Patent Number: 055132278
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nozzles assemblies and more specifically to nozzle assemblies which enable quick and easy connection/disconnection in cramped and hazardous environments such as encountered in nuclear reactors. 2. Description of the Prior Art It is essential that a hermetic, radiation proof, seal be maintained between the interior and exterior of a pressure vessel such as a nuclear reactor. It is also necessary to monitor the operations of a reactor using In-Core Instruments (ICI). However, this latter requirement necessitates the provision of nozzles through which the instruments can be sealingly introduced into the core. Examples of such arrangements are shown in U.S. Pat. No. 4,723,795 issued on Feb. 9, 1988 in the name of Shenoy and U.S. Pat. No. 4,655,483 issued on April 7, 1987 in the name of Margotta. These documents disclose techniques for providing fluid tight connections between a nozzle and a column which is concentrically supported within the nozzle. FIG. 1 shows a less preferred embodiment of the type of nozzle to which the present invention pertains. This arrangement is such as to provide a fluid-tight, radiation proof, seal for a plurality of ICI (In Core Instruments) and allows the operative connection with external controls and monitoring arrangements. This arrangement features the use of a GRAYLOC hub 10 which is clamped securely to a GRAYLOC flange 12 formed at the upper end of an ICI nozzle 14. However, with this arrangement when it is required to disassemble the same, the GRAYLOC clamp 16 is unbolted and each individual ICI nut 18 is then removed and the individual ICIs are then clustered together under a bullet nose. The above-mentioned GRAYLOC hub and GRAYLOC clamp are products of the Gray Tool Company, Houston, Texas. FIGS. 7 and 8 are sectional views of the two main styles of conventional ICI flanges currently in use at nuclear power plants. Typically, there are 6 to 10 ICI flanges on the reactor vessel closure head, each of which houses up to six ICIs. FIG. 7 shows a standard bolted flange assembly 200 mounted to a closure head nozzle 201 of a reactor head. The standard bolted flange assembly 200 includes a mating flange 202 having a plurality of circumferentially-spaced holes for receiving nut and bolt assemblies 203. A flexitallic gasket 204 is fitted between the mating flange 202 and the closure head nozzle 201 to effect a fluid-tight, radiation proof seal. A plurality of ICI assemblies 205 are mounted to the mating flange 202 and secured in place with drive nuts 206. Gaskets 207 ensure a fluid and radiation tight seal between the ICI assemblies 205 and the mating flange 202. During refueling and servicing of a reactor plant using the standard bolted flange assemblies 200, the nut and bolt assemblies 203 and each of the individual ICI nuts 206, along with the respective seals 204 and 207, must be removed. The ICI assemblies must be removed from the mating flange 202 regardless of whether the ICIs are scheduled to be replaced since the lower portions of the ICI assemblies 205 disposed within the pressure vessel remain in place while the closure head (not shown), along with the nozzles 201, is lifted off of the pressure vessel. The mating flange 202 is typically very heavy and unwieldy requiring two or more people to manipulate. Accordingly, this arrangement requires a significant amount of time and effort to disassemble and reassemble each time the head of the reactor is removed. The other type of conventional flange assembly is the GRAYLOC flange assembly shown in FIG. 8. This assembly includes a GRAYLOC hub 210 positioned over the opening of the closure head nozzle 211. The closure head nozzle 211 includes a GRAYLOC flange 212 which is clamped securely to the hub 210 by a GRAYLOC clamp 213. A metal GRAYLOC seal ring 214 is positioned between the GRAYLOC flange 212 and the hub 210. The GRAYLOC clamp 213 includes a pair of large matching clamshell clamps secured together with four stud and nut sets inserted through holes 215. The ICI assemblies 216 are secured to the GRAYLOC hub 210 by drive nuts 217 and are sealed against leakage by GRAFOIL gaskets 218 which are compressed by torquing the drive nuts 217 to a high value. During refueling and servicing of a reactor with the conventional GRAYLOC flange assembly, it is necessary to unbolt and remove the GRAYLOC clamps 213 prior to lifting the ICI assembly from the closure head nozzle 211. As with the embodiment of FIG. 7, each of the individual ICI nuts 217, along with the seals 218, are removed from the hub 210 regardless of whether the ICIs are scheduled to be replaced. The GRAYLOC hub 210 and clamps 213 are quite heavy and difficult to maneuver over the comparatively delicate instrumentation. This operation requires two or more people to complete. The clamps and stud and nut sets require a significant amount of work to manipulate, and the drive nuts 217 at each of the ICI locations require substantial torque to effect a seal. The above-described conventional flange assemblies have significant drawbacks in that the disassembly process is both labor intensive and time consuming. The disassembly process is especially tedious because it is carried out in very cramped conditions and in a radioactive environment. Accordingly, the operators are required to wear protective suiting and must be careful to monitor the amount of time for which they are exposed to the radiation. Therefore, there is a need for an arrangement which can reduce both the effort and time required to achieve the disassembly of an ICI nozzle which is carried out each time a refueling or instrument change is required, in order to reduce the reactor down time and, more importantly, to reduce the health risks associated with working in the above mentioned hazardous environment. SUMMARY OF THE INVENTION It is an object of the present invention to provide a nozzle assembly for use with nuclear reactors and the like type of pressure vessels, which nozzle design enables very quick disassembly and which reduces the difficulty and amount of physical effort required for disassembly. Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the appended claims. To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the device of a first embodiment of this invention may comprise a seal arrangement which features a modified GRAYLOC hub in which a stepped bore receives a grafoil seal arrangement and a retaining nut which presses the grafoil seal into engagement with an inner wall portion of the hub and outer wall portion of an ICI (in core instrument) supporting column. A loading ring is threaded onto a portion of the column. Bolts associated with the ring are screwed down onto a belleville washer which is disposed between the loading ring and the top of the retaining nut for maintaining a desired amount of load on the seals irrespective of thermal variations. More specifically, a first aspect of the invention includes a device which features a hub which is clamped to a flange formed on the upper end of a nozzle in a manner to establish a hermetic seal between the hub and the flange, the hub being formed with a stepped bore therein through which a column member extends; seal means disposed in the bore about the column member; a retaining nut threadedly received in the stepped bore, the retaining nut being adapted to press the seal means into sealing engagement with a wall portion of the stepped bore and a wall portion column member which is located within the stepped bore in a manner which establishes a hermetic seal between the hub and the column member; a resilient washer disposed on the upper side of the retaining nut; and an annular load ring which is threadedly received on a portion of the column, the load having a plurality of through holes in which bolts are threadedly received for adjusting the pressure applied by the resilient washer to the top of the retainer nut. A second aspect of the present invention includes a sealing arrangement for a device having a nozzle portion and a column member disposed through the nozzle portion, which features: a hub which is clamped to a flange formed on the upper end of the nozzle in manner to establish a hermetic seal between the hub and the flange, the hub being formed with a stepped bore through which the column member extends; seal means disposed in the bore about the column member, the seal being supported by a seal carrier; a retaining nut threadedly received in the stepped bore, the retaining nut being adapted to press the seal into sealing engagement with a wall portion of the stepped bore and a wall portion column member which is located within the stepped bore in a manner which establishes a hermetic seal between the hub and the column member; and an annular load ring which is threadedly received on a portion of the column, the load ring including means for selectively applying a force to the top of the retainer nut. A third aspect of the present invention includes a nuclear reactor including an in-core-instrument, a head which is lifted when the reactor is refuelled, and a nozzle arrangement which includes a column arrangement through which the in-core-instrument is disposed, the nozzle comprising: a GRAYLOC flange which is associated with the nozzle; a GRAYLOC hub releasably connected to the GRAYLOC flange; a stepped bore formed in the GRAYLOC hub through which the column arrangement is disposed; a grafoil seal arrangement disposed in the stepped bore; a retaining nut which is threadedly received in the stepped bore and which can apply a pressure to the grafoil seal arrangement; and loading means threadedly received on the column arrangement for applying pressure on the retaining nut. A further aspect of the invention comes in that the arrangement set forth above further features: an elastomeric spacer which can be inserted into the stepped bore when the retaining nut is removed, the elastomeric spacer protecting threads which are formed on the wall of the stepped bore and engaging the external wall of a bullet shaped cover which is placed over the top of the column arrangement when the nuclear reactor is conditioned for a predetermined operation. In accordance with a second embodiment of the present invention, the device may comprise a nozzle assembly for use with a sealed containment vessel, such as a nuclear reactor. The nozzle assembly includes a hub clamped to a flange formed on the upper end of a nozzle in a manner to establish a hermetic seal between the hub and the flange, the hub being formed with a stepped bore therein. A plug member extends through the stepped bore in the hub. A seal member is disposed in the bore about the plug member for creating a seal between the plug member and the hub. A compression collar is disposed about the plug member, the compression collar having a first end adapted to engage and press the seal member into sealing engagement with the stepped bore, a second end opposite the first end, and a flange intermediate the first and second ends. A retaining nut is threaded onto the hub, the retaining nut having a retaining portion engaging the flange of the compression collar to maintain the collar in pressing engagement with the seal means to create a hermetic seal between the hub and the plug member. In the preferred embodiment, the second end of the compression collar extends outside the retaining nut such that the collar can be engaged and compressed by an external source, such as a hydraulic loading tool, prior to threading the retaining nut onto the hub. The plug member includes a plurality of bores extending therethrough, and a plurality of instrument guide tubes extending through the bores in the plug member, the guide tubes being hermetically sealed to the plug member. The preferred embodiment also includes a seal carrier disposed in the bore of the hub about the plug member, and at least one graphite containing sealing member carried by the seal carrier. The seal carrier includes a plurality of J-shaped slots to facilitate installation and removal of the seal member. In a further aspect of the second embodiment of the present invention, in accordance with its objects and purposes, the device hereof may also comprise a nuclear reactor including an in-core-instrument, a head which is lifted when the reactor is refuelled, a nozzle through which the in-core-instrument is disposed, and a nozzle arrangement as described above. The nozzle arrangement includes a compression collar disposed about the plug member, the compression collar having a first end for engaging and pressing the seal member into sealing relationship with the hub and the plug member, a second end opposite the first end, and an abutment flange intermediate the first and second ends. A retaining nut is threadedly received on the hub and engages the abutment flange on the compression collar to retain the collar in pressing engagement with the seal member. It is also preferred that the second end of the compression collar extends outside the retaining nut such that the collar can be engaged and compressed by an external source, such as a hydraulic loading tool, while threading the retaining nut onto the hub. The plug member includes a stepped portion for receiving the seal member, the stepped portion engaging the seal means to provide a self-sealing tendency when the reactor is pressurized. In accordance with a further aspect of the second embodiment of the present invention, a bullet nose is provided for creating a sealed chamber about the instrument guide tubes above the plug member during refueling of the reactor, the bullet nose having an upper tapered end and a lower end for sealing engagement with the plug member. The bullet nose and the plug member both have a smaller diameter than the stepped bore formed in the hub so that the head can be lifted up over the bullet nose and plug member when refueling. In accordance with a further aspect of the second embodiment of the present invention, a loading tool is provided for engaging and compressing the compression collar while threading the retaining nut onto the hub. The loading tool comprises a tool block for engaging the compression collar and a plurality of load arms connected between the tool block and the reactor. The tool block includes pistons for receiving fluid pressure for creating a load on the compression collar while threading the retaining nut onto the hub. In a further aspect of the second embodiment of the present invention, the invention may comprise a method of connecting an instrument assembly to a nozzle opening of a sealed containment vessel. The method includes the steps of: providing a seal plug assembly with at least one instrument guide tube extending therethrough; inserting the seal plug assembly into a hub of the nozzle opening so that the instrument guide tube extends into the sealed vessel; placing a compression collar about the seal plug assembly; compressing the compression collar to form a seal between the seal plug assembly and the hub of the nozzle opening; and threading a hold down nut onto the hub of the nozzle opening after the compression collar is compressed so as to engage and maintain compression in the compression collar. In the preferred method, the step of compressing the compression collar comprises engaging a first portion of the compression collar with a hydraulic compression tool. The step of threading the hold down nut comprises engaging a second portion of the compression collar with the hold down nut while the compression collar is being compressed by the hydraulic compression tool.