Silicon removal method and silicon removal system for boric acid water of primary loop of nuclear power plant

Abstract

The invention discloses a silicon removal method and a silicon removal system for primary loop boric acid water of a nuclear power plant. The silicon removal method comprises the following steps: S1, selecting a filter element of a filter for the primary loop boric acid water of the nuclear power plant; s2, changing the boric acid water of the primary loop of the nuclear power plant; s3, removing silicon from boric acid water in a boric acid tank of the REA system: filling a PTR system desalting bed and / or a TEP system desalting bed with mixed bed resin and silicon removal resin; boric acid water in a boric acid tank of the REA system is conveyed to a nanofiltration membrane through a PTR system to remove silicon; preparing new boric acid water in a boric acid tank of the REA system to replace boric acid water to be subjected to silicon removal; the silicon removal system comprises a TEP system desalting bed, an REA system boric acid tank, a PTR system loading well or transfer well, a PTR system desalting bed and a nanofiltration membrane silicon removal device; both the TEP system desalting bed and the PTR system desalting bed are filled with silicon removal resin. The silicon removal method and the silicon removal system can effectively reduce the silicon concentration of the boric acid water of the primary loop.

Description

Technical Field

[0001] This invention relates to the field of water chemistry control technology in nuclear power plants, and in particular to a method and system for removing silicon from boric acid water in the primary loop of a nuclear power plant. Background Technology

[0002] During the operation of a nuclear power unit, the silicon in the boric acid water in the primary loop of a nuclear power plant does not corrode materials on its own. However, in the presence of other impurities (such as calcium, magnesium, and aluminum), silicon can be transformed into low-soluble compounds (aluminosilicates, silicates, zeolites based on magnesium, calcium, and aluminum), which can concentrate on the fuel rods and form precipitates. This can lead to localized overheating of the fuel rods and increase the risk of under-deposit corrosion and damage to the fuel cladding. Silicon in the primary loop of a nuclear power plant can enter other nuclear auxiliary systems. For example, after water replacement in the primary loop, silicon in the boric acid water is recovered by the Coolant Storage and Treatment System (TEP) and enters the boric acid tank of the Reactor Boron and Water Makeup System (REA). During unit start-up and shutdown, it is replaced with boric acid by the Safety Injection System and enters the In-Containment Replacement Water Tank (IRWST). The problem of high silicon levels in the boric acid water of the primary loop and nuclear auxiliary systems is common in pressurized water reactor nuclear power plants both domestically and internationally.

[0003] Nuclear power plants use enriched boric acid in their primary loop, which, compared to natural boric acid, allows for higher levels of nuclear reaction control and increases the pH of the boric acid solution in the primary loop, thus improving corrosion protection of system equipment and increasing the reliability of the nuclear power unit's safe operation. However, the increased pH of the boric acid solution in the primary loop can cause the glass fiber filter element of the traditional primary loop coolant filter to easily release silicon. Therefore, nuclear power units using enriched boric acid have higher requirements for controlling the silicon content of the primary loop boric acid solution, necessitating a more efficient method for silicon content control. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for removing silicon from boric acid water in the primary loop of a nuclear power plant.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for removing silicon from boric acid water in the primary loop of a nuclear power plant, comprising the following steps: S1. Select the filter element for the boric acid water filter in the primary loop of the nuclear power plant; S2. Replace the boric acid water in the primary loop of the nuclear power plant. The boric acid water to be desiliconized enters the boric acid tank of the REA system through the TEP system. The boric acid water is replenished from the boric acid of the REA system and the deoxygenated and demineralized water of the TEP system. S3. Use at least one of the following methods to remove silica from the boric acid water in the boric acid tank of the REA system: The REA system boric acid tank is connected to the PTR system, and mixed bed resin and desiliconizing resin are filled in the desalination bed of the PTR system and / or the desalination bed of the TEP system. The boric acid solution in the REA system's boric acid tank is transported to the nanofiltration membrane via the PTR system for silica removal; Prepare fresh boric acid solution in the boric acid tank of the REA system to replace the boric acid solution to be removed.

[0006] Preferably, in step S1, the primary loop of the nuclear power plant uses natural boric acid and the filter uses a glass fiber filter element; or, the primary loop of the nuclear power plant uses enriched boric acid and the filter uses a silicone-free filter element, the filter material of the silicone-free filter element including polyester composite fiber.

[0007] Preferably, in step S1, the filter includes an RCV system downflow filter, an RCV system resin trapping filter, an RCV system shaft seal injection filter, an RCV system shaft seal return filter, and a TEP system filter.

[0008] Preferably, in step S2, the volume of boric acid water to be replenished is calculated using equation (1), which is expressed as follows: (1) in, This represents the total volume of the boric acid solution in the primary loop. To replenish the volume of boric acid solution, To replenish the silicon concentration of the boric acid solution, The silica concentration of the boric acid solution in the previous circuit before water replacement. This refers to the silica concentration in the boric acid solution after water exchange in the first loop.

[0009] Preferably, in step S3, the silicone resin is a strong base anion exchange resin containing iron oxide and / or triethylamine; and / or, the mixed bed resin is GR-3-9 NG mixed bed resin; and / or, the filling volume ratio of the silicone resin and the mixed bed resin is 1:(1~3).

[0010] Preferably, the silicon removal method further includes the following steps: S4. Establish a reference model for the influence of the filter material of the primary loop boric acid water on the silicon concentration of the boric acid water, and compare the changes in the silicon concentration of the boric acid water during actual operation of the primary loop with the reference model.

[0011] This invention also proposes a desiliconization system for boric acid water in the primary loop of a nuclear power plant. The desiliconization system adopts the aforementioned method for desiliconization of boric acid water in the primary loop of a nuclear power plant. The desiliconization system includes a TEP system desalination bed, an REA system boric acid tank, a PTR system loading well or transfer well, a PTR system desalination bed, and a nanofiltration membrane desiliconization device. Both the TEP system desalination bed and the PTR system desalination bed are filled with desiliconization resin. The TEP system desalination bed, the REA system boric acid tank, and the PTR system loading well or transfer well are connected in sequence. The PTR system loading well or transfer well is connected to the PTR system desalination bed, the nanofiltration membrane desiliconization device, and the TEP system desalination bed, respectively, to remove silicon from the boric acid water in the primary loop and the boric acid water to be desiliconized in the REA system boric acid tank.

[0012] Preferably, the desiliconization system further includes a reactor primary loop, which is connected to the TEP system boric acid tank. The TEP system boric acid tank is then connected to the TEP system desalination bed to desiliconize the boric acid water from the primary loop. The desiliconized boric acid water then enters the REA system boric acid tank; and / or, The REA system's boric acid tank is connected to the RPE system's transfer tank, which in turn connects to the TEP system. Silicon removal then occurs via the TEP system's desalination bed; and / or, The filter for the primary loop boric acid water uses a silicone-free filter element.

[0013] Preferably, the REA system boric acid tank is connected to the PTR system loading well or transfer well via the REA system pipeline and the PTR system pipeline. The boric acid water in the REA system boric acid tank is mixed with the demineralized water of the TEP system and then enters the PTR system loading well or transfer well. It is desiliconized by the PTR system desalination bed and nanofiltration membrane desiliconization device, and then returned to the PTR system loading well or transfer well via the PTR system pipeline.

[0014] Preferably, the boric acid water from the PTR system loading well or transfer well enters the TEP system through the PTR system pipeline, and then undergoes desiliconization through the TEP system desalination bed; and / or, The REA system boric acid tank is connected to the waste treatment system to replace the silica-boronic acid water to be removed.

[0015] The beneficial effects of this invention are: The present invention discloses a method for removing silicon from the primary loop boric acid water in nuclear power plants. First, a filter element of appropriate material for the primary loop boric acid water filter is selected. Then, the primary loop boric acid water is replaced in an appropriate amount. For the boric acid water in the REA system boric acid tank, the method of filtration with ion exchange resin (including desiliconizing resin and mixed bed resin), purification with nanofiltration membrane, and replacement with fresh boric acid water is used to remove the silicon. This effectively solves the problem of high silicon content in the primary loop of nuclear power plants, reduces equipment corrosion and scaling caused by silicon deposition, extends equipment service life, and reduces equipment maintenance and replacement costs.

[0016] The present invention relates to a desiliconization system for the primary loop boric acid water in nuclear power plants. The primary loop boric acid water is transported to the TEP system desalination bed for desiliconization. The boric acid water from the REA system boric acid tank is introduced into the PTR system loading well or transfer well and then transported to the PTR system desalination bed, nanofiltration membrane desiliconization device, and TEP system desalination bed for desiliconization. The desiliconized boric acid water can be returned to the original system, thereby realizing primary loop water exchange and desiliconization, and REA system boric acid tank desiliconization, effectively reducing the silicon concentration of the primary loop boric acid water. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic diagram of the desiliconization system of boric acid water in the primary loop of a nuclear power plant in some embodiments of the present invention; Figure 2 This is a graph showing the change in silica concentration in the primary loop of Unit F3 in the embodiment; Figure 3 This is a graph showing the change in silicon concentration after boron production in the boric acid box of the REA system for different units in the embodiments; Figure 4 These are graphs showing the changes in silicon concentration in the primary circuit of different units in the embodiments after being filled with boric acid water; The labels in the attached diagram are as follows: 11. TEP system boric acid tank; 12. TEP system transfer pump; 13. TEP system desalination bed; 14. TEP system evaporator; 15. TEP system desalination water tank; 21. REA system boric acid tank; 22. REA system boric acid pump; 23. REA system desalination water pump; 31. PTR system loading well or transfer well; 32. PTR system purification pump; 33. PTR system desalination bed; 4. Nanofiltration membrane desiliconization device; 5. RPE system transfer box; 6. Waste treatment system; 71. Reactor primary loop; 72. Main pump; 73. RCV system filter; 74. Charge pump. Detailed Implementation

[0018] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the invention and do not constitute a limitation on the scope of protection of this invention.

[0019] It should be noted that in this invention, RCP system refers to reactor coolant system, also known as primary loop system; RCV system refers to chemical and volume control system; TEP system refers to coolant storage and treatment system; REA system refers to reactor boron and water supply system; PTR system refers to reactor and spent fuel pool cooling and treatment system; and RPE system refers to nuclear island exhaust and drainage system.

[0020] This invention proposes a method for removing silicon from boric acid water in the primary loop of a nuclear power plant, comprising the following steps: S1. Select the filter element for the boric acid water filter in the primary loop of the nuclear power plant.

[0021] In some embodiments, the primary loop of the nuclear power plant uses natural boric acid, and the filter uses a glass fiber filter element. During normal operation of the unit, the silicon in the glass fiber filter element has little impact on water quality. In other embodiments, the primary loop of the nuclear power plant uses enriched boric acid, in which case a silicon-free filter element is used. Alternatively, before the cold-state test of a new unit during commissioning, a glass fiber filter element can be used, and a silicon-free filter element is selected when entering the hot-state test phase.

[0022] Silicone-free filter cartridges can use polyester composite fibers as filter media. Silicone-free filter cartridges use silicon-free and aluminum-free filter media, which is a high-molecular polymer composite material, mainly composed of polyester composite fibers. The main elements contained in the material are C, O, H, and trace amounts of other elements. Immersion tests show that the amount of chemical element leaching is extremely low, and there are no large amounts of ions and elements that affect water chemistry.

[0023] The filters include RCV system downflow filters, RCV system resin trap filters, RCV system shaft seal injection filters, RCV system shaft seal return filters, and TEP system filters.

[0024] After the primary coolant (boric acid water) filter is put into operation, continuous sampling and testing of silicon content are conducted upstream and downstream of the filter to track the release of silicon from the filter element. This is used to supervise the standardization of filter element manufacturing and filter element replacement work in nuclear power plants, and to guide the investigation of whether there are other operations that accidentally introduce impurities such as silicon into the reactor primary loop, so as to plan primary loop water quality control measures in advance.

[0025] S2. Replace the boric acid water in the primary loop of the nuclear power plant. The boric acid water to be desiliconized enters the boric acid tank of the REA system through the TEP system. The boric acid water is replenished from the boric acid in the REA system and the deoxygenated and demineralized water in the TEP system.

[0026] In step S2, the volume of boric acid water to be replenished is calculated using equation (1), which is expressed as follows: (1) in, This represents the total volume of the boric acid solution in the primary loop. To replenish the volume of boric acid solution, To replenish the silicon concentration of the boric acid solution, The silica concentration of the boric acid solution in the previous circuit before water replacement. This refers to the silica concentration in the boric acid solution after water exchange in the first loop.

[0027] The primary loop water replenishment is automatic. The concentration of the replenished boric acid solution must be kept the same as that of the primary loop boric acid solution; otherwise, there is a risk of accidental boration or dilution in the primary loop.

[0028] When replacing water in the primary circuit, it is necessary to consider the impact of the water replacement on changes in the content of other additives in the boric acid water of the primary circuit and on the stable operation of the unit. The primary circuit water in a nuclear power plant contains boron. During normal operation, lithium hydroxide monohydrate is added to the boric acid water to ensure the primary circuit pH is alkaline (referred to as B-Li coordination) to reduce the risk of primary circuit corrosion. Therefore, when replacing water in the reactor's primary circuit, the lithium content will also decrease. If the B-Li coordination requirements are not met, lithium needs to be added to the primary circuit in advance to avoid situations where the B-Li coordination lithium concentration is unqualified.

[0029] The REA system borate tank 21 stores all the borate required for reactivity control during normal unit operation. During normal unit operation, the REA system borate tank 21 is nearly full at the end of each fuel cycle. When the RCP system reaches the refueling shutdown boron concentration and the pressurizer is full, the level in the REA system borate tank 21 reaches its minimum value. At this point, the remaining borate capacity should be sufficient to bring the unit from startup to full power immediately back to cold shutdown.

[0030] S3. Use at least one of the following methods to remove silica from the boric acid water in the boric acid tank 21 of the REA system: The first method: The REA system boric acid tank 21 is connected to the PTR system, and mixed bed resin and desiliconizing resin are filled in the PTR system desalination bed 33 and / or the TEP system desalination bed 13 to desiliconize the boric acid water.

[0031] In some embodiments, the silicone resin is a strong base anion exchange resin containing iron oxide and / or triethylamine, and the mixed bed resin is GR-3-9 NG mixed bed resin. The packing volume ratio of the silicone resin and the mixed bed resin can be 1:(1~3), such as 1:1, 1:2, 1:3, etc. This packing volume ratio can be adjusted appropriately to avoid affecting the normal purification function of the PTR system desalination bed 33 and the TEP system desalination bed 13.

[0032] Strong base anion exchange resins can be used to remove silicon from water with low boron concentrations. However, once the resin is saturated with boron, it transforms from the OH- form to the borate form. Since the dissociation constant pKa of boric acid is close to 9.2, while that of silica is close to 9.7, their ion exchange penetration abilities are similar, significantly reducing the silicon removal capacity of the strong base anion exchange resin. If the desiliconizing resin contains certain special functional groups (such as iron oxides or triethylamine), it can be used to remove silica from boric acid solutions. This special desiliconizing resin can be packed into suitable reactor boric acid water purification desalination beds (such as PTR system desalination bed 33 and TEP system desalination bed 13) to remove silicon from boric acid water. PTR system desalination bed 33 and TEP system desalination bed 13 are normally packed with mixed-bed resin; additional desiliconizing resin is added to achieve the purpose of silicon removal.

[0033] The boric acid water in the REA system boric acid tank 21 can be transported to the PTR system loading well or transfer well 31 by mixing with demineralized water under the drive of the REA system boric acid pump 22 and the REA system demineralized water pump 23. Upon contact with air, oxygen enters the water. After desiliconizing resin is filled into the PTR system desalination bed 33, the PTR system can be put into operation to remove silica from the boric acid water. After silica removal, the boric acid water is transported to the TEP system boric acid tank 11 through the PTR system pipeline and the TEP system pipeline. It is then treated by the TEP system desalination bed 13 and the TEP system evaporator 14 before being transported back to the REA system boric acid tank 21. Further silica removal is achieved by filling the TEP system desalination bed 13 with desiliconizing resin.

[0034] The PTR system's desalination bed 33 has a large resin packing volume, allowing for the removal of a large amount of silica. However, due to the high purification flow rate of the PTR system's purification loop (normal flow rate is approximately 90 m³ / s), it is not ideal for removing silica. 3 The silicon removal efficiency will decrease to some extent ( / h). Furthermore, it is necessary to prevent the release of sulfonic acid groups from the oxidizing resin in the oxygen-containing boric acid water. These groups will be converted into sulfate ions upon heating in the TEP system evaporator 14, leading to an increase in the sulfate concentration in the boric acid water. A preventative measure could be to first purge the oxygen-containing boric acid water with TEG nitrogen to reduce the oxygen content before it enters the TEP system evaporator 14 for boron production.

[0035] Filling the desilication bed 13 of the TEP system with desilication resin can also be used directly for desilication in the boric acid tank 21 of the REA system. The boric acid water in the boric acid tank 21 of the REA system can be transferred to the boric acid water tank 11 of the TEP system through the REA system and the RPE system. The boric acid water does not come into contact with air during the transfer process. Then, this boric acid water can be treated by the desilication bed 13 of the TEP system and the evaporator 14 of the TEP system and transferred back to the boric acid tank 21 of the REA system. Therefore, filling the desilication bed 13 of the TEP system with desilication resin can be used directly for desilication in the boric acid tank 21 of the REA system.

[0036] The TEP system's desalination bed 13 has a small resin packing volume, resulting in a small amount of silica removal. However, due to the TEP system's low purification flow rate (normal flow rate approximately 4m³ / h), it is effective in removing silica. 3 (h), therefore, the silicon removal efficiency is relatively high. When using this silicon removal method, since the boric acid solution does not come into contact with air, it will not cause an increase in the sulfate concentration in the boric acid solution.

[0037] The second method: the boric acid water in the boric acid tank 21 of the REA system is transported to the nanofiltration membrane through the PTR system for silicon removal.

[0038] When the boric acid water in the REA system boric acid tank 21 needs desiliconization, it is mixed with demineralized water through the REA system pipeline and PTR system pipeline, driven by the REA system boric acid pump 22 and the REA system demineralized water pump 23, and then transported into the PTR system loading well or transfer well 31. After the boric acid water in the REA system boric acid tank 21 undergoes desiliconization through the nanofiltration membrane in the PTR system loading well or transfer well 31, it is transported to the TEP system boric acid water tank 11 through the PTR system pipeline and TEP system pipeline. Then, it is treated by the TEP system demineralized bed 13 and the TEP system evaporator 14, and then transported back to the REA system boric acid tank 21.

[0039] The third method: Prepare fresh boric acid solution in the boric acid tank 21 of the REA system to replace the boric acid solution to be desiliconized.

[0040] In emergency situations, fresh boric acid can be prepared in the boric acid tank 21 of the REA system to replace the silica-containing boric acid solution and reduce the silica content in the tank. The displaced silica-containing boric acid solution can be directly discharged into the waste gas, wastewater, and solid waste system for treatment, or it can be temporarily stored and then purified.

[0041] In step S3, when desiliconizing the boric acid tank 21 of the REA system, units using natural boric acid in the reactor primary loop 71 preferentially use desiliconizing resin (i.e., the first method), while units using boric acid enrichment in the reactor primary loop 71 preferentially use nanofiltration membrane desiliconization (i.e., the second method). This helps to save costs. To improve desiliconization efficiency and optimize the desiliconization effect, all three methods can be used simultaneously for desiliconization.

[0042] S4. Establish a reference model for the influence of the filter material of the primary loop boric acid water on the silica concentration of the boric acid water, and compare the changes in silica concentration of the boric acid water during actual operation of the primary loop with the reference model. The comparison results can serve as an auxiliary judgment for the cause of high silica concentration in the primary loop, guide the optimization of the boric acid water quality in the primary loop, and also verify the silica removal effect of using silica-free filter cartridges.

[0043] Specifically, the changes in silica concentration in the primary loop boric acid water were investigated after all filters used were glass fiber or silica-free cartridges. Two fitting curves (referred to as Fitting Curve 1 and Fitting Curve 2) were obtained, representing a reference model for the influence of filter material on silica concentration in boric acid water. This reference model can be used to understand the silica concentration trends in the primary loop of nuclear power plants after using glass fiber or silica-free cartridges for boric acid water filters.

[0044] If only a portion of the filters in the primary loop of a new unit use silica-free filter cartridges, the series of silica concentration values ​​in the primary loop boric acid water should fall between fitted curve 1 and fitted curve 2 over time. If all filters in the primary loop boric acid water of a nuclear power unit use silica-free filter cartridges, the series of silica concentration values ​​in the primary loop boric acid water should conform to fitted curve 2 over time. Otherwise, the cause should be investigated, and the boric acid water quality should be adjusted.

[0045] The present invention proposes a method for removing silicon from the primary loop boric acid water in nuclear power plants. First, a filter element of appropriate material is selected for the primary loop boric acid water filter. Then, an appropriate amount of water is replaced in the primary loop. After the primary loop water replacement, the silicon in the boric acid water enters the TEP system, and then is concentrated in the TEP system evaporator 14 before entering the REA system boric acid tank 21, where it is finally concentrated and accumulated. Silicon in the REA system boric acid tank 21 can be removed by ion exchange resin filtration (including silicon removal resin and mixed bed resin), nanofiltration membrane purification, and replacement with fresh boric acid water. The silicon in the primary loop of the nuclear power plant is ultimately purified and removed in the REA system boric acid tank 21. The silicon removal method of the present invention effectively solves the problem of high silicon levels in the primary loop of nuclear power plants, reduces equipment corrosion and scaling caused by silicon deposition, extends equipment service life, and reduces equipment maintenance and replacement costs.

[0046] When the filter in the primary loop boric acid water does not use a silicon-free filter element, the silicon concentration in the REA system boric acid tank 21 rises rapidly, requiring frequent treatment by the nuclear power plant or direct discharge. The silicon removal method of this invention replaces the filter element in contact with the primary loop boric acid water with a silicon-free filter element, suppressing silicon release at the source. Furthermore, by centrally treating the silicon in the REA system boric acid tank, the operating costs of the nuclear power plant and the environmental emission pressure are reduced.

[0047] This invention also proposes a silicon removal system for boric acid water in the primary loop of a nuclear power plant, employing the aforementioned silicon removal method for boric acid water in the primary loop of a nuclear power plant, such as... Figure 1As shown, the desiliconization system includes a TEP system desalination bed 13, an REA system boric acid tank 21, a PTR system loading or transfer well 31, a PTR system desalination bed 33, and a nanofiltration membrane desiliconization device 4. The TEP system desalination bed 13, the REA system boric acid tank 21, and the PTR system loading or transfer well 31 are connected sequentially. The PTR system loading or transfer well 31 is connected to the PTR system desalination bed 33, the nanofiltration membrane desiliconization device 4, and the TEP system desalination bed 13, respectively, to desiliconize the primary loop boric acid water and the boric acid water to be desiliconized in the REA system boric acid tank 21. Both the TEP system desalination bed 13 and the PTR system desalination bed 33 are filled with desiliconizing resin.

[0048] In some embodiments, the filter for the primary loop boric acid water uses a silica-free filter element, which, compared to traditional glass fiber filter elements, is less prone to releasing silica, thus helping to reduce the silica concentration in the boric acid water. The filter includes an RCV system filter 73 and a TEP system filter (located downstream of the TEP system desalination bed 13). The RCV system filter 73 includes an RCV system downflow filter, an RCV system resin trapping filter, an RCV system shaft seal injection filter, and an RCV system shaft seal return filter.

[0049] The desiliconization system also includes a reactor primary loop 71. A main pump 72 is installed on the RCP system line of the reactor primary loop 71 to drive the coolant boric acid solution to circulate in the primary loop. The primary loop is connected to the RCV system, which includes an RCV system filter 73 for filtering and purifying the boric acid solution in the primary loop. A charge pump 74 is installed on the RCV system line to pressurize and re-inject low-silicon-concentration boric acid solution into the reactor primary loop 71.

[0050] The reactor primary loop 71 is connected to the TEP system boric acid tank 11 via the RCV system, allowing the primary loop boric acid water to enter the TEP system boric acid tank 11 through the RCV system pipeline. The TEP system boric acid tank 11 is connected to the TEP system desalination bed 13, where the primary loop boric acid water undergoes desiliconization. The desiliconized boric acid water then enters the REA system boric acid tank 21. A TEP system transfer pump 12 is installed on the TEP system pipeline between the TEP system boric acid tank 11 and the TEP system desalination bed 13 to transport the boric acid water from the TEP system boric acid tank 11 to the TEP system desalination bed 13 for desiliconization.

[0051] The TEP system also includes a TEP system evaporator 14 connected to the TEP system desalination bed 13 to evaporate and concentrate the desiliconized boric acid water, producing desalinated water and concentrated boric acid. The separated desalinated water is transported to the TEP system desalinated water tank 15, and the concentrated boric acid is transported to the REA system boric acid tank 21. In some embodiments, an REA system desalinated water pump 23 is provided on the REA system pipeline connected to the TEP system desalinated water tank 15 to transport desalinated water, and an REA system boric acid pump 22 is provided on the REA system pipeline connected to the REA system boric acid tank 21 to transport boric acid. Further, the boric acid in the REA system boric acid tank 21 and the desalinated water from the TEP system are mixed to produce fresh boric acid water with a low silica concentration, which is injected into the primary loop through the RCV system for use.

[0052] In some embodiments, the REA system boric acid tank 21 is connected to the RPE system transfer tank 5, and the RPE system transfer tank 5 is connected to the TEP system boric acid water tank 11, so that the boric acid water to be desiliconized from the REA system boric acid tank 21 enters the TEP system boric acid water tank 11, and then undergoes desiliconization through the TEP system desalination bed 13.

[0053] In some embodiments, the REA system boric acid tank 21 is connected to the waste treatment system 6 (such as a three-waste system) to replace the silicon-containing boric acid water and receive other wastes for further processing.

[0054] The REA system boric acid tank 21 is connected to the PTR system loading well or transfer well 31 through the REA system pipeline and the PTR system pipeline. The boric acid water in the REA system boric acid tank 21 is mixed with the demineralized water of the TEP system to obtain boric acid water, which enters the PTR system loading well or transfer well 31, is desiliconized through the PTR system desalination bed 33 and the nanofiltration membrane desiliconization device 4, and then returns to the PTR system loading well or transfer well 31 through the PTR system pipeline.

[0055] In some embodiments, a PTR system purification pump 32 is installed on the PTR system pipeline between the PTR system loading well or transfer well 31 and the PTR system desalination bed 33 to perform preliminary purification of the boric acid water in the PTR system loading well or transfer well 31. The boric acid water is then transported to the PTR system desalination bed 33 for further silica removal purification, and then returned through the PTR system pipeline. The nanofiltration membrane silica removal device 4 is connected in parallel with the PTR system purification pump 32. The boric acid water purified by the nanofiltration membrane silica removal device 4 can be transported to the PTR system desalination bed 33 for further silica removal purification.

[0056] The nanofiltration membrane silicon removal device 4 can be implemented using existing technology. In some embodiments, the nanofiltration membrane silicon removal device 4 includes a nanofiltration container, which contains a nanofiltration membrane. At least one nanofiltration container is provided according to actual filtration requirements to achieve purposes such as primary nanofiltration and secondary nanofiltration.

[0057] In some embodiments, the PTR system loading well or transfer well 31 is connected to the TEP system boric acid water tank 11 through the PTR system pipeline, so that the boric acid water from the PTR system loading well or transfer well 31 enters the TEP system and is desiliconized through the TEP system desalination bed 13.

[0058] The present invention relates to a desiliconization system for the primary loop boric acid water in nuclear power plants. The primary loop boric acid water is transported to the TEP system desalination bed for desiliconization. The boric acid water from the REA system boric acid tank is introduced into the PTR system loading well or transfer well and then transported to the PTR system desalination bed, nanofiltration membrane desiliconization device, and TEP system desalination bed for desiliconization. The desiliconized boric acid water can be returned to the original system, thereby realizing primary loop water exchange and desiliconization, and REA system boric acid tank desiliconization, effectively reducing the silicon concentration of the primary loop boric acid water.

[0059] The following is an illustration through specific examples: Taking two "Hualong One" nuclear power units (Units F3 and F4) as examples, the desiliconization method of boric acid water in the primary loop of the nuclear power plant of the present invention is used for desiliconization. The method includes the following steps: S1. Select the filter elements for the boric acid water filter in the primary loop of the nuclear power plant. For Unit F3, which is operating for the first time, all primary loop boric acid water filters will use glass fiber filter elements, while for Unit F4, all primary loop boric acid water filters will use silicone-free filter elements.

[0060] S2. Replace the boric acid water in the primary loop of the nuclear power plant. The boric acid water to be desiliconized enters the boric acid tank of the REA system through the TEP system. The boric acid water is replenished from the boric acid in the REA system and the deoxygenated and demineralized water in the TEP system.

[0061] The expected value for the silicon concentration in the primary loop boric acid solution is 600 ppb, and the limit is 1000 ppb. Figure 2 The diagram shows the trend of primary circuit silicon concentration during the operation of Unit F3. During normal operation, the primary circuit silicon concentration will continue to rise slowly. By changing the primary circuit boric acid water multiple times, the primary circuit silicon concentration is reduced and maintained below the expected value.

[0062] S3. The following three methods are used to remove silica from the boric acid water in the boric acid tank of the REA system: The first method involves connecting the REA system's boric acid tank to the PTR system. Mixed-bed resin and desiliconizing resin are then loaded into the desalination beds of both the PTR and TEP systems to remove silica from the boric acid water. The desiliconizing resin is a strong-base anion exchange resin containing iron oxide and triethylamine. The mixed-bed resin is GR-3-9 NG mixed-bed resin, and the volume ratio of the desiliconizing resin to the mixed-bed resin can be 1:2.

[0063] The second method: The REA system boric acid tank is connected to a nanofiltration membrane through the PTR system loading well or transfer well to remove silica from the boric acid water using nanofiltration.

[0064] The third method: Prepare fresh boric acid solution in the boric acid tank of the REA system to replace the boric acid solution to be removed.

[0065] The desired silica concentration in the boric acid solution of the REA system boric acid tank is 3000 ppb. Figure 3 The diagram shows the silicon concentration changes after boron production in the borate tanks of two REA systems in different units. In Unit F3, the silicon concentration in the two REA systems (F3REA2110BA and F3REA3110BA) gradually increased after boron production, far exceeding the expected value and approaching 10,000 ppb. After the silicon removal operation in step S3, the silicon concentration decreased to below the limit value, at 2,000-3,000 ppb. In Unit F4, the silicon concentration in the two REA systems (F4REA21140BA and F4REA3110BA) increased slightly after boron production, but remained far below the limit value, maintaining around 1,000 ppb.

[0066] S4. Establish a reference model for the influence of the filter material of the primary loop boric acid water on the silicon concentration of the boric acid water, and compare the changes in silicon concentration of the boric acid water during actual operation of the primary loop with the reference model.

[0067] Specifically, the changes in silica concentration in the primary loop boric acid water were investigated by fitting the filters using either glass fiber or silica-free filter elements. Two fitting curves (denoted as Fitting Curve 1 and Fitting Curve 2) were obtained, representing a reference model for the influence of filter material on silica concentration in boric acid water. For example... Figure 4 As shown, the F3 unit, which uses glass fiber filter cartridges for the primary loop boric acid water, can reduce the silica concentration in the primary loop to below the desired value of 600 ppb after multiple primary loop water changes. The F4 unit, which uses silica-free filter cartridges for the primary loop boric acid water, maintains the silica concentration in the primary loop below 150 ppb, far below the desired value. The fitted curve equation for the silica concentration change in the first cycle of primary loop boric acid water after the F3 unit is filled with boric acid water, i.e., fitted curve 1, is y = -0.0097x. 2 + 4.3822x + 26.868. The fitted curve equation for the silicon concentration change of the primary loop boric acid water after Unit F4 is filled with boric acid water and put into operation, i.e., fitted curve 2, is y = -0.0223x + 42.519. The actual silicon concentration change of the primary loop boric acid water during the operation of the unit is compared with the reference model to guide the optimization of the boric acid water quality in the reactor primary loop.

[0068] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for removing silicon from boric acid water in the primary loop of a nuclear power plant, characterized in that, Includes the following steps: S1. Select the filter element for the boric acid water filter in the primary loop of the nuclear power plant; S2. Replace the boric acid water in the primary loop of the nuclear power plant. The boric acid water to be desiliconized enters the boric acid tank of the REA system through the TEP system. The boric acid water is replenished from the boric acid of the REA system and the deoxygenated and demineralized water of the TEP system. S3. Use at least one of the following methods to remove silicon from the boric acid water in the boric acid tank of the REA system: The REA system boric acid tank is connected to the PTR system, and mixed bed resin and desiliconizing resin are filled in the desalination bed of the PTR system and / or the desalination bed of the TEP system. The boric acid solution in the boric acid tank of the REA system is transported to the nanofiltration membrane for silicon removal via the PTR system. Prepare fresh boric acid solution in the boric acid tank of the REA system to replace the boric acid solution to be removed.

2. The method for removing silicon from boric acid water in the primary loop of a nuclear power plant according to claim 1, characterized in that, In step S1, the primary loop of the nuclear power plant uses natural boric acid, and the filter uses a glass fiber filter element; or, the primary loop of the nuclear power plant uses enriched boric acid, and the filter uses a silicone-free filter element, the filter material of which includes polyester composite fiber.

3. The method for removing silicon from boric acid water in the primary loop of a nuclear power plant according to claim 1, characterized in that, In step S1, the filter includes an RCV system downflow filter, an RCV system resin trapping filter, an RCV system shaft seal injection filter, an RCV system shaft seal return filter, and a TEP system filter.

4. The method for removing silicon from boric acid water in the primary loop of a nuclear power plant according to claim 1, characterized in that, In step S2, the volume of boric acid water to be replenished is calculated using equation (1), which is expressed as follows: （1） in, This represents the total volume of the boric acid solution in the primary loop. To replenish the volume of boric acid solution, To replenish the silicon concentration of the boric acid solution, The silica concentration of the boric acid solution in the previous loop before water replacement. This refers to the silica concentration in the boric acid solution after water exchange in the first loop.

5. The method for removing silicon from boric acid water in the primary loop of a nuclear power plant according to claim 1, characterized in that, In step S3, the desilicone resin is a strong base anion exchange resin containing iron oxide and / or triethylamine; and / or, the mixed bed resin is GR-3-9 NG mixed bed resin; and / or, the volume ratio of the desilicone resin to the mixed bed resin is 1:(1~3).

6. The method for removing silicon from boric acid water in the primary loop of a nuclear power plant according to claim 1, characterized in that, The silicon removal method further includes the following steps: S4. Establish a reference model for the influence of the filter material of the primary loop boric acid water on the silicon concentration of the boric acid water, and compare the changes in the silicon concentration of the boric acid water during actual operation of the primary loop with the reference model.

7. A desiliconization system for boric acid water in the primary loop of a nuclear power plant, characterized in that, The method for removing silicon from boric acid water in the primary loop of a nuclear power plant according to any one of claims 1 to 6, wherein the silicon removal system includes a TEP system desalination bed (13), an REA system boric acid tank (21), a PTR system loading well or transfer well (31), a PTR system desalination bed (33), and a nanofiltration membrane silicon removal device (4); both the TEP system desalination bed (13) and the PTR system desalination bed (33) are filled with silicon removal resin; The TEP system desalination bed (13), the REA system boric acid tank (21), and the PTR system loading well or transfer well (31) are connected in sequence. The PTR system loading well or transfer well (31) is connected to the PTR system desalination bed (33), the nanofiltration membrane desiliconization device (4), and the TEP system desalination bed (13) respectively, so as to remove silicon from the primary loop boric acid water and the boric acid water to be desiliconized in the REA system boric acid tank (21).

8. The desiliconization system for boric acid water in the primary loop of a nuclear power plant according to claim 7, characterized in that, The desilicon removal system also includes a reactor primary loop (71), which is connected to the TEP system boric acid water tank (11). The TEP system desalination bed (13) is connected through the TEP system boric acid water tank (11) to remove silicon from the primary loop boric acid water. The desiliconized boric acid water enters the REA system boric acid tank (21). And / or, the REA system boric acid box (21) is connected to the RPE system transfer box (5), which is connected to the TEP system through the RPE system transfer box (5), and then the TEP system desiliconization is performed through the TEP system desalination bed (13); And / or, the filter for the primary loop boric acid water uses a silicone-free filter element.

9. The desiliconization system for boric acid water in the primary loop of a nuclear power plant according to claim 7, characterized in that, The REA system boric acid tank (21) is connected to the PTR system loading well or transfer well (31) through the REA system pipeline and the PTR system pipeline. The boric acid water in the REA system boric acid tank (21) is mixed with the demineralized water of the TEP system and then enters the PTR system loading well or transfer well (31). It is desiliconized through the PTR system desalination bed (33) and the nanofiltration membrane desiliconization device (4) and then returned to the PTR system loading well or transfer well (31) through the PTR system pipeline.

10. The desiliconization system for boric acid water in the primary loop of a nuclear power plant according to claim 7, characterized in that, The boric acid water from the loading well or transfer well (31) of the PTR system enters the TEP system through the PTR system pipeline, and then undergoes desiliconization through the desalination bed (13) of the TEP system; and / or, The REA system boric acid tank (21) is connected to the waste treatment system (6) to replace the boric acid water to be removed.

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