Patent Number: 052727408
Section: claims

1. An radioactivity trapping agent contained in a nuclear fuel based on sintered uraniferous oxides, for trapping the radioactivity of fission products which appear in the course of irradiation of said fuel, comprising an oxygenated compound stable at high temperatures, including, in combination, at least two metallic oxides and at least one oxide of a non-radioactive isotope of a radioactive fission product which appears during the irradiation, and whose radioactivity is to be trapped. 2. A trapping agent according to claim 1 wherein in the stable oxygenated compound the metallic oxides are selected from the group consisting of Al.sub.2 O.sub.3, CeO.sub.2, Nb.sub.2 O.sub.5, SiO.sub.2, TiO.sub.2, UO.sub.2, V.sub.2 O.sub.3, Y.sub.2 O.sub.3 and ZrO.sub.2. 3. A trapping agent according to either one of claims 1 and 2 wherein the metallic oxide is a silico-aluminate, silico-zirconate, silico-niobate or silico-cerate. 4. A trapping agent according to claims 1 or 2 wherein the stable oxygenated compound is pollucite or zeolite containing Cs. 5. A trapping agent according to claims 1 or 2, wherein characterised in that the stable oxygenated compound additionally contains a stable defined compound of an alkali metal and/or alkaline earth metal other than the fission product to be trapped. 6. A trapping agent according to claim 1 or 2, wherein said agent is included in nuclear fuel elements comprising a sintered uraniferous oxide surrounded by a metal sheath. 7. A trapping agent according to claim 6 wherein said agent is included in the sintered uraniferous oxide, the oxide being in pellet form. 8. A trapping agent according to claim 6 wherein said agent coats the sintered uraniferous oxide, the oxide being in pellet form. 9. A trapping agent according to claim 6 wherein said agent internally coats said sheath. 10. A trapping agent according to claim 6 wherein said agent is included in the fuel elements by at least two means selected from the group consisting of inclusion in the oxide, coating the oxide which is in pellet form, and internally coating the sheath. 11. A trapping agent according to claim 5 wherein said stable oxygenated compound comprises Rb, Na or K for Cs or Ca, Ba or Mg for Sr. 12. A nuclear fuel comprising sintered uraniferous oxides which produce radioactive fission products during irradiation of said fuel, and a trapping agent for the radioactivity of said fission products, said trapping agent comprising a high temperature-stable oxygenated compound including, in combination, at least two metallic oxides and at least one additional oxide which is an oxide of a non-radioactive isotope of a radioactive fission product whose radioactivity is to be trapped.