atw - International Journal for Nuclear Power | 2.2024

Environment and Safety
45
⁃ To provide medical assistance and manage the
treatment of radiation injuries
⁃ To protect property and the environment from
contamination and damage
⁃ To prepare for the resumption of normal social and
economic activity
It is important to note that Emergency Planning cannot
be discussed without considering nuclear accidents
and the relative risks associated with these accidents.
In 1975, Professor N. Rasmussen produced a report
for the Nuclear Regulatory Commission namely,
WASH-1400, ‘The Reactor Safety Study’. WASH 1400 put
into consideration the course of events that may arise
during a serious accident at conventional modern Light
Water Reactors. The report established the radiological
consequences of these events and the probabilities at
which they occur using the Fault Tree and Event Tree
techniques which is known today as part of Probabilistic
Risk (or Safety) Assessment (PRA/PSA). It was
concluded that risks to individuals posed by nuclear
power stations were acceptably smaller than other
tolerable risks, in fact a conclusion was also drawn
that the probability of a complete core meltdown is
approximately 1 in 20,000 per reactor year [13], [14], [15] .
Despite the significance and relevance of this new
method introduced in the WASH-1400 report, a storm
of criticism and several questions were raised years
after its release. As soon as the report was published,
several reports that either peer reviewed the methodology
or judged the probabilities and consequences
of various nuclear accidents at commercial reactors
were developed [16], [17], [18] . To this date, several PRA
related studies have been performed to assess the risks
associated with nuclear power plants. In more recent
years (at NuScale Power), C. Williams et al, in her study
to integrate defense-in-depth metrics into new reactor
designs explains an approach for augmenting the
traditional defense-in-depth philosophy with quantitative
risk data from plant specific PRA in such a way
that is well structured, can be used consistently and
allows for a clear acceptance criterion [19] .
2. Emergency Planning Zone
Emergency Planning zones define the areas beyond the
boundary of a reactor facility, in which implementation
of operational and protective actions are or might be
required during a nuclear emergency, to protect public
health, safety, and the environment [20]. In 2015, the
Nuclear Energy Institute published a white paper that
provides a proposed approach for re-evaluating the
size of the plume exposure pathway EPZ and the ingestion
exposure pathway EPZ for SMRs. The paper argued
that SMR designs have a significantly reduced potential
for accident-related offsite releases, and therefore, the
consequences from an accident involving an SMR facility
are expected to have a limited impact on public
health and safety. A suggestion was made that the EPZ
size for an SMR facility should be determined using a
dose/distance approach based on appropriate protective
action guidelines established by Federal agencies,
and that considers the consequences from a spectrum
of accidents. Moreover, the paper also identified proposed
changes to existing regulations and guidance
documents to support the implementation of scalable
EP requirements for SMR facilities. The proposed approach
in this paper maintains consistency with the
safety philosophy applied to large light water reactors,
i.e., a framework that is technology-neutral, dose-based,
and consequence-oriented [21].
2.1 Regulatory History and Policy Considerations
governing EPZ for SMR
The USNRC has a compilation of a few documents that
provide the regulatory history associated with NRC‘s
consideration of establishing a scalable, dose-based,
and consequence-oriented plume exposure pathway
(PEP) emergency planning zone (EPZ) for small
modular reactors (SMRs) [22] .
It also summarizes the staff’s evaluation of potential
policy issues associated with use of mechanistic source
terms in DBA dose analyses and siting.
Each nuclear power plant‘s EPZ size and shape is
determined individually, considering specific site
conditions, distinctive geographical features of the
area, and demographic information. EPZ-specific
strategies offer a solid foundation to introduce further
measures outside the planning zone in case highly
improbable events occur [35]
2.2 Radiological Safety
People‘s perception of nuclear power plants‘ safety has
been impacted by the historical nuclear accidents
(Three Mile Island plant, Chernobyl, Fukushima Daiichi),
which raised questions about the safety of nucler
reactors. The lesson learned from the Fukushima accident
is that it is necessary to emphasize the safety of
nuclear power plants to enhance public acceptance of
nuclear power and reduce the public’s fear of radiation
(effects); some called “radiophobia”. Several researchers
have conducted experiments that highlight the
importance of thoroughly validating the anticipated
safety features of SMRs. Consequently, it can be inferred
that Small Modular Reactors (SMRs) have the capacity
to provide improved radiological safety and robustness
in the face of unplanned, service disruptions. The
quantity and kind of radioactive materials that could
be released into the environment after a nuclear accident
are referred to as the „source term.“ A study done
by Lulik [36] and his team used an empirical approximation
to determine the source term based on the expression
given as,
Vol. 69 (2024)