Patent Number: 
Section: claims

1. A method of making a nuclear fuel pellet for a nuclear power reactor, the method comprising the following steps:providing a nuclear fuel material in powder form, wherein the nuclear fuel material is based on UO2;pressing the powder thereby obtaining a green pellet is obtained;providing a liquid that comprises an additive which is to be added to the green pellet, the additive comprises B and/or Cr;contacting the green pellet with the liquid wherein the liquid, with the additive, penetrates into the pellet; andsintering the so treated green pellet,wherein with said additive larger grains in the nuclear fuel material are present in the pellet after the sintering step as compared with the grain size obtained if the additive had not been added but otherwise produced in the same manner. 2. A method according to claim 1, wherein said additive is in the form of particles dispersed in said liquid. 3. A method according to claim 1, comprising a step of controlling the penetration depth of the liquid, and thereby of the additive, into the green pellet. 4. A method according to claim 3, wherein said step of controlling the penetration depth is done by selecting one or both of the following:the viscosity of the liquid with included additive,the amount of the liquid, with the additive, which is added to the green pellet when contacting the green pellet with the liquid, with the additive. 5. A method according to claim 3, wherein the penetration depth of the liquid, with the additive, into the green pellet is controlled to obtain an outer portion of the green pellet containing substantially more liquid, and thereby more additive, than an inner portion of the green pellet, wherein the sintered pellet has a larger grain size in the outer portion than in the inner portion. 6. A method according to claim 1, wherein said liquid with additive is selected and said method is performed wherein the liquid with additive will penetrate into the pores which exist between the grains in the green pellet. 7. A method according to claim 6, wherein said liquid with additive is selected and said method is performed wherein the liquid with additive will not penetrate into the pores which exist in the grains in the green pellet. 8. A method according to claim 6, wherein said liquid with additive is selected and said method is performed wherein the liquid with additive will penetrate also into the pores which exist in the grains in the green pellet. 9. A method according to claim 1, wherein said liquid is selected and said method is performed wherein at least 99% of the liquid will leave the pellet before or during the sintering step. 10. A method according to claim 1, wherein said additive constitutes or includes a substance which causes said larger grains in the sintered pellet, wherein said substance is selected and the method is performed wherein at least 90% of the substance leaves at least an outer portion of the pellet before and/or during the sintering step. 11. A method according to claim 10, wherein at least 95% of the substance leaves at least an outer portion of the pellet before and/or during the sintering step. 12. A method according to claim 11, wherein at least 99% of the substance leaves at least the outer portion of the pellet before and/or during the sintering step. 13. A method according to claim 12, wherein the substance completely leaves at least the outer portion of the pellet before and/or during the sintering step. 14. A method according to claim 1, wherein said additive comprises B and wherein at least 90% of said B is 11B. 15. A method according to claim 1, wherein said liquid is selected so the additive does not dissolve in the liquid, and wherein the nuclear fuel material in the green pellet is not dissolved by the liquid. 16. A method according to claim 1, wherein said liquid is an oil, preferably a mineral oil. 17. A method of making and using nuclear fuel, comprising:making a plurality of nuclear fuel pellets according to the method of claim 1;arranging the nuclear fuel pellets in cladding tubes;arranging the cladding tubes, with the nuclear fuel pellets, in the core of a nuclear power reactor in a nuclear power plant, wherein at least 20% of the nuclear fuel material in said core are made of pellets made in accordance with the aforementioned method of making the plurality of nuclear fuel pellets; andoperating the nuclear reactor to produce energy. 18. A method of making and using nuclear fuel according to claim 17,wherein at least 50% of the nuclear fuel material in said core are made of pellets made in accordance with the aforementioned method of making the plurality of nuclear fuel pellets. 19. A method of making and using nuclear fuel according to claim 18,wherein 100% of the nuclear fuel material in said core are made of pellets made in accordance with the aforementioned method of making the plurality of nuclear fuel pellets.