22
NuclearPlantJournal.com Nuclear Plant Journal, July-August 2015
Research &
Development
Poolside Measurements
EPRI
has
developed
and
demonstrated a nondestructive evaluation
(NDE)
technology
for
poolside
inspection of nuclear fuel structural
materials (rods, channels, spacers, etc.)
that will enable nuclear plants to more
quickly measure critical parameters
and address regulatory and operational
considerations. The frequency-scanning
eddy current technique (F-SECT) has
been successfully demonstrated at
nuclear plants in Spain and Switzerland,
and ongoing hot cell examinations will
enable EPRI to benchmark the accuracy
and applicability of the technology
against destructive examinations results.
Under normal reactor operations,
zirconium-based alloys used in fuel
assembly structural components and
fuel rod cladding are susceptible to
hydrogen pickup, which can result in the
formation of hydrides that can render the
components and rods more brittle than
surrounding material. If the hydrogen
pickup exceeds certain levels, regulatory
margins can be at risk.
Historically,
fuel
assembly
components and fuel rods have been
inspected at hot cell facilities using
destructive
examinations.
While
this provides a proven approach for
measuring hydride pickup, corrosion
oxide thickness, and wall thickness, it is
expensive, time-consuming, and requires
considerable coordination and buy-in
from the nuclear plant owner and the fuel
supplier. It also requires access to one
of a small number of hot cell facilities
available worldwide. Over the past 10-15
years, EPRI alone has invested about $20
million in benchmarking studies at hot
cell facilities.
Building on technology originally
developed for testing gas turbine thermal
barrier coatings, EPRI collaborated with
the Italian vendor Centro Elettrotecnico
Sperimentale Italiano (CESI) to adapt
the F-SECT technology for nuclear
plant applications, including fuel. The
F-SECT technology can quickly measure
a number of properties critical to fuel
cladding and component structural
integrity, including oxide thickness,
wall thickness, and hydrogen pickup.
Analyzing these measurements with
respect to potential impacts on operating
margins or how they could affect future
fuel designs could potentially be done in
a matter of days compared to months to
over a year for hot cell testing.
EPRI has held discussions with all
of the nuclear fuel vendors regarding
future use of the F-SECT technology.
Three fuel vendors participated in early
laboratory evaluations in 2012-2014,
and one fuel supplier collaborated with
EPRI to conduct field demonstrations
at two European plants in 2014 and
2015. At the Cofrentes plant in Spain,
F-SECT tests were conducted to evaluate
oxide thickness, remaining metal wall
thickness, and hydrogen content in
BWR fuel channels susceptible to
distortion due to asymmetric corrosion
and hydrogen pickup. All tests were
successfully completed within the
scheduled timeframe, encompassing 929
total measurements, many more than
the 64 originally planned. Analysis of
the F-SECT data is ongoing, and when
complete, these data will be compared to
the destructive evaluation data from the
hot cell.
Additional field trials in 2015,
coupled with hot cell comparative testing
and ongoing modeling, are expected to
provide the data and understanding with
which to assess the commercial viability
of the technology. Information from the
F-SECT assessments also will guide the
improvement and refinement of EPRI’s
fuel reliability guidelines and help
inform plant owners on operational and
regulatory margins.
Contact: Rob Daum, EPRI,
telephone: (704) 595-2779, email:
.
Virtual Sensors
Diagnosing faults in vertical pumps
at nuclear power plants can be challenging
because such problems can develop at the
opposite end of the machine from where
practical physical measurements can be
made. EPRI is developing a model-based,
virtual sensor technology to diagnose
common pump faults using limited
vibration data. By creating a model that
recognizes characteristics of common
pump problems based on vibration data
taken at the motor end of the pump, this
tool could serve as a “virtual sensor” (as
opposed to a physically installed sensor)
and assist in troubleshooting and fault
diagnostics.
If development and testing is
successful, this technology will assist
nuclear plant operators in making
informed decisions about pump health.
For vertical pumps used at nuclear plants
to move raw water or circulating water,
the ability to diagnose faults prior to
intrusive maintenance would help avoid
costs associated with rigging and pulling
these large pumps up for inspection and
repair.
Progress to date in developing the
virtual sensor model includes:
• Proof-of-concept
testing:
In
2013, EPRI incorporated a seven-
horsepower, 150 gallon-per-minute,
Profile of the three-stage vertical
pump being used for fault trials and
virtual sensor development.
