Patent Number: 048511854
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 illustrate schematically a portion of a conventional refueling water pool 1 within a tank having concrete side walls 2, 3 and 4 and a concrete bottom wall 5. The pool 1 comprises water, with additives if desired, and the water level 6 is a small distance below the upper surfaces of the side walls 2, 3 and 4. Although not necessary to the invention, FIGS. 1 and 2 illustrate a pair of rails 7 and 8 for supporting a manipulator crane (not shown). FIGS. 1 and 2 also illustrate a radiation emitting reactor component 9, such as the "upper internals" of a nuclear reactor, which have been removed from the reactor and placed in the water pool 1. It will be observed that the upper portion 10 of the component 9 is above the level 6 of the water pool 1, and therefore, there is no water shield around such portion. Even if the water level were raised to the level of the upper surfaces of the side walls 2, 3 and 4, there still would be a portion of the component 9 which is not covered by the water, and normally, the bank is not filled with water to the level of the upper surfaces of the side walls 2, 3 and 4. Accordingly, the unshielded portion 10 emits radiation to which maintenance personnel would be exposed during maintenance, refueling, etc. of a nuclear reactor of the construction described. FIG. 1 also schematically illustrates a crane 11 which is used for removing the reactor cover and for removing components from within the reactor. In accordance with the invention, after the component 9 is removed from the reactor and placed in the water pool 1, a reinforced, inverted vessel 12, which may have the hollow cylindrical shape shown, is lowered over the component 9 until the pool parts 13, 14, 15 and 16 of the supporting structure for the vessel 12 rest on the upper surfaces of the side walls 2 and 4 and the lower rim 17 is immersed in the water pool 1 as shown in FIG. 4. Since the vessel 12 is evacuated in the manner set forth hereinafter, water from the pool 1 enters the vessel 12 and lowers the level of the water pool 1, and the lower rim 17 is immersed in the water pool 1 by an amount sufficient to maintain it immersed therein when the level of the water pool 1 lowers during evacuation of the vessel 12. The dimension of interior diameter of the vessel 12 is greater than the dimension of the exterior diameter of the component 9. The difference between the interior dimension of the vessel 12 and the exterior dimension of the component 9 and the height of the vessel 12 from the lower rim 17 to the end wall 18 thereof are selected so that when the vessel 12 is positioned as shown in FIG. 4, the end wall 19 is spaced from the top 19 of the component 9 and the interior of the vessel 12 is spaced from the exterior of the component 9 by a distance to provide a water covering for the component 9 sufficient to provide the desired shielding of the upper portion 10 of the component 9. For example, the dimensions may be selected so as to provide two feet of water above the top 19 and and two feet of water between the component 9 and the interior of the wall of the vessel 12 when the vessel is evacuated as set forth thereinafter. After the vessel 12 is put in place as illustrated in FIGS. 3 and 4, air is removed from the vessel 12 as illustrated schematically in FIG. 5. Although other types of pumping apparatus may be used to remove air from the vessel 12, a preferred embodiment of the pumping apparatus comprise a pump 20 in the form of a rotary blower driven by an electric motor 21 connected to a motor controller 22. The pump 20 may, for example, be a model 22-U-RAI rotary blower manufactured by the Rods Div. of Dresser Industries, Inc. 900 W. Mount St., Connersville, Ind., and having a 20 cfm capacity at 12.2 psig inlet pressure and be driven by a one horse power motor. The motor controller 22 is connected by a line 22a to a conventional water level detector 23 at the side of the vessel 12 which causes the controller 22 to energize the motor 21 when the water level 24 in the vessel 12 decreases below a desired level and to deenergize the motor 21 when the water level 24 is at the desired level. The intake side of the pump 20 is connected by a pipe 25, a silencer 26, a pipe 27, a check valve 28 and a pipe 29 to the interior of the vessel 12. Except for the opening for the pipe 29 in the end wall 18, and except for the open end thereof which is below the upper surface of the water pool 1, the vessel 12 is gas tight. The pump 20 discharges air and any water which may accompany the air through pipes 30 and 31 and a silencer 32 into the water pool 1. The water level within the vessel 12 may be visually observed by means of a conventional liquid level indicating means in the form of a glass sight tube 33 attached to a side wall of the vessel 12 and connected for fluid flow to the interior of the vessel 12. It will be apparent that the vessel 12 acts as a "Bell" jar in that when air is exhausted from within the vessel 12, water from the pool 1 will flow into the interior of the vessel 12 and provide a water surface level 24 within the vessel 12 which is above the water surface level 6 in the water pool 1. Thus, after the vessel 12 is positioned as illustrated in FIG. 4 and the pump 20 is operated, the water surface level within the vessel 12 can be raised to the lower surface of the bottom wall 18, but normally, it will be raised only by an amount sufficient to provide the desired shielding of the top 19 of the component 9 and will be spaced from the lower surface of the end wall 18. For example, to raise the water surface level in the vessel 4.6 ft. above the water surface level 6 in the pool 1 requires a vacuum in the vessel of only -2 p.s.i. However, because of the pressures exerted on the walls of the vessel 12 when it is evacuated and because of handling and lifting forces involved, it is necessary that the vessel 12 be reinforced and that the walls thereof be supported if the thickness of such walls is to be kept to an acceptable value. One design of such a vessel 12 and its supports for shielding a component 9 having a diameter of approximately 10 ft. and extending above the pool water level 6 by approximately 16 in. is illustrated in FIGS. 3 and 4. The vessel 12 has a side wall 34 in the form of a hollow cylinder having an outside diameter of 14 ft., a thickness of 1/4 in. and a height of 51/2 ft. The end wall 18 has a thickness of 3/8 in., and preferably, the side wall 34 and the end wall are made from stainless steel. The end wall 18 and the side wall 34 are welded together in a conventional and air tight manner, and the side wall 34 is internally reinforced by three stainless steel stiffening rings 35, 36 and 37 which are welded to the side wall 34 and which, for example, can be a W4.times.8.44 stainless steel structural member. The end wall 18 is reinforced with respect to buckling by four I-beams 38-41 preferably, of stainless steel, which can be welded on their lower flanges to the end wall 18 and secured to carbon steel main suspending beams 42 and 43 which are secured at their ends to legs 44-47. The main beams 42 and 43 are laterally braced by L-shaped structural members 48-52 of carbon steel. The supporting legs 44-47 are braced by L-shaped carbon steel braces, such as the braces 53 and 54 (FIG. 4), which are secured at their ends to the main beams and the legs respectively. The various structural members can be of the following characteristics. Members 38-41--W12.times.26 structural members-stainless steel PA0 Main beams 42, 43--W21.times.50 structural members-carbon steel PA0 Legs 44-47--W10.times.22 structural members-carbon steel PA0 Lateral members 48-52--31/2".times.31/2".times.1/4 structural members-carbon steel PA0 Leg braces 53, 54--31/2.times.31/2".times.1/4 structural members-carbon steel As shown in FIG. 3, the motor 21 and the pump 20 may be mounted on a support plate 55 secured to the end wall 18. When it is desired to lower the level of the water in the vessel 12 for the removal of vessel 12 and the component 9, the motor 21 is deenergized, and a vent valve 56 (FIG. 5), which can be a one inch valve and which is connected to the pipe 29 by a pipe 57, is opened to permit air to enter into the upper part of the vessel 12. Although preferred embodiments of the present invention have been described and illustrated, it will be apparent to those skilled in the art that various modifications may be made without departing from the principles of the invention.