A method for designing a radiation resistant fuel solution for a medical isotope reactor

Abstract

The application provides a design method of a medical isotope reactor fuel solution, which comprises: the fuel solution comprises uranyl nitrate and nitric acid; the concentration of F ‑ ≤1mg / L, Cl ‑ ≤1mg / L, total boron equivalent ≤4.0μg / gU, Ru ion ≤0.02g / L, Cr ion ≤0.05g / L, Al ion ≤11.12g / L, and other impurities meet the requirements of GB / T 10266 standard; the concentration of acid, the concentration of uranium and the temperature of the fuel solution are controlled to control the pH value of the fuel solution; the operation power density of the fuel solution is not greater than 2.0kW / L, and a catalyst is used to prevent the fuel solution from generating precipitates during operation. The design method of the medical isotope reactor fuel solution provided by the application can realize long-term stable operation of the fuel solution, and is safe and economical.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of production of liquid fuel design, and particularly relates to a design method of a radiation-resistant fuel solution for a medical isotope reactor. BACKGROUND

[0002] Medical Isotope Production Reactors (MIPR) is a kind of homogeneous solution reactor for producing medical isotopes in aqueous solution, using uranyl nitrate or uranyl sulfate as fuel, mainly used in the medical field. In 1944, the Los Alamos laboratory first built a homogeneous solution nuclear reactor (LOPO and HYPO) using uranyl sulfate as nuclear fuel, at that time, this type of reactor was mainly used for nuclear physics research, neutron activation and neutron photography. It was found that the structural materials were severely corroded by the fuel solution at high temperature and high pressure, so this type of nuclear reactor was not further developed in the power reactor. In 1992, the American Power Company proposed the concept of a medical isotope production reactor using uranyl nitrate. Due to its large negative temperature coefficient of production system, good inherent safety, high U utilization rate, less radioactive waste, good economy and other advantages, it has attracted widespread attention. 235

[0003] The fuel solution will generate many radioactive and non-radioactive substances during operation, generating useful medical isotopes 99 Mo、 131 I、 89 Sr and more than 200 other fissile nuclei such as Dy, Eu, Gd, Sm, in addition to which water will undergo radiolysis under the action of various rays, and the radiation products include H3O + , OH - , H + , HO2, H2O2, H2, etc. NO3 - ions will also undergo radiolysis, and the decomposition products include N2, O2, NO x gas, etc. Corrosion of reactor structural materials will also produce various corrosion products, including ions and compounds of elements such as Fe 3+ , Cr 2+ , Ni 2+ , Ti 2+ , F - , Cl - , etc. Some of the above substances are prone to generate precipitates, such as H2O2 will react with UO2 2+ ​The ion reaction generates a low-solubility (UO2)O2·2(H2O) precipitate, and the uranium precipitate is not conducive to the stable control of the reactivity. To avoid the generation of (UO2)O2·2(H2O), the concentration of H2O2 and the pH should be reduced. When the content of the fission product Mo, Zr reaches a certain level, a zirconium molybdate precipitate is generated, the molybdate is a difficultly soluble substance, and the content of Mo should be reduced. F - , Cl - The corrosiveness of the ions to the structural material can cause the reduction of the service life of the container, and Dy, Eu, Gd, Sm and the like with large neutron absorption cross sections can affect the reactivity, which can affect the stable operation and safety of the homogeneous aqueous solution reactor.

[0004] Therefore, there is an urgent need for a design method of a long-term stable operation, safe and economical irradiation-resistant fuel solution for a medical isotope reactor. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a design method of a long-term stable operation, safe and economical irradiation-resistant fuel solution for a medical isotope reactor.

[0006] To solve the above technical problem, the present application provides a design method of an irradiation-resistant fuel solution for a medical isotope reactor, comprising:

[0007] The fuel solution comprises uranyl nitrate and nitric acid;

[0008] The F - ≤1mg / L, Cl - ≤1mg / L, the total boron equivalent is ≤4.0μg / gU, the Ru ion is ≤0.02g / L, the Cr ion is ≤0.05g / L, the Al ion is ≤11.12g / L, and other impurities meet the requirements of GB / T10266 standard;

[0009] The concentration of the acid in the fuel solution, the uranium concentration and the temperature control the pH value of the fuel solution;

[0010] The operating power density of the fuel solution is not greater than 2.0kW / L, and a catalyst is used to make the fuel solution not generate a precipitate during the operation.

[0011] Further, when the fuel solution is high-concentration uranium and the enrichment degree is >90%, the uranium concentration of the uranyl nitrate in the fuel solution is controlled to be below 90g / L, the initial nitric acid concentration is controlled to be 0.2mol / L-0.5mol / L, the full-power operation temperature of the fuel solution is controlled to be 60℃-90℃, and the pH is controlled to be -0.4

[0012] Further, the fuel solution is low-concentration uranium, enrichment <20%, the initial uranium concentration of the fuel solution is controlled at 200-300 gU / L, the initial nitric acid concentration is controlled at 0.1-0.3 mol / L, and the full-power operation temperature of the fuel solution is controlled at 60-90℃, and the pH value is controlled at -0.4

[0013] Further, the control of the amount of F - , Cl - , Ru ions, Cr ions, Al ions and total boron equivalent in the fuel solution during the initial and reaction processes is completed by periodic purification.

[0014] Further, the fuel solution is purified at least once every half year, and the purification ratio is more than 70%.

[0015] Further, the catalyst is one or more of nitrate of Ag + , Cu 2+ and Fe 3+ , and the ion concentration of the nitrate is controlled at 500-3500 mg / L.

[0016] The design method of the radiation-resistant fuel solution for the medical isotope reactor provided by the application controls the content of impurities in the uranium nitrate fuel solution during the initial and operation processes, such as controlling the amount of F - , Cl - , Ru ions, Cr ions, Al ions and total boron equivalent within a certain range, which not only reduces the corrosion of the fuel solution to the reactor container, but also reduces the influence of the large absorption cross-section elements generated during the operation of the fuel solution on the reactivity and the amount of the radiation product precipitated during the operation.

[0017] Further, the design method of the radiation-resistant fuel solution for the medical isotope reactor provided by the application controls the nitric acid concentration, the uranium nitrate concentration and the temperature of the fuel solution, which is beneficial to control the pH value of the fuel solution within the range of -0.4

[0018] Meanwhile, the design method of the radiation-resistant fuel solution for the medical isotope reactor provided by the application controls the operation power density of the fuel solution to be not more than 2.0 kW / L and adds a certain concentration of catalyst, which not only reduces the amount of the radiation and fission product H2O2, molybdate, H2, O2, NO x , but also accelerates the decomposition of H2O2, which is beneficial to reduce H2O2 and UO22 + The ion reaction generates (UO2)O2·2(H2O) with low solubility. Thus, stable operation of the fuel solution can be achieved, the reactivity loss is reduced, and the economy and safety of the operation of the homogeneous aqueous solution reactor are improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A design method of a radiation-resistant fuel solution for a medical isotope reactor is provided for the embodiments of the present application.

[0020] Figure 2 A stability diagram of (UO2)O2·2(H2O) at different pH and H2O2 concentrations at room temperature is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0021] Reference Figure 1 The design method of the radiation-resistant fuel solution for the medical isotope reactor provided by the embodiments of the present application includes the following control measures.

[0022] 1) The fuel solution includes uranyl nitrate and nitric acid, that is, the radiation-resistant fuel solution for the medical isotope reactor provided by the present application is prepared from uranyl nitrate UO2(NO3)2 and nitric acid.

[0023] 2) The ion concentration of F - ≤1mg / L, Cl - ≤1mg / L, the total boron equivalent ≤4.0μg / gU, the Ru ion ≤0.02g / L, the Cr ion ≤0.05g / L, the Al ion ≤11.12g / L, and other impurities meet the requirements of GB / T10266 standard.

[0024] By controlling the ion concentration of F - , Cl - in the fuel solution, the corrosion of these acidic ions to the reactor container can be reduced, and the amount of Gd, Eu, Sm with large absorption cross section produced in the radiation operation process of the fuel solution and the corrosion-sensitive Ru and Cr, Al and other elements is controlled within a small range. By reducing the amount of radiation products that will cause precipitation reaction in the radiation operation process of the fuel solution, the fuel solution can not precipitate during the operation process, thereby ensuring the normal and stable operation and safe operation of the reactor.

[0025] 3) The concentration of nitric acid, the uranium concentration and the temperature in the fuel solution are controlled, so as to control the pH value of the fuel solution. Not only can it be ensured that the normal and stable operation and safe operation of the reactor will not be affected due to too low acidity causing UO3·2H2O precipitation and UO2(NO3)2 and fission product precipitation, but also it can be ensured that the severe corrosion of the contact material will not be caused due to too high acidity.

[0026] Referring to Figure 2 Figure 2 shows the relationship between (UO2)O2-2(H2O) and pH and H2O2 at room temperature by thermodynamic calculation, and the saturation concentration of (UO2)O2-2(H2O) at different H2O2 concentrations and pH. As can be seen from the figure, in order to avoid the formation of (UO2)O2-2(H2O) precipitate, the concentration of H2O2 and pH should be reduced.

[0027] Since the UO2(NO3)2solution (NO3 - / U = 2) is acidic, when it is dissolved in water, it will undergo primary or secondary hydrolysis reactions to different degrees due to different uranium concentrations, acidities and temperatures, and UO2(NO3)2partially generates free UO2 2+ ions. When NO3 - / U = 2, it is UO2(NO3)2. When NO3 - / U > 2, the solution is a mixed solution of UO2(NO3)2and nitric acid. At the same NO3 - / U ratio, the pH of the solution decreases with the increase of the concentration of uranyl nitrate. Therefore, when changing from a low uranyl nitrate concentration, such as 50 g U / L, to a high uranyl nitrate concentration, such as 230 g U / L, the concentration of nitric acid needs to be reduced to maintain the same pH and maintain the stability of the fuel solution system.

[0028] The pH control of the solution during the initial and running processes is mainly to maintain a high solubility of UO2(NO3)2and its fission products, and to reduce the corrosion of the fuel solution to its contact materials. When pH > 3, UO2 2+ in the fuel solution will undergo a hydrolysis reaction to form UO3-2H2O precipitate. The relationship between the UO2(NO3)2and nitric acid concentrations and the pH of the homogeneous nuclear reactor is shown in Table 1.

[0029] Table 1

[0030]

[0031]

[0032] As can be seen from Table 1, during the running process of the fuel solution, the pH change range of the fuel solution should be controlled. If the pH is too large, the fuel solution will hydrolyze to form precipitate, which is not conducive to the control of reactivity and affects the normal and safe operation of the reactor. If the pH is too small, it will adversely affect the corrosion of the container. Therefore, by controlling the concentration of nitric acid, the uranium concentration and the temperature in the fuel solution, the pH value of the fuel solution is controlled at -0.4 < pH < 2.5.

[0033] Specifically, when the fuel solution is selected as low enriched uranium (enrichment <20%), the initial uranyl nitrate concentration should be controlled in the range of 200gU / L to 300gU / L. High uranyl nitrate concentration will introduce more NO3 - Root ions, causing more N2 and NO x production, on the other hand, reduces the solution acidity and accelerates the corrosion of the container. Therefore, due to the need to control the solution acidity, the nitric acid concentration should be adjusted according to the uranyl nitrate concentration to compensate for the acidity of the solution, and the initial nitric acid concentration should be controlled in the range of 0.2mol / L to 0.5mol / L.

[0034] When the fuel solution is selected as high enriched uranium (enrichment ≥90%), the uranyl nitrate concentration is less than 90gU / L, and the nitric acid concentration is set to 0.2mol / L to 0.5mol / L.

[0035] As a specific embodiment of the present application, the amount of F - , Cl - , Ru ions, Cr ions, Al ions and total boron equivalent generated by irradiation in the initial and reaction process of the fuel solution is controlled by regular purification.

[0036] Among them, the fuel solution is purified at least once every half year, and the purification ratio is more than 70%.

[0037] The initial impurity limit of the reactor uranyl nitrate solution is shown in Table 2. The content of the initial additional nitric acid HNO3 in the fuel solution is (0.20±0.02)mol / L. During operation, the HNO3 content is controlled to be 0.1mol / L to 0.3mol / L by adding acid.

[0038] Table 2

[0039] Element Suggested limit Total boron equivalent ≤4.0 μg / g U Cl ≤1 mg / L F ≤1 mg / L Cr ion 0.05 g / L Ru ion 0.02 g / L Al ion 11.12 g / L Other impurities Meet the requirements of GB / T 10266 standard

[0040] In addition, the temperature will affect the corrosion of the contact material and the catalytic efficiency of the catalyst. If the temperature is too high, the solution will boil uniformly, which will significantly accelerate the corrosion of the contact material. If the temperature is too low, the H2O2 generated by irradiation is not easy to decompose, which will easily cause the reaction of H2O2 and UO2 2+ ions to generate (UO2)O2·2(H2O) with low solubility, which will affect the stable operation of the fuel solution reactor. In addition, if the temperature is too low, the catalytic efficiency of the catalyst will also decrease. Moreover, when the temperature is low, the viscosity of the solution is large, which will also affect the normal and stable operation of the homogeneous aqueous solution reactor. Therefore, considering both aspects and through test and test data analysis, the full power operation temperature of the fuel solution is controlled in the range of 60℃ to 90℃.

[0041] Meanwhile, in order to ensure that the pH value of the fuel solution is within the required range, nitric acid can be directly added to the fuel solution through the acid supplement tank to ensure that the pH value of the fuel solution is controlled within -0.4 < pH < 2.5. In this way, the acidity is not too low to cause hydrolysis and precipitation, and the acidity is not too high to slow down the corrosion rate of the contact material.

[0042] 4) The operating power density of the fuel solution is controlled to be not more than 2.0 kW / L, and a catalyst is used to prevent the fuel solution from generating precipitates during high-power operation. Under the condition that the solution volume, temperature and acid concentration are constant, if the power density of the fuel solution is too high, the radiolysis and fission product rate per unit time will be higher, and the amounts of H2O2, molybdate, H2, O2 and NOx will be higher, so that zirconium molybdate, iron molybdate and (UO2)O2·2(H2O) precipitates are more likely to be generated in the homogeneous aqueous solution reactor solution, and the amount of gas to be treated is also increased, which affects the normal and stable operation of the homogeneous aqueous solution reactor. Adding a catalyst to the homogeneous aqueous solution reactor can catalyze and accelerate the decomposition of H2O2, so that the fuel solution can be stably operated.

[0043] Among them, the appropriate concentration of the catalyst should be selected according to the catalytic factor and operating temperature of the catalyst.

[0044] As a specific embodiment of the present application, the catalyst is one or more of nitrate salts of Ag + , Cu 2+ and Fe 3+ .

[0045] Among them, the concentration of nitrate ions is controlled within 500 mg / L to 3500 mg / L.

[0046] When the reaction power of the fuel solution is controlled, one or more catalysts of nitrate salts of Ag + , Cu 2+ and Fe 3+ are used to catalyze the decomposition of H2O2, the intergranular corrosion of the container is avoided, and the contents of Ru 3+ , Cr 6+ and Al 3+ in the solution are strictly controlled.

[0047] The present application provides a design method of a radiation-resistant fuel solution for a medical isotope reactor, which controls the operating power, impurity content, acidity, temperature, concentration of uranyl nitrate and catalyst of the fuel solution, and controls the concentrations of F - , Cl - , molybdate, Dy, Eu, Gd, Sm, Ru and Cr, and Al ions, so that the fuel solution neither generates precipitates nor causes excessive corrosion of the reactor container during operation, thereby obtaining a radiation-resistant fuel solution for a medical isotope reactor which can be stably and safely operated for a long time and is safe and economical.

[0048] The design method of the irradiation-resistant fuel solution for a medical isotope reactor is specifically illustrated by the following examples.

[0049] Example 1

[0050] The fuel solution of this example is stable in irradiation-resistant operation, specifically: the fuel solution is a low-concentration uranyl nitrate solution, the enrichment is <20%, the uranyl nitrate concentration is 230 g U / L, the initial nitric acid concentration is controlled at 0.2 mol / L, the initial fuel volume is 126.4 L, the fuel solution is operated at full power of 200 kW, the full power operation temperature is 67℃±5℃, and the solution pH is maintained at -0.4

[0051] Example 2

[0052] The fuel solution of this example is stable in irradiation-resistant operation, specifically: the fuel solution is a high-concentration uranyl nitrate solution, the enrichment is >90%. The uranyl nitrate concentration is 46 g U / L, the initial nitric acid concentration is controlled at 0.2 mol / L, the initial fuel volume is 96.4 L, the fuel solution is operated at full power of 200 kW, the full power operation temperature is 67℃±5℃, and the solution pH is maintained at -0.4

[0053] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A design method for a radiation-resistant fuel solution for a medical isotope reactor, characterized in that, The application relates to a method for controlling the quality of a fuel solution. The fuel solution comprises uranyl nitrate and nitric acid; The amount of F-≤1 mg / L, Cl-≤1 mg / L, total boron equivalent ≤4.0 μg / gU, Ru ion ≤0.02 g / L, Cr ion ≤0.05 g / L, Al ion ≤11.12 g / L and other impurities in the fuel solution generated by irradiation during the initial stage and the reaction process is controlled to meet the requirements of GB / T10266 standard; The concentration of acid in the fuel solution, the uranium concentration and the temperature are controlled to control the pH value of the fuel solution; The operation power density of the fuel solution is not greater than 2.0 kW / L, and a catalyst is used to prevent the fuel solution from generating precipitates during the operation process; When the fuel solution is high-concentration uranium and the enrichment degree is greater than 90%, the uranium concentration of uranyl nitrate in the fuel solution is controlled to be below 90 g / L, the initial nitric acid concentration is controlled to be 0.2 mol / L-0.5 mol / L, the full-power operation temperature of the fuel solution is controlled to be 60-90 DEG C, and the pH value is controlled to be -0.4 When the fuel solution is low-concentration uranium and the enrichment degree is less than 20%, the initial uranium concentration of the fuel solution is controlled to be 200-300 gU / L, the initial nitric acid concentration is controlled to be 0.2 mol / L-0.5 mol / L, the full-power operation temperature of the fuel solution is controlled to be 60-90 DEG C, and the pH value is controlled to be -0.4 The amount of F-, Cl-, Ru ion, Cr ion and Al ion and the total boron equivalent in the fuel solution generated by irradiation during the initial stage and the reaction process is controlled by periodic purification.

2. The method of designing a radiation tolerant fuel solution for a medical isotope reactor as claimed in claim 1, wherein: The fuel solution is purified at least once every half year, and the purification ratio is above 70%.

3. The method of designing a radiation tolerant fuel solution for a medical isotope reactor as defined in claim 1, wherein: The catalyst is one or several of the nitrates of Ag + , Cu 2+ and Fe 3+ , the ionic concentration of which is controlled between 500 mg / L and 3500 mg / L.

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