Resuscitation method for spent fuel pool purification filter resin
By alternating the purification targets in the spent fuel water tank purification system and utilizing oxidation properties to revive ion exchange resins, the problem of cation exchange resin failure was solved, achieving resin regeneration and water quality stability, and reducing operating costs and waste generation.
Patent Information
- Application Number
- CN202511186943.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-25
- Publication Date
- 2025-11-28
AI Technical Summary
During the purification process of boric acid solutions containing hydrazine and potassium ions, the cation exchange resin in the spent fuel pool purification filter undergoes group degradation, leading to the release of total organic carbon (TOC). The anion exchange filter adsorbs TOC, causing the water quality to deviate. New resins become ineffective quickly, increasing radioactive solid waste and operating costs.
By alternating the purification targets in the purification system and utilizing the oxidation properties of the spent fuel water tank, hydrazine on the cation exchange resin reacts with hydrogen peroxide, and the released TOC is adsorbed by the anion exchange resin. Combined with real-time monitoring and frequent switching, this ensures that the resin recovers and the water quality meets the requirements.
It extends the service life of the resin, reduces radioactive solid waste and operating costs, avoids frequent resin replacement, ensures safe and stable water quality, and meets the technical specifications of nuclear power plants.
Smart Images
Figure CN121016868A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nuclear power technology, specifically relating to a method for revitalizing resin in a spent fuel pool purification filter. Background Technology
[0002] The intermediate-pressure safety injection system is a passive safety system. Its function is to inject boric acid solution from the top and / or bottom of the reactor core to ensure core cooling and flooding in the event of a primary circuit leak and a pressure below 5.9 MPa. The VVER unit is designed with four intermediate-pressure safety injection tanks, each with a volume of 60 m³. 3 The water volume accounts for 50m³ 3 The volume of nitrogen gas is 10m³. 3 The system stores a boric acid solution at a temperature of 70-75℃ and a concentration of 16-20 g / L. During major overhauls of pressurized water reactor nuclear power plants, the intermediate-pressure safety injection tank is regularly inspected according to the maintenance program. This requires the boric acid solution in the intermediate-pressure safety injection tank to be drained to other boric acid storage tanks in advance. However, the 16-20 g / L boric acid solution in the intermediate-pressure safety injection tank contains 100-200 mg / L of potassium ions and more than 100 mg / L of hydrazine, resulting in a pH value above 6.5. If this solution enters the boric acid storage tank, it will increase the potassium ion concentration, affecting the water quality control of the primary loop. Therefore, it needs to be purified using a spent fuel water pool purification filter. However, the following problems were discovered during the actual purification process:
[0003] During the purification of boric acid solutions containing hydrazine and potassium ions, the cation exchange resin in the spent fuel water tank purification filter underwent group degradation, releasing a large amount of TOC (total organic carbon). This caused the anion exchange resin in the anion filter, which was connected in series with the cation filter, to adsorb a large amount of TOC and release it as well, resulting in a deviation in the water quality of the boric acid storage tank. Even after unloading the ion exchange resin in the spent fuel water tank purification filter and replacing it with new resin, the problem of the new resin rapidly failing during purification still occurred.
[0004] Therefore, it is urgent to reduce the generation of primary loop radioactive solid waste, improve water quality safety, and reduce operating costs. Summary of the Invention
[0005] To overcome the problems existing in related technologies, a method for regenerating resin in a spent fuel water tank purification filter is provided, the method comprising:
[0006] Step 1: After the water quality analysis is completed by receiving the drainage from the medium-pressure injection tank, the boric acid storage tank is put into operation to purify the water in the spent fuel water tank. When the TOC concentration of the water at the outlet of the purification system exceeds the preset threshold, the purification target of the purification system is switched from the boric acid storage tank to the spent fuel water tank. This allows the hydrazine adsorbed on the ion exchange resin in the purification system to react with the hydrogen peroxide in the spent fuel water tank. The irradiation of the water in the spent fuel water tank can also decompose the TOC released by the cation exchange resin into sulfate ions, which are then adsorbed and removed by the anion exchange resin in the purification system.
[0007] Step 2: When the TOC concentration at the outlet of the purification system is between 100-200 μg / L, switch the purification target of the purification system from the spent fuel water tank to the boric acid storage tank.
[0008] Step 3: Repeat steps 1 and 2 until the potassium ion concentration in the boric acid storage tank is purified to the preset threshold.
[0009] In one possible implementation, the purification system of the spent fuel water tank is equipped with multiple filters, which are arranged in order from upstream to downstream: a first mechanical filter, a cation filter, and an anion filter, with a second mechanical filter connected in parallel with the first mechanical filter.
[0010] Before step 1, step 4 is included: loading cation exchange resin into the first mechanical filter, the second mechanical filter, and the cation exchanger; loading anion exchange resin into the anion exchanger; after the resin loading is completed, rinsing with demineralized water to ensure it is qualified; then using boric acid solution from the boric acid storage tank to saturate the anion exchange resin in the anion exchanger with boric acid; taking samples at the outlet and inlet of the filtration system to analyze the boric acid concentration; when the difference between the boric acid concentration at the outlet and the boric acid concentration at the inlet is less than 0.5 g / L, the boric acid saturation is completed, the valves at the outlet and inlet of the purification system are closed, and the system is placed in standby mode.
[0011] In one possible implementation, step 5 is included before step 1, wherein during the overhaul, when any one or more medium-pressure injection tanks drain water into the boric acid storage tank, the water in the boric acid storage tank is sampled and analyzed, including the concentration of hydrazine and potassium ions in the water.
[0012] In one possible implementation, step 1 further includes step 11: during the process of purifying the water in the boric acid storage tank by the purification system, the TOC concentration and hydrazine concentration of the outlet water of each filter in the purification system are sampled and analyzed at a preset frequency. When the TOC concentration at the outlet of any filter in the purification system exceeds 1.0 mg / L, the purification target of the purification system is switched from the boric acid storage tank to the spent fuel water pool.
[0013] In one possible implementation, step 2 further includes step 21: during the process of purifying the water in the spent fuel pool by the purification system, the TOC concentration and hydrazine concentration of the water at the outlet of each filter of the purification system are sampled and analyzed at a preset frequency, and the sulfate ion concentration at the outlet of the anion exchanger of the purification system is analyzed; if the TOC concentration of the water at the outlet of the first mechanical filter or the second mechanical filter is less than 0.1 mg / L, and the TOC concentration of the water at the outlet of the cation exchanger is less than 0.2 mg / L, the purification target of the purification system is switched from the spent fuel pool to the boric acid storage tank.
[0014] In one possible implementation, step 5 is included after step 3, in which the purification system is put into operation to purify the water in the spent fuel pool until the TOC concentration and sulfate concentration of the water at the outlet of the anion exchanger are lower than 0.05 mg / L and lower than 0.005 mg / L.
[0015] The beneficial effects of this disclosure are as follows: The method provided by this disclosure makes full use of the oxidation performance of the spent fuel water tank, realizes the recovery of ion exchange resin, reduces the additional operating costs and the amount of radioactive solid waste generated due to frequent resin replacement, extends the service life of the resin, avoids the addition of traditional chemical agents, and realizes the recovery of ion exchange resin while purifying water by switching between boric acid storage tank and spent fuel water tank, thus extending the service life of the resin, saving the operating cost of the unit, and solving the problem of cation exchange resin failure in filter caused by purifying water in boric acid storage tank. Attached Figure Description
[0016] Figure 1 This is a flowchart of the spent fuel water tank purification filter resin regeneration method disclosed in this disclosure.
[0017] Figure 2 This is a schematic diagram illustrating an example of a spent fuel water pool purification system.
[0018] Figure 3 This is a schematic diagram illustrating a comparison of the purification effects of a boric acid storage tank. Detailed Implementation
[0019] The present disclosure will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0020] Unless otherwise defined, the technical and scientific terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains; the terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure; the term "comprising" and any variations thereof in this disclosure are intended to cover non-exclusive inclusion. Clearly, the embodiments described in this disclosure are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.
[0021] In this disclosure, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0022] During a major overhaul at a nuclear power plant, the water quality of the boric acid storage tank after receiving boric acid solution from the intermediate-pressure safety injection tank was monitored and found to be: potassium concentration 8.57 mg / L, boric acid concentration 17.4 g / L, and hydrazine concentration 7.29 mg / L, all of which met the standards. To reduce the potassium ion concentration in the boric acid storage tank, the spent fuel pool purification system was put into operation to purify the boric acid storage tank. After 11 hours of purification, the water quality of the boric acid storage tank was monitored and it was found that the TOC in the tank had risen to 1000 μg / L (normally around 150 μg / L, and the requirement is less than or equal to 500 μg / L). After investigation, the TOC at the outlet of the cation exchange filter rose to 4000 μg / L (normally around 300 μg / L). The reason was that the cation exchange resin loaded in the mechanical filter and the cation exchange filter released a large amount of organic groups.
[0023] To investigate the cause of TOC release from cation exchange resin, a simulation experiment was conducted. 25 mL of cleaned nuclear-grade cation exchange resin was immersed in 200 mL of sample, with shaking for 1 minute every 15 minutes. Data are detailed in Table 1. The results showed that boric acid solution containing hydrazine at a concentration exceeding 1 mg / L could deactivate the cation exchange resin, causing a large release of sulfonic acid groups. This also drastically reduced the resin's adsorption capacity for potassium ions, affecting its performance and causing water quality deterioration. However, after using an oxidizing agent to consume the hydrazine in the boric acid solution, the resin's performance was not affected. Furthermore, the performance of temporarily deactivated resin could be restored by circulating and rinsing it with a boric acid solution containing oxidizing agents.
[0024] Table 1 Results of resin immersion test
[0025]
[0026] Table 2 shows the water quality analysis results of the medium-pressure injection tanks. As can be seen from Table 2, the average concentration of hydrazine in each medium-pressure injection tank is about 150 mg / L.
[0027] Table 2. Water quality analysis results of the medium-pressure safety injection tank.
[0028]
[0029] During each major overhaul, one or two intermediate-pressure safety injection tanks are periodically inspected. The boric acid solution in these tanks needs to be drained into a boric acid storage tank beforehand. The boric acid storage tank contains 1200m³ of solution. 3 The boric acid solution was kept at a temperature above 70℃. Table 3 shows the water quality analysis results of the boric acid storage tank after receiving the drainage from the medium-pressure injection tank. As shown in Table 3, the potassium ion concentration of the boric acid storage tank after receiving the drainage from the medium-pressure injection tank basically meets the theoretical dilution ratio. However, considering the volatility of hydrazine and its reaction with dissolved oxygen in boric acid, the concentration is lower than the theoretical dilution concentration. Due to the high potassium ion concentration in the boric acid storage tanks (No. 1 boric acid storage tank: 7.22 mg / L, No. 4 boric acid storage tank: 6.96 mg / L), in order to reduce the impact on the water quality control of the primary loop during the start-up phase, the potassium ion concentration in the boric acid storage tanks needs to be purified to 1.0 mg / L before use. However, purification will cause the cation exchange resin in the filter to become ineffective.
[0030] Table 3. Water quality analysis results of boric acid storage tank
[0031]
[0032] The spent fuel pool was filled with a volume of approximately 1200 m³. 3 A boric acid solution with a concentration between 16-20 g / L was used as a coolant to store spent fuel assemblies. Because the coolant in the spent fuel water tank came into contact with air and under the irradiation of the spent fuel assemblies, it developed strong oxidizing properties. Tests showed that the hydrogen peroxide content in the solution was approximately 5 mg / L. Since hydrazine in the boric acid storage tank has reducing properties, the oxidizing property of the hydrogen peroxide in the spent fuel water tank could be cleverly utilized to conduct a redox reaction to consume it. The reaction formula is shown below:
[0033] N₂H₄ + 2H₂O₂ = N₂↑ + 4H₂O
[0034] However, the overhaul schedule is tight, and some pipelines require isolation for maintenance. Therefore, it's impossible to consume the hydrazine in the boric acid storage tank through prolonged water exchange between the spent fuel water tank and the boric acid storage tank. To address these issues, this application provides a method for revitalizing the purified filter resin in the spent fuel water tank to purify the wastewater flowing from the medium-pressure injection system to the boric acid storage tank during maintenance. Figure 1 As shown, the method includes:
[0035] Step 1: After the water quality analysis is completed by receiving the drainage from the medium-pressure injection tank, the boric acid storage tank can be purified by the waste fuel water pool purification system at a preset flow rate (e.g., 9.8 kg / s). The TOC, hydrazine, and potassium ion concentrations at the purification system outlet and in the boric acid storage tank are monitored periodically. Data analysis shows that some of the TOC released by the cation exchange resin is absorbed by the anion exchange resin in the anion filter after the cation filter. If the TOC concentration in the purified system outlet water exceeds a preset threshold, to prevent excessive TOC in the boric acid storage tank, the purification system is switched from purifying the boric acid storage tank to purifying the waste fuel water pool. Water from the waste fuel water pool is then introduced into the purification system, allowing the hydrazine adsorbed on the ion exchange resin in the purification system to react with the hydrogen peroxide in the waste fuel water pool. The high radiation of the waste fuel water pool also causes the TOC released by the cation exchange resin to rapidly decompose into sulfate ions, which are then adsorbed and removed by the anion exchange resin in the purification system.
[0036] Step 2: When the TOC concentration at the outlet of the purification system is between 100-200 μg / L, the resin in the purification system is instructed to return to normal, and the purification target of the purification system is switched from the spent fuel water tank to the boric acid storage tank.
[0037] Step 3: Repeat steps 1 and 2 until the potassium ion concentration in the boric acid storage tank is purified to a preset threshold (e.g., 1.0 mg / L). Compared to related technologies where the cation exchange resin in the mechanical and cation filters of the purification system rapidly fails after purifying the boric acid storage tank, the alternating cyclic purification method of this disclosure fully utilizes the oxidation performance of the spent fuel water pool. This effectively reduces the potassium ion concentration in the boric acid storage tank and also enables the reuse of the ion exchange resin. When the potassium ion concentration in the boric acid storage tank is purified to the preset threshold, the TOC concentration at the outlet of the purification system has recovered to the normal level of 100-200 μg / L.
[0038] In one application example, such as Figure 2As shown, the purification system of the spent fuel water tank is equipped with multiple filters, arranged sequentially from upstream to downstream: a first mechanical filter 7, a cation exchange filter 9, and an anion exchange filter 10. A second mechanical filter 8 is connected in parallel with the first mechanical filter 7. For example, the first mechanical filter, the second mechanical filter, and the cation exchange filter are all mechanical filters containing cation exchange resin, used to purify mechanical impurities and harmful ions in the spent fuel water tank. The anion exchange filter is a filter containing anion exchange resin. The cation exchange filter and the anion exchange filter are used to purify the water quality and remove radioactive substances, thereby ensuring that the water quality meets the requirements of the technical specifications and reducing the radiation dose to workers. The first mechanical filter 7 and the second mechanical filter 8 are alternately used, and the purification system operates by putting one set of mechanical filters, one set of cation exchange filters, and one set of anion exchange filters into operation. The method described before step 1 also includes steps 4 and 5.
[0039] Step 4: Load 2.4m³ of the first mechanical filter 7, the second mechanical filter 8, and the cation exchanger 9. 3 The cation exchange resin is loaded with 2.4 m³ of cation exchange resin in the anion exchanger 10. 3 After the anion exchange resin is loaded, it is first rinsed with demineralized water to ensure it is qualified. Then, the anion exchange resin in the anion exchanger 10 is saturated with boric acid using boric acid solution in the boric acid storage tank 5. The boric acid concentration is sampled and analyzed at the outlet and inlet of the filtration system. When the difference between the boric acid concentration at the outlet and the boric acid concentration at the inlet is less than 0.5 g / L, the boric acid saturation is completed, the valves at the outlet and inlet of the purification system are closed, and the system is placed in standby mode.
[0040] Step 5: During the overhaul, with one or more medium-pressure injection tanks draining water into the boric acid storage tank, take samples of the water in the boric acid storage tank for analysis, including the concentration of hydrazine and potassium ions in the water.
[0041] Step 1 also includes step 11: During the process of purifying the water in the boric acid storage tank by the purification system, the TOC concentration and hydrazine concentration of the outlet water of each filter in the purification system are sampled and analyzed at a preset frequency. When the TOC concentration at the outlet of any filter in the purification system exceeds 1.0 mg / L, the purification target of the purification system is switched from the boric acid storage tank to the spent fuel water pool.
[0042] Step 2 further includes step 21: During the process of purifying the spent fuel water tank using the purification system, the TOC concentration and hydrazine concentration of the water at the outlet of each filter in the purification system are sampled and analyzed at a preset frequency, and the sulfate ion concentration at the outlet of the anion exchanger is analyzed; if the TOC concentration of the water at the outlet of the first mechanical filter 7 or the second mechanical filter 8 is lower than 0.1 mg / L, and the TOC concentration of the water at the outlet of the cation exchanger 9 is lower than 0.2 mg / L, the purification target of the purification system is switched from the spent fuel water tank to the boric acid storage tank. Figure 3 As shown, the content of potassium ions and hydrazine decreased significantly after purification. While purifying the water, the ion exchange resin was revitalized, extending its service life.
[0043] Step 3 is followed by step 5, in which the purification system is put into operation to purify the water in the spent fuel water tank 6 until the TOC concentration and sulfate concentration in the outlet water of the anion exchanger 10 are lower than 0.05 mg / L and lower than 0.005 mg / L.
[0044] This disclosure, through in-depth engineering practice analysis, identifies the causes of ion exchange resin failure in the water purifier after drainage from the medium-pressure safety injection system. By employing an alternating purification method, it breaks away from the traditional single purification mode, fully utilizing the oxidation performance of the spent fuel water tank to revitalize the ion exchange resin. This reduces additional operating costs and the generation of radioactive solid waste caused by frequent resin replacement, extends the resin's lifespan, and avoids the need for traditional chemical reagents. By switching purification between the boric acid storage tank and the spent fuel water tank, ion exchange resin revitalization is achieved simultaneously with water purification, extending resin lifespan, saving unit operating costs, and solving the problem of cation exchange resin failure in the filter caused by purifying the water in the boric acid storage tank.
[0045] The method disclosed herein monitors hydrazine concentration and TOC content in real time, enabling timely and accurate system switching operations. This ensures the continuity and stability of the purification process, avoids purification interruptions due to resin failure, improves the purification efficiency of the boric acid storage tank and spent fuel pool, ensures that the water quality meets the requirements of the nuclear power plant's technical specifications, and guarantees the safety and stability of the primary loop water quality of the nuclear power plant.
[0046] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.
Claims
1. A method for revitalizing resin in a spent fuel water tank purification filter, characterized in that, The method includes: Step 1: After the water quality analysis is completed by receiving the drainage from the medium-pressure injection tank, the boric acid storage tank is put into operation to purify the water in the spent fuel water tank. When the TOC concentration of the water at the outlet of the purification system exceeds the preset threshold, the purification target of the purification system is switched from the boric acid storage tank to the spent fuel water tank. This allows the hydrazine adsorbed on the ion exchange resin in the purification system to react with the hydrogen peroxide in the spent fuel water tank. The irradiation of the water in the spent fuel water tank can also decompose the TOC released by the cation exchange resin into sulfate ions, which are then adsorbed and removed by the anion exchange resin in the purification system. Step 2: When the TOC concentration at the outlet of the purification system is between 100-200 μg / L, switch the purification target of the purification system from the spent fuel water tank to the boric acid storage tank. Step 3: Repeat steps 1 and 2 until the potassium ion concentration in the boric acid storage tank is purified to the preset threshold.
2. The method according to claim 1, characterized in that, The purification system of the spent fuel water tank is equipped with multiple filters, which are arranged in the order of upstream to downstream: a first mechanical filter, a cation filter, and an anion filter. The second mechanical filter is connected in parallel with the first mechanical filter. Before step 1, step 4 is included: loading cation exchange resin into the first mechanical filter, the second mechanical filter, and the cation exchanger; loading anion exchange resin into the anion exchanger; after the resin loading is completed, rinsing with demineralized water to ensure it is qualified; then using boric acid solution from the boric acid storage tank to saturate the anion exchange resin in the anion exchanger with boric acid; taking samples at the outlet and inlet of the filtration system to analyze the boric acid concentration; when the difference between the boric acid concentration at the outlet and the boric acid concentration at the inlet is less than 0.5 g / L, the boric acid saturation is completed, the valves at the outlet and inlet of the purification system are closed, and the system is placed in standby mode.
3. The method according to claim 1, characterized in that, Before step 1, there is also step 5, during the overhaul, when any one or more medium-pressure injection tanks drain water into the boric acid storage tank, the water in the boric acid storage tank is sampled and analyzed, including the concentration of hydrazine and potassium ions in the water.
4. The method according to claim 2, characterized in that, Step 1 also includes step 11: During the process of purifying the water in the boric acid storage tank by the purification system, the TOC concentration and hydrazine concentration of the outlet water of each filter in the purification system are sampled and analyzed at a preset frequency. When the TOC concentration at the outlet of any filter in the purification system exceeds 1.0 mg / L, the purification target of the purification system is switched from the boric acid storage tank to the spent fuel water pool.
5. The method according to claim 2, characterized in that, Step 2 also includes step 21: During the process of purifying the water in the spent fuel pool by the purification system, the TOC concentration and hydrazine concentration of the water at the outlet of each filter of the purification system are sampled and analyzed at a preset frequency, and the sulfate ion concentration at the outlet of the anion exchanger of the purification system is analyzed; if the TOC concentration of the water at the outlet of the first mechanical filter or the second mechanical filter is less than 0.1 mg / L, and the TOC concentration of the water at the outlet of the cation exchanger is less than 0.2 mg / L, the purification target of the purification system is switched from the spent fuel pool to the boric acid storage tank.
6. The method according to claim 1, characterized in that, Step 3 is followed by step 5, in which the purification system is put into operation to purify the water in the spent fuel pool until the TOC concentration and sulfate concentration in the anion exchanger outlet water are below 0.05 mg / L and below 0.005 mg / L.