Patent Number: 048328995
Section: claims

1. A spectral shift pressurized-water reactor comprising: a pressure vessel enclosing a reactor core which includes fissile material fuel, said pressure vessel having an inlet and an outlet for circulating water coolant moderator in heat transfer relationship with said core, said core comprising a plurality of square-shaped adjacent fuel assemblies vertically disposed therein for generating heat by nuclear fission, and said fuel assemblies having a fuel enrichment which provides a measure of excess reactivity at the beginning of core life which is later drawn upon to lengthen core life;  a plurality of substantially evenly spaced vertical guide tubes disposed in each of said fuel assemblies and adapted to have rod members moved therein and therefrom during reactor operation, and a portion of said guide tubes in each of said fuel assembly disposed in a cross-like configuration along the two diagonals which connect the corners of said square-shaped fuel assemblies;  three separate types of rods adapted to be moved into and out of said guide tubes, a first type of said rods comprising neutron-absorbing control rods so that insertion of said control rods into said core will substantially decrease reactivity and withdrawal of said control rods from said core will substantially increase reactivity, a second type of said rods comprising neutron-spectral-shift displacer rods which have lower absorptivity for neutrons than said control rods, the third type of said rods comprising gray rods which have an absorptivity for neutrons intermediate that of said control rods and said displacer rods, and said rods all having substantially the same cross-sectional dimension;  said gray rods and said control rods operable to be moved into and out of said core in a portion of said guide tubes which are positioned in said cross-like configuration, and said displacer rods operable to be moved into and out of substantially all of the remainder of said guide tubes, approximately half of said fuel assemblies operable to have only displacer rods moved therein and therefrom, those of said fuel assemblies into which only said displacer rods are to be moved being alternated in position in said core with those of said fuel assemblies into which said control rods and said gray rods are to be moved, and the total number of said displacer rods very substantially exceeding the total number of said control rods and said gray rods;  spider members and associated shafts and drive members therefor positioned above said core, a separate spider member provided for substantially all of each of said fuel assemblies, each of said spider members having only one type of said rods connected thereto in the form of arrays, said control rods and said gray rods being connected to said spider members as cross-like arrays to move into said guide tubes which are similarly disposed, and said displacer rods connected to said spider members as composite arrays which interfit into substantially all said guide tubes in a single fuel assembly in addition to those proximate guide tubes of adjacently positioned fuel assemblies so that those spiders which have displacer rods connected thereto service one fuel assembly in addition to proximate portions of those fuel assemblies which are positioned adjacent thereto.  a pressure vessel enclosing a reactor core which includes fissile material fuel, said pressure vessel having an inlet and an outlet for circulating water coolant moderator in heat transfer relationship with said core, said core comprising a plurality of square-shaped adjacent fuel assemblies vertically disposed therein for generating heat by nuclear fission, and said fuel assemblies having a fuel enrichment which provides a measure of excess reactivity at the beginning of core life which is later drawn upon to lengthen core life;  a plurality of spaced vertical guide tubes disposed in each of said fuel assemblies and adapted to have rod members moved therein and therefrom during reactor operation, and a portion of said guide tubes in each said fuel assembly disposed in a cross-like configuration along the two diagonals which contact the corners of said square-shaped fuel assemblies;  three separate types of rods adapted to be moved into and out of said guide tubes, a first type of said rods comprising neutron-absorbing control rods so that insertion of said control rods into said core will substantially decrease reactivity and withdrawal of said control rods from said core will substantially increase reactivity, a second type of said rods comprising neutron-spectral-shift displacer rods which have a lower absorptivity for neutrons than said control rods, the third type of said rods comprising gray rods which have an absorptivity for neutrons intermediate that of said control rods and said displacer rods, and said control rods and said displacer rods and said gray rods when inserted into said core displacing an equivalent volume of said water coolant moderator;  said displacer rods and said gray rods adapted to be fully inserted into said core at the beginning of core life, and said displacer rods and said gray rods collectively have a sufficiently low absorption for neutrons that when all of said displacer rods and said gray rods are fully inserted into said core at the beginning of core life, supplemental neutron absorption is required to control reactor operation;  said gray rods and said control rods operable to be moved into and out of said core in a portion of said guide tubes which are positioned in said cross-like configuration, and said displacer rods operable to be moved into and out of substantially all of the remainder of said guide tubes, approximately half of said fuel assemblies operable to have only displacer rods moved therein and therefrom, those of said fuel assemblies into which only said displacer rods are to be moved being alternated in position in said core with those of said fuel assemblies into which said control rods and said gray rods are to be moved, the volume of said water coolant moderator which is displaced by said displacer rods when fully inserted into said core very substantially exceeding the total volume of said water coolant moderator displaced by said control rods and said gray rods when fully inserted into said core, and the volume of said water coolant moderator which is displaced by said control rods if fully inserted into said core substantially exceeding the volume of said water coolant moderator displaced by said gray rods when fully inserted into said core;  spider members and associated shafts and drive members therefor positioned above said core, a separate spider member provided for substantially all of each of said fuel assemblies, each of said spider members having only one type of said rods connected thereto in the form of arrays, said control rods and said gray rods being connected to said spider members as cross-like arrays to move into said guide tubes which are similarly disposed, and said displacer rods connected to said spider members as composite arrays which interfit into substantially all said guide tubes in a single fuel assembly in addition to those proximate guide tubes of adjacently positioned fuel assemblies so that those spiders which have displacer rods connected thereto serve one fuel assembly in addition to proximate portions of those fuel assemblies which are positioned adjacent thereto.  a pressure vessel enclosing a reactor core which includes fissile material fuel, said pressure vessel having an inlet and an outlet for circulating water coolant moderator in heat transfer relationship with said core, said core comprising a plurality of square-shaped adjacent fuel assemblies vertically disposed therein for generating heat by nuclear fission, and said fuel assemblies having a fuel enrichment which provides a measure of excess reactivity at the beginning of core life which is later drawn upon to lengthen core life;  a plurality of substantially evenly spaced vertical guide tubes disposed in each of said fuel assemblies and adapted to have rod members moved therein and therefrom during reactor operation, and a portion of said guide tubes in each said fuel assembly disposed in a cross-like configuration along the two diagonals which connect the corners of said square-shaped fuel assemblies;  three separate types of rods adapted to be moved into and out of said guide tubes, a first type of said rods comprising neutron-absorbing control rods so that insertion of said control rods into said core will substantially decrease reactivity and withdrawal of said control rods from said core will substantially increase reactivity, a second type of said rods comprising displacer rods which have a substantially lower absorptivity for neutrons than said control rods, each said neutron-spectral-shift displacer rod comprising a hollow thin-walled Zircaloy member containing a filling of solid or annular zirconium- or aluminum-containing material for providing internal support and mass for said thin-walled tubular member, each said displacer rod having overall neutron-absorbing and -moderating characteristics essentially not exceeding those of hollow tubular Zircaloy members with or without a filling of zirconium oxide pellets or aluminum oxide pellets, the third type of said rods comprising gray rods which have an absorptivity for neutrons intermediate that of said control rods and said displacer rods, and said rods all having substantially the same cross-sectional dimensions;  said gray rods and said control rods operable to be moved into and out of said core in a portion of said guide tubes which are positioned in said cross-like configuration, and said displacer rods operable to be moved into and out of substantially all of the remainder of said guide tubes, approximately half of said fuel assemblies operable to have only displacer rods moved therein and therefrom, those of said fuel assemblies into which only said displacer rods are to be moved being alternated in position in said core with those of said fuel assemblies into which said control rods and said gray rods are to be moved, and the total number of said displacer rods very substantially exceeding the total number of said control rods and said gray rods;  spider members and associated shafts and drive members therefor positioned above said core, a separate spider member provided for substantially all of each of said fuel assemblies, each of said spider members having only one type of said rods connected thereto in the form of arrays, said control rods and said gray rods being connected to said spider members as cross-like arrays to move into said guide tubes which are similarly disposed, and said displacer rods connected to said spider members as composite arrays which interfit into substantially all said guide tubes in a single fuel assembly in addition to those proximate guide tubes of adjacently positioned fuel assemblies so that those spider members which have displacer rods connected thereto serve one fuel assembly in addition to proximate portions of those fuel assemblies which are positioned adjacent thereto.  a pressure vessel enclosing a reactor core which includes fissile material fuel, said pressure vessel having an inlet and an outlet for circulating water coolant moderator in heat transfer relationship with said core, said core comprising a plurality of square-shaped adjacent fuel assemblies vertically disposed therein for generating heat by nuclear fission, and said fuel assemblies having a fuel enrichment which provides a measure of excess reactivity at the beginning of core life which is later drawn upon to lengthen core life;  a plurality of spaced vertical guide tubes disposed in each of said fuel assemblies and adapted to have rod members moved therein and therefrom during reactor operation, and a portion of said guide tubes in each said fuel assembly disposed in a cross-like configuration along the two diagonals which connect the corners of said square-shaped fuel assemblies;  three separate types of rods adapted to be moved into and out of said guide tubes, a first type of said rods comprising neutron-absorbing control rods so that insertion of said control rods into said core will substantially decrease reactivity and withdrawal of said control rods from said core will substantially increase reactivity, a second type of said rods comprising neutron-spectral-shaft displacer rods which have a substantially lower absorptivity for neutrons than said control rods, each said neutron-spectral-shift displacer rod comprising a hollow thin-walled Zircaloy member containing a filling of solid or annular zirconium- or aluminum-containing material for providing internal support and mass for said thin-walled tubular member, each said displacer rod having overall neutron-absorbing and -moderating chracteristics essentially not exceeding those of hollow tubular Zircaloy members with or without a filling of zirconium oxide pellets or aluminum oxide pellets, the third type of said rods comprising gray rods which have an absorptivity for neutrons intermediate that of said control rods and said displacer rods, and said control rods and said displacer rods and said gray rods when inserted into said core displacing an equivalent volume of said water coolant moderator;  said displacer rods and said gray rods adapted to be fully inserted into said core at the beginning of core life, and said displacer rods and said gray rods collectively have a sufficiently low absorption for neutrons that when all of said displacer rods and said gray rods are fully inserted into said core at the beginning of core life, supplemental neutron absorption is required to control reactor operation;  said gray rods and said control rods operable to be moved into and out of said core in a portion of said guide tubes which are positioned in said cross-like configuration, and said displacer rods operable to be moved into and out of substantially all of the remainder of said guide tubes, approximately half of said fuel assemblies operable to have only displacer rods moved therein and therefrom, those of said fuel assemblies into which only said displacer rods are to be moved being alternated in position in said core with those of said fuel assemblies into which said control rods and said gray rods are to be moved, the volume of said water coolant moderator which is displaced by said displacer rods when fully inserted into said core very substantially exceeding the total volume of said water coolant moderator displaced by said control rods and said gray rods if fully inserted into said core, and the volume of said water coolant moderator which is displaced by said control rods if fully inserted into said core substantially exceeding the volume of said water coolant moderator displaced by said gray rods when fully inserted into said core;  spider members and associated shafts and drive members therefor positioned above said core, a separate spider member provided for substantially all of each of said fuel assemblies, each of said spider members having only one type of said rods connected thereto in the form of arrays, said control rods and said gray rods being connected to said spider members as cross-like arrays to move into said guide tubes which are similarly disposed, and said displacer rods connected to said spider members as composite arrays which interfit into substantially all said guide tubes in a single fuel assembly in addition to those proximate guide tubes of adjacent positioned fuel assemblies so that those spider members which have displacer rods connected thereto serve one fuel assembly in addition to proximate portions of those fuel assemblies which are positioned adjacent thereto. 2. The reactor as specified in claim 1, wherein the substantial majority of said fuel assemblies which have only displacer rods movable therein and therefrom are surrounded by four adjacent fuel assemblies, and those of said spiders and associated shafts and drives which serve said substantial majority of said fuel assemblies which have only displacer rods movable therein also control the movement of displacer rods into the proximate guide tubes of said four surrounding adjacent fuel assemblies. 3. The reactor as specified in claim 1, wherein the total number of said control rods substantially exceeds the total number of said gray rods. 4. The reactor as specified in claim 1, wherein said reactor has chemical shim control capability. 5. The reactor as specified in claim 1, wherein each of said spiders and associated shafts and drive members is separately controllable. 6. The reactor as specified in claim 1, wherein said displacer rods and said gray rods collectively have a sufficiently low absorption for neutrons that when all of said displacer rods and said gray rods are fully inserted into said core at the beginning of core life, supplemental neutron-absorption is required to control reactor operation. 7. A spectral shift pressurized-water reactor comprising: 8. The reactor as specified in claim 7, wherein the substantial majority of said fuel assemblies which have only displacer rods movable therein and therefrom are surrounded by four adjacent fuel assemblies, and those of said spiders and associated shafts and drives which serve said substantial majority of said fuel assemblies which have only displacer rods movable therein also control the movement of displacer rods into the proximate guide tubes of said four surrounding adjacent fuel assemblies. 9. The reactor as specified in claim 7, wherein said displacer rods are formed of Zircaloy tubes with or without a filling of low-neutron-absorbing solid pellets or annular pellets. 10. The reactor as specified in claim 9, wherein said solid pellets or annular pellets are ZrO.sub.2 or Al.sub.2 O.sub.3. 11. The reactor as specified in claim 9, wherein said gray rods comprise hollow stainless steel tubes. 12. The reactor as specified in claim 7, wherein said reactor has chemical shim control capability. 13. The reactor as specified in claim 7, wherein each of said spiders and associated shafts and drive members is separately controllable. 14. A spectral shift pressurized-water reactor comprising: 15. The reactor as specified in claim 14, wherein the substantial majority of said fuel assemblies which have only displacer rods movable therein and therefrom are surrounded by four adjacent fuel assemblies, and those of said spider members and associated shafts and drives which serve said substantial majority of said fuel assemblies which have only displacer rods movable therein also control the movement of displacer rods into the proximate guide tubes of four adjacent fuel assemblies. 16. The reactor as specified in claim 14, wherein the total number of said control rods substantially exceeds the total number of said gray rods. 17. The reactor as specified in claim 14, wherein said reactor has chemical shim control capability. 18. The reactor as specified in claim 14, wherein each of said spider members and associated shafts and drive members is separately controllable. 19. The reactor as specified in claim 14, wherein said gray rods comprise hollow stainless steel tubes. 20. A spectral shift pressurized-water reactor comprising: 21. The reactor as specified in claim 20, wherein the substantial majority of said fuel assemblies which have only displacer rods movable therein and therefrom are surrounded by four adjacent fuel assemblies, and those of said spider members and associated shafts and drives which serve said substantial majority of said fuel assemblies which have only displacer rods movable therein also control the movement of displacer rods into the proximate guide tubes of said four surrounding adjacent fuel assemblies. 22. The reactor as specified in claim 20, wherein said gray rods comprise hollow stainless steel tubes. 23. The reactor as specified in claim 20, wherein said reactor has chemical shim control capability. 24. The reactor as specified in claim 20, wherein each of said spider members and associated shafts and drive members is separately controllable.