After the unit enters refueling cold shutdown, the primary circuit of the reactor 1 is connected to the spent fuel pool 6. During the refueling process, the spent fuel pool purification system 5 is continuously put into operation to purify the radioactivity of the spent fuel pool 6 and the reactor 1 until the refueling is completed;

[0105] In step (3.2), after the unit is shut down for maintenance after unloading, a boric acid storage water tank 4-spent fuel pool purification system 5-spent fuel pool 6 combined purification system is established to activate corrosion products to reduce radiation dose, according to the operation window.

[0106] Step 4: Control of activated corrosion products after startup

[0107] After step (4.1) of the unit cover is completed and before hydrazine is added to the primary circuit for deoxidation, the upper charging and lowering conditions are established as soon as possible through the upper charging pump 8. Before the activated corrosion products are converted into a colloidal state, they are removed by the primary circuit coolant purification system 2. This reduces the impurity ions introduced during the overhaul process and reduces the probability of their deposition and activation in the irradiated area of the core.

[0108] Step (4.2): During the overhaul of the unit, the radioactivity of the boric acid storage water tank 4 receiving the drainage of each system in the primary circuit and the spent fuel pool will increase due to fuel operation. The spent fuel pool purification system 5 will continue to be put into use to treat the radioactivity of the boric acid storage water tank 4 and the spent fuel pool 6 to achieve the radioactivity target (water tank: total γ <5.0E5Bq / m 3 , Spent fuel pool: total γ <1.0E6Bq / m 3 ).

[0109] The analysis of the control effect of activated corrosion products during overhaul start-up and shutdown is as follows:

[0110] 1) Before the overhaul, the radioactivity of the spent fuel pool, boron-containing water tank, and nuclear island planned maintenance channel was pre-treated, and the source term of activated corrosion products was reduced by more than 90%;

[0111] 2) During the shutdown process, the remaining exchange capacity of the resin is fully utilized to remove an average of about 2.0 Ci of activated corrosion products, significantly reducing the source term;

[0112] 3) After natural oxidation, establish a top-fill and bottom-drain system and use a primary purification system to remove at least 1.5 Ci of activated corrosion products. The average values of nuclides such as Co-58 and Ag-110m are reduced by more than 30% compared with those before this method was used.

[0113] 4) During the maintenance cold shutdown period, the radioactivity of the JNK water tank was reduced by more than 80% by optimizing the use of the maintenance time window for reprocessing;

[0114] 5) During the refueling period, the radioactivity levels in the reactor pit and spent fuel pool decreased by approximately 70%, effectively reducing the radiation dose to maintenance personnel;

[0115] 6) After the control method was implemented, the collective dose of the OT112 overhaul reached the best value in the history of Unit 1; the collective dose of the OT302 overhaul was 42.3% of the first overhaul of this unit; the collective dose of the OT402 overhaul reached the lowest collective dose of unit overhauls in the past ten years; and the collective dose of the OT212 overhaul was significantly lower than the previous overhaul.

[0116] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Any content not described in detail in the present invention may be adapted from existing technologies.

Claims

1. A control system for activated corrosion product source term in a nuclear power plant, characterized in that: The system comprises: a reactor (1), a primary coolant purification system (2), a primary coolant purification system (3), a boric acid storage water tank (4), a spent fuel pool purification system (5), a spent fuel pool (6), a main pump (7), and a charging pump (8); the reactor (1) is circulated into the primary coolant purification system (2) via the main pump (7); the reactor (1) is connected to the primary coolant purification system (3) via the charging pump (8) to establish a charging and discharging operation; the boric acid storage water tank (4) is connected to the spent fuel pool purification system (5) to form a circulation loop for purifying activated corrosion products; the spent fuel pool (6) is connected to the spent fuel pool purification system (5) to form a circulation loop for purifying activated corrosion products; The spent fuel pool (6) is connected to the reactor (1), and the spent fuel pool (6) and the reactor (1) are purified by the spent fuel pool purification system (5); Two boric acid storage water tanks (4) are connected in parallel, and each boric acid storage water tank (4) is connected to a spent fuel pool purification system (5) to form a circulation loop for purifying activated corrosion products.

2. A method for controlling an activated corrosion product source term in a nuclear power plant, using the control system for an activated corrosion product source term in a nuclear power plant according to claim 1, characterized in that: The method comprises: Step 1: Activate corrosion product control before shutdown; Step (1.1), two months before the shutdown, use the spent fuel pool purification system (5) to purify the radioactivity of the boric acid storage tank (4); Step (1.2), before the safety passage is repaired, a boric acid water tank-safety passage-boric acid water tank cycle is established to jointly flush the activated corrosion products deposited in the safety passage. After the flushing is completed, the boric acid water tank is purified; Step (1.3), one week before the shutdown, use the spent fuel pool purification system (5) to purify the radioactivity in the spent fuel pool (6); Step (1.4), flush the spare series of the primary coolant purification system (2) one day before shutdown, and analyze the anions and TOC; after the flushing is qualified, close the outlet valve of the spare series and keep the inlet valve open; Step 2: Control of activated corrosion products during shutdown phase; In step (2.1), when the unit power is reduced to 40%, stop adding ammonia to the primary circuit; Step (2.2), when the unit enters the boron injection stage at the minimum monitorable power level, the standby series of the primary coolant purification system (2) is put into operation, and the primary coolant purification system (2) is maintained to jointly purify the primary circuit at the maximum flow rate that can be achieved, and the radioactivity of the primary circuit and the post-bed is tracked regularly; In step (2.3), during the cooling phase of the unit, the primary coolant purification system (2) is maintained at the maximum flow rate that can be achieved for combined purification until the main pump (7) stops operating, and the radioactivity of the primary circuit and the bed is tracked regularly; Step (2.4), after the unit is naturally oxidized, a primary circuit charging and discharging condition is established through the charging pump (8), and the primary circuit purification system (3) is continuously put into operation for combined purification at the maximum flow rate that can be achieved, and the time is maintained for more than 25 hours; Step 3: Control of activated corrosion products after shutdown; Step (3.1), after the unit enters the refueling cold shutdown, the primary circuit of the reactor (1) is connected to the spent fuel pool (6). During the refueling process, the spent fuel pool purification system (5) is continuously put into operation to purify the radioactivity of the spent fuel pool (6) and the reactor (1) until the refueling is completed; Step (3.2), after the unit is shut down for maintenance after unloading, a boric acid storage water tank (4)-spent fuel pool purification system (5)-spent fuel pool (6) is established to jointly purify activated corrosion products to reduce radiation dose according to the operation window; Step 4: Control of activated corrosion products after startup; After the unit cover is closed in step (4.1), before adding hydrazine to the primary circuit for deoxidation, establish the upper charging and lowering working conditions as soon as possible through the upper charging pump (8). Before the activated corrosion products are converted into colloidal state, they are removed by the primary circuit coolant purification system (2) to reduce the impurity ions introduced during the overhaul process and reduce the probability of their deposition and activation in the core irradiation area; In step (4.2), during the overhaul of the unit, the radioactivity of the boric acid storage water tank (4) receiving drainage from various systems of the primary circuit and the spent fuel pool will increase due to fuel operation. The spent fuel pool purification system (5) will continue to be put into use to deradiate the radioactivity of the boric acid storage water tank (4) and the spent fuel pool (6) to achieve the radioactivity target.

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