Patent Number: 
Section: description

FIG. 1 shows a RPV 10 that has been retrofitted for practicing the present invention in an ice condenser plant. It is noted that FIG. 1 shows the structures and components of plant out of scale and proportion for ease of illustration. The RPV 10 is located in a reactor cavity 12 and has a head assembly 14 extending upwardly into a tight compartment 16 located at the end of a refueling canal. The head assembly 14 generally includes a RPV closure head 20, a plurality of CRDM assemblies (represented by CRDM 22), a seismic support platform 24 for laterally supporting the CRDMs 22, a CRDM cooling shroud 26 surrounding the CRDMs 22 and extending from the RPV closure head 20 to the seismic support platform 24 and a plenum 28. During power operations, a concrete missile shield 30(shown in phantom) will be removably supported independently of the head assembly 14 at about the level of the plant""s operating deck 31 over the head assembly 14. The RPV closure head 20 shown in FIG. 1 is bolted to the RPV 10 on studs 32. Also, the head 20 is covered with head insulation 34. The CRDM cooling shroud 26 shown in FIG. 1 includes an original CRDM cooling shroud 40 (or a replacement panel), which may be supported by the closure head 20 via a support ring 42 or other suitable means. The cooling shroud of an existing ice condenser plant extends from the support ring 42 to a terminal end 44 spaced from the seismic support platform 24. The retrofitted CRDM cooling shroud 26 includes one or more shroud extension panels 46 supported by the lower panel 40 and extending to the bottom of the seismic support platform 24. Each extension panel 46 may be fabricated of from one or more sections. For example, each section could be fabricated of three 120xc2x0 arcuate sections which are welded or otherwise suitably jointed together. The lower panel 40 of the CRDM cooling shroud 26 may have one or more inlet air nozzles or ports 48 for introducing cooling air from the general atmosphere in the compartment 16 into the CRDM shroud 26. The air ports 48 are preferably located below the CRDM electromagnetic coils (not shown). The air nozzles or ports 48 may have a rectangular, circular or other regular or irregular cross-section. The seismic support 24 may have a circumferential track 49 for supporting a movable hoist (not shown) for supporting a stud tensioner (not shown). A stud tensioner may be employed to tension and/or detension the RPV nuts 50 which seal the RPV closure head 20 against the RPV 10 during power operations at pressures of up to 2250 psi or more and temperatures of up to 650xc2x0 F. or more. The seismic support platform 24 is supported by. lift rods 52 bolted to mounts 54 on the closure head 20. The seismic support platform 24 has lift connections or lugs 56 that connect with a detachable lift rig such as lifting tripod 58 having stabilizers 60. The lift rig 58 also has a lift eye 62 that may be engaged by an overhead polar crane (not shown) for removing and replacing the head assembly 14 as a unit. In an ice condenser plant, a cable tray or bridge (not shown) may be employed for supporting CRDM cables, control rod position indicator cables, thermocouple lines and electrical lines (not shown)between the seismic support plate 24 and the walls of the RPV compartment 16. The seismic support platform 24 will have internal apertured spacer plates (not shown) for laterally supporting the upper ends of the CRDMs 22. The aperatures are sized to provide a total cross sectional area sufficient to permit the cooling air to flow through the seismic support platform 24 at acceptable pressure drops. Struts (not shown) will extend horizontally from the seismic support platform 24 to the walls of the RPV cavity 16 to horizontally stabilize the seismic support platform 24. The plenum 28 is mounted on top of the seismic support platform 24. The plenum 28 must fit between the seismic support platform 24 and the missile shield 30 during power operations. Also, the plenum 28 must not interfere with the assembly of the lift rig 58 or its stabilizers 60 during refueling operations. A plurality of spool pieces 70 are connected between the plenum 28 and the ductwork 72 of the ventilation system 74. As is shown in FIG. 1, each spool piece 70 has a first end 80 connected with the plenum 28 such that there is a lifting lug 56 between each of the connections with the first ends 80. Also, each spool piece 70 has a second end 82 connected adjacent the seismic support plate 24 to the existing ductwork 72 via a union 84. FIG. 1 also shows a retrofitted ventilation system 74 including a ventilation fan 86 for pulling heated air from the plenum 28 and blowing the air through a heat exchanger 88 and discharging the air to the general atmosphere of the containment building. Alternatively, the heat exchanger 88 may be located upstream of the ventilation fan 86. In addition to retrofitting the integrated head assembly 14 in an existing ice condenser plant, the flow of cooling air through the ventilation system 74 must be reversed to provide the direction of flow shown in FIG. 1. FIG. 2 illustrates an existing ice condenser plant prior to a modification in accordance with the present invention. The RPV head 20 has a cooling shroud 40 with a terminal end 44 spaced from its seismic support platform 24, which opens the terminal end 44 and CRDMs 22 to the local atmosphere in the RPV compartment 16. The shroud 40 also has a plurality of air ports 89 connected (via ductwork 90 and unions 84) with the plant ductwork 72 extending to a plant ventilation system 74, for directing air from the general atmosphere in the containment building into the shroud 40 to cool the CRDMs 22. In the preferred practice of the present invention, the portion of the ductwork 90 extending below the seismic support plate 56 between the RPV head 20 and the existing ductwork 72 is replaced by a removable spool piece 70. As is illustrated by FIG. 1, spool pieces 70 preferably extend from a plenum 28 mounted on the seismic support plate 24 to the ductwork 72 via the unions 84. Thus, in the practice of the present invention, an existing RPV integrated head assembly 14 in an ice condenser plant may be retrofitted by: removing the portions of the ductwork 72 (illustrated in phantom by ductwork 90) that originally extended below the unions 84 to outlets adjacent the original cooling shroud panel 40; employing extension panels 52 to extend the existing CRDM cooling shroud 40 to the seismic support platform 24; mounting the plenum 28 on the seismic support platform 24 in air flow communication with interior portion of the extended CRDM cooling shroud 26; and connecting one end 80 of the removable spool pieces 70 to the plenum 28 and connecting the second end 82 of the removable spool pieces 70 to the ductwork 72 adjacent to the seismic support platform 24. Advantageously, in the course of a later refueling operation, personnel working from the operating deck can safely remove the RPV integrated head 14 with reduced exposure to radiation. Also, no scaffolding is required for assembly and disassembly of the spool pieces with the result of increased safety and reduced costs. Finally, the spool pieces 70 may remain with the integrated head assembly 14 during its removal. While a present preferred embodiment of the present invention has been shown and described, it is to be understood that the invention may be otherwise variously embodied within the scope of the following claims of invention.