Journal of
Environmental Radioactivity 60 (2002) 23–48
Atmospheric transport patterns and possible
consequences for the European North after a
nuclear accident
A. Baklanova,*, A. Mahurab,e, D. Jaffeb, L. Thaningc,
R. Bergmanc, R. Andresd
a
Danish Meteorological Institute, DMI, Lyngbyvej 100 2100, Copenhagen, Denmark
Atmospheric Sciences Department, University of Washington, Seattle 98195, USA
c
Defence Research Establishment, FOA 90182, Umea(, Sweden
d
Institute of Northern Engineering, University of Alaska Fairbanks 99775-5910, USA
e
Institute of Northern Ecological Problems, Kola Science Centre, Apatity 184200, Russia
b
Received 28 December 1999; accepted 9 August 2000
Abstract
The main purpose of this study is to examine possible impacts and consequences of a
hypothetical accident at the Kola nuclear plant in north–west Russia on different geographical
regions: Scandinavia, central Europe, European FSU and Taymyr. The period studied is
1991–1996. An isentropic trajectory model has been used to calculate forward trajectories that
originated over the nuclear accident region. Atmospheric transport patterns were identified
using the isentropic trajectories and a cluster analysis technique. From the trajectory model
results, a number of cases were chosen for examination in detail using more complete
transport models. For this purpose, the models MATHEW/ADPIC, DERMA and a newly
developed FOA Random Displacement Model have been used to simulate the radionuclide
transport and contamination in the case of a nuclear accident and their results have been
compared with those of the trajectory modelling. Estimation of the long-term consequences
for populations after an accident has been performed for several specific dates by empirical
models and correlation between fallout and doses to humans on the basis of the Chernobyl
accident exposures in Scandinavia. r 2002 Elsevier Science Ltd. All rights reserved.
*Corresponding author. Tel.: +45-391-57441; fax: 45-391-57460.
E-mail address: [email protected] (A. Baklanov).
0265-931X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 6 5 - 9 3 1 X ( 0 1 ) 0 0 0 9 4 - 7
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
Keywords: Nuclear accident; Radionuclide; Regional scale modelling; Isentropic trajectory; Cluster
analysis; Radioactive contamination; Kola Peninsula
1. Introduction
For major industrial facilities, it is important to develop worst-case accident
scenarios and an understanding of the consequences associated with these scenarios.
To estimate risks from a nuclear facility and to develop environmental monitoring
networks and emergency preparedness systems, it is important to determine:
*
*
*
*
the
the
the
the
geographical regions most likely to be impacted;
probability and transport time to different geographical regions;
probability and effects of precipitation; and
deposition fields and effects on the population in case of an accident.
Previously, our studies (Baklanov, Mahura & Morozov, 1994; Jaffe, Mahura &
Andres, 1997a; Thaning & Baklanov, 1997; Jaffe et al., 1997b; Bergman, Thaning &
Baklanov, 1998; Baklanov et al., 1998) and studies of Barnitsky and Saltbones (1997)
and Saltbones, Barnitsky and Foss (1997) discussed various approaches to estimate
such risks. However, the transport and residence time of radionuclides at different
atmospheric levels can differ widely, especially in Arctic regions. Therefore, the
probability that air parcels from the accident area would be transported to other
geographical regions and time of their transport should be studied at different
altitudes based on 3-D trajectories. Furthermore, different parameterisations of
physical atmospheric processes (e.g., precipitation scavenging and mixing height)
and exposure pathways need to be developed and evaluated for Arctic regions.
The main purpose of this study is to examine the atmospheric transport patterns,
the contribution of removal processes, and the possible impact and consequences on
different Arctic and European regions from a hypothetical accident at the Kola
Nuclear Reactors (KNR) in north-western Russia. The results of this study could be
used in the event of an accident to make an initial estimate of the probability of
radionuclide transport from the accident location. It is very important to have a
probabilistic assessment of the long-range transport of pollutants, especially for
studies of social and economical consequences of the radioactive risk in the Barents
Euro–Arctic region.
2. Methodology
2.1. Kola nuclear reactors and impact region specification
The Kola–Barents region of the Russian Arctic has the greatest concentration and
number of nuclear reactors in the world. There are about 180 operating nuclear
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
25
reactors, 135 reactors to be decommissioned, a nuclear weapons test range on the
Novaya Zemlya Archipelago, and over 10 storage sites for nuclear waste and spent
nuclear fuel (Bergman & Baklanov, 1998). In this study we focus on the possible
airborne releases from the Kola Nuclear Power Plant (KNPP) located in the
Murmansk region, Russia (67.451N, 32.451E) which uses the old generation of
reactors (VVER-440/230). These reactors are subject to potentially severe accidents
(IAEA, 1992) and this plant is one of the main potential radiological risks in the
Russian North. In addition, one comparative study was done for hypothetical
releases from a submarine reactor, situated, as an example, in the Ara bay at the
northern cost of the Kola Peninsula.
In this study, we examined the atmospheric transport pathways from the Kola
Peninsula region and possible radiological impact on different geographical regions
(Fig. 1): Scandinavia, Europe, central Former Soviet Union (FSU) and Taymyr.
More detailed impact studies of the possible contamination for the worst case
scenarios for the European North were also conducted. The period studied is 1991–
1996.
2.2. Trajectory modelling and cluster analysis
Although isentropic trajectory models use an assumption of adiabatic motion and
neglect various physical effects, they are still very useful tools for evaluating synoptic
scale flow patterns (Merrill, Bleck & Boudra, 1986; Harris & Kahl, 1990; Harris &
Fig. 1. Chosen geographical regions and model grid domain.
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
Kahl, 1994; Jaffe, Mahura & Andres, 1997a; Jaffe et al., 1997b; Mahura, Jaffe,
Andres, Dasher & Merrill, 1997; Mahura, Jaffe, Andres & Merriil, 1999).
Uncertainties in these models are related to the interpolation of meteorological
data, applicability of the considered horizontal and vertical scales, and assumptions
of vertical transport (Merrill et al., 1985; Draxler, 1987; Kahl, 1996). A computed
atmospheric trajectory represents the modelled pathway of an air parcel in time and
space and is considered an estimate of the mean motion of a defusing cloud of
material.
In this study, the original US National Center for Environmental Prediction
(NCEP) gridded wind fields from the database DS.082 (NCEP Global Tropo
Analysis, daily, from July 1976 to present) were interpolated to potential
temperature (isentropic) surfaces for the period 1991–1995 using the techniques
described by Merrill et al. (1986). Then the wind fields on these surfaces were used to
calculate trajectories for the model grid domain located between 20–801N and 601W
–127.51E. Forward isentropic trajectories for the KNPP region were computed twice
per day (at 00 and 12 UTC) at different potential temperature levels (from 255 K to
330 K with a step of 5 K). The National Center for Atmospheric Research (NCAR,
Boulder, CO) and the Arctic Region Supercomputing Center (ARSC, Fairbanks,
ALK) computer resources were used to compute more than 233 thousand
trajectories (Jaffe et al., 1997b). We used four trajectories for every calculation in
time. The initial points of trajectories were located on the corners of a 11 by 11
latitude–longitude box with KNPP in the centre. Only cases when the wind field was
reasonably consistent along the transport pathway (i.e., all four trajectories showed
similar direction of transport for one time period) were included in further analysis.
Trajectories, showing a strong divergence of flow, were assigned to a complex
trajectory category. Such trajectories reflect larger uncertainties in air parcel
transport and are excluded from further analysis.
An analysis of different scenarios for hypothetical accidents at KNPP, performed
by Baklanov, Bergman and Segerståhl (1996), shows that the height of radionuclide
releases could vary mainly from 100 m up to 500 m and durations from several hours
to several days. Therefore, from all trajectories we chose only 12,845 trajectories with
the total duration of 5 days and longer and starting at these heights. To study
altitudinal variations of flow patterns, particularly within the boundary layer and the
free troposphere, we also considered trajectories originating over the KNPP region
at 1.5 and 3 km above sea level (asl).
Cluster analysis of trajectories is useful to identify climatological flow patterns for
a specific location or geographical area (Harris & Kahl, 1990, 1994; Harris, 1992;
Jaffe et al., 1997a; Mahura, Jaffe, Andres, Merrill, & Dasher 1997; Jaffe et al., 1997b;
Mahura et al., 1999). In this study, the procedure of disjoint cluster analysis on the
basis of Euclidean distances was used to divide trajectories into different groups
(Mahura et al., 1999). Latitude and longitude on each time step were used as criteria,
where both represent direction and velocity of air parcel motion. Within each cluster,
individual trajectories were averaged to obtain a mean cluster trajectory or
‘‘transport pathway’’. Thus, large numbers of trajectories were reduced to a
relatively small number of mean cluster trajectories, which could be interpreted
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27
based on common synoptic conditions. Using this technique, the flow climatology
was summarised for the KNPP region for 1991–1996 for each year, season and
month. Note that trajectories which cross the top grid boundary at 801N (i.e.,
showing transport to the central Arctic territories) were not used in cluster analysis
because of their short duration and mathematical termination at the model
boundary. These trajectories usually do not pass the most populated regions and
hence are of less interest to our study.
2.3. Modelling of radionuclide contamination and possible consequences
This section describes the methods of modelling atmospheric transport and
deposition from potential accidents on the nuclear sites at the Kola Peninsula for
different worst-case scenarios for certain meteorological situations.
2.3.1. Regional scale contamination models
For the simulation of radioactive contamination on the regional scale of Northern
Europe for worst-case scenarios, the MATHEW/ADPIC model (Forster, 1992), a
newly developed FOA Random Displacement Model FOA-RDM (Lindqvist, 1999),
and the Danish Emergency Response Model of the Atmosphere (DERMA)
(Srensen, 1998) are used and compared.
The MATHEW/ADPIC was developed at Lawrence Livermore National
Laboratory (LLNL), USA (Forster, 1992), and has been adjusted at the Swedish
Defence Research Establishment (FOA) for the FOA-environment. In ADPIC, the
dispersion is described by a particle-in-cell model. The 3D model wind field, in which
the particles are advected, is mass consistent and is produced by interpolating real
wind data from the European Centre for Medium-Range Weather Forecasts
(ECMWF, Reading, UK) with 0.751 and 6 h resolution into the MATHEW model
grid. The FOA version of the MATHEW/ADPIC model was compared with the
ETEX-1 Fullscale Experiment and showed good results (Tveten & Mikkelsen, 1995).
The new FOA Random Displacement Model (FOA-RDM) for long-range
atmospheric diffusion (Lindqvist, 1999) uses weather data taken also from the
ECMWF. Movement (trajectories) of the particles was simulated in a co-ordinate
system using latitude and longitude as the horizontal co-ordinates and a pressurerelated Z-co-ordinate as the vertical co-ordinate (the ECWMF data are also given in
this system). In comparison with the ADPIC model, where the atmospheric
boundary layer (ABL) height was a constant for the area, in the new model the ABL
height for the stable case (SBL) is calculated according to Zilitinkevich and Mironov
(1996) and for the unstable case taking the bulk Richardson number into account.
Radioactive decay is taken into account in the model through the inclusion of
mother and possible daughter nuclides only during the airborne transport for shortlived nuclides (like 131I). Decay of surface deposited long-living nuclides (like 137Cs)
after the transport simulation time is not included in this version of the model. The
FOA model has been compared with the ETEX-1 full-scale experiment, and has been
proved to be capable of producing a realistic evolution in time for the concentration
at one station (Risoe, Denmark) situated at a distance of about 1200 km from the
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release point (Rennes, France) (Lindqvist, 1999). The new FOA model was much
faster than the MATHEW/ADPIC model.
The DERMA is a 3D Lagrangian Gaussian puff long-range dispersion model,
developed by the Danish Meteorological Institute (Srensen, 1998), and uses the
DMI-HIRLAM high resolution meteorological data (0.151 or 0.451 horizontal
resolution). Among 27 institutions from most European countries, USA, Canada
and Japan, which contributed to model validations based on the ETEX experiment,
the DERMA model was emphasised as being very successful (Graziani, Klug &
Mosca, 1998). Dry/wet deposition processes and radioactive decay are taken into
account according to Baklanov (1999).
2.3.2. Meteorological data and choice of cases
For selection of the worst case scenarios based on the synoptic situation, we used
several criteria from the isentropic trajectories starting from the Kola nuclear
reactors. The following criteria were used to choose the cases for more detailed
study:
(1)
(2)
(3)
(4)
(5)
(6)
direction of transport of an accidental release to the study region: the Barents
Euro–Arctic region, the Nordic countries, the Baltic Sea region;
high precipitation over the study region during transport;
stably-stratified ABL and the ABL height (transport in the ABL or in the free
troposphere);
short travel time of a release from the Kola Peninsula to the study region;
large coverage of the Scandinavian and European region by the radioactive
plume; and
winter and summer seasons.
Using meteorological data from the ECMWF for the selected time periods, the
analysis is based on simulating the transport in air of a hypothetical radioactive
release and estimating the deposition pattern on meso- and regional scales. In these
case studies, a set of assumed release heights, durations and particle size distributions
are applied to study the dependence of the resulting deposition pattern due to these
parameters.
We do not attempt to describe the probability for the chain of events leading to
significant radioactive releases. However, based on a previous assessment (NACC,
1998) of the maximum extent of release of 137Cs in reactor fuel used in submarines,
we scale the deposition derived from our calculation of unit release to reflect release
of 100% of the inventory. The radioactive deposition at various distances associated
with other release assumptions may thus easily be obtained from the unit release
simulations by scaling.
2.3.3. Models for risk/consequences analysis
Beside the dispersion calculations, an analysis of the risk levels and possible
consequences for the population in the local/meso-scale scenario will be carried out
using the MELCOR Accident Consequence Code System (MACCS), developed by
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
29
Sandia National Laboratory, USA (MACCS, 1990). The use of the third part
‘Chronic’ of the MACCS code for the estimation of long-term effects on the
population might be problematic in Northern regions because in the model there is
no way to correctly describe the specific food chain ‘lichen–reindeer–man’.
Therefore, some long-term regional consequences will be estimated by using
empirical models and correlation between fallout and doses for humans, on the
basis of investigations of the Chernobyl effects on Scandinavia (Moberg, 1991;
Dahlgaard, 1994; Bergman & Ulvsand, 1994). For more detailed analysis of possible
consequences for the population of different administrative regions in the Nordic
countries, a method of integration of mathematical modelling and GIS-analysis for
radiation risk assessment was used (Rigina & Baklanov, 2000).
3. Results and discussions
3.1. Atmospheric transport patterns
3.1.1. Parameters of the KNPP impact
Although atmospheric transport from the KNPP region to other geographical
regions can occur at any time, rapid transport, with minimal dilution, is the greatest
concern. This is especially valid for emergency response and preparedness measures.
In this study we analysed all forward trajectories originated over the plant to
investigate the likelihood of impact on distant areas. We assumed that any isentropic
trajectory, which crosses into the chosen geographical region, could bring air parcels
containing radionuclides. Therefore, only trajectories crossing boundaries of these
regions were used for further analysis. To analyse the probability of the plant
impact, we estimated several parameters: (1) number and percentage of trajectories
reaching the boundaries of the geographical regions; (2) number and percentage of
days if at least one trajectory reached the region; (3) average transport time of air
parcels; (4) probability of transport within different atmospheric layers; (5)
likelihood of very rapid transport (i.e., transport in 1 day or less). Such evaluations
were performed over 1991–1995, by individual year, season and month. The four
regions are shown in Fig. 1 and a summary of transport from the plant to these
regions is presented in Table 1. Monthly variations in the average time of transport
(in days) and number of trajectories reaching the regions during 1991–1995 are
shown in Figs. 2 and 3.
The winter months show the lowest probability of transport (less than 20% of
trajectories) from the KNPP area to the Scandinavian region with the highest during
spring and summer (Fig. 3). The Taymyr region reflects the higher occurrence of the
transport during October–January (more than 40%), and lowest occurrence during
May–August with a minimum in June (19.1%). For the European region, there are
two periods when the probability of transport is higher: during November–February
(approximately 4%) and during July–August (3.5%). The lowest probability, less
than 1%, is observed during May and October. The central FSU region is
characterised by lower probability during spring and summer months (on average
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Table 1
Summary of the transport from the KNPP to other geographical regions
Parameter vs. Region
Trajectories reaching
the regions
# vs. % of trajectories
Days when trajectories
reached the regions
# vs. % of days
Transport time:
average 7SD
(in days)
Highest occurrence
of transport (months)
Fast transport
events % trajectories
Highest occurrence
of fast transport
(months)
Transport within
boundary layer
(% trajectories)
Scandinavia
European
Central FSU
Taymyr
3834 (28.4)
363 (2.7)
3192 (23.7)
4535 (33.6)
812 (44.5)
148 (8.1)
788 (43.2)
1014 (55.5)
1.371.2
4.572.2
2.771.8
3.472.0
Apr, Jun–Sep
Aug–Feb
Sep–Mar
72.8
Jul–Aug,
Nov–Feb
0.8
16.0
1.9
Mar–Nov
Dec
Dec–Mar, May
Dec–Jan,
Apr–May
70
60
55
27
Fig. 2. Monthly variations in the average transport time (in days) from the KNPP region to other
geographical regions based on the forward trajectories during 1991–1995.
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
31
Fig. 3. Monthly variations in the average percentage of trajectories originating over the KNPP region at
lower altitudes within the boundary layer and reaching other geographical regions during 1991–1995.
less than 20%). This probability gradually increases during fall and winter months
reaching absolute maximum in February (36.2%).
It is well known that in the cases of transport within the boundary layer higher
surface concentrations of radionuclides are more likely. As seen from Table 1,
boundary layer transport on a yearly basis is predominant for the Scandinavian,
European and central FSU regions, but free troposphere transport prevails for the
Taymyr region. It should also be noted that the European region is characterised by
boundary layer transport during all seasons except in summer, when transport
occurs 50% of the time on the border between the boundary layer and free
troposphere. Although the Taymyr region shows transport near the border between
layers and in the free troposphere throughout the year, during summer months the
transport pattern is shifted completely to higher layers in the free troposphere.
The cases of the fast transport (1 day or less), as shown in Table 1, account on
average for approximately 73%, 16%, 2.1% and less than 1% for Scandinavian,
central FSU, Taymyr and European regions, respectively. In this study we found
that the lowest probability of fast transport events is observed for the European
region, and all these fast transport events took place during December. In
comparison with other regions, the Scandinavian region is characterised by the
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
highest probability of fast transport due to its proximity to the KNPP area. This
probability on average is 72.8% of the total number of trajectories reaching the
region, and it decreases during winter to 61%. For the central FSU region, the
probability of such transport is higher during winter (up to 30%) and it decreases by
a factor of 1.5–2 in other months. The Taymyr region also has a low probability of
fast transport events. Although, on average, this probability is approximately 1.8%,
during fall months it is less than 1% and there is a flat maximum of 4% during
December–January.
In this study we found that approximately 96% of all trajectories which reach the
Scandinavian region do so in less than 4 days. Seventy five percent of trajectories
reaching the central FSU region do so in less than 3 days and 40%, in 1.5–2 days.
Seventy five percent of trajectories reaching the Taymyr region do so in less than 4
days with a significant number of trajectories (up to 50%) at 1.5–2.5 days of
transport.
Based on the analysis of these results we found that the highly populated
Scandinavian and central FSU regions are at the greatest risk in comparison with the
European region. Radionuclide transport to the central FSU region can occur in one
day, but averages 2.7 days with 45% of the cases resulting from free troposphere
transport. To the Scandinavian region, transport can occur in 0.5 days, but averages
1.3 days with most of the transport resulting from boundary layer transport.
3.1.2. Atmospheric transport pathways
In this study we were primarily interested in the rapid transport from the KNPP
region. Also, we found that the average transport times to specific geographical
regions (as shown in Table 1) are less than 5 days, thus we decided to use only
forward trajectories of this duration in the cluster analysis. Fig. 4 shows the
atmospheric transport pathways from the KNPP region using trajectories originating within the boundary layer. The mean trajectory for each cluster is given with
points indicating 12 h intervals. Two numbers were used for each cluster. The first is
an arbitrary identifier of the cluster. The second is the percentage of trajectories
within the cluster.
In our study, six clusters were identified for the KNPP region. Four of them (# 1,
2, 3 and 4 with 27%, 22%, 10% and 16% of occurrence, respectively) show westerly
flow. Cluster # 6 (7%) shows easterly flow toward the Northern Atlantic both within
the boundary layer and free troposphere. Cluster # 5, which occurs 18% of the time,
is transport to southwest through the Scandinavian Peninsula into the Baltic Sea.
As noted previously, we did not consider trajectories that cross the top of the
model grid domain and move into the central Arctic. Throughout the year, westerly
flow is predominant for the KNPP region. Transport from the west varies from 68%
(fall) to 94% (spring) of the time. Transport from the east occurs from 3% (winter)
to 26% (summer) of the cases. Transport with the southward component take place
15% of the time (winter) increasing up to 25% (fall). Analysing trajectories at higher
altitudes, 1.5 and 3 km asl, we also found that in the free troposphere the probability
of westerly transport is 90%.
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
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Fig. 4. Atmospheric transport pathways (cluster mean trajectories) from the KNPP region based on the
forward trajectories during 1991–1995.
3.2. Airflow and precipitation factor probability
3.2.1. Airflow probability field
To test and compare the results of clustering we calculated the airflow probability
field using all 12,845 forward trajectories during 1991–1995. Such probability fields
show geographical variations of airflow patterns from the chosen site. In a
climatological sense, the pathway of airflow from the chosen site could be
represented by a superposition of the probability of air parcels reaching each grid
region on a geographical map (Merrill, 1994). The regions with higher occurrence of
trajectory passages are areas where the probability of KNPP impact will be higher.
Fig. 5 shows the airflow probability field for KNPP constructed using 1991–1995
trajectories. The areas of higher probability, which are located close to the KNPP
region, indicate that trajectories have spent more time in this geographical area.
Since all trajectories start near the site, the cumulative probability is 100% there.
Thus the field was altered using a correction factor which adjusts the contribution at
greater distances. The airflow probability field also shows that westerly flow is
predominant for the KNPP region.
3.2.2. Precipitation factor probability field
To account for the contribution of radionuclide wet removal during transport of
an air parcel, we calculated simultaneously for each trajectory point (i.e., at latitude,
longitude and pressure level point) the value of relative humidity. Based on
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
Fig. 5. Airflow probability field for the trajectories originated over the KNPP region during 1991–1995
(isolines are shown every 10%).
calculated temporal and spatial distribution of the relative humidity, we constructed
the relative humidity (precipitation factor) probability fields over the studied
geographical areas. Several atmospheric layers: surface–1.5, 1.5–3, 3–5, and above
5 km, were examined to determine altitudinal differences in the possibility of removal
processes. We assumed that areas with the relative humidity above 65% were areas
where water vapour could be condensed and later removed in the form of
precipitation. Fig. 6 shows the relative humidity probability field for the lowest layer.
Our analysis showed that contribution of the precipitation factor dominates in the
low troposphere layers in the areas associated with the activity of the Icelandic low
and along main tracks of the cyclone systems.
3.3. Modelling of radionuclide transport for worst case scenarios
Since the isentropic trajectory calculation and the regional transport model both
use real meteorological data for the specific synoptic situation, albeit from different
data sources, we expect these to show broadly similar transport patterns for a given
day. The calculations for regional scale (up to 4000 km) have been carried out for the
European territory with a focus on the regions of Scandinavia, Finland and
Northwest Russia including the Kola Peninsula. The release parameters for the
model calculations include the particle size distribution, site, height and duration of
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
35
Fig. 6. Precipitation factor probability field based on the relative humidity fields for the trajectories
originated over the KNPP region during 1991–1995 in the boundary layer.
release. A sensitivity analysis to variations of the release parameters and
intercomparison of the long-range scale transport models are a topic for a separate
paper. In general, we found that the simulations by the three different regional
models give very similar deposition and concentration patterns.
Several cases of assumed, hypothetical release into the atmosphere have been
simulated and analysed in order to achieve a better understanding of possible effects
on the North European population from radioactive contamination. The
dependence of the resulting deposition pattern and radiation exposure of the
populations on certain release characteristics has been studied for simulated cases of
accidental release from the KNPP and for some accidents involving a nuclear
submarine or icebreaker. The following five weather situations (worst-case scenarios)
for our comparative case studies were selected: # 1: July 6–11, 1993 (Fast transport
to Finland and Scandinavia); # 2: 28 December 1996–2 January 1997 (Large
contamination of Scandinavia and Finland); # 3: 01–06 November 1995 (Large
contamination of Scandinavia and Western Europe); # 4: 17–22 July 1991
(Transport to Scandinavia and the Baltic countries); # 5: 19–24 October 1995
(Transport to northern Scandinavia, the Norwegian and Baltic Seas).
3.3.1. Case study # 1, 6 July 1993
The unit release of radioactive caesium (1 Bq) from the KNPP, which starts at 00
UTC, 6 July 1993, took place during 1 h, and the height of the primary radioactive
plume is 400–600 m. Horizontal release scale is 100 m (750 m from the site), the
average particle radius is 0.5 m. The meteorological situation (6–10 July 1993) over
the northern Europe is, in the troposphere, characterised by low-pressure systems
moving in easterly direction over Sweden and then towards north–east over Finland.
During 6–8 July on the north–east side of such a low-pressure system, the wind
direction in the troposphere becomes between north and east over northern Sweden
and Finland and a transport from the Kola Peninsula to Scandinavia is made
possible. During the first 2 days, a warm front is moving to the south over northern
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Sweden causing some precipitation. In the end of the period, the wind becomes
southerly more or less over whole Sweden.
In this case, forward isentropic trajectories show transport of air parcels from the
KNPP region (with 12 h intervals) from 6 July, 12 UTC initially towards
Scandinavia, then southwards turning towards Russia and later, with the northward
component, towards the Taymyr region (Fig. 7a). The trajectory indicated that air
masses from KNPP would reach the north–east extremity of Sweden in less than half
a day. Fig. 8 presents high resolution simulation results of the total ground
contamination in a case of 60 PBq release (1 PBq=1015 Bq) 5 days after the release.
Fig. 7. Forward isentropic trajectories for the selected case studies # 1 (a) and # 5 (b).
Fig. 8. Ground-contamination (total deposition, Bq/m2)) for case study # 1,4 days after a maximum
hypothetical release (60 PBq) from the KNPP, release height: 450–550 m.
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
37
The modelled transport of radionuclides has very similar results with the
isentropic trajectories, calculated on the base of meteodatabase of US NCEP,
during all five modelled days. But some differences can already be seen after the first
day. The isentropic trajectories reached the Swedish coast, then the Baltic sea, then
southern Finland. The high resolution dispersion modelling completely confirm the
isentropic trajectories, but showed, due to the splitting of trajectories, additional
deposition over central Sweden after the first day and a trace of deposition over the
Baltic states. There are two possible reasons for this difference. First, the initial
release height was 400–600 m, but the isentropic trajectories were calculated
beginning at 500 m asl. The dispersion was calculated with the deeper vertical
resolution (from a level of 60 m), therefore the radioactive contamination of the
middle Sweden and Baltic states was due to air transport at lower than 500 m levels.
The trajectory calculation at a height of 400 m, using the MATHEW model and
ECMWF data, completely confirms this hypothesis. The second reason might be the
gravitational settling of radioactive particles. During transport, large particles fall
into lower levels and are transported by other air parcels. The dispersion model
considers the processes of gravitational settling and deposition of radioactive
particles but the isentropic trajectory model did not take these effects into
consideration.
It should be noted that the main direction of radioactive plume transport and
deposition are very similar the pathway of isentropic trajectories, despite different
meteorological data sets and model assumptions.
3.3.2. Case study # 2 for 28 December 1996
For this case a sensitivity to the release coordinates was studied. By allowing unit
releases to occur simultaneously at a fjord and at the power plant (and with the same
release profile in time) comparisons of differences in deposition patterns in and
outside the Kola region are made. The calculations were done for all the European
territory for different particle sizesF0.3–7 m. The unit release (1 Bq) from the KNPP
or from a submarine reactor at the Ara bay (about 200 km from the KNPP) starts
on 28 December 1996 00 UTC, and takes place during 1 h, and the height of the
primary radioactive plume is 100 m. The remaining input data and conditions are
similar to the previous case study. Fig. 9 illustrates the deposition patterns over
north-western Russia and Fenno–Scandia 5 days after the unit releases from the
KNPP and from a submarine reactor at the Ara bay. The patterns associated with
the release from the fjord site in comparison to the release at the KNPP (both
releases are at the same height, date and time), clearly exhibit a strong site
dependence of rainfall and wind direction on the resulting deposition on a regional
scale. The calculations for unit release indicate that large areas as far away as in
southern Scandinavia will obtain deposition of a fraction of the order of 10 13 per m2
(see Fig. 9). This corresponds to a deposition of 100 Bq/m2 per 1 PBq of airborne
release of 137Cs in the accident.
A relatively high deposition may affect large areas of distant European countries
according to these case studies, thus indicating long range transport for considerable
contamination (>1 kBq/m2 per 10 PBq of airborne release of 137Cs at distances
38
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
Fig. 9. Ground-contamination (total deposition, Bq/m2) 5 days after unit hypothetical release (1 Bq) from
a nuclear reactor of the KNPP (left map) and from a submarine reactor at the Ara bay (right map) for case
study # 2.
B1000–2000 km from point of the release), although the radiological effects due to
external exposure seem to be more regionally confined. However, the experiences
from the Chernobyl accident have led to a better understanding, among other things,
of the efficient uptake and the persistence of radioactive Cs in food-chains at boreal
latitudes. This implies, beside the direct radiological aspect, that the deposition also
involves risk for long-term adverse economic effects, e.g., generally for agricultural
production and notably for reindeer herding (Bergman & Ulvsand, 1994). Thus,
further analyses to elucidate the potential impact are motivated, in particular a closer
study of the probable source strength in various release scenarios.
3.3.3. Case study # 3 on 01 November 1995
The unit radioactive release (1 Bq) starts on 95.11.01 00 UTC, and takes place over
1 h. Input data and conditions for the simulation are similar to the previous cases.
Calculations were done for four different release heights (20–60 m, 450–550 m, 1000–
1100 m, 1900–2200 m) and for three nuclides: 137Cs, 131I and 132Te with corresponding decay rates.
The radioactive plume is transported to the Scandinavian Peninsula and then
southwards to other West European countries: Denmark, UK, Germany and the
Czech Republic. During this time, precipitation takes place over the Norwegian
coast and central Germany. The large ground contamination in these areas is,
therefore, mainly due to wet deposition. For a basic scenario of a severe hypothetical
accident at the KNPP with a Cs release of 10 PBq (Baklanov, Bergman, &
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
39
Segerstahl, 1996) for this case study the average ground contamination levels in the
Scandinavian areas affected by significant deposition will be about 100–1000 Bq/m2.
For a hypothetical submarine accident with a Cs release of about 1 PBq the
deposition levels will be less than 100 Bq/m2 over the main territory of Scandinavia
and up to 1 kBq/m2 over the Kola Peninsula.
Variations of the height of the primary radioactive plume (20–60 m, 450–550 m,
1000–1100 m, 1900–2200 m) show a very similar character of the cloud transport and
deposition pattern for the release into the ABL. If the height of the primary
radioactive release is above the ABL (1000–1100 m, 1900–2200 m), the transport and
deposition pattern differ significantly. The maximum of the total deposition, 12 h
after the release start was up to 66% higher for the lowest release (20–60 m), and up
to 10% higher for the release of 200–500 m height than for the release of 1000–
1100 m height.
Calculations for the unit release (1 Bq) of three different nuclides: 137Cs, 131I and
132
Te with corresponding decay rates show slight differences of the total deposition
levels during the simulated period of 5 days: after 114 h the ground-contamination
levels were 4.5% lower for 131I and 1.8% lower for 132Te than for 137Cs (Fig. 10).
Due to the possible large releases of 131I and 132 Te for hypothetical accidents at the
KNPP or vessel reactors, significant contributions of these nuclides to the total doses
for the acute phase are possible not only for the Kola Peninsula, but also for large
territories of Scandinavia and the European countries.
Fig. 10. Ground-contamination (total deposition of 131I, Bq/m2)) for case study # 3,4 days and 18 h after a
unit hypothetical release (1 Bq) from a nuclear reactor on the Kola peninsula.
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
3.3.4. Case study # 4 for 17 July 1991
Release transport to Scandinavia and the Baltic countries is common for this
meteorological situation. Calculations were done for release heights of 450–550 m
and 200–500 m with separate calculations of the wet and dry deposition. The unit
release of radioactive caesium (1 Bq) from the KNPP, which starts July 17 1991 12.00
UTC, takes place for 1 h, and the height of the primary radioactive plume is 200–
500 m or 450–550 m. Horizontal release scale is 100 m (750 m from the site), the
average radius of particles is 3 mm. The simulation duration is 5.5 days (132 h).
The radioactive cloud is transported during the first 6 h from the Kola Peninsula
to the northern parts of Finland (Lapland) and Norway (Finnmark); after 48 h it
reaches the central part of Norway and then (96 h) moves southward to Sweden,
southern Norway and Denmark. After that (114 h) it moves out of the Scandinavian
Peninsula to East-European countries: Poland, Estonia, Latvia, Lithuania, Belarus
and Ukraine. Variations of the height of the primary radioactive plume: 200–500 m
or 450–550 m show a very similar character of the cloud transport and deposition
pattern, but the maximum concentration at the surface layer for the lower release
after 96 h was 25% higher than for the higher release. The total deposition levels
differed only 3% 6 h after the start of the release.
Total deposition and wet deposition 132 h after the start of the unit hypothetical
release at 450–550 m release height are presented in Fig. 11. During this time,
precipitation takes place over the Scandinavian peninsula and the Baltic region.
Large ground contamination in these areas is, therefore, mainly due to wet
deposition. However, the maximum of the total deposition on the Kola region is 6
times higher than the maximum of the wet deposition. So, dry deposition dominates
in the ground-contamination close to the release site and is insignificant over other
European countries for this case.
3.3.5. Case study # 5 for 19 October 1995
This case highlights the possible consequences of an accident at the KNPP on the
regional scale for a weather situation on 19–24 October 1995. The release lasts 5 h,
Fig. 11. Ground-contamination for case study # 4 5,5 days after a hypothetical release from KNPP: the
left map - total deposition, the right map - wet deposition only.
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
41
starting on 19 October 1995 01 UTC, and amounts to about 60 PBq of caesium.
Approximately 67% is released during the last hour. The height of the primary
radioactive plume is 150–250 m.
In this case, the forward isentropic trajectories indicate (Fig. 7b) that air in the
KNPP region would be transported to the Scandinavian region in less than 1 day.
The isentropic surface for these trajectories intersects the surface of the earth after
the first day and thus the back trajectory calculations by the isentropic trajectory
model ends. The weather situation was dominated by a low pressure system which
was approaching the Norwegian coast when the release took place. Fig. 12 presents
maps of the resulting Cs air concentration in the surface layer 1 day after accident
and ground contamination 5 days after the release. First, the radioactive cloud
moved towards west – northwest on the north side of the low pressure system. The
radioactive cloud then moved out over the Atlantic Ocean and went around (anticlockwise) the low pressure system. The modelled transport of radionuclides has
broadly similar results with the isentropic trajectories on the first day meteorological
database, during the first day before the trajectory calculation ends. During this
phase there was precipitation and the large ground contamination in this area was
mainly due to wet deposition. Later, when the cloud was moving south–east,
precipitation ceased and, consequently, the deposition became much less until the
cloud reached the Baltic region where again precipitation took place. The resulting
contamination pattern (Fig. 12) emphasises the importance of wet deposition. Note
that only wet deposition, due to large scale precipitation (which is rather weak,
typically 0.5–1 mm/h) was calculated. Although not presented here, calculations with
much higher precipitation rates for a couple of hours, simulating showers, have been
carried out. These calculations have shown that the model can produce small areas
Fig. 12. Calculated Cs air concentration at 2 m height 1 day after an accident (left, isolines: min F 0.03,
max F 30 Bq/m3) and deposition pattern (right: min F 0.3, max F 300 kBq/m2) from a hypothetical
release of 60 PBq from the KNPP for case study # 5.
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
with contamination levels over 1 MBq/m2 at distances larger than 500 km from the
source.
The area with Cs fallout level over 30 kBq/m2 is about 250,000 km2. Under certain
wind directions, this level of fallout might cover the main part of the territory of the
Scandinavian Peninsula with a population of 9 millions. After the Chernobyl
accident such a level of contamination was recorded over a large territory of Europe,
in particular over parts of Sweden and Norway. The maximal level of fallout in the
central part of the Kola Peninsula (B350 km2) reaches 300–1400 kBq/m2.
3.3.6. Comparative analysis
As the first conclusion from this preliminary comparison of the simulation results,
we can suppose the following. The isentropic trajectory model (Merrill et al., 1986)
gives a reasonably good estimate for the most likely trajectories of air parcels from
the KNPP on the regional scale for northern Europe. Although, for detailed case
studies and for transport of radioactive cloud and deposition patterns, it is necessary
to use meteorological data with higher resolution and a regional scale dispersion
models.
3.4. Estimation of possible consequences
3.4.1. Case study, potential release and resulting deposition
A conspicuous feature in the calculated deposition patterns is the similar levels of
deposition arising in most parts of Northern Europe exposed to the radioactive
release. It is reasonable to expect that the notable characteristics of relative high
deposition at long distances will prevail also under most other weather conditions.
The Chernobyl case and results from several calculations based on other weather
data support this presumption. However, to analyse the possible radiological
consequences of such a release, the source strength of the most important
radionuclides, the fraction of the inventory released in accidents, and the time–
course of the release need to be considered.
Table 2 presents certain characteristics for contaminated regions resulting for the
case studies/episodes under consideration with the unit releases (1 Bq). In the case of
an accidental release of 1 PBq of 137Cs for the five case studies considered, the
maximal total fallout concentration in the study region reaches 43–81 kBq/m2, and
contaminated areas with 137Cs deposition exceeding 10 Bq/m2 can reach about 540–
1930 thousands km2. Plume transport time to the Nordic countries (northern
Norway or Finland) is 3–17 h and to Sweden 6–31 h.
3.4.2. Contamination in food-chains
Radioactive uptake in food-chains often exhibits a considerable seasonal variation
depending on when the deposition has occurred. Generally, agricultural systems
based mainly on cultivation of grass crops and on pastures for feeding of animal
herds are sensitive in the year of fallout. Soon after deposition, milk from dairy cows
remaining on pasture exposed to the radioactive deposition is particularly affected,
and if the deposition contains 131I this nuclide will probably be radioecologically the
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
Table 2
General characteristics of contaminated regions for the considered case studies in case of an unit release
(1 Bq) from KNPP
Case study:
number
and data
Case type
Transport time to
Nordic countries/
Sweden, hour
Max deposition/max
for Sweden,
10 12 Bq/m2
Contaminated areas
>10 14 Bq/m2,
105 km2
# 1, 06.07.93
Fast transport to
Nordic c./Sweden
Stable stratification
Large contaminated
areas
Fast transport to
Nordic c./Sweden
Transport to
Norway/sea area
4/7
81/1.7
5.4
17/31
5/12
43/1.4
12.1/1.2
9.5
19.3
3/6
27.4/6.8
3.9
3/7
23/0.5
17.7
# 2, 28.12.96
# 3, 01.11.95
# 4, 17.07.91
# 5, 19.10.95
most important factor in the early phase after the fallout. Direct deposition of 131I or
137
Cs on pasture and crops at levels below 1 kBq/m2 is not likely to lead to
restrictions in normal agricultural practice or formal acceptance for commercial use
of the food-products, even during summer when the resulting contamination will
attain its maximum.
The concentration in reindeer is high during winter when feeding on lichens
exposed to fallout of radioactive caesium (134Cs and 137Cs). The ratio between
activity concentration (Bq/kg) in reindeer meat and deposition density (Bq/m2) will
be close to 1 (kg/m2) in the latter half of the first winter season after the fallout
( hman & A
( hman, 1994). This implies contamination about one order of magnitude
(A
higher in the lichen–reindeer–man food-chain than in grass–cow–milk. Intake of
radioactive caesium in groups or populations consuming much reindeer meat is
therefore expected to be particularly high. This is accentuated by the persistence and
high availability during several years over the lichen pathway for 137Cs, as well as the
fact that reindeer herding is extensive, and constitutes an important component of
the economies of northern Fenno–Scandia and the Kola Peninsula.
Assuming a release of 1 PBq of 137Cs in our case studies, the levels of 137Cs
attained in reindeer meat during winter slaughter are expected to be of the order of
1 kBq/kg in large parts of the areas affected by deposition on the Kola Peninsula,
and even one order of magnitude higher in somewhat smaller areas several hundreds
of kilometres from the point of release. With other wind directions, similar
deposition patterns are likely to occur within the same range from the source, but
over other parts of Fenno–Scandia and Kola.
3.4.3. Possible consequences for populations
As an illustration, for the considered scenarios # 1 and # 5 with a maximum
theoretically possible Cs release (60 PBq) from KNPP, estimation of the possible
effects on the North European population from the radioactive contamination has
been performed. The areas (Figs. 8 and 12), where the Cs deposition exceeds 30 kBq/
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
m2, are about 190,000 km2 in the first case and 250,000 km2 (mostly over Norway) in
the fifth case. The maximum levels of fallout reached 1000–4900 kBq/m2 close to the
KNPP and in Finland (B1400 km2) for the first case and 300–1400 kBq/m2 in the
central part of the Kola Peninsula (B350 km2) for the fifth case study. Here we
consider the worst possible scenario, whereas a moderate scenario of a hypothetical
accident at the KNPP might give about 10 times lower Cs release (Baklanov et al.,
1996).
Total dose to humans includes the contributions of inhalation, external exposure
and ingestion. Direct modelling of processes of the radionuclide transport in
the environment, transfer in food-chains and exposure of populations is a difficult
and time-consuming process. Therefore, some rough long-term consequences
have been estimated by empirical models and correlations between fallout and
doses for humans, compiled by Swedish researchers on the basis of Chernobyl effects
on Scandinavia (Moberg, 1991; Dahlgaard, 1994; Bergman & Ulvsand, 1994).
Proceeding from these compilations, the possible total dose to humans has
been calculated. The relative contribution of the pathways according to an
estimation made for accidents at the reactors VVER 440/230 is illustrated by Slaper
et al. (1994). Ingestion and external exposure from deposited nuclides are the
major dose-contributing pathways. This implies that deposited radionuclides
contribute approximately 85% to the total dose. Similar results were obtained
for the other probabilistic source terms. For the adult population, 70% of the
70-year follow-up dose is received in the first year. The two major dose-contributing
nuclides are 131I and 137Cs, which together contribute 60–80% to the total dose.
In addition 134Cs contributes approximately 12–25%; other nuclides contributes less
than 5% each and all other nuclides combined contribute no more than a maximum
25%.
In the zone with levels exceeding 30 kBq/m2 a preliminary estimate for the
situation considered in case # 5 indicates a total dose of 2.1 mSv for an adult man (in
the general group). By integrating the total radioactive contamination and
calculating the doses for the populations for counties of the Nordic countries and
north–west Russia, we can roughly obtain collective dose to the population. The
collective doses to the population of Swedish provinces, impacted by the
hypothetical release, are presented in Fig. 13.
For districts of the Northern European region such estimations can only roughly
indicate the level of the human risk because they do not take into account secondary
pathways through the seas and some important characteristics of certain significant
food-chains in these Boreal and Arctic vegetation zones, e.g., particularly efficient
retainment of the radioactive deposition in lichens; persistent high availability of
137
Cs in berries, game, mushrooms, fresh water fish and specific consumption
patterns. Approximate estimations for districts of reindeer-breeding show that
(mainly due to high consumption of reindeer meat) the total dose in such groups of
the population likely needs to be increased by about a factor of 10–100. Fig. 14
presents individual doses for man in the general and critical groups for the main
contaminated counties for the case study # 5 with maximum deposition over
northern Norway and for the maximum possible release (60 PBq). In Sweden,
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
45
Fig. 13. Consequences for population of Swedish counties for case study # 5.
Fig. 14. Individual doses for man at the different counties for case study # 5.
reindeer herders attained wholebody concentrations of 137Cs that were about 50
times higher than in the Swedish populations as a whole, both in the sixties, as a
consequence of atmospheric nuclear weapons tests, and after the Chernobyl accident
(Moberg, 1991; AMAP, 1998). For the general population in the northern parts of
Fenno–Scandia, products from Boreal forest biotopes contribute in the long term as
much to the cumulative dose as the fraction due to the use of agricultural products
(Dahlgaard, 1994). The dose to the general population in these regions thus should
be increased by about a factor of 2 to cover the contributions from forest products to
the dose commitment.
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A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
4. Conclusions
The main results of our study are
1. A methodology for estimating potential nuclear risk/vulnerability levels has
been developed and tested by evaluating the impacts from a theoretical nuclear
accident in north–west Russia on Scandinavia, Central Europe, European FSU and
Taymyr. This methodology includes using atmospheric transport patterns and the
contribution of the precipitation factor to better understand the possible impact and
consequences from a hypothetical accident.
2. The comparison with the high resolution simulation results shows that the
isentropic trajectory model gives reasonably good estimates for the probabilistic
analysis of possible trajectories of air parcels from the KNR region on the regional
scale. However, for detailed case studies of radionuclide transport and deposition, it
is necessary to use higher resolution meteorological data and dispersion models.
3. Comparison of the simulated consequences obtained by different transport
models showed high sensitivity in the estimation of the boundary layer height,
especially for cases of the stable stratification, which are common for the Arctic
regions. The resulting contamination pattern emphasises the importance of wet
deposition.
4. Highly populated regions of Scandinavia and central FSU are at the greatest
risk in comparison with the European region. Radionuclide transport to the central
FSU region can occur in 1 day, but averages 2.7 days with 55% of the trajectories
occurring in the boundary layer. To the Scandinavian region, it can occur in 0.5 day,
but averages 1.3 days with most occurrences (70%) resulting from transport in the
boundary layer.
5. During all seasons, westerly flow is predominant for the KNR region within the
boundary layer and on average it occurs 75% of the time throughout the year.
Within the free troposphere, westerly flow predominates up to 90% of the time
throughout the year.
6. Contribution of the precipitation factor dominates in the low tropospheric
layers in the areas associated with the activity of the Icelandic low and along main
tracks of the cyclone systems.
7. In this study, we have showed that a major nuclear accident in the Kola region
may cause severe consequences not only in the neighbourhood areas, but also might
give rise to significant radiological risks to Scandinavian and Northern European
populations. A relatively high deposition may affect very large areas far downwind in
the European countries, although the radiological effects due to external exposure
are more regionally confined.
Acknowledgements
Support for this research has come from the Swedish Agency for Civil Emergency
. CB Project, the Alaska Department of Environmental Conservation
Planning O
UAF-ADEC Project 96-001 and INTAS-96-1802 Project. This work was supported
A. Baklanov et al. / J. Environ. Radioactivity 60 (2002) 23–48
47
in part by a grant of HPC time from the Arctic Region Supercomputing Center
(ARSC, Fairbanks, Alaska, USA). The computer facilities of the National Center
for Atmospheric Research (NCAR, Boulder, Colorado, USA), ARSC, Swedish
Defence Research Establishment (FOA, Ume(a, Sweden), Danish Meteorological
Institute (DMI, Copenhagen, Denmark) and databases of NCAR and European
Centre for Medium-Range Weather Forecast (ECMWF, Reading, UK) have been
used in this work. The authors are very grateful for the collaboration with J. Merrill,
R. Platner, R. Honrath, D. Dasher, O. Rigina, S. Morozov, and J. H. Srensen.
Thanks to Drs. G. Shaw, S.-A. Bowling, J. Harrington and J. Kelley-Danielson for
constructive discussions and D. Fielding and R. Huebert (ARSC) for computer
advice.
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