Patent Number: 
Section: claims

1. A pressurized water nuclear reactor comprising:a pressure vessel;an upper removable head for sealably engaging an upper opening in the pressure vessel;a core having an axial dimension supported within the pressure vessel;a plurality of nuclear fuel assemblies supported within the core;at least some of the fuel assemblies having at least one instrumentation tube extending therethrough;an upper core plate extending over the nuclear fuel assemblies;an upper support plate attached to either the upper removable head or the pressure vessel and extending across the upper opening in the pressure vessel;a plurality of support columns extending at least partially between the upper core plate and the upper support plate, at least some of the support columns having an axially extending opening therethrough with the opening extending a length of the support column and being aligned axially with a corresponding instrumentation tube through an opening in the upper core plate; andan axially slidable sleeve through which a measurement device can travel as the measurement device is moved into or out of one of the instrumentation tubes during reactor outages, the sleeve extending at least partially through and into an upper end in at least some of the support columns that are aligned with the corresponding instrumentation tube, the sleeve having at least a portion thereof captured within the axially extending opening in the support column and, during an outage in which the core is to be accessed, substantially the entire sleeve is configured to be axially moveable within the corresponding support column's axially extending opening and extendable from the corresponding support column through an opening in the upper support plate into an area above the upper support plate in a manner that varies an axial length of the sleeve a distance that withdraws the measurement device completely from the instrument tube without the sleeve leaving the upper end of the support column while continuing to shield a portion of the measurement device that was shielded from a reactor coolant during reactor operation, from the coolant above the upper support plate. 2. The pressurized water nuclear reactor of claim 1 wherein a plurality of the support columns have the axially slidable sleeve extending through the upper end of the corresponding support column and the upper end of the support column is attached to and communicates through the upper support plate, including an instrumentation grid assembly positioned within the upper removable head above the upper support plate extending over each of the slidable sleeves and having openings through which the slidable sleeves communicate, an upper portion of the slidable sleeves being attached to the instrumentation grid assembly and the instrumentation grid assembly being movable in an axial direction to slide each of the slidable sleeves within the corresponding support column. 3. The pressurized water nuclear reactor of claim 2 including a plurality of guide studs axially extending from an upper surface of and spaced around the upper support plate and through corresponding openings in the instrumentation grid assembly, for laterally supporting the instrumentation grid assembly as it moves axially. 4. The pressurized water nuclear reactor of claim 3 wherein at least some of the guide studs are spaced around the perimeter of the instrumentation grid assembly. 5. The pressurized water nuclear reactor of claim 4 wherein there are approximately four guide studs substantially equally spaced around the perimeter of the instrumentation grid assembly. 6. The pressurized water nuclear reactor of claim 2 wherein the slidable sleeve comprises a plurality of concentric telescoping tubes that extend between the instrumentation grid assembly and the corresponding support column with an upper tube of the telescoping tubes sliding within a lower tube of the telescoping tubes. 7. The pressurized water nuclear reactor of claim 1 wherein a lower portion of the slidable sleeve is enlarged and restrained below a narrowed opening within an upper portion of the support column so that the slidable sleeve is captured within the opening within the support column. 8. The pressurized water nuclear reactor of claim 1 including an in core instrument thimble assembly that passes through and slides within the slidable sleeve and passes into the instrumentation tube in the fuel assembly when the reactor is operating wherein the slidable sleeve extends axially, without completely leaving the axially extending opening in the support column, to at least a distance above the upper support plate to raise the in-core instrument thimble assembly to at least the mid plane of the upper core plate without the in-core instrument thimble assembly extending above the slidable sleeve when the reactor is shutdown and the core is to be accessed. 9. The pressurized water nuclear reactor of claim 8 wherein the slidable sleeve extends above the upper support plate for at least 15.4 ft. (47 m.). 10. A nuclear electrical power generating facility having a pressurized water reactor nuclear steam supply system comprising:a pressure vessel;an upper removable head for sealably engaging an upper opening in the pressure vessel;a core having an axial dimension supported within the pressure vessel;a plurality of nuclear fuel assemblies supported within the core;at least some of the fuel assemblies having at least one instrumentation tube extending axially therethrough;an upper core plate extending over the nuclear fuel assemblies;an upper support plate attached to either the upper removable head or the pressure vessel and extending across the upper opening in the pressure vessel;a plurality of support columns extending at least partially between the upper core plate and the upper support plate, at least some of the support columns having an axially extending opening therethrough with the opening extending a length of the support column and being aligned axially with a corresponding instrumentation tube through an opening in the upper core plate; andan axially slidable sleeve through which a measurement device can travel as the measurement device is moved into or out of one of the instrumentation tubes during reactor outages, the sleeve extending at least partially through and into an upper end in at least some of the support columns that are aligned with the corresponding instrumentation tube, the sleeve having at least a portion thereof captured within the axially extending opening in the support column and, during an outage in which the core is to be accessed, substantially the entire sleeve being configured to be axially moveable within the corresponding the support column's axially extending opening and extendable from the corresponding support column through an opening in the upper support plate to an area above the upper support plate in a manner that varies an axial length of the sleeve a distance that withdraws the measurement device completely from the instrument tube without the sleeve leaving the upper end of the support column while continuing to shield a portion of the measurement device that was shielded from a reactor coolant during reactor operation, from the coolant above the upper support plate. 11. A pressurized water nuclear reactor comprising:a pressure vessel;an upper removable head for sealably engaging an upper opening in the pressure vessel;a core having an axial dimension supported within the pressure vessel;a plurality of nuclear fuel assemblies supported within the core;at least some of the fuel assemblies having at least one instrumentation tube extending axially therethrough;an upper core plate extending over the nuclear fuel assemblies;an upper support plate attached to either the upper removable head or the pressure vessel and extending across the upper opening in the pressure vessel;a plurality of support columns extending at least partially between the upper core plate and the upper support plate, at least some of the support columns having an axially extending opening therethrough with the opening extending a length of the support column and being aligned axially with a corresponding instrumentation tube through an opening in the upper core plate;an axially slidable sleeve through which a measurement device can travel as the measurement device is moved into or out of one of the instrumentation tubes during reactor outages, the sleeve extending at least partially through and into an upper end in at least some of the support columns that are aligned with the corresponding instrumentation tube, the sleeve having at least a portion thereof captured within the axially extending opening in the support column and, during an outage in which the core is to be accessed, substantially the entire sleeve being configured to be axially moveable within the corresponding support column's axially extending opening and extendable from the corresponding support column through an opening in the upper support plate into an area above the upper support plate in a manner that varies an axial length of the sleeve a distance that withdraws the measurement device completely from the instrument tube without the sleeve leaving the upper end of the support column while continuing to shield a portion of the measurement device that was shielded from a reactor coolant during reactor operation, from the coolant above the upper support plate;wherein a plurality of the support columns have the axially slidable sleeve extending through the upper end of the corresponding support column and the upper end of the support column is attached to and communicates through the upper support plate, including an instrumentation grid assembly positioned above the upper support plate extending over each of the slidable sleeves and having openings through which the slidable sleeves communicate, an upper portion of the slidable sleeves being attached to the instrumentation grid assembly and the instrumentation grid assembly being movable in an axial direction to slide each of the slidable sleeves within the corresponding support column;wherein the slidable sleeve comprises a plurality of concentric telescoping tubes that extend between the instrumentation grid assembly and the corresponding support column with an upper tube of the telescoping tubes sliding within a lower tube of the telescoping tubes; andincluding a spiral spring extending around at least one of the concentric telescoping tubes below an attachment of the slidable sleeve to the instrumentation grid assembly and between the attachment of the slidable sleeve to the instrumentation grid assembly and another of the telescoping tubes to provide a force on the telescoping tubes in an axial downward direction when the instrumentation grid assembly is in a lower most position, to prevent vibration of the telescoping tubes. 12. The pressurized water nuclear reactor of claim 11 wherein a first end of the spring extends at least partially into the opening in the instrumentation grid assembly through which the slidable sleeve extends and a second end of the spring extends axially below the opening in the instrumentation grid assembly and the second end of the spring is surrounded by and captured within a can housing that is slidably mounted within the opening in the instrumentation grid assembly. 13. The pressurized water nuclear reactor of claim 12 wherein an upper portion of the can housing is captured within the opening in the instrumentation grid assembly.