POWER July 2021 - 9

GLOBAL MONITOR
novation: Clean Energy Future (NICE
Future) initiative, experts
envisioned
an interesting array of nuclear energy
prospects that could retain and even
expand the sector's relevance in lowcarbon
power markets. They proposed
that along with district heating, and
high-temperature heat
for
industrial
processes, new roles for nuclear power
and heat could involve hydrogen and
synthetic fuel production; seawater desalination
and purification; and off-grid
power and heat applications in remote
regions. But to retain nuclear power
plant capacity factors-and stabilize
their revenue generation-as well as
provide grid flexibility, stability, and that
inherent, coveted
integration within
a renewables-heavy grid, experts argue
coupling baseload nuclear power
to large-scale energy storage systems
(ESS) may be the best option over the
near term.
However, not all ESS systems are suited
to nuclear, and benefits vary widely
depending on their application. " ESS can
be integrated either to the plant directly
known as behind-the-meter [BTM] storage
(storage and control is at the power
plant-level), or ESS can be integrated
to the grid known as front-of-the-meter
[FTM] storage (storage and control is
at the grid-level), " explained researchers
from the Korea Advanced Institute
of Science and Technology (KAIST) and
the Canadian Nuclear Laboratories (CNL)
in a March 2021-published comprehensive
evaluation of various large-scale
ESS technologies that could be applied
to existing pressurized water reactors
(PWRs)-which represent about 67% of
the world's operating reactors.
One key advantage BTM technologies
offer is a " direct integration with
ESS such that the generated steam
from the nuclear reactor can be more
efficiently stored and discharged in the
form of thermal or mechanical energy, to
minimize conversion losses, " they wrote.
" Another advantage of this option, when
compared to a direct integration of ESS
with renewables, is that direct integration
with nuclear power can avoid the off-design
efficiency and component degradation
issues due to the intermittent nature
of the renewable input source. "
While each ESS technology may play
various functions on the grid, an ideal
application for BTM-integrated ESS in
a PWR would be for energy management-to
essentially provide balancing,
such as time-shifting, peak-shaving, and
seasonal energy storage. That essentialJuly
2021 | POWER
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9
ly narrows suitable ESS technologies to
three main types: thermal energy storage
(TES); tank-based compressed gas
energy storage (CGES); and liquid-air
energy storage (LAES). " The main rationale
for the selection is that they can
be installed as large-scale ESS without
the geological constraints and that they
do not suffer from AC-DC [alternating
current-direct current] conversion loss
and relevant transmission issues, " the
researchers said.
The researchers nixed pumped hydro
storage and cavern-based compressed
air energy storage, owing to their locational
constraints. Also eliminated was
lithium-ion storage, which is gaining
prominence as a utility-scale option at
other resources, owing to " its limitations
in terms of capacity and cost. " If
ESS is to provide load-shifting and energy
management for PWRs, energy
capacity needs " expansion for several
hours at the [necessary] power level of
several hundred MWs, " they said. Meanwhile,
though hydrogen energy systems
are widely touted as a serious option
to address seasonal storage, currently
proposed solutions are yet to be demonstrated,
and they are currently inefficient,
costly, and, according to a 2017 study by
the Idaho National Laboratory (INL), may
be unable to perform energy arbitrage.
For the KAIST and CNL researchers,
CGES and LAES are promising for their
high-density and recent development
progress. Under their CGES evaluation,
the researchers notably highlighted compressed
CO2
energy storage (CCES),
looking separately at compressed supercritical
CO2
which involves storing liquid CO2
and trans-critical CCES,
in a lowpressure
tank and then reheating it before
compression. LAES, which involves
liquefaction of air, is also promising, but
though Highview Power is slated to begin
operating its first 50-MW/250-MWh
LAES facility in 2022, the company's initial
projects are still smaller-scale facilities
designed for grid stability applications.
That leaves TES. In the NICE Future
Initiative report, Charles Forsberg, principal
research scientist at the Massachusetts
Institute of Technology's (MIT's)
Department of Nuclear Science and Engineering,
highlighted several different
variations, though he noted " there is
no single optimum or best heat storage
technology, " because " different types of
nuclear plants deliver heat at different
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POWER July 2021

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