Core plate lifting fixture and related process

Handling: hand and hoist-line implements – Grapple – Expanding

Reexamination Certificate

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Details

C294S906000

Reexamination Certificate

active

06186568

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention generally relates to nuclear reactor vessels, and specifically to a unique lifting fixture and related process for the core support plate.
In a nuclear reactor pressure vessel, the core support plate provides lateral support and guidance to the control rod guide tubes, peripheral support pieces, in-core flux monitor guide tubes, and start-up neutron sources. The core plate itself is formed with an array of holes through which the control rod guide tubes pass. The core plate assembly is bolted to a support ledge between the central and lower portions of the core shroud. During core shroud replacement procedures, the core plate is typically removed and transported underwater to another location where it is cut or sliced into multiple pieces for disposal. After removal and during transport, the core plate is typically supported in an upright orientation on a support stand provided with an annular array of vertical supports, each of which has a horizontal support ledge upon which the core plate rests. Because of the geometry of the core plate, as well as the configuration of certain cutting tools, it is necessary to flip the core plate to an upside down orientation prior to slicing to allow access to the support structure of the core plate on the underside.
BRIEF SUMMARY OF THE INVENTION
This invention provides a core plate lifting fixture particularly useful for combined lifting and flipping of the core plate prior to slicing in an underwater environment. Despite inherent space limitations, the fixture is designed to withstand heavy loads, particularly moment loads encountered during the flipping operation. In a typical situation, four fixtures are attached at selective locations about the core plate. Each fixture can be installed within, or removed from a selected core plate hole via radially movable jaws actuated by a vertically oriented screw mechanism. The fixture is configured to have attachment or lifting eyes or bails projecting from both the upper and lower sides of the core plate, and the screw mechanism is accessible from both sides of the fixture (and hence, both sides of the core plate). Each of the lifting bails is also pivotable about a horizontal axis, within an approximate 180° range to enable easy access to the screw mechanism and to permit some swiveling motion for the hooks.
The invention also relates to a method of flipping or inverting the core plate, generally described as follows. The core plate is supported on a stand which is, in turn, supported on a turntable. Each of the four fixtures is inserted into a selected core plate hole, and the radial jaws are moved outwardly by turning the screw device from a remote location. After the fixtures are attached to the core plate, a crane is employed to lift the core plate by means of at least two of the fixtures, turned sideways and flipped over, and then set back down. The jaws are then radially retracted and the fixtures removed from the core plate. A more detailed description of the method is disclosed further herein.
In its broader aspects, therefore, the present invention relates to a lifting fixture comprising a housing; a plurality of jaws movable radially in and out of the housing to secure the fixture to a component to be lifted; at least one lifting bail extending from one end of the housing; and a screw mechanism operatively connected to the plurality of jaws for moving the jaws between a radial inward retracted position and a radial outward locked position.
In another aspect, the invention relates to a method of inverting a nuclear reactor core plate supported on a stand comprising a) attaching at least first and second lifting fixtures to the core plate, each fixture having an upper lifting bail and a lower lifting bail projecting, respectively, from upper and lower sides of the core plate; b) operatively attaching first and second grapples connected to a crane for selective movement to the upper lifting bails, respectively, of the first and second lifting fixtures; c) lifting the core plate off the stand; d) selectively manipulating the grapples to tilt the core plate on end and resting it on the stand, with the first grapple and first lifting fixture closest to the stand; e) releasing the first grapple, rotating the core plate and attaching the first grapple to the lower lifting bail of the second lifting fixture; f) releasing the second grapple from the upper lifting fixture of the second lifting fixture, rotating the core plate and attaching the second grapple to the lower lifting bail of the first lifting fixture; g) selectively manipulating the grapples to lift and level the core plate; and h) lowering the core plate onto the stand.


REFERENCES:
patent: 1835418 (1931-12-01), McHardy
patent: 2538693 (1951-01-01), Maisch
patent: 2610888 (1952-09-01), Pace
patent: 3116663 (1964-01-01), Musgrave
patent: 3265431 (1966-08-01), Burner
patent: 3307871 (1967-03-01), Russell et al.
patent: 3314714 (1967-04-01), Brubaker
patent: 3355792 (1967-12-01), Cunningham
patent: 4948187 (1990-08-01), Blaseck
patent: 5328180 (1994-07-01), Benavides et al.
patent: 5988719 (1999-11-01), Lavender

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