Uranium molybdenum niobium alloy fuel pellet and preparation method and application thereof
Technical Field
The invention relates to the technical field of uranium-based alloy metal fuel pellet preparation, and particularly relates to a uranium-molybdenum-niobium alloy fuel pellet and a preparation method and application thereof.
Background
The uranium-molybdenum alloy has good high-temperature mechanical property and radiation resistance. Ordinary uranium is alpha phase below 668 deg.c, and has poor anticorrosive performance and radiation resistance. It can generate irradiation growth under irradiation conditions. Alpha-uranium is orthorhombic lattice, anisotropic, and under irradiation, the crystal grows anisotropically, the [010] axis of the lattice grows, the [100] axis shortens, and the [001] axis is basically unchanged. The presence of textured uranium can therefore undergo significant changes in macroscopic dimensions, resulting in significant deformation of the fuel element, with a reduction in strength and consequent destruction. Compared with the conventional alpha-phase uranium, the gamma-uranium has greatly improved irradiation stability, and the isotropy of the cubic structure effectively reduces the distortion effect caused by irradiation growth. In order to improve the irradiation stability of the fuel, a uranium alloy is generally formed by adding a small amount of alloy elements into metallic uranium as a fuel material. Molybdenum atoms in the uranium molybdenum alloy have extremely slow diffusion speed, so that the thermal activation energy and soaking time of gamma-phase eutectoid reaction are greatly improved, and the metastable gamma-uranium with a cubic structure can still be kept after the uranium molybdenum alloy is cooled to room temperature under conventional conditions. Adding enough alloy elements capable of partially or completely stabilizing cubic lattice gamma phase to obtain isotropic lattice structure and enhance its radiation resistance.
Since the function of maintaining the stability of the gamma phase is mainly assumed by the Mo element, the content of the third alloying element is not too high. The primary requirement for this is that the neutron absorption cross section must be small. In order to prevent the melting point from being greatly lowered, the melting point of the alloy element is also required to be relatively high, so that Nb is preferably selected. As an alloy with important application prospect, the uranium molybdenum niobium ternary alloy has been researched by scholars at home and abroad, but a large number of documents do not introduce a detailed preparation process.
At present, the prior art at home and abroad generally adopts methods such as vacuum induction melting, electric arc melting and the like to obtain homogeneous uranium alloy, but has the defect of complex process, repeated melting needs to be carried out for many times, the process period is long, and the risk of material loss and impurity increase is increased. Therefore, a new preparation process is urgently needed to solve the above problems.
Disclosure of Invention
The invention aims to provide a uranium molybdenum niobium alloy fuel pellet as well as a preparation method and application thereof, so as to solve the problems that in the prior art, a uranium molybdenum niobium ternary alloy is prepared by adopting methods such as vacuum induction melting or arc melting, repeated melting is needed for many times, the process period is long, and the risk of material loss and impurity rise is increased.
In order to solve the technical problems, the invention adopts the following technical scheme:
according to a first aspect of the invention, a method for preparing uranium molybdenum niobium alloy fuel pellets is provided, which comprises the following steps: s1: preparing metal uranium ingots into uranium powder by a hydrogenation dehydrogenation method; s2: adding molybdenum powder and niobium powder into the uranium powder and uniformly mixing to form uranium molybdenum niobium metal powder, wherein the content of molybdenum is 6-8 wt%, the content of niobium is 1-2 wt%, and then pressing the uranium molybdenum niobium metal powder into a blank under the pressure of 5-8 tons; s3: and (3) putting the blank into a high-temperature heating furnace in an argon atmosphere, heating to 1200-1450 ℃ at the speed of 7-10 ℃/min, preserving heat for 1.5-3 h, cooling to 800-1000 ℃ at the speed of 7-10 ℃/min, preserving heat for 3-5h, and cooling to room temperature along with the furnace to finally obtain the gamma-U uranium-molybdenum-niobium alloy fuel pellet.
Step S1 includes: and heating the metal uranium ingot to the temperature of 270-300 ℃ in a hydrogen atmosphere to enable the metal uranium ingot to fall off in the form of hydride powder, completing hydrogenation, and then heating the hydride powder in vacuum to enable hydrogen to be dissociated and released, thereby forming uranium powder.
Step S2 includes: and keeping the pressure of 5-8 tons for 4-6min by using a tablet press, and pressing the uranium molybdenum niobium metal powder into a blank with the diameter of 5-15 mm.
Step S3 includes: and (3) putting the blank into a tungsten crucible, and then putting the blank into a high-temperature heating furnace for high-temperature treatment.
According to a preferred embodiment of the present invention, step S3 includes: and (3) putting the blank into a high-temperature heating furnace in an argon atmosphere, heating to 1200-1400 ℃ at the speed of 7-10 ℃/min, preserving heat for 2-3h, cooling to 800-1000 ℃ at the speed of 7-10 ℃/min, preserving heat for 3-5h, and cooling to room temperature along with the furnace to finally obtain the gamma-U uranium molybdenum niobium alloy fuel pellet.
According to another preferred embodiment of the present invention, step S3 includes: and (3) putting the blank into a high-temperature heating furnace in an argon atmosphere, heating to 1300 ℃ and 1400 ℃ at the speed of 7-10 ℃/min, preserving heat for 2-3h, cooling to 900 ℃ and 1000 ℃ at the speed of 7-10 ℃/min, preserving heat for 3-5h, and cooling to room temperature along with the furnace to finally obtain the gamma-U uranium molybdenum niobium alloy fuel pellet.
According to a preferred embodiment of the present invention, step S3 includes: and (3) putting the blank into a high-temperature heating furnace in an argon atmosphere, heating to 1300 ℃ at the speed of 7 ℃/min, preserving heat for 2h, cooling to 1000 ℃ at the speed of 7 ℃/min, preserving heat for 3h, and cooling to room temperature along with the furnace to finally obtain the gamma-U uranium molybdenum niobium alloy fuel pellet.
According to the preparation process provided by the invention, firstly, a metal uranium ingot is prepared into uranium powder by a hydrogenation dehydrogenation method, then molybdenum powder, niobium powder and uranium powder in a certain proportion are uniformly mixed and pre-pressed for forming, and a formed U-Mo-Nb blank is sintered at high temperature under the argon atmosphere and subjected to component homogenization treatment, so that the gamma-U metal fuel pellet is finally obtained. The preparation process provided by the invention has a short period, and the obtained uranium molybdenum niobium fuel pellet has a gamma phase, and the gamma phase is isotropic, so that the irradiation growth of the fuel is greatly reduced, and the prepared metal fuel pellet has better irradiation resistance.
According to a second aspect of the invention there is provided a uranium molybdenum niobium alloy fuel pellet comprising: 6-8 wt.% molybdenum, 1-2 wt.% niobium, balance uranium and unavoidable impurities; the uranium molybdenum niobium alloy fuel pellets contain complete gamma phase uranium.
According to a third aspect of the invention, there is provided the use of a method of manufacturing pellets of uranium molybdenum niobium alloy as described above in the field of nuclear fuel.
The current commercial nuclear fuel is mainly UO2The composite fuel pellet belongs to ceramic fuel, but the uranium loading of the fuel is low, a novel nuclear fuel is researched internationally nowadays, the metal fuel belongs to one of the fuel, the metal material is usually prepared by smelting-heat treatment and other processes, most of the uranium-molybdenum alloy is also prepared into the metal fuel pellet by smelting-sintering, and the invention can also prepare the gamma-phase uranium by a large amount of experiments and finds out the powder solid phase sintering process, and simultaneously directly forms the pellet once. Conventional sintering is typically used below 1000 c for the forming process, while the present invention seeks to provide higher and appropriate temperatures to change the phase of the uranium and pellet forming, all in one pass. According to the invention, the preparation of the gamma-phase stable uranium-molybdenum-niobium alloy is realized by adding Mo and Nb elements in a certain ratio and reasonably controlling process parameters, and finally the metal fuel pellet of the gamma-phase uranium-molybdenum-niobium ternary alloy is prepared.
According to the preparation process provided by the invention, firstly, the highest temperature and the heat preservation time in the step S3 are most critical, the highest temperature is determined according to the melting point of the alloy and is beyond the melting point of the alloy, and on the other hand, a certain time is needed for Mo and Nb to diffuse and dissolve into U, the higher the temperature is, the faster the diffusion is, the higher the temperature is, the too high temperature can cause the coarse grains to influence the performance of the alloy, the invention finds out a proper range of the highest temperature of 1200-. Secondly, the content ratio of Mo and Nb in the step S2 is also critical, if the content of Mo and Nb is too low, gamma-U cannot be completely formed, alpha-U appears, which can cause the irradiation performance of the fuel to be reduced, and if the content of Mo and Nb is too high, Mo and Nb which are not completely dissolved can appear, a second phase is formed, and the uranium loading is reduced. Thirdly, the pressure in the step S2 is a key for forming the powder into a blank, if the pressure is too low and the blank is not dense enough, the blank is oxidized seriously after sintering and can not be in a desired pellet shape, and the invention finds out a proper pressure of 5-8 tons according to a large amount of experiments.
In summary, the preparation method of the uranium molybdenum niobium alloy fuel pellet provided by the invention has the following beneficial effects:
1) the uniformity of the components is better: the preparation method adopts a powder solid phase sintering process, prepares uranium powder by a hydrogenation dehydrogenation method, uniformly mixes U-Mo-Nb powder, presses and molds the powder, and then sinters the powder to realize the preparation of the gamma-phase stable uranium molybdenum niobium alloy, and simultaneously the prepared alloy has good component uniformity;
2) the preparation process cycle is shortened: the traditional smelting process needs alloy smelting, alloy powdering and sintering to prepare the gamma-phase metal fuel pellet, while the powder solid phase sintering adopted by the invention can change the phase of uranium and pellet forming by adopting one procedure, so that the gamma-phase uranium molybdenum niobium metal fuel pellet is prepared, the raw material loss is lower, and the process period is shorter.
Drawings
FIG. 1 shows the XRD results of pellets of uranium molybdenum niobium metal fuel prepared in example 1;
FIG. 2 shows the XRD results of uranium molybdenum niobium metal fuel pellets prepared in comparative example 1;
figure 3 is an XRD result of the uranium molybdenum metal fuel pellets prepared in comparative example 2.
Detailed Description
The present invention will be further described with reference to the following specific examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.
Example 1
Carrying out a hydrogenation experiment on the uranium ingot at the temperature of 280 ℃/1h, closing hydrogen and introducing argon, simultaneously heating to 500 ℃, keeping for 2.5h, and cooling to normal temperature to obtain metal uranium powder.
Preparing U-Mo-Nb powder with the corresponding proportion, wherein the content of molybdenum is 8 wt.%, the content of niobium is 1.2 wt.%, the balance is uranium and inevitable impurities, uniformly mixing, keeping for 5min at 7tons by using a tablet press, and pressing into a blank with the diameter of 10 mm.
And (3) putting the blank sample into a heating furnace in an argon atmosphere in a glove box, heating to 1300 ℃ at the speed of 7 ℃/min, preserving heat for 2h, cooling to 1000 ℃ at the speed of 7 ℃/min, preserving heat for 3h, cooling to room temperature along with the furnace, and finally preparing the U-Mo-Nb metal fuel pellet.
The XRD results of the uranium molybdenum niobium metal fuel pellets produced are shown in fig. 1, which are isotropic γ -U pellets.
Comparative example 1
Carrying out a hydrogenation experiment on the uranium ingot at 280 ℃/1h, closing hydrogen and introducing argon, simultaneously heating to 500 ℃, keeping for 2.5h, and cooling to normal temperature to obtain metal uranium powder.
Preparing U-Mo-Nb powder with the corresponding proportion, wherein the content of molybdenum is 8 wt.%, the content of niobium is 1.2 wt.%, the balance is uranium and inevitable impurities, uniformly mixing, keeping for 5min at 7tons by using a tablet press, and pressing into a blank with the diameter of 10 mm.
And (3) putting the blank sample into a heating furnace in an argon atmosphere in a glove box, heating to 1100 ℃ at the speed of 7 ℃/min, preserving heat for 2h, cooling to 1000 ℃ at the speed of 7 ℃/min, preserving heat for 3h, cooling to room temperature along with the furnace, and finally preparing the U-Mo-Nb metal fuel pellet.
This comparative example 1, which used the same uranium molybdenum niobium content and substantially the same experimental conditions as example 1, differs only in that the maximum soak temperature used in example 1 was 1300 c, while the maximum soak temperature used in comparative example 1 was 1100 c, and the XRD results of the uranium molybdenum niobium metal fuel pellets produced are shown in fig. 2, from which it was shown that alpha-U was clearly detected in addition to gamma-U, thus indicating that gamma-U could not be completely formed at the maximum soak temperature of 1100 c. This is because the maximum holding temperature does not allow sufficient time for Mo and Nb to uniformly diffuse and dissolve in U.
Comparative example 2
Carrying out a hydrogenation experiment on the uranium ingot at 280 ℃/1h, closing hydrogen and introducing argon, simultaneously heating to 500 ℃, keeping for 2.5h, and cooling to normal temperature to obtain metal uranium powder.
Adding 8 wt.% of molybdenum into uranium powder to obtain U-Mo powder in a corresponding proportion, uniformly mixing, keeping for 5min at 7tons by using a tablet press, and pressing into a blank with the diameter of phi 10 mm.
And (3) putting the blank sample into a heating furnace in an argon atmosphere in a glove box, heating to 1300 ℃ at the speed of 7 ℃/min, preserving heat for 2h, cooling to 1000 ℃ at the speed of 7 ℃/min, preserving heat for 3h, cooling to room temperature along with the furnace, and finally preparing the U-Mo metal fuel pellet.
This comparative example 2 employed substantially the same experimental conditions as in example 1, except that no Nb element was added to this comparative example 2, and the XRD results of the uranium molybdenum metal fuel pellets produced are shown in fig. 3, from which it is shown that α -U appears in addition to γ -U, indicating that the content ratio of the alloying elements also has an important influence on the production of γ -U by the powder solid-phase sintering method.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.