Patent Number: 051695960
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein like reference numerals refer to like elements, FIG. 1 depicts a shield building 1 which encloses a containment vessel 3, yet spaced outwardly thereof with the space formed between the two referred to herein as the annulus 4. The containment vessel 3 is desirably made of steel and has a generally cylindrical side 5 and a generally hemispherical or ellipsoidal top 6a and bottom 6b. Illustrated by way of example inside the containment vessel 3 is a portion of the primary system of a pressurized water reactor including a reactor vessel 2 and two steam generators 8, both well known in the art. The shield building includes a generally cylindrical side wall 7 which terminates at its lower end with a floor 9, and at its upper end by a frustoconical roof 11. The wall 7, made of, for example, reinforced concrete, includes a plurality of openings 15 spaced circumferentially about the upper end of the wall 7 for allowing air to enter the shield building 1. Each opening 15 in this embodiment has a wire mesh screen positioned in it to prevent debris and the like from entering through the opening 15. The frustoconical roof 11 is desirably made of a structural material, such as reinforced concrete and includes an angled roof portion 17 which closes the upper end of the wall 7 and includes a skirt 16 extending from its lower edge and extending concentrically with a portion of wall 7 thereby providing additional protection from external conditions. The frustoconical roof 11 includes a circular opening 19 in the center of the roof 11 with a cupola-like structure 22 extending upwardly over the roof 11 and surrounding the opening 19. A circular platform 21 is located directly above the center of the containment vessel 3 and below the opening 19 in the roof 11. The platform 21 is supported from the roof 11 by beams 23 attached to the periphery of the circular opening 19. A wire mesh screen 25 is positioned surrounding the beams 23 forming a cylinder like apparatus between the platform 21 and the opening 19. This prevents larger objects such as birds and the like from entering the shield building 1. The cupola structure 22 includes a water storage tank 27 of a toroidal-like configuration. The water storage tank 27 provides a source of water for the inside the shield building 1 for cooling when ambient air passing over the containment vessel may be insufficient, for example, in the unlikely event of an accident in which large quantities of heat are generated inside vessel 3. One means of access inside the shield building 1 is through a door 29 located in the lower end of the wall 7. Another means of access is through one of the openings 15. An elevator (not shown) positioned outside of the shield building 1 is used to access the opening 15 at the top of the shield building wall 7. The opening 15 adjacent the elevator has hinges or the like (not shown) allowing it to be opened or removed. A partially fixed, partially movable air baffle means 30 is disposed within the shield building 1 and comprises three major components, i.e., a sectional movable baffle means 31, a fixed baffle means 33 and a combined fixed and movable baffle means 35. Referring to FIGS. 1 and 2, the fixed baffle 33 is shown as a unitary structure while the movable baffle 31, and combined fixed and movable baffle 35 are divided into defined sections respectively herein referred to as movable sections 31a, and combined fixed and movable sections 35a. The fixed baffle 33 is supported and attached from the shield building roof 11. Each movable sections 31a is supported by at least two vertical columns 38, made of for example concrete, positioned beneath each movable section 31a and each vertical column 38 extends to the floor 9. A plurality of support means 42 are for additional support of the movable sections 31a and are attached and positioned at one end to each movable section 31a. Each support means 42 on the other end is attached to the shield building wall 7. The air baffle 30 is positioned in the annulus 4 dividing the annulus 4 into an inner annulus 37 and outer annulus 39 surrounding the inner annulus 37. The air baffle 30 generally has a shape that conforms to the shape of the containment vessel 3. The movable baffle means 31 is the lower part of the air baffle means 30, the fixed baffle means 33 is the upper part thereof, with the combined fixed and movable baffle means 35 positioned between the fixed baffle means 33 and the movable baffle means 31. The movable baffle means 31 is positioned surrounding a major portion of the cylindrical side 5 portion of the containment vessel 3. The fixed baffle means 33 is positioned surrounding the top hemispherical or ellipsoidal portion 6a of the containment vessel 3. The fixed baffle means 33 has a frustoconical shape with both ends open allowing air passage. Referring to FIGS. 1 and 3, the combined fixed and movable baffle means 35 is divided into sections and each section 35a is comprised of two metal plates 40a and b. Each outer plate 40a is attached to the outer surface of the adjacent movable sections 31a. The inner plate 40b is attached to the fixed baffle 33 adjacent the inner wall thereof and extends into engagement with the adjacent movable section 31a. Each outer plate 40a, at its upper portion, is contiguous to and overlapping with the fixed baffle 33 and the lower end of each plate 40a is secured by suitable means, such as by bolts (not shown), to the adjacent movable section 31a. Each inner plate 40b is attached, at its top, to the lower end of the fixed baffle 33 by a suitable securing means such as by bolts (not shown), an elastomer material 41 may be positioned between the bolts and the inner plate 40b. The elastomer material 41 may comprise a long, thin, belt like configuration extending the entire width of the lower surface of fixed baffle 33. The elastomer material 41 functions as a supplemental biasing means spring means with each inner plate 40b to result in a slight horizontal outward movement of the inner plate 40b which may be designed to be biased outwardly a small but fixed amount when the bottom portion thereof is disengaged from adjacent baffle segment 31a. Inner plate 40b, at its lower end, is contiguous to and overlapping with each adjacent baffle section 31a. A plurality of long, thin, belt-like elastomer pads 55 are also attached at the top and extend the entire width of each respective movable section 31a and is positioned to be between each inner plate 40b and movable section 31a when the movable sections 31a are in the normal position. Elastomer pad 55 functions to cushion and form a general seal between the movable section 31a and inner plate 40b. When the movable section 31a is moved up and away from the containment vessel 3 (as illustrated in phantom in FIGS. 3 and 4) the inner plate 40b is biased to move slightly in an outwardly direction. The outer plate 40a moves generally with the movable sections 31a as it is moved up and away from the containment vessel 3. When the movable section 31a are returned to the normal position the elastomer pad 55 on each movable section 31a pushes slightly against the bottom portion of each inner plate 40b and forces it into the normal position thus effecting a seal between elastomer 55 and plate 40 b. Concurrently, the outer plate 40a moves with the movable sections 31a when each movable section 31a is returned to the normal position, as shown in FIG. 3, so that the upper edges of sections 31a engage fixed baffle 33. Referring to FIG. 1, the shield building 1 and air baffle 30 cooperate to form a passive containment cooling system which functions to provide a pathway for natural circulation to occur thereby removing ambient heat dissipated by the containment vessel 3. The passive containment cooling system is designed to function in the unlikely event of an accident where a large energy release occurs or when normal cooling fans are not available or the like. Heat removal is accomplished by allowing air to flow into the opening 15 of the shield building 1 and down the outer annulus 39. The air then flows around the bottom of the movable shield baffle means 31 and upward in the inner annulus 37 thereby cooling the containment vessel 3. The air is directed along the inner boundary of the fixed baffle means 33 then through the opening 19 containing the wire mesh 25 at the top of the shield building 1. Referring to FIG. 5, in this embodiment of the invention, the defined sections 31a of the movable baffle 31 are comprised of flat planar surfaces 44 at angle increments of approximately six degrees. As shown in FIG. 6, the movable baffle means 31 is divided into several defined sections 31a. A sealing means 45 is positioned between adjacent movable baffle sections 31a to prevent significant air leakage across the air baffle boundary providing an essentially continuous inner surface. The sealing means 45 in this embodiment may comprise, for example, a dichotomous seal creating a seam 45a at the center of the seal 45. One segment of seal 45 is rigidly attached to each respective movable baffle section 31a. The splitting of the sealing means 45 enables the seal to follow the movable shield baffle sections 31a to which the seal is attached when the movable baffle 31 is moved up and away. The two portions of the seal 45 are compressed together as the movable baffle 31a is moved into its operating position. As shown in FIGS. 4 and 7, a plurality of support means 42 are rigidly and pivotally attached to the wall 7 of the shield building 1 and to the movable baffle section 31a respectively. FIG. 3 illustrates an example of an appropriate vertically aligned configurations for support means 42 and includes outer support means 42a, inner support means 42b, and cross brace 43. Each of the plurality of movable baffle sections 31a is supported in an adequate manner, for example by outer support means 42a at the outer edges and inner support means 42b in conjunction with cross brace 43 at the midsection of the movable baffle section 31a. This configuration of outer support means 42a, inner support means 42b, and cross brace 43 is repeated in this example at seven vertical locations along each plurality of baffle sections 31a. Referring to FIG. 5, each inner support means 42b at the midsection of each movable baffle section 31a is further supported by a cross brace 43. Regulations require that equipment or systems essential to the operation of nuclear facilities be capable of withstanding seismic events. The cross braces 43 are an example of support means which will provide the required additional support that may be required during seismic events. The support means 42 are all parallel to each other on each movable baffle section 31a and include a pivotal clevis mount 41 at each end which allows movement in a vertical plane. Referring to FIG. 4, a lifting means 47 positioned inside the shield building 1 at the intersection of the roof 11 and the wall 7 comprises a cable with a hook on the end and a means for lowering and raising the cable. The lifting means 47 may be moved circumferentially around the shield building by a monorail 49 to allow each movable baffle sections 31a to be lifted. At least two eyebolt devices 51 are attached to the movable baffle section 31a. The cable is lowered with a lifting bridle (not shown) attached to the hook. A lifting bridle comprises at least two or more cables connected or bonded together at one of the cable ends and a device for latching, such as metal rings, attached at the bonded point of the cables and at the unconnected ends of each cable. The lifting bridle attaches to one or more eyebolts 51 and the cable is lifted thereby lifting the movable baffle section 31a. A personnel basket 57 may be used in this embodiment and is positioned at the intersection of the wall 7 and roof 11 with the capability to support maintenance workers inside the personnel basket 57. The personnel basket 57 includes a basket-like structure attached by cable to a monorail 59 allowing it to move circumferentially around the containment vessel 3. Maintenance personnel inside the basket can attach the lifting bridle to the eyebolts 51 and perform disengagement, adjustment, and like activities. Referring to FIG. 8, each section 31a of the movable baffle 31 is retained in the up and away position by at least two hinged support devices 53 located on the wall 7. These supports are positioned and hinged so that they fold out of the way as the movable section 31a is raised and may be rotated into position to support the movable section 31a after it is raised. Hinged support devices 53 swing generally horizontally outwardly to support the adjacent baffle segment 31a in a manner similar to a door and are positioned up against the wall 7 when movable sections 31a are being lifted up and away from the containment vessel 3. Each support device 53 is rotated perpendicular to the shield building wall 7 after the movable section 31a is lifted slightly above support devices 53. Movable sections 31a are then slightly lowered onto support devices 53. Support devices 53 may be accessed from the floor 9, as shown in FIG. 1, to rotate the hinged platform devices 53. As best seen in FIG. 9, when the support device 53 is not in use support device 53 is positioned against wall 7 (as illustrated in phantom). To support the movable baffle 31 in the position up and away from the containment vessel 3 (FIG. 1), support device 53 is rotated perpendicular to wall 7. An alternative method of retaining each movable baffle sections 31a up and away from the containment vessel 3 is for the hoisting means 47 (FIG. 4) to maintain the movable baffle means 31 in the up and away position from the containment vessel 3. The method by which the movable baffle sections 31a are moved up and away from the containment vessel 3 allowing access to the outer surface of the containment vessel as desired, is as follows. Referring to FIG. 4, first the personnel basket 57 is lowered to a position adjacent a movable section 31a. A lifting bridle (not shown) is attached to the hoisting means 47 cable. The lifting bridle is lowered to a position near the personnel basket 57 to allow a person inside the personnel basket 57 to grasp the lifting bridle. The lifting bridle is attached to eyebolts 51 on one movable section 31a. The personnel basket 57 is raised to a position so as not to interfere with the lifting of the movable sections 31a. Next, the hoisting means 47 lifts the movable section 31a with the removable section inner plate 40b remaining stationary and the outer plate 40a moving with the movable section 31a. The movable section 31a is maintained in the up and away position by the hoisting means 49. An alternate means of maintaining the baffle sections 31a in the up and away position is by hinged support devices 53 located on the wall 7 of the shield building 1. The hinged support devices 53 are hinged out of the way so that platform devices 53 fold out of the way as the movable section 31a is raised and may be rotated into position to support the movable section 31a after it is raised. The lifting of each movable section 31a is repeated until all sections 31a have been moved and the entire outer surface of containment 3 is accessible. The procedure is reversed to return the movable sections 31a to the normal position.