Structural alloy for molten salt reactor and component design method thereof

Abstract

The invention discloses a structural alloy for a molten salt reactor and a component design method of the structural alloy, and belongs to the technical field of multi-principal-element high-entropy alloy materials. The method comprises the following steps: determining the molar content of chromium according to the fluorination corrosion resistance and high-temperature oxidation resistance of the Hastelloy N alloy; the molar content of nickel is determined according to the nickel in the overlapped non-telluride area of the Hastelloy N alloy and the 316 alloy and the thermodynamic activity relation of nickel and chromium; the iron and the molybdenum respectively meet the thermodynamic activity relation with the chromium and are in a non-telluride area of the alloy, the molar content of the iron is determined according to the fluoridation dissolution resistance of the iron in the 316 alloy, and the molar content of the iron and the molybdenum is determined according to the stable phase structure of the molybdenum in the alloy at the temperature of 1000 DEG C as follows: more than 90% of a face-centered cubic solid solution main phase and less than 10% of a hard precipitated phase; and finally obtaining the structural alloy for the molten salt reactor. The structural alloy for the molten salt reactor, which is obtained by the method, has excellent corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of multi-principal-element high-entropy alloy materials technology, and more specifically to a structural alloy for molten salt reactors and its composition design method. Background Technology

[0002] Molten salt reactors typically use molten fluoride salts as the primary coolant, dissolving nuclear fuels such as uranium as fluoride salts in the molten salt coolant. This achieves advantages such as high-temperature output, atmospheric pressure operation, online fuel cycle, and small modularity, making it one of the most promising fourth-generation nuclear energy systems. However, conventional stainless steel and nickel-based alloys experience severe dealloying and surface dissolution in molten fluoride salts. This is because the surface passivation oxide film relied upon by conventional corrosion-resistant alloys is easily damaged in fluoride salts, leaving the alloys completely unprotected and causing selective dissolution of easily fluorinated elements such as Cr and Fe. Furthermore, as the nuclear fission reaction proceeds, the fission product tellurium is directly released into the molten salt coolant, posing a tellurium-induced corrosion embrittlement challenge to the reactor's structural alloys.

[0003] Historically, researchers have developed the Hastelloy N (Ni-16Mo-7Cr-5Fe) structural alloy for molten salt reactors by reducing the content of easily fluorinated Cr and Fe and optimizing the content of fluorinated-resistant Ni and Mo. This significantly reduced the fluorination rate of molten salt, but resulted in severe tellurium embrittlement. Tests on dozens of commercial alloys showed that traditional iron-based alloys and nickel-based alloys with Cr content higher than 23% exhibited almost no tellurium embrittlement, but due to their high Fe and Cr content, they suffered severe fluorination. In contrast, nickel-based alloys with Cr content not exceeding 15% all experienced severe tellurium embrittlement. Therefore, existing commercial alloys cannot simultaneously possess both resistance to fluorination and tellurium embrittlement, failing to meet the service requirements of molten salt reactor structural materials for liquid fuel reactors. This seriously threatens reactor safety and necessitates redesign. Summary of the Invention

[0004] To address the above problems, this invention discloses a structural alloy for molten salt reactors and its composition design method. The structural alloy for molten salt reactors obtained according to the composition design method of this invention has excellent corrosion resistance.

[0005] The first objective of this invention is to provide a method for designing the composition of structural alloys for molten salt reactors, comprising the following steps: Nickel, chromium, iron, molybdenum, and cobalt were selected as the main alloying elements; The molar content of chromium was determined based on the fluorination corrosion resistance and high-temperature oxidation resistance of Hastelloy N alloy. Based on the Gibbs free energy and Nernst equation of telluride and fluoride of each principal alloying element, the E-pTe at the service temperature of 700℃ was obtained. 2- Phase diagram; Thermodynamic activity relationship at service temperature of 700℃ was obtained based on the reaction equilibrium of chromium ion concentration reached by the dissolution of tellurization and fluorination of chromium telluride in each principal component. The thermodynamic activity relationship between chromium and nickel at a service temperature of 700℃ is as follows: .

[0006] The thermodynamic activity relationship between chromium and iron at a service temperature of 700℃ is as follows: .

[0007] The thermodynamic activity relationship between chromium and molybdenum at a service temperature of 700℃ is as follows: .

[0008] The thermodynamic activity relationship between chromium and cobalt at a service temperature of 700℃ is as follows: .

[0009] The molar content of nickel was determined based on the fact that nickel in the alloy satisfies the overlapping green safety zone of Hastelloy N alloy and 316 alloy, and the thermodynamic activity relationship between chromium and nickel at a service temperature of 700°C. The molar content of iron in the alloy is determined based on the thermodynamic activity relationship between chromium and iron at a service temperature of 700℃ and within the non-telluric region of the alloy, as well as the fluorination resistance of the 316 alloy. The molar content of molybdenum in the alloy is determined based on the thermodynamic activity relationship between chromium and molybdenum at the service temperature of 700℃, and the fact that the stable phase structure of the alloy at 1000℃ is more than 90% face-centered cubic solid solution main phase and less than 10% hard precipitate phase. The molar content of cobalt in the alloy is determined based on the thermodynamic activity relationship between chromium and cobalt at a service temperature of 700℃ and in the non-telluric region of the alloy. The structural alloy for molten salt reactors is obtained based on the molar content of nickel, chromium, iron, molybdenum and cobalt, and the stable phase structure of the alloy at 1000℃ being more than 90% face-centered cubic solid solution main phase and less than 10% hard precipitate phase.

[0010] In this invention, the composition design of the structure for use in molten salt reactors, which is both resistant to fluoride dissolution and telluride, requires that the molar content of Ni be 20 at%~35 at%, the molar content of Cr be 5 at%~20 at%, the molar content of Fe be 20 at%~30 at%, the molar content of Co be 20 at%~30 at%, and the molar content of Mo be 5 at%~15 at%.

[0011] A second objective of this invention is to provide a structural alloy for molten salt reactors obtained by the above-described composition design method.

[0012] In a preferred embodiment of the present invention, the structural alloy for molten salt reactors has a molar content of 25 at for Ni, a molar content of 15 at for Cr, a molar content of 25 at for Fe, a molar content of 25 at for Co, and a molar content of 10 at for Mo.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Based on the theoretical guidance of the quantitative relationship between the tellurization threshold of key alloying elements (Ni, Fe, Mo, Co) and the active element Cr in a molten salt environment at 700℃, this invention successfully prepared a multi-principal element alloy that meets the target composition requirements. Experimental results show that this high-entropy alloy exhibits excellent comprehensive corrosion resistance in a tellurium-containing LiF-NaF-KF molten salt environment at 700℃: on the one hand, it effectively inhibits the fluorination dissolution tendency of elements such as Cr and Fe, and its resistance to fluorination dissolution is superior to that of the traditional nickel-based alloy Hastelloy N; on the other hand, by controlling the Ni content, the surface tellurization degree is significantly reduced, and at the optimal composition (such as Ni... 25 Cr 15 Fe 25 Co 25 Mo 10 Under these conditions, its tellurium corrosion resistance is even better than that of austenitic stainless steel 316. This achievement verifies the effectiveness and potential of the multi-principal element alloying strategy in solving the problem of synergistic corrosion of tellurium embrittlement and fluorination dissolution in molten salt reactor structural materials.

[0014] Based on the key theoretical understanding of the quantitative relationship between the tellurization threshold of key alloying elements (Ni, Fe, Mo, Co) and active element Cr in a molten salt environment at 700℃, this invention provides an important basis for the design and development of novel alloys that can simultaneously resist telluric embrittlement and fluorination dissolution. Attached Figure Description

[0015] Figure 1 The potentials of Cr, the alloying element most easily dissolved by fluorination corrosion, and nickel, the alloying element most easily dissolved by tellurization, in a 700 ℃ LiF-NaK-KF eutectic molten salt are calculated as pTe. 2- Relationship diagram.

[0016] Figure 2 The thermodynamic activity of Cr, the alloying element most easily dissolved by fluorination corrosion, in the LiF-NaK-KF eutectic molten salt at 700 ℃. α Thermodynamic activity of other alloying elements α The quantitative relationship diagrams are shown below, where (a) is the quantitative relationship diagram of the thermodynamic activities of Cr and Ni, (b) is the quantitative relationship diagram of the thermodynamic activities of Cr and Fe, (c) is the quantitative relationship diagram of the thermodynamic activities of Cr and Mo, and (d) is the quantitative relationship diagram of the thermodynamic activities of Cr and Co.

[0017] Figure 3 The results of electron probe microanalysis of the alloy prepared in Example 1 after corrosion by tellurium-containing LiF-NaK-KF eutectic molten salt are shown in the figures. (a) is the scanning result, (b) is the surface scan result of Ni element distribution in the cross section, (c) is the surface scan result of Te element distribution in the cross section, (d) is the surface scan result of Co element distribution in the cross section, (e) is the surface scan result of Mo element distribution in the cross section, (f) is the surface scan result of Cr element distribution in the cross section, and (g) is the surface scan result of Fe element distribution in the cross section.

[0018] Figure 4 The results of electron probe microanalysis of the alloy prepared in Example 2 after corrosion by tellurium-containing LiF-NaK-KF eutectic molten salt are shown in the figures. (a) is the scanning result, (b) is the surface scan result of Ni element distribution in the cross section, (c) is the surface scan result of Te element distribution in the cross section, (d) is the surface scan result of Co element distribution in the cross section, (e) is the surface scan result of Mo element distribution in the cross section, (f) is the surface scan result of Cr element distribution in the cross section, and (g) is the surface scan result of Fe element distribution in the cross section.

[0019] Figure 5 The results of electron probe microanalysis of the alloy prepared in Example 3 after corrosion by tellurium-containing LiF-NaK-KF eutectic molten salt are shown in the figures. (a) is the scanning result, (b) is the surface scan result of Ni element distribution in the cross section, (c) is the surface scan result of Te element distribution in the cross section, (d) is the surface scan result of Co element distribution in the cross section, (e) is the surface scan result of Mo element distribution in the cross section, (f) is the surface scan result of Cr element distribution in the cross section, and (g) is the surface scan result of Fe element distribution in the cross section.

[0020] Figure 6 The results of electron probe microanalysis of the alloy prepared in Comparative Example 1 after corrosion by tellurium-containing LiF-NaK-KF eutectic molten salt are shown in the figures. (a) is the scanning result, (b) is the surface scan result of Ni element distribution in the cross section, (c) is the surface scan result of Te element distribution in the cross section, (d) is the surface scan result of Mo element distribution in the cross section, (e) is the surface scan result of Cr element distribution in the cross section, and (f) is the surface scan result of Fe element distribution in the cross section.

[0021] Figure 7 The results of electron probe microanalysis of the alloy prepared in Comparative Example 1 after corrosion by tellurium-containing LiF-NaK-KF eutectic molten salt are shown in the figures. (a) is the scanning result, (b) is the surface scan result of Ni element distribution in the cross section, (c) is the surface scan result of Te element distribution in the cross section, (d) is the surface scan result of Cr element distribution in the cross section, and (e) is the surface scan result of Fe element distribution in the cross section. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0024] This invention provides a structural alloy and alloy design method for molten salt reactors. Traditional corrosion-resistant alloys mainly use Ni, Fe or Ni-Mo as the matrix and dop with a certain amount of active element Cr. This invention uses a quaternary or higher alloy system with nickel (Ni), chromium (Cr), iron (Fe), molybdenum (Mo) and cobalt (Co) as basic components. Through multi-principal element alloying and composition optimization, the following synergistic effects are achieved: unique resistance to telluride corrosion embrittlement and fluoride corrosion dissolution, as well as good oxidation resistance and high-temperature mechanical properties.

[0025] Compared to the Hastelloy N alloy (Ni-16Mo-7Cr-5Fe), for which a large amount of data has been accumulated, this pentagonal system only adds Co. Co has the second-highest resistance to fluorination dissolution after Ni, and its tellurization threshold potential is better than Ni and close to Mo, which is acceptable. In addition, Ni-Cr-Fe-Co-Mo pentagonal alloys and their quaternary subclasses (such as Cr-Fe-Co-Ni) and close relatives (such as Canteralloy Cr-Mn-Fe-Co-Ni) exhibit potentially excellent mechanical properties, radiation resistance, and resistance to conventional corrosion, showing potential for application as reactor structural alloys.

[0026] Preferably, the activity of easily tellurized and easily fluorinated elements is reduced simultaneously, thereby reducing the concentration of each element, thus obtaining comprehensive resistance to fluorination dissolution and tellurium embrittlement.

[0027] Determination of the thermodynamic activity relationship at a service temperature of 700℃: Figure 1 The potentials of Cr, the alloying element most easily dissolved by fluorination corrosion, and nickel, the alloying element most easily dissolved by tellurization, in a 700 ℃ LiF-NaK-KF eutectic molten salt are calculated as pTe. 2- Relationship diagram. Chromium and nickel at a service temperature of 700℃, based on the Gibbs free energy and Nernst equation of nickel-chromium telluride at 700℃, yield the wave potential -pTe in this salt environment. 2- The figure clearly shows the equilibrium lines for tellurization and fluorination of chromium and nickel at a service temperature of 700℃. The reaction equations corresponding to each equilibrium line are shown in Table 1.

[0028] Table 1. Reaction equations corresponding to each equilibrium line. During long-term service of the alloy, the structural alloying element Cr undergoes fluorination and dissolution. The concentration of CrF2 corrosion products in the molten salt gradually increases and tends to stabilize. Its maximum concentration can be determined by 2U 3+ +Cr 2+ =2U 4+ The chemical equilibrium of +Cr shows that the activity increases with increasing Cr activity in the alloy. Assuming the nickel tellurization reaction (a1) is in equilibrium, the equilibrium tellurium ion activity in the salt is obtained through the nickel tellurization reaction. If the reaction between chromium telluride and chromium fluoride (b3) reaches equilibrium at this point, theoretically, nickel tellurization can still be avoided even at a higher CrF2 concentration. This leads to the derivation of the minimum CrF2 concentration at which Ni tellurization does not occur in the alloy. If the CrF2 concentration generated by chromium fluorination happens to coincide with the minimum CrF2 concentration at which Ni tellurization does not occur, a quantitative relationship between the activities of the main elements Ni and Cr in the alloy and the tellurization threshold can be theoretically derived. Extending the calculation to a broader range of alloys, a quantitative relationship between Cr and other alloys can be obtained.

[0029] The molar content of Cr was determined as follows: Since Hastelloy N contains about 7% Cr, it has good resistance to high-temperature oxidation. Therefore, the Cr content in the alloy is higher than 7 at%, in order to ensure its resistance to high-temperature oxidation. Moreover, the higher the Cr content, the better the high-temperature oxidation resistance of the alloy. At the same time, in order to meet the requirements of fluorination resistance, the content should not exceed 15 at.

[0030] The molar content of Ni is determined as follows: Figure 2 The thermodynamic activity of Cr, the alloying element most easily dissolved by fluorination corrosion, in the LiF-NaK-KF eutectic molten salt at 700 ℃. α Thermodynamic activity of other alloying elements α The following quantitative relationship diagram is satisfied. At an service temperature of 700 ℃, the quantitative relationship between the thermodynamic activities of Cr and Ni is as follows:

[0031] .

[0032] The activity of a metallic element in an alloy can reflect its content; the higher the activity, the higher the content. However, the content of an alloying element is not equivalent to its activity. For example, Hastelloy N has a Cr content of 7%, but its Cr activity at 700°C is only about 0.076. The activity of the alloying element can be calculated using the CALPHAD method.

[0033] like Figure 2 As shown in (a), based on the quantitative relationship between Cr and Ni, alloy 316 exhibits high Cr activity and low Ni activity, placing it in the region where Ni tellurization does not occur. Hastelloy N alloy, as a nickel-based alloy, with only 7 at% Cr added, exhibits high Ni activity and low Cr activity, placing it in the tellurization corrosion region of Ni. This is consistent with... Figure 2 The corrosion results shown are consistent. Clearly, to achieve both the fluorination resistance of Hastelloy N and meet the non-tellurization threshold requirement, the Ni / Cr activity of the alloy should fall within [a certain range]. Figure 2 The green area shown in (a) has a Ni activity of less than 0.34, so the Ni content should not exceed 35 at.

[0034] The molar contents of Fe, Mo, and Co were determined as follows: At a service temperature of 700 ℃, the quantitative relationship of the thermodynamic activities of Cr and other elements is as follows: .

[0035] .

[0036] .

[0037] For Fe and Mo elements, from Figure 2 In (b) and (c), the Fe, Mo and Cr activities of the 316 alloy and the Hastelloy N alloy satisfy the quantitative thermodynamic activity relationship given by the above formula, and both remain in the region where Fe and Mo tellurization corrosion does not occur. Figure 2As shown, the non-telluric acid region indicates that within the corresponding activity range of Cr and alloying element M (Ni, Fe, Mo, Co), the material will not undergo tellurization corrosion of the corresponding alloying element M; the telluric acid region indicates that the material will undergo tellurization corrosion of the alloying element M. Common corrosion-resistant alloys, such as 316 stainless steel, contain more than 60% Fe, making them susceptible to fluorination corrosion. Experiments conducted by Oak Ridge National Laboratory (ORNL) on various nickel-based alloys with different compositions show that a Cr content of 23% in nickel-based alloys effectively mitigates tellurization corrosion. However, because Cr is susceptible to fluorination dissolution, the content of Cr, the most easily fluorinated alloying element, is below 20 at%, and the content of Fe, the next most easily fluorinated alloying element, is below 40 at%, to ensure resistance to fluorination corrosion dissolution. Furthermore, the lower the Cr and Fe contents, the better the alloy's resistance to fluorination corrosion dissolution.

[0038] The composition of the alloy should maintain a stable phase structure of more than 90% face-centered cubic (FCC) solid solution main phase and less than 10% hard precipitates (including σ precipitates and μ precipitates) at 1000℃. Generally, the molar content of Mo in the alloy should be less than 15 at%, in order to ensure good mechanical strength and ductility at high temperature.

[0039] For the element Co, Co satisfies the thermodynamic activity relationship between Cr and Co at the service temperature of 700℃ and is in the non-telluric region of the alloy, so the molar content of Co should be less than 30 at.

[0040] Preferred alloy compositions meeting the requirements include pentagonal alloys with Ni content of 20 to 35 at%, Cr content of 5 to 20 at%, Fe content of 20 to 30 at%, Co content of 20 to 30 at%, and Mo content of 5 to 15 at%. Three alloys meeting the composition requirements were initially selected and prepared: Ni x Cr 40-x Fe 25 Co 25 Mo 10 (x=25, 28, 32), with reference to existing candidate structural alloys Hastelloy N and 316 for molten salt reactors, as shown in Table 2, corrosion performance was verified in LiF-NaF-KF eutectic molten salt containing tellurium (Li2Te + Te) at 700℃.

[0041] Example 1 The preparation method of structural alloy for molten salt reactors includes the following steps: weighing 32% Ni, 8% Cr, 25% Fe, 25% Co and 10% Mo metal particles according to molar percentage; The vacuum arc melting method was adopted, with the furnace gauge pressure at -0.05MPa. The melting was carried out by turning the furnace 8 times, each lasting 3 minutes, and electromagnetic stirring was turned on. After the melting was completed, the furnace was allowed to cool naturally to room temperature to obtain alloy ingots. The melting current was about 400-600A. Under an inert gas atmosphere, the alloy ingot was annealed at 1000℃ for 1 hour, and then air-cooled to room temperature to obtain a novel structural alloy for molten salt reactors. The inert gas atmosphere in this step prevents alloy oxidation.

[0042] Example 2 The preparation method of structural alloy for molten salt reactors includes the following steps: weighing 28% Ni, 12% Cr, 25% Fe, 25% Co and 10% Mo metal particles according to molar percentage; The vacuum arc melting method was adopted, with the furnace gauge pressure at -0.05MPa. The melting was carried out by turning the furnace 8 times, each lasting 3 minutes, and electromagnetic stirring was turned on. After the melting was completed, the furnace was allowed to cool naturally to room temperature to obtain alloy ingots. The melting current was about 400-600A. Under an inert gas atmosphere, the alloy ingot was annealed at 1000℃ for 1 hour and then air-cooled to room temperature to obtain a novel structural alloy for molten salt reactors.

[0043] Example 3 The preparation method of structural alloy for molten salt reactors includes the following steps: weighing 25% Ni, 15% Cr, 25% Fe, 25% Co and 10% Mo metal particles according to molar percentage; The vacuum arc melting method was adopted, with the furnace gauge pressure at -0.05MPa. The melting was carried out by turning the furnace 8 times, each lasting 3 minutes, and electromagnetic stirring was turned on. After the melting was completed, the furnace was allowed to cool naturally to room temperature to obtain alloy ingots. The melting current was about 400-600A. Under an inert gas atmosphere, the alloy ingot was annealed at 1000℃ for 1 hour and then air-cooled to room temperature to obtain a novel structural alloy for molten salt reactors.

[0044] Comparative Example 1 is Hastelloy N alloy, and Comparative Example 2 is 316 alloy.

[0045] Table 2. Chemical composition (at.%) of alloys in the examples and comparative examples The corrosion experiment was conducted as follows: In a high argon atmosphere (oxygen content < 5 ppm, water content < 0.1 ppm), a boron nitride crucible containing 50 g of FLiNaK salt (the mass ratio of each component in the molten salt was LiF:NaF:KF = 14.606:5.847:29.574) was placed in a muffle furnace and dried at 200 ℃ for 6 h. The temperature was then increased to 400 ℃ and dried for 12 h to eliminate the influence of water impurities on the experiment. The salt was then heated to 550 ℃ to melt, and 0.05 g of Te particles were added to the salt to provide sufficient Te vapor partial pressure. The temperature was maintained for 1 h. Then, the salt was heated to 700 ℃, and 0.25 g of Li2Te was added to obtain a saturated dissolved tellurium ion concentration. The temperature was maintained for at least 1 h to allow the system to stabilize, thus obtaining the extreme tellurization corrosion simulation molten salt environment required for the experiment. The alloy samples of Examples 1 to 3 and the alloy samples of Comparative Examples 1 to 2 were separately placed in the above-mentioned molten salt environment for corrosion for 24 hours.

[0046] Corrosion assessment: The cross-section of the corroded sample was analyzed using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).

[0047] Figures 3-7 The following are the electron probe microanalysis (EPMA) results of the alloys of Examples 1-3 and Comparative Examples 1-2 after corrosion by tellurium-containing LiF-NaK-KF eutectic molten salt. The scanning results of the electron probe microanalysis after corrosion show that... Figure 6 The most severe surface tellurization and slight fluorination and dissolution of Cr and Fe along the grain boundaries occur in the Hastelloy N. Figure 7 In 316, only slight surface tellurization occurred, but selective fluorination and dissolution of Cr and Fe were severe, resulting in significant Cr and Fe depletion along grain boundaries. In contrast, Figures 3-5 No significant Cr and Fe fluorination dissolution was observed in the multi-principal element alloys of Examples 1-3, and their resistance to fluorination dissolution was superior to that of the Hastelloy N alloy. The degree of surface tellurization in Examples 1-3 gradually decreased with decreasing Ni content, with the Ni content in Example 3 showing the highest degree of tellurization. 25 Cr 15 Fe 25 Co 25 Mo 10 The alloy surface exhibits the slightest tellurization, and its resistance to tellurium corrosion embrittlement is even better than that of alloy 316, combining the best resistance to both tellurization and fluorination corrosion.

[0048] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

[0049] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0050] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method of designing a composition of a structural alloy for a molten salt reactor, characterized by, The method comprises the following steps: nickel, chromium, iron, molybdenum and cobalt are selected as main alloying elements; the molar content of chromium is determined according to the fluoridation corrosion resistance and high-temperature oxidation resistance of Hastelloy N alloy; E-pTe at 700℃ service temperature is obtained according to Gibbs free energy of each principal alloying element telluride and fluoride and Nernst equation 2- phase diagram; the thermodynamic activity relationship at a service temperature of 700 DEG C is obtained according to the tetracalcium of each main element and the fluoridation dissolution of tetracalcium chromium to reach the reaction equilibrium chromium ion concentration; the molar content of nickel is determined according to the non-tetracalcium area of Hastelloy N alloy and 316 alloy and the thermodynamic activity relationship between chromium and nickel at a service temperature of 700 DEG C; the molar content of iron is determined according to the thermodynamic activity relationship between chromium and iron at a service temperature of 700 DEG C and the non-tetracalcium area of the alloy, and according to the fluoridation dissolution resistance of 316 alloy; the molar content of molybdenum is determined according to the thermodynamic activity relationship between chromium and molybdenum at a service temperature of 700 DEG C and the non-tetracalcium area of the alloy, and according to the stable phase structure of the alloy at 1000 DEG C, which is more than 90 % of face-centered cubic solid solution main phase and less than 10 % of hard precipitated phase; the molar content of cobalt is determined according to the thermodynamic activity relationship between chromium and cobalt at a service temperature of 700 DEG C and the non-tetracalcium area of the alloy; a structural alloy for molten salt reactor is prepared according to the molar content of nickel, chromium, iron, molybdenum and cobalt and the stable phase structure of the alloy at 1000 DEG C, which is more than 90 % of face-centered cubic solid solution main phase and less than 10 % of hard precipitated phase.

2. The composition design method of a structural alloy for a molten salt reactor according to claim 1, characterized by, The thermodynamic activity relationship of chromium and nickel at the service temperature of 700°C is: .

3. The composition design method of a structural alloy for a molten salt reactor according to claim 1, characterized by, The thermodynamic activity relationship of chromium and iron at the service temperature of 700°C is: .

4. The composition design method of a structural alloy for a molten salt reactor according to claim 1, characterized by, The thermodynamic activity relationship of chromium and molybdenum at a service temperature of 700°C is: .

5. The composition design method of a structural alloy for a molten salt reactor according to claim 1, characterized by, The thermodynamic activity relationship of chromium and cobalt at a service temperature of 700°C is: .

6. A method of designing a composition of a corrosion-resistant structural alloy for a molten salt reactor according to any one of claims 1 to 5, characterized in that, In the structural alloy for molten salt reactor, the molar content of Ni is 20 at% to 35 at%, the molar content of Cr is 5 at% to 20 at%, the molar content of Fe is 20 at% to 30 at%, the molar content of Co is 20 at% to 30 at%, and the molar content of Mo is 5 at% to 10 at%.

7. A structural alloy for a molten salt reactor according to claim 6, wherein In the structural alloy for molten salt reactor, the molar content of Ni is 25 at%, the molar content of Cr is 15 at%, the molar content of Fe is 25 at%, the molar content of Co is 25 at%, and the molar content of Mo is 10 at%.

Images