# US 5,350,542 A · Nuclear fuel with isotopically depleted burnable absorber > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,350,542 A - Document ID: US5350542A - Status: Granted - Kind: A - Application number: 08/083,523 - Filed: 1993-06-30 - Granted: 1994-09-27 - Earliest claimed: 1991-09-18 - Assignees: Combustion Engineering, Inc. - Inventors: Leonard N. Grossman; Alf I. Jonsson - Web page: https://patentgrep.com/patent/US5350542A ## CPC - G21C 7/04: of burnable poisons (burnable poisons in fuel rods G21C3/326) - G21C 3/18: Internal spacers or other non-active material within the casing, e.g. compensating for expansion of fuel rods or for compensating excess reactivity (interlayers G21C3/20) - Y02E 30/30: Nuclear fission reactors - G21C: NUCLEAR REACTORS (fusion reactors, hybrid fission-fusion reactors G21B; nuclear explosives G21J) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract By using AVLIS or other methods capable of providing a depleted isotopic mixture, troublesome isotopes such as Gd.sup.154, Gd.sup.156 and Er.sup.166 are selectively removed from naturally occurring isotopic mixtures, while avoiding the additional costs associated with complete fractionation of the mixture. Such mixtures can be used to provide a burnable nuclear fuel absorber having a selectively depleted isotope or isotopes. In particular, the invention concerns burnable absorbers containing erbium with a depleted 166 isotope, gadolinium with a depleted 156 isotope or with depleted 154 and 156 isotopes, and methods for making such absorbers. ## Claims ### Claim 1 An isotopic mixture of isotopes of an element gadolinium suitable for use as a burnable absorber, wherein: said mixture comprises a naturally occurring but depleted isotopic mixture that is selectively and substantially depleted only with respect to a first naturally occurring isotope, said first isotope having an isotope mass that is one less than a second naturally occurring isotope of said element, said second isotope having a thermal neutron cross-section which is higher than the thermal neutron cross-section of said first isotope. ### Claim 2 (depends on 1) The isotopic mixture of claim 1 wherein said first isotope is Gd.sup.156 and said second isotope is GD.sup.157. ### Claim 3 A method of treating a naturally occurring isotopic mixture of isotopes of an element gadolinium comprising using an isotopic separation process sufficient to selectively remove a substantial portion of only a first naturally occurring isotope having an isotope mass that is one less than a second naturally occurring isotope of said element, said second isotope having a thermal neutron cross-section higher than the thermal neutron cross-section of said first isotope and said first isotope being depleted to about 50% or more of its natural concentration. ### Claim 4 (depends on 3) The method of claim 3 wherein said first isotope is Gd.sup.156 and said second isotope is Gd.sup.157. ### Claim 5 An isotopic mixture of isotopes of an element gadolinium suitable for use as a burnable absorber, wherein: said mixture comprises a naturally occurring but depleted isotopic mixture that is selectively and substantially depleted only with respect to a first group of one or more naturally occurring isotopes, said first group of one or more isotopes each having an isotope mass that is one less than a corresponding second group of one or more isotopes of said element, each of said second group of one or more isotopes having a thermal neutron cross-section that is higher than the thermal neutron cross-section of each of said corresponding first group of one or more isotopes. ### Claim 6 (depends on 5) The isotopic mixture of claim 5 wherein said first group of one or more isotopes is Gd.sup.156 and said corresponding second group of one or more isotopes is Gd.sup.157. ### Claim 7 (depends on 5) The isotopic mixture of claim 5 wherein said first group of one or more isotopes is Gd.sup.154 and Gd.sup.156, and said corresponding second group of one or more isotopes is Gd.sup.155 and Gd.sup.157. ### Claim 8 A method of treating a naturally occurring isotopic mixture of isotopes of an element gadolinium comprising using an isotopic separation process sufficient to selectively and substantially remove only a first group of one or more naturally occurring isotopes having an isotope mass that is one less than a corresponding second group of isotopes having a thermal neutron cross-section higher than the thermal neutron cross-section of each of said corresponding first group of isotopes and each of said first group of isotopes being depleted to about 50% or more of its natural concentration. ### Claim 9 (depends on 8) The method of claim 8 wherein said first group of one or more isotopes is Gd.sup.156 and said corresponding second group of one or more isotopes is Gd.sup.157. ### Claim 10 (depends on 8) The method of claim 8 wherein said first group of one or more isotopes is Gd.sup.154 and Gd.sup.156, and said corresponding second group of one or more isotopes is Gd.sup.155 and Gd.sup.157. ### Claim 11 (depends on 3) The method of claim 3 wherein said isotopic separation process is AVLIS. ### Claim 12 (depends on 8) The method of claim 8 wherein said isotopic separation process is AVLIS.