POWER June 2015 - 52

PLANT MOTHBALLING
3. Let 'er down slowly. Like a jigsaw
puzzle, everything must fit into place. Courtesy:
TVA
4. A patriotic touch. Many components on the turbine floor were modernized.
Courtesy: TVA
nents, or equipment refurbished to like-new
condition, is that it is just like building a new
power plant. Program steps included:
ling, and rust preventive coatings should be
applied to exposed surfaces.
Refurbishment and Restoration
Skaggs said that when the Watts Bar Unit
2 plant design was reissued to restart construction,
the natural evolution of a nuclear
plant since the 1970s required the TVA to
make modifications. Much of the equipment
was replaced. For example, changes in piping
prompted replacing pipe supports. Some
conduit was added and cable re-pulled. Also,
new digital instrumentation allowed remote
monitoring with hand-held computers.
" From an equipment scope, we broke
down the components into active components
or passive components. Active components
provide a function, for example.
pumps, valves, motors, switchgears, relays.
Passive components include piping, cables,
and pipe supports. We put together a program
to verify they meet the original specifications
from the vendor or industry requirements, "
said Skaggs.
The process resulted in the creation of the
TVA's refurbishment/restoration program.
The program was intended to restore Unit 2
equipment and components to their original
specifications to meet the 40-year licensing
basis requirement. If items couldn't be
restored, they were replaced. Skaggs noted
that the TVA did not rely on the layup and
preservation options for the active and passive
components.
The advantage of installing new compo52
■
Refurbishing or replacing active components
and instruments based on programmatic
requirements, vendor input,
operational experience, or sound technical
judgment to achieve like-new status.
■ Determining potential degradation mechanisms
and contributing environmental factors
for each component category.
■ Developing acceptance criteria from the
licensing basis, design specifications, and
vendor specifications.
■ Establishing inspections and testing to
identify degradation in accordance with
applicable vendor and design specifications
or requirements.
■ Verifying final confirmation of restoration
through preoperational testing.
Skaggs and his team engaged with vendors
that provided equipment and replacement
parts for the components being used at
Watts Bar to confirm that current specifications
were met. A sampling of the equipment
and systems covered, and actions taken as
part of the refurbishment/restoration program,
follows.
Pumps. All pumps were refurbished to
original equipment manufacturer's acceptable
conditions. Parts that were found unacceptable,
such as age-related degradation
of rubber or soft material gaskets in seals,
were replaced. Missing parts were replaced
with an approved equivalent component.
For example, rebuilt high-pressure and
low-pressure inlet valves were installed on
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the main feedwater pump. If refurbishment
was not an option, pumps were entirely replaced.
For example, eight new raw water
cooling pumps were installed at the river
intake water station.
Valves. In the auxiliary and reactor building,
more than 470 motor-operated valves
were disassembled, cleaned, lubricated, and
refitted with replacement parts.
Piping/Tubing. Borescope surveys and
ultrasonic testing were used to inspect piping
and internals at different locations. The
carbon-steel piping in the feedwater system
was replaced with chrome-moly piping,
which has increased high-temperature
strength and better corrosion resistance
due to the chromium and molybdenum
content in the steel. Copper-alloy condenser
tubes were replaced with an alloy
that is highly resistant to raw water. More
than 27,000 tubes that carry the cooling
water were replaced to ensure no leaks and
a long condenser life.
Snubbers. Dynamic restraints, known
as snubbers, are designed to protect components
from excessive shock or sway as a result
of seismic disturbances, water hammer,
or other transient forces. At Watts Bar Unit
2, all snubbers were disassembled, cleaned,
and inspected; lubricants and elastomers
were replaced.
Reactor Vessel/Nuclear Steam Supply
System (NSSS). Portions of the NSSS were
modified to meet regulatory requirements
concerning potential operational embrittlement.
Early performance of this activity
supported the reduction of personnel radiological
dose. Traceability of the reactor vessel
(Figures 2 and 3) and NSSS were certified
POWER | June 2015
http://www.powermag.com
POWER June 2015

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