Method for sulphurizing a uo2 powder and method for making nuclear fuel pellets based on uo2 or mixed oxide (u,pu)o2 oxide with added sulphur

17:

• A sulphidation method for a UO2 powder comprising sulfurating the UO2 powder by bringing the powder into contact with a gaseous sulphidation agent.

18:

• The method according to claim 17, wherein the gaseous sulphidation agent is selected from hydrogen sulphide (H2S) and carbon sulphide (CS2).

19:

• The method according to claim 18, wherein the gaseous sulphidation agent is H2S.

20:

• The method according to claim 17, wherein the gaseous sulphidation agent is mixed with hydrogen and/or an inert gas.

21:

• The method according to claim 20, wherein the inert gas is argon or nitrogen.

22:

• The method according to claim 20, wherein the gaseous mixture of the sulphidation agent with hydrogen and/or the inert gas comprises, by volume, 2.5% to 25% of sulphidation agent, from 37.5% to 72.5% of hydrogen, and from 60% to 2.5% of inert gas.

23:

• The method according to claim 20, wherein the gaseous mixture of the sulphidation agent with hydrogen and/or the inert gas has a total gas flow rate from 1 to 500 ml/min.

24:

• The method according to claim 23, wherein the gaseous mixture has a total gas flow rate of 200 ml/min.

25:

• The method according to claim 17, wherein the sulfurating is carried out at a temperature from 800° C. to 1200° C. for a period of time from 1 to 11 hours.

26:

• The method according to claim 17, wherein the sulfurating is carried out at a temperature from 970° C. to 980° C. for a period of time from 1 to 11 hours.

28:

• The method according to claim 27, wherein the sulfurated powder is incorporated in the matrix by simple mixing.

29:

• The method according to claim 27, wherein the level of sulphur in the load subjected to the lubrication, pelletizing and sintering operations is from 50 ppm to 1%.

30:

• The method according to claim 27, wherein the level of sulphur in the load subjected to the lubrication, pelletizing and sintering operations is from 100 ppm to 1000 ppm.

31:

• The method according to claim 27, wherein all or part of the matrix subjected to the lubrication, pelletizing and sintering operations is subjected, prior to the lubrication operation, to a grinding operation.

32:

• The method according to claim 31, wherein the grinding operation is performed in a ball mill.

33:

• The method according to claim 27, wherein all or part of the UO2 powder in the load is a powder that has been subjected, prior to grinding, to a reducing treatment such that the powder has an O/U atomic ratio of 2.00 to 2.04.

34:

• The method according to claim 27, wherein a pore forming agent is incorporated in the load during lubrication.

35:

• The method according to claim 27, wherein the pelletizing operation is carried out using a hydraulic press.

36:

• The method according to claim 27, wherein the sintering operation is carried out at a temperature between 1650° C. and 1750° C. in a hydrogenated atmosphere.

37:

• The method according to claim 36, wherein the sintering operation is carried out at a temperature of 1700° C. in a hydrogenated atmosphere.

38 The method according to claim 36, wherein the atmosphere is humidified.

39 The method according to claim 27, wherein the pellets produced are subjected to dry precision grinding.