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Flamanville, France - Dome Installation page 68
Nuclear
Plant
Journal
Nuclear Energy
Momentum
page 4
6
A Robust
Reactor
Page 40
A Bright
Future
page 22
Mitigation
of Fuel
Channel
By James Tusar, Exelon Generation.
James Tusar
James Tusar is a graduate of
Pennsylvania State University with
a BS in Nuclear Engineering, of
Drexel University
with an MS in
Environmental
Engineering, and
has a Professional
Engineer’s
License in Nuclear
Engineering. He is
currently Manager
of BoilingWater
Reactor Design for
Exelon Generation
which includes
responsibility
for nuclear fuel
design, reactor
core design, core
management, core monitoring systems,
and reload coordination. James
has been recognized for his nuclear
industry accomplishments with eight
(8) Nuclear Energy Institute (NEI) Top
Industry Practice (TIP) Awards and
he also received the 2013 Outstanding
Engineering Alumnus Award from the
Pennsylvania State University.
Nuclear Energy Institute’s Top Industry
Practice (TIP) Awards highlight the
nuclear industry’s most innovative
techniques and ideas.
This was a 2012 NEI Process Award
Winner.
The team members who participated
included:
James Tusar, Manager, BWR
Design, Nuclear Fuels, Exelon; Michael
Reitmeyer, Senior Project Manager,
Nuclear Fuels, Exelon; Giuseppe Ru-
binaccio, Manager, Reactor Engineer-
ing, Limerick, Exelon; Atul A. Karve,
Manager, Advanced Methods, Global
Nuclear Fuel.
A significant issue facingBoilingWa-
ter Reactors (BWRs) since the late 1990’s
has been fuel channel distortion that has
caused interference with control blade
motion leading to safety, operational,
and economic concerns. These observa-
tions were initially unexpected and cor-
related with the industry’s move toward
Zircaloy-2channelsand2-year fuelcycles
that required greater control of first cycle
fuel bundles. The impact of fuel chan-
nel – control blade interference is friction
between the fuel channel and the control
blade that can result in bundle lift, incom-
plete insertion of a control blade or deg-
radation in scram speed (safety concerns),
andno-settleor slow-
to-settle
control
blades during reac-
tivity manipulations
(operational
con-
cerns). An exhaus-
tive list of operating
experience exists in
this area. The list
spans various BWR
reactor typesandfuel
vendors which illus-
trates the breadth of
this issue.
Anunprecedent-
ed, multi-faceted ap-
proach to resolve this
issue has been undertaken by Exelon and
Global Nuclear Fuel (GNF). The indus-
try-leading approach consists of:
Cell frictionpredictivecapabilitywith
1.
first-of-its-kind software to allow
core design and operating strategy
solutions,
Lead Use Channel (LUC) programs,
2.
which allow for first time in-reactor
operation of new fuel channel
materials, support the introduction
of channels that are more resistant to
deformation.
Irradiated fuel channel measurements
3.
and hot cell examinations which
support characterization of new
materialsand themodelingofchannel
behavior in the predictive software,
Use of Zircaloy-4 fuel channels on
4.
fresh fuel in control cells to mitigate
shadow corrosion induced channel
bowing,
Limited re-channeling of irradiated
5.
fuel assemblies with new fuel
channels to eliminate control blade
settling issues, and
Coordinationandprojectmanagement
6.
of regular industry conference calls
on channel distortion including EPRI
industry research efforts.
The first step in this initiative was to
characterize the observed channel distor-
tionviaon-sitemeasurements followedby
hot cell examinations. Exelon supported
channel measurement campaigns at mul-
tiple plants, including Limerick Unit 1,
Limerick Unit 2, Clinton, Peach Bottom
Unit 2, and Peach Bottom Unit 3. Also,
fuel channel coupon retrieval efforts for
hot cell examination were performed at
Limerick Unit 1. These investigations
enabled the identification of a previously
unknown distortion mechanism. The new
mechanism, referred to as shadow corro-
sion-induced channel bow, is influenced
by differential hydrogen pickup caused by
shadow corrosion on the fuel channel wall
adjacent to an inserted control rod blade.
This leads to differential growth of the
fuel channel sides preferentially towards
the control blade. Shadow corrosion bow
occurs predominantly in the third cycle of
operation (at high exposures or burn-up)
on channels that were extensively con-
trolled during their early years of opera-
tion.
The channel measurements also
lead to an improved understanding and
characterization of fluence gradient in-
duced channel bowing and channel bulge.
These data comprise a major fraction of
the datasets used to develop models for
the deformation mechanisms used in the
Cell Friction Methodology. Additionally,
measurements made on control rod drive
performanceof impactedcellsatLimerick
Unit 1 provided a calibration and qualifi-
cation data set for the methodology.
With this new knowledge, an
industry leading approach was developed
to optimize the in-core performance
of recrystallized-annealed Zircaloy-2
channels. The approach is called the
Cell Friction Methodology and it is a tool
that predicts channel distortion and the
associated frictional forces to estimate
the relative probability of interference
occurring during the fuel cycle. The Cell
FrictionMethodologyisintegratedwiththe
three-dimensional core simulator software
and is being actively used by Exelon and
other GNF customers to mitigate channel-
control blade interference issues during
various stages of core design (shuffling
of fuel bundles to reduce cell friction) and
60
NuclearPlantJournal.com Nuclear Plant Journal, July-August 2013
The July-August 2013 issue of the
Journal featured an Exelon Industry
Innovation about BWR fuel channel
mitigation.
Do you have an Industry Innovation
to share in the Journal?
Contact Michelle Gaylord below.
Other areas of editorial
participation include:
• News Releases
• Meeting & Training Calendar
• Plant Profiles
• Cover Pictures
