Page 46 - May-June 2013
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46
NuclearPlantJournal.com Nuclear Plant Journal, May-June 2013
Fuel
Reliability:
Achieving
Zero
Failures
By Rob Schneider, Global Nuclear Fuel.
Rob Schneider
Rob Schneider is an engineer in the
GNF Fuel Technology and Design
group, with over 25 years nuclear
experience. His background includes
18 years at GNF in Wilmington, N.C.
in BWR fuel reliability, specializing in
helping utilities prevent fuel failures,
and minimizing the consequences of
failures when they do occur. Prior
experience includes 5 years in the GE
Hitachi nuclear services business,
where he was SRO certified and worked
on outage projects and startup testing,
and the U.S. Navy Nuclear Propulsion
Program. Rob has a Chemical
Engineering degree from Manhattan
College in New York.
In March 2013, Global Nuclear
Fuel (GNF) met the INPO challenge for
zero-leaker fuel reliability, with all of
GNF’s North American BWR customers
operating over 1.4 million rods with no
leakers. More than a story of success for
GNF and its customers, achieving this
milestone opens the door on a new era
of fuel reliability expectations. It is also
an occasion to look back at the road to,
and lessons learned in, achieving zero-
leaker fuel reliability; to reflect on the
cost of leakers on plant performance and
what operating leaker-free means; and to
consider what we must do to maintain
leaker-free performance.
In March 2013, Global Nuclear Fuel
(GNF) met the INPO challenge for zero-
leaker fuel reliability, with GNF’s North
American BWR customers operating over
1.4 million rods with no leakers. More
than a story of success for GNF and its
customers, achieving this milestone opens
the door on a new era of fuel reliability
expectations. It is also an occasion to look
back at the road to, and lessons learned
in, achieving zero-leaker fuel reliability;
to reflect on the cost of leakers on plant
performance and what operating leaker-
free means; and to consider what we must
do to maintain leaker-free performance.
How is zero-leaker fuel
reliability achieved?
Implementation of lessons learned
from failure events has played the
most important role in the systematic
identification and elimination of failure
mechanisms. Because GNF has the
largest BWR installed base, and GNF fuel
is exposed to the widest variety of BWR
operating conditions, fuel reliability
challenges have often been encountered
first by GNF, and solved first by GNF. For
example, today’s improved debris filters
are a result of higher debris inventories
faced in a small number of plants, but the
challenge of solving the debris problems
for those plants now yields benefits for
the entire BWR fleet. Similarly, when
missing-pellet surface induced “duty-
related” failures were first identified,
corrective actions were taken for GNF
fuel to fleet-wide benefit.
GNF has collaborated closely over
the years with utility fuel engineering
teams and operational staff to solve
these problems and reduce fuel failures.
Recently, this collaboration was
reinforced by fuel reliability initiatives
such as “Zero by 2010” and “Driving
to Zero” supported by INPO and the
EPRI Fuel Reliability Program, which
increased the visibility and importance
of fuel reliability among utility senior
management. These programs enable
more widespread implementation of
innovative fuel designs and facilitate
exchange of operational experience. The
success of these efforts is indicated by the
decreased fuel failure rate in recent years,
as outlined in Figure 1.
With respect to the specific challenges
overcome on the way to reaching zero
failures, there are four broad failure
mechanisms that have affected BWR fuel
over the past twenty or so years: debris
fretting; duty-related or PCI (pellet-clad
interaction) type; manufacturing defects;
and crud or corrosion. Three of these
challenges have been largely resolved in
recent years, as crud/corrosion has not
affected a US plant in approximately 10
years, manufacturing related failures have
been eliminated for the most part, and
PCI-type failures are rare now, largely
due to widespread implementation of
operating practices to reduce the duty
applied to the fuel.
Recently, debris fretting has been
the failure mechanism that has affected
the most plants, caused the most fuel
failures, and has been the most difficult
to eliminate. Three factors are most
important in the U.S. BWR fleet debris
failure rate improvement seen from 2006
through today:
Reloads with “non-line of sight”
•
Defender
TM
lower-tie plate debris
filters began operating in 2006 and
are now near 100% of most GNF
supplied cores.
Figure 1: 40+ year path to zero fuel
failures.
