Continuous precipitation equipment and method suitable for americium nitrate

Abstract

The continuous precipitation equipment comprises an evaporation condensation pipe and an evaporation reaction tank, the condensation pipe is connected with an evaporation reactor, and an inner cylinder of the evaporation reaction tank is connected with a high-acid feed liquid and deionized water inlet, a steam inlet and a steam outlet. A continuous precipitation method suitable for americium nitrate comprises the following steps that S1, an americium nitrate solution is transferred into an evaporation concentration reactor through a liquid inlet and concentrated, and steam enters the evaporation concentration reactor through a steam inlet and is discharged through a steam outlet; s2, deionized water is added through a liquid inlet to dilute the americium nitrate solution, and then the americium nitrate solution enters a reactor mixing tank through a ball valve and a flow pump; oxalic acid enters the reactor mixing tank through a liquid inlet of the reactor mixing tank and is preliminarily mixed with the americium nitrate solution in the reactor mixing tank by virtue of a stirrer; s3, the solution stays in an ultrasonic channel, and further reacts under the ultrasonic action to obtain americium oxalate hydrate solid.

Description

Technical Field

[0001] This patent relates to the field of spent fuel reprocessing technology, and specifically to a continuous precipitation device and method suitable for americium nitrate. Background Art

[0002] In recent years, with the development of advanced nuclear fuel cycle research, the international community has paid more and more attention to the research on the integrated process of spent fuel reprocessing / separation. At present, the more influential nuclear fuel integrated separation processes carried out internationally are Japan's PUREX-TRUEX integrated process, Russia's SuperPUREX process and China's PUREX-TRPO process. These processes have been improved and simplified and finally verified by thermal tests, and the minor actinide element americium has been successfully separated. However, there are many problems in its transformation. In order to transform it into a granular solid form suitable for storage, it is necessary to convert the americium nitrate solution into an oxide in one step. The most mature method for this type of conversion is to use oxalic acid precipitation. Compared with hydrogen peroxide precipitation, the solution and solid involved in it are more stable and safer than the hydrogen peroxide process; it is also more satisfactory for its treatment of solutions containing high concentrations of elements that can catalyze the decomposition of hydrogen peroxide. However, when using oxalic acid precipitation, facing the low solubility of oxalic acid under acidic conditions, there are many problems in the pre-treatment of desulfurization. For example: the use of organic acids causes container corrosion and interference from precipitated impurities, the reduction of metal concentration in the precipitated solution by alkali neutralization, and problems with tail gas processing; in the precipitation process, not only the concentration of precipitated metal americium must be met, but also the shielding and protection of high-concentration americium must be considered: the commonly used kettle precipitation reactor has a high single dose for operators, etc. There are no good solutions to these drawbacks. At present, the extraction and preparation of americium in China is still in the experimental stage, and there are no reports on the industrialization of the preparation of americium oxide abroad.

[0003] Americium-241 does not require reactor irradiation, but is directly obtained through the decay of separated plutonium-241 isotopes in spent fuel. It has the characteristics of low energy, high probability of gamma radiation and high specific activity, and is widely used in neutron sources, thickness gauges and smoke alarms. In recent years, as radioisotope batteries have become popular, americium-241 has received widespread attention as the best raw material for small isotope nuclear batteries.

[0004] In order to realize the closed loop of separation and integrated americium extraction, it is necessary to design and invent a simple, efficient and feasible americium nitrate transformation process. This is of great significance to the development and acceleration of the industrial production and product application of americium isotopes in my country. Summary of the invention

[0005] The purpose of the present invention is to: In view of the above problems, the present invention invents a continuous precipitation process equipment and method suitable for americium nitrate. The first purpose is to use this system process to achieve salt-free denitration of americium nitrate feed liquid. The principle of this system uses an azeotropic denitration pretreatment method. On the one hand, it avoids the equipment corrosion and tail gas problems caused by the use of neutralizers and organic acids in the denitration of the high-acid americium-containing solution after the separation process. On the other hand, the americium nitrate solution is also concentrated, which improves the precipitation efficiency and reduces the americium retention in the mother liquor and the excessive volume of the mother liquor. The purpose of the present invention is also to provide a continuous precipitation device and method for the system. After the pre-treatment, the gram-liter americium nitrate solution is mixed with oxalic acid and enters the continuous precipitation channel and the ultrasonic generator. Under the action of ultrasonic enhancement, the crystal hydrate grows fully. At the same time, when a large amount of high-concentration americium oxalate is precipitated by continuous feeding, it also avoids the exposure of operators to the high radiation dose (~270mSv / h) from the americium nitrate feed solution compared to the current mainstream kettle precipitation.

[0006] The technical scheme of the present invention is as follows: a continuous precipitation device suitable for americium nitrate comprises a steam concentration condenser and a steam concentration reaction tank, the condenser is connected to the steam concentration reactor, the inner cylinder of the steam concentration reactor is connected to a high acid feed liquid and a deionized water inlet, a steam inlet and a steam outlet, the lower end of the steam concentration reactor is connected to a flow pump through a ball valve, and the flow pump is connected to a reaction liquid mixing tank through a pipeline; a reaction liquid mixing tank cover is provided above the reaction liquid mixing tank, a liquid inlet and a thermometer sleeve are provided above the reaction liquid mixing tank cover, an agitator is provided in the middle of the reaction liquid mixing tank, and a stirring paddle is connected to the lower end of the agitator; the lower end of the reaction liquid mixing tank body is connected to the flow pump through a ball valve, the flow pump is connected to an ultrasonic channel through a pipeline, the ultrasonic channel is spirally distributed from bottom to top on the outer side of an ultrasonic generator shaft, the upper end of the ultrasonic generator shaft is connected to the ultrasonic generator, the end of the ultrasonic channel is connected to a flat filter after passing through the ball valve, and a solution outlet is provided at the bottom of the flat filter.

[0007] A bracket is arranged outside the ultrasonic generator.

[0008] The effective volume of the reaction liquid mixing tank is 3L, its inner layer is 316L stainless steel and its outer layer is lead.

[0009] The stirrer in the reaction liquid mixing tank is 1.5 cm away from the bottom of the tank body, the stirring paddle is a four-blade spiral stirring paddle with a blade diameter of 3 cm, and the stirring speed is controlled at 300-500 r / min.

[0010] The flat plate filter has a metal filter cloth with a pore size of 15 μm.

[0011] A method for continuous precipitation of americium nitrate comprising the following steps:

[0012] S1: transferring the americium nitrate solution into a steam concentration reactor through a liquid inlet to concentrate the americium nitrate solution, and steam enters the steam concentration reactor through a steam inlet and is discharged through a steam outlet;

[0013] S2: adding deionized diluted americium nitrate solution through the liquid inlet, and then passing the americium nitrate solution into the reactor mixing tank through the ball valve and the flow pump; while oxalic acid enters the reactor mixing tank through the liquid inlet of the reactor mixing tank, and is preliminarily mixed with the americium nitrate solution in the reactor mixing tank with the aid of a stirrer, and the preliminarily mixed solution enters the ultrasonic pipeline under the action of the flow pump;

[0014] S3: The solution stays in the ultrasonic channel and further reacts under the action of ultrasound, oxalic acid hydrate crystallizes, and the suspension generated by the reaction is filtered through a flat filter through a ball valve at the end of the ultrasonic pipeline to obtain americium oxalate hydrate solid.

[0015] In S1, the generated evaporated condensate enters the condensate storage tank through the condenser pipe to serve as seasoning liquid, waiting to enter the device again.

[0016] In the S1, the steam is saturated steam at 0.25 MPa and 120°C.

[0017] In S3, the mother liquor flows to the rear end through the precipitation mother liquor outlet for concentration and recovery.

[0018] The process also includes S4, wherein deionized water is introduced from a deionized water inlet to wash the ultrasonic pipe and the americium oxalate solid obtained by filtration, and the americium oxalate filter cake is obtained after drying; the americium oxalate filter cake is then placed in a quartz crucible, transferred into a calcining furnace, heated to 750° C., and kept warm for 6 hours to finally obtain americium dioxide powder.

[0019] The remarkable effects of the present invention are:

[0020] (1) High industrial safety and controllable product purity: The azeotropic denitration method is adopted. Compared with the denitration method of organic acids such as methanol and formic acid in general industry, it avoids the uncontrollability of the exothermic reaction during the induction period and the accumulation of intermediate products such as nitrous acid, which leads to problems such as product purity. Herman D et al. in the United States used NH 4 Although acidity adjustment by adding OH can effectively avoid product contamination, it also causes the loss of americium in the tail gas due to the mixing of ammonia vapor and nitrate.

[0021] (2) Low radiation protection pressure and high product conversion rate: Compared with general kettle batch precipitation, it is obviously not suitable for the environment with a dose of up to 270mSv / h per 1 gram liter of metal. The continuous precipitation method improves the processing efficiency per unit volume of the equipment while meeting the ALARA principle (the principle of as low as reasonably practicable) of personnel operation. Ultrasonic intervention can accelerate the crystallization growth of oxalic acid hydrate and reduce the retention of precipitates in the pipeline. Shortening the precipitation time also reduces the loss of americium in the mother liquor.

[0022] (3) Simplify the process and improve the operation stability: Compared with the process of adding organic acid and other reagents for the first decomposition, then adjusting the pH value for the second time, and finally settling and stirring, the process of introducing manual intervention by personnel is more complicated. The present invention simplifies the precipitation steps while meeting the level of industrial automation. The key control points are easy to grasp and are more stable and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of a continuous precipitation device for americium nitrate;

[0024] In the figure: condenser (1), steam concentration reactor (2), high acid liquid and deionized water inlet (3), steam inlet (4), steam outlet (5), ball valve (6), flow pump (7), stirrer (8), thermometer sleeve (9), solution feed port (10), reaction liquid mixing tank cover (11), stirring paddle (12), reaction liquid mixing tank (13), ball valve (14), flow pump (15), ultrasonic pipeline (16), ultrasonic generator (17), ultrasonic generator shaft (18), flat filter inlet valve (19), flat filter (20), precipitation mother liquid outlet (21), ultrasonic generator bracket (22). DETAILED DESCRIPTION

[0025] Many specific details are described in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present application, so the present application is not limited by the specific implementation disclosed below.

[0026] The terms used in one or more embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of the present application. The singular forms of "a", "said" and "the" used in one or more embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of the present application refers to and includes any or all possible combinations of one or more associated listed items.

[0027] It should be understood that, although the terms first, second, etc. may be used to describe various information in one or more embodiments of the present application, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0028] A continuous precipitation device suitable for americium nitrate comprises a condenser 1, the condenser 1 is connected to a steam concentration reactor 2, the condenser 1 condenses and collects the steam generated by the steam concentration reactor 2, the inner cylinder of the steam concentration reactor 2 is connected to a high-acid feed liquid and a deionized water inlet 3, a steam inlet 4, and a steam outlet 5, the steam enters the interlayer through the steam inlet 4, conducts heat to the feed liquid, and is finally discharged through the steam outlet 5, the lower end of the steam concentration reactor 2 is connected to a flow pump 7 through a ball valve 6, and the flow pump 7 is connected to a reaction liquid mixing tank 13; the low-acid feed liquid after seasoning passes through the ball valve 6 and enters the reaction liquid mixing tank body 13 under the control of the flow pump 7, and the reaction liquid mixing tank 13 is provided with a reaction liquid mixing tank cover above 11, a liquid inlet 10 and a thermometer sleeve 9 are arranged above the reaction liquid mixing tank cover 11, a stirrer 8 is arranged in the middle of the reaction liquid mixing tank 13, and the lower end of the stirrer 8 is connected to a stirring paddle 12; the lower end of the reaction liquid mixing tank body 13 is connected to a flow pump 15 through a ball valve 14, and the mixed liquid enters an ultrasonic channel 16 under the action of the flow pump 15 after passing through the ball valve 14, and the ultrasonic channel 16 is spirally distributed from bottom to top on the outer side of the ultrasonic generator shaft 18, and a bracket 22 is arranged outside the ultrasonic generator 17, and the end of the ultrasonic channel 16 is connected to a flat filter 20 after passing through a ball valve 19, and a solution outlet 21 is arranged at the bottom of the flat filter 20.

[0029] The effective volume of the reaction liquid mixing tank 13 is 3L, and the material is inner layer 316L + outer layer lead (316L thickness is 3mm, lead thickness is 5mm, and the effective shielding amount of americium-241 metal is 8.26g);

[0030] In the present invention, the stirrer 8 in the reaction liquid mixing tank 13 is 1.5 cm away from the bottom of the tank body, the stirring paddle 12 is a four-blade spiral stirring paddle with a blade diameter of 3 cm, and the stirring speed is controlled at 300-500 r / min;

[0031] In the present invention, the thermometer sleeve 9 is a chuck interface, the inner end of which extends toward the inner cavity of the ultrasonic reaction body 13 and forms a protective cavity, and the protective cavity is air-heat-conducting;

[0032] In the present invention, a diaphragm pump 15 is provided at the front end of the mixed liquid ultrasonic pipeline 16; the ultrasonic pipeline 16 has an inner diameter of φ15 mm and a length of 2.1 m and is spirally distributed on the ultrasonic generator shaft 18;

[0033] In the present invention, an ultrasonic pipe 16 is spirally distributed from bottom to top on the outer side of the ultrasonic generator shaft 18;

[0034] In the present invention, the diameter of the ultrasonic generating shaft 18 is φ50 mm and the length is 50 cm;

[0035] A method for continuous precipitation of americium nitrate comprising the following steps:

[0036] S1: transferring the americium nitrate solution into the steam concentration reactor 2 through the liquid inlet 3 to concentrate the americium nitrate solution, and steam enters the steam concentration reactor 2 through the steam inlet 4 and is discharged through the steam outlet 5;

[0037] S2: adding deionized diluted americium nitrate solution through the liquid inlet 3, and then the americium nitrate solution enters the reactor mixing tank 13 through the ball valve 6 and the flow pump 7; while oxalic acid enters the reactor mixing tank 13 through the liquid inlet 10 of the reactor mixing tank, and is preliminarily mixed with the americium nitrate solution in the reactor mixing tank 13 by means of the stirrer 8, and the preliminarily mixed solution enters the ultrasonic pipe 16 under the action of the flow pump 15;

[0038] S3: The solution stays in the ultrasonic channel 16 and further reacts under the action of ultrasound, oxalic acid hydrate crystallizes, and the suspension generated by the reaction passes through the ball valve 19 at the end of the ultrasonic pipeline and is filtered through the flat filter 20 to obtain americium oxalate hydrate solid.

[0039] S4: Deionized water is introduced from the deionized water inlet 3 to wash the ultrasonic pipe and the americium oxalate solid obtained by filtration, and the americium oxalate filter cake is obtained after drying; the americium oxalate filter cake is then placed in a quartz crucible, transferred into a calcining furnace and heated to 750° C., and kept warm for 6 hours to finally obtain americium dioxide powder.

[0040] In the present invention, the evaporation rate of step S1 is 5L / h; since nitric acid and water form an azeotropic mixture, the azeotropic point increases with the increase of pressure, but when it reaches a certain value, the boiling point decreases with the increase of nitric acid concentration, and this point is 68%±0.5%. At normal temperature and pressure, the azeotropic point temperature is generally 120.5°C. At this temperature, nitric acid is concentrated by distillation, and while reducing the volume and molar number of nitric acid, the concentration is always maintained at about 68%, that is, 14±0.5 mol.

[0041] In the present invention, the azeotropic point of the nitric acid and water in step S1 is 120.5°C (the boiling point of water at room temperature is 100°C, and the boiling point of nitric acid at room temperature is 86°C);

[0042] In the present invention, in step S1, the acidity of the solution is controlled to be 14.4 mol / L, and the acidity of the solution is controlled to be 0.3-0.8 mol / L after the americium nitrate solution is concentrated and diluted with deionized water, and the americium concentration in the americium nitrate solution is ≥1 g / L, and the volume of the precipitation stock solution is determined according to the concentration of the precipitated metal;

[0043] In the present invention, the evaporated condensate produced in step S1 enters the condensate storage tank through the condenser tube 1 to serve as the seasoning liquid, waiting to enter the evaporation and concentration system again. At this time, the acidity of the condensate is greater than 6 mol / L and less than 14.4 mol / L.

[0044] In the present invention, the oxalic acid concentration in step S2 is 0.9 mol / L, and the amount of oxalic acid added needs to be 0.1 mol in excess, that is, the chemical reaction of precipitating americium oxalate solution from americium nitrate using oxalic acid is as follows:

[0045] 2Am(NO 3 ) 3 +3H 2 C 2 O 4 +xH 2 O=Am 2 (C 2 O 4 ) 3 ·xH 2 O+6HNO 3

[0046] The concentration is 0.9 mol / L, and an excess of 0.1 M oxalic acid needs to be added x L:

[0047]

[0048] V: volume of the precipitation stock solution;

[0049] m: amount of americium metal in americium nitrate solution;

[0050] In the present invention, the inlet flow rate of the oxalic acid solution in the reaction liquid mixing tank 13 in step S2 is 0.1-0.5 L / h, and the inlet flow rate of the americium nitrate is 0.5-3.5 L / h, and the two solutions can be inlet at the same time;

[0051] In the present invention, the mixed solution of the americium nitrate solution and the oxalic acid in step S3 is introduced into the ultrasonic channel via a flow pump, and the residence time is optimally controlled to be 10 to 20 minutes;

[0052] In the present invention, the americium oxalate hydrate suspension in step S3 is filtered through a flat filter provided with a metal filter cloth, and the pore size of the filter cloth is 10 to 50 μm;

[0053] In the present invention, deionized water is used in S4 to clean the pipes and the tiny particles attached to the surface of the americium oxalate hydrate. If the acidity is ≥ 0.3 mol, the americium oxalate hydrate will be reversely dissolved, resulting in the loss of precipitate and excessive mother liquor.

[0054] Example:

[0055] 14.0L of americium nitrate solution (acidity 5.5mol, americium concentration 0.21g / L) separated by the TRPO process needs to be adjusted in acidity, volume, and metal americium concentration to meet the precipitation requirements. To achieve the optimal precipitation conditions, if the acidity of americium nitrate is adjusted to 0.3-0.8mol and the americium concentration is ≥1g / L, it is calculated that the americium nitrate solution needs to be concentrated at least 85 times.

[0056] 1) Transfer 14.0L of americium nitrate solution into the steam concentration reactor 2 through the liquid inlet 3, and concentrate the americium nitrate solution 85 times at an evaporation rate of 5L / h. The jacket layer in the steam concentration reactor 2 provides energy for the reaction process through steam. The steam enters through the steam inlet 4. The steam is 0.25MPa, 120℃ saturated steam. The steam is discharged through the steam outlet 5. During the steam concentration process, keep an eye on the liquid level gauge. When the volume is concentrated to 165ml of americium nitrate solution, turn off the steam concentration reaction. At this time, a highly concentrated americium nitrate solution with an acidity of about 14±0.5mol and an americium concentration of 17.85g / L is obtained. The condensate is introduced into the condensate storage tank through the condenser 1, and serves as the seasoning liquid for the next batch of americium nitrate, and circulates in this system. Heating

[0057] 2) Add deionized water to dilute 18 times (add about 2.805L of deionized water) through the deionized water inlet 3 to obtain an americium nitrate solution with an acidity of 0.8mol, a volume of 2.97L, and an americium concentration of 0.992g / L. 0.43L of 0.9mol / L oxalic acid needs to be prepared. The seasoned americium nitrate solution enters the reactor mixing tank 13 through the ball valve 6 and the flow pump 7, and the oxalic acid enters the reactor mixing tank 13 through the reactor mixing tank liquid inlet 10 at a speed of 0.28L / h. The solution is preliminarily mixed in the reactor mixing tank with the aid of the stirrer 8. To prevent uneven mixing of the feed liquid, the speed of the stirring paddle 12 is controlled at 450r / min to ensure that the americium nitrate solution and the oxalic acid solution are fully mixed. At this speed, the feed liquid will not splash, and it also plays a role in full mixing. When the volume of the feed liquid in the reactor mixing tank 13 reaches 2.2 L, the leaf outlet valve is opened, and the feed liquid after preliminary mixing enters the ultrasonic pipeline 16 at a flow rate of 2.2 L / h under the action of the flow pump 15.

[0058] Calculation basis: 3.14×21dm×(0.075dm) 2 ×1 / 6h=2.2L

[0059] That is, the flow rate of the mixed liquid from the reactor mixing tank 13 into the ultrasonic channel 16 through the flow pump 15 is controlled at 2.2 L / h;

[0060] 3) The diameter of the ultrasonic generator shaft 18 is φ50mm and the length is 50cm. The inner diameter of the ultrasonic pipeline is φ15mm and the length is 2.1m. The reaction solution stays in the ultrasonic channel 16 for more than 10 minutes. Under the action of ultrasonic enhancement, the mixed solution further reacts and the oxalic acid hydrate crystals grow faster. The suspension generated by the reaction is filtered through the flat filter 20 (metal filter cloth pore size: 15μm) through the ball valve 19 at the end of the ultrasonic pipeline to obtain americium oxalate hydrate solid. The mother liquor 3.4L flows to the rear end through the precipitation mother liquor outlet 21 for concentration and recovery.

[0061] 4) After the precipitation stock solution and oxalic acid are completely fed, deionized water is introduced from the deionized water inlet 3 at 100 mL / min for 10 min, and the ultrasonic pipe and the americium oxalate solid obtained by filtration are washed. After drying, 5.73 g of americium oxalate filter cake (bound water: 10.87) is obtained. The Am concentration in the precipitation mother liquor is analyzed by a high-purity germanium gamma spectrometer and is 15.1 mg / L. The precipitation rate of the americium element is calculated to be 98.24%.

[0062] 5) 5.73 g of americium oxalate hydrate obtained after precipitation was placed in a quartz crucible, transferred to a calcining furnace and heated to 750° C. for 6 hours. Finally, 3.26 g of americium dioxide powder was obtained.

[0063] The above description is only a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this patent should be included in the scope of protection of this patent.

[0064] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present application.

[0065] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0066] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The optional embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can understand and use the present application well.

Claims

1. A continuous precipitation device suitable for americium nitrate, characterized in that: The invention comprises a steam concentration condenser (1) and a steam concentration reaction tank (2). The condenser (1) is connected to the steam concentration reactor (2). The inner cylinder of the steam concentration reactor (2) is connected to a high-acid feed liquid and a deionized water inlet (3), a steam inlet (4), and a steam outlet (5). The lower end of the steam concentration reactor (2) is connected to a flow pump (7) through a ball valve (6). The flow pump (7) is connected to a reaction liquid mixing tank (13) through a pipeline. A reaction liquid mixing tank cover (11) is provided above the reaction liquid mixing tank (13). A liquid inlet (10) and a thermometer sleeve (9) are provided above the reaction liquid mixing tank cover (11). The reaction liquid mixing tank (13) is provided with a liquid mixing tank cover (11). ) is provided in the middle of the mixing tank (13), the lower end of which is connected to a stirring paddle (12); the lower end of the reaction liquid mixing tank (13) is connected to a flow pump (15) through a ball valve (14), the flow pump (15) is connected to an ultrasonic channel (16) through a pipeline, the ultrasonic channel (16) is spirally distributed from bottom to top on the outer side of an ultrasonic generator shaft (18), the upper end of the ultrasonic generator shaft (18) is connected to an ultrasonic generator (17), the end of the ultrasonic channel (16) is connected to a flat filter (20) after passing through a ball valve (19), and a solution outlet (21) is provided at the bottom of the flat filter (20).

2. A continuous precipitation device for americium nitrate according to claim 1, characterized in that: A bracket (22) is provided outside the ultrasonic generator (17).

3. A continuous precipitation device suitable for americium nitrate according to claim 1, characterized in that: The effective volume of the reaction liquid mixing tank (13) is 3L, and its inner layer is 316L stainless steel and its outer layer is lead.

4. A continuous precipitation device for americium nitrate according to claim 1, characterized in that: The stirrer (8) in the reaction liquid mixing tank (13) is 1.5 cm away from the bottom of the tank body, and the stirring paddle (12) is a four-blade spiral stirring paddle with a blade diameter of 3 cm. The stirring speed is controlled at 300-500 r / min.

5. A continuous precipitation device for americium nitrate according to claim 1, characterized in that: The flat plate filter (20) is provided with a metal filter cloth with a pore size of 15 μm.

6. A method for continuous precipitation of americium nitrate, using the continuous precipitation device for americium nitrate as claimed in claim 1, characterized in that: The following steps are involved: S1: transferring the americium nitrate solution into the steam concentration reactor (2) through the liquid inlet (3) to concentrate the americium nitrate solution, and steam enters the steam concentration reactor (2) through the steam inlet (4) and is discharged through the steam outlet (5); S2: adding a deionized diluted americium nitrate solution through the liquid inlet (3), and then the americium nitrate solution enters the reactor mixing tank (13) through the ball valve (6) and the flow pump (7); while oxalic acid enters the reactor mixing tank (13) through the liquid inlet (10) of the reactor mixing tank, and is preliminarily mixed with the americium nitrate solution in the reactor mixing tank (13) by means of a stirrer (8), and the preliminarily mixed solution enters the ultrasonic pipe (16) under the action of the flow pump (15); S3: The solution stays in the ultrasonic channel (16) and further reacts under the action of ultrasound, causing oxalic acid hydrate to crystallize. The suspension generated by the reaction passes through the ball valve (19) at the end of the ultrasonic pipeline and is filtered through a flat filter (20) to obtain americium oxalate hydrate solid.

7. A method for continuous precipitation of americium nitrate according to claim 6, characterized in that: In S1, the generated evaporated condensate enters the condensate storage tank through the condenser pipe (1) to serve as seasoning liquid, waiting to enter the device again.

8. A method for continuous precipitation of americium nitrate according to claim 6, characterized in that: In the S1, the steam is saturated steam at 0.25 MPa and 120°C.

9. A method for continuous precipitation of americium nitrate according to claim 6, characterized in that: In S3, the mother liquor flows to the rear end through the precipitation mother liquor outlet (21) to be concentrated and then recovered.

10. A method for continuous precipitation of americium nitrate according to claim 6, characterized in that: The method further comprises S4, wherein deionized water is introduced from the deionized water inlet (3) to wash the ultrasonic pipe and the americium oxalate solid obtained by filtration, and the americium oxalate filter cake is obtained after drying; the americium oxalate filter cake is then placed in a quartz crucible, transferred into a calcining furnace, heated to 750° C., and kept warm for 6 hours to finally obtain americium dioxide powder.

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