Preparation method of simulated spent fuel
阅读说明：本技术 一种模拟乏燃料的制备方法 (Preparation method of simulated spent fuel ) 是由 周小毛 王玲钰 李腾 崔大庆 于 2021-06-22 设计创作，主要内容包括：本发明属于核材料制备技术领域,涉及一种模拟乏燃料的制备方法,包括如下步骤：(1)把柠檬酸溶于乙二醇,持续搅拌并加入目标元素的相应的金属盐至溶解；(2)水浴下持续搅拌,直至溶胶化达到溶胶为红色透明且有丁达尔效应现象,然后渐次升温直至凝胶化,且每次升温前无肉眼可见的挥发物质溢出,转入烘箱烘干,然后渐次升温直至不再发泡；(3)产物转入马弗炉进行灰化,冷却后取出进行研磨,然后转入管式炉在还原性气氛下还原；(4)产物添加粘结助剂后压制成型,然后转入烧结炉,在还原性气氛下烧结成型。利用本发明的制备方法,能够制备得到各元素达到分子水平的分散、物理性能和化学组成与真实乏燃料更为接近、产品性能好的模拟乏燃料。(The invention belongs to the technical field of nuclear material preparation, and relates to a preparation method of a simulated spent fuel, which comprises the following steps: (1) dissolving citric acid in ethylene glycol, continuously stirring and adding corresponding metal salt of the target element until the corresponding metal salt is dissolved; (2) continuously stirring in a water bath until the sol is red and transparent and has a Tyndall effect phenomenon, gradually heating until the sol is gelatinized, transferring the sol to an oven for drying without macroscopic volatile substances overflowing before each heating, and gradually heating until the sol is not foamed; (3) transferring the product into a muffle furnace for ashing, cooling, taking out, grinding, and transferring into a tubular furnace for reduction in a reducing atmosphere; (4) and adding a bonding assistant into the product, pressing and forming, transferring into a sintering furnace, and sintering and forming in a reducing atmosphere. By utilizing the preparation method, the simulated spent fuel with the elements reaching the molecular level, the physical properties and the chemical composition closer to those of the real spent fuel and good product performance can be prepared.)
1. The preparation method of the simulated spent fuel is characterized in that the preparation method adopts a chemical method to mix raw materials, and specifically comprises the following steps:
(1) dissolving citric acid in ethylene glycol, continuously stirring and adding corresponding metal salt of the target element until the corresponding metal salt is dissolved;
(2) continuously stirring in a water bath until the sol is red and transparent and has a Tyndall effect phenomenon, gradually heating until the sol is gelatinized, transferring the sol to an oven for drying without macroscopic volatile substances overflowing before each heating, and gradually heating until the sol is not foamed;
(3) transferring the product into a muffle furnace for ashing, cooling, taking out, grinding, and transferring into a tubular furnace for reduction in a reducing atmosphere;
(4) and adding a bonding assistant into the product, pressing and forming, transferring into a sintering furnace, and sintering and forming in a reducing atmosphere.
2. The method of claim 1, wherein: in the step (1), the corresponding metal salt is selected from UO2(NO3)2·6H2O、Y(NO3)3·6H2O、La(NO3)3·6H2O、Ce(NO3)3·6H2O、Nd(NO3)3·6H2O、Sr(NO3)2、ZrOCl2.8H2O、Ba(NO3)2、(NH4)2MoO4·4H2O、RuCl3·xH2O、Rh(NO3)3、Pd(NH3)4Cl2.H2One or more of O.
3. The method of claim 2, wherein: in the step (1), the corresponding metal salt is added in sequence of firstly adding the molybdenum-containing metal salt, then sequentially adding the metal salt including the uranium-containing metal salt and the palladium-containing metal salt, and finally adding the ruthenium-containing metal salt, wherein the solution is clear without insoluble particle residues before each addition.
4. The method of claim 1, wherein: in the step (2), the temperature of the water bath is 50-70 ℃, the procedure of gradually heating up to gelation is to keep the temperature at 5 ℃ per liter for 1-2 hours, and the next heating up is carried out when no volatile matter overflows visible to the naked eye.
5. The method of claim 1, wherein: in the step (2), the drying temperature of the oven is 80-120 ℃, the procedure of gradually raising the temperature until no foaming is carried out is that the temperature is raised by 3 ℃ per liter for 10-30 minutes, and the next temperature raising is carried out when no continuous foaming is carried out.
6. The method of claim 1, wherein: in the step (3), the ashing temperature is 200 ℃ and 250 ℃, and the temperature is kept for 3-12 hours.
7. The method of claim 1, wherein: in the step (3), the reducing atmosphere reduced under the reducing atmosphere is 4-95 v/v% H2Ar, wherein argon is used as equilibrium gas, the reduction temperature is 400-600 ℃, and the reduction time is 3-12 hours.
8. The method of claim 1, wherein: in the step (4), the reducing atmosphere formed by sintering in the reducing atmosphere consists of reducing gas and argon, wherein the reducing gas is selected from hydrogen, carbon monoxide or ammonia, the content is 4-95 v/v%, the argon is equilibrium gas, the sintering forming temperature is 1200-1500 ℃, and the temperature is kept for 6-12 h.
Technical Field
The invention belongs to the technical field of nuclear material preparation, and relates to a preparation method of a simulated spent fuel.
Background
Nuclear power plays an important role in the energy structure of the world today due to its safety, cleanliness, low carbon, economy and high efficiency. The number of global commercial nuclear power stations will rapidly increase in the coming decades, and the development of nuclear power industry in China is particularly rapid. However, along with the development of nuclear power industry, the amount of spent fuel (also called irradiated nuclear fuel, which is a nuclear fuel that has undergone irradiation and has a burn-up depth reaching the discharge design level and is usually discharged from the reactor of a nuclear power plant) produced in the nuclear power industry is increasing. Due to its strong radiotoxicity and large number of long half-life nuclides, spent fuel poses a potential threat to the environment, such as the inability to properly handle the natural world in which humans depend for survival.
Most of the fuel used by the nuclear power reactor contains a certain mass fraction235UO of U2Sintered body, spent fuel discharged from reactor still having UO as main body2But is initiated by235The effects of U content, burnup during combustion and cooling time after discharge will contain different proportions of fission product elements and transuranic elements. The existing treatment mode of the spent fuel mainly extracts partial useful substances through post-treatment, and the rest substances are solidified and then are subjected to geological treatment, or the geological treatment is directly carried out through a one-time-through mode. Both of these approaches require extensive studies of various physical and chemical properties of spent fuels during research and development. However, because the real spent fuel has super strong radioactivity and complex element composition, the real spent fuel is not directly adopted, but the simulated spent fuel is adopted. The simulated spent fuel has similar physical properties (such as density, hardness, porosity, particle size and split phase) and chemical composition with the real spent fuel.
At present, traceable documents for preparing simulated spent fuel adopt the traditional physical method for mixing materials, namely uranium dioxide and oxide to be doped with fission product elements are ground and uniformly mixed, and then the mixture is subjected to cold press molding and high-temperature sintering in a reducing atmosphere, so that the physical properties and the chemical composition similar to those of real spent fuel are obtained. However, the method still has the following problems or disadvantages:
1. the material mixing process has large demand on the use amount of raw materials, and is not suitable for small-batch production at laboratory level.
2. In the mixing process, the raw materials are seriously lost, and elements with small component content are easy to agglomerate, so that the uniform mixing is difficult to realize.
3. The mixing step is complicated and takes a long time, and the long-time and high-strength contact of the raw material with the grinding part easily causes the sintered body to introduce an impurity phase.
4. The element dispersion obtained by the physical mixing method can only reach a submicron level, and if the element dispersion is obtained at an atomic level, high temperature is further needed.
5. The sintering temperature is higher, which easily causes the elements with different properties to volatilize inconsistently, thereby leading the element composition of the obtained sintered body to be greatly different from the target simulated spent fuel composition.
Disclosure of Invention
The invention aims to provide a preparation method of simulated spent fuel, which can prepare the simulated spent fuel with the advantages of mild condition, simple operation, low sintering temperature (less than or equal to 1500 ℃), safe sintering atmosphere and suitability for small-batch production in laboratory scale, wherein each element reaches the dispersion of molecular level (the phenomenon of element agglomeration is reduced), the physical property and the chemical composition are closer to those of the real spent fuel, and the product performance is good.
In order to achieve the purpose, in a basic embodiment, the invention provides a preparation method of a simulated spent fuel, which adopts a chemical method to mix raw materials, and specifically comprises the following steps:
(1) dissolving citric acid in ethylene glycol, continuously stirring and adding corresponding metal salt of the target element until the corresponding metal salt is dissolved;
(2) continuously stirring in a water bath until the sol is red and transparent and has a Tyndall effect phenomenon, gradually heating until the sol is gelatinized, transferring the sol to an oven for drying without macroscopic volatile substances overflowing before each heating, and gradually heating until the sol is not foamed;
(3) transferring the product into a muffle furnace for ashing, cooling, taking out, grinding, and transferring into a tubular furnace for reduction in a reducing atmosphere;
(4) and adding a bonding assistant into the product, pressing and forming, transferring into a sintering furnace, and sintering and forming in a reducing atmosphere.
The invention adopts a chemical method (sol-gel method) to mix materials, namely, uranyl nitrate and most of metal salt of a simulated fission product to be doped are dissolved in a citric acid-glycol-water solution, the dispersion of elements is realized by virtue of the coordination capacity of citric acid and most of metal ions, and the dispersion of elements of a fission product which is difficult to coordinate or easy to hydrolyze is realized by virtue of the characteristic that citric acid and glycol further form sol-gel. And then the simulated spent fuel with similar physical properties and chemical composition with the real spent fuel is obtained through a series of steps of drying, calcining, grinding, reducing, cold pressing and sintering.
In a preferred embodiment, the present invention provides a method for preparing simulated spent fuel, wherein in step (1), the corresponding metal salt is selected from UO2(NO3)2·6H2O、Y(NO3)3·6H2O、La(NO3)3·6H2O、Ce(NO3)3·6H2O、Nd(NO3)3·6H2O、Sr(NO3)2、ZrOCl2.8H2O、Ba(NO3)2、(NH4)2MoO4·4H2O、RuCl3·xH2O、Rh(NO3)3、Pd(NH3)4Cl2.H2One or more of O.
In a preferred embodiment, the invention provides a method for preparing simulated spent fuel, wherein in the step (1), the corresponding metal salts are added in sequence, namely, the molybdenum-containing metal salt is added, then the metal salts including uranium-containing metal salt and palladium-containing metal salt are added in sequence, and finally the ruthenium-containing metal salt is added, and the solution is clarified without insoluble particle residues before each addition.
In a preferred embodiment, the invention provides a preparation method of simulated spent fuel, wherein in the step (2), the temperature of the water bath is 50-70 ℃, the gradual temperature rise until gelation procedure is that the temperature is kept at 5 ℃ per liter for 1-2 hours, and the next temperature rise is carried out when no volatile substances are overflowed by naked eyes.
In a preferred embodiment, the invention provides a preparation method of a simulated spent fuel, wherein in the step (2), the oven drying temperature is 80-120 ℃, the procedure of gradually raising the temperature until no foaming is carried out is to keep the temperature at 3 ℃ per liter for 10-30 minutes, and the next temperature raising is carried out when no continuous foaming is carried out.
In a preferred embodiment, the invention provides a preparation method of simulated spent fuel, wherein in the step (3), the ashing temperature is 200-250 ℃, and the temperature is kept for 3-12 hours.
In a preferred embodiment, the invention provides a preparation method of simulated spent fuel, wherein in the step (3), the reducing atmosphere reduced under the reducing atmosphere is 4-95 v/v% H2Ar, wherein argon is used as equilibrium gas, the reduction temperature is 400-600 ℃, and the reduction time is 3-12 hours.
In a preferred embodiment, the invention provides a preparation method of a simulated spent fuel, wherein in the step (4), the reducing atmosphere formed by sintering under the reducing atmosphere consists of a reducing gas and argon, the reducing gas is selected from hydrogen, carbon monoxide or ammonia and has the content of 4-95 v/v%, the argon is equilibrium gas, the sintering forming temperature is 1200-1500 ℃, and the temperature is kept for 6-12 h.
The preparation method of the simulated spent fuel has the advantages that the preparation method of the simulated spent fuel has mild conditions, simple operation, low sintering temperature (less than or equal to 1500 ℃), safe sintering atmosphere and suitability for small-batch production in laboratory scale, and the simulated spent fuel with the elements reaching the molecular level, the physical property and the chemical composition closer to those of real spent fuel and the good product performance can be obtained.
In addition, the preparation method disclosed by the invention has the advantages that the whole energy consumption of the mixed materials is low, the material loss in the mixing process can be reduced, and the content of a pollution phase is reduced, so that the preparation method is particularly suitable for small-batch production in a laboratory scale.
Drawings
Fig. 1 is a flow chart illustrating a method for preparing simulated spent fuel according to the present invention.
Fig. 2 is a graph of raw BES after calcination for the simulated spent fuel prepared in example 1.
FIG. 3 is an electron microscope Mapping image of each target element after the simulated spent fuel prepared in example 1 is calcined.
Detailed Description
The following examples further illustrate specific embodiments of the present invention.
An exemplary process flow of the method for preparing the simulated spent fuel of the invention is shown in fig. 1, and comprises the following steps:
(1) calculating the theoretical contents of fission products and elements after uranium according to the initial composition, the burnup and the cooling time of the pre-simulated spent fuel, and screening out pre-doped elements (the doped target elements can be one or more, and the target elements are not easy to volatilize at the sintering temperature), wherein part of the elements can be replaced by stable isotopes with similar properties, part of the radionuclides can be replaced by natural nuclides, and the alpha radioactivity can be used235U simulation, beta radioactivity can be used90Sr simulation; the amount of the corresponding metal salt (which, in addition to being soluble, also needs to be such that its acid radical or ligand does not affect the coordination of the metal ion and the sol-gelation process, and does not introduce impurities, i.e. can be completely volatilized in gaseous form in the reduction and preceding steps) is calculated according to the expected mass of the preparation and the theoretical content of the target element, in terms of molar ratio citric acid (complexing agent): metal salt (dispersant): calculating the usage amount of citric acid and glycol (water is used as a dissolving aid) by 2:1: 8;
(2) dissolving citric acid in ethylene glycol in a low-temperature water bath, continuously stirring and sequentially adding corresponding metal salts until the corresponding metal salts are dissolved, wherein deionized water can be replenished for many times in the process, the sample dissolving step comprises the steps of dissolving insoluble salts firstly, adding easily-hydrolyzed salts after sol is formed, and adding the salts with relatively dark colors finally;
(3) continuously stirring in a water bath until the sol is gelatinized to a certain degree, wherein the sample is red and transparent sol with a Tyndall effect phenomenon, gradually heating (no obvious visible volatile substance overflows before heating each time), transferring into an oven after gelation, continuously drying for a period of time at the same temperature, and continuously and slowly heating until the sample is not foamed, wherein the sample is brown xerogel;
(4) transferring the sample into a muffle furnace, slowly heating for ashing, cooling until organic matters, acid radicals and ligands are completely volatilized, taking out raw materials (the raw materials are metal oxides of target elements which are uniformly mixed, have fine particles and can reach a nanometer level, and are favorable for reducing the sintering temperature, and the main body after reduction is UO2) Repeatedly grinding by using an agate mortar to destroy agglomerated particles possibly existing, and then transferring the agglomerated particles into a tubular furnace to reduce the agglomerated particles in a reducing atmosphere;
(5) adding the bonding assistant, pressing and forming under high pressure, transferring into a sintering furnace, and sintering and forming at high temperature in a reducing atmosphere.
Exemplary operating steps of the above exemplary preparation method are as follows:
1) setting up a device required by an experiment, preparing required consumable supplies and calculating the usage amount of each required raw material;
2) dissolving citric acid in ethylene glycol solution in a low-temperature water bath, continuously stirring and sequentially adding the raw materials until the raw materials are completely dissolved;
3) dissolving in 50-70 deg.C water bath to obtain sol, and gradually heating to 90 deg.C to obtain gel;
4) transferring the gel into an oven to be dried at the temperature of 90-120 ℃ and slowly raising the temperature until the gel is not foamed to obtain dry gel;
5) transferring the dried gel into a muffle furnace, slowly heating to 250 ℃, and calcining for a period of time to obtain a raw material;
6) cooling, taking out the raw material, and repeatedly grinding for a period of time by using an agate mortar;
7) transferring the sample into a tubular furnace, introducing reducing gas, and reducing at the temperature of 400-;
8) cooling, taking out, adding bonding auxiliary agent (such as zinc stearate) with certain mass, and cold pressing at 300MPa for 10min for molding;
9) and transferring the mixture into a sintering furnace, and carrying out heat preservation for a period of time at the temperature of 1200-1500 ℃ in a reducing atmosphere for sintering and forming.
The applications of the above exemplary preparation method and operation steps are as follows.
Example 1:
in the embodiment, the simulated fuel consumption is 44.5GW/tU, spent fuel after the reactor core is discharged and cooled for 1000 years, and the target element content and the corresponding raw material use amount of theoretical calculation are shown in the table 1.
Table 1 simulates theoretical element content and corresponding raw material addition amount of spent fuel
8.52g of citric acid was weighed into 10mL of ethylene glycol at 60 ℃ in a water bath and 8mL of water was added. Then weighing the corresponding raw materials according to the weight ratio in the table 1, and adding and dissolving (NH) in sequence4)2MoO4·4H2O、ZrOCl2.8H2O、Y(NO3)3·6H2O、La(NO3)3·6H2O、Ce(NO3)3·6H2O、Nd(NO3)3·6H2O、Sr(NO3)2、Ba(NO3)2、UO2(NO3)2·6H2O、RuCl3·xH2And O. Sequentially adding Pd (NH) after a period of sol3)4Cl2.H2O and Rh (NO)3)3. Then gradually heating at 70 deg.C, 80 deg.C, 85 deg.C and 90 deg.C to volatilize part of nitride, chloride and water. Then the operations are carried out according to the steps 4) to 9) to finally obtain 5.399g of simulated spent fuel with 5.1 percent of theoretical loss. The BES diagram of the simulated calcined spent fuel is shown in figure 2, the electron microscopy diagram of each target element is shown in figure 3, and the element agglomeration phenomenon is not seen.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations. The foregoing examples or embodiments are merely illustrative of the present invention, which may be embodied in other specific forms or in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. The scope of the invention should be indicated by the appended claims, and any changes that are equivalent to the intent and scope of the claims should be construed to be included therein.