Cutting by use of rotating axially moving tool – With product handling or receiving means
Reexamination Certificate
1998-05-06
2001-10-30
Howell, Daniel W. (Department: 3722)
Cutting by use of rotating axially moving tool
With product handling or receiving means
C408S097000, C408S204000
Reexamination Certificate
active
06309147
ABSTRACT:
TECHNICAL FIELD
The invention relates to an underwater remote drilling tool and, in particular, to an underwater remote drilling tool for drilling holes in the core shroud support plate between two jet pump diffusers in a nuclear reactor vessel.
BACKGROUND
In order to perform maintenance and modifications to nuclear reactor vessel internals, it is necessary at times to perform machining on the existing internal components. One such repair involves the addition of several restraint rods, (usually four) which anchor to the lower shroud support plate area, and extend upward to connect over the top of the shroud cylinder. Although the configurations of each plant vary, therefore creating some differences in the designs of each system, there is a common need in most designs to produce holes in the shroud support plate, adjacent the jet pump diffusers for attachment of repair components. The governing nature of the reactor vessel internal components is such that essentially all work is performed in-situ, underwater (obtaining depths of up to 100 feet), keeping radiation exposure of the workers to a minimum. Foreign materials exclusion (FME) is of utmost concern due to its potentially deleterious effect on the nuclear fuel, monitoring systems, flow of coolant/moderator, etc. The working envelope is typically very restrictive, and thus, all tooling must be compact and remotely operated.
The conventional method for performing machining operations on reactor vessel internal components utilizes a metal removal process called electrical discharge machining (EDM). By creating an electrical spark across a small gap between an electrode and the workpiece, the material is essentially eroded away, producing a swarf by-product. It has been shown that any swarf left after the EDM process poses no detrimental concerns as a foreign material. As there are no real mechanical reaction forces between the workpiece and electrode, the tooling developed need not be very substantial, thereby lending itself to packaging tools within the restrictive interference envelopes.
The EDM process, though predominantly utilized, is a very slow, time consuming process. Typical best anticipated times to produce a 3 inch diameter hole in a 1 ½ inch thick workpiece are upwards of 16 hours. Effects of ambient pressure, side arcing, electrode wear, hole breakthrough, swarf flushing and tooling failures due to long submersion times can all contribute to excessive delays during the EDM process. Moreover, inherent to the EDM process is the quick heating/cooling cycle generated with each spark. This rapid heating/cooling creates a re-cast layer on the machined surface. Depending on the material being machined, it is sometimes necessary to grind or hone the re-cast layer to remove any microfissures that may be detected.
Conventional machining inside the reactor vessel has historically not been attempted due to the generation/retention requirements of the chips produced. Thus, there is a need for improved productivity and process reliability of machining reactor vessel internals.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the invention to provide an underwater remote drilling tool and methods that reduce the time for machining existing internal components of a nuclear reactor vessel. It is another object of the invention to provide an underwater remote drilling tool that utilizes a standard tooling system while maintaining control of all foreign material, minimizing deleterious effects on the material being drilled. It is still another object of the invention to provide an underwater remote drilling tool with increased tool reliability.
These and other objects of the invention are achieved by providing a support base insertable between two jet pump diffusers in a nuclear reactor vessel for supporting a machining tool, the vessel including a core shroud and a core shroud support plate. The support base includes a first leg having a first extendible member engageable with the core shroud; a second leg having a second extendible member engageable with one of the two jet pump diffusers; and a third leg having a third extendible member engageable with the other of the two jet pump diffusers. The support base is positionable on the core shroud support plate, and when the first, second and third extendible members are extended, the support base is substantially immovably secured between a vessel wall and the core shroud. The support base may include a centering device disposed substantially between the second and third legs, the centering device centering the support base between the two jet pump diffusers.
In accordance with another aspect of the invention, a support base for supporting a machining tool includes a first leg having a first extendible member; a second leg spaced from the first leg and having a second extendible member; and a third leg spaced from the first and second legs and having a third extendible member. The first, second and third extendible members are selectively extendible and retractable by a hydraulic driving device. In a preferred arrangement, the support base may include additional elements such as a substantially centrally disposed aperture, enabling access to a support base supporting surface for the machining tool; a sealing member disposed substantially coaxial with the aperture and between the aperture and the supporting surface; and leveling structure for leveling the support base on the support base supporting surface. The support base may further include structure for receiving at least one positioning dowel of the machining tool and structure for receiving at least one fixing member of the machining tool. Still further, the support base may include a centering device disposed substantially between the second and third legs, the centering device centering the support base between the two jet pump diffusers.
A method of securing a support base for a machining tool between two jet pump diffusers in a nuclear reactor vessel is also provided. The method includes positioning the support base between the core shroud and the vessel wall; positioning the support base between the two jet pump diffusers; and extending, with the hydraulic driving device, the first, second and third extendible members such that the first leg engages the core shroud and the second and third legs engage the two jet pump diffusers, respectively.
In accordance with yet another aspect of the invention, there is provided a drilling tool for drilling a bore in the shroud support plate. The drilling tool includes a rotatable spindle; a substantially cylindrical drill bit coupled to the spindle; a sleeve surrounding the drill bit, the sleeve being fixed from rotation such that it does not rotate with the drill bit; and a chip collection system collecting chip produced during drilling. An induction ring may be provided surrounding a connection area between the spindle and the drill bit, wherein the chip collection system includes a fluid inlet into the induction ring and into the spindle. The drill bit may include a flute having a flute inlet at a cutting end of the drill bit and a flute outlet at a spindle end of the drill bit. The induction ring includes a ring outlet disposed adjacent the flute outlet, wherein the chip collection system further includes the flute and the ring outlet. The chip collection system may further include a mesh chip basket communicating with the ring outlet, the mesh chip basket being configured to collect the chip produced during drilling.
A housing may be provided surrounding the spindle, the drill bit and the sleeve. The housing includes a drilling tool base plate having a locating dowel facing the shroud support plate, wherein the locating dowel is shaped to fit into a corresponding locating hole on a support base secured to the shroud support plate. The drilling tool base plate may further include an attachment member for securing the drilling tool to the support base and alternatively or additionally a hydraulic swing clamp shaped to fit through a swing clamp hole in the suppor
Kasik James F.
Kazirskis Benedict
Matsumoto Jack T.
Pence Vernon W.
General Electric Company
Howell Daniel W.
Nixon & Vanderhye P.C.
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