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 thimble extending axially therethrough;an upper internals assembly supported above the core and having axially extending instrumentation guide paths supported therethrough with each of the instrumentation thimbles that are configured to receive instrumentation through the upper internals assembly being aligned with one of the instrumentation guide paths, the upper internals assembly including an instrumentation grid assembly plate supported above the instrumentation guide paths and axially movable relative to a lower portion of the upper internals; andat least one in-core instrumentation thimble assembly extending through a corresponding one of the instrumentation guide paths into an instrumentation thimble, the in-core instrumentation thimble assembly having an upper portion connected to the instrumentation grid assembly plate and retractable with raising of the instrumentation grid assembly plate to move a portion of the in-core instrumentation thimble assemblies within the instrumentation thimbles, into the upper internals assembly, the in-core instrumentation thimble assembly including a lower section comprising a sensor region and an upper section through which signal cabling is routed, both the lower section and the upper section being enclosed within an outer sheath that encloses the corresponding instrument guide path, the outer sheath having an upper portion connected to the instrumentation grid assembly plate with the signal cabling extending at least partially through the instrumentation guide path, through and around an outside of the outer sheath, making a plurality of revolutions around the outer sheath prior to extending through a passage from the interior of the reactor vessel to an exterior thereof, with the number of revolutions sufficient to stretch along an extended length of the outer sheath as the outer sheath is extended with a raising of the instrumentation grid assembly plate to remove the in-core instrumentation thimble assembly from the corresponding instrument thimble, without disconnecting the signal cabling that was housed within the pressure vessel and upper removable head. 2. The pressurized water nuclear reactor of claim 1 wherein the signal cabling is coiled around the outside of an upper portion of the outer sheath. 3. The pressurized water nuclear reactor of claim 2 wherein the coil is in the form of a spiral spring. 4. The pressurized water nuclear reactor of claim 1 wherein the passage from the interior to the exterior of the pressure vessel is an outwardly extending flange on the upper internals assembly. 5. The pressurized water nuclear reactor of claim 1 wherein the instrumentation grid assembly plate is configured to move axially from a lower position to an upper position and the instrumentation guide paths are formed from a tubular housing that substantially extends up to the lower position. 6. The pressurized water nuclear reactor of claim 5 wherein the instrumentation grid assembly plate in the upper position is spaced above the tubular housing. 7. The pressurized water nuclear reactor of claim 6 wherein an upper portion of the tubular housing is configured as a telescoping tube with an upper portion of the telescoping tube connected to the instrumentation grid assembly plate. 8. The pressurized water nuclear reactor of claim 1 wherein the signal cabling exits the outer sheath below an upper end of the outer sheath.