Treatment method of zirconium alloy cladding

Abstract

The invention relates to the technical field of nuclear fuel aftertreatment, and provides a zirconium alloy cladding treatment method which comprises the steps that a zirconium alloy cladding is heated to the target temperature in the nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of the zirconium alloy cladding; and oxidizing the zirconium alloy cladding with the zirconium nitride layer in an oxygen-containing atmosphere to obtain a product containing zirconium oxide. The zirconium alloy cladding is subjected to pre-nitriding treatment, and then the zirconium alloy cladding with the zirconium nitride layer is subjected to oxidation treatment; according to the process for inducing rapid oxidation of the zirconium alloy cladding through pre-nitridation, rapid damage to the zirconium alloy cladding structure can be achieved, the oxidation treatment efficiency of the zirconium alloy cladding can be improved, the oxidation efficiency of the zirconium alloy cladding is improved, the oxidation time is shortened, the specific surface area and reaction activity in the subsequent reduction and chlorination process are improved, and meanwhile, the specific surface area and the reaction activity are improved. The method is beneficial for recovering zirconium metal by applying a reducing agent through chlorination, the efficiency and economy of zirconium alloy cladding recovery are improved, and efficient recovery of zirconium resources is promoted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear fuel reprocessing, and particularly relates to a zirconium alloy cladding treatment method. BACKGROUND

[0002] The current zirconium alloy cladding of nuclear fuel is mainly disposed near the earth's surface, which not only has high disposal cost and potential environmental hazards, but also causes serious waste of zirconium resources. In addition, the zirconium metal content in the zirconium alloy cladding is as high as 95%, and the market nuclear-grade zirconium raw material (ZrO2) is priced at 50,000-200,000 yuan / ton. The zirconium metal can be efficiently recovered, which not only realizes the strategic resource recycling, but also reduces the volume of radioactive waste, and simultaneously relieves the dual challenges of resource shortage and environmental pressure.

[0003] At present, the recovery and reprocessing process of the zirconium alloy cladding mainly adopts a direct chlorination method, that is, the zirconium alloy cladding is subjected to a chlorination reaction with chlorine to generate zirconium chloride, and then the zirconium chloride is reduced to obtain zirconium metal. However, the method faces many challenges in practical application, such as slow chlorination reaction rate, difficulty in releasing the fission products in the zirconium alloy cladding, and low purity of the chlorination product, i.e., zirconium chloride. SUMMARY

[0004] Therefore, the embodiments of the present application provide a zirconium alloy cladding treatment method, which improves the oxidation efficiency of the zirconium alloy cladding and is beneficial to the application of a reducing agent for chlorination and recovery of zirconium metal.

[0005] The embodiments of the present application provide a zirconium alloy cladding treatment method, which comprises the following steps.

[0006] The zirconium alloy cladding is heated to a target temperature under a nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of the zirconium alloy cladding.

[0007] The zirconium alloy cladding with the zirconium nitride layer is subjected to oxidation in an oxygen-containing atmosphere to obtain a product containing zirconium oxide.

[0008] In some embodiments, the content of nitrogen in the nitrogen atmosphere is 90% to 100%.

[0009] In some embodiments, the thickness of the zirconium nitride layer is H, wherein 0 < H < 200 μm.

[0010] In some embodiments, the target temperature is 400-1200 °C.

[0011] In some embodiments, the treatment method comprises the following steps.

[0012] The oxidation of the zirconium alloy cladding with the zirconium nitride layer is ended until the mass of the product containing zirconium oxide remains unchanged.

[0013] In some embodiments, the zirconium alloy cladding with the zirconium nitride layer is oxidized at the target temperature.

[0014] In some embodiments, the oxygen-containing atmosphere comprises oxygen and nitrogen, wherein the oxygen content in the oxygen-containing atmosphere is 20% to 60%.

[0015] In some embodiments, the oxygen-containing atmosphere is an air atmosphere.

[0016] In some embodiments, the processing method comprises:

[0017] heating a plurality of zirconium alloy claddings to different target temperatures under the same nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of each of the zirconium alloy claddings;

[0018] recording first mass change data of each of the zirconium alloy claddings with the zirconium nitride layer during oxidation under the same oxygen-containing atmosphere;

[0019] converting the first mass change data into a first specific surface mass gain to obtain a first oxidation kinetics curve of the first specific surface mass gain versus time.

[0020] In some embodiments, the processing method comprises:

[0021] heating a plurality of zirconium alloy claddings to the same target temperature under nitrogen atmospheres with different nitrogen contents, so that a zirconium nitride layer is formed on the surface of each of the zirconium alloy claddings;

[0022] recording second mass change data of each of the zirconium alloy claddings with the zirconium nitride layer during oxidation under the same oxygen-containing atmosphere;

[0023] converting the second mass change data into a second specific surface mass gain to obtain a second oxidation kinetics curve of the second specific surface mass gain versus time.

[0024] In some embodiments, the processing method comprises:

[0025] heating a plurality of zirconium alloy claddings to the same target temperature under the same nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of each of the zirconium alloy claddings;

[0026] recording third mass change data of each of the zirconium alloy claddings with the zirconium nitride layer during oxidation under oxygen-containing atmospheres with different oxygen contents;

[0027] converting the third mass change data into a third specific surface mass gain to obtain a third oxidation kinetics curve of the third specific surface mass gain versus time.

[0028] The zirconium alloy cladding processing method provided by the embodiments of the present application first performs pre-nitriding processing on the zirconium alloy cladding, and then performs oxidation processing on the zirconium alloy cladding with a zirconium nitride layer. Specifically, the zirconium alloy cladding is first heated in a nitrogen atmosphere, so that a substantially complete zirconium nitride layer is formed on the surface of the zirconium alloy cladding. Then, the zirconium alloy cladding with the zirconium nitride layer is subjected to oxidation processing. During the oxidation process, the ZrN layer expands in volume, which can cause the zirconium oxide to crack and form pores, thereby providing a diffusion channel for oxygen to penetrate into the interior of the zirconium alloy cladding and accelerating the oxidation process. Through this pre-nitriding induced rapid oxidation process of the zirconium alloy cladding, the rapid destruction of the structure of the zirconium alloy cladding can be achieved, and the oxidation processing efficiency of the zirconium alloy cladding can be improved. Not only is the oxidation efficiency of the zirconium alloy cladding improved, but the oxidation time is also shortened, and preliminary purification processing is achieved. In addition, during the oxidation process of the zirconium alloy cladding with the zirconium nitride layer, the particle size of the zirconium oxide is also refined, which is beneficial to improving the specific surface area and reaction activity in the subsequent reduction and chlorination processes, and is beneficial to the application of the reducing agent for chlorination to recover zirconium metal, thereby improving the efficiency and economy of the recovery of the zirconium alloy cladding and promoting the efficient recovery of zirconium resources. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A flowchart of the zirconium alloy cladding processing method provided by some embodiments of the present application is shown in the figure.

[0030] Figure 2 An oxidation kinetics curve and a schematic diagram of the oxidation kinetics curve in the related art are shown in the figure, wherein the target temperature in the present application is 1000℃, and the temperature of the oxidation reaction of the zirconium alloy cladding in the related art is 1000℃.

[0031] Figure 3 An oxidation kinetics curve and a schematic diagram of the oxidation kinetics curve in the related art are shown in the figure, wherein the target temperature in the present application is 1100℃, and the temperature of the oxidation reaction of the zirconium alloy cladding in the related art is 1100℃. DETAILED DESCRIPTION

[0032] The embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0033] The various technical features and embodiments described in the detailed description can be combined in any suitable manner, and in particular, various technical features and embodiments can be combined in different embodiments, unless the context clearly dictates otherwise. In addition, the use of the terms "first", "second", "third", etc. does not imply a relative importance, but is merely used to distinguish one element from another. The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] In the related art, in order to improve the chlorination efficiency, a process path of first oxidizing and then chlorinating the zirconium alloy cladding is proposed, that is, the zirconium alloy cladding is oxidized to obtain zirconium oxide, the zirconium oxide is then chlorinated to obtain zirconium chloride, and finally zirconium metal is obtained by reduction; this method can destroy the structure of the zirconium alloy cladding, promote the migration and release of the fission products, and the oxidation products can be directly purified using the mature sponge zirconium production process. However, due to the excellent oxidation resistance of zirconium alloy, direct oxidation of zirconium alloy often generates a dense and continuous zirconium oxide layer on the surface of the zirconium alloy cladding, forming a reaction kinetic barrier, which limits the mass transfer of the reaction, limits the further diffusion of oxygen to the inside of the zirconium alloy cladding, and causes the overall oxidation process of the zirconium alloy cladding to be slow. In some cases, the applicant found that, due to the thermodynamic reaction of zirconium and oxygen being more favorable than the reaction of zirconium and nitrogen, if the zirconium alloy cladding is treated in a mixed atmosphere containing oxygen and nitrogen, zirconium and oxygen will preferentially react, resulting in the formation of a small amount of ZrN only in the local area of the zirconium alloy cladding, thereby causing the oxidation degree of the zirconium alloy cladding to be unevenly distributed in space, and it is difficult to achieve rapid oxidation of the zirconium alloy cladding as a whole.

[0035] Please refer to Figure 1 The embodiment of the present application provides a treatment method for a zirconium alloy cladding, comprising:

[0036] S100, heating the zirconium alloy cladding to a target temperature under a nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of the zirconium alloy cladding;

[0037] Exemplarily, the zirconium nitride layer can substantially cover all or part of the surface of the zirconium alloy cladding.

[0038] S200, oxidizing the zirconium alloy cladding with the zirconium nitride layer in an oxygen-containing atmosphere to obtain a product containing zirconium oxide.

[0039] The zirconium alloy cladding is first subjected to a pre-nitriding treatment, that is, the zirconium alloy cladding is first heated to a target temperature under a nitrogen atmosphere, so that a zirconium nitride layer (i.e. ZrN layer) is formed on the surface of the zirconium alloy cladding; this zirconium nitride layer can avoid the reaction kinetic barrier caused by the dense zirconium oxide (i.e. ZrO2) in the direct oxidation of the zirconium alloy cladding in the related art.

[0040] The zirconium alloy cladding with the zirconium nitride layer is further subjected to oxidation treatment. The zirconium alloy cladding with the zirconium nitride layer is subjected to oxidation treatment in an oxygen-containing atmosphere. Since ZrN is extremely easy to be oxidized, and cracks and pores are generated along with volume expansion, a channel is provided for oxygen to diffuse into the interior of the zirconium alloy cladding, the mass transfer rate of oxygen is increased, and the structural damage of the zirconium alloy cladding is accelerated. In addition, the nitrogen atoms released by the oxidation of ZrN can react with the adjacent Zr to form a "dynamic ZrN band" migrating along the Zr matrix of the zirconium alloy cladding, continuously driving the oxidation reaction process.

[0041] The method for treating the zirconium alloy cladding provided in the embodiments of the present application first subjects the zirconium alloy cladding to pre-nitriding treatment, and then subjects the zirconium alloy cladding with the zirconium nitride layer to oxidation treatment. Specifically, the zirconium alloy cladding is first heated in a nitrogen atmosphere, so that a substantially complete zirconium nitride layer is formed on the surface of the zirconium alloy cladding. Then, the zirconium alloy cladding with the zirconium nitride layer is subjected to oxidation treatment. During the oxidation of the ZrN layer, volume expansion occurs, which leads to the cracking and pore formation of zirconia, thereby providing a diffusion channel for oxygen to penetrate into the interior of the zirconium alloy cladding, accelerating the oxidation process. Through this pre-nitriding induced rapid oxidation process of the zirconium alloy cladding, the rapid destruction of the structure of the zirconium alloy cladding can be achieved, and the efficiency of the oxidation treatment of the zirconium alloy cladding can be improved. Not only is the oxidation efficiency of the zirconium alloy cladding improved, and the oxidation time is shortened, but also preliminary purification treatment is achieved. In addition, the particle size of the zirconia is refined during the oxidation of the zirconium alloy cladding with the zirconium nitride layer, which is beneficial to improving the specific surface area and reaction activity in the subsequent reduction and chlorination processes, and is beneficial to the application of the reducing agent for chlorination to recover zirconium metal, thereby improving the efficiency and economy of the recovery of the zirconium alloy cladding, and promoting the efficient recovery of zirconium resources.

[0042] In some embodiments, the content of nitrogen in the nitrogen atmosphere is 90% to 100%. Preferably, the content of nitrogen in the nitrogen atmosphere is 99.99% to 100%. Illustratively, the nitrogen atmosphere can be free of oxygen. Preferably, the nitrogen atmosphere uses high-purity nitrogen with a content of nitrogen of 99.99% to 100%. The nitrogen atmosphere is substantially free of other gas components, which is beneficial to the sufficient reaction of nitrogen and zirconium, and can substantially avoid the reaction of zirconium and oxygen, thereby affecting the formation of the zirconium nitride layer.

[0043] In some embodiments, the thickness of the zirconium nitride layer is H, wherein 0 μm < H and H ≤ 200 μm.

[0044] Illustratively, the thickness H of the zirconium nitride layer can be 25 μm, 50 μm, 70 μm, 100 μm, 150 μm, or 200 μm, etc.

[0045] The unit "μm" is micrometers.

[0046] In this embodiment, the thickness H of the zirconium nitride layer is greater than 0 μm and not greater than 200 μm, which can take into account the time length of the pre-nitriding reaction of the zirconium alloy cladding, meet the efficiency requirement of the treatment method of the zirconium alloy cladding, and provide an appropriate amount of nitrogen element for the subsequent formation of the "dynamic ZrN belt".

[0047] In some embodiments, the target temperature is 400-1200 °C.

[0048] For example, the target temperature can be 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, 850 °C, 900 °C, 1000 °C, 1100 °C, or 1200 °C, etc.

[0049] In this embodiment, the target temperature is 400-1200 °C, and the zirconium alloy can react with nitrogen to form a zirconium nitride layer.

[0050] In some embodiments, the treatment method comprises:

[0051] S300, until the mass of the product containing zirconium oxide remains unchanged, and the oxidation of the zirconium alloy cladding with the zirconium nitride layer is ended.

[0052] In this embodiment, the oxidation reaction is basically ended when the mass of the product containing zirconium oxide remains unchanged, and the oxides of part of the semi-volatile fission products in the zirconium alloy cladding, such as RhO2, RuO4, and Tc2O7, are volatilized to achieve separation. Based on whether the mass of the product containing zirconium oxide continues to change, the reaction progress of the zirconium alloy cladding with the zirconium nitride layer can be determined, which is simple, convenient, and easy to operate.

[0053] In some embodiments, the zirconium alloy cladding with the zirconium nitride layer is oxidized at the target temperature.

[0054] In this way, the target temperature in the pre-nitriding treatment process can be used for the oxidation treatment of the zirconium alloy cladding with the zirconium nitride layer, which is beneficial to the nitriding treatment and oxidation treatment of the zirconium alloy cladding in the space of one device, is simple and convenient, and reduces the operation difficulty.

[0055] In some embodiments, the oxygen-containing atmosphere comprises oxygen and nitrogen, and the content of oxygen in the oxygen-containing atmosphere is 20-60%. For example, the content of oxygen in the oxygen-containing atmosphere is 20%, 30%, 40%, 50%, or 60%, etc.

[0056] In some embodiments, in the oxygen-containing atmosphere, the ratio of oxygen to nitrogen can be 2:8-6:4. For example, the content of oxygen in the oxygen-containing atmosphere is 20-60%, and the content of nitrogen is 80-40%.

[0057] Thus, in the case that oxygen can react with the zirconium nitride layer to form zirconia, the nitrogen in the oxygen-containing atmosphere can continue to form zirconium nitride with the zirconium alloy cladding, accelerating the oxidation reaction process.

[0058] In some embodiments, the oxygen-containing atmosphere is an air atmosphere. That is, the oxygen-containing atmosphere can directly use air, directly use air to perform the oxidation reaction with the zirconium alloy cladding having the zirconium nitride layer, and the air is easy to obtain and low in cost.

[0059] In some embodiments, the treatment method comprises:

[0060] S401, heating a plurality of zirconium alloy claddings to different target temperatures in the same nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of each zirconium alloy cladding;

[0061] S402, recording first mass change data of each zirconium alloy cladding having the zirconium nitride layer in the oxidation process in the same oxygen-containing atmosphere;

[0062] S403, converting the first mass change data into a first specific surface mass gain to obtain a first oxidation kinetics curve of the first specific surface mass gain-time.

[0063] Here, each zirconium alloy cladding is pre-nitrided at a different target temperature, one zirconium alloy cladding having the zirconium nitride layer corresponds to one first mass change data, and corresponds to one first oxidation kinetics curve.

[0064] Exemplarily, the first mass change data of the zirconium alloy cladding having the zirconium nitride layer in the oxidation process can be recorded by a thermogravimetric analysis software.

[0065] In some embodiments, the first mass change data of the zirconium alloy cladding having the zirconium nitride layer in the oxidation process can be recorded in seconds. Real-time monitoring of the oxidation reaction of the zirconium alloy cladding having the zirconium nitride layer is achieved.

[0066] The way of converting the mass change data into the specific surface mass gain can comprise: the mass change data is represented as m, the total surface area of the zirconium alloy cladding having the zirconium nitride layer is represented as A, and the specific surface mass gain is represented as Δm, wherein the specific surface mass gain is the ratio of the mass change data to the total surface area of the zirconium alloy cladding having the zirconium nitride layer, i.e., Δm = m / A. The unit of m is g (gram), the unit of A is m 2 (plain meter), and the unit of Δm is g / m 2 (gram per plain meter).

[0067] The first mass change data can be represented as m1, and the first specific surface mass gain can be represented as Δm1.

[0068] It should be noted that the total surface area A of the zirconium alloy cladding with the zirconium nitride layer includes the sum of the inner surface area and the outer surface area of the zirconium alloy cladding. For example, the zirconium alloy cladding is substantially a hollow cylindrical tube, and the total surface area A of the zirconium alloy cladding with the zirconium nitride layer includes the sum of the inner surface area and the outer surface area of the cylindrical tube.

[0069] In this embodiment, each zirconium alloy cladding is pre-nitrided at a different target temperature, and data processing and analysis can be performed during the preparation of the product containing zirconia. A first oxidation kinetics curve with the first specific surface mass gain as the vertical coordinate and the time as the horizontal coordinate is established. Different target temperatures correspond to different first oxidation kinetics curves. The first oxidation kinetics curve can be used to describe the change of the oxidation reaction rate of the zirconium alloy cladding with the zirconium nitride layer with time, and the form of the first oxidation kinetics curve can reflect the dynamic mechanism of the oxidation process. The slopes of the first oxidation kinetics curves corresponding to different target temperatures are compared to evaluate the influence of the target temperature on the oxidation rate.

[0070] In some embodiments, the processing method comprises:

[0071] S501, heating a plurality of zirconium alloy claddings to the same target temperature in a nitrogen atmosphere with different nitrogen contents, so that a zirconium nitride layer is formed on the surface of each zirconium alloy cladding;

[0072] S502, recording second mass change data of each zirconium alloy cladding with the zirconium nitride layer during the oxidation process in the same oxygen-containing atmosphere;

[0073] S503, converting the second mass change data into a second specific surface mass gain to obtain a second oxidation kinetics curve of the second specific surface mass gain-time.

[0074] Here, each zirconium alloy cladding is pre-nitrided in a nitrogen atmosphere with different nitrogen contents. One zirconium alloy cladding with the zirconium nitride layer corresponds to one second mass change data and one second oxidation kinetics curve.

[0075] For example, the second mass change data of the zirconium alloy cladding with the zirconium nitride layer during the oxidation process can be recorded by a thermogravimetric analysis software.

[0076] In some embodiments, the second mass change data of the zirconium alloy cladding with the zirconium nitride layer during the oxidation process can be recorded in seconds. Real-time monitoring of the oxidation reaction of the zirconium alloy cladding with the zirconium nitride layer is achieved.

[0077] The second mass change data can be represented as m2, and the first specific surface mass gain can be represented as Δm2.

[0078] In the embodiment, each zirconium alloy cladding is pre-nitrided in a nitrogen atmosphere with different nitrogen content, and a second oxidation kinetics curve with ordinate as second specific mass gain and abscissa as time is established in the process of producing a product containing zirconia, which can be used to describe the change of oxidation reaction rate of zirconium alloy cladding with zirconium nitride layer with time, and the form of the second oxidation kinetics curve can reflect the dynamic mechanism of the oxidation process. The slopes of the second oxidation kinetics curves corresponding to the nitrogen atmospheres with different nitrogen content are compared to evaluate the influence of nitrogen content in the nitrogen atmosphere on the oxidation rate.

[0079] In some embodiments, the processing method comprises:

[0080] S601, heating a plurality of zirconium alloy claddings to the same target temperature in the same nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of each zirconium alloy cladding;

[0081] S602, recording third mass change data of each zirconium alloy cladding with the zirconium nitride layer in an oxygen-containing atmosphere with different oxygen content during the oxidation process;

[0082] S603, converting the third mass change data into third specific mass gain to obtain a third oxidation kinetics curve of the third specific mass gain-time.

[0083] Here, each zirconium alloy cladding with the zirconium nitride layer is oxidized in an oxygen-containing atmosphere with different oxygen content, and each zirconium alloy cladding with the zirconium nitride layer corresponds to a third mass change data and a third oxidation kinetics curve.

[0084] Exemplarily, the third mass change data of the zirconium alloy cladding with the zirconium nitride layer during the oxidation process can be recorded by a thermogravimetric analysis software.

[0085] In some embodiments, the third mass change data of the zirconium alloy cladding with the zirconium nitride layer during the oxidation process can be recorded in seconds. Real-time monitoring of the oxidation reaction of the zirconium alloy cladding with the zirconium nitride layer is achieved.

[0086] The third mass change data can be represented as m3, and the third specific mass gain can be represented as Δm3.

[0087] In this embodiment, each zirconium alloy cladding with a zirconium nitride layer is oxidized in an oxygen-containing atmosphere with different oxygen content, and in the process of preparing a product containing zirconium oxide, a third oxidation kinetics curve with the ordinate being the third specific surface mass gain and the abscissa being time is established, the third oxidation kinetics curve can be used to describe the change of the oxidation reaction rate of the zirconium alloy cladding with the zirconium nitride layer with time, and the form of the third oxidation kinetics curve can reflect the dynamic mechanism of the oxidation process. By comparing the slopes of the third oxidation kinetics curves corresponding to the oxygen-containing atmospheres with different oxygen content, the influence of the oxygen content in the oxygen-containing atmosphere on the oxidation rate can be evaluated.

[0088] In some embodiments, the processing method comprises:

[0089] heating the zirconium alloy cladding to a target temperature in a nitrogen atmosphere, so that a zirconium nitride layer is formed on the surface of the zirconium alloy cladding;

[0090] oxidizing the zirconium alloy cladding with the zirconium nitride layer in an oxygen-containing atmosphere at the target temperature to obtain a product containing zirconium oxide;

[0091] terminating the oxidation of the zirconium alloy cladding with the zirconium nitride layer until the mass of the product containing zirconium oxide remains unchanged.

[0092] In this embodiment, compared with the process in the related art without pre-nitriding but directly oxidizing, the oxidation time can be shortened by at least about 65%, and the efficiency is significantly improved.

[0093] In order to more clearly describe the processing method of the present application, two comparison tests are performed.

[0094] Comparison Test One

[0095] In this application, the target temperature is 1000℃, the zirconium alloy cladding is heated to 1000℃ in a nitrogen atmosphere with a nitrogen content of 100%, so that a zirconium nitride layer is formed on substantially the entire surface of the zirconium alloy cladding; the zirconium alloy cladding with the zirconium nitride layer is oxidized in an air atmosphere at 1000℃ to obtain a product containing zirconium oxide.

[0096] In the related art, the zirconium alloy cladding is directly oxidized in an air atmosphere at 1000℃ to obtain a product containing zirconium oxide.

[0097] Please refer to Figure 2 , Figure 2 In this application, the middle red curve is the oxidation kinetics curve of the zirconium alloy cladding pre-nitrided and then oxidized at 1000℃, Figure 2 In the related art, the blue curve is the oxidation kinetics curve of the zirconium alloy cladding directly oxidized at 1000℃, Figure 2It can be seen from the above that, by using the treatment method of nitriding first and then oxidizing in the present application, the oxidation process can be accelerated, and the oxidation treatment efficiency of the zirconium alloy cladding can be improved.

[0098] Comparison Test Two

[0099] In the present application, the target temperature is 1100 DEG C, the zirconium alloy cladding is heated to 1100 DEG C in a nitrogen atmosphere with a nitrogen content of 100%, so that a zirconium nitride layer is formed on substantially the entire surface of the zirconium alloy cladding; the zirconium alloy cladding with the zirconium nitride layer is oxidized in an air atmosphere at 1100 DEG C to obtain a product containing zirconium oxide.

[0100] In the related art, the zirconium alloy cladding is directly oxidized in an air atmosphere at 1100 DEG C to obtain a product containing zirconium oxide.

[0101] Please refer to Figure 3 , Figure 3 The middle red curve is the oxidation kinetics curve of the zirconium alloy cladding in the present application, which is pre-nitrided and then oxidized at 1100 DEG C, Figure 3 The blue curve in the above figure is the oxidation kinetics curve of the zirconium alloy cladding directly oxidized at 1100 DEG C in the related art, from Figure 3 It can be seen from the above that, by using the treatment method of nitriding first and then oxidizing in the present application, the oxidation process can be accelerated, and the oxidation treatment efficiency of the zirconium alloy cladding can be improved.

[0102] In the embodiments of the present application, the product containing zirconium oxide can be directly purified by using the mature sponge zirconium production process to obtain porous sponge zirconium.

[0103] In some embodiments, the treatment method comprises:

[0104] S700, chlorinating the product containing zirconium oxide to obtain a zirconium chloride product;

[0105] S800, reducing the zirconium chloride product to obtain zirconium metal.

[0106] In the process of performing step S200, other fission products and actinides in the zirconium alloy cladding are also converted into oxides, among which, the oxides of some semi-volatile fission products such as RhO2, RuO4, Tc2O7, etc. are volatilized to realize separation, while the semi-volatile or non-volatile oxides U3O8, PuO2, CoO, Cs2O, etc. remain in the product containing zirconium oxide.

[0107] The product containing zirconia is subjected to chlorination treatment, so that the zirconia and the oxides of impurity elements are converted into chlorides. In the chlorination process, the different sublimation temperatures of the chlorides are utilized to realize the separation of the zirconium element from other impurity elements. For example, the chlorides of U, Co, Sn and the like have a relatively low vapor pressure, so they can be evaporated at a relatively low temperature to be removed; ZrO2 is converted into volatile ZrCl4 metal salt through chlorination treatment, and the volatile ZrCl4 metal salt can be subsequently collected and further reduced and recovered; the chlorides of Cs, Pu and the like, such as CsCl and PuCl4, sublimate at temperatures higher than 460°C and 600°C respectively, and thus remain in the ash, thereby realizing effective separation and treatment of each nuclide in the zirconium alloy cladding. The chlorinated zirconium product is then reduced to obtain zirconium metal, realizing efficient recovery of the zirconium metal. Compared with the direct chlorination recovery of the zirconium alloy cladding in the prior art, the present application can be compatible with the existing sponge zirconium preparation process, without the need to build a dedicated corrosion-resistant equipment, thereby reducing the equipment investment and process development cost.

[0108] In some embodiments, before heating the zirconium alloy cladding to the target temperature under a nitrogen atmosphere, the treatment method comprises:

[0109] The zirconium alloy cladding is placed in a crucible, and the crucible is hung by a platinum wire inside a high-temperature thermogravimetric oxidation furnace.

[0110] In this embodiment, the zirconium alloy cladding is subjected to pre-nitriding treatment and oxidation treatment in the high-temperature thermogravimetric oxidation furnace.

[0111] The material of the crucible is not limited, and exemplarily, the crucible includes but is not limited to an alumina material.

[0112] The treatment method of the zirconium alloy cladding provided by the embodiments of the present application is further described below in three embodiments.

[0113] Embodiment one

[0114] 1) Preparation of sample

[0115] The zirconium alloy cladding is cut into short segments with a length of 1 cm as samples, and the samples are placed in a crucible, and the crucible is hung by a platinum wire inside a high-temperature thermogravimetric oxidation furnace. The samples are subjected to thermogravimetric test under controlled atmosphere and temperature conditions.

[0116] 2) Implementation of temperature rising program and pre-nitriding stage

[0117] During the heating of each group of samples to the target temperature under a nitrogen atmosphere, the temperature was increased from room temperature to different target temperatures at a constant heating rate (e.g., 25℃ / min). The different target temperatures were 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, and 1200℃. Changes in sample mass were continuously recorded during the heating process, and temperature and time data were acquired simultaneously. The start time of the heating program is represented by t = 0s.

[0118] During the heating process, high-purity nitrogen with a nitrogen content of 99.99% is continuously introduced into the thermogravimetric oxidation furnace. The flow rate of the nitrogen atmosphere is controlled at 2L / min to ensure the sufficiency and stability of the nitrogen atmosphere supply during the pre-nitriding reaction.

[0119] 3) Implement the isothermal oxidation stage

[0120] While maintaining the target temperature, the zirconium alloy cladding with the zirconium nitride layer is oxidized in an oxygen-containing atmosphere. Air is continuously supplied to the thermogravimetric oxidation furnace at a flow rate of 2 L / min to ensure sufficient and stable air supply during the oxidation reaction. The target temperature is maintained for isothermal nitriding in the air atmosphere, and the mass of the zirconium oxide-containing product remains constant, at which point the oxidation reaction is terminated. Throughout the entire oxidation process, the initial mass change of the sample is continuously recorded to obtain the cumulative mass of the oxidation product over time.

[0121] 4) Data processing and analysis

[0122] The first mass change data (in g) obtained during the oxidation process is converted into the first specific surface area mass gain (g / m²). 2 The first oxidation kinetic curve, representing the first specific surface area gain versus time, is plotted with the vertical axis representing the ordinate and the horizontal axis representing the time (s) during the isothermal oxidation process. By comparing the slope and characteristic changes of the curves at different target temperatures, the influence of the target temperature on the oxidation rate is evaluated, and the oxidation kinetic behavior and reaction control mechanism are analyzed.

[0123] In this embodiment, it can be learned that a target temperature of 400℃-1200℃ is beneficial to the prenitriding and oxidation reactions.

[0124] Example 2

[0125] 1) Prepare samples

[0126] The zirconium alloy cladding was cut into 1cm segments as samples, which were then placed in crucibles and suspended inside a high-temperature thermogravimetric oxidation furnace using platinum wires. Thermogravimetric analysis (TGA) was performed on the samples under controlled atmosphere and temperature conditions.

[0127] 2) Implement the heating process and pre-nitriding stage

[0128] During the heating of each group of samples to the target temperature under a nitrogen atmosphere, the temperature was increased from room temperature to the same target temperature of 1100℃ at a constant heating rate (e.g., 25℃ / min). Changes in sample mass were continuously recorded during the heating process, and temperature and time data were acquired simultaneously. The start time of the heating program is represented by t = 0s.

[0129] During the heating process, nitrogen atmospheres with different nitrogen contents are continuously introduced into the thermogravimetric oxidation furnace. The nitrogen and oxygen contents in the nitrogen atmosphere are: 10%-90%, 20%-80%, 30%-70%, 40%-60%, 50%-50%, 60%-40%, 70%-30%, 90%-10%, and 100%-0. The flow rate of the nitrogen atmosphere is controlled at 2L / min to ensure the sufficiency and stability of the nitrogen atmosphere supply during the pre-nitriding reaction.

[0130] 3) Isothermal oxidation stage

[0131] While maintaining the target temperature, the sample with the zirconium nitride layer was oxidized in an oxygen-containing atmosphere. Air was continuously supplied to the thermogravimetric oxidation furnace at a flow rate of 2 L / min to ensure sufficient and stable air supply during the oxidation reaction. The target temperature was maintained for isothermal nitriding in the air atmosphere until the mass of the zirconium oxide-containing product remained constant, at which point the oxidation reaction was terminated. Throughout the entire oxidation process, the second mass change data of the sample was continuously recorded to obtain the cumulative mass of the oxidation product over time.

[0132] 4) Data processing and analysis

[0133] The second mass change data (in g) obtained during the oxidation process was converted into the second specific surface area mass gain (g / m²). 2 The second oxidation kinetic curve is plotted as the second specific surface area mass gain versus time, with the vertical axis representing the ordinate and the horizontal axis representing the time (s) during the isothermal oxidation process. The slope and characteristic changes of the curves under nitrogen atmospheres with different nitrogen contents are compared to evaluate the effect of nitrogen content on the oxidation rate, and further analyze the oxidation kinetic behavior and reaction control mechanism.

[0134] In this embodiment, according to the second oxidation kinetic curve, the nitrogen content in the nitrogen atmosphere is 90% to 100%, which is conducive to the full reaction of nitrogen and zirconium and promotes the subsequent oxidation reaction.

[0135] Example 3

[0136] 1) Prepare samples

[0137] The zirconium alloy cladding was cut into 1cm segments as samples, which were then placed in crucibles and suspended inside a high-temperature thermogravimetric oxidation furnace using platinum wires. Thermogravimetric analysis (TGA) was performed on the samples under controlled atmosphere and temperature conditions.

[0138] 2) Implement the heating process and pre-nitriding stage

[0139] During the heating of each group of samples to the target temperature under the same nitrogen atmosphere, the temperature was increased from room temperature to the same target temperature of 1100℃ at a constant heating rate (e.g., 25℃ / min). The change in sample mass was continuously recorded during the heating process, and temperature and time data were collected simultaneously. The start time of the heating program is represented by t = 0s.

[0140] During the heating process, high-purity nitrogen with a nitrogen content of 99.99% is continuously introduced into the thermogravimetric oxidation furnace. The flow rate of the nitrogen atmosphere is controlled at 2L / min to ensure the sufficiency and stability of the nitrogen atmosphere supply during the pre-nitriding reaction.

[0141] 3) Implement the isothermal oxidation stage

[0142] The temperature was maintained at the target temperature. Samples with zirconium nitride layers were oxidized under oxygen-containing atmospheres with varying oxygen contents: 0-100%, 10%-90%, 20%-80%, 30%-70%, 40%-60%, 50%-50%, 60%-40%, 70%-30%, and 90%-10%. The flow rate of the oxygen-containing atmosphere was controlled at 2 L / min. The isothermal oxidation process continued until the mass of the product containing zirconium oxide remained constant, at which point the oxidation reaction was terminated. Throughout the oxidation process, the third mass change data of the samples was continuously recorded to obtain the cumulative mass of the oxidation product over time.

[0143] 4) Data processing and analysis

[0144] The third mass change data (in g) obtained during the oxidation process was converted into the third specific surface area mass gain (g / m²). 2 The third oxidation kinetic curve is plotted, with the vertical axis representing the surface area gain versus time (s) during the isothermal oxidation process. The slope and characteristic changes of the curves under different oxygen contents in oxygen-containing atmospheres are compared to evaluate the effect of oxygen content on the oxidation rate, and further analyze the oxidation kinetics and reaction control mechanism.

[0145] In this embodiment, according to the third oxidation kinetic curve, in the oxygen-containing atmosphere composed of oxygen and nitrogen, the oxygen content is 20% to 60% and the nitrogen content is 80% to 40%. When oxygen can react with the zirconium nitride layer to form zirconium oxide, the nitrogen in the oxygen-containing atmosphere can continue to react with the zirconium alloy cladding to form zirconium nitride, thus accelerating the oxidation reaction process.

[0146] In the description of this specification, the references to the terms "an embodiment," "some embodiments," and "exemplary" refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0147] The various embodiments / implementations provided in this application can be combined with each other without creating contradictions. The above descriptions are merely preferred embodiments of this application and are not intended to limit this application. For those skilled in the art, this application can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method of treating a zirconium alloy cladding, characterized by, The method comprises: heating a zirconium alloy cladding under a nitrogen atmosphere to a target temperature, so that a zirconium nitride layer is formed on the surface of the zirconium alloy cladding; oxidizing the zirconium alloy cladding with the zirconium nitride layer under an oxygen-containing atmosphere to obtain a product containing zirconium oxide.

2. The treatment method according to claim 1, characterized in that, The content of nitrogen in the nitrogen atmosphere is 90% to 100%.

3. The treatment method of claim 1, wherein, The thickness of the zirconium nitride layer is H, wherein 0 μm < H and H ≤ 200 μm.

4. The treatment method of claim 1, wherein The target temperature is 400°C-1200°C.

5. The treatment method of claim 1, wherein The method comprises: oxidizing the zirconium alloy cladding with the zirconium nitride layer until the mass of the product containing zirconium oxide remains unchanged.

6. The treatment method of claim 1, wherein oxidizing the zirconium alloy cladding with the zirconium nitride layer at the target temperature.

7. The treatment method according to any one of claims 1 to 6, characterized in that, The oxygen-containing atmosphere comprises oxygen and nitrogen, wherein the content of oxygen in the oxygen-containing atmosphere is 20% to 60%.

8. The treatment method according to any one of claims 1 to 6, characterized in that, The oxygen-containing atmosphere is an air atmosphere.

9. The treatment method of claim 1, wherein, The method comprises: heating a plurality of zirconium alloy claddings under the same nitrogen atmosphere to different target temperatures, so that a zirconium nitride layer is formed on the surface of each zirconium alloy cladding; recording first mass change data of each zirconium alloy cladding with the zirconium nitride layer during oxidation under the same oxygen-containing atmosphere; converting the first mass change data into a first specific surface mass gain to obtain a first oxidation kinetics curve of the first specific surface mass gain-time.

10. The treatment method of claim 1, wherein, The method comprises: heating a plurality of zirconium alloy claddings under nitrogen atmospheres with different nitrogen contents to the same target temperature, so that a zirconium nitride layer is formed on the surface of each zirconium alloy cladding; recording second mass change data of each zirconium alloy cladding with the zirconium nitride layer during oxidation under the same oxygen-containing atmosphere; converting the second mass change data into a second specific surface mass gain to obtain a second oxidation kinetics curve of the second specific surface mass gain-time.

11. The treatment method of claim 1, wherein, The method comprises: heating a plurality of zirconium alloy claddings under the same nitrogen atmosphere to the same target temperature, so that a zirconium nitride layer is formed on the surface of each zirconium alloy cladding; recording third mass change data of each zirconium alloy cladding with the zirconium nitride layer during oxidation under oxygen-containing atmospheres with different oxygen contents; converting the third mass change data into a third specific surface mass gain to obtain a third oxidation kinetics curve of the third specific surface mass gain-time.

Images