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
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
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
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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