Method and device for directly recovering nitric acid from medium-high radioactive waste liquid and nuclear fuel reprocessing plant system

Abstract

The invention discloses a method and device for directly recovering nitric acid from medium-high radioactive waste liquid and a nuclear fuel reprocessing plant system.The method comprises the steps that the medium-high radioactive waste liquid is continuously introduced into an evaporator to be subjected to evaporation treatment, and the evaporation treatment conditions are strictly controlled; the acidity of secondary steam generated by evaporation treatment is the same as the original acidity of the medium-high-radioactivity waste liquid, so that balanced evaporation is realized; condensing the secondary steam to obtain a secondary steam condensate; and rectifying the secondary steam condensate to obtain a nitric acid product. Compared with the prior art, the method has the advantages that the evaporation treatment process is more stable and easier to control, the acidity of the secondary steam condensate is higher, a nitric acid product can be obtained by directly performing rectification treatment and concentration subsequently, the evaporation concentration multiple of the residual evaporation liquid is high, the volume reduction effect is obvious, the nitric acid recovery rate is high, the economical efficiency is good, and the content of nitric oxide in tail gas is very low; extra nitrogen oxide treatment is not needed, and the device and the technological process are simple.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear engineering, and in particular relates to a method and a device for directly recovering nitric acid from medium- and high-level radioactive waste liquid, and a nuclear fuel reprocessing plant system comprising the device. Background Art

[0002] The operation of nuclear facilities such as nuclear fuel reprocessing plants will produce a large amount of medium- and high-level radioactive waste liquid containing nitric acid, which has the characteristics of high radioactivity and strong corrosiveness. At present, the treatment of these waste liquids generally adopts evaporation concentration to achieve waste liquid purification and volume reduction, and acid recovery treatment is used to recycle and reuse nitric acid. However, the above treatment method has at least the following shortcomings in actual operation:

[0003] (1) Evaporation and concentration treatment usually uses the method of destroying nitric acid while evaporating, and destroys nitric acid by adding denitrification reagents (such as formaldehyde, formic acid, etc.). The denitrification reaction process will cause the evaporation and concentration process to be unstable and difficult to control, and may even cause boiling. At the same time, the denitrification reaction will produce a large amount of high-concentration nitrogen oxide gas. In addition, during the denitrification process, the acidity of the secondary steam condensate is relatively high, which is not conducive to subsequent treatment.

[0004] (2) Acid recovery treatment, which absorbs and distills the nitrogen oxides in the radioactive process tail gas generated during the denitration process of the above-mentioned evaporation and concentration treatment. However, the existing technology is still not thorough in treating nitrogen oxides, resulting in a relatively high content of nitrogen oxides in the tail gas, which cannot be directly discharged. At the same time, it also results in a low recovery rate of nitric acid and poor economic efficiency.

[0005] (3) Since the radioactive purification and volume reduction of the waste liquid, and the separation and recovery of nitric acid are achieved in steps, the entire treatment system is large and complex. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method and device for directly recovering nitric acid from medium- and high-level radioactive waste liquid, and a nuclear fuel reprocessing plant system in view of the above-mentioned deficiencies in the prior art. Compared with the prior art, the evaporation treatment process is more stable and easier to control, the acidity of the secondary steam condensate is relatively high, and the nitric acid product can be directly concentrated by distillation treatment subsequently. The evaporation concentration multiple of the residual liquid is high, the volume reduction effect is obvious, the nitric acid recovery rate is high, the economy is good, the nitrogen oxide content in the tail gas is very low, no additional nitrogen oxide treatment is required, and the device and process flow are simple.

[0007] The technical solution adopted to solve the technical problem of the present invention is:

[0008] According to a first aspect of the present invention, there is provided a method for directly recovering nitric acid from medium- and high-level radioactive waste liquid, comprising:

[0009] The medium- and high-level radioactive waste liquid is continuously introduced into the evaporator for evaporation treatment, and the evaporation treatment conditions are strictly controlled so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the medium- and high-level radioactive waste liquid, thus achieving balanced evaporation;

[0010] condensing the secondary steam to obtain secondary steam condensate;

[0011] The secondary steam condensate is distilled to obtain nitric acid product.

[0012] Optionally, the method further comprises: performing radioactive purification treatment on the non-condensable gas remaining after condensation; and / or condensing the vaporized product produced by the distillation treatment to obtain a distillation condensate, and performing radioactive purification treatment on the distillation condensate.

[0013] Optionally, in the method, the acidity of nitric acid in the high-level radioactive waste liquid is controlled below 68.4 wt %.

[0014] Optionally, the temperature of the evaporation treatment in this method is 50 to 125° C. and the pressure is -95 to -5 kPa.

[0015] Optionally, the purification coefficient of the secondary steam condensate by evaporation treatment in this method is controlled within the range of 100 to 50,000.

[0016] Optionally, the evaporation concentration multiple of the residual liquid in the evaporation treatment of the present method is controlled within the range of 10 to 100.

[0017] Optionally, the acidity of the secondary steam condensate in the method is controlled within the range of 1.5 to 3 mol / L.

[0018] Optionally, the acidity of the evaporation residue obtained by the evaporation treatment of the present method is controlled within the range of 3 to 10 mol / L.

[0019] Optionally, the temperature of the distillation treatment in the present method is 50 to 125° C. and the pressure is -90 to -5 kPa kPa.

[0020] Optionally, the purification coefficient of the distillation condensate by the distillation treatment of the present method is controlled within the range of 50 to 1000.

[0021] Optionally, the acidity of the distillation condensate obtained by the distillation treatment of the present method is controlled within the range of 0 to 0.3 mol / L.

[0022] According to a second aspect of the present invention, there is provided a device for directly recovering nitric acid from medium- and high-level radioactive waste liquid, comprising a waste liquid acid recovery evaporation unit and a nitric acid distillation unit, wherein the waste liquid acid recovery evaporation unit comprises an evaporator and a condenser, wherein:

[0023] The evaporator is used to evaporate the continuously introduced intermediate and high-level radioactive waste liquid, and strictly control the evaporation treatment conditions so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the intermediate and high-level radioactive waste liquid, thereby achieving balanced evaporation;

[0024] The condenser is connected to the evaporator and is used to condense the secondary steam to obtain secondary steam condensate;

[0025] The nitric acid distillation unit is connected to the condenser and is used to perform distillation treatment on the secondary steam condensate to obtain a nitric acid product.

[0026] Optionally, the system further comprises one or more of a waste liquid receiving and feeding unit, a tail gas purification unit, a concentrated liquid temporary storage unit, and a deep purification treatment unit, wherein:

[0027] A waste liquid receiving and feeding unit is connected to the evaporator and is used to receive the medium- and high-level radioactive waste liquid generated in the upstream process and transport the medium- and high-level radioactive waste liquid to the evaporator;

[0028] The tail gas purification unit is connected to the condenser and is used to perform radioactive purification on the non-condensable gas remaining after condensation in the condenser;

[0029] The concentrated liquid temporary storage unit is connected to the evaporator and is used to receive the residual liquid produced by the evaporation process;

[0030] The deep purification treatment unit is connected to the nitric acid distillation unit, which is also used to condense the vapor produced by the distillation treatment to obtain the distillation condensate. The deep purification treatment unit is used to receive the distillation condensate and perform radioactive purification treatment on it.

[0031] Optionally, the waste liquid acid recovery evaporation unit comprises a first waste liquid acid recovery evaporation unit and a second waste liquid acid recovery evaporation unit, wherein:

[0032] The first waste liquid acid recovery evaporation unit comprises a first evaporator and a first condenser, intermediate and high-level radioactive waste liquid is continuously introduced from the first evaporator, and the inlet of the first condenser is connected to the secondary steam outlet of the first evaporator;

[0033] The second waste liquid acid recovery evaporation unit comprises a second evaporator, the feed inlet of the second evaporator is connected to the condensate outlet of the first condenser, and the secondary steam outlet of the second evaporator is connected to the nitric acid distillation unit.

[0034] Optionally, the evaporation residue outlet of the second evaporator is also connected to the feed inlet of the first evaporator.

[0035] According to a third aspect of the present invention, a nuclear fuel reprocessing plant system is provided, comprising an extraction and stripping unit, a fuel dissolution unit, a seasoning unit, and also comprising the above-mentioned device for directly recovering nitric acid from the intermediate and high-level radioactive waste liquid, wherein the waste liquid acid recovery evaporation unit in the device is connected to the extraction and stripping unit, and is used to receive the intermediate and high-level radioactive waste liquid generated by the extraction and stripping unit and evaporate it, and the nitric acid distillation unit in the device is connected to the fuel dissolution unit and / or the seasoning unit, and is used to return the nitric acid product obtained by the distillation treatment to the fuel dissolution unit and / or the seasoning unit for reuse.

[0036] Compared with the prior art, the method and device for directly recovering nitric acid from medium- and high-level radioactive waste liquid and the nuclear fuel reprocessing plant system of the present invention have the following beneficial effects:

[0037] (1) The evaporation process does not require the addition of denitrification agents for denitrification treatment, which can maintain the acidity of the liquid in the evaporator from continuing to increase. The evaporation process is more stable and easier to control. At the same time, it can also avoid the introduction of water when adding denitrification agents, thereby reducing the amount of radioactive wastewater generated in the end;

[0038] (2) Acidity control can be achieved by controlling evaporation treatment parameters and selecting the evaporation endpoint, so that the acidity of the secondary steam condensate is the same as the acidity of the medium- and high-level radioactive waste liquid feed, thereby maintaining the acidity of the feed liquid in the evaporator stable, that is, achieving balanced evaporation, thereby increasing the acidity of the secondary steam condensate, and at the same time increasing the evaporation concentration multiple of the evaporation residue. Furthermore, since the acidity of the secondary steam condensate is relatively high, it can be directly distilled and concentrated to obtain a nitric acid product. Since the evaporation concentration multiple of the evaporation residue is high, the volume of the concentrated liquid (i.e., the evaporation residue) can be minimized, and the volume reduction effect is obvious, which is beneficial to the subsequent temporary storage and treatment of the waste liquid, and the nitric acid recovery rate is higher, and the economic efficiency is better;

[0039] (3) The nitrogen oxide content in the remaining tail gas after the secondary steam generated by evaporation is condensed is very low, and no additional nitrogen oxide treatment is required, which can save a lot of absorption equipment, simplify the device and process flow, and reduce the amount of tail gas, which can reduce the processing flux of the tail gas treatment equipment and greatly save equipment costs;

[0040] (4) The distillation condensate obtained after condensation of the vapor produced by the distillation treatment has a low radioactivity level and low acidity, and has a good radioactivity purification effect, which is convenient for subsequent treatment.

[0041] (5) It can simultaneously achieve radioactive purification, concentration and volume reduction of medium- and high-level radioactive waste liquids, as well as separation, recovery and reuse of nitric acid in the waste liquids. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of a method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to an embodiment of the present invention;

[0043] Figure 2 It is a schematic structural diagram of a device for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to an embodiment of the present invention.

[0044] In the figure: 11-first waste liquid acid recovery evaporation unit; 12-second waste liquid acid recovery evaporation unit; 20-nitric acid distillation unit; 30-waste liquid receiving and feeding unit; 40-tail gas purification unit; 50-concentrated liquid temporary storage unit. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0046] In the description of the present invention, it should be noted that the term "upper" and the like to indicate orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0047] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0048] In view of the problems that denitrification agents are needed in the prior art, the denitrification reaction process will lead to unstable evaporation and concentration process, which is difficult to control and may even cause bumping phenomenon, as well as high nitrogen oxide content in tail gas, low recovery rate, and complex system, the present invention discloses a method for directly recovering nitric acid from medium and high radioactive waste liquid, comprising:

[0049] The medium- and high-level radioactive waste liquid is continuously introduced into the evaporator for evaporation treatment, and the evaporation treatment conditions are strictly controlled so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the medium- and high-level radioactive waste liquid, thereby achieving balanced evaporation; the secondary steam is condensed to obtain secondary steam condensate; the secondary steam condensate is subjected to rectification treatment to obtain nitric acid product

[0050] Correspondingly, the present invention also discloses a device for directly recovering nitric acid from medium- and high-level radioactive waste liquid, comprising a waste liquid acid recovery evaporation unit and a nitric acid distillation unit, wherein the waste liquid acid recovery evaporation unit comprises an evaporator and a condenser, wherein: the evaporator is used to perform evaporation treatment on the continuously introduced medium- and high-level radioactive waste liquid, and strictly control the evaporation treatment conditions so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the medium- and high-level radioactive waste liquid, thereby achieving balanced evaporation; the condenser is connected to the evaporator and is used to condense the secondary steam to obtain a secondary steam condensate; the nitric acid distillation unit is connected to the condenser and is used to perform distillation treatment on the secondary steam condensate to obtain a nitric acid product.

[0051] Furthermore, the present invention also discloses a nuclear fuel reprocessing plant system, comprising an extraction and stripping unit, a fuel dissolution unit, a seasoning unit, and also comprising the above-mentioned device for directly recovering nitric acid from the medium- and high-level radioactive waste liquid, wherein the waste liquid acid recovery evaporation unit in the device is connected to the extraction and stripping unit, and is used to receive the medium- and high-level radioactive waste liquid generated by the extraction and stripping unit and evaporate it, and the nitric acid distillation unit in the device is connected to the fuel dissolution unit and / or the seasoning unit, and is used to return the nitric acid product obtained by the distillation treatment to the fuel dissolution unit and / or the seasoning unit for reuse.

[0052] Example 1

[0053] like Figure 1 As shown, this embodiment discloses a method for directly recovering nitric acid from medium- and high-level radioactive waste liquid, comprising:

[0054] The intermediate and high-level radioactive waste liquid is continuously introduced into the evaporator for evaporation treatment (acid recovery evaporation), and the evaporation treatment conditions are controlled so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the intermediate and high-level radioactive waste liquid, thereby achieving balanced evaporation;

[0055] condensing the secondary steam to obtain secondary steam condensate;

[0056] The secondary steam condensate is subjected to distillation treatment (acid recovery distillation) to obtain nitric acid product.

[0057] Specifically, the evaporation treatment (acid recovery evaporation) of the present method is divided into two stages: acidity accumulation and equilibrium evaporation. The initial stage is an acidity accumulation process. As evaporation proceeds, nitric acid in the feed high-level radioactive waste liquid accumulates in the waste liquid acid recovery evaporation unit. The acidity of the feed liquid in the waste liquid acid recovery evaporation unit continues to rise, the boiling point continues to rise, and the acidity of the secondary steam gradually increases. When the acidity of the secondary steam increases to the same as the original acidity of the feed high-level radioactive waste liquid, since the flow rates of the evaporation feed and the evaporation discharge are the same, the nitric acid input and output in the medium-level and high-level radioactive waste liquid reach a balanced state at this time, and enter the equilibrium evaporation stage. In the equilibrium evaporation stage, the acidity of the feed liquid in the waste liquid acid recovery evaporation unit will remain unchanged and will no longer accumulate, and the evaporation treatment can continue to increase the evaporation concentration multiple.

[0058] After evaporation treatment and subsequent secondary steam condensation, secondary steam condensate with higher acidity and lower radioactivity level, a small amount of evaporation residue with concentrated radionuclides and a small amount of evaporated tail gas with non-condensable gas can be obtained.

[0059] Since the acidity of the secondary steam condensate in the method is relatively high and the radioactivity level is reduced, the method can directly perform distillation treatment on the secondary steam condensate to concentrate the nitric acid product. Compared with the problems of high energy consumption and low economy in the subsequent distillation process caused by the low acidity of the secondary steam condensate in the prior art, the method has low energy consumption and good economy.

[0060] In some embodiments, the method further includes: temporarily storing a small amount of residual liquid containing concentrated radioactive nuclides for subsequent centralized treatment; and / or, performing radioactive purification treatment on the non-condensable gas remaining after condensation, and after separating the radioactive substances, the tail gas is discharged through a chimney; and / or, condensing the vaporized product produced by the distillation treatment to obtain a distillation condensate, and performing radioactive purification treatment on the distillation condensate.

[0061] In some embodiments, the intermediate- and high-level radioactive waste liquid refers to the intermediate- and high-level radioactive waste liquid generated in the main process such as the extraction and stripping unit in the nuclear fuel reprocessing plant, but is not limited thereto. The intermediate- and high-level radioactive waste liquid may also be intermediate- and high-level radioactive waste liquid containing nitric acid from other sources.

[0062] By adopting the method, nitric acid in the medium- and high-level radioactive waste liquid generated in the main processes such as the extraction and stripping unit in the nuclear fuel reprocessing plant can be directly recovered.

[0063] In some embodiments, the nitrous acid content in the nitric acid product is less than 100 ppm, and the method further includes: returning the nitric acid product with a nitrous acid content less than 100 ppm to the main processes such as the fuel dissolution unit and the seasoning unit in the nuclear fuel reprocessing plant for reuse.

[0064] In some embodiments, the distillation treatment (acid recovery distillation) is to directly pass the secondary steam condensate with high acidity and reduced radioactivity obtained by acid recovery evaporation from the middle of the nitric acid distillation unit, and heat it with a heating medium, so that the nitrous acid content in the nitric acid product is less than 100ppm. In this way, the nitric acid distillation unit can have both a distillation section and a stripping section, so that the light and heavy components can be concentrated separately and backmixing can be reduced.

[0065] In this embodiment, the heating medium is hot saturated steam, but it is not limited to this, and it can also be other media with a temperature higher than the boiling point of nitric acid liquid.

[0066] In some embodiments, the acidity of nitric acid in the intermediate and high-level radioactive waste liquid is controlled below 68.4 wt %, so that the nitric acid can be continuously concentrated during the distillation process.

[0067] In some embodiments, the temperature of the evaporation treatment is 50 to 125° C. and the pressure is -95 to -5 kPa. Under greater negative pressure conditions, the temperature can be controlled lower, which is beneficial to alleviate equipment corrosion.

[0068] In some embodiments, the purification coefficient of the secondary steam condensate by evaporation treatment is controlled within the range of 100 to 50,000, and the steaming method of acid recovery evaporation is more stable and gentle, and the purification coefficient of the secondary steam condensate is higher.

[0069] In some embodiments, the evaporation concentration multiple of the residual liquid is controlled within the range of 10 to 100 by the evaporation process, and the equilibrium evaporation stage is no longer limited by the acidity of the feed liquid, and the concentration multiple is higher.

[0070] In some embodiments, the acidity of the secondary steam condensate is controlled within the range of 1.5 to 3 mol / L, which is higher than the acidity of the condensate from denitration evaporation, and the subsequent distillation and concentration treatment is more economical and saves energy.

[0071] In some embodiments, the acidity of the evaporation residue obtained by evaporation is controlled within the range of 3 to 10 mol / L, which can meet the requirements for subsequent waste liquid treatment.

[0072] In some embodiments, the temperature of the distillation treatment is 50 to 125° C. and the pressure is -90 to -5 kPa. Under greater negative pressure conditions, the temperature can be controlled lower, which is beneficial to alleviating equipment corrosion.

[0073] In some embodiments, the purification coefficient of the distillation condensate is controlled within the range of 50 to 1000 by the distillation process. Compared with the second stage evaporation in the prior art, the distillation has a higher reflux ratio and a higher purification coefficient.

[0074] In some embodiments, the acidity of the distillation condensate obtained by distillation treatment is controlled within the range of 0 to 0.3 mol / L, and the distillation has a higher reflux ratio than the second-stage evaporation in the prior art, and the acidity of the distillation condensate is lower.

[0075] Depending on the conditions of the medium- and high-level radioactive waste liquid (radioactivity level, acidity, etc.), the evaporation treatment can adopt a single-stage evaporation or a two-stage or above evaporation to steam the medium- and high-level radioactive waste liquid (i.e., evaporation treatment without adding denitrification agents).

[0076] In this embodiment, a two-stage evaporation treatment is adopted to perform steam treatment on the medium- and high-level radioactive waste liquid. Specifically, the residual evaporation liquid generated by the primary evaporation treatment in the first evaporator is a small amount of residual evaporation liquid with concentrated radionuclides, which is sent to the concentrated liquid temporary storage unit through a conveying device, and the purified evaporated condensate obtained by condensing the secondary steam generated by the primary evaporation treatment is sent to the secondary evaporation treatment; the residual evaporation liquid generated by the secondary evaporation treatment in the second evaporator is sent back to the first evaporator through a conveying device to perform the primary evaporation treatment again, and the secondary steam generated by the secondary evaporation treatment is directly sent to the distillation treatment.

[0077] Compared with the prior art, the method for directly recovering nitric acid from medium- and high-level radioactive waste liquid in this embodiment has the following beneficial effects:

[0078] (1) The evaporation process does not require the addition of denitrification agents for denitrification treatment, which can maintain the acidity of the liquid in the evaporator from continuing to increase. The evaporation process is more stable and easier to control. At the same time, it can also avoid the introduction of water when adding denitrification agents, thereby reducing the amount of radioactive wastewater generated in the end;

[0079] (2) Acidity control can be achieved by controlling evaporation treatment parameters and selecting the evaporation endpoint, so that the acidity of the secondary steam condensate is the same as the acidity of the medium- and high-level radioactive waste liquid feed, thereby maintaining the acidity of the feed liquid in the evaporator stable, that is, achieving balanced evaporation, thereby increasing the acidity of the secondary steam condensate, and at the same time increasing the evaporation concentration multiple of the evaporation residue. Furthermore, since the acidity of the secondary steam condensate is relatively high, it can be directly distilled and concentrated to obtain a nitric acid product. Since the evaporation concentration multiple of the evaporation residue is high, the volume of the concentrated liquid (i.e., the evaporation residue) can be minimized, and the volume reduction effect is obvious, which is beneficial to the subsequent temporary storage and treatment of the waste liquid, and the nitric acid recovery rate is higher, and the economic efficiency is better;

[0080] (3) The nitrogen oxide content in the remaining tail gas after the secondary steam generated by evaporation is condensed is very low, and no additional nitrogen oxide treatment is required, which can save a lot of absorption equipment, simplify the device and process flow, and reduce the amount of tail gas, which can reduce the processing flux of the tail gas treatment equipment and greatly save equipment costs;

[0081] (4) The distillation condensate obtained after condensation of the vapor produced by the distillation treatment has a low radioactivity level and low acidity, and has a good radioactivity purification effect, which is convenient for subsequent treatment.

[0082] (5) It can simultaneously achieve radioactive purification, concentration and volume reduction of medium- and high-level radioactive waste liquids, as well as separation, recovery and reuse of nitric acid in the waste liquids.

[0083] Example 2

[0084] This embodiment discloses a method for directly recovering nitric acid from medium- and high-level radioactive waste liquid, comprising the following steps:

[0085] Step S1, continuously passing the intermediate and high-level radioactive waste liquid into the evaporator for evaporation treatment (acid recovery evaporation), and controlling the evaporation treatment conditions so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the intermediate and high-level radioactive waste liquid, thereby achieving balanced evaporation.

[0086] Step S2, condensing the secondary steam to obtain secondary steam condensate.

[0087] The acidity of nitric acid in the medium- and high-level radioactive waste liquid is about 19wt%, and the concentration of β and γ radioactive activities is about 8.7E+08Bq / L; the temperature of the evaporation treatment is 118-122°C, and the pressure is -7--12kPa; the purification coefficient of the secondary steam condensate by the evaporation treatment is controlled within the range of 250-10000; the evaporation concentration multiple of the evaporation treatment is controlled within the range of 40 or so; the acidity of the secondary steam condensate is controlled within the range of 2-2.4mol / L; and the acidity of the evaporation residue obtained by the evaporation treatment is controlled within the range of 7.5-8.5mol / L.

[0088] Step S3, distilling the secondary steam condensate (acid recovery distillation) to obtain a nitric acid product with a mass concentration of more than 52% and a nitrous acid content of less than 100 ppm.

[0089] Among them, the secondary steam condensate is directly introduced from the middle of the nitric acid distillation unit (distillation tower) and heated by hot saturated steam. The temperature of the distillation treatment is 95-115°C and the pressure is -15--5kPa. The purification coefficient of the distillation treatment on the distillation condensate is controlled in the range of 50-1000; the acidity of the distillation condensate obtained by the distillation treatment is controlled in the range of 0.02-0.05mol / L.

[0090] After testing and calculation, the recovery rate of nitric acid is about 98%.

[0091] Example 3

[0092] This embodiment discloses a method for directly recovering nitric acid from medium- and high-level radioactive waste liquid, comprising the following steps:

[0093] Step S1, continuously passing the intermediate and high-level radioactive waste liquid into the evaporator for evaporation treatment (acid recovery evaporation), and controlling the evaporation treatment conditions so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the intermediate and high-level radioactive waste liquid, thereby achieving balanced evaporation.

[0094] Step S2, condensing the secondary steam to obtain secondary steam condensate.

[0095] The acidity of nitric acid in the medium- and high-level radioactive waste liquid is about 13wt%, and the concentration of β and γ radioactive activities is about 1.3E+09Bq / L; the temperature of the evaporation treatment is 120-125°C, and the pressure is -7--12kPa; the purification coefficient of the secondary steam condensate by the evaporation treatment is controlled within the range of 250-10000; the evaporation concentration multiple of the evaporation treatment is controlled within the range of 50 or so; the acidity of the secondary steam condensate is controlled within the range of 1.8-2.2mol / L; and the acidity of the evaporation residue obtained by the evaporation treatment is controlled within the range of 9-10mol / L.

[0096] Step S3, distilling the secondary steam condensate (acid recovery distillation) to obtain a nitric acid product.

[0097] Among them, the secondary steam condensate is directly introduced from the middle of the nitric acid distillation unit (distillation tower) and heated by hot saturated steam. The temperature of the distillation treatment is 95-115°C and the pressure is -15--5kPa. The purification coefficient of the distillation treatment on the distillation condensate is controlled within the range of 50-1000. The acidity of the distillation condensate obtained by the distillation treatment is controlled within the range of 0.02-0.05mol / L. The mass concentration of the nitric acid product is controlled to be above 52% and the nitrous acid content is less than 100ppm.

[0098] S4, returning the nitric acid product to the main processes such as the fuel dissolution unit and the seasoning unit in the nuclear fuel reprocessing plant for reuse.

[0099] After testing and calculation, the recovery rate of nitric acid is about 98%.

[0100] Example 4

[0101] like Figure 2 As shown, this embodiment discloses a device for directly recovering nitric acid from medium- and high-level radioactive waste liquid, including a waste liquid acid recovery evaporation unit and a nitric acid distillation unit 20, wherein the waste liquid acid recovery evaporation unit includes an evaporator and a condenser, wherein:

[0102] The evaporator is used to evaporate the continuously introduced medium- and high-level radioactive waste liquid, and strictly control the evaporation treatment conditions so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the medium- and high-level radioactive waste liquid, thereby achieving balanced evaporation;

[0103] A condenser, connected to the evaporator, is used to condense the secondary steam generated by evaporation to obtain a secondary steam condensate with higher acidity and lower radioactivity level;

[0104] The nitric acid distillation unit 20 is connected to the condenser and is used to perform distillation treatment on the secondary steam condensate obtained in the condenser to obtain a nitric acid product.

[0105] In some embodiments, the system further includes one or more of a waste liquid receiving and feeding unit 30, a tail gas purification unit 40, a concentrated liquid temporary storage unit 50, and a deep purification treatment unit.

[0106] Specifically, the waste liquid receiving and feeding unit 30 is connected to the waste liquid acid recovery and evaporation unit, and is used to receive the medium and high-level radioactive waste liquid generated in the upstream process (for example, the medium and high-level radioactive waste liquid generated in the main process such as the extraction and stripping unit in the nuclear fuel reprocessing plant) and transport the medium and high-level radioactive waste liquid to the waste liquid acid recovery and evaporation unit.

[0107] The tail gas purification unit 40 is connected to the condenser and is used to purify the radioactivity of the small amount of non-condensable gas remaining after condensation in the condenser;

[0108] The concentrated liquid temporary storage unit 50 is connected to the evaporator through a conveying device and is used to temporarily store a small amount of concentrated evaporation liquid of radionuclides generated by the evaporation process;

[0109] The deep purification treatment unit is connected to the nitric acid distillation unit 20. The nitric acid distillation unit 20 is also used to condense the vapor produced by the distillation treatment to obtain a distillation condensate. The deep purification treatment unit is used to receive the distillation condensate and perform radioactive purification treatment on it.

[0110] In this embodiment, the radioactive purification treatment adopts membrane treatment or ion exchange treatment, but is not limited thereto.

[0111] In this embodiment, the waste liquid receiving and feeding unit 30 includes a feeding trough and a conveying device (not shown in the figure). The feeding trough conveying device includes a first conveying device and a second conveying device, wherein: the feeding trough is connected to the waste liquid outlet of the upstream process through the first conveying device, and the intermediate and high-level radioactive waste liquid generated in the upstream process is conveyed to the feeding trough for temporary storage through the first conveying device; the feeding trough is connected to the waste liquid acid recovery and evaporation unit through the second conveying device, and the intermediate and high-level radioactive waste liquid in the feeding trough is then conveyed to the waste liquid acid recovery and evaporation unit through the second conveying device.

[0112] In addition, the waste liquid receiving and feeding unit 30 may also include a conditioning tank (not shown in the figure), the conditioning tank is connected to the waste liquid outlet of the upstream process, and the feeding tank is indirectly connected to the waste liquid outlet of the upstream process through the conditioning tank and the first conveying device. The intermediate and high-level radioactive waste liquid generated in the upstream process is first introduced into the conditioning tank for sampling analysis and conditioning treatment, so that the acidity of the intermediate and high-level radioactive waste liquid fed is as stable as possible, and by setting the conditioning tank, the acidity of the feed can be adjusted when the evaporation has entered the equilibrium evaporation stage, so that it is as close as possible to the acidity of the secondary steam condensate.

[0113] In this embodiment, considering that the non-condensable gas may contain radioactive droplets and aerosol waste liquid, the tail gas purification unit 40 specifically includes one or more of a filter, an adsorber, a leaching device, and a demisting device (not shown in the figure) to separate the radioactive substances therein, and different process combinations are selected according to the characteristics of the non-condensable gas. This embodiment is not further limited, and the tail gas is ensured to be treated until the radioactivity reaches the emission standard. The tail gas after the radioactive purification treatment by the tail gas purification unit 40 can be sent to the chimney through a pipeline and discharged to the environment.

[0114] According to the conditions of the intermediate and high-level radioactive waste liquid (radioactivity level, acidity, etc.), the waste liquid acid recovery evaporation unit can use one-stage evaporation to steam the intermediate and high-level radioactive waste liquid (i.e., evaporation without adding denitrification reagent), or can use two-stage or more evaporation to steam the intermediate and high-level radioactive waste liquid. In other words, the number of evaporators can be one or two or more, and correspondingly, the number of condensers can be one or two or more, which is selected and adjusted specifically according to the number of stages of evaporation treatment and condensation treatment required by the waste liquid acid recovery evaporation unit.

[0115] In this embodiment, a two-stage evaporation treatment is used to steam the medium- and high-level radioactive waste liquid. That is, the waste liquid acid recovery evaporation unit includes a first waste liquid acid recovery evaporation unit 11 and a second waste liquid acid recovery evaporation unit 12. The first waste liquid acid recovery evaporation unit 11 includes a first evaporator and a first condenser (not shown in the figure), and the second waste liquid acid recovery evaporation unit 12 includes a second evaporator (not shown in the figure). That is, the evaporator includes the first evaporator and the second evaporator, and the condenser is the first condenser, wherein:

[0116] After the intermediate and high-level radioactive waste liquid is continuously introduced from the first evaporator, a primary evaporation treatment is performed. The residual liquid produced by the primary evaporation treatment is a small amount of residual liquid with concentrated radionuclides, which is sent to the concentrated liquid temporary storage unit 50 through a conveying device. The inlet of the first condenser is connected to the secondary steam outlet of the first evaporator. The secondary steam produced by the primary evaporation treatment is condensed by the primary cooler to obtain secondary steam condensate and non-condensable gas.

[0117] The feed inlet of the second evaporator is connected to the condensate outlet of the first condenser, and the secondary steam outlet of the second evaporator is connected to the nitric acid distillation unit. The secondary steam generated by the secondary evaporation treatment is directly sent to the nitric acid distillation unit 20 for distillation treatment.

[0118] It should be noted that, in some embodiments, the second waste liquid acid recovery evaporation unit 12 may also include a second evaporator and a second condenser (not shown in the figure), that is, the condenser may also include a first condenser and a second condenser, wherein: the feed inlet of the second evaporator is connected to the condensate outlet of the first condenser, and the purified secondary steam condensate obtained after condensation of the first condenser is transported to the second evaporator for secondary evaporation treatment; the inlet of the second condenser is connected to the steam outlet of the second evaporator, and the condensate outlet of the second condenser is connected to the nitric acid distillation unit 20, and the purified secondary steam condensate obtained after the secondary steam generated by the secondary evaporation treatment is condensed by the second condenser is transported to the nitric acid distillation unit 20 through a conveying device for distillation treatment.

[0119] Furthermore, the evaporation residue outlet of the second evaporator can also be connected to the feed inlet of the first evaporator, and the evaporation residue produced by the secondary evaporation treatment is sent back to the first evaporator through a conveying device for re-primary evaporation treatment.

[0120] The device for directly recovering nitric acid from medium- and high-level radioactive waste liquid in this embodiment is used in the method described in the embodiment, and has the following beneficial effects compared with the prior art:

[0121] (1) The evaporation process does not require the addition of denitrification agents for denitrification treatment, which can maintain the acidity of the liquid in the evaporator from continuing to increase. The evaporation process is more stable and easier to control. At the same time, it can also avoid the introduction of water when adding denitrification agents, thereby reducing the amount of radioactive wastewater generated in the end;

[0122] (2) Acidity control can be achieved by controlling evaporation treatment parameters and selecting the evaporation endpoint, so that the acidity of the secondary steam condensate is the same as the acidity of the medium- and high-level radioactive waste liquid feed, thereby maintaining the acidity of the feed liquid in the evaporator stable, that is, achieving balanced evaporation, thereby increasing the acidity of the secondary steam condensate, and at the same time increasing the evaporation concentration multiple of the evaporation residue. Furthermore, since the acidity of the secondary steam condensate is relatively high, it can be directly distilled and concentrated to obtain a nitric acid product. Since the evaporation concentration multiple of the evaporation residue is high, the volume of the concentrated liquid (i.e., the evaporation residue) can be minimized, and the volume reduction effect is obvious, which is beneficial to the subsequent temporary storage and treatment of the waste liquid, and the nitric acid recovery rate is higher, and the economic efficiency is better;

[0123] (3) The nitrogen oxide content in the remaining tail gas after the secondary steam generated by evaporation is condensed is very low, and no additional nitrogen oxide treatment is required, which can save a lot of absorption equipment, simplify the device and process flow, and reduce the amount of tail gas, which can reduce the processing flux of the tail gas treatment equipment and greatly save equipment costs;

[0124] (4) The distillation condensate obtained after condensation of the vapor produced by the distillation treatment has a low radioactivity level and low acidity, and has a good radioactivity purification effect, which is convenient for subsequent treatment.

[0125] (5) It can simultaneously achieve radioactive purification, concentration and volume reduction of medium- and high-level radioactive waste liquids, as well as separation, recovery and reuse of nitric acid in the waste liquids.

[0126] Example 5

[0127] This embodiment discloses a nuclear fuel reprocessing plant system, including an extraction and stripping unit, a fuel dissolution unit, a seasoning unit, and also includes the device for directly recovering nitric acid from medium- and high-level radioactive waste liquid as described in Embodiment 4, wherein:

[0128] The waste liquid acid recovery evaporation unit in the device is connected to the extraction and stripping unit, and is used to receive the medium and high radioactive waste liquid generated by the extraction and stripping unit and evaporate it;

[0129] The nitric acid distillation unit 20 in the device is connected to the fuel dissolution unit and / or the seasoning unit, and is used to return the nitric acid product obtained by distillation to the fuel dissolution unit and / or the seasoning unit for reuse.

[0130] The nuclear fuel reprocessing plant system of this embodiment includes the device described in Example 4, and therefore has all the advantages of the device, which will not be described in detail here.

[0131] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for directly recovering nitric acid from medium and high-level radioactive waste liquid, include: The medium- and high-level radioactive waste liquid is continuously introduced into the evaporator for evaporation treatment, and the evaporation treatment conditions are strictly controlled so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the medium- and high-level radioactive waste liquid, thereby achieving balanced evaporation; condensing the secondary steam to obtain secondary steam condensate; The secondary steam condensate is distilled to obtain nitric acid product.

2. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1, It is characterized in that Also includes: The non-condensable gas remaining after condensation is subjected to radioactive purification treatment; and / or, The vaporized product produced by the distillation treatment is condensed to obtain a distillation condensate, and the distillation condensate is subjected to radioactive purification treatment.

3. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, It is characterized in that The acidity of nitric acid in the medium and high-level radioactive waste liquid is controlled below 68.4wt%.

4. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, It is characterized in that The temperature of the evaporation treatment is 50 to 125°C, and the pressure is -95 to -5 kPa.

5. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, It is characterized in that The purification coefficient of the secondary steam condensate by evaporation treatment is controlled in the range of 100 to 50,000.

6. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, It is characterized in that The evaporation concentration multiple of the residual liquid is controlled within the range of 10 to 100 in the evaporation treatment.

7. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, It is characterized in that The acidity of the secondary steam condensate is controlled in the range of 1.5 to 3 mol / L.

8. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, wherein the acidity of the evaporation residue obtained by evaporation treatment is controlled within the range of 3 to 10 mol / L.

9. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, wherein the temperature of the distillation treatment is 50 to 125°C and the pressure is -90 to -5 kPa.

10. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, wherein the purification coefficient of the distillation condensate is controlled within the range of 50 to 1000.

11. The method for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 1 or 2, wherein the acidity of the distillation condensate obtained by distillation treatment is controlled within the range of 0 to 0.3 mol / L.

12. A device for directly recovering nitric acid from medium- and high-level radioactive waste liquid. It is characterized in that It comprises a waste liquid acid recovery evaporation unit and a nitric acid distillation unit (20), wherein the waste liquid acid recovery evaporation unit comprises an evaporator and a condenser, wherein: The evaporator is used to evaporate the continuously introduced intermediate and high-level radioactive waste liquid, and strictly control the evaporation treatment conditions so that the acidity of the secondary steam generated by the evaporation treatment is the same as the original acidity of the intermediate and high-level radioactive waste liquid, thereby achieving balanced evaporation; The condenser is connected to the evaporator and is used to condense the secondary steam to obtain secondary steam condensate; The nitric acid distillation unit is connected to the condenser and is used to perform distillation treatment on the secondary steam condensate to obtain a nitric acid product.

13. The device for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 12, It is characterized in that The system further comprises one or more of a waste liquid receiving and feeding unit (30), an exhaust gas purification unit (40), a concentrated liquid temporary storage unit (50), and a deep purification treatment unit; A waste liquid receiving and feeding unit is connected to the evaporator and is used to receive the medium- and high-level radioactive waste liquid generated in the upstream process and transport the medium- and high-level radioactive waste liquid to the evaporator; The tail gas purification unit is connected to the condenser and is used to perform radioactive purification on the non-condensable gas remaining after condensation in the condenser; The concentrated liquid temporary storage unit is connected to the evaporator and is used to receive the residual liquid produced by the evaporation process; The deep purification treatment unit is connected to the nitric acid distillation unit, which is also used to condense the vapor produced by the distillation treatment to obtain the distillation condensate. The deep purification treatment unit is used to receive the distillation condensate and perform radioactive purification treatment on it.

14. The device for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 12 or 13, It is characterized in that The waste liquid acid recovery evaporation unit comprises a first waste liquid acid recovery evaporation unit (11) and a second waste liquid acid recovery evaporation unit (12), wherein: The first waste liquid acid recovery evaporation unit comprises a first evaporator and a first condenser, intermediate and high-level radioactive waste liquid is continuously introduced from the first evaporator, and the inlet of the first condenser is connected to the secondary steam outlet of the first evaporator; The second waste liquid acid recovery evaporation unit comprises a second evaporator, the feed inlet of the second evaporator is connected to the condensate outlet of the first condenser, and the secondary steam outlet of the second evaporator is connected to the nitric acid distillation unit.

15. The device for directly recovering nitric acid from medium- and high-level radioactive waste liquid according to claim 14, It is characterized in that The evaporation residue outlet of the second evaporator is also connected to the feed inlet of the first evaporator.

16. A nuclear fuel reprocessing plant system, comprising an extraction stripping unit, a fuel dissolution unit, and a seasoning unit. It is characterized in that It also includes a device for directly recovering nitric acid from medium- and high-level radioactive waste liquid as described in any one of claims 12 to 15, The waste liquid acid recovery evaporation unit in the device is connected to the extraction and stripping unit, and is used to receive the medium and high radioactive waste liquid generated by the extraction and stripping unit and evaporate it; The nitric acid distillation unit in the device is connected to the fuel dissolution unit and / or the seasoning unit, and is used to return the nitric acid product obtained by distillation treatment to the fuel dissolution unit and / or the seasoning unit for reuse.

Images