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NuclearPlantJournal.com Nuclear Plant Journal, March-April 2015
Predictive
Maintenance...
cooling tower superstructure
Embedded reinforcing steel corrosion
leading to structural degradation
Erosion of concrete surface paste
Differential settlement of the cooling
tower basin wall/base slab
Algal growth and vegetation
obstruction
Predictive Maintenance
for Concrete Structures
Understanding deterioration mecha-
nisms well in advance of deficient struc-
tural behavior is important. When devel-
oping a predictive maintenance program
for concrete structures, the Locating,
Qualifying, and Quantifying (LLQ)
methodology can help evaluate deteriora-
tion and cause mechanisms. Once cause
mechanisms are identified a maintenance
program can be formulated and rehabili-
tation methods can be planned without
interrupting operations to meet end-of-
life or extended service criteria.
Tools
utilizing
Risk
Based
Inspection (RBI) Programs developed
for mechanical and electrical systems
are also available for civil and structural
assets. These tools provide an indication
of the current condition of structures and
assist in prioritizing maintenance.
Building Envelope
The building envelope of nuclear
structures provides critical protection
for process equipment. Nuclear power
plants, like many other industrial and
energy processing facilities that use
water for cooling are built close to a
body of water. Facilities are built with
heavily reinforced concrete and located
in wet environments below grade with
walls and floors exposed in active water
above grade often in harsh and corrosive
environments.
Water infiltration below-grade can
damage interior surface treatments,
spread nuclear waste contaminants,
corrode metal structures and components.
Water
infiltration
above-grade
through roofs and walls can be
destructive. Uncontrolled water allows
mold to propagate and degrades material
properties like thermal conductance, fire
resistance and adhesion of fireproofing
materials. Water infiltration and increased
vapor transmission can also cause paints
and coatings to de-bond. Water intrusion
can become a safety issue if floors
become wet.
Roofing Systems
Roofing systems at many nuclear
facilities are often 30 to 40 years old and
the service life of these roofing systems are
close to or have already expired. Recently,
a roof leak resulted in an electrical fault
causing loss of power to reactor coolant
pumps and both units of a nuclear facility
automatically shut down. The roof leak
allowed water to seep down the outside
of a conduit into a current transformer
enclosure for a reactor coolant pump 13-
kV supply breaker. This caused a phase-
to-ground fault and reactor coolant pump
to trip. The fault was not cleared by the
supply breaker because of an overcurrent
relay failure, so fault current was exposed
to the service transformer which isolated
causing an unplanned unit trip.
As a result of this event and
unplanned outage, this facility developed
an extensive roof survey and prioritization
program. The roof replacement and
prioritization process was based on a
thorough analysis of current conditions,
as well as the current risk levels to
ongoing operations.
Predictive Maintenance
for Building Envelope
Components
Building envelope components can
be incorporated into a water management
predictive maintenance program. Devel-
opment of the inspection protocols and
routine maintenance programs can be
based on manufacturer recommendations
for material life, industry experience and
subject matter expert expertise. To avoid
unplanned events it is important to gather
information about each component, in-
cluding date of installation, repair history,
leak history and the location of penetra-
tions and equipment.
Conclusion
Despite the perception of a long
life, civil and structural assets should
be part of a comprehensive predictive
maintenance program because they are
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Contact:
Michelle Gaylord
telephone: (630) 364-4780
Nuclear Plant Journal
1400 Opus Place
Suite 904
Downers Grove, IL 60515
USA
Annual
Editorial
Schedule
Nuclear
Plant
Journal
essential in the functionality of process
equipment and related operating assets.
There are numerous benefits of predictive
maintenance since maintenance is
performed when it needs to be done
helping to eliminate unplanned outages,
keep repair costs lower and the service
life of the facility will be achieved or
possibly extended.
Contact:LeoNadeau,STRUCTURAL
TECHNOLOGIES, telephone: (860) 670-
