Process for manufacturing a pellet of at least one metal oxide
View Patent ↗The present invention relates to a process for sintering a compacted powder of at least one oxide of a metal selected from an actinide and a lanthanide, this process comprising the following successive steps, carried out in a furnace and under an atmosphere comprising an inert gas, dihydrogen and water: (a) a temperature increase from an initial temperature T I up to a hold temperature T P , (b) maintaining the temperature at the hold temperature T P , and (c) a temperature decrease from the hold temperature T P down to a final temperature T F , in which the P(H 2 )/P(H 2 O) ratio is such that: 500<P(H 2 )/P(H 2 O)≤50 000, during step (a), from T I until a first intermediate temperature T i1 between 1000° C. and T P is reached, and P(H 2 )/P(H 2 O)≤500, at least during step (c), from a second intermediate temperature T i2 between T P and 1000° C., until T F is reached.
1. A process for sintering a compacted powder of at least one oxide of a metal M 1 selected from an actinide and a lanthanide, this process comprising the following successive steps (a) to (c), carried out in a furnace and under an atmosphere comprising an inert gas, dihydrogen and water, of:
(a) increasing the temperature from an initial temperature T I to a hold temperature T P , T P being between 1 400° C. and 1 800° C.,
(b) maintaining the temperature at the hold temperature T P for a duration between 1 h and 10 h, and
(c) decreasing the temperature from the hold temperature T P to a final temperature T F ,
wherein the ratio of the partial pressures P(H 2 )/P(H 2 O) in said atmosphere is such that:
500<P(H 2 )/P(H 2 O)≤50 000, during step (a), from T I until a first intermediate temperature T i1 between 1 000° C. and T P is reached, and
P(H 2 )/P(H 2 O)≤500, at least during step (c), from a second intermediate temperature T i2 between T P and 1 000° C., until T F is reached.
2. The process according to claim 1 , wherein the first intermediate temperature T i1 is between 1 300° C. and T P .
3. The process according to claim 1 , wherein the second intermediate temperature T i2 is between T P and 1 300° C.
4. The process according to claim 1 , wherein the ratio P(H 2 )/P(H 2 O)≤500 is implemented as soon as the first intermediate temperature T i1 is reached and maintained until T F is reached.
5. The process according to claim 1 , which further comprises, between steps (a) and (b), the following successive steps (a 1 ) to (a 3 ) of:
(a 1 ) maintaining, for a duration between 1 h and 10 h, the temperature at the hold temperature T P ,
(a 2 ) decreasing the temperature from the hold temperature T P to a third intermediate temperature T i3 ,
(a 3 ) increasing the temperature from the third intermediate temperature T i3 to the hold temperature T P ,
and wherein the ratio P(H 2 )/P(H 2 O) in said atmosphere is such that:
500<P(H 2 )/P(H 2 O)≤50 000, during steps (a), (a 1 ) and (a 2 ), and
P(H 2 )/P(H 2 O)<500, during steps (a 3 ), (b) and (c).
6. The process according to claim 5 , wherein the third intermediate temperature T i3 is between 20° C. and 500° C.
7. The process according to claim 1 , wherein T P is 1 700° C.
8. The process according to claim 1 , wherein at least one from T I and T F is room temperature.
9. The process according to claim 1 , wherein increasing the temperature in step (a) is performed at a rate between 30° C./h and 400° C./h.
10. The process according to claim 1 , wherein decreasing the temperature in step (c) is performed at a rate between 100° C./h and 900° C./h.
11. The process according to claim 1 , further comprising, after step (c), an oxidation heat treatment.
12. The process according to claim 1 , wherein the inert gas is chosen from the group consisting of argon, helium and nitrogen.
13. The process according to claim 1 , wherein the volume ratio between the inert gas and dihydrogen is between 90/10 and 98/2.
14. The process according claim 1 , wherein M 1 is an actinide.
15. The process according to claim 1 , wherein M 1 is a lanthanide.
16. The process according to claim 1 , wherein the compacted powder further comprises at least one oxide of a metal M 2 selected from Sc, Y, an actinide and a lanthanide, M 2 being different from M 1 , whereby, at the end of step (c), a mixed oxide comprising M 1 and M 2 is obtained.
17. The process according to claim 16 , wherein M 2 is an actinide.
18. A process for manufacturing a pellet of at least one oxide of a metal M 1 chosen from an actinide and a lanthanide, said process comprising the following successive steps of:
preparing a powder of said at least one oxide of metal M 1 ,
compacting the powder prepared as a pellet, and
heat treating the pellet of compacted powder by the sintering process according to claim 1 .
19. The process according to claim 14 , wherein M 1 is selected from the group consisting of U, Pu and Th.
20. The process according to claim 15 , wherein M 1 is Ce.
21. The process according to claim 17 , wherein M 2 is selected from the group consisting of U, Pu and Th.
22. The process according to claim 18 , wherein the pellet is a nuclear fuel pellet.