Patent Number: 047117559
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to ice condenser containments, also known as ice baskets, employed for condensing steam generated from the primary water of a nuclear reactor in the event of an accidential loss of coolant and, more particularly, to a handling tool for, and method of, selectively installing and removing removable cruciforms which may be employed as a replacement for the original, nonreplaceable cruciforms of conventional ice baskets, or as an original assembly component of an improved ice basket. 2. State of the Relevant Art Ice condenser containments, also known as ice baskets, are employed with nuclear reactors for condensing the steam from the primary water of the reactor in the event of an accidental loss of coolant. In a typical installation, there are provided approximately 2,000 ice baskets, each of which is approximately one foot in diameter and 48 feet in height and is filled with approximately 1,500 pounds of ice. The sidewalls of the ice basket, substantially cylindrical in configuration, are perforated to permit rapid exposure of the steam to the ice and corresponding, rapid cooling. Each such ice basket incorporates, at spaced intervals therein, stiffening rings comprising structural elements which provide lateral rigidity and support, to accommodate not only the weight of ice contained therein but also seismic and other disturbances. Conventional ice baskets furthermore include elements known as cruciforms, comprising generally x-shaped metal straps which extend diametrically across the interior of the basket and are welded at the ends of the straps to the interior sidewalls of the basket, typically at or adjacent the stiffening rings. Typically, the cruciforms are formed of 1/8 inch thick metal, and are 1 1/2 inches in height. Further, typically, seven (7) such cruciforms are assembled within the basket, spaced at approximately six (6) foot vertical intervals. While not structural members of the baskets and thus not necessary to add radial stiffness to the ice basket cross-section, the cruciforms are necessary elements for satisfying various requirements of the ice bed within the basket. For example, cruciforms are necessary to assure that the geometry of the ice bed within the basket is contained during the entire meltout period of a postulated loss of coolant accident. Specifically, as the ice melts upwardly and away from the bottom of the ice baskets, ice contained therein at higher elevations cannot be permitted to fall down into the bottoms of the baskets, since this presents the potential of creating bypass flow routes for the emerging steam which would accompany the loss of coolant. The cruciforms also serve to prevent large masses of ice from falling during seismic disturbances; falling masses of ice could impose unacceptable impact loads on the ice basket and related, underlying supporting structure. The presence of the cruciforms, however, compounds a maintenance problem which exists in the operation of nuclear power systems employing such ice condenser containments. Particularly, due to sublimation of the ice, the initial volume and weight thereof decreases with time and thus the ice must be replenished, or replaced. A minimum required amount of ice is typically at least 1,200 pounds for each ice basket, for assuring its effectiveness for counteracting the accidental loss of coolant, as above referenced. The cruciforms impose a substantial obstacle to replenishing the supply of ice, as the latter is depleted due to sublimation. For example, the successively lower compartments of the basket, as delineated by the cruciforms, may contain inadequate charges of ice due to sublimation loss, which changes remain spaced apart due to the presence of cruciforms. Thus, while access may be had to the upper, open end of the ice basket for recharging the first and possibly the second upper compartments, the lower compartments are inaccessible, yet may contain an inadequate charge of ice. The ice basket thus loses its required cooling capability, presenting a potentially serious deficiency. Various solutions have been proposed heretofore to overcome the problems thus presented in the replenishment of the ice in view of the obstacles presented by the cruciforms. One such solution is the removal of the original cruciforms, as permitted in view of their not comprising a structural support element of the basket. A known, replaceable cruciform design exists which has been proposed for installation in place of the previously permanent, but removed, original cruciforms. The replaceable cruciform of known design requires that it be rotated onto its side, effectively reducing its width such that it can be passed downwardly throuch the ice basket; at the desired elevation for installation, the cruciform then must be rotated back to a horizontal position. Individual, spring-activated locking devices then are released by remote actuation from the top open end of the ice basket, by tools which afford the requisite reaching length into the ice basket, so as to lock the cruciform onto the coupling or stiffening ring within the basket at the corresponding elevation. The known, replaceable cruciform, however, is extremely difficult to install and remove, and is virtually impossible to install at elevations within the ice basket lower than approximately 24 feet from the open top thereof. Accordingly, there exists a need for a removable cruciform which is readily installed or removed, at every required elevation within the ice basket, and, additionally, for a handling tool which is employable in combination with such a removable cruciform, and to a related method of use thereof, to achieve the convenient and efficient installation and/or removal such a removable cruciform at every required elevation within the ice basket. SUMMARY OF THE INVENTION The present invention provides a handling tool and a related method of operation, for selectively installing and/or removing a removable cruciform of an improved type, comprising the subject matter of the concurrently filed patent application entitled "REMOVABLE CRUCIFORM FOR ICE CONDENSER ICE BASKET" of the common coinventors hereof, and assigned to the common assionee hereof. The removable cruciform of the related application is spring acuated and may be compressed relatively to its normal outer perimeter boundaries, whereby it may be moved, while in a horizontal orientation, axially into or out of an ice basket, and, further, may be released to engage a stiffening ring in the ice basket at a desired elevation, thereby to be temporarily, but securely, structurally locked in position. Alternatively, the cruciforms of the related invention may be compressed and removed from their installed positions within an ice basket, thereby to afford unimpeded access to the corresponding compartments defined thereby throughout the entire height of the ice basket, for maintenance and related purposes. Thus, the configuration of the cruciform of the related invention is especially well adapted for compression and movement through an ice basket, and for expansion into an installed position to afford the required support functions. However, the substantial height and limited accessibility within the ice baskets, particularly at the sucessively lower elevations at which cruciforms must be installed and/or removed, present substantial obstacles to accomplishing those functions. The handling tool and method of the present invention, while of general applicability for use with compressible cruciforms, are particularly advantageous for selective insertion or removal of the cruciform of the related invention as hereinabove set forth. More particularly, the handling tool of the present invention is of generally elongated configuration, so as to facilitate its movement in an axial direction throughout the elevation of an ice basket, and for that purpose includes a main frame having a harness by which the tool is supported from a derrick which lowers the tool into or raises the tool from within an ice basket. A pair of parallel support plates extend in an axial direction downwardly from the frame and carry a mounting bar at the lower ends thereof. A pair of clamping shoes pivotally mounted to the support plate at the lower ends thereof and extending below the mounting bar are selectively actuated between engaged and disengaged positions by an air cylinder mounted on the frame. The tool is lowered to dispose the clamping shoes about the spring housing of the referenced, removable cruciform, with the direction of movement of the clamping shoes between the engaged and disengaged positions aligned with the axis of compression/expansion of the cruciform. The associated air cylinder for the clamping shoes then is actuated, thereby to pivot the shoes toward their engaged position and clamp the housing therebetween, compressing same and thereby retracting the radially extending legs of the removable cruciform. A guide assembly conveniently is incorporated into the noted mounting bar, and includes a pair of guide fingers respectively disposed at the opposite ends of the bar, the fingers having outer configurations defining arcuate segments of a radius corresponding to the interior radius of the ice basket interior wall such that the guide fingers may be received over and supported on a corresponding retaining ring. The guide fingers have horizontally extending shanks received in corresponding slide channels within the mounting bar and angle-mounted actuating lever arms which are driven in vertical reciprocation by corresponding air cylinders mounted to the depending side support plate so as to function in a cam follower manner to project the guide fingers to an outer, retaining ring engaging position, and to retract the guide fingers, through the shanks thereof, to withdraw same from the retaining ring and thus enable movement of the tool axially through the ice basket. In operation, to install a removable cruciform, the tool is positioned over a removable cruciform with the clamping shoes thereof in a disengaged position and aligned in the direction of motion thereof with the axis of compression/expansion of the spring housing. The corresponding air cylinder then is actuated and the clamping shoes moved to the engaged position to compress the spring housing, and thereby to retract the radially extending legs of the cruciform. The tool, with the guide fingers as well retracted, then is inserted into the ice basket and lowered to a position just above the required elevation. Just prior to being lowered into precise alignment at that elevation, the guide assembly is actuated to project the guide fingers outwardly, whereupon further, slight lowering of the tool engages the guide fingers over the corresponding retaining ring. The clamping assembly then is deactuated, to thereby release the spring housing and permit the same to expand, projecting the legs and the corresponding extensions outwardly so as to receive the retaining ring in the corresponding channels thereof and thereby lock the releasable cruciform in position. The guide fingers then are retracted and the tool axially withdrawn from within the ice basket. For removing a cruciform from within the ice basket, the tool is inserted with the guide fingers retracted and the shoes disengaged, so as to position the clamping shoes about the spring housing in alignment with the axis of compression/expansion thereof. When so aligned in position, the clamping shoes are actuated to engage and compress the spring housing, releasing the removable cruciform from the corresponding retaining ring, and then the tool, with the engaged, removable cruciform, is axially, vertically withdrawn from within the ice basket. Accordingly, the tool of the invention, and the method of the operation which it affords, will be seen to function in an efficient and reliable manner, minimizing the required operating time for removing and/or installing removable cruciforms, despite the inherent inaccessibility thereof in view of the height of the typical ice baskets and the required positioning of the cruciforms therein, to enable them to perform their intended functions. The foregoing and other advantages of the removable cruciform handling tool of the present invention will be more apparent from the following drawings and detailed description in relation thereto.