IEEE Power & Energy Magazine - March/April 2022 - 58

the support of a larger grid. Due to its distributed nature, a
microgrid can reduce power transmission losses and provide
increased resiliency (avoidance or minimization of power
disruptions during contingency conditions) by maintaining
the electricity supply to critical loads in the event of grid
disruptions due to natural causes (e.g., earthquakes) or manmade
events (e.g., cyberattacks).
Unfortunately, the intermittent nature and seasonal variations
of these renewable resources create challenges, especially
in standalone microgrids. As a result, a microgrid
with renewable sources alone cannot fully meet the needs
of most off-grid applications without including a sizeable
amount of storage, typically in the form of batteries. At present,
such storage systems are relatively expensive for large
microgrids, and their manufacture has its own environmental
issues. Therefore, there remains a need for some additional
controllable sources that can fill the gap between the
renewable energy supply and the load demand.
An emerging solution is the small modular reactor (SMR),
which can provide a low-carbon sustainable energy supply
through one or more small nuclear units. This approach is
being pursued in part to address the historically challenging
economics of large-scale nuclear power plant construction.
Standardization, factory production, and simplified on-site
installation are expected to reduce the total time and cost
for SMR projects. A set of SMRs can complement renewable
sources in a microgrid environment to provide a reliable
supply of power with a near-zero greenhouse gas footprint.
A conceptual system is illustrated in Figure 1.
In this article, the concept, advantages, complementary
features, and potential challenges of control and energy management
for integrating SMRs and renewable energy-based
microgrids are discussed. The properties of different SMR
types will be presented, along with some key considerations
related to their integration, control, and coordination. Both
electricity production and district/process heat are considered.
Some key open issues are highlighted to stimulate research
and development.
SMRs
Unlike existing large-scale nuclear power plants, the output
capacity of SMRs is more comparable to those of renewable
energy plants. The flexibility offered by modular design
allows system designers to specify the number of units to
be employed. As demand changes over time, more units
could be added or removed accordingly. Most SMRs are
equipped with passive safety features that
lower the risk
of catastrophic accidents, and also include load-following
capabilities to meet changes in demand. They are well suited
to applications with varying load demand in the presence
of uncertainties and variability associated with renewables.
They not only provide electricity but also thermal energy
for applications in remote communities and industrial sites.
The definition of " small " for SMRs refers to single-reactor
units of less than 300 MWe power generation capacity. For
example, consider the 160 MWe/525 MWt Holtec SMR-160
reactor design, which involves a containment structure that is
62 m tall (though partially buried underground) on a 4.6-acre
site. Several SMR designs are sized to be well suited for placement
on brownfield sites previously used for comparably rated
fossil-fuel plants, thus allowing for reuse of existing infrastructure
such as local transmission substations and site services.
The modular aspect refers to two salient features: modularity
in reactor design, and the potential to link multiple
modules to form a larger system. A standardized reactor
module can be produced in volume in a factory. Therefore,
the manufacture of the reactor systems and site construction
can be carried out in parallel. In addition, the use of standardized
modules can potentially reduce the site-specific engineering
requirements by providing turnkey facility reference
Solar Panels
Residential
Loads
Battery Storage
Electrical
Network
Wind Turbines
Pair of
Small
Modular
Reactors
figure 1. A microgrid with SMRs and renewable energy resources.
58
ieee power & energy magazine
march/april 2022
Thermal
Loop
Switchyard
Industrial Loads
IEEE Power & Energy Magazine - March/April 2022

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