POWER March 2021 - 27

NUCLEAR
properties, and fertile particles with both
PyC and SiC coating layers formed into
annular cylinders, " the DOE noted.
Peach Bottom 1, an experimental 115MWth
prismatic HTGR in York County,
Pennsylvania, that reached criticality
in 1966, used pyrocarbon-only coated
particles. However, that reactor " also
contained fuel test elements in which a
large number of different types of particles
were irradiated, including TRISO
particles with various kernel types, and
post-irradiation examination of these elements
yielded a large amount of data on
fuel performance, " the DOE said. Other
reactors that bolstered TRISO research
and development include the 1967-completed
46-MWth Arbeitsgemeinschaft
Versuchsreaktor (AVR) unit in Germany-
the first " pebble-bed " reactor design.
AVR initially used the two-layered bistructural
isotropic (BISO) particle design
before adopting TRISO as a standard
fuel for the remainder of its operational
years, which ended in the late 1980s.
During the 1970s, TRISO coatings
grew more sophisticated, gaining from
advances in fabrication technology, SiC
and pyrocarbon coating properties, coated
particle irradiation performance, fuel
performance modeling, and fission product
release observations. The robustness
of these new fuel forms was put to test
at the Fort Saint Vrain HTGR in Colorado,
which operated between 1976 and 1989.
HTGR fuel development has since burgeoned
in Germany, China, Japan, South
Africa, France, Russia, and South Korea.
China, notably, has made remarkable
progress to develop TRISO-coated particle
fuel for its Shidaowan HTGR pebblebed
module (HTR-PM), a Generation IV
reactor. Fuel loading (Figure 2) at that
project is expected to begin this April.
Bolstering Commercial TRISO
Development
Several high-temperature reactor developers
have leveraged data from DOEsupported
AGR TRISO fuel experiments.
In tandem, the DOE has been working to
establish a pilot-scale TRISO fuel manufacturing
capability in the U.S. Initially,
the fabrication process was a joint activity
between the Idaho National Laboratory
(INL), Oak Ridge National Laboratory
(ORNL), and an industrial fuel vendor,
BWX Technologies (BWXT).
BWXT told POWER it worked with the
DOE for more than 15 years under the
AGR program to develop and manufacture
TRISO-coated kernels at its specialty fuel
facility in Lynchburg, Virginia, to support
March 2021 | POWER
awards, it noted.
X-energy, too, has long had the DOE's
2. Fuel loading at the Shidaowan hightemperature
gas-cooled reactor pebble-bed
module (HTR-PM) in China, slated to begin
in April 2021, will involve putting 870,000
spherical TRISO fuel elements into the two
small reactors that will drive a single 210MWe
turbine. Courtesy: China National
Nuclear Corp. (CNNC)
the government's vision of developing
" passively safe, compact nuclear reactors
capable of economically generating electricity
and hydrogen " before it ceased TRISO
production in the spring of 2017. Last
November, however, the company said its
Nuclear Operations Group had completed
its TRISO nuclear fuel line restart project,
which means the company's Lynchburg,
Virginia, facility is now actively producing
the fuel again. BWXT said restarting its
existing TRISO fuel production capability
and increasing its capacity would position
the company to meet emergent client
interests in Department of Defense
microreactors, space reactors, and civil
advanced reactors. " By co-locating the
TRISO production line with other existing
uranium processing capabilities, BWXT
has a vertically integrated facility capable
of handling all TRISO-related needs from
feedstock preparation through uranium
recovery and purification, " it said.
X-energy, Kairos, USNC Making
Crucial Progress
The DOE is also working with Kairos
Power, developer of a fluoride salt-
cooled high-temperature reactor (FHR).
Similar to a molten salt reactor, FHRs
use solid TRISO fuel instead of liquid
fuel dissolved in the coolant. " [Kairos's]
design would use TRISO fuel in a pebble
form with a fluoride-lithium-beryllium
(FLiBe) salt coolant to allow high temperature
output by the FHR, " the DOE
said. " In addition, the previous extensive
DOE TRISO fuel qualification studies ...
would shorten the timeline to demonstrate
this reactor type. " The DOE has
backed the development of the Kairos
design through an assortment of funding
opportunities, including via Gateway for
Accelerated Innovation in Nuclear (GAIN)
vouchers and other industry partnership
www.powermag.com
backing. X-energy's TRISO-X fuel pebbles,
which build off the AGR experiments,
comprise pebbles that contain
thousands of specially coated TRISO fuel
particles. These particles " seal uranium
particles in a protective coating, are virtually
indestructible, retain the waste
inside, and make meltdown impossible
while releasing no carbon emissions. The
entire process releases even less carbon
than wind or solar, " the DOE said. The inherent
safety of the design would allow
a fabrication facility to be constructed
within 500 meters of factories or urban
areas, it suggested.
For now, X-energy continues to run
a TRISO-X fuel fabrication pilot line at
the ORNL Uranium Building, co-located
within the ORNL AGR TRISO Fuel
laboratory area. The TRISO-X pilot line
reportedly has full production size (engineering-scale)
fabrication equipment
to make UCO kernels, coat them with a
buffer layer, two PyC layers, and the SiC
layer that acts as a fission product containment
barrier for the fuel. The same
pilot line production equipment could be
used in X-energy's commercial TRISO-X
fuel fabrication facility that the DOE is
funding under the ARDP program.
Ultra Safe Nuclear Corp. (USNC), another
notable TRISO fuel developer, is spearheading
development of its proprietary
Fully Ceramic Microencapsulated (FCM)
fuel, which consists of coated nuclear
fuel particles embedded inside a dense
and fully sealed SiC matrix. " The specific
coated fuel particles are TRISO microspheres
that provide micro-encapsulation
of the fuel with multiple pyrocarbon and a
SiC coating layer, " USNC CEO Francesco
Venneri explained to POWER. " Using
FCM technology, an additional layer of
protection against radionuclide release is
added by taking advantage of SiC as the
matrix for these coated fuel particles. This
macro-encapsulation further enhances radionuclide
retention capability of the fuel,
and allows for design and deployment of
ultra-safe nuclear energy systems. "
USNC, notably, in September opened
a new facility in Salt Lake City, Utah, to
support the development of its FCM
fuel and materials that will be used in its
own Micro-Modular Reactors (MMR), as
well as other nuclear reactors, including
gas-cooled reactors, light water reactors,
CANDU reactors, and molten salt-
cooled reactors. ■
-Sonal Patel is a POWER
senior associate editor.
27
http://www.powermag.com
POWER March 2021

Table of Contents for the Digital Edition of POWER March 2021
