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NuclearPlantJournal.com Nuclear Plant Journal, September-October 2013
Robotic System...
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Continued from page 32)
images into digital profilograms. Each
digital profilogram is measured at 430
points, with an accuracy of 20 microns,
to calculate the required thickness of
O-rings. The groove measurements
are also analyzed to determine whether
repairs or localized honing is required.
The profilograms of the sealing groove
surfaces are also recorded to a database
for comparing groove degradation
between outages. The position of each
profilogram is tracked to within 0.39" on
the RPV and RVH so that deformations
can be closely monitored over time.
The inspection robots are also
equipped with a second camera that
examines the sealing surface for foreign
material and scratches. This high
resolution, rad hardened camera detects
any anomalies, 40 microns or larger
with an accuracy of 20 microns. Figure
2 shows an actual image captured by the
inspection system.
The RVH inspection robot supplies
the same sensor suite as the RPV
inspection robot, but has a specialized
chassis to accommodate the inverted
inspection conditions. The RVH
inspections are conducted upside down
to gain a suitable view of the sealing
surfaces. To suspend beneath the RVH,
the RVH inspection robot is equipped
with a magnetic chassis.
The dual robotic inspection
system was developed in 2011 and has
successfully completed inspections on
various nuclear power plants throughout
Europe. Inspections to date have been
performed on VVER-1000 reactors,
a design similar to US PWRs, with
comparable reactor vessel and head
sealing mechanics.
Conclusion
Prior to the development of Diakont’s
robotic inspection system, manual
inspections were typically employed to
inspect RPV and RVH seals – a process
that exposes personnel to significant dose
levels and is subject to reliability issues.
Manual inspection of the RPV and RVH
seals can take several hours, exposing
inspection personnel to high doses that
often approach half of their annual dose
limits. This inspection method is also
subject to human error, which can cause
reliability issues and pressure boundary
leaks which are only discovered after plant
startup. During significant leakages, plant
operators have to shut down the reactor to
correct the issue, causing forced outages
which increase plant operating costs and
increase regulatory scrutiny.
Utilizing the RPV and RVH robotic
inspection system, the total time spent
by nuclear power plant workers near
the RPV and RVH is reduced to as little
as twenty minutes; the time required
to deploy and retrieve the robotics.
Diakont’s automated inspection system
reduces personnel dose exposure nearly
tenfold compared to traditional manual
inspection protocols. Reducing radiation
exposure and maintaining the safety
of plant personnel is a top priority for
nuclear power plants.
Reliability is another key benefit
delivered by the robotic inspection
system. The laser profilometry system
provides high-precision measurements
of the sealing surfaces with an accuracy
of 20 microns. This advanced system
also inspects the sealing surfaces for
scratches and foreign material that can
cause pressure boundary leakage once the
reactor is brought up to power. Further,
any anomalies that could be overlooked
due to human error are captured by the
high-accuracy inspection system. This
greatly increases the inspection reliability
and reduces the risk of leakage once the
plant is brought up to power.
Additionally, images captured by the
laser profilometry system are processed
and stored as digital profilograms. These
profilograms are saved on a database
providing a quantitative baseline
that is used for tracking the rate of
degradation of sealing surfaces over
time. Plant operators compare the digital
profilograms from each outage to ensure
that the sealing grooves don’t deform at
a rate that could cause leakage problems
during the year.
Inspections using the RPV and
RVH robotic inspection system have
demonstrated greatly reduced dose
exposure for personnel and increased
reliability. These are fundamental
advantages for nuclear power plants
pursuing increased levels of safety and
operational efficiency.
Contact:Keith Reeser, Diakont,
telephone: (858) 551-5551, email:
Figure
1:
Laser
Profilometry
Measurement System for RPV and
RVH Sealing Groov
es.
Figure 2: High-Resolution Image
Captured from Inspection System.
Figure 3: RVH Inspection Robot with
Magnetic Chassis.
