atw - International Journal for Nuclear Power | 2.2024

Environment and Safety
53
No. Step Description/Factors considered
3 Plant Design
4 Postulated
Initiating Events
⁃ The plant design should include details about the planned number of operating reactors, power levels,
electrical distribution, water sources and returns, emergency core cooling systems, spent fuel storage, etc.
⁃ Description of the containment must be provided
⁃ Major design features typical to SMR designs that may affect determination of the EPZ were also put in
consideration
⁃ An EPZ limited by site boundary may be considered due to the nature of small reactors and low rated
thermal power levels. These work together to reduce the amount of radioactive materials that could
potentially be released to the environment.
⁃ The independent construction of SMR modules divides the source term into smaller, discrete reactors and
this makes a large-scale offsite consequence less possible as compared to a single unit large reactor. Thus,
an EPZ limited by site boundary may be considered
⁃ Different SMR containment designs such as compact, high pressure, double-wall and water immersed
containment structures lower the potential offsite consequences and hence an EPZ limited by site boundary
may be considered.
Various member states’ approaches to identify postulated initiating events and their impacts differ. Some
member states consider a specific set of events where the applicant supplements any additional events
required by regulations while other member states have a criterion where the applicant evaluates initiating
events and determines the most severe set of events to include in siting and determination of EPZ sizes.
Therefore, an applicant must identify the postulated initiating events which could result in release of radioactive
material. One must also address how lessons learned from industry events are met through the plant
design.
5 Safety Analysis Safety analysis criteria may differ from state to state due to the systems involved, system integration and
safety significance of the system.
6 Selecting events;
Planning Bases
A list of credible accidents that would bound the analysis must be established.
The plant design needs to address which accident sequences were analyzed and results as part of the
analysis.
7 Source Term When estimating source terms for accident scenarios identified during safety analyses, the designers may
use mechanistic source terms to account for the design-specific accident scenarios and accident progression.
Use of mechanistic source terms may form part of the designer’s request for a smaller EPZ than that
which would be granted to a large light water reactor.
8 Release Data Release height i.e., stack or ground release, time before release, magnitude of release
(gross activity, isotopic activity, effluent flow rates), duration of release, type of effluent (liquid, gas, metallic
etc.)
9 Site Meteorology Wind direction, wind speed, stability category, precipitation, mixing height, humidity.
10 Atmospheric
Dispersion
Modelling
11 Determining
Offsite Dose
Consequences
12 Generic Dose
Criteria
13 Local Infrastructure
Characteristics
14 Public and
Political Policy
Site specific meteorological data from nearest weather station, recent data period of one year
should be used, weather data should be statistically analyzed to determine weather conditions used
for planning purposes.
Offsite dose consequences resulting from postulated initiating events and source term must be analyzed.
Different member states may determine the generic dose criteria through diverse levels of government,
differing ministries and agencies. That is to say, the dose criteria in one state may be published by various
ministries for individual, societal or industrial sectors that are regulated by the ministries.
The EPZ size evaluation should identify those local infrastructure characteristics and factors that could
affect plant safety and any significant impediments to implementing Emergency Planning and Response.
Public and Political policies could put into consideration affected groups’ input within the area
of the proposed site, neighboring states, and states’ public policies in determining EPZ sizes.
15 Establish EPZs Local or provincial governments make a final decision depending on site suitability in some states
whereas in other states, the national government makes the final decision.
16 Are the offsite
consequences
at a distance
greater than
dose criteria?
⁃ If the offsite dose consequences exceed the dose criteria at a given distance, then expand the EPZs
⁃ Continue comparing the offsite dose consequences with dose criteria for a longer distance until the offsite
dose consequences do not exceed the dose criteria.
⁃ Member states must confirm the analysis and establish the EPZs
⁃ Applicants and states establish and maintain the emergency preparedness and planning within EPZ
distances.
Tab. 8.
Steps or processes involved in the Generalized Approach to determine EPZ sizes [46]
Vol. 69 (2024)