Page 17 - May-June 2013
Basic HTML Version
Nuclear Plant Journal, May-June 2013 NuclearPlantJournal.com
17
Research &
Development
Fuel Reliability Program
An industry-wide effort led byEPRI’s
Fuel Reliability Program to eliminate
fuel failures is bearing fruit at nuclear
power plants. As shown in the graphics
below, U.S. boiling and pressurized water
reactors have significantly increased the
number of consecutive cycles in which
a fuel failure has not occurred over the
past five years. In both light water reactor
designs, the number of units operating for
five or more cycles without a failure has
doubled, while the number of units with
two or fewer cycles has been reduced by
a third.
Originally known as the Zero by
Ten Initiative, but since renamed Driving
to Zero, the initiative defined roles
for nuclear plant operators and other
stakeholders to increase fuel reliability.
While the initiative targeted U.S. nuclear
plants, the underlying framework and
technical guidance is applicable to all
light water reactors. Note that when the
industry implemented the initiative in
2007, about 30% of U.S. commercial
reactors were experiencing a fuel failure.
By December 2010, this figure had been
reduced to 6%, a figure that has remained
relatively constant through 2012. While
zero failures has not been achieved,
the near-zero performance represents a
significant accomplishment.
Through the Fuel Reliability
Program, EPRI has assisted nuclear plants
in achieving failure-free fuel, primarily
through a set of five fuel reliability
guidelines that provide recommendations
for avoiding each failure mechanism.
These guidelines are reviewed every
four years to assess whether they require
updating.
For PWRs, grid-to-rod fretting
remains the dominant failure mechanism
in U.S. reactors. Of the 41 units that
planned to transition to robust fuel designs
to avoid this mechanism, 34 have fully
transitioned. All but two units will have
transitioned by spring 2016. For BWRs,
foreign material-induced failures have
been the dominant failure mechanism
since 2008. While the number of units
affected by debris failures has not been
large (typically one or two per year), it
has been a persistent and troublesome
mechanism. EPRI continues to work with
industry to address this failure mechanism
for both BWRs and PWRs
.
Contact: Jeff Deshon, telephone:
Dose Reduction
Activities related to refueling
operations continue to account for
significant radiation exposure at both
plant and individual levels. Finding and
validating improved dose reduction
options for refueling activities will be
important in meeting current standards
and responding to future standards
and goals. EPRI examined a range of
refueling dose reduction techniques and
has compiled a best practices document
(EPRI Product 1025309) based on input
from a working group consisting of BWR
and PWR operators, refueling vendors,
and the Institute of Nuclear Power
Operations.
The working group spent two days
each at Exelon’s Dresden boiling water
reactor and at Luminant’s Comanche
Peak pressurized water reactor to review
detailed site data related to refueling
activities, radiation fields, radiation
sources, and reactor-specific challenges
to exposure reduction. The participants
used their site- or task-specific knowledge
and experience to identify opportunities
for improvement, focusing particularly
on refueling efficiency, radiation field
reduction, and reductions in individual
and cumulative personnel exposure.
Opportunities identified during the
assessments included:
Outage planning: Including a
•
dedicated ALARA (as low as
reasonably achievable) specialist
in the planning process results in a
more efficient and effective outcome.
Use of 3D dose modeling based on
EPRI-developed dose rate algorithms
also shows promise for optimizing
planning and performance.
Reactor cavity activity: Increased
•
purification flow rate and the addition
of submicron submersible filters
and submersible demineralizers can
reduce the cavity radionuclide and
crud inventory. In BWRs, reactor
water cleanup systems should be
optimized and augmented with
portable systems if necessary.
Reactor disassembly and reassembly:
•
Automated closure systems that
simultaneously manipulate multiple
reactor head studs can reduce
personnel exposure and reduce
outage critical path times.
Radiation field reduction: Custom
•
head-shielding packages, advanced
remote
shielding,
temporary
shielding on bridge cranes and
work platforms, and molded flexible
shielding materials can reduce
worker dose.
Cavity decontamination: Underwater
•
robotic cleaning and inspection
systems show great promise for
reducing
personnel
exposure,
eliminating industrial safety hazards,
and improving the outage schedule
and critical time path.
Contact: Phung Tran, telephone:
(650) 855-2158, email:
.
Source: Electric Power Research
Institute’s (EPRI) Nuclear Executive
Update, March, 2013.
