TVA - Sequoyah Nuclear

FACED WITH AN EMERGENT NEED TO REPLACE A REACTOR COOLANT SYSTEM PRIMARY CHECK VALVE AT THE SEQUOYAH NUCLEAR PLANT, THE TENNESSEE VALLEY AUTHORITY TURNS TO TRI TOOL TO DELIVER QUALITY ON AN EXPEDITED TIME FRAME.

Due to the “as found” condition and previous seating issues, the

replacement of System 63 Safety Injection System check valve

number 559 was required during the recent Unit 2 refueling

outage. This valve is considered a Reactor Coolant System

(RCS) primary check valve and is a 6 inch swing check made of

stainless steel that is approximately 24 inches long and weighs

approximately 600 lbs. The valve is located in a very congested

area that required special considerations due to various

radiological conditions. Due to the valve being part of the

Emergency Core Cooling System and a primary check valve for

the RCS, the interior of the check valve and associated piping is

very contaminated.

The replacement of the check valve was an emergent job for

which the site had not planned. Once the scope was identified, the

utility contacted Tri Tool directly for support because of positive

previous experience with them. Combining the efforts with the

Sequoyah Nuclear Plant, owned by Tennessee Valley Authority (TVA), is located on 525 acres in Soddy-Daisy, Tennessee. With two Westinghouse PWR units that produce 1,160 megawatts of electricity each, there is enough power generated to supply 1.3 million homes a day.

The TVA is the nation’s largest public power provider and is owned by the U.S. government. TVA also provides flood control, navigation and land management for the Tennessee River system and continues to provide economic development for state and local governments.

site Projects and Modifications Contractor, Tri Tool was able to

mobilize a crew of pipefitters, machinists and welders within a 24

hour timeframe to support this critical path activity for the site.

“ Because this was presented as an emergent need, we went with a company we’ve used before and trusted. Tri Tool was able to

mobilize a team immediately. It took them six days to execute the entire repair. The professionalism of their project manager, machinists and welders was exemplary and the quality of their work was beyond compare. They took ownership of what we needed them to do without us having to provide direct oversight. I will continue to work with Tri Tool and would highly recommend this company.

David Charles HaneyModifications Manager

Utilizing Tri Tool’s 212B ID mounted beveling and 608 OD

clamshell lathe machines, the cut out and removal of the existing

valve was precisely executed. The craftsmen had to work closely

with radiological control personnel to remove the component

without creating any unnecessary debris and remaining within

the plant requirements for Foreign Material Exclusion. Personnel

safety considerations associated with the task included; working

from a scaffold, lifting and rigging heavy equipment, deployment

of rotating equipment and welding hazards, all completed in a

very congested, highly contaminated, high radiological dose and

high temperature environment. All were considered in the Job

Safety Analysis while developing a plan for mitigation of each

jobsite hazard. The valve replacement project was completed with

no safety or human error issues due to the diligent and thorough

(albeit emergent and rapid) planning efforts of the entire

site team.

The reinstallation of the new check valve was performed

through a teaming effort of Tri Tool and site personnel. Careful

consideration was given to the rigging path with emphasis on

protection of people and other plant equipment. The weight of

the valve with the other pre-assembled components weighed

approximately 750 lbs. The pre-fabricated piece was mobilized

from the welding shop to the point of installation with

zero incidents.

Once rigged into place, the fit-up of the new check valve and

pipe to the existing piping system was extremely critical. The

welding process was closely monitored by site Quality Control /

Quality Assurance personnel, with the final acceptance criteria

being radiography of all the welded joints. All of the work was

performed with zero Safety or Human Performance issues.

With minimal upfront planning, Tri Tool supervisors took ownership of the job and drove the actions necessary to safely and effectively implement the “like for like” replacement of the new valve into an existing piping system. The skilled machinists utilizing portable Tri Tool equipment were able to safely and efficiently sever, remove and prep the existing components to facilitate installation of the new check valve.

Tri Tool’s welders were tested and qualified to TVA’s Quality Program to enable them to perform the welding of the new valve. The valve was installed in compliance with ASME Section XI, Repair/Replacement requirements. Post welding of all large bore welds required an In-Service Inspection of the final weld profile. Additionally, these welds were subjected to 100% radiographic testing acceptance criteria as called out in ASME Section IX. All

initial welds performed under these requirements by Tri Tool welders exceeded the acceptable, prescribed standards.

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