Powder of an alloy based on uranium and on molybdenum useful for manufacturing nuclear fuels and targets intended for producing radioisotopes

Abstract

The invention relates to a powder of an alloy based on uranium and molybdenum in a metastable phase, which is formed of particles which have an elongation index at least equal to 1.1, a non-zero closed porosity value and which are composed of grains having a molybdenum content, for which the variations within the same grain are of at most 1% by mass. It also relates to a method allowing preparation of this alloy powder as well as to the use of said powder for manufacturing nuclear fuels and targets for producing radioisotopes. Applications: Manufacturing of nuclear fuels, notably for experiment nuclear reactors; manufacturing of targets for producing radioisotopes, notably for the medical industry.

Claims

1. A powder of an alloy comprising uranium and molybdenum in a metastable phase, which is formed of particles which have an elongation index at least equal to 1.1 and at most equal to 2, a closed porosity value higher than 0% and at most equal to 5% by volume, and dimensions ranging from 20 m to 100 m, and which are composed of grains having a molybdenum content, the variations of the molybdenum content within a same grain being of at most 1% by mass.

2. The powder of claim 1, wherein the closed porosity of the particles consists of closed pores having a size at most equal to 3 m.

3. The powder of claim 1, which is a powder of a binary alloy of uranium and molybdenum.

4. The powder of claim 3, wherein the molybdenum content ranges from 5% to 15% by mass.

5. The powder of claim 1, which is a powder of a ternary UMoX alloy wherein X represents a metal other than uranium and molybdenum.

6. The powder of claim 5, wherein X is selected from titanium, zirconium, chromium, silicon, niobium, platinum, tin, bismuth, ruthenium and palladium.

7. The powder of claim 5, wherein the molybdenum content ranges from 5% to 15% by mass, while the X metal content is at most 6% by mass.

8. A nuclear fuel, comprising a powder of an alloy comprising uranium and molybdenum in a metastable phase as claimed in claim 1.

9. A target for producing radioisotopes, comprising a powder of an alloy comprising uranium and molybdenum in a metastable phase as claimed in claim 1.

10. A method for preparing a powder of an alloy comprising uranium and molybdenum in a metastable phase as claimed in claim 1, which comprises: a) putting at least one first reagent selected from uranium oxides and mixtures thereof, uranium fluorides and mixtures thereof, into contact with a second reagent consisting of molybdenum and a third reagent consisting of a reducing metal, the first, second and third reagents being in a divided form; b) reacting the first, second and third reagents at a temperature at least equal to a melting temperature of the third reagent and under an inert atmosphere, whereby particles are obtained, the particles comprising a core made of the alloy comprising uranium and molybdenum and a layer of an oxide or fluoride of the reducing metal covering the core; c) cooling the so obtained particles at a rate at least equal to 450 C./hour; and d) removing the layer of oxide or fluoride of the reducing metal from the so cooled particles and thereby obtaining the powder of the alloy comprising uranium and molybdenum.

11. The method of claim 10, wherein the first reagent is a powder of a uranium oxide selected from the group consisting of uranium dioxide, uranium trioxide, uranium sesquioxide, uranium tetraoxide and mixtures thereof.

12. The method of claim 11, wherein the uranium oxide powder is formed of particles having dimensions from 1 m to 100 m.

13. The method of claim 11, wherein the uranium oxide powder has a stoichiometric ratio O/U equal to 2 or substantially equal to 2.

14. The method of claim 10, wherein the second reagent is in the form of a powder comprising particles having dimensions of less than 250 m.

15. The method of claim 10 wherein the third reagent is selected from alkaline metals and alkaline earth metals.

16. The method of claim 15, wherein the third reagent is an alkaline earth metal in a form of a powder, shavings or turnings.

17. The method of claim 16, wherein the third reagent is magnesium or calcium.

18. The method of claim 10, wherein step a) comprises depositing in a reaction enclosure at least one layer of pellets consisting of a homogeneous mixture of the first and second reagents and at least two layers of the third reagent, the layer of pellets being inserted between both layers of the third reagent.

19. The method of claim 10, wherein step b) is carried out at a temperature equal to or greater than 900 C. but lesser than a melting temperature of the alloy comprising uranium and molybdenum.

20. The method of claim 19, wherein step b) is carried out at a temperature from 950 C. to 1,150 C.

21. The method of claim 10, wherein step b) comprises a rise in temperature from 50 C. to 200 C./hour.

22. The method of claim 10, wherein step d) comprises dissolving the layer of oxide or fluoride of the reducing metal.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents the X-ray diffractogram of a powder of a binary alloy UMo according to the invention (curve A) as well as that of a powder of a reference binary alloy UMo in a metastable phase (sheet JCPDScurve B).

(2) FIG. 2 illustrates a picture taken with a scanning electron microscope, at a magnification of 313, of the powder of the binary alloy UMo according to the invention, the X-ray diffractogram of which is illustrated in FIG. 1, in a polished section.

(3) FIGS. 3A, 3B and 3C illustrate pictures taken with a scanning electron microscope, at magnifications of 2,500 (FIG. 3A), 4,000 (FIG. 3B) and 6,322 (FIG. 3C) respectively, of particles of the powder of the binary alloy UMo as shown in FIG. 2 and in which the closed pores which these particles include, are indicated with black arrows.

(4) FIG. 4 illustrates a picture taken with a scanning electron microscope at a magnification of 5,000, of a particle of the powder of the UMo binary alloy shown in FIG. 2 and in which are indicated the different marked points (noted from 1 to 10) at which carried out an energy dispersion spectrometry analysis (elementary volume of a marked point: 1 m.sup.3).

(5) FIG. 5 illustrates a picture taken with a scanning electron microscope, at a magnification of 100, of a powder of a ternary alloy UMoTi according to the invention.

(6) FIG. 6 illustrates a picture taken with a scanning electron microscope, at a magnification of 5,000, of a particle of the powder of the ternary alloy UMoTi shown in FIG. 5 and in which are indicated the different marked points (noted from 1 to 3) at which was carried out an energy dispersion spectrometry analysis (elementary volume of a marked point: 1 m.sup.3).

DETAILED SUMMARY OF PARTICULAR EMBODIMENTS

Example 1

Preparation of a Powder of a Binary Alloy UMo According to the Invention

(7) 100 g of a powder of a binary alloy UMo with 10% by mass of molybdenum is prepared in the following way.

(8) First of all, pellets measuring 12 mm in diameter and with a thickness of 2 mm, of a homogeneous mixture U/Mo are manufactured.

(9) To do this, 102.1 g of a UO.sub.2 powder (O/U 2), the particles of which have dimensions (as determined by laser diffraction) ranging from 1 to 50 m, are mixed with 10 g of molybdenum powder, the particles of which (as measured by laser diffraction) have dimensions ranging from 1 to 150 m, in a Turbula mixer for 20 minutes and at a rate of 45 cycles/minute. This mixture is then subject to uniaxial compression by applying a stress of 100 MPa.

(10) After which, layers of UO.sub.2/Mo pellets and layers of magnesium shavings for which the largest dimension ranges from 1 to 3 mm, are deposited in a molybdenum crucible, so as to form a stack in which each layer of UO.sub.2/Mo pellets is inserted between two layers of magnesium shavings.

(11) This crucible is hermetically sealed under a slight pressure, of less than 1 bar, of argon. Next, it is placed in an oven which is heated at a rate of 150 C./hour until it attains the temperature of 1,100 C. The crucible is then left in the oven at this temperature so that the dwelling time of the crucible in the oven is a total of 24 hours.

(12) At the end of this treatment, the crucible is cooled down at a rate of 1,000 C./hour by immersing it in a water bath at room temperature.

(13) The powder contained in the crucible is recovered and is treated with an aqueous solution of 3.7% hydrochloric acid in an amount of 50 mL of solution per gram of powder. After decantation, the powder is collected by filtration, it is washed with distilled water and it is dried. This same operation is carried out 3 times for 30 minutes.

(14) 100 g of a powder of a UMo alloy are thereby obtained, the particles of which are totally cleared of magnesium and of magnesium oxide.

(15) X-ray diffractometry and scanning electron microscopy (SEM) analyses show that this powder is characterized by particles: in which the alloy is 100% in a cubic centered phase, i.e. in a metastable phase, with a parameter of 3.417 (cf. the X-ray diffractograms illustrated in FIG. 1); the dimensions of which are comprised between 20 and 100 m (cf. FIGS. 2, 3A, 3B and 3C); which have an elongation index or parameter (as determined from SEM pictures, such as those shown in FIGS. 2, 3A, 3B and 3C, by the methodology described in the aforementioned reference [6]) which is comprised between 1.1 and 2; which have closed pores, the size of which (i.e. the equivalent diameter as determined from SEM pictures, such as those shown in FIGS. 3A, 3B and 3C, by the methodology described in the aforementioned reference [6]) does not exceed 3 m; and the closed porosity of which (as determined from SEM pictures, such as those shown in FIGS. 3A, 3B and 3C, according to the ASTM E1245-03 standard) does not represent more than 5% of the total volume of these particles.

(16) Moreover, an analysis of one particle by SEM coupled with energy dispersion spectrometry (EDS) analysis gives for the 10 marked points (noted from 1 to 10elementary volume of a marked point: 1 m.sup.3) shown in FIG. 4, the uranium and molybdenum mass contents which are shown in Table I hereafter.

(17) TABLE-US-00001 TABLE I U Mo Marked points (% by mass) (% by mass) 1 86.84 13.16 2 86.77 13.23 3 86.63 13.37 4 87.91 12.09 5 87.08 12.92 6 86.72 13.28 7 86.57 13.43 8 87.56 12.44 9 87.32 12.68 10 86.38 13.62 Average standard deviation 86.98 0.48 13.02 0.48

(18) As shown by this table, the variation of the molybdenum content is less than 1% by mass.

Example 2

Preparation of a Powder of a Ternary Alloy UMoTi According to the Invention

(19) 100 g of a powder of a ternary alloy UMoTi are prepared with 9% by mass of molybdenum and 1% by mass of titanium according to the same operating procedure as the one described in Example 1 hereinbefore, except that 9 g of molybdenum and 1 g of titanium are used, the amount of magnesium used being as earlier of about 37 g.

(20) FIG. 5 shows a picture taken with a scanning electron microscope of the thereby obtained UMoTi alloy powder.

(21) An analysis of a particle of this powder with SEM coupled with EDS analysis gives, for the 3 marked points (noted from 1 to 3elementary volume of a marked point: 1 m.sup.3) shown in FIG. 6, the uranium, molybdenum and titanium mass contents are shown in Table II hereafter.

(22) TABLE-US-00002 TABLE II U Mo Ti Marked points (% by mass) (% by mass) (% by mass) 1 92.4 6.24 1.72 2 91.95 6.10 1.95 3 92.16 6.07 1.77 Average 92.05 0.09 6.14 0.07 1.81 0.10 std. deviation

(23) This table shows that not only the distribution of molybdenum is very homogeneous but that of titanium is also very homogeneous.

CITED REFERENCES

(24) [1] FR 2 777 688 [2] U.S. Pat. No. 5,978,432 [3] JP 55-054508 [4] J. S. Lee et al., Journal of Nuclear Materials, 306, 147-152, 2002 [5] J. M. Park et al., Journal of Nuclear Materials, 397, 27-30, 2010 [6] C. Souchier, <<Analyse d'images>>, in Techniques de l'Ingnieur, Trait Analyse Chimique et Caractrisation, P855, 1-18, 1998