POWER March 2020 - 26

NUCLEAR
A New Frontier for Nuclear Fuels
Though much attention has been focused on the exciting realm of nuclear reactor
technology innovation, major efforts to improve nuclear fuels-and boost power
generation safety and economics-are underway. Part 1 of this two-part series
focuses on ongoing nuclear fuel developments that could have an impact on the
existing fleet. Part 2, which will be published in the April 2020 issue of POWER, surveys
global nuclear fuel developments that support the emerging fleet of advanced
nuclear reactors, including small modular reactors and micro-reactors.
Sonal Patel
A
sk Dr. Tatiana Ivanova, a long-time
nuclear engineer and head of the
Nuclear Science division at Parisbased
intergovernmental organization
Nuclear Energy Agency (NEA), why so
much activity is ongoing to transform
nuclear fuel-and her answer is simple:
" It is the core of nuclear power plants. "
Fuel design optimization is " a cornerstone
for the industry to deploy new,
modern fuel for light-water reactors
[LWRs], advanced reactors, and small
modular reactors, " she said. " Also, it is a
very important part in storing, recycling,
and disposing of used nuclear fuel. That
is why a study of performance and reliability
of nuclear fuel have remained a
high priority in the research portfolios of
all nuclear countries. "
What's notable, she explained to POWER
in February, is that all LWRs around
the world currently use fuel systems
comprising uranium oxide (UO2
) encased
within a zirconium-based alloy cladding
(and to a much smaller degree, some
reactors use uranium-plutonium oxide,
or mixed-oxide [MOX] fuels). Over many
decades, this oxide fuel-zircaloy system
has been optimized, it has matured, and
it has generally met all performance and
safety requirements. But over the last
10 years, cascading concerns stemming
from the Fukushima disaster and a rapidly
changing sector have required a transformation-an
urgent revival that starts
at that core, with safety and economics
as key priorities, she said.
Urgency for Accident Tolerant Fuels
Safety, perhaps, has been the foremost
driver of rapid fuel design optimization.
As Fukushima showed, " because of the
highly exothermic nature of zirconiumsteam
reactions, under some low-frequency
accidents [when core cooling
is temporarily lost and part of the core
is uncovered], low-probability accidents
26
may lead to an excess generation of heat
and hydrogen, resulting in undesirable
core damage, " Ivanova said. That's why
in 2012, the NEA, a specialized agency
within the Organisation for Economic
Co-operation and Development (OECD),
jumped into action to gauge the interest
of its 14 OECD members in the development
of enhanced accident-tolerant
fuels (ATF) for LWRs, she said.
Barely eight years later, boosted by
national programs, the progress it has
achieved is remarkable. Activity is espean
initial lead test assembly has been installed
in a U.S. commercial power plant,
and that prototypic pin segments have
been installed in the Idaho National Laboratory's
(INL's) Advanced Test Reactor's
(ATR's) water loop by 2023, and have full
cores licensed for higher burns by 2026.
Among notable projects are tests of
GNF's iron-chromium-aluminum fuel cladding
material known as " IronClad " and
coated zirconium fuel cladding known as
" ARMOR " at Southern Nuclear's Edwin
I. Hatch Nuclear Plant in Georgia, which
Positive market signals are especially
imperative to the development of
advanced fuel designs.
cially notable in the U.S., where the Department
of Energy (DOE) aggressively
implemented plans under its Congressionally
mandated Enhanced Accident Tolerant
Fuel program. As the DOE notes, the
urgency is underscored by nine recent
reactor retirements, many for economic
reasons. Much of the U.S. nuclear fleet,
in particular, already have 60-year operating
licenses that will expire in the 2030s,
and getting these new fuels to market
before then would increase the performance
of these reactors and ultimately
improve their chances of applying for extended
operation with the Nuclear Regulatory
Commission (NRC), it said.
Under the DOE's program that today
casts a wide net of collaboration that includes
several U.S. utilities, universities,
and the Electric Power Research Institute
(EPRI), the DOE is funding and technically
backing several industry-led ATF fuel
concepts, including fuel pellet and cladding
materials developed by GE-Hitachi
joint venture Global Nuclear Fuel (GNF),
Westinghouse, General Atomics, and
Framatome. The vendors must ensure
www.powermag.com
are slated to end in March 2020. In January,
the company also installed IronClad
and ARMOR materials at Exelon's Clinton
plant in Illinois. In April 2019, Exelon's Byron
Unit 2 in Illinois completed installation
of Westinghouse's EnCore Fuel, which
encapsulates chromium-coated zirconium
cladding for enhanced oxidation and corrosion
resistance; higher-density ADOPT
pellets-which are chromia (Cr2
O3
O3
alumina (Al2 ) doped UO2
) and
-pellets-for
improved fuel economics; and uranium
silicide pellets.
Also in April 2019, Framatome completed
installation of four GAIA lead fuel assemblies
containing enhanced ATF (EATF) pellets and
cladding-advanced chromium coating that
is added to its proprietary M5 zirconium-alloy
cladding-at Southern Nuclear's Vogtle 2 in
Georgia (Figure 1). As Framatome explained,
the combination " improves high-temperature
oxidation resistance and reduces hydrogen
generation during loss of cooling. " The
chromium coating, meanwhile, also " greatly
reduces creep to maintain a coolable geometry
and has mechanical properties that
allow for more operator response time. FurPOWER
| March 2020
http://www.powermag.com
POWER March 2020

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