atw - International Journal for Nuclear Power | 2.2024

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Environment and Safety
population. These codes can estimate the doses and
health effects for different scenarios and locations and
help to identify the appropriate protective actions and
emergency planning zones (EPZs) for the facility [24] .
One of the consequence assessment methods that is
used by the USNRC and other regulatory bodies is the
MACCS code which stands for MELCOR Accident
Consequence Code System, and it is a suite of programs
that can model the atmospheric dispersion of radionuclides,
the deposition and resuspension of contaminants,
the ingestion of contaminated food and
water, the evacuation and relocation of people, and the
economic costs and health risks of the accident. MACCS
can be used to perform probabilistic risk assessments
(PRAs) that account for the frequency and severity of
different accident sequences, and to determine the EPZ
size based on the dose criteria and the protective action
guidelines [79] .
5.5 The iPWR stand-alone case
C. Zeliang et al. [86] noted that over the years, the iPWR
SMR type has stood out from the rest of the small
modular reactors because it integrates the major of
known primary system components to inherently
eliminate or lower potential accident initiators and
employ simplified Passive Safety Systems to counter
and mitigate the remaining accident initiators. These
design aspects are substantiated by substantial operating
experience (PWRs) and legacy PWR designs. The
iPWR design characteristics offers the potential to
eliminate some potential accidents initiators (e.g.,
large loss of coolant accidents (LOCAs), control rod
ejection accident), decrease the probability of failure
for remaining initiators; and enhanced features to
mitigate the consequences [87], [88], [89], [90], [91] .
To deploy iPWR Small Modular Reactors soon, as part
of emergency preparedness and response plan, it is
very important to assess their potential radiological
impact and emergency planning zones. C. Zeliang and
his co-authors [86] in their research work, tried to
provide an analysis and estimation of the envelope of
the potential impact from a severe accident in an iPWR.
The source term was calculated from the solution
of the lumped aerosol concentration equation in the
containment, by using different approaches for
estimating the various parameters. The first approach
comprised a straightforward use of the methodology
and parameters used for large reactors differing only
in the lower power level of an iPWR. To account for the
anticipated enhanced aerosol retention in the containment
and the slower (in time) core damage progression
in case of iPWR, two additional approaches
were also used.
6. Conclusions
Determination of the Emergency Planning Zone
surrounding a nuclear power station reflects both the
technical aspects and the associated (regulatory)
compliance – foremost safety-in-design and operations.
The necessity of a defined EPZ gives the public
assurance and assures the careful consideration of the
impact of accidents involving NPPs. EPZs are required
under various regulatory and governmental frameworks
at all NPPs stations. This expectation will not be
any different for Micro to Small Modular Reactors, in
both new sites and existing sites. For SMRs/MMRs,
smaller EPZ is expected, since potentially, the “sourceterm”
is smaller than conventional (large) NPPs. Prior
to the recent certified SMR designs, the EPZ was
conservatively based on recommendations by an
expert panel. Some 40+-years later some to many
( national) regulatory frameworks remain unchanged
(except incremental developments) with respect to
the EPZ. In brief, these perspectives summarize the
spectrum of aspects, as follows:
⁃ Insights from all the papers collated offer a holistic
perspective on EPZ requirements for large reactors
applied to, and SMRs (including MMRs) going
forward. Together, they provide a comprehensive
understanding of the challenges and solutions
associated with determination of the EPZ for (alltypes
of) SMRs – importantly integrating both
national regulatory expectations and technical
considerations. They collectively contribute to the
ongoing dialogue on ensuring the safety-in-design
of nuclear power, particularly in the context of
Small Modular Reactors.
⁃ When implementing SMR, an EPZ is a crucial factor
to consider since it is critical to build trust and thus
public acceptance in this new technology. Public
acceptance or social license take time, effective
communication, transparency, engagement, and
continuous education [92], [93], [94] .
⁃ The existing research focuses on specific designs
that may establish emergency planning zones for
Small Modular Reactors. Some regulators intend to
develop a technology neutral, open access approach
used to establish the EPZ of SMRs.
⁃ In some new nuclear power nations with a weak
regulator, the vendor determines the EPZ of the
plant. This is because the vendor has more
experience and knows the best criteria to determine
the emergency planning zone.
⁃ It is also important to note that the EPZ for SMRs is
scalable depending on the results of accident
analysis, the technology type, novel features, and
specific design criteria and policy factors which
vary amongst different countries.
⁃ The safety culture in the SMR industry needs to be
explored deeply to better understand all the safety
systems in place in case of an SMR related
emergency.
Acknowledgement.
The co-authors note and thank Mr. Anthime Farda,
World Nuclear University Summer Institute graduate,
for providing references regarding the French
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