Patent Description:
Thermal sleeves include an outside diameter (OD) and an inside diameter (ID) and include flanges. Thermal sleeves are subject to wear at the flanges and the OD / ID. It has been observed that thermal sleeves are subject to wear between the upper head and the CRDM penetration housing in a nuclear reactor. This wear has been measured using laser metrology to determine the amount that a particular thermal sleeve has "dropped.

Thermal sleeve flange and OD / ID wear results in recurring maintenance costs. Thermal sleeve failure due to OD / ID wear requires costly repair before a return to power is possible. Wear predictions through Pressurized Water Reactor Owners Group (PWROG) programs can be used to identify which sleeves will need eventual intervention. Proactive elimination of the thermal sleeves can eliminate or greatly delay future thermal sleeve inspections for any type of wear.

A method for removing a worn thermal sleeve and replacing it with a temporary "compressible thermal sleeve" has been developed. The method does not require removal of the CRDM motor assembly from the top side of the reactor head. The method, however, does not address the failure mechanism due to thermal sleeve wear and CRDM penetration housing. Thus, even a compressible thermal sleeve will most likely continue to wear along with the CRDM penetration housing.

In response to operational experience of thermal sleeve wear at a number of nuclear plants there is a clear need for eliminating thermal sleeves used in nuclear reactors. Thermal sleeve flange and / or ID / OD wear have been identified during inspection of nuclear reactors. Moreover, there is a need for replacing the thermal sleeves with extension tubes attached directly to the CRDM penetration housing of the nuclear reactor. Accordingly, there is a strong and repeated need for permanent thermal sleeve replacement to remove the need for multiple, varied thermal sleeve inspections over time.

Document <CIT> discloses a prior art method of replacing a damaged thermal sleeve in a reactor vessel head adapter that connects a control rod drive mechanism to a reactor vessel head.

In one aspect, the present disclosure provides a method for installing an extension tube in a nuclear reactor comprising a control rod drive mechanism (CRDM) housing with a threaded head penetration nozzle and a thermal sleeve disposed therein. The method comprises removing the thermal sleeve from the threaded head penetration nozzle and aligning the extension tube with a threaded end of the threaded head penetration nozzle. The extension tube comprises a threaded end and non-threaded end, the threaded end sized and configured to threadably couple to the threaded head penetration nozzle. The method further comprises threading the threaded end of the extension tube to the threaded end of the threaded head penetration nozzle, torqueing the extension tube to the threaded end of the threaded head penetration nozzle, gauging the alignment of the extension tube relative to the threaded head penetration nozzle, installing retention fillet welds between the extension tube and the threaded end of the threaded head penetration nozzle, and installing a guide funnel to the non-threaded end of the extension tube.

In one aspect, the present disclosure provides a method for installing an extension tube in a nuclear reactor comprising a control rod drive mechanism (CRDM) housing with a non-threaded head penetration nozzle and a thermal sleeve disposed therein. The method comprises removing the thermal sleeve from the non-threaded head penetration nozzle, machining the non-threaded head penetration nozzle of the CRDM housing, installing and aligning a threaded adapter to the machined end of the non-threaded head penetration nozzle of the CRDM housing, joining the threaded adapter to the machined end of the non-threaded head penetration nozzle of the CRDM housing, machining a bore defined by the non-threaded head penetration nozzle of the CRDM housing, machining a bore defined by the threaded adapter, machining an outside diameter of a joint between the machined end of the non-threaded head penetration nozzle of the CRDM housing and the threaded adapter, installing the extension tube to the threaded adapter, and installing retention fillets welds between the extension tube and the threaded adapter.

In addition to the foregoing, various other method and/or system and/or program product aspects are set forth and described in the teachings such as text (e.g., claims and/or detailed description) and/or drawings of the present disclosure.

The foregoing is a summary and thus may contain simplifications, generalizations, inclusions, and/or omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is NOT intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matter described herein will become apparent in the teachings set forth herein.

In one or more various aspects, related systems include but are not limited to circuitry and/or programming for effecting herein-referenced method aspects; the circuitry and/or programming can be virtually any combination of hardware, software, and/or firmware configured to affect the herein-referenced method aspects depending upon the design choices of the system designer. In addition to the foregoing, various other method and / or system aspects are set forth and described in the teachings such as text (e.g., claims and/or detailed description) and/or drawings of the present disclosure.

Further, it is understood that any one or more of the following-described forms, expressions of forms, examples, can be combined with any one or more of the other following-described forms, expressions of forms, and examples.

The novel features of the described forms are set forth with particularity in the appended claims. The described forms, however, both as to organization and methods of operation, may be best understood by reference to the following description, taken in conjunction with the accompanying drawings in which:.

This application is related to <CIT>, titled ANTI-ROTATION ARRANGEMENTS FOR THERMAL SLEEVES.

Before explaining various aspects of methods for eliminating thermal sleeves in nuclear reactors, or more particularly, methods for replacing the thermal sleeves with extension tubes which attach directly to control rod drive mechanism (CRDM) penetration housings of the nuclear reactor in detail, it should be noted that the illustrative aspects are not limited in application or use to the details of construction and arrangement of parts illustrated in the accompanying drawings and description. The illustrative aspects may be implemented or incorporated in other aspects, variations and modifications, and may be practiced or carried out in various ways. Further, unless otherwise indicated, the terms and expressions utilized herein have been chosen for the purpose of describing the illustrative aspects for the convenience of the reader and are not for the purpose of limitation thereof.

In one aspect, the present disclosure is directed, as stated above, to methods for eliminating thermal sleeves in nuclear reactors. In another aspect, the present disclosure is directed to methods for replacing the thermal sleeves with extension tubes which attach directly to CRDM penetration housings of the nuclear reactor. In one aspect, the thermal sleeve can be removed from underneath the reactor vessel closure head (RVCH) using exiting equipment and processes for thermal sleeve removal. An extension tube, which attaches directly to the CRDM penetration housing, is installed. In accordance with one aspect, there are two main components required to eliminate a thermal sleeve. First is the extension tube and second is the upper guide sleeve. The purpose of the upper guide sleeve is to provide the final guidance for the drive rod into the CRDM through the latch stop plate.

Generally speaking, there are two styles of CRDM penetration housings - threaded and non-threaded. Threaded penetrations have a <NUM> (<NUM><NUM>/<NUM>")-<NUM> UN-2A thread. Non-threaded penetrations have a bare tubular end with radii on both the OD and ID to face transitions.

For threaded penetrations, an extension tube may be manufactured to a specific length which would set a funnel height at the same elevation as existing thermal sleeves when threaded on and tightened. For non-threaded penetrations, a penetration nozzle may be welded on to the penetration which would then provide the proper male thread for attaching the extension tube.

A special Compressible Guide Sleeve (CGS) has been designed to provide the same functions that the guide sleeve does on replacement RVCHs and AP1000 pressurized water reactors, for example. The CGS can be installed from underneath the RVCH, along with the extension tube. The present disclosure provides a new and innovative process of retrofitting an extension tube onto an in-service RVCH.

Thermal sleeves that exhibit flange and / or ID / OD wear are suitable candidates for elimination and replacement with extension tubes to eliminate recurring maintenance costs and failures which require costly repairs before a return to power is possible. Wear predictions through PWROG programs can be used to identify which thermal sleeves will need eventual intervention. Proactive elimination combined with engineering justification can eliminate or greatly delay future thermal sleeve inspections for a many types of wear.

<FIG> is a schematic cross-sectional view of an upper portion of a conventional nuclear reactor <NUM> illustrating a portion of a reactor vessel <NUM> penetrated by a plurality of head penetration nozzles <NUM> which extend downward from a CRDM housing <NUM>. <FIG> is a schematic cross-sectional view of a conventional reactor vessel head penetration illustrating a CRDM housing <NUM>, a head penetration nozzle <NUM>, and a thermal sleeve <NUM>. Continuing to refer to <FIG>, as well as to the sectional view of <FIG>, a thermal sleeve <NUM> including a guide funnel <NUM> is positioned within each head penetration nozzle <NUM> beneath each CRDM housing <NUM> such that each guide funnel <NUM> is positioned directly above, and spaced a distance from, a corresponding guide tube <NUM> extending from an upper support plate <NUM> within reactor vessel <NUM>. The thermal sleeve <NUM> is housed within the head penetration nozzle <NUM> within the reactor vessel <NUM> except within region <NUM> (<FIG>) where the thermal sleeve <NUM> is exposed to the reactor coolant.

The current belief is that wear of thermal sleeve <NUM> and head penetration nozzle <NUM> in region <NUM> illustrated in <FIG> and <FIG> results from rotation of the thermal sleeve <NUM> within the head penetration nozzle <NUM> about a central axis <NUM> of the thermal sleeve <NUM>. it is believed that vortices in the reactor coolant flowing within the reactor vessel <NUM> come into contact with the thermal sleeve <NUM> (i.e., in region <NUM>) causing the thermal sleeve <NUM> to rotate about its central axis <NUM> relative to the head penetration nozzle <NUM>.

The present disclosure provides methods for eliminating thermal sleeves <NUM> in a nuclear reactor <NUM> and, more particularly, methods for replacing thermal sleeves <NUM> in a nuclear reactor <NUM> with extension tubes attached directly to a CRDM penetration housing <NUM> of the nuclear reactor <NUM>. These methods squarely fulfill the strong and repeated need for permanent thermal sleeve <NUM> replacement to remove the need for multiple, varied thermal sleeve <NUM> inspections over time.

<FIG> is a section view <NUM> of a thermal sleeve <NUM> and a CDRM housing <NUM> in an un-worn condition. The thermal sleeve <NUM> includes a flange <NUM> defines an outside diameter <NUM> (OD) and an inside diameter <NUM> (ID) that are subject to wear. The thermal sleeve <NUM> is subject to wear between the upper head and the CRDM penetration housing <NUM> in a nuclear reactor.

<FIG> is a section view <NUM> of the thermal sleeve <NUM> and the CDRM housing <NUM> in a substantially worn condition. As discussed above, the thermal sleeve <NUM> shows substantial wear at the flange <NUM> and the OD <NUM> and ID <NUM>. This wear my be manifested by a drop of the thermal sleeve <NUM>.

<FIG> is a section view <NUM> of the thermal sleeve <NUM> and the CDRM housing in a worn condition to the point of thermal sleeve <NUM> separation. As shown, the thermal sleeve <NUM> has developed a crack <NUM> resulting in the separation of the thermal sleeve <NUM>. The section view <NUM> also shows additional wear of the flange <NUM>, OD <NUM>, and ID <NUM> relative to the section view <NUM> shown in <FIG>.

With reference to <FIG>, extension tubes can be retrofitted in a variety of reactor vessel <NUM> (<FIG>) heads which currently have thermal sleeves <NUM> (<FIG>), <NUM> (<FIG>) installed. Typical CRDM penetration designs have either "threaded" or "non-threaded" ends protruding through the reactor vessel <NUM> head. With reference also to <FIG>, an extension tube <NUM> that can be installed in the nuclear reactor <NUM> in place of thermal sleeves <NUM>, <NUM> is shown. The extension tube <NUM> comprises a substantially cylindrical body <NUM> and a threaded end <NUM> that would protrude through the reactor vessel <NUM> head once installed and threadably couple to threaded penetration nozzle. <FIG> illustrates an extension tube <NUM> that can be installed in the nuclear reactor <NUM> in place of thermal sleeves <NUM>, <NUM>. The extension tube <NUM> comprises a substantially cylindrical body <NUM> and a non-threaded end <NUM> that would protrude through the reactor vessel <NUM> head once installed and couple to a non-threaded penetration nozzle by a suitable weld, for example.

<FIG> is a schematic cross-sectional view of an upper portion of a conventional nuclear reactor <NUM> illustrating a portion of a reactor vessel head <NUM> penetrated by a plurality of head penetration nozzles <NUM> which extend downward from a CRDM housing <NUM>. An extension tube <NUM> is coupled to the distal end <NUM> of the head penetration nozzle <NUM>. The distal end <NUM> of the extension tube includes a guide funnel <NUM>. The head penetration nozzles <NUM> include a compressible guide sleeve <NUM>. A threaded penetration adapter <NUM> is coupled between the extension tube <NUM> and the head penetration nozzle <NUM>. In one aspect, the threaded penetration adapter <NUM> is employed for non-threaded penetration nozzles <NUM> in order to facilitate the installation of the extension tube <NUM> on a non-threaded head penetration nozzle <NUM>. The threaded penetration adapter <NUM> is welded to the end of the non-threaded head penetration nozzle <NUM>. Compressible guide sleeves <NUM> are further described in commonly owned patent application number <CIT>, titled THERMAL SLEEVE.

<FIG> is a section view of the threaded penetration adapter <NUM> coupled between the extension tube <NUM> and the head penetration nozzle <NUM>. The threaded penetration adapter <NUM> includes a body <NUM> with an upper end adapted and configured to couple to the non-threaded end of the head penetration nozzle <NUM> and a lower end adapted and configured to couple to the extension tube <NUM>. In one aspect, the upper end of the body <NUM> of the threaded penetration adapter <NUM> may be welded to the non-threaded head penetration nozzle <NUM> at connection <NUM> and the lower end of the threaded adapter body <NUM> may be welded to the extension tube <NUM> at connection <NUM>. In one aspect, the connection <NUM> is a bimetallic weld in the extension tube <NUM> to transition to steel. In various aspects, the threaded penetration adapter <NUM> may include threads to threadably couple to the non-threaded head penetration nozzle <NUM> and / or the extension tube <NUM>, for example.

<FIG> is a section view of a head penetration nozzle <NUM> with the extension tube <NUM>. The head penetration nozzle <NUM> extends downward from a latch housing <NUM> and penetrates the reactor vessel head <NUM>. The latch housing <NUM> contains a CRDM motor <NUM> and a compressible guide sleeve <NUM>. The latch housing <NUM> is coupled to the head penetration nozzle <NUM> via a bimetallic weld <NUM>. The head penetration nozzle <NUM> is coupled to an extension tube <NUM> within the reactor vessel head <NUM> through a threaded penetration adapter <NUM>. The extension tube <NUM> is coupled to a guide funnel <NUM>. As shown in <FIG>, the thermal sleeve in the head penetration nozzle <NUM> has been replaced by the extension tube <NUM>.

<FIG> is a section view of the head penetration nozzle <NUM> located through the reactor vessel head <NUM>. The end of the head penetration nozzle outside the reactor vessel head <NUM> comprises a CRDM head adapter <NUM>. The head penetration nozzle <NUM> defines a space <NUM>, which normally contains a thermal sleeve that is notably missing.

<FIG> is a section view of the head penetration nozzle <NUM> with the extension tube <NUM>. The head penetration nozzle <NUM> is coupled to the extension tube <NUM> via an optional threaded penetration adapter <NUM>. The compressible guide sleeve <NUM>, shown in detail in <FIG>, is normally contained within a space <NUM> defined by the head penetration nozzle <NUM>.

<FIG> is a perspective view of a compressible guide sleeve <NUM>, which is received in the space <NUM> defined by the head penetration nozzle <NUM>, as shown in <FIG>. The compressible guide sleeve <NUM> comprises a three-leaf compressible flex section <NUM> for compressibility and stiffness. In various aspects, the compressible guide sleeve may comprise at least two and more than three compressible sleeves. Each of the leaf compressible flex sections <NUM> includes a flange <NUM> that is positioned within the CRDM housing <NUM>. The compressible guide sleeve <NUM> is installed into the CRDM penetration to facilitate drive rod guidance into the latch housing <NUM> (<FIG>). The bottom end of the compressible guide sleeve <NUM> comprises an alignment feature <NUM>. Existing thermal sleeve elimination modifications in new RVCHs employ a smaller guide sleeve similar to a truncated thermal sleeve. The purpose of the guide sleeve is to provide guidance for the drive rod into the CRDM latch assembly. The compressible guide sleeve <NUM> accomplishes the same function as the guide sleeve and is installed from underneath the reactor vessel head <NUM> (FIGS- <NUM>-<NUM>), after the extension tube <NUM> has been attached to the head penetration nozzle <NUM>. While the design of the compressible guide sleeve <NUM> allows for it to be flexible enough to be installed through the CRDM penetration, it is also stiff ; rigid enough that it requires a specialized fixture to compress the compressible guide sleeve <NUM> prior to installation. This stiffness is sufficient for it to remain in place during all of a nuclear plant's design basis conditions.

The entire extension tube <NUM> installation process occurs underneath the RVCH and requires no modifications or removals of the CRDM and requires no modifications to the upper internal components. Under-the-head installation processes are known and have been developed by the owner of the present application. The replacement of the thermal sleeve with the entire extension tube <NUM> eliminates all future thermal sleeve wear at the installation location. The extension tube <NUM> requires no inspections for wear throughout its life.

<FIG> illustrates an extension tube <NUM> with a guide funnel <NUM> and a threaded penetration adapter <NUM>. in one aspect, the guide funnel <NUM> is collapsible and is configured to fail before CRDM or fuel damage can occur in the event of misalignment during head installation. In one aspect, the threaded penetration adapter <NUM> includes a threaded end with female threads <NUM> to threadably couple to male threads <NUM> (<FIG>) of the head penetration nozzle <NUM> (<FIG>). During the thermal sleeve replacement process, retention fillet welds <NUM> are provided between the threaded penetration adapter <NUM> and the head penetration nozzle <NUM> to stabilize the connection. The threaded penetration adapter <NUM> is coupled to the extension tube <NUM> by a weld <NUM>. The extension tube <NUM> is coupled to the guide funnel <NUM> by retention fillet welds <NUM>.

<FIG> is a process <NUM> for removing a thermal sleeve in need of removal. The process <NUM> will now be described with reference to <FIG> and <FIG>. The thermal sleeve <NUM> (<FIG>), <NUM> (<FIG>) in need of removal is identified <NUM>. The ID of the thermal sleeve <NUM>, <NUM> is flapped and cleaned <NUM>. The electrical discharging machining (EDM) head is installed <NUM> on one section of the thermal sleeve <NUM>, <NUM> and the a series of cuts is performed. Once the series of cuts is completed, the thermal sleeve <NUM>, <NUM> is removed <NUM> and the head penetration nozzle <NUM> is cleaned and inspected <NUM>. The thermal sleeve <NUM>, <NUM> removal is now complete <NUM>.

<FIG> is a process <NUM> for installing a threaded extension tube. The process <NUM> will now be described with reference to <FIG>, <FIG>, and <FIG>. Once the thermal sleeve <NUM>, <NUM> is removed <NUM> the threaded extension tube <NUM> is installed <NUM>. The extension tube <NUM> is torqued <NUM> to the head penetration nozzle <NUM> using a torque tool. The alignment of the extension tube <NUM> is gauged <NUM>. Retention fillet welds <NUM> are installed <NUM>. A compressible guide sleeve <NUM> is installed <NUM> and the alignment of the extension tube <NUM> is finally gauged <NUM>. The installation is now complete and the extension tube <NUM> is in its final installed arrangement <NUM>. Details of the extension tube installation process <NUM> will now be described in more detail.

Still with reference to <FIG>, <FIG> and <FIG> illustrate the process step of installing <NUM> the threaded extension tube <NUM>. As shown in <FIG>, the extension tube <NUM> comprising a threaded penetration adapter <NUM> is aligned with a threaded head penetration nozzle <NUM> extending through the reactor vessel head <NUM>. The threaded head penetration nozzle <NUM> comprises a threaded end <NUM> with male threads <NUM> configured to threadably couple the female threads <NUM> of the threaded end of the threaded penetration adapter <NUM>. As previously discussed, the threaded penetration adapter <NUM> is coupled to the extension tube <NUM> by a weld <NUM>. As shown in <FIG>, the female threads <NUM> of the threaded end of the threaded penetration adapter <NUM> is threadably coupled to the male threads <NUM> of the threaded end <NUM> of the threaded head penetration nozzle <NUM>.

Still with reference to <FIG>, <FIG> and <FIG> illustrate torqueing <NUM> the extension tube <NUM> to the head penetration nozzle <NUM> using a torque tool <NUM>.

Still with reference to <FIG>, <FIG> illustrates the process of gauging <NUM> the extension tube <NUM> alignment after it has been properly torqued <NUM> to the head penetration nozzle <NUM>, where <FIG> is a section view <NUM> of an extension tube <NUM> alignment gauging test, <FIG> is a perspective view of a gauge <NUM> used in the gauging <NUM> process, and <FIG> is a section view of the alignment of a drive rod <NUM> relative to the extension tube <NUM>. The gauge <NUM> is inserted into the guide funnel <NUM>, through the extension tube <NUM>, the head penetration nozzle <NUM>, and into the CRDM housing <NUM>. The gauge <NUM> is rotated to fit into the guide funnel <NUM>. The alignment of the extension tube <NUM> is measured relative to a nominal centerline with a maximum offset permitted from the nominal centerline. Datum A is measured at a point along the extension tube <NUM> and at a first radial offset <NUM> extending radially from the gauge <NUM> located at the end of the extension tube <NUM> near the guide tube <NUM>, a second radial offset <NUM> located within the head penetration nozzle <NUM> just outside the reactor vessel head <NUM>, and a third radial offset <NUM> located inside the CRDM housing <NUM>. The amount of shift relative to datum A is determined at each radial offset <NUM>, <NUM>, <NUM> location. In <FIG>, the alignment of a drive rod <NUM> is shown relative to the inlet of the guide funnel <NUM>.

Once the gauging <NUM> of the extension tube <NUM> alignment, the retention fillet welds <NUM> are installed <NUM>. Still with reference to <FIG>, <FIG> illustrates the retention fillet welds <NUM> installed <NUM> between the threaded end <NUM> of the head penetration nozzle <NUM> and the threaded penetration adapter <NUM> coupled to the extension tube <NUM> by a weld <NUM>.

Following the installation <NUM> of the retention fillet welds <NUM>, the compressible guide sleeve <NUM> is installed <NUM>. Still with reference to <FIG>, <FIG> illustrate the process of installing <NUM> the compressible guide sleeve <NUM>. As shown in <FIG>, the three-leaf compressible flex sections <NUM> of the compressible guide sleeve <NUM> are compressed to contract the flanges <NUM> of the compressible flex sections <NUM> to a size suitable for introducing into the guide funnel <NUM>. <FIG> illustrates a compression tool <NUM> that may be employed to compress the compressible guide sleeve <NUM> prior to inserting the compressible guide sleeve <NUM> into the guide nozzle <NUM>. <FIG> illustrates the compressible guide sleeve <NUM> in its compressed configuration inserted through the head penetration nozzle <NUM> and the CRDM head adapter <NUM> such that the flanges <NUM> of the compressible flex sections <NUM> are positioned just above a counterbore ledge <NUM> defined within the CRDM head adapter <NUM> section of the head penetration nozzle <NUM>. In <FIG> the compressible flex sections <NUM> of the compressible guide sleeve <NUM> are released such that the flanges <NUM> of the compressible flex sections <NUM> engage the counterbore ledge <NUM> defined within the CRDM head adapter <NUM> section of the head penetration nozzle <NUM>. The counterbore ledge <NUM> retains the compressible guide sleeve <NUM> within the CRDM head adapter <NUM> section of the head penetration nozzle <NUM>. <FIG> illustrates the compressible guide sleeve <NUM> in its final installed state. A final gauging <NUM> of the extension tube <NUM> can now be performed.

Still with reference to <FIG>, <FIG> illustrate the final installed arrangement <NUM> of the extension tube <NUM>. <FIG> is a section view of the reactor vessel head <NUM> illustrating the extension tube <NUM> coupled to the head penetration nozzle <NUM> installed inside the reactor vessel head <NUM>. <FIG> is a detailed view of the installed extension tube <NUM> coupled to the head penetration nozzle <NUM> showing the extension tube retention welds <NUM>. <FIG> is a section view of the extension tube <NUM> coupled to the head penetration nozzle <NUM> installed inside the reactor vessel head <NUM>. <FIG> is an elevation view of the extension tube <NUM> coupled to the head penetration nozzle <NUM> installed inside the reactor vessel head <NUM>.

<FIG> illustrates a head penetration nozzle <NUM> with threads <NUM> that are not usable, due to wear, damage, or sizing mismatch. <FIG> is a section view of the head penetration <NUM> nozzle shown in <FIG>. With reference now to <FIG>, <FIG>, and <FIG>, if the male threads <NUM> on the threaded end <NUM> of the CRDM head penetration nozzle <NUM> are not usable, due to wear, damage, or sizing mismatch, in one aspect, a threaded adapter <NUM> may be employed as a contingency. The threaded adapter <NUM> is welded <NUM> below the male threads <NUM> of the head penetration nozzle <NUM>. The threaded adapter <NUM> includes male threads <NUM> suitable for threadably coupling the female thread <NUM> on the threaded adapter <NUM> of the extension tube <NUM>.

The installation of an extension tube <NUM> in the field becomes more complicated at nuclear plants without CRDM housings comprising threaded head penetration nozzles <NUM>. Additional field machining would be required to prepare the non-threaded CRDM housing for welding, as well as perform post-welding cleanup. Design of the extension tube <NUM> remains common between threaded and non-threaded CRDM housings. A process for installing an extension tube <NUM> on a non-threaded CRDM housing is described hereinbelow.

<FIG> is a process <NUM> for installing an extension tube on a non-threaded CRDM housing. With reference also to <FIG>, the process <NUM> begins by machining <NUM> a non-threaded CRDM housing <NUM>. In other words, the CRDM housing <NUM> does not include a threaded head penetration nozzle with a threaded end <NUM> with male threads <NUM> as described with reference to <FIG>. <FIG> is a section view of a non-threaded CRDM housing <NUM> before machining. The machining <NUM> step involves preparing the face <NUM> (<FIG>, premachining) of the non-threaded CRDM housing <NUM> geometry for machine welding and turning-back the ID bore <NUM> of the non-threaded CRDM housing <NUM>. <FIG> is a section view of the non-threaded CRDM housing <NUM> after machining <NUM>. <FIG> is a detail view of the section view of the non-threaded CRDM housing shown in <FIG>. As shown in <FIG>, the face <NUM> (post-machining) of the non-threaded CRDM housing <NUM> is machined back to remove the radii and install the prep weld. <FIG> shows a detailed view of the machined face <NUM> of the non-threaded CRDM housing <NUM>.

<FIG> illustrates a gap <NUM> defined between the machined end face <NUM> of the non-threaded CRDM housing <NUM> and the non-threaded end <NUM> of the threaded adapter <NUM>. With continued reference to <FIG> and with reference also to <FIG> and <FIG>, the next step in the process <NUM> is installing and aligning <NUM> a threaded adapter <NUM> to the machined non-threaded CRDM housing <NUM>. As shown in <FIG>, the threaded adapter <NUM> comprises male threads <NUM> sized and configured to receive the female threads <NUM> of the extension tube <NUM> (See <FIG>, for example) and a non-threaded end <NUM> configured to abut the machined end face <NUM> of the non-threaded CRDM housing <NUM>. The threaded adapter <NUM> also defines a bore <NUM>. As shown in <FIG>, a gap <NUM> is defined between the machined end face <NUM> of the non-threaded CRDM housing <NUM> and the non-threaded end of the threaded adapter <NUM>.

<FIG> illustrates the threaded adapter <NUM> joined to the non-threaded CRDM housing <NUM>. With continued reference to <FIG>, and with reference also to <FIG>, the next step in the process <NUM> is joining <NUM> the threaded adapter <NUM> to the non-threaded CRDM housing <NUM>. In one aspect, the threaded adapter <NUM> is joined <NUM> to the CRDM housing by the a penetration welding technique to form a joint <NUM>. In one aspect, the threaded adapter <NUM> may be joined <NUM> to the non-threaded CRDM housing <NUM> by a full penetration weld that joins <NUM> the threaded adapter <NUM> to the non-threaded CRDM housing <NUM> with no gaps in between the filler material and the roots of the joint <NUM>. In one aspect, the threaded adapter <NUM> may be welded to the non-threaded CRDM housing <NUM> may be performed using a specialized semiautomatic gas tungsten arc welding (GTAW) weld head, for example.

<FIG> illustrates machined bores <NUM>, <NUM> defined by the non-threaded CRDM housing and the threaded adapter. With continued reference to <FIG>, and with reference also to <FIG>, the next step in the process <NUM> is machining <NUM> the bore <NUM> defined by the threaded adapter <NUM> and / or the bore <NUM> defined by the non-threaded CRDM housing <NUM>. This step removes an integral backing ring / alignment ring.

<FIG> illustrates a machined / ground OD <NUM> of the joint <NUM>. With continued reference to <FIG>, and with reference also to <FIG>, the next step in the process <NUM> is machining / grinding <NUM> the OD <NUM> of the joint <NUM>, such as the penetration weld cap, for inspections. <FIG> and <FIG> show the threaded adapter <NUM> attached to the non-threaded CRDM housing <NUM> installed below the reactor vessel head <NUM> and ready to receive the extension tube <NUM>.

<FIG> illustrates the threaded adapter <NUM> of the extension tube <NUM> installed on the threaded adapter attached to the non-threaded CRDM housing from below the reactor vessel head <NUM>. With continued reference to <FIG>, and with reference also to <FIG> and <FIG>, the next step in the process <NUM> is installing the threaded adapter <NUM> of the extension tube <NUM> on the threaded adapter <NUM> attached to the non-threaded CRDM housing from below the reactor vessel head <NUM>. This step includes threading and torqueing the extension tube <NUM> on the threaded adapter <NUM> in manner similar to that described above wit reference to <NUM>-<NUM>.

<FIG> illustrates retention fillet welds <NUM> between the threaded adapter <NUM> of the extension tube <NUM> and the threaded adapter <NUM> of the non-threaded CRDM housing <NUM>. With continued reference to <FIG>, and with reference also to <FIG> and <FIG>, the next step in the process <NUM> is installing <NUM> retention fillet welds <NUM>. The process <NUM> may comprise installing a guide funnel <NUM> as described above with reference to <FIG>, for example. The process <NUM> may further comprise gauging the alignment of the extension tube using the same process described above with reference to <FIG>, for example. The process <NUM> may further comprise installing a compressible guide sleeve <NUM> using the same process described above with reference to <FIG>, for example.

Claim 1:
A method for installing an extension tube (<NUM>) in a nuclear reactor (<NUM>) comprising a control rod drive mechanism, CRDM, housing (<NUM>) with a threaded head penetration nozzle (<NUM>) and a thermal sleeve (<NUM>) disposed therein, the method comprising:
removing the thermal sleeve (<NUM>) from the threaded head penetration nozzle (<NUM>);
aligning the extension tube (<NUM>) with a threaded end (<NUM>) of the threaded head penetration nozzle (<NUM>), the extension tube comprising a threaded end (<NUM>) and non-threaded end, the threaded end (<NUM>) sized and configured to threadably couple to the threaded head penetration nozzle (<NUM>);
threading the threaded end (<NUM>) of the extension tube (<NUM>) to the threaded end (<NUM>) of the threaded head penetration nozzle (<NUM>);
torqueing the extension tube (<NUM>) to the threaded end (<NUM>) of the threaded head penetration nozzle (<NUM>);
gauging the alignment of the extension tube (<NUM>) relative to the threaded head penetration nozzle (<NUM>);
installing retention fillet welds (<NUM>) between the extension tube (<NUM>) and the threaded end (<NUM>) of the threaded head penetration nozzle (<NUM>); and
installing a guide funnel (<NUM>) to the non-threaded end of the extension tube (<NUM>).