Design method of irradiation-resistant fuel solution for medical isotope reactor

Abstract

The invention provides a design method of an irradiation-resistant fuel solution for a medical isotope reactor. The design method comprises the following steps: the fuel solution comprises uranyl nitrate and nitric acid; f <-> generated by irradiation in the initial and reaction processes of the fuel solution is controlled to be less than or equal to 1mg / L, Cl <-> is controlled to be less than or equal to 1mg / L, the total boron equivalent is controlled to be less than or equal to 4.0 mu g / gU, Ru ions are controlled to be less than or equal to 0.02 g / L, Cr ions are controlled to be less than or equal to 0.05 g / L, Al ions are controlled to be less than or equal to 11.12 g / L, and other impurities Controlling the acid concentration, uranium concentration and temperature in the fuel solution to control the pH value of the fuel solution; the operating power density of the fuel solution is controlled to be not greater than 2.0 kW / L, and the fuel solution does not generate precipitates in the operating process by using a catalyst. According to the design method of the radiation-resistant fuel solution for the medical isotope reactor, the fuel solution can stably run for a long time and is safe and economical.

Description

Technical Field

[0001] The invention relates to the technical field of production reactor liquid fuel design, and in particular to a design method for a radiation-resistant fuel solution for a medical isotope reactor. Background Art

[0002] Medical Isotope Production Reactors (MIPR) are aqueous solution homogeneous reactors used to produce medical isotopes. They use uranyl nitrate or uranyl sulfate as fuel and are mainly used in the medical field. In 1944, the Los Alamos Laboratory first built homogeneous solution nuclear reactors (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. Experiments have found that under high temperature and high pressure, the structural materials are severely corroded by the fuel solution, so this type of nuclear reactor has not been further developed in power reactors. In 1992, the American Babcock & Wilcox Company proposed the concept of uranyl nitrate medical isotope production reactors. Because its production system has a large negative temperature coefficient, good inherent safety, 235 It has the advantages of high U utilization rate, less radioactive waste and good economy, and has attracted widespread attention.

[0003] During operation, the fuel solution will generate many radioactive and non-radioactive substances, which can generate usable medical isotopes. 99 Mo, 131 I. 89 Sr and more than 200 other fission nuclides such as Dy, Eu, Gd, Sm, etc. In addition, water will undergo radiolysis under the action of various rays, and the radiation products include H3O + OH - , H + , HO2, H2O2, H2, etc., NO3 - Ions can also undergo radiolysis, and their decomposition products include N2, O2, NO x Gas, etc. Corrosion of the stack structure material will also produce various corrosion products, including Fe 3+ Cr 2+ 、Ni 2+ 、Ti 2+ 、F - , Cl - There are some reactions in the above substances that easily form precipitation, such as H2O2 reacting with UO2 2+The ion reaction generates a low-solubility (UO2)O2·2(H2O) precipitate. The uranium precipitate is not conducive to the stable control of reactivity. To avoid the formation of (UO2)O2·2(H2O), the concentration and pH of H2O2 should be reduced. When the fission products Mo and Zr reach a certain content, zirconium molybdate precipitate will be generated. Molybdate is a poorly soluble substance, so the Mo content should be reduced. F in the fuel solution - , Cl - The corrosiveness of ions to structural materials will reduce the life of the container, and Dy, Eu, Gd, Sm, etc. with large neutron absorption cross-sections will affect the reactivity, which will affect the operating stability and safety of the uniform aqueous solution reactor.

[0004] Therefore, there is an urgent need for a design method for a radiation-resistant fuel solution for medical isotope reactors that can operate stably and safely and economically over a long period of time. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a design method for a radiation-resistant fuel solution for a medical isotope reactor which can operate stably for a long time and is safe and economical.

[0006] In order to solve the above technical problems, the present invention provides a design method of a radiation-resistant fuel solution for a medical isotope reactor, comprising:

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

[0008] Control the F generated by the initial and reaction irradiation of the fuel solution - ≤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, other impurities meet the requirements of GB / T10266 standard;

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

[0010] The operating power density of the fuel solution is controlled to be no greater than 2.0 kW / L, and a catalyst is used to prevent precipitation of the fuel solution during operation.

[0011] Furthermore, when the fuel solution is highly enriched uranium and the enrichment is greater than 90%, the uranium concentration of uranyl nitrate in the fuel solution is controlled below 90 g / L, the initial nitric acid concentration is controlled at 0.2 mol / L to 0.5 mol / L, the full-power operating temperature of the fuel solution is controlled at 60° C. to 90° C., and the pH is controlled at -0.4<2.5 during operation.

[0012] Furthermore, the fuel solution is low-enriched uranium with an enrichment of <20%, the initial uranium concentration of the fuel solution is controlled at 200 gU / L-300 gU / L, the initial nitric acid concentration is controlled at 0.1 mol / L-0.3 mol / L, the full-power operating temperature of the fuel solution is controlled at 60°C-90°C, and the pH is controlled at -0.4<2.5 during operation.

[0013] Furthermore, the control of the F generated by the initial irradiation of the fuel solution and during the reaction process - , Cl - , Ru ions, Cr ions, Al ions and the total boron equivalent are achieved through regular purification.

[0014] Furthermore, the fuel solution is purified at least once every six months, with a purification rate of more than 70%.

[0015] Furthermore, the catalyst is Ag + , Cu 2+ and Fe 3+ One or more of the nitrates, wherein the nitrate ion concentration is controlled at 500 mg / L to 3500 mg / L.

[0016] The present invention provides a method for designing a radiation-resistant fuel solution for a medical isotope reactor, which controls the content of impurities in the uranyl nitrate fuel solution during the initial operation and operation, such as controlling F - , Cl - , Ru ions, Cr ions, Al ions and the total boron equivalent are within a certain range, which is not only beneficial to reducing the corrosion of the fuel solution to the reactor container, but also can reduce the influence of the large absorption cross-section elements produced in the fuel solution during operation on the reactivity and reduce the amount of irradiation products precipitated during operation.

[0017] In addition, the present invention provides a method for designing a radiation-resistant fuel solution for a medical isotope reactor, which controls the nitric acid concentration, the uranyl nitrate concentration and the temperature of the fuel solution in the fuel solution, which is beneficial to controlling the pH value of the fuel solution within the range of -0.4<pH<2.5, ensuring that the pH value of the fuel solution is within the required operating range, and can not only ensure that the acidity of the fuel solution is not too low so that hydrolysis precipitation does not occur, but also ensure that the acidity is not too high so that the corrosion rate of the contact material can be alleviated.

[0018] At the same time, the present invention provides a design method for a radiation-resistant fuel solution for a medical isotope reactor, which controls the operating power density of the fuel solution to be no more than 2.0 kW / L, and adds a certain concentration of catalyst, which can not only reduce radiolysis and fission products H2O2, molybdate, H2, O2, NO x The catalyst can also accelerate the decomposition of H2O2, which is beneficial to reduce H2O2 and UO22 + The ion reaction generates low-solubility (UO2)O2·2(H2O), which can meet the stable operation of the fuel solution, reduce the reactivity loss, and improve the economy and safety of the uniform aqueous solution reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A control measure diagram of a design method for a radiation-resistant fuel solution for a medical isotope reactor provided in an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the stability of (UO2)O2·2(H2O) at different pH values ​​and H2O2 concentrations at room temperature provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0021] See also Figure 1 , a design method for a radiation-resistant fuel solution for a medical isotope reactor provided in an embodiment of the present invention includes the following control measures.

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

[0023] 2) Control the F generated by the initial irradiation of the fuel solution and during the reaction - ≤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, other impurities meet the requirements of GB / T10266 standard.

[0024] By controlling the F content in the fuel solution - , Cl - The ion concentration can reduce the corrosion of these acidic ions on the reactor container, and the amount of Gd, Eu, Sm with large absorption cross-sections, and corrosion-sensitive elements such as Ru, Cr, and Al produced in the fuel solution during the irradiation operation can be controlled within a smaller range. By reducing the amount of irradiation products that will undergo precipitation reactions in the fuel solution during the irradiation operation, the fuel solution will not precipitate during operation, thereby ensuring the normal, stable and safe operation of the reactor.

[0025] 3) Control the concentration of nitric acid, uranium concentration and temperature in the fuel solution, thereby controlling the pH value of the fuel solution. This can not only ensure that the low acidity will not cause the precipitation of UO3·2H2O and the precipitation of UO2(NO3)2 and fission products in the fuel solution, thus affecting the normal, stable and safe operation of the reactor, but also ensure that the high acidity will not cause severe corrosion of the contact materials.

[0026] See also Figure 2 , the relationship between (UO2)O2·2(H2O) and pH and H2O2 obtained by thermodynamic calculation at room temperature, and the saturation concentration of (UO2)O2·2(H2O) at different H2O2 concentrations and pH. It can be seen from the figure that in order to avoid the formation of (UO2)O2·2(H2O) precipitation, the concentration of H2O2 and pH should be reduced.

[0027] Since UO2(NO3)2 solution (NO3 - / U=2) is acidic. When it is dissolved in water, it will undergo primary or secondary hydrolysis reactions to varying degrees due to different uranium concentrations, acidity and temperatures. UO2(NO3)2 partially generates free UO2 2+ ions, in NO3 - When / U=2, it is UO2(NO3)2. - When / U>2, the solution is a mixed solution of UO2(NO3)2 and nitric acid. - At the same time, the pH of the solution decreases with the increase of uranyl nitrate concentration under the ratio of 1:1 / U. Therefore, when changing from a low uranyl nitrate concentration such as 50 gU / L to a high uranyl nitrate concentration such as 230 gU / 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 operation is mainly to maintain a high solubility of UO2(NO3)2 and its fission products, while reducing the corrosion of the fuel solution to its contact materials. When the pH is greater than 3, the UO2 in the fuel solution 2+ A hydrolysis reaction will occur to form UO3·2H2O precipitate. The relationship between the concentration of UO2(NO3)2 and nitric acid and pH in a uniform nuclear reactor is shown in Table 1.

[0029] Table 1

[0030]

[0031]

[0032] It can be seen from Table 1 that the pH variation of the fuel solution should be controlled during the operation of the fuel solution. If the pH is too high, the fuel solution will hydrolyze to generate precipitation, which is not conducive to the control of reactivity and affects the normal, stable and safe operation of the reactor. If the pH is too low, it will have an adverse effect on the corrosion of the container. Therefore, by controlling the concentration of nitric acid, uranium concentration and temperature in the fuel solution, the pH value of the fuel solution is controlled at -0.4<pH<2.5.

[0033] Specifically, under the premise of meeting the power requirements, when the fuel solution uses low-enriched uranium (enrichment <20%), the initial uranyl nitrate concentration should be controlled at 200gU / L-300gU / L. A high uranyl nitrate concentration will introduce more NO3 - Root ions, resulting in greater N2 and NO x On the other hand, reducing the acidity of the solution accelerates the corrosion of the container. Therefore, due to the need to control the acidity of the solution, the concentration of nitric acid should be adjusted according to the concentration of uranyl nitrate to compensate for the acidity of the solution and control the initial nitric acid concentration at 0.2mol / L to 0.5mol / L.

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

[0035] As a specific embodiment of the present invention, the F generated by the initial irradiation of the fuel solution and during the reaction is controlled. - , Cl - , Ru ions, Cr ions, Al ions and the total boron equivalent are achieved through regular purification.

[0036] The fuel solution is purified regularly at least once every six months, with a purification rate of more than 70%.

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

[0038] Table 2

[0039] element Recommended limits Total Boron Equivalent ≤4.0 μg / gU Cl ≤1mg / L F ≤1mg / L Cr ions 0.05g / L Ru ions 0.02g / L Al ions 11.12g / 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 evenly, 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 can easily cause H2O2 and UO2 to react. 2+ The ion reaction generates low-solubility (UO2)O2·2(H2O), which causes the reaction to generate precipitation, affecting 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 uniform aqueous solution reactor. Therefore, taking both aspects into consideration and through experiments and test data analysis, the full-power operating temperature of the fuel solution is controlled at 60℃~90℃.

[0041] At the same time, in order to ensure that the pH value of the fuel solution is within the required operating range, nitric acid can be directly added to the fuel solution through the acid replenishment tank to ensure that the pH of the fuel solution is controlled at -0.4<pH<2.5. This can ensure that the acidity is not too low to prevent hydrolysis precipitation, and at the same time ensure that the acidity is not too high to reduce the corrosion rate of the contact materials.

[0042] 4) Control the operating power density of the fuel solution to no more than 2.0kW / L, and use a catalyst to prevent the fuel solution from precipitating during high-power operation. Under the condition of a certain solution volume, temperature, and acid concentration, if the power density of the fuel solution is too high, the higher the rate of radiolysis and fission products per unit time, including the amount of H2O2, molybdate, H2, O2, and NOx, the more likely the uniform aqueous solution reactor solution will generate zirconium molybdate, iron molybdate, and (UO2)O2·2(H2O) precipitates. At the same time, the amount of gas treatment will also increase, affecting the normal and stable operation of the uniform aqueous solution reactor. Adding a catalyst to the uniform aqueous solution reactor can catalytically accelerate the decomposition of H2O2 and enable the fuel solution to operate stably.

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

[0044] As a specific embodiment of the present invention, the catalyst is Ag + , Cu 2+ and Fe 3+ One or more of the nitrates.

[0045] Among them, the nitrate ion concentration is controlled at 500mg / L to 3500mg / L.

[0046] When controlling the reaction power of the fuel solution, Ag is used + , Cu 2+ and Fe 3+ One or more catalysts in the nitrate catalyze the decomposition of H2O2, avoid intergranular corrosion of stainless steel containers, and strictly control the Ru content in the solution. 3+ and Cr 6+ 、Al 3+ content.

[0047] The present invention provides a method for designing a radiation-resistant fuel solution for a medical isotope reactor, by controlling the operating power, impurity content, acidity, temperature, uranyl nitrate concentration and catalyst addition of the fuel solution, and by controlling F - , Cl - The concentrations of ions such as molybdic acid, Dy, Eu, Gd, Sm, Ru, Cr, and Al can be adjusted so that the fuel solution will not precipitate during operation and will not cause excessive corrosion to the reactor container, thereby obtaining a radiation-resistant fuel solution for medical isotope reactors that can operate stably for a long time and is safe and economical.

[0048] The following is a specific description of a method for designing a radiation-resistant fuel solution for a medical isotope reactor provided by the present invention through examples.

[0049] Example 1

[0050] The present embodiment is a fuel solution that is resistant to radiation and stable in operation, specifically: the fuel solution is a low-concentration uranyl nitrate solution, the enrichment is less than 20%, the uranyl nitrate concentration is 230gU / L, the initial nitric acid concentration is controlled at 0.2mol / L, the initial fuel volume is 126.4L, the fuel solution runs at full power of 200kW, the full power operating temperature is 67℃±5℃, and the solution pH is maintained at -0.4<pH<2.5 by the acid supplement tank during operation. The content of Fe(NO3)3 added as a catalyst is 3000mg / L, the fuel solution is purified once every six months, and the purification rate is 70%. The element content limits of the fuel solution at the beginning and during operation are shown in Table 2. The fuel solution of the present embodiment does not produce precipitation during operation under the conditions of 200kW and 67℃±5℃, and the fuel solution after operation remains clear, and its turbidity value is below 20.

[0051] Example 2

[0052] The present embodiment is a fuel solution that is resistant to radiation and operates stably, specifically: the fuel solution is a highly concentrated uranyl nitrate solution with an enrichment of >90%. The uranyl nitrate concentration is 46gU / L, the initial nitric acid concentration is controlled at 0.2mol / L, the initial fuel volume is 96.4L, the fuel solution operates at full power of 200kW, the full power operating temperature is 67℃±5℃, and during operation, it is maintained at -0.4<pH<2.5 through the acid supplement tank. The added catalyst Fe(NO3)3 content is 3500mg / L, the fuel solution is purified once every six months, and the purification rate is 70%. The element content limits of the fuel solution at the beginning and during operation are shown in Table 2. The fuel solution of the present embodiment does not produce precipitation during operation under the conditions of 200kW and 67℃±5℃, and the fuel solution after operation remains clear, and its turbidity value is below 20.

[0053] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for designing a radiation-resistant fuel solution for a medical isotope reactor, characterized in that: include: The fuel solution includes uranyl nitrate and nitric acid; Control the F generated by the initial and reaction irradiation of the fuel solution - ≤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, other impurities meet the requirements of GB / T 10266 standard; Control the acid concentration, uranium concentration and temperature in the fuel solution to control the pH value of the fuel solution; The operating power density of the fuel solution is controlled to be no greater than 2.0 kW / L, and a catalyst is used to prevent precipitation of the fuel solution during operation.

2. The method for designing a radiation-resistant fuel solution for a medical isotope reactor according to claim 1, characterized in that: When the fuel solution is highly enriched uranium and the enrichment is greater than 90%, the uranium concentration of uranyl nitrate in the fuel solution is controlled below 90 g / L, and the initial nitric acid concentration is controlled below 0.2mol / L~0.5mol / L, the fuel solution full power operating temperature is controlled at 60℃~90℃, and the pH is controlled at -0.4<pH<2.5 during operation.

3. The method for designing a radiation-resistant fuel solution for a medical isotope reactor according to claim 1, characterized in that: The fuel solution is low-enriched uranium with an enrichment of less than 20%. The initial uranium concentration of the fuel solution is controlled at 200 gU / L to 300 gU / L, the initial nitric acid concentration is controlled at 0.1 mol / L to 0.3 mol / L, the full-power operating temperature of the fuel solution is controlled at 60° C. to 90° C., and the pH is controlled at -0.4<pH<2.5 during operation.

4. The method for designing a radiation-resistant fuel solution for a medical isotope reactor according to claim 1, characterized in that: The control of the F generated by the irradiation of the fuel solution at the beginning and during the reaction - , Cl - , Ru ions, Cr ions, Al ions and the total boron equivalent are achieved through regular purification.

5. The method for designing a radiation-resistant fuel solution for a medical isotope reactor according to claim 4, characterized in that: The fuel solution is purified at least once every six months, with a purification rate of more than 70%.

6. The design method of the radiation-resistant fuel solution for medical isotope reactor according to claim 1 The method is characterized by: The catalyst is Ag + , Cu 2+ and Fe 3+ One or more of the nitrates, The nitrate ion concentration is controlled at 500 mg / L to 3500 mg / L.

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