Waste salt treatment process and system based on melt crystallization method

Abstract

The invention provides a waste salt treatment process and system based on a melt crystallization method, the waste salt treatment process is a process combining pulling crystallization, zone condensation and cold finger / cooling plate crystallization, and matrix salt is recovered from a chloride molten salt system containing strontium element and / or barium element and / or cesium element. The invention aims to solve the problems that the treatment scale and the product purity are difficult to consider at the same time, the volatilization loss is serious, and dual targets are difficult to realize under complex working conditions in the existing dry post-treatment waste salt melt crystallization purification technology. A waste salt melt crystallization purification technology which can adapt to complex working conditions, give consideration to high purification efficiency and high resource recovery rate and meet the large-scale treatment requirement is researched and developed, radioactive waste salt containing splitting elements is treated through process fusion, efficient purification of the waste salt is finally achieved, and the high removal rate and recovery rate are achieved.

Description

Technical Field

[0001] This invention relates to the field of waste salt purification technology for spent fuel reprocessing, and particularly to a waste salt treatment process and system based on melt crystallization. Background Technology

[0002] Nuclear energy, as a high-quality new energy source with high stability, high energy density and low carbon emissions, has become a key candidate energy source for solving the energy shortage problem due to its unique advantages, and its position in the global energy supply system is becoming increasingly important.

[0003] However, the use of nuclear energy inevitably generates a large amount of spent fuel, which contains various highly toxic radioactive elements. If disposed of directly without proper treatment, it will cause long-term and serious harm to the ecological environment and human health. This problem has become one of the core bottlenecks restricting the large-scale development of nuclear energy. Therefore, efficient reprocessing of spent fuel to separate and recover radioactive elements and reduce environmental risks is a necessary prerequisite for the safe use of nuclear energy.

[0004] Currently, spent fuel reprocessing technologies are mainly divided into two categories: aqueous reprocessing and dry reprocessing. Among them, dry reprocessing technology has received widespread attention from the scientific research and industrial communities due to its significant advantages, such as compact process flow, strong radiation resistance of the electrolytic medium, short spent fuel cooling time, and small amount of radioactive waste generated. Especially in the field of high burnup spent fuel processing in advanced nuclear energy systems, it is recognized as an ideal alternative to traditional reprocessing technologies and has broad application prospects.

[0005] Among the many dry reprocessing technologies, the oxide spent fuel processing technology based on molten salt electrorefining technology has been studied the most extensively. However, this process has the following problems in actual operation: highly radioactive fission products such as Sr and Cs will continue to accumulate in the chloride-based molten salt, which will not only cause significant deterioration of the core physicochemical properties of the molten salt such as melting point, viscosity and conductivity, affecting the stability and efficiency of the reprocessing process, but will also eventually form a large amount of highly radioactive waste salt.

[0006] From the perspectives of both environmental safety and technological economy, efficient purification of the aforementioned radioactive waste salts containing reactive fragment elements such as Sr and Cs is crucial. On the one hand, purification enables the recycling of the matrix molten salt, reducing molten salt replenishment costs and improving the economics of the reprocessing process. On the other hand, it can minimize the amount of final radioactive waste generated, reducing waste disposal difficulties and environmental risks, which is of decisive significance for promoting the industrial application of dry reprocessing technology.

[0007] Because fragmented elements such as Sr and Cs are chemically reactive, their chlorides are highly similar in chemical properties to matrix molten salts such as LiCl and KCl. This leads to problems such as high separation difficulty, low purification efficiency, and large reagent consumption when using traditional chemical separation methods such as precipitation and electrolytic extraction to purify waste salts, making it difficult to meet the needs of large-scale treatment.

[0008] To address this challenge, melt crystallization technology, leveraging its core characteristic of separating substances based on differences in melting points and the solubility of impurities in the solid and liquid phases, has become the mainstream technology choice for large-scale waste salt purification. Currently, melt crystallization technologies used for dry post-treatment waste salt purification mainly include zone condensation crystallization technology based on reaction vessels and cold source directional crystallization technology based on cold fingers / cooling plates.

[0009] While regional condensation crystallization technology offers advantages in terms of processing scale, the purity of the crystallized product obtained in a single process is relatively low. It is only suitable for waste salt treatment scenarios with low impurity content. Furthermore, the separation and transfer of the crystallized product from the mother liquor presents process defects such as complex operation, high risk of radioactive leakage, and large material loss, which urgently require targeted improvements. As for cold source directional crystallization technology, it can obtain crystallized products with higher purity in a single process, making it more suitable for extracting pure matrix salt from waste salt with high concentration of impurities. However, this technology suffers from problems such as small single-processing capacity, low processing efficiency, and severe loss of molten salt due to volatilization during crystallization, which restricts its large-scale application.

[0010] Furthermore, existing research on the dry post-treatment waste salt melt crystallization purification is mostly limited to single, idealized treatment scenarios such as the purification of low-concentration impurity salts. It fails to fully consider the complex conditions in actual industrial processing where the impurity concentration in the waste salt gradually increases as the treatment progresses. Under these complex conditions, achieving both high impurity removal rates and high base salt recovery rates simultaneously remains a key technical challenge that current technologies have not addressed, severely hindering the industrial application of melt crystallization technology in the dry post-treatment waste salt purification field. Summary of the Invention

[0011] This invention provides a waste salt treatment process and system based on melt crystallization. Addressing the problems of existing dry post-treatment waste salt melt crystallization purification technologies, such as difficulty in balancing treatment scale and product purity, significant volatilization losses, and challenges in achieving dual objectives under complex operating conditions, this invention develops a waste salt melt crystallization purification technology that can adapt to complex operating conditions, balance high purification efficiency and high resource recovery rate, and meet the needs of large-scale treatment. By integrating processes to treat radioactive waste salt containing fragmented elements, this invention ultimately achieves highly efficient purification of waste salt, reaching a high removal rate and recovery rate.

[0012] This invention provides a waste salt treatment process based on melt crystallization, which combines pulling crystallization, zone condensation and cold finger / cooling plate crystallization processes to recover base salt from a chloride molten salt system containing strontium and / or barium and / or cesium.

[0013] A waste salt treatment process based on melt crystallization according to the present invention includes the following steps: S1. Place the chloride molten salt in the reaction chamber of the Czochralski-zone condensation crystallization apparatus and heat it to melt. S2. The first crucible of the lifting-regional condensation crystallization device used to contain the chloride molten salt is repeatedly lifted by the first automatic lifting mechanism until the upper section of the chloride molten salt cools and crystallizes to form condensation holes; S3. The lifting-regional condensation crystallization device is provided with multiple interval heating zones along the height direction. The heating zones are controlled to cool down sequentially from top to bottom so that the chloride molten salt solidifies from top to bottom, and the part of the chloride molten salt near the bottom is kept in a liquid state. S4. Collect the upper part of the condensed molten salt in step S3 to recover the matrix salt; S5. Cool the liquid molten salt from step S3 and transfer it to a cold finger / cooling plate crystallization device, and use the cold finger or cooling plate to crystallize and separate the matrix salt and recover it.

[0014] The waste salt treatment process based on melt crystallization according to the present invention further includes: S6. The liquid molten salt from step S3 is drawn into the receiving tank and cooled by extending the salt extraction pipe into the condensation hole.

[0015] According to the waste salt treatment process based on melt crystallization provided by the present invention, the temperature of the chloride molten salt during crystallization in steps S1 to S3 is less than or equal to 800 °C. In step S2, the lifting rate of the first automatic lifting mechanism is 0.1-150 mm / min; The cooling rate in step S3 is 3-8 ℃ / h.

[0016] According to the present invention, a waste salt treatment process based on melt crystallization is provided, wherein the chloride molten salt includes at least one of strontium chloride, barium chloride, and cesium chloride, and the mass fraction of strontium chloride, barium chloride, and cesium chloride is 0.1% to 10%.

[0017] This invention also provides a waste salt treatment system based on melt crystallization, which applies the waste salt treatment process based on melt crystallization as described above, including: The Clift-Zone Condensation Crystallization Apparatus includes a first reactor, a first sleeve, and a first crucible arranged sequentially from the outside to the inside. The upper end of the first sleeve is connected to a first automatic lifting mechanism for driving the first sleeve and the first crucible to move up and down. A cold finger / cooling plate crystallization apparatus includes a second reactor, a second crucible disposed in the second reactor, a cooling element, a second automatic lifting mechanism, and a cooling medium circulation mechanism. One end of the cooling element extends into the second crucible, and the other end is connected to the second automatic lifting mechanism. The cooling medium circulation mechanism is connected to the cooling element through a pipeline and is used to provide cooling medium to the interior of the cooling element and drive the cooling medium to circulate.

[0018] According to the waste salt treatment system based on melt crystallization provided by the present invention, both the first reactor and the second reactor are closed environments, or a protective gas is circulated in both the first reactor and the second reactor.

[0019] According to the present invention, a waste salt treatment system based on melt crystallization method is provided. The pull-zone condensation crystallization device includes a first heating mechanism. The first reactor part extends into the first heating mechanism. The first heating mechanism is provided with multiple spaced heating zones along its height direction. Each heating zone is independently temperature controlled. Each heating zone is equipped with a corresponding temperature sensing element.

[0020] According to the present invention, a waste salt treatment system based on melt crystallization method is provided. The cold finger / cooling plate crystallization device includes a second heating mechanism and a plurality of temperature measuring elements. The second reactor part extends into the second heating mechanism. The temperature measuring ends of a portion of the temperature measuring elements are located in the molten salt in the second crucible, and the temperature measuring ends of another portion of the temperature measuring elements are located inside the cooling element.

[0021] A waste salt treatment system based on melt crystallization according to the present invention further includes: A vacuum salt extraction device includes a vacuum pump, a safety tank, and a liquid receiving tank connected in sequence. The safety tank and the liquid receiving tank are connected by a pipeline. The safety tank is used to provide a negative pressure environment for the liquid receiving tank. The liquid receiving tank is equipped with a salt extraction pipe, one end of which extends into the liquid receiving tank and the other end is used to connect to the first crucible.

[0022] This invention provides a waste salt treatment process and system based on melt crystallization. Through the synergistic adaptation of multiple crystallization technologies—including Czochralski crystallization, zone condensation, and cold finger / cooling plate crystallization—it precisely utilizes the differences in melting point and solid-liquid solubility between Sr, Ba, and Cs chlorides and matrix salts (such as LiCl and KCl) to achieve stepwise deep removal of target impurities. This allows for the construction of a complete, efficient, and flexibly adaptable waste salt treatment system. By rationally configuring and optimizing the sequence of each treatment step, the impurity removal rate and overall treatment efficiency are effectively improved. In large-scale treatment scenarios, zone condensation technology can handle large quantities of matrix salt while significantly suppressing salt volatilization. For high-concentration waste salt, cold finger or cooling plate crystallization technology can shorten the treatment cycle and further improve treatment efficiency while ensuring full recovery of the matrix salt. This invention can flexibly adapt to complex working conditions with fluctuating impurity concentrations in waste salt. Whether it is high-concentration or low-concentration molten salt containing Sr, Ba, and Cs chlorides, it can achieve efficient treatment by adjusting the process parameters of each crystallization unit. Compared with the limitations of existing technologies that can only adapt to single impurity concentration conditions, the continuous and synergistic treatment mode of this process can avoid process interruption or decrease in treatment efficiency caused by changes in impurity concentration. The stability and reliability of the treatment process are significantly improved, which is more in line with the actual needs of industrial-scale waste salt treatment. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of the lifting-regional condensation crystallization device provided by the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the cold finger / cooling plate crystallization device provided by the present invention.

[0026] Figure 3 This is a schematic diagram of the vacuum salt extraction device provided by the present invention.

[0027] Figure 4 This is one of the schematic diagrams of the waste salt treatment process provided by the present invention.

[0028] Figure 5 This is the second flow chart of the waste salt treatment process provided by the present invention.

[0029] Figure 6This is a schematic diagram of a condensation hole formed by the lifting method provided by the present invention (wherein, (a) and (b) it is difficult to form an effective condensation hole without the lifting method, and (c), (d), (e), and (f) regular condensation holes can be formed by the lifting-regional condensation process).

[0030] Figure 7 This is a schematic diagram of the surface crystallization of the cold finger and cooling plate provided by the present invention.

[0031] Figure label: 100. Lift-zone condensation crystallization device; 10. First reactor; 11. First sleeve; 12. First crucible; 13. First automatic lifting mechanism; 14. Heating zone; 200. Cold finger / cooling plate crystallization device; 20. Second reactor; 21. Second crucible; 22. Cold finger; 23. Cooling plate; 24. Second automatic lifting mechanism; 25. Cooling medium circulation mechanism; 26. Second heating mechanism; 300. Melting furnace; 400. Vacuum salt extraction device; 40. Vacuum pump; 41. Safety tank; 42. Liquid receiving tank; 43. Salt extraction pipe; 44. Vacuum instrument. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] In the description of this invention, it should be understood that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] In this invention, unless otherwise expressly specified and limited, the first feature "on" or "below" the second feature may be in direct contact with the first and second features, or indirect contact through an intermediate medium. In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] This invention provides a waste salt treatment process based on melt crystallization, which combines pulling crystallization, zone condensation and cold finger / cooling plate crystallization processes to recover base salt from a chloride molten salt system containing strontium and / or barium and / or cesium.

[0037] Traditional single-removal methods cannot meet the engineering requirements for treatment removal rate and reuse rate. Zone condensation has a large processing capacity, but the reusable portion is insufficient. Using multiple condensation processes to improve the removal rate leads to long processing times and low efficiency. Czochralski crystallization has a fast processing speed and can form regular condensation pores, resulting in a large processing capacity but a low removal rate. Cold finger / cooling plate crystallization has a high removal rate and short processing time, but its processing capacity is small, making it unsuitable for large-scale applications. This invention utilizes the large processing capacity of zone condensation crystallization technology, the easy formation of regular condensation pores in Czochralski crystallization technology, and the high removal efficiency of cold finger / cooling plate crystallization technology. It can recover matrix salt from large-scale waste salt in a short time. Specifically, it uses Czochralski-zone condensation crystallization to treat large-scale waste salt initially, and then uses cold finger / cooling plate crystallization to treat the remaining high-concentration waste salt. This approach balances processing scale, removal rate, and matrix salt recovery rate, meeting the large-scale quality treatment requirements of practical engineering applications.

[0038] It is understood that the waste salt treatment process of the present invention is applicable to multiple operating scenarios. For example, for large-scale high-concentration waste salt, a pull-zone condensation crystallization step is performed first, followed by a cold finger / cooling plate crystallization step; or for small-scale low-concentration waste salt, a zone condensation step can be used first to minimize salt volatilization loss while taking into account treatment efficiency; or for high-concentration waste salt, a second-stage cold source directional crystallization step can be directly activated to meet the strict requirements for removal efficiency and treatment speed in engineering applications.

[0039] The chloride molten salt system may include one or more combinations of LiCl-CsCl molten salt, LiCl-SrCl2 molten salt, and LiCl-SrCl2-CsCl molten salt, preferably including LiCl-SrCl2 molten salt and LiCl-SrCl2-CsCl molten salt.

[0040] Chloride molten salts may include at least one of strontium chloride, barium chloride, and cesium chloride, wherein the mass fraction of strontium chloride, barium chloride, and cesium chloride is 0.1% to 10%.

[0041] For example, the present invention provides a waste salt treatment process based on melt crystallization, comprising the following steps: S1. Place the chloride molten salt in the reaction chamber of the Czochralski-zone condensation crystallization apparatus 100 and heat it to melt; S2. The first crucible 12 of the lifting-regional condensation crystallization device 100, used to hold the chloride molten salt, is repeatedly lifted by the first automatic lifting mechanism 13 until the upper section of the chloride molten salt cools and crystallizes to form condensation holes; specifically, the lifting rate can be controlled to be 0.1-150 mm / min, preferably 1 mm / min; Figure 6 As shown, regular condensation holes can be formed by the lifting operation, and the lifting operation is stopped when the growth height reaches 10cm. S3. The lifting-regional condensation crystallization device 100 is provided with multiple spaced heating zones 14 along its height. The heating zones 14 are sequentially cooled from top to bottom to solidify the chloride molten salt, while maintaining the portion of the chloride molten salt near the bottom in a liquid state. Specifically, the heating temperature of each heating zone 14 can be controlled to vary within the range of 400-800℃. When the molten salt to be purified in the upper layer of the crucible solidifies, because the heating zone 14 still maintains a certain heating temperature, the remaining impurities do not solidify and flow to the lower layer of the crucible, while the purified molten salt remains in the upper layer. The multiple heating zones 14 are cooled sequentially from top to bottom, with a cooling rate set to 3-8℃ / h. After all the molten salt in the previous zone has solidified, the next zone is slowly cooled and crystallized, thus gradually completing the purification of the molten salt in the crucible. The molten salt corresponding to the last heating zone 14 remains liquid for subsequent transfer. S4. Collect the upper part of the condensed molten salt in step S3 to recover the matrix salt; then repeat the regional condensation operation to perform multiple regional condensation crystallizations to obtain LiCl crystal salt with a Sr and Cs removal rate of more than 95% in the upper part. This part of the salt can be reused, and the remaining bottom liquid molten salt is used for the next step of processing. S5. Cool the liquid molten salt from step S3 and transfer it to the cold finger / cooling plate crystallization device 200. Use the cold finger 22 or cooling plate 23 to crystallize and separate the matrix salt and recover it. Transfer the molten salt collected multiple times to the crucible of the cold finger / cooling plate crystallization device 200. Heat and melt the high-concentration salt first. Then, use an automatic lifting mechanism to place the cold finger / cooling plate 2cm above the molten salt. By introducing a cooling medium into the cold finger / cooling plate, the cold finger 22 or cooling plate 23 can crystallize and separate a relatively pure matrix salt from the high-concentration waste salt.

[0042] In the above steps S1 to S3, the temperature of the chloride molten salt during crystallization is less than or equal to 800°C, preferably 650-750°C.

[0043] Furthermore, waste salt treatment processes also include: S6. The liquid molten salt from step S3 is drawn into the receiving tank 42 through the salt extraction pipe 43 inserted into the condensation hole and cooled.

[0044] The liquid molten salt obtained in step S3 can be transferred using a vacuum salt extraction device 400, allowing it to cool to a certain temperature in the receiving tank 42 before being transferred to the cold finger / cooling plate crystallization device 200. Based on the discovery of effective formation and control of condensation holes during the Czochralski-zone condensation crystallization process, this invention creatively introduces a negative pressure salt extraction device. The salt extraction pipe 43 is inserted through the condensation holes into the liquid molten salt at the bottom of the crucible, successfully constructing a separation and transfer channel for the liquid molten salt, overcoming the engineering bottleneck of difficult molten salt transfer in existing technologies. By utilizing vacuum pressure difference to achieve smooth transport of high-concentration molten salt, the continuity and integrity of the processing flow are ensured, thereby achieving uninterrupted waste salt treatment and significantly enhancing the practical value and economy of this process and system.

[0045] This invention also provides a waste salt treatment system based on melt crystallization, which can apply the waste salt treatment process based on melt crystallization described in the above embodiments, such as... Figure 1 and Figure 2 As shown, it includes: The lifting-regional condensation crystallization apparatus 100 includes a first reactor 10, a first sleeve 11 and a first crucible 12 arranged sequentially from the outside to the inside. The upper end of the first sleeve 11 is connected to a first automatic lifting mechanism 13, which is used to drive the first sleeve 11 and the first crucible 12 to move up and down. The cold finger / cooling plate crystallization apparatus 200 includes a second reactor 20, a second crucible 21 disposed in the second reactor 20, a cooling element, a second automatic lifting mechanism 24, and a cooling medium circulation mechanism 25. One end of the cooling element extends into the second crucible 21, and the other end is connected to the second automatic lifting mechanism 24. The cooling medium circulation mechanism 25 is connected to the cooling element through a pipeline and is used to provide cooling medium to the interior of the cooling element and drive the cooling medium to circulate.

[0046] Specifically, the first reactor 10 has a reaction chamber, the upper part of which is sealed to a glove box (not shown in the figure) through a flange, providing an anhydrous and oxygen-free inert environment for waste salt treatment. The first sleeve 11 can be placed into the reaction chamber from the opening and the opening is sealed. The first sleeve 11 has a placement cavity for placing the first crucible 12. The first crucible 12 is used to hold molten salt. The first automatic lifting mechanism 13 can lift the first sleeve 11 and the first crucible 12 upward at a certain speed, so that the molten salt in them can slowly cool and crystallize on the inner side of the crucible wall. Due to the density change caused by the phase change, regular condensation holes can be formed in the center of the molten salt.

[0047] The second reactor 20 of the cold finger / cooling plate crystallization device 200 can also be sealed to the glove box via a flange, providing an anhydrous and oxygen-free inert environment for waste salt treatment. The cold finger / cooling plate crystallization device 200 can also have a second sleeve installed between the second reactor 20 and the second crucible 21, similar to the configuration of the Czochralski-zone condensation crystallization device 100. The cooling element includes at least one of a cold finger 22 and a cooling plate 23. The cooling element has an internal cavity and an inlet and outlet, forming an inlet and outlet channel via connecting pipes. The cooling medium circulation mechanism 25 provides a gaseous cooling medium, such as argon, nitrogen, or helium, which cools the high-temperature gas flowing out of the cooling element to room temperature. The gaseous cooling medium is circulated within the heat exchange components, cooling element, and connecting pipes via a gas compressor. The pipes can be equipped with regulating valves and flow meters to adjust the gas flow rate into the cooling element. The cooling gas flow rate can be set to 5-100 L / min, preferably 20-30 L / min.

[0048] After cooling and crystallization for 60-210 minutes, the cooling element is lifted from the molten salt at a speed of 10 cm / min using the second automatic lifting mechanism 24. The crystallized salt on the cooling element is carried out with it and can be transferred to the melting furnace 300 for heating to melt the salt and collect it in a crucible. The remaining high-concentration waste salt that cannot be processed in the second crucible 21 can be extracted for further post-processing.

[0049] To further construct a reliable reaction environment, a protective gas can be introduced into the first reactor 10 and the second reactor 20. The protective gas can be one or more of argon, nitrogen, and helium, thereby effectively isolating air, ensuring the purity of the basic salt, preventing the leakage of radioactive materials, and reducing environmental and operational safety risks. At the same time, it maintains the stability of the reaction system and avoids the impact of external environmental fluctuations on the continuity and stability of processes such as melting and crystallization and impurity separation, providing a reliable environmental guarantee for the efficient recovery of high-purity basic salt.

[0050] In some embodiments, such as Figure 1 As shown, the lifting-regional condensation crystallization device 100 includes a first heating mechanism. The first reactor 10 partially extends into the first heating mechanism. The first heating mechanism has multiple spaced heating zones 14 along its height direction. Each heating zone 14 is independently temperature-controlled to achieve molten salt zoned condensation and ensure temperature control accuracy. Furthermore, each heating zone 14 is equipped with a corresponding temperature sensing element to detect temperature changes in the heating zone 14 in real time and optimize temperature control. The temperature sensing element can be, for example, a thermocouple, and can be positioned at the middle height of each heating zone 14 to ensure accurate temperature measurement.

[0051] In some embodiments, such as Figure 2 As shown, the cold finger / cooling plate crystallization device 200 includes a second heating mechanism 26 and multiple temperature measuring elements. The second reactor 20 extends into the second heating mechanism 26. The temperature measuring ends of some of the temperature measuring elements are located in the molten salt in the second crucible 21, and the temperature measuring ends of other temperature measuring elements are located inside the cooling element. By real-time detection of the molten salt temperature and the cooling element temperature, the two work together to keep the crystallization temperature gradient in the optimal range. This not only improves the purity and crystallization efficiency of the crystallized product, but also avoids crystal defects caused by temperature fluctuations, ensuring the stability and reliability of the basic salt recovery.

[0052] In some embodiments, such as Figure 3 As shown, the waste salt treatment system also includes: The vacuum salt extraction device 400 includes a vacuum pump 40, a safety tank 41, and a liquid receiving tank 42 connected in sequence. The safety tank 41 and the liquid receiving tank 42 are connected by a pipeline. The safety tank 41 is used to provide a negative pressure environment for the liquid receiving tank 42 and also to prevent the molten salt from being drawn back and causing danger. The liquid receiving tank 42 is provided with a salt extraction pipe 43. One end of the salt extraction pipe 43 extends into the liquid receiving tank 42, and the other end is used to connect to the first crucible 12.

[0053] Specifically, the receiving tank 42 can be located inside the glove box, while the safety tank 41 and the receiving tank 42 can be located outside the glove box. A sealed connection can be provided between the salt extraction pipe 43 and the first crucible 12. By transferring the molten salt at the bottom of the first crucible 12 to the receiving tank 42 for cooling, the impact of high temperature on subsequent devices can be avoided, improving reliability. The vacuum pump 40 is used to provide the power for salt extraction, and its pumping rate can be set to ≥8 L / s. Its connection to the safety tank 41 ensures that the vacuum degree inside the container is <80Pa during pumping. It is also equipped with a vacuum instrument 44 and a digital pressure gauge to monitor the vacuum degree.

[0054] This invention provides a waste salt treatment process and system based on melt crystallization. Through the synergistic adaptation of multiple crystallization technologies—including pull crystallization, zone condensation, and cold finger / cooling plate crystallization—it precisely utilizes the differences in melting point and solid-liquid solubility between Sr, Ba, and Cs chlorides and matrix salts (such as LiCl and KCl) to achieve stepwise deep removal of target impurities. This allows for the construction of a complete, efficient, and flexibly adaptable waste salt treatment system. By rationally configuring and optimizing the sequence of each treatment step, the impurity removal rate and overall treatment efficiency are effectively improved. In large-scale treatment scenarios, zone condensation technology can handle large quantities of matrix salt while significantly suppressing salt volatilization. For high-concentration waste salt, cold finger 22 or cooling plate 23 crystallization technologies can shorten the treatment cycle and further improve treatment efficiency while ensuring full recovery of the matrix salt. This invention can flexibly adapt to complex working conditions with fluctuating impurity concentrations in waste salt. Whether it is high-concentration or low-concentration molten salt containing Sr, Ba, and Cs chlorides, it can achieve efficient treatment by adjusting the process parameters of each crystallization unit. Compared with the limitations of existing technologies that can only adapt to single impurity concentration conditions, the continuous and synergistic treatment mode of this process can avoid process interruption or decrease in treatment efficiency caused by changes in impurity concentration. The stability and reliability of the treatment process are significantly improved, which is more in line with the actual needs of industrial-scale waste salt treatment.

[0055] The waste salt treatment system of this invention is equipped with a controller that can control the automatic heating, cooling, lifting mechanism movement, salt extraction and other processes, achieving precise automated control, greatly reducing the workload of manual operation, reducing the waiting time between processes, effectively improving the processing efficiency, and adapting to the needs of large-scale waste salt treatment; by automatically controlling the program to replace manual direct contact with radioactive waste salt, the risk of radioactive leakage can be avoided, and at the same time, abnormal alarm and emergency shutdown functions can be set to ensure the safety of equipment and operators.

[0056] refer to Figure 4 and Figure 5 The process flow of the present invention will be described below with reference to specific embodiments.

[0057] Example 1: After uniformly mixing and drying, 20 kg of LiCl-SrCl2 (0.6 wt%)-CsCl (1.6 wt%) molten salt is placed into the first crucible 12 inside the first stainless steel sleeve 11. The first sleeve 11 is then placed into the first reactor 10. The multi-section heating zone 14 is heated to 640°C by the first heating mechanism and maintained at this temperature for more than 12 hours to ensure that the 20 kg of LiCl-SrCl2 (0.6 wt%)-CsCl (1.6 wt%) molten salt is completely melted and uniformly mixed.

[0058] Combination Figure 1 The lifting-regional condensation crystallization process employs a first automatic lifting mechanism 13 for lifting. During the slow lifting process, the solution in the first crucible 12 is gradually cooled, causing a solid with regularly spaced condensation holes to form on the upper layer of the molten salt. The formation of these condensation holes provides a transport channel for the salt extraction process, ensuring the reliability of the salt extraction operation.

[0059] Next, the controller controls the first heating zone 14 to undergo programmed cooling and condensation, slowly cooling within the temperature range of 640℃-590℃ at a rate of 5℃ / h. Heating control of the first heating zone 14 is stopped when the temperature reaches 590℃. During this operation, the lower heating zone 14 maintains its original heating temperature of 640℃. After the first heating zone 14 is turned off, programmed cooling and condensation begins for the second heating zone 14, similarly slowly cooling within the temperature range of 640℃-590℃ at a rate of 5℃ / h. Heating control of the second heating zone 14 is stopped when the temperature reaches 590℃. During this operation, the remaining lower heating zone 14 maintains its original heating temperature. The remaining heating zones 14 are cooled sequentially from top to bottom using the same method until all the molten salt in the upper part is cooled. Understandably, after the molten salt to be purified in the upper layer of the crucible solidifies, since the heating zone 14 still maintains a certain heating temperature, the remaining impurities do not solidify and flow to the lower layer of the crucible, while the purified molten salt remains in the upper layer of the crucible. The multiple heating zones 14 cool down sequentially from top to bottom, thereby gradually completing the purification of the molten salt to be purified in the crucible.

[0060] Afterwards, the condensed molten salt was removed, and the more transparent salt phase at the top of the salt column was taken as the purified LiCl molten salt. The upper 50% LiCl molten salt after four condensation purifications, compared to before purification, contained less Sr... 2+ Cs + The removal rates were all greater than 95%.

[0061] Combination Figure 3The salt extraction tube 43 of the vacuum salt extraction device 400 is inserted into the molten salt in the first crucible 12 to transport the liquid molten salt to the receiving tank 42. When the molten salt is purified to the final temperature-controlled position using the aforementioned pull-regional condensation crystallization device 100, this section is heated and kept at a constant temperature to melt the salt into a liquid state. This section of molten salt is then extracted in liquid form using the salt extraction tube 43 for further processing. The remaining salt is melted and condensed again, and the final section is melted again to extract the high-concentration salt. This process is repeated 2-4 times, with approximately 1-2 kg of bottom molten salt extracted each time. This salt is then collected in the cold finger / cooling plate crystallization device 200 for the next step. The remaining upper salt, which accounts for 60% of the total weight of the molten salt, is melted and extracted using the vacuum salt extraction device 400, ultimately merging into the collection device to obtain approximately 60% upper salt body, of which Sr... 2+ Cs + The removal rate can reach about 98%.

[0062] Combination Figure 2 The high-concentration bottom salt to be purified is collected in the second crucible 21 of the cold finger / cooling plate crystallization device 200, heated and melted. Then, the cooling medium circulation mechanism 25 (argon gas is used in this embodiment) is activated to pre-cool the surface of the cooling element. The cooling element is then slowly inserted into the molten salt, and the molten salt solidifies layer by layer on the surface of the cold finger 22 and / or cooling plate 23 to form a solid salt layer. It is understood that when the molten salt to be purified on the surface of the cold finger 22 and / or cooling plate 23 solidifies, the remaining impurities do not solidify and flow to the outer layer of the molten salt. The purified salt remains in solid form on the surface of the cold finger 22 and / or cooling plate 23. After cooling and crystallization are completed, the second automatic lifting mechanism 24 can transfer the cooling element along with the crystal salt to the melting furnace 300 for collection. Repeating this operation yields high-purity matrix salt.

[0063] like Figure 7 As shown, transparent and pure LiCl salt crystals are obtained around the cooling finger 22 and the outer periphery of the cooling plate 23. It is understandable that when processing salts of different concentrations, the reaction conditions or process parameters can be adjusted accordingly. For example, high-concentration salts require the treatment of Sr... 2+ Ba 2+ and Cs + When the initial total mass fraction of the plasma is 5%, the argon (or other cooling gas) flow rate can be set to 12-15 L / min, and the molten salt temperature to 630℃-650℃. After a period of crystallization, the Sr on the cold finger 22 and / or cooling plate 23... 2+ Ba 2+ and Cs + Plasma removal rates can reach approximately 98%. Another example is the Sr removal required in high-concentration salt solutions. 2 + Ba 2+and Cs + When the initial total mass fraction of the plasma is 13%, the argon (or other cooling gas) flow rate can be set to 20-25 L / min, the molten salt temperature to 610℃-630℃, and the Sr on the cold finger 22 and / or cooling plate 23 can be set accordingly. 2+ Ba 2+ and Cs + The plasma removal rate can reach approximately 95%. Each crystallization of cooling plate 23 can purify about 300g of salt from the molten salt. After 10-15 crystallization purifications of cooling plate 23, a salt body accounting for about 20% of the total mass is obtained, of which Sr... 2+ Cs + The removal rate can reach about 95%.

[0064] According to the above molten salt purification process, strontium and / or barium and / or cesium ions in molten salt with a mass fraction of 80% can be purified, including but not limited to Sr, Cs and Ba in LiCl-CsCl-SrCl2, LiCl-SrCl2 and LiCl-BaCl2 molten salts.

[0065] Comparative Example 1: The only difference between the waste salt treatment process and Example 1 is that only regional condensation is used to remove Sr from large-scale LiCl molten salt.

[0066] Comparative Example 2: The only difference between the waste salt treatment process and Example 1 is that only the cold finger / cooling plate crystallization method is used to remove Sr from large-scale LiCl molten salt.

[0067] Comparative Example 3: The only difference between the waste salt treatment process and Example 1 is that only the Czochralski method was used to remove Sr from large-scale LiCl molten salt.

[0068] Experimental results showed that the method in Comparative Example 1 is suitable for large-scale processing and can effectively suppress salt volatilization, but its removal efficiency is limited under high-concentration waste salt conditions; only 50% of the waste salt treated at the 20kg level can be recycled as LiCl salt. The method in Comparative Example 2 has a fast processing rate and high removal rate, suitable for deep purification of high-concentration waste salt, but it suffers from significant volatilization losses during processing. The method in Comparative Example 3 has a fast processing rate, but its removal rate is limited when used alone.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A waste salt treatment process based on melt crystallization, characterized in that, The matrix salt is recovered from a chloride molten salt system containing strontium and / or barium and / or cesium by combining Czochralski crystallization, zone condensation and cold finger / cooling plate crystallization processes.

2. The waste salt treatment process based on melt crystallization according to claim 1, characterized in that, Includes the following steps: S1. Place the chloride molten salt in the reaction chamber of the Czochralski-zone condensation crystallization apparatus and heat it to melt. S2. The first crucible of the lifting-regional condensation crystallization device used to contain the chloride molten salt is repeatedly lifted by the first automatic lifting mechanism until the upper section of the chloride molten salt cools and crystallizes to form condensation holes; S3. The lifting-regional condensation crystallization device is provided with multiple interval heating zones along the height direction. The heating zones are controlled to cool down sequentially from top to bottom so that the chloride molten salt solidifies from top to bottom, and the part of the chloride molten salt near the bottom is kept in a liquid state. S4. Collect the upper part of the condensed molten salt in step S3 to recover the matrix salt; S5. Cool the liquid molten salt from step S3 and transfer it to a cold finger / cooling plate crystallization device, and use the cold finger or cooling plate to crystallize and separate the matrix salt and recover it.

3. The waste salt treatment process based on melt crystallization according to claim 2, characterized in that, Also includes: S6. The liquid molten salt from step S3 is drawn into the receiving tank and cooled by extending the salt extraction pipe into the condensation hole.

4. The waste salt treatment process based on melt crystallization according to claim 2, characterized in that, The temperature of the chloride molten salt during crystallization in steps S1 to S3 is less than or equal to 800 °C. In step S2, the lifting rate of the first automatic lifting mechanism is 0.1-150 mm / min; The cooling rate in step S3 is 3-8 ℃ / h.

5. The waste salt treatment process based on melt crystallization according to any one of claims 1-4, characterized in that, The chloride molten salt includes at least one of strontium chloride, barium chloride, and cesium chloride, wherein the mass fraction of strontium chloride, barium chloride, and cesium chloride is 0.1% to 10%.

6. A waste salt treatment system based on melt crystallization, employing the waste salt treatment process based on melt crystallization as described in claim 1, characterized in that, include: The Clift-Zone Condensation Crystallization Apparatus includes a first reactor, a first sleeve, and a first crucible arranged sequentially from the outside to the inside. The upper end of the first sleeve is connected to a first automatic lifting mechanism for driving the first sleeve and the first crucible to move up and down. A cold finger / cooling plate crystallization apparatus includes a second reactor, a second crucible disposed in the second reactor, a cooling element, a second automatic lifting mechanism, and a cooling medium circulation mechanism. One end of the cooling element extends into the second crucible, and the other end is connected to the second automatic lifting mechanism. The cooling medium circulation mechanism is connected to the cooling element through a pipeline and is used to provide cooling medium to the interior of the cooling element and drive the cooling medium to circulate.

7. The waste salt treatment system based on melt crystallization method according to claim 6, characterized in that, Both the first reactor and the second reactor are closed environments, or a protective gas is passed through the first reactor and the second reactor.

8. The waste salt treatment system based on melt crystallization method according to claim 6, characterized in that, The lifting-regional condensation crystallization device includes a first heating mechanism, with the first reactor extending into the first heating mechanism. The first heating mechanism has multiple spaced heating zones along its height, and each heating zone is independently temperature-controlled. Each heating zone is equipped with a corresponding temperature sensing element.

9. The waste salt treatment system based on melt crystallization method according to claim 6, characterized in that, The cold finger / cooling plate crystallization device includes a second heating mechanism and multiple temperature measuring elements. The second reactor part extends into the second heating mechanism. The temperature measuring ends of a portion of the temperature measuring elements are located in the molten salt inside the second crucible, and the temperature measuring ends of another portion of the temperature measuring elements are located inside the cooling element.

10. The waste salt treatment system based on melt crystallization according to any one of claims 6-9, characterized in that, Also includes: A vacuum salt extraction device includes a vacuum pump, a safety tank, and a liquid receiving tank connected in sequence. The safety tank and the liquid receiving tank are connected by a pipeline. The safety tank is used to provide a negative pressure environment for the liquid receiving tank. The liquid receiving tank is equipped with a salt extraction pipe, one end of which extends into the liquid receiving tank and the other end is used to connect to the first crucible.

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