Attachment B TCT Replacement Procedure.docx

Conceptual Procedure to remove and replace NIST Thermal Column Tank (TCT)

Revision E

Paul Brand/Paul Liposky

02/24/2023

This procedure is intended to serve as input for a sophisticated engineering process. It is the sublimation of several years of engineering analysis by engineers from the NCNR. It should not be considered a specification, because this procedure is anticipated to materially change during the execution of the contract that is the result of this procurement.

1. Existing Condition The TCT that is currently positioned in the Thermal Column tunnel of the NBSR is leaking water at several locations, notably at the surface facing the reactor (probably at a failing weld). The horizontal location of the leak is not known.

The TCT is bolted to the NBSR reactor frame with 56 AL-7075-T6 bolts.

When the reactor is operating, the TCT is exposed to gaseous CO2. When CO2 comes in contact with water leaking from the TCT, carbonic acid is formed, which is expected to further attack the outside surface of the TCT.

A replacement tank is available. It needs two minor modifications to allow helium blanket gas to enter and leave the TCT while it is being operated. These features were omitted when the replacement TCT was fabricated.

A history and design description of the TCT is available in the Background statement of the Statement of Work.

Purpose To remove the present TCT and replace it with a new one.

Procedure Mini-Mobilization (has been procured under separate contract and can be executed otherwise uncoordinated with the present contract).

Remove Thermal Column Door and set aside Remove Graphite Blocks that fill tunnel cavity between Thermal Column Door and TCT and set aside.

Remove steel shields lining the top and both sides of the of the Thermal Column tunnel cavity Remove triangular filler blocks that fill the V-grooves in which the TCT bronze feet can slide, and which fix 5 degrees of freedom of the TCT. The only operable degree of freedom of the TCT is its position along the horizontal axis of these V-groove slides.

Perform Laser Scan of cavity with TCT in place. V-grooves provide a datum for any dimensional decisions (in addition to the bolt pattern and the assumed perpendicularity of the TCT south surface to the V-groove axis).

Put everything back together.

Final Mobilization (will not happen – or at least will be postponed) if Mini-Mobilization indicates that TCT has no clear path out of TCT cavity).

Remove Thermal Column Door and set aside.

Remove Graphite blocks Remove steel shields lining the top and both sides of the of the Thermal Column tunnel cavity Remove triangular filler blocks that fill the V-grooves.

Remove the helium gas lines on the left and rightmost top of the TCT. Make sure no remaining plumbing parts interfere with the TCT moving back and forth in the V-grooves.

Remove the covers of the flanged elbows that connect the TCT to its cooling pump system and the flanged elbows themselves.

In the following this procedure defines two shielding monoliths that also serve as the transport mechanism for the old and new TCT’s. They are identified as Tools 1 and 25 further down in the procedure, where they will also be further defined. They both have V-groove features in them that need to be properly aligned with the V-grooves in the floor mounting surface of the TCT. At this point Tools 1, and 25 need to be internally adjusted to provide this alignment. It is desirable to have the V-grooves in Tool 1 be aligned a bit below the V-grooves in the mounting surface, whereas the V-grooves in Tool 25 should be aligned a bit above the V-grooves in the mounting surface. Access holes through the back of these tools should allow for large feeler gauges to sense for proper alignment. CCTV could be helpful here as well.

At this point we are ready for the actual removal of the TCT. A Shielding monolith made of steel with a hole pattern that is equal to that of the TCT is moved into the position of the Thermal Shield Door. Each fastener of the TCT is now directly accessible through one of the holes. This shielding monolith will be referred to as Tool 1. Further features of Tool 1 are:

Tool 1 rides on wheels, just like the Thermal Shield Door. Wheel can be electrically driven so that Tool 1 can be moved back and forth from a remote location.

Tool 1 has alignment features that allow it to rock backward by 1 or 2 degrees.

There is extra clearance to allow for the alignment features to be exercised.

The hole pattern consists of 56 THRU holes that are 1.25” in diameter.

On the outside surface of Tool 1 bronze shoulder bearings are inserted.

There are additional holes and features on Tool that allow access into the tunnel cavity with flexible camera’s Further features of Tool 1 might be derived from form, fit and function descriptions of tooling in the remainder of this procedure.

Use an extended 3/8” hex tool to try to remove 56 bolts from the TCT. This Tool is named Tool 2 and consists of a short extension of a 3/8” Hex key from a 1” diameter steel rod. Tool 2 is long enough to reach outside Tool 1, while engaged with the TCT bolts. Tool 2 is equipped with an outside 7/8” Hex that allows an impact wrench to be engaged. As a result of this action there are three possibilities, two of which are contingencies for which tooling will be prepared prior to mobilization.

The 56 bolts come loose without further work. This the preferred outcome. Mark associated holes for insertion of regular ½-13 fastener with 1” thread engagement. Note that the present fasteners are manufactured for 2” thread engagement.

[CONTINGENCY FOR WHICH TOOLING WILL BE PREPARED BEFORE MOBILIZATION] Bolt snaps on its threaded section, which extends over 2.25” from the bolt end. Because the bolt is engaged with the mounting surface where the TCT meets the Reactor Frame, there is only a .25” length where the bolt can snap. We will define a series of tools that is designed to cope with this situation.

Use ¼”, 5/16”, 3/8”, 7/16” and 19/32” drills mounted into a 1” rod to drill out the remaining part of the snapped off bolt until just inside the mounting surface. These tools are coded Tool 3, 4, 5, 6, and 7 respectively. They are designed with a hard stop of 1” diameter that prevents the tools from going too deep because the 1” diameter cannot enter the counterbore cavity of the TCT. The drills (with the exception of Tool 7 are mounted on a 19/32” diameter shoulder and protrude the minimal amount from the 19/32 DIA to provide a much stiffness as possible to prevent the drills from wandering. Note that 19/32” is the size of the clearance holes for the ½”-13 fasteners for the TCT.

There is now a remaining ½”-13 AL 7075-T6 threaded stub present in the steel mounting surface of the TCT. Using Tools 8, which is 5/16” drill mounted on a 1” DIA rod that is shouldered down to 19/32” DIA over a length that allows the 1” diameter to act like a hard stop, while the drill enters the Al 7075-T6 stub fully penetrating it (about 2”). Note that 5/16” is the tap drill size for a 3/8-16 thread.

The 5/16” drilled hole is now tapped 3/8-16 using Tool 9, which is a 3/8”-16 tap attached to a 1” rod that is shouldered down to 19/32 over a length such that the 1” DIA functions as a stop for stopping the tapping operation at a fully threaded depth of 1.5”. The function of the stub left in the mounting surface now acts as a threaded insert.

Once the 3/8”-16 hole is tapped notice has to be taken of the position of this hole and that eventually a 3/8”-16 bolt (with only 1” thread engagement) needs to be reserved for this hole position instead of a ½”-13 bolt. The 3/8”-16 bolt is fabricated by modifying a ½”13 bolt, so the shank diameter remains constant.

[CONTINGENCY OF WHICH TOOLING WILL BE PREPARED BEFORE MOBILIZATION] Inside hexagon of Al 7075-T6 rounds out before the bolt snaps and or comes loose.

Drill 0.438” into remainder of cap screw head to about 3/8 deep. This is done with Tool 10, which is a .438” bit protruding from a 1” extension rod, where the 1” diameter acts as a stop limiting the hole in the bolt from going deeper than 3/8”.

Tool 11 is a #5 center drill mounted on a 1” DIA rod, which follows the .438” pilot into the shank of the bolt for a total depth of about 0.75”.

Tool 12 is a 9/16 drill mounted on a 1” DIA Rod. Tool 12 is used to remove the head of the damaged bolt. Drill in no more than .625 keeping the center hole that was drilled using Tool 11 alive.

Use Tool 13 to drill a 5/16 tap drill in the Al 7075 -T6 bolt shank. Drill protrusion to be designed such that drill depth does not exceed 1.5” Tap using Tool 14, which is a 3/8”-16 UNC LH tap (set?) to the bottom of the 5/16” hole.

Insert 3/8-16 UNC-LH 1” LG bolt in threaded hole and fasten using Tool 15, which is 5/16” Hex tool attached to 1” rod, until bolt head is seated on top of ½”-13 AL 7075 T6 bolt shank. Clearance hole dimension is such that 3/8” bolt clears the 19/32” clearance hole.

Continue applying torque until ½”-13 UNC bolt snaps at the threaded section that is not engaged in the mounting surface. Calculations have shown that the ½”-13 shank that is THRU drilled with a 3/8 hole and thus forms a ½” tube with 1/16” wall thickness can support sufficient torque to snap the ½” UNC bolt at the minor thread diameter. This is counterintuitive and has to be tested prior to mobilization.

Continue as in the previous contingency.

Once all 56 bolts have been removed select 4 mounting holes to be opened up to 21/32”, which is the tap hole size for ¾-10 UNC. Use Tool 16, which is 21/32” drill protruding about 3” from 1” rod.

Tap 4 mounting holes ¾”-10 UNC using Tool 17, which is ¾”-10 UNC tap mounted on 1” rod. Make sure tapped depth is at least 1.25”.

Remove temporary Thermals Cooling Door and perform a thorough cleanout of all the chips and bolt remains that have been produced in the procedure thus far.

Insert 4 x ¾”-10 UNC threaded rod in the four tapped holes and install ¾” 10 nut against bronze surface of replacement TCT door (Tool 1). Install ¾” washers if needed to provide proper bearing surface. Threaded rod + washer + nut forms Tool 18.

Withdraw TCT towards replacement Thermal Column Door and mount using 4 x Tool 18.

Cut Tool 18 flush with the holding nuts (4x) Withdraw Assembly of Thermal Cooling Door and Old TCT a couple of inches away from the Reactor. Mount Clamshell pair (Tool 19) around TCT and fasten using features on Thermal Column Door and Clamshells. Use portal crane (Tool 20) that straddles the Thermal Column Tunnel Cavity to bring Clamshell pair (Tool 19) in place.

Repeat previous steps until TCT is fully out and fully covered. It has yet to be determined how many pairs of clamshells are involved in this part of the procedure.

Cover the growing shield with a final clamshell that acts as a front cover for the entire assembly, which now assumes the function of cask. (Tool 21) Withdraw cask a couple more inches and place a shield in front of the Thermal Shield Tunnel (Tool 22).

Withdraw cask further and place more shielding (two more instances of Tool 22). Note that Tool(s) 22 allow for camera entry so that a CCTV inspection of the Thermal Shield Tunnel can be made. We will be on the lookout for remains of molten lead and inspect the quality of the TCT mounting surface as well as perform a general inspection of the integrity of the reactor vessel (on the part that has now been made visible). Tool 22 also allows for entry of minor tools that allow the mounting surface to be cleaned of gasket remains (if necessary).

Cask is transported to final resting place (decision pending as to where).

Clean mounting surface using scraping or grinding tools (Tools 23, 24) though small openings in Tool(s) 22 (we need a solution to get rid of any debris created during this operation, which is made difficult because of the fact that the TCT is no longer there: assume remote vacuum cleaning under CCTV).

Mount new TCT on V-Grooves of the second instance of Temporary Thermal Column Door (Tool 25, which looks a lot like Tool 1, with vertical channels instead of pockets for the plumbing flanges, which is supposed to reduce the risk to those flanges during pre-assembly). Use expanding anchor bolt (Tool 26). Drive Door/TCT assembly towards Tools 22 and remove them one by one, further inching the assembly toward the TCT cavity.

Use internal alignment mechanisms to align v-grooves of Tool 25 and TCT mounting floor. Perhaps this step should take place before the old TCT is removed, so one has the benefit of shielding by the TCT.

Insert push rods (Tool 27), which react against clips mounted on Tool 25.

Disengage Tool 26 and use Tool 27 to push TCT towards Reactor.

Insert appropriate Bolts in appropriate holes (1/2” or 3/8”) and begin a rotary fastening pattern using Tool 2.

Attach Helium Blanketing line Attach Elbows Perform Leak Test Insert covers for Elbows Insert V-Groove Inserts.

Reinstall Graphite Reinstall Regular Thermal Column Door.

End of Procedure