Reliability Engineering and System Safety 135 (2015) 9–14
Contents lists available at ScienceDirect
Reliability Engineering and System Safety
journal homepage: www.elsevier.com/locate/ress
Alternative evacuation strategies for nuclear power accidents
Gregory D. Hammond n,1, Vicki M. Bier
University of Wisconsin-Madison, Department of Industrial and Systems Engineering, 3270A Mechanical Engineering Building, 1513 University Ave., Madison,
WI 53706, USA
art ic l e i nf o
a b s t r a c t
Article history:
Received 21 March 2014
Received in revised form
4 October 2014
Accepted 12 October 2014
Available online 27 October 2014
In the U.S., current protective-action strategies to safeguard the public following a nuclear power
accident have remained largely unchanged since their implementation in the early 1980s. In the past
thirty years, new technologies have been introduced, allowing faster computations, better modeling of
predicted radiological consequences, and improved accident mapping using geographic information
systems (GIS). Utilizing these new technologies, we evaluate the efficacy of alternative strategies, called
adaptive protective action zones (APAZs), that use site-specific and event-specific data to dynamically
determine evacuation boundaries with simple heuristics in order to better inform protective action
decisions (rather than relying on pre-event regulatory bright lines). Several candidate APAZs were
developed and then compared to the Nuclear Regulatory Commission’s keyhole evacuation strategy (and
full evacuation of the emergency planning zone). Two of the APAZs were better on average than existing
NRC strategies at reducing either the radiological exposure, the population evacuated, or both. These
APAZs are especially effective for larger radioactive plumes and at high population sites; one of them is
better at reducing radiation exposure, while the other is better at reducing the size of the population
evacuated.
Published by Elsevier Ltd.
Keywords:
Nuclear incidents
Evacuation
Nuclear power plants
Emergency preparedness
Protective action recommendations
1. Introduction
Current strategies used to determine who to evacuate following a
nuclear-power plant accident have not changed significantly since
the emergency planning guidelines were established in the early
1980s. While plans and studies have been modified and updated, this
has been done under the constraint of a roughly constant evacuation
area. Consequently, changes to protective actions have focused on
issues such as in which order people should be evacuated, or in
which direction they should evacuate [1,19]. Yet in the past thirty
years, the task has radically changed; new technologies have been
introduced, allowing faster computation, better modeling of predicted radiological consequences, improved accident mapping using
geographic information systems (GIS), and new means to communicate. Additionally, the populations surrounding nuclear-power
plants are denser; more people live closer to reactors than ever
before. In the past 30 years, the average population living within
n
Corresponding author.
E-mail addresses: gregory.hammond@afit.edu (G.D. Hammond),
[email protected] (V.M. Bier).
1
Present address: Air Force Institute of Technology, Department of Systems
Engineering and Management, 2950 Hobson Way, Wright-Patterson AFB, OH,
45433, USA.
http://dx.doi.org/10.1016/j.ress.2014.10.016
0951-8320/Published by Elsevier Ltd.
16 km of these plants has increased by 62%, from approximately
40,000 to almost 65,000 per site. Furthermore, at 12 of the 65 reactor
sites in the U.S., populations have more than doubled [2]. In the wake
of the Fukushima Daiichi nuclear accident – considering the range of
new capabilities and the greater population at risk – this study
sought to reexamine the U.S. nuclear-power plant evacuation strategy by removing the constraint of a constant evacuation area or
predetermined evacuation zones.
This research is a proof of concept; its purpose was to develop
alternative evacuation strategies for use during the early phase of
nuclear-power plant accidents in order to take advantage of some
of the recent technological advances. The early phase is defined by
the U.S. Environmental Protection Agency (EPA) as “the period at
the beginning of a nuclear incident when immediate decisions for
effective use of protective actions are required and must therefore
usually be based primarily on the status of the nuclear facility and
the prognosis for worsening conditions” ([25], p. 5). Thus, the early
phase is filled with uncertainty. The plant operators and emergency response officials know only that the situation at the reactor
is a cause for concern and that an off-site radiological release is
possible, so they can only guess at the extent of the problem.
Despite this imperfect knowledge, officials must act and make
decisions to protect the public from potential radiation exposure,
generally in the form of evacuations (because distance is the best
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G.D. Hammond, V.M. Bier / Reliability Engineering and System Safety 135 (2015) 9–14
protection) and/or sheltering in place. In the earliest periods of
this phase, decisions are made based on predictions of the
radiological release [25].
Notwithstanding the likely discrepancies between early phase
projected doses and actual off-site doses that will be observed
later, protective action recommendations must be made in the
early phase, because evacuation in advance of the plume (ideally
at least 1 h before the plume’s passage) is the best way to reduce
dose [12,23]. This research explored alternative methods to
determine who should be evacuated during the early phase. An
ideal strategy would be able to perfectly evacuate the at-risk
population before the radioactive plume passes. At present, of
course, neither the APAZs developed in this research nor the NRC’s
method can achieve this standard; however, as will be shown, the
APAZs demonstrate progress towards meeting that standard.
Because no method is perfect, the comparison between APAZs
and the NRC’s method was framed as a multi-attribute decision
problem using the objectives of minimizing the population to be
evacuated and maximizing the total radiological dose avoided.
These objectives are based on the current regulatory position of
the NRC, which focuses evacuation efforts on high-risk areas [27],
as well as the EPA guideline that informs the NRC’s policy, which
states that evacuation risk should not exceed the risk from the
avoided dose [11]. While there is general acceptance that avoiding
radiological dose is beneficial, some might argue that instead of
minimizing the population evacuated, the goal should be to
maximize the size of evacuation. Because distance is a highly
effective defense against radiation [12,23], some might argue that
if the entire population surrounding a nuclear power plant could
be evacuated prior to passage of the plume, that population could
be guaranteed safety, suggesting that the objectives of high total
dose avoided and high population evacuated would yield a
desirable (if conservative) outcome. This logic is flawed, however,
because maximizing the population evacuated can expose many
people to risks greater than the risk of the radiological release, and
ignores the risks and costs of evacuations.
Evacuation can have adverse health impacts. Evacuation risks
include travel, events in which travel is the contributing cause, and
activities other than travel (i.e., preparation or reception activities)
[3,30]. Witzig and Weerakkody have estimated travel risk to be
6 10 8 fatalities per vehicle-km; this risk is considered to be an
upper bound as the actual risk is expected to be lower than normal
automobile travel due to conditions of heavier traffic and lower travel
speeds [3,30]. Injuries or fatalities in which travel contributed to their
occurrence is the second category of risk. An example is an individual
who evacuates the wrong direction and drives into a radioactive
plume; it is believed to be an order of magnitude greater than travel
risk [30]. The last evacuation risk, estimated to be 5 10 6 per
person, is due to evacuation preparations and the arrival at the
reception center ([3,30]). These three risks collectively form evacuation risk. For a given emergency, the evacuation risk is a function of
the number of individuals that leave. When larger numbers of people
evacuate who are not required to evacuate (i.e., shadow evacuations),
the collective risk to the population will significantly increase [3]. The
EPA evacuation risk estimate (for fatalities) corresponds to Witzig
and Weerakkody’s upper bound estimate meaning that for radiation
doses of less than 3 mSv, the evacuation risk is greater than the
radiation risk [11]. Maximizing the evacuation area relocates many
people who would receive doses less than 3 mSv, exposing them to
needless risk. As noted by Aumonler and Morrey, “evacuation risks
constitute a harm which should be considered in a decision as to
whether to evacuate a population put at risk by a radiological
incident” ([3], p. 290). For this reason, a safer course of action would
evacuate those whose radiation risk is greater than their evacuation
risk, but not those whose evacuation risk is greater than their
radiation risk.
Minimizing the population evacuated and maximizing the total
dose avoided embodies the EPA’s position that the protective
actions should not be “higher than justified on the basis of
optimization of cost and the collective risk of effects on health”
([11], p. 135). Thus, for this research, a high dose avoided and low
population evacuated are assumed to be preferred.
Using these two objectives, APAZs were compared to the NRC’s
strategy using a concept called the “efficient frontier,” to allow
decision makers to evaluate alternatives using their own value
systems. Alternatives are plotted on the basis of the decision
objectives (i.e., dose avoided and population evacuated). Dominated options can be excluded from consideration; the decision
maker can then select a preferred option based on his or her
preferences from among the non-dominated strategies on the
efficient frontier.
Current U.S. response protocols have been previously well
documented. The interested reader is encouraged to review these
earlier articles for a more in-depth understanding [11,21,23,24,28].
While the regulations that dictate emergency response have been
updated (such as the EPA’s Protective Action Guides and Planning
Guidance for Radiological Incidents [25] and the NRC’s guidance
for protective action strategies [27]), as noted earlier, the fundamental initial evacuation strategy has remained constant. In the
event of a nuclear-power plant accident, plant operators would
determine evacuation areas using the NRC’s guidance for protective action strategies [27]. Based on the postulated source term
and forecast meteorological conditions, a projected radiological
plume is calculated and then fit to pre-established evacuation
zones; this is the NRC’s keyhole strategy. (This strategy has been
criticized because the plume model provides a simplified view of a
complex process that may not correlate with the observed plume
causing the wrong people to evacuate [23]).
This research proposes an alternative method to determine the
evacuation area. In this approach, instead of fitting the projected
plume to pre-established zones, the evacuation area would be
determined by applying a heuristic enlargement strategy directly
to the forecast plume.
2. Calculations
2.1. Development and testing of APAZs
Candidate APAZs (described subsequently) were tested using
weather data from five nuclear power plants: Limerick; Catawba;
Turkey Point; Pilgrim; and Arkansas Nuclear One. These plants
were selected based on their proximity to National Weather
Service (NWS) data-collection sites. The forecast and hindcast
weather data (i.e., predicted and observed weather conditions)
used in this analysis was produced by the National Oceanic and
Atmospheric Agency (NOAA) and the NWS.
The source term varied depending on the plant’s output power
and reactor type. The source term for each nuclear-power plant
was calculated using the time that the core was assumed to be
uncovered in an unmitigated short-term station blackout (STSBO)
scenario, described in the State-of-the-Art Consequence Analysis
(SOARCA) [9]. The total release ranged from 3.3 1018 Bq to
1.2 1019 Bq. These postulated releases are of the same order of
magnitude as that from the Fukushima Daiichi accident [26].
Forecast and hindcast plumes used in this research were
generated with NRC’s Radiological Assessment System for Consequence AnaLysis (RASCAL) [6]. Nineteen candidate APAZ strategies
were tested using 120 weather observations from summer 2012
and winter 2012–2103. Protective action zones, formed by enlarging a forecast plume in accordance with a given heuristic, were
compared to the hindcast plumes.
G.D. Hammond, V.M. Bier / Reliability Engineering and System Safety 135 (2015) 9–14
The forecast plume generated from RASCAL was used to
identify a mandated evacuation zone in which the 4-day total
effective dose equivalent (TEDE) was predicted to be greater than
or equal to 0.01 Sv, based on established policy [11]. Each of the 19
enlargement strategies was then applied to the mandated
evacuation zone.
The APAZ enlargement strategies consisted of varied offsets
around the forecast evacuation zone (meaning that an additional
X km was added to the size of the evacuation zone). Some of them
had a uniform offset of varying distances (e.g., 4 km) around the
forecast evacuation zone. Other strategies applied an offset in
either a perpendicular or lateral direction to the prevailing wind
direction. Other strategies applied a radial offset around the
reactor in combination with an offset around the evacuation area.
Furthermore, some strategies applied a multiplication factor to the
predicted TEDE and then applied an offset. Many different strategies were tested in order to represent a wide range of policy
options.
The candidate APAZ heuristics were evaluated based the goals
of minimizing the evacuation area and maximizing the adequacy
of protective actions, as follows. First, the forecast plume was
determined. It was then enlarged according to the relevant APAZ
heuristic to determine the evacuation area. Next, the hindcast
plume was determined, as a basis for assessing the adequacy of the
APAZ. Area was measured as the ratio of the APAZ area to the
hindcast evacuation area. Adequacy of the APAZ was measured by
the fraction of the hindcast evacuation area that was also included
in the APAZ evacuation area.
The average area evacuated and average adequacy were compared for all nineteen heuristics. The comparison indicated that
most heuristics fell on an efficient frontier. Results are shown in
Fig. 1. The frontier extends from APAZ I (with small evacuation
area but low adequacy) to APAZ T (with a large evacuation area
and high adequacy). That the different strategies form a coherent
efficient frontier indicates that no strategy can perfectly predict
the location of the hindcast plume. Instead, the various strategies
represent different trade-offs between the competing objectives
of a small evacuation area and high adequacy. Three APAZs (B, D,
and E) were retained for further comparison, because they are
simple to implement and represent a range of policy choices.
Fig. 1. Ratio of APAZ to hindcast area as a function of APAZ adequacy.
11
APAZs B, D, and E were subjected to additional sensitivity
analyses. Using a second set of 40 weather predictions and
observations, the effect of dispersion model, source term, and
evacuation timing were evaluated. The first sensitivity analysis
compared our primary dispersion model (RASCAL), which is a 2-D
plume model, with the 3-D HYSPLIT transport model [15]. A paired
t-test was performed to check for adequacy differences between
RASCAL and HYSPLIT. The t-test suggested that APAZ adequacy
using the two different models was not statistically distinguishable. This result means that regardless of the hindcast model used,
on average, APAZ adequacy will remain roughly the same.
The second analysis considered the effect of alternative source
terms. The initial screening was conducted using an unmitigated
STSBO source term. To ensure that APAZs are robust with respect
to the source term, APAZ adequacy and evacuation area were
compared for the STSBO and a: long-term station black-out
(LTSBO), STSBO with reactor core isolation cooling (RCIC) for
boiling water reactors (BWR); and an LTSBO and thermally
induced steam generator tube rupture (SGTR) for pressurized
water reactors (PWR). For the alternative source terms, the four
APAZs remained in their relative locations along the efficient
frontier.
The third analysis investigated the effect of forecast age. It was
used to determine the effect of timing of the evacuation order.
When any predictive PAR strategy is used (i.e., APAZs or keyhole),
emergency response officials must make a determination of when
to generate the forecast plume. Thus, the purpose of this analysis
was to determine the effective time horizon for APAZs to understand their reliability in regards to the actual time of release. In the
sensitivity analysis, forecast age was allowed to increase from zero
hours (as had been used previously), up to 24 h before the release.
This analysis showed that neither APAZ adequacy nor its area
varied significantly as the forecast age increased. There is some
variation, but that variation appears to be due to statistical noise
rather than a significant difference. In all of the above analyses,
APAZs B, D, and E all remained on the efficient frontier, indicating
that they are all reasonably robust candidate evacuation strategies.
2.2. Comparison of APAZs to NRC evacuation strategies
This phase of the research compared the three selected APAZ
strategies to other protective action strategies. The APAZs included
in this comparison were: (1) APAZ B (with a 5-km radial area
around the reactor, plus a 2-km offset around the 0.01-Sv
boundary); (2) APAZ D (with a 4-km offset around the 0.01-Sv
boundary); and (3) APAZ E (with a 6-km offset around the 0.01-Sv
boundary). The comparison PAR strategies were: (1) evacuation of
the entire EPZ [9]; and (2) the keyhole strategy (utilizing the
predefined NRC sectors [10]). The comparison was based on both
the total radiological dose avoided (defined as the sum of TEDE for
all persons evacuated) and the total population evacuated. Preferred strategies were assumed to be those with a high total dose
avoided and a low population evacuated.
Six nuclear-power plants were selected for this phase of the
analysis: Surry; Peach Bottom; Grand Gulf; Kewaunee; San Onofre;
and Braidwood; they are broadly representative of U.S. plants in
terms of geographic region, surrounding population, and reactor
type (BWR or PWR).
We considered eight different weather observations per plant,
chosen to include both summer and winter, days with and without
precipitation, and differing times of day (i.e., mid-day or evening).
Source terms were derived from the SOARCA report: long-term
station black-out, STSBO, and STSBO with reactor-core isolation
cooling for BWRs; long-term station black-out, STSBO, and steam
generator tube rupture for PWRs. In total, 182 different cases were
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G.D. Hammond, V.M. Bier / Reliability Engineering and System Safety 135 (2015) 9–14
analyzed (due to some weather conditions not being observed at
some plants during the study period).
The evaluation was performed using ArcGIS mapping software.
We began with the geographic boundaries of census block groups,
as obtained from the U.S. Census Bureau’s TIGER/Line Shapefiles
([7]). The geographic boundaries of the census blocks groups were
then overlaid with 2010 census data ([8]) to determine how many
people lived in each block group.
Next, the hindcast plume (exported from RASCAL as a shapefile) was overlaid on the population data. The information from
these two layers (population and hindcast plume) was used to
compute the potential radiation dose that would be incurred if any
given block group was not evacuated.
The forecast plume (also exported from RASCAL as a shapefile)
was then used to determine which geographic areas would be
evacuated using APAZs B, D, and E, and the keyhole evacuation
area. (It should be noted that the plumes were generally complicated in shape, and spanned multiple sectors.) In all cases, the
keyhole was taken to be the union of all sectors in which the
forecast plume was projected to fall, plus two additional sectors,
one on either side of that region.
Occasionally, the dose from the forecast plume exceeded
0.01 Sv beyond the outer boundary of the EPZ. In the keyhole
strategy, evacuations past the EPZ were limited to areas where
dose projections indicated that protective actions would be
necessary [9], since NRC strategies are not defined beyond the
EPZ. This strategy was implemented by evacuating the relevant
keyhole area, plus all RASCAL program grid elements beyond the
EPZ with doses exceeding 0.01 Sv.
With the population, hindcast dose, and plume location known,
for each evacuation strategy, the analysis then generated two
statistics of interest: total dose avoided, given in TEDE (person-Sv);
and total population evacuated. Total population evacuated was
computed as the sum of the populations of all evacuated census
blocks; total dose avoided was based on the populations and
corresponding hindcast doses of all evacuated census blocks (i.e.,
all areas with doses greater than 0.01 Sv TEDE). The total dose
avoided and population evacuated for each strategy were then
compared to the total dose avoided and population evacuated that
could have been achieved with perfect advance knowledge of the
hindcast plume.
3. Results
Fig. 2 below shows that APAZ B achieved comparable or better
dose avoidance than could have been achieved by evacuating only
the relevant portions of the hindcast plume on 77% of all cases, but
evacuated significantly more people than the hindcast plume area
in 41% of all cases. (The ideal is to achieve a comparable or better
dose avoided in 100% of cases, and over-evacuate in 0% of cases.)
We see that APAZs B (0.77, 0.41), D (0.88, 0.59), and E (0.92, 0.82)
still form an efficient frontier. The keyhole strategy (0.67, 0.52) is
dominated by APAZ B, and evacuation of the entire EPZ (0.88, 0.88)
is dominated by APAZ D. Thus, it appears that APAZs are more
efficient than keyhole evacuation or evacuation of the entire EPZ.
On average, APAZ B is better at both avoiding radiological dose
and minimizing over-evacuation than the keyhole strategy. In
practical terms, when APAZ B is better than the keyhole strategy,
it avoids about two more latent cancer fatalities (LCF) and
evacuates about 4000 fewer people. Likewise, APAZ D is better
than evacuation of the entire EPZ at minimizing over-evacuation.
Compared to the keyhole strategy, APAZ D is better at avoiding
dose (achieving approximately five fewer LCF), but evacuates
approximately 6000 more people.
Fig. 2. Comparison of results.
Fig. 3. Effect of plume size on performance.
Breaking down the results further, as shown in Fig. 3, we found
that for small accidents (i.e., those where the radioactive plume
did not extend more than 8 km from the reactor, those where the
plume travelled over a large body of water, or those with a
population of less than 60,000 near the reactor), APAZs B and D
and the keyhole strategy were comparable. However, for large
accidents (i.e., those with plumes that traveled more than 8 km
from the reactor, or at locations with more than 60,000 people
within the EPZ), APAZs B and D were preferred to the keyhole
strategy. APAZ B reduced the evacuated population by as much as
23,000 for large accidents (averaged over multiple sites, weather
conditions, and source terms), and avoided between three and
eight LCF. APAZ D was comparable to the keyhole strategy with
regard to the size of the evacuated population, but avoided on
average from 6 to 12 additional LCF in large accidents.
4. Discussion
As described in the introduction, there is considerable uncertainty during the early phase of emergency response. Discussion
is warranted to describe how we addressed this uncertainty.
G.D. Hammond, V.M. Bier / Reliability Engineering and System Safety 135 (2015) 9–14
McKenna has characterized the uncertainty in three domains:
transport; individual dose response; and source term [23]. Transport consists of variability in both weather patterns throughout
the release and the atmospheric transport model. As noted in
Section 2.1, both elements were examined in this study. The
meteorological effects were addressed by comparing forecast to
hindcast plumes, holding other effects constant. Then, through
sensitivity analysis, other effects were evaluated to ensure that the
chosen heuristic was sufficiently robust to account for different
release mechanisms, the timing of evacuation decisions, and
RASCAL model effects. (The plume model effects were explored
by comparing results from RASCAL with the HYSPLIT 3-D plume
model [15]) None of these effects were found to be significant.
This research did not directly address dosimetery uncertainty.
However, the impact of this uncertainty was minimized by using
the EPA assumption [11] of no shielding. As a result, projected
doses were likely higher than those that would be expected
following an actual release. While not entirely satisfying, this
conservatism is consistent with current emergency-response
protocols.
Furthermore, while the source term uncertainty was not
directly modeled, the results provided yield some insight into its
implications. Source term uncertainty is a significant challenge; at
best it is a factor of 10, but it could be a factor of 100–10,000 [23].
However, source terms were likely over-estimated because RASCAL assumes a near worst case scenario in which the radionuclides
leave the reactor core quickly [26]. Moreover, any errors in source
terms would apply equally to the APAZs and the NRC strategies.
Finally, as was shown in Fig. 3, if the predicted source terms are too
large, then we would expect to see little difference between the
APAZs and the NRC strategies, because the true plumes will be
small. However, if the predicted source terms are too small, then a
distinguishable effect would be observed, because the true plume
will be larger than thought. The assumptions and sensitivity
analyses do not eliminate the inherent uncertainty in source
terms, but it is not a threat to the validity of this research.
Additionally, this research did not address the means and
methods needed to communicate these alternative evacuation
strategies with the public. In the event of a nuclear power
accident, many residents are likely to ignore the protective action
guidelines. Previous studies have demonstrated that compliance to
a given directive during nuclear power emergencies is highly
dependent on the nature of the directive. Individuals are willing
to evacuate, or even shelter in place; however, when asked to
shelter in place while others leave (as is the case of selective
evacuations such as these strategies), they are much less willing to
stay, with approximately 50% to 60% of respondents indicating that
they would ignore the directive and leave ([16,18]; [20]). Evacuation compliance is further complicated by the tendency of individuals to not follow prescribed evacuation routes [22] as well as
misperceptions regarding one’s location relative to the plant [17].
To overcome these challenges, these strategies would need to be
effectively communicated in simple, understandable terms. The
application of risk communication to these alternative strategies
should be further investigated.
The study is also limited because it assumed perfect evacuation
in advance of the plume. Using the baseline assumption of 100%
evacuation of the target population before passage of the plume,
the APAZ strategies can be compared to other strategies without
the use of a transportation model. Not using a transportation
model simplifies the calculations significantly. While 100% evacuation is likely unrealistic, it allows for a fair comparison. Based on
these results the total populations evacuated for the keyhole
strategy and APAZ B were roughly equivalent; likewise, evacuation
of the entire EPZ was roughly equivalent to APAZ E. If anything, the
assumption of 100% evacuation in advance of the plume benefits
13
those strategies (APAZ E and the entire EPZ) that evacuated larger
areas, since these large evacuations are not penalized for excessive
road congestion, even though in reality individuals may get stuck
in traffic jams while attempting to evacuate.
Lastly, the findings of this study is limited to the comparison
of protection levels offered by different evacuation strategies.
Research comparing the protective strategies of sheltering in place
and evacuation in the event of nuclear terrorism suggests that
sheltering in place followed by a delayed evacuation provides the
greatest level of protection during the early response phase
[4,5,29]. Additional research by Denning et al. [13] extends this
finding to nuclear power accidents. The purpose of this paper was
not to compare sheltering in place and evacuation; rather it sought
to present alternative evacuation strategies. Future research
should consider the impact of these alternative strategies as
applied to delayed evacuation and sheltering in place.
5. Conclusion
The objective of this research was to identify alternative
evacuation strategies as a proof of concept. In this, the research
was successful; it identified candidate evacuation methods that
perform better than those currently employed. Should these
potential gains be considered significant enough by policy makers,
future research should further develop the framework into a
concept of operations that addresses potential implementation
issues and assumed administrative burdens. Indeed, the main
significance of this work is not the choice of one APAZ or another,
but rather the methodology that was used to test and evaluate
alternatives.
We found current strategies to be adequate for smaller accidents; however, we found a distinguishable difference for larger
accidents. Therefore, policy makers should seriously consider
implementing the findings of this research. Authorities that value
balancing evacuation and radiological should consider adopting
either APAZ B or APAZ D. Likewise, APAZ E is a viable option for
decision makers who to prefer to maximize radiological risk
avoidance. Such an action would strengthen the overall defensein-depth of nuclear-power plants.
Note, however, that altering the current evacuation strategy is
likely to have significant costs and consequences. Indeed, such an
action would directly affect the emergency response network,
requiring evacuation areas at all levels of government to be redrawn. Moreover, the human response to these alternative protocols must also be investigated. Previous studies have also found
benefits with alternative strategies [14,20], but the solutions were
dismissed due to concerns of impracticality. Accordingly, the
practical importance of the improvements achievable using APAZs
should most appropriately be seen as a value judgment. In other
words, the APAZ approach, which can improve readiness for larger
radioactive releases (and also minimize unnecessary evacuations),
must be evaluated in the context of its implementation costs and
administrative burdens. The NRC, in its statutory role of ensuring
the safe use of radioactive material and protection of the population, should assess the importance of the improvements we
identified, through further study, as they relate to public safety
and policy.
Acknowledgements
The authors gratefully acknowledge the NOAA Air Resources
Laboratory (ARL) for the provision of the HYSPLIT transport and
dispersion model and the Nuclear Regulatory Commission (NRC) for
the provision of the RASCAL consequence management software
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used in this publication. They would also like to thank the reviewers
for their insightful comments and recommendations.
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