The data set “Spatial radionuclide deposition data from the 60 radial km area around the Chernobyl nuclear power plant: results from a
sampling survey in 1987” is the latest in a series of data to be published
by the Environmental Information Data Centre (EIDC) describing samples
collected and analysed following the Chernobyl Nuclear Power Plant accident
in 1986. The data result from a survey carried out by the Ukrainian
Institute of Agricultural Radiology (UIAR) in April and May 1987 and includes
sample site information, dose rate, radionuclide (zirconium-95, niobium-95,
ruthenium-106, caesium-134, caesium-137 and cerium-144) deposition, and
exchangeable (determined following 1M NH4Ac extraction of soils)
caesium-134 and 137.
The purpose of this paper is to describe the available data and methodology
used for sample collection, sample preparation and analysis. The data will
be useful in reconstructing doses to human and wildlife populations,
answering the current lack of scientific consensus on the effects of
radiation on wildlife in the Chernobyl Exclusion Zone and evaluating
future management options for the Chernobyl-impacted areas of Ukraine and
Belarus.
The data and supporting documentation are freely available from the
EIDC under the terms and conditions
of the Open Government Licence (Kashparov et al., 2019; 10.5285/a408ac9d-763e-4f4c-ba72-73bc2d1f596d).
Background
The dynamics of the release of radioactive substances from the number four
reactor at the Chernobyl Nuclear Power Plant (ChNPP) and meteorological
conditions over the 10 d following the accident on 26 April
1986 resulted in a complex pattern of contamination over most of Europe
(IAEA, 2006).
The neutron flux rise and a sharp increase in energy emissions at the time of
the accident resulted in the heating of the nuclear fuel and the leakage of fission
products. The destruction of the fuel rods caused an increase in heat transfer
to the surface of the superheated fuel particles and coolant and led to the release of
radioactive substances into the atmosphere (Kashparov et al., 1996).
According to the latest estimates (Kashparov et al., 2003; UNSCEAR, 2008),
100 % of inert radioactive gases (largely 85Kr and 133Xe),
20 %–60 % of iodine isotopes, 12 %–40 % of 134,137Cs and 1.4 %–4 % of
less volatile radionuclides (95Zr, 99Mo, 89,90 Sr,
103,106 Ru, 141,144 Ce, 154,155 Eu, 238-241 Pu, etc.) in
the reactor at the moment of the accident were released to the atmosphere.
As a result of the initial explosion on 26 April 1986, a narrow (100 km long and up to 1 km wide) relatively straight trace of radioactive
fallout formed to the west of the reactor in the direction of the Red Forest and
Tolsty Les village (this has subsequently become known as the “western
trace”). This trace was mainly finely dispersed nuclear fuel (Kashparov et
al., 2003, 2018) and could only have been formed as a consequence of the
short-term release of fuel particles with overheated vapour at a
comparatively low height during the stable atmospheric conditions at nighttime (the accident occurred at 01:24 local time – LT). At the time of the accident, surface winds
were weak and did not have any particular direction; only at a height of
1500 m was there a southwestern wind with the velocity of 8–10 m s-1 (IAEA, 1992). Cooling of the release cloud, which included steam,
resulted in the decrease in its volume, water condensation and wet
deposition of radionuclides as mist (as the released steam cooled; Saji,
2005). Later, the main mechanism of the fuel particle formation was the
oxidation of the nuclear fuel (Kashparov et al., 1996; Salbu et al., 1994).
There was an absence of data on the meteorological conditions in the area of
ChNPP at the time of the accident (the closest observations were more than
100 km away to the west; Izrael et al., 1990). There was also a lack of
source term information and data on the composition of the dispersed radioactive
fallout. Consequently, it was not possible to make accurate predictions of the deposition for the area close to the ChNPP (Talerko, 2005).
The relative leakage of fission products of uranium (IV) oxide in an inert
environment at temperatures up to 2600 ∘C decreases in the order from volatile (Xe, Kr, I, Cs, Te, Sb and Ag) and semi-volatile (Mo, Ba, Rh, Pd and Tc) to nonvolatile (Sr, Y, Nb, Ru, La, Ce and Eu; Kashparov et al., 1996; Pontillon et al., 2010). As a result of the estimated potential remaining heat release
from fuel at the time of the accident (∼ 230 W kg-1 U)
and the heat accumulation in the fuel (National Report of Ukraine, 2011), highly
mobile volatile fission products (Kr, Xe, iodine, tellurium and caesium) were
released from the fuel of the reactor and raised to a height of more than 1 km on 26 April 1986 and to approximately 600 m over the following
days (IAEA, 1992; Izrael et al., 1990). The greatest release of radiocaesium
occurred during the period of maximum heating of the reactor fuel on
26–28 April 1986 (Izrael et al., 1990). This caused the formation of
the western, southwestern (towards the settlements of Poliske and Bober),
northwestern (ultimately spreading to Sweden and wider areas of western
Europe), and northeastern condensed radioactive traces. Caesium deposition
at distances from Chernobyl was largely determined by the degree of
precipitation (e.g. see Chaplow et al., 2015, discussing deposition across
Great Britain). After the covering of the reactor by dropping materials
(including 40 t of boron carbide, 2500 t of lead, 1800 t of sand and clay,
and 800 t of dolomite) from helicopters over the period 27 April–10 May 1986 (National Report of Ukraine, 2011), the ability for heat exchange in the fuel reduced, which caused a rise in temperature
and a consequent increase in the leakage of volatile fission products, and the
melting of the materials which had been dropped onto the reactor.
Subsequently, there was a sharp reduction in the release of radionuclides
from the destroyed reactor on 6 May 1986 (National Report of Ukraine,
2011) due to aluminosilicates forming thermally stable compounds with many
fission products and fixing caesium and strontium at high temperatures (a
process known prior to the Chernobyl accident; Hilpert et al., 1983).
The changes in the annealing temperature of the nuclear fuel during the
accident had a strong effect on both the ratio of different volatile fission
products released (the migratory properties of Xe, Kr, I, Te and Cs increased
with the temperature rise and were influenced by the presence of UO2)
and the rate of the destruction of the nuclear fuel which oxidized to form
micronized fuel particles (Salbu et al., 1994; Kashparov et al., 1996). The
deposition of radionuclides such as 90Sr, 238-241Pu and 241Am,
which were associated with the fuel component of the Chernobyl releases, was
largely limited to areas relatively close to the ChNPP. Areas receiving the
deposition of these radionuclides were the Chernobyl Exclusion Zone (i.e.
the area of approximately 30 km radius around the ChNPP), adjacent
territories to the north of the Kiev region in the west of the Chernihiv
region, and the Bragin and Hoyniki districts of the Gomel region (Belarus).
Deposition was related to the rate of the dry gravitational sedimentation of
the fuel particles caused by their high density (about 8–10 g cm-3; Kashparov et al., 1996); sedimentation of the lightweight
condensation particles containing iodine and caesium radioisotopes was
lower, and hence, these were transported further.
After the Chernobyl accident, western Europe and the Ukrainian–Belorussian
Polessye were contaminated with radionuclides (IAEA, 1991, 1992, 2006).
However, the area extending to 60 km around the ChNPP was the most
contaminated (Izrael et al., 1990). Work on the assessment of the
radiological situation within the zone started within a few days of the
accident; the aim of this work was the radiation protection of the
population and personnel. Subsequently, further quantification of
terrestrial dose rates was carried out by an aerial gamma survey by the State
Hydrometeorological Committee, together with Ministries of Geology and Defence of the USSR (as reported in Izrael et al., 1990). Large-scale
sampling of soil was also conducted, with samples analysed using
gamma spectrometry and radiochemistry methods (see Izrael et al., 1990).
These studies showed high variability in dose rates and radionuclide
activity concentrations, with spatial patterns in both radioactive
contamination and the radionuclide composition of fallout (Izrael et al.,
1990).
The initial area from which the population was evacuated was based on an
arbitrary decision in which a circle around the Chernobyl nuclear power plant,
with a radius of 30 km, was defined (IAEA, 1991). In the initial phase after
the accident (before 7 May 1986), 99 195 people were evacuated from 113
settlements, including 11 358 people from 51 villages in Belarus and 87 837
people from 62 settlements in Ukraine (including about 45000 people
evacuated between 14:00 and 17:00 LT on 27 April from the town of Pripyat located 4 km from the ChNPP; Aleksakhin et al., 2001).
The analysis of the data available in May 1986 showed that the extent of the
territory with radioactive contamination, where comprehensive measures were
required to protect the population, extended far beyond the 30 km Chernobyl
Exclusion Zone (CEZ). A temporary annual effective dose limit of 100 mSv for
the period from 26 April 1986 to 25 April 1987 (50 mSv from
external exposure and 50 mSv from internal exposure) was set by the USSR's Ministry of
Health. To identify areas outside of the CEZ where the population required
evacuation, dose criteria had to be defined. Using the average value of the dose rate of gamma radiation in open air for an area (estimated for 10 May 1986) was proposed to help define an evacuation zone. An
exposure dose rate of 5 mR h-1 estimated for 10 May 1986
(approximating to an effective dose rate (EDR) of gamma radiation in the air of
50 µSv h-1) equated to an external annual dose of 50 mSv for the period from 26 April 1986 to 25 April 1987.
At the end of May 1986, an approach for identifying areas where evacuation was
required, using the estimated internal dose rates, was proposed. This used the
average density of the surface contamination of the soil with long-lived
biologically significant nuclides (137Cs, 90Sr and 239,240Pu) in
a settlement and modelling to estimate the contamination of foodstuffs and,
hence, diet. The numerical values suggested for identifying areas for evacuation
were 15 Ci km-2 (555 kBq m-2) of 137Cs, 3 Ci km-2 (111 kBq m-2) of 90Sr, and 0.1 Ci km-2 (3.7 kBq m-2) of 239,240Pu; this equated to an internal dose of 50 mSv over the first year after the accident.
However, in reality, the main criterion for the evacuation was the exposure
dose rate (R h-1), and where the exposure dose rate exceeded 5 mR h-1 (EDR in air of about 50 µSv h-1) the evacuated population were not allowed to return.
Hence, in 1986 the boundary of the population evacuation zone was set at an
exposure dose rate of 5 mR h-1 (EDR of about 50 µSv h-1). However, the ratio of short-lived gamma-emitting radionuclides (95Zr, 95Nb, 106Ru and 144Ce), deposited as fuel particles to 134,137Cs deposited as condensation particles, was inconsistent across the evacuated areas. Therefore, after the radioactive decay of the short-lived radionuclides, the residual dose rate across the evacuated areas varied considerably and was largely determined by the pattern of long-lived 137Cs deposition (e.g. Fig. 1; Kashparov et al., 2018).
Caesium-137 deposition in the Ukrainian 30 km exclusion zone
estimated for 1997 (from UIAR, 1998).
The first measurements of the activity concentration of radionuclides in the soil
showed that radionuclide activity concentration ratios depended on the distance
and direction from the ChNPP (Izrael et al., 1990). Subsequent to this
observation a detailed study of soil contamination was started in 1987
(Izrael et al., 1990). Taking into account the considerable heterogeneity of
terrestrial contamination with radioactive substances in a large area,
sampling along the western, southern and northern traces was carried out in
stages, finishing in 1988.
In 1987 the State Committee of Hydrometeorology and the
Scientific Centre of the Defence Ministry of the USSR established a survey
programme to monitor radionuclide activity concentrations in the soil. For this
purpose, 540 sampling sites were identified at a distance of 5 to 60 km
around the ChNPP, using a polar coordinate system centred on the ChNPP.
A total of 15 sampling sites were selected on each of the 36 rays drawn every 10∘ (Loshchilov et al., 1991; Figs. 3–4). Radionuclide activity
concentrations in the soil samples collected on the radial network were
determined by the UIAR and used to calculate the radionuclide contamination
density. These data are discussed in this paper, and the full data set is
freely available from Kashparov et al. (2019).
Data
The data (Kashparov et al., 2019) include the location of the sample sites (angle
and distance from the ChNPP), dose rate, radionuclide deposition data,
counting efficiency and information on exchangeable 134,137Cs.
The data are presented in a table with 21 columns and 540 rows of data (plus
column headings) as one Microsoft Excel Comma Separated Value File (.csv) as
per the requirements of the Environmental Information Data Centre. Table A1 in the Appendix presents an explanation of the column headings and units used in the data (Kashparov et al., 2019).
Sampling
To enable long-term monitoring and contamination mapping of the 60 km zone
around the ChNPP, 540 points were defined and sampled in April–May 1987.
The sampling strategy used a radial network with points at every
10∘ (from 10 to 360∘); sampling points were
located at distances of 5, 6, 7, 8.3, 10, 12, 14.7, 17, 20, 25, 30, 37.5, 45, 52.5 and 60 km (Figs. 3–4). The locations of the sampling points were identified using military maps
(1 : 10 000 scale) and the local landscape. Sampling sites (identified using an
index post) were estimated to be within 10 m of the distances and directions as
recorded in the accompanying data set. Sites were resampled regularly until
1990 and sporadically thereafter; however, data for these subsequent
samplings are not reported here as they are unavailable (including to the
UIAR).
Samples were not collected from points located in swamps, rivers and lakes;
in total, 489 samples were collected. A corer with a diameter of 14 cm was
used to collect soil samples down to a depth of 5 cm from five points at
each location, using the envelope method (with approximately 5–10 m between
sampling points; Fig. 2; Loshchilov et al., 1991). Soil cores were
retained intact during transportation to the laboratory. At each sampling
point, the exposure dose rate was determined 1 m above ground level.
Soil sampling using a ring of 14 cm diameter to collect a 5 cm
deep soil core (courtesy of UIAR, 1989).
Analysis
Using a high-purity germanium detector (GEM-30185; EG&G, ORTEC, USA) and a
multichannel analyser (ADCAM-300; EG&G, ORTEC, USA), the activity concentration
of gamma-emitting radionuclides (zirconium-95 (95Zr), niobium-95
(95Nb), ruthenium-106 (106Ru), caesium-134 (134Cs),
caesium-137 (137Cs) and cerium-144 (144Ce)) was determined in one
soil sample from each sampling site. Information on the gamma lines used in the
analyses and the radioisotope half-lives assumed for decay correction are
presented in Appendix 2. Soil samples were analysed in a 1 L Marinelli
container. The other four cores were sent to different laboratories in the
Soviet Union (data for these cores are unfortunately not available). Using a
1M NH4Ac solution (pH 7), a 100 g subsample of soil was leached (solid to liquid ratio of 1 : 5). The resultant leachate solution was shaken for 1 h and
then left at room temperature for 1 d before filtering through ashless
filter paper (3–5 µm). The filtrate was then put into a suitable
container for gamma analysis to determine the fraction of exchangeable
134,137Cs. Measured activity concentrations were reported at a 68 %
confidence level (which equates to 1 standard deviation).
The fallout density of 144Ce (kBq m-2) within the 60 km
zone around the ChNPP decay corrected to 6 May 1986.
The fallout density of 137Cs (kBq m-2) within the 60 km
zone around the ChNPP decay corrected to 6 May 1986.
Decay radiation information from the master library, integrated in the spectrum-analysing software tool Gelicam (EG&G, ORTEC, USA), was used in the gamma analyses. Activities of 106Ru and 137Cs in the samples were
estimated via their gamma radiation emitting progenies, namely 106Rh and
137mBa, respectively.
Calibration of the spectrometer was conducted using certified standards
(soil equivalent multi-radionuclide standard; V. G. Khlopin Radium
Institute, Russia). Quality assurance and/or quality control procedures included
regular monitoring of the system performance, efficiency, background and
full width at half maximum (FWHM) for the 144Ce, 137Cs and
95Nb photo peaks. To validate the accuracy and precision of the method
employed for 137Cs activity concentration measurements, quality control
samples (i.e. different matrix samples including water, soil and sawdust
spiked with known certified activities of radionuclides) and certified
reference materials (CRMs) were analysed alongside the samples. Analysis of
IAEA CRMs showed satisfactory results for radionuclide mean activity
concentrations with results being within the 95 % confidence interval; the
limit of detection for 137Cs in all samples was 1 Bq. Subsamples were
analysed in a different laboratory (USSR Ministry of Defence), and the results
for the two laboratories were within the error of determination.
The density of soil contamination (Bq m-2) was calculated from the
estimated radionuclide activity concentrations in soils. It has been
estimated that uncertainty from using a single soil sample (of the area 0.015 m2) to estimate the value of the contamination density of a sampling site
(the area from which five cores were collected) may be up to 50 % (IAEA,
2019).
The data described in this paper (Kashparov et al., 2020) comprise the exposure
dose rate (mR h-1), date of gamma activity measurement, density of
contamination (Bq m-2) of 95Zr, 95Nb, 106Ru, 134Cs,
137Cs and 144Ce (with associated activity measurement
uncertainties), and density of contamination of 134+137Cs in an
exchangeable form. Reported radionuclide activity concentration values are
for the date of measurement (samples were analysed within 1.5 months of
collection).
For the presentation below, radionuclide activity concentrations have been decay
corrected to 6 May 1986 (the date on which releases from the reactor
in effect stopped), using the following equation:
AT=A0/e-λt,
where AT equals the
radionuclide activity concentration at the time of measurement (t);
AO is the activity concentration on 6 May 1986, and
λ is the decay constant (i.e. 0.693/radionuclide physical half-life; see Table 1 for radionuclide half-lives).
Relationship between fallout density of 144Ce (1) and
137Cs (2) and distance from the ChNPP towards the south (a)
(150–210∘), the west (b) (240–300∘) and the north (c) (330–30∘).
The average activity concentrations of radionuclides with half-life
(T1/2)>1 d estimated in the fuel of the ChNPP number
four reactor recalculated for 6 May 1986 (Begichev et al., 1990).
The contamination density of 144Ce and 137Cs are presented in
Figs. 3–4; the activity concentrations, as presented in the figures, have
been decay corrected to 6 May 1986. The density of 144Ce
contamination decreased exponentially with distance (Figs. 3 and 5)
because 144Ce was released in the fuel particles, which had a high dry deposition velocity (Kuriny et al., 1993). The fallout density of 144Ce
decreased by 7–9 times, between the 5 and 30 km sampling sites, and by
70–120 times, between the 5 and 60 km sampling sites (Fig. 5).
The fallout density of 137Cs decreased similarly to that of 144Ce
along the southern “fuel trace” (Fig. 5a). The contamination density of
137Cs along the western trace decreased less than the 144Ce
contamination density due to the importance of the condensation component of
the fallout in this direction (with a resultant R2 value for the
relationship between 137Cs and a distance lower than for 144Ce
and 137Cs in different directions; Fig. 5b). The comparative
decrease in 137Cs contamination density along the northern trace (mixed
fuel and condensation fallout) was in between that of the southern and
western traces (Fig. 5c), although there were caesium hotspots in the
northern condensation trace (Figs. 4 and 5c). The activity ratio of
144Ce to 137Cs decreased with the distance from the ChNPP due to the
condensation component being more important for 137Cs; the condensation
component had a lower deposition velocity compared with the fuel particles (with
which 144Ce was associated; Fig. 6). The ratio 144Ce /137Cs
for the Chernobyl reactor fuel on 6 May 1986 can be estimated to be 15
from the data presented in Table 1. The ratio was about 11 (geometric mean of
1167 measurements) in the Chernobyl fuel particles larger than 10 µm due
to the caesium escape during the high-temperature annealing (Kuriny et al., 1993).
The ratio of 144Ce /137Cs in the deposition exceeded five in the
southeast and in the south up to 60 and 30 km from the ChNPP, respectively
(Fig. 6). Thus, activities of 134,137Cs in the condensate and in the
fuel components in these directions were of approximate equal importance.
The condensation component of caesium was more important in the north and
dominated in the west (Fig. 8; Loshchilov et al., 1991; Kuriny et al.,
1993); the more rapidly changing 144Ce /137Cs ratios in these
directions are reflective of this (Fig. 6).
144Ce /137Cs ratio within the 60 km
zone around the ChNPP decay corrected to 6 May 1986.
A good correlation (R2=0.98) was observed between fallout densities
of 95Zr (estimated from the activity concentration of the daughter product
95Nb)
Niobium-95 (T1/2=34 d) is the daughter
radionuclide of 95Zr (T1/2=65 d), and the ratio of their
activities at an equilibrium equals 95Nb /95Zr = 2.1.
and
144Ce (Fig. 7a) because both radionuclides were released and
deposited as fuel particles (Kuriny et al., 1993; Kashparov et al., 2003;
Kashparov, 2003). The fallout density ratio of
144Ce /95Zr =0.73±0.05, decay corrected to 6 May 1986, was similar to that estimated for the Chernobyl reactor fuel
(144Ce /95Zr=0.68; Table 1).
The activity ratio of 144Ce to 106Ru in the fallout was correlated
(R2=0.93) and was 3.9±0.4 decay corrected to 6 May 1986
(Fig. 7b). The value was close to the ratio of 144Ce /106Ru
estimated for the fuel in the ChNPP number four reactor (4.7; Table 1). Excess
106Ru activity relative to 144Ce activity in some soil samples was
observed, likely due to the presence of “ruthenium particles” (a matrix of
iron group elements with a high content of 103,106Ru; Kuriny et al.,
1993; Kashparov et al., 1996).
There was a weak correlation (R2=0.41) between 144Ce and 137Cs activities in the fallout because, as already discussed, caesium was
largely deposited as condensation particles while cerium was deposited in
fuel particles only. However, in highly contaminated areas close to the
ChNPP, a significant part of the 137Cs was deposited as fuel particles
and the activity ratio of 144Ce /137Cs of 9.1 (Fig. 7c)
broadly corresponded to that of 15 in the reactor fuel (Table 1).
Different radioisotopes of caesium escaped from the nuclear fuel and were
deposited in the same way. This similar behaviour of 134Cs and
137Cs resulted in a strong correlation (R2=0.99) between their
activities in the soil samples, and the ratio of
134Cs /137Cs =0.57±0.07 was similar to that estimated for the reactor fuel (0.64; Table 1).
Correlation between deposition densities of different
radionuclides decay corrected to 6 May 1986.
The fallout density of 238Pu (kBq m2) corrected to
6 May 1986; estimated from measurements of 144Ce in the soil and
estimated activity concentrations in the fuel of the ChNNP reactor number
four (note that no data were available for less than 5 km from ChNPP and no
interpolation for this area has been attempted).
Use of the data
Apart from adding to the available data, with which contamination maps for
the CEZ and surrounding areas can be generated (e.g. Kashparov et al., 2018),
the data discussed in this paper can be used to make predictions for less
well studied radionuclides.
The determination of beta- and alpha-emitting radionuclides in samples
requires radiochemical extraction, which is both time-consuming and
relatively expensive. Large-scale surveys of the deposition of alpha- and
beta-emitting radionuclides are therefore more difficult than those for
gamma-emitting radionuclides and are not conducive to responding to a
large-scale accident such as that which occurred at Chernobyl. Above we have
demonstrated that the deposition behaviour of different groups of
radionuclides was determined by the form in which they were present in the
atmosphere (i.e. associated with fuel particles or condensation particles).
Spatial distribution, interpolated as for Fig. 8, of the effective
dose rate within the 60 km zone around the ChNPP on 10 May 1986 (a)
and 10 August 1986 (b). Note that no data were available for less than 5 km from ChNPP, and no interpolation for this area has been attempted.
We propose that 144Ce deposition can be used as a marker of the
deposition of fuel particles; fuel particles were the main deposition form
of nonvolatile radionuclides (i.e. Sr, Y, Nb, Ru, La, Ce, Eu, Np, Pu, Am and
Cm). Therefore, using 144Ce activity concentrations determined in soil
samples and estimates of the activities in reactor fuel, we can make
estimates of the deposition of radionuclides such as Pu isotopes and Cm that
have been relatively less studied. For example, activity ratios of
238Pu, 239Pu, 240Pu and 241Pu to 144Ce, at the time
of measurement would be 8.4×10-4, 6.2×10-4,
9.7×10-4 and 1.1×10-1, respectively (estimated
by decay correcting data presented in Table 1). Fallout densities of these
plutonium isotopes can therefore be calculated for all sampling points where the
deposition density of 144Ce was measured either in this study (e.g.
Fig. 3) or in other data sets. As an example of the application of the
data in this manner, Fig. 8 presents the estimated deposition of
238Pu; Fig. 8 was prepared using the triangulated irregular
network (TIN) interpolation within MapInfo. The first maps of the 90Sr and
239+240Pu surface contamination from the Chernobyl accident were
prepared in the frame of an international project (IAEA, 1992) in a similar
way.
The dynamic spatial distribution of the gamma dose rate can be reconstructed
using the data on radionuclide contamination densities (Kashparov et al.,
2019) in combination with the ratios between the activities of radionuclides in
fuel and in condensed components of the Chernobyl fallout (Table 1) and also the
dose coefficients for exposure to contaminated ground surfaces, (Sv s-1 Bq m-2; Eckerman and Ryman, 1993). A total of 5 d after the deposition, the following radionuclides were major contributors (about 95 %) to the gamma dose rate: 136Cs, 140La, 239Np, 95Nb,
95Zr, 131I, 148m Pm, 103Ru, 140Ba and 132Te.
After 3 months the major external dose contributors were 95Nb,
95Zr, 148mPm, 134Cs, 103Ru, 137mBa, 110mAg,
136Cs and 106Rh. A total of 3 years thereafter, the major contributors were
137mBa, 134Cs, 106Rh, 110mAg and 154Eu. At the present
time, the gamma dose can be estimated to be mainly (99 %) due to the
gamma-emitting daughter radionuclide of 137Cs (137mBa). Bondar (2015), from a survey of the CEZ along the Ukrainian–Belarussian border,
showed a good relationship between 137Cs contamination (ACs-137; in
the range of 17–7790 kBq m-2) and ambient dose rates at 1 m above the
ground (Dext; in the range of 0.1–6.0 µSv h-1). The
relationship was described by the following equation with a correlation
coefficient of 0.99:
Dext=0.0009×ACs-137+0.14.
As an example of the application of the data in this manner, Fig. 9
presents the estimated external effective gamma dose rate 5 and 95 d
after the cessation of the radioactive releases from the reactor on 6 May 1986.
The estimated effective dose rate values exceed the evacuation dose criteria
of 50 µSv h-1 over a large area (especially in the north and west)
of the 60 km area around the ChNPP on 10 May 1986 (Fig. 9a); as
discussed above, a dose rate of 50 µSv h-1 on 10 May 1986
equated to a total dose, over the first year after the accident, of 50 mSv –
the value used to define areas for evacuation. On 10 August 1986
the area estimated to exceed 50 µSv h-1 was restricted to the
north (Fig. 9b). The dose rate decreased quickly after the accident due to
the radioactive decay of short-lived radionuclides. The dominance of these
short-lived radionuclides and a lack of knowledge about the radionuclide
composition of the fallout made it difficult, in 1986, to estimate the external
dose rates to the public for an evaluation date of 10 May 1986 (most
dose rate measurements were made after 10 May). This likely
resulted in the overestimation of dose rates for some villages in 1986,
leading to their evacuation when the external dose rate would not have been
in excess of the 50 mSv limit used by the authorities.
There is a need for deposition data for the CEZ and surrounding areas for a
number of reasons. These include exploring the risks associated with future
management options for the CEZ (e.g. management of the water table, forest
fire prevention, increased tourism, etc.) and also the return of abandoned
areas outside the CEZ to productive use. The long-term effect of
radiation exposure on wildlife in the CEZ is an issue of much debate (e.g.
see the discussion in Beresford et al., 2019). Improved data, which can be used
to map the contamination of a range of radionuclides, will be useful in
improving dose assessments to wildlife (including retrospective assessments
of earlier exposure rates). The CEZ has been declared a “radioecological
observatory” (Muikku et al., 2018; where a radioecology observatory is
defined as a radioactively contaminated field site that provides a focus for
joint, long-term radioecological research). The open provision of data, as
described in this paper, fosters the spirit of collaboration and openness
required to make the observatory site concept successful and joins a growing
amount of data made available for the CEZ (Kashparov et al., 2017; Fuller et
al., 2018; Kendrick et al., 2018; Gaschak et al., 2018; Beresford et al.,
2018; Lerebours and Smith, 2019).
Data availability
The data described here (10.5285/a408ac9d-763e-4f4c-ba72-73bc2d1f596d; Kashparov et al., 2019) are freely available for registered users of the Natural Environment Research Council (NERC) Environmental Information Data Centre (https://eidc.ac.uk/, last access: 17 August 2020) under the terms of the Open Government Licence.
A detailed explanation of the column headings and units (where
applicable) which accompany the data (Kashparov et al., 2019).
Column_headingExplanationUnitsIdentifierUnique identification numberNot applicableAngle_degreeA number between 10 and 360 indicates the direction from the ChNPP in degrees; 90∘ is due east, 180∘ is due south, 270∘ is due west and 0/360∘ is due north. See Fig. 1.DegreesDistance_from_ChNPP_kmDistance from the Chernobyl Nuclear Power Plant (ChNPP) reactor number four in kilometres.KilometresDate_gamma_measurementDate of gamma measurement. An empty cell indicates a network point located in a water body where sample collection was not possible.dd-month-yyyyExposure_dose_rate_mR/hDose rate in the air at a height of 1 m.Milliroentgen per hourAbsorbed_dose_rate_microGray/hAbsorbed dose rate is the energy deposited in matter by ionizing radiation per unit mass.Microgray per hourZr-95_Bqm2Density of soil contamination with zirconium-95.Becquerel per square metreZr-95_relative_errorRelative uncertainty in determination of zirconium-95 (at 68 % confidence interval).PercentageNb-95_Bqm2Density of soil contamination with niobium-95.Becquerel per square metreNb-95_relative_errorRelative uncertainty in determination of niobium-95 (at 68 % confidence interval).PercentageRu-106_Bqm2Density of soil contamination with ruthenium-106.Becquerel per square metreRu-106_relative_errorRelative uncertainty in determination of ruthenium-106 (at 68 % confidence interval).PercentageCs-134_Bqm2Density of soil contamination with caesium-134.Becquerel per square metreCs-134_relative_errorRelative uncertainty in determination of caesium-134 (at 68 % confidence interval).PercentageCs-137_Bqm2Density of soil contamination with caesium-137.Becquerel per square metreCs-137_relative errorRelative uncertainty in determination of caesium-137 (at 68 % confidence interval).PercentageCe-144_Bqm2Density of soil contamination with cerium-144.Becquerel per square metreCe-144_relative_errorRelative uncertainty in determination of cerium-144 (at 68 % confidence interval).PercentageExch_Cs-134+Cs-137_Bqm2Density of soil contamination with the exchangeable form of caesium.Becquerel per square metreNote on empty cellsAn empty cell means that data is not available. InstrumentGamma spectrometer with a semiconductor detector GEM-30185; EG&G, ORTEC, USA. (Results reported at 68 % confidence level.)
Decay radiation information from the master library, integrated
into a spectrum-analysing software tool, Gelicam (EG&G ORTEC, USA), used in gamma analyses. Activities of 106Ru and 137Cs in samples were
estimated via their gamma-radiation-emitting progenies, namely 106Rh and
137mBa, respectively.
Soil samples were collected by the USSR Ministry of
Defence and delivered to UIAR. Sample preparation, analysis and data
interpretation were carried out by UIAR staff. In addition, VK, SL and VP prepared the samples and measured radionuclide activity concentrations in the samples. VK analysed the results, and MZ created the database and prepared the figures (maps) in the paper. The paper was prepared by JSC, NAB, VK, SL and MZ.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
Funding for the UKCEH staff enabled their contributions to preparing this
paper, and the accompanying data set (Kashparov et al., 2019) was provided by
the TREE project (http://www.ceh.ac.uk/tree, last access: 17 August 2020). This research was funded by NERC,
the Environment Agency (EA) and Radioactive Waste Management Ltd under the RATE
programme and associated iCLEAR (https://tree.ceh.ac.uk/content/iclear-0, last access: 17 August 2020; funded by NERC) projects.
Financial support
This research has been supported by the Natural Environment Research Council (TREE and iCLEAR projects; grant nos. NE/L000318/1 and NE/R009619/1, respectively), the Environment Agency (TREE project) and the Radioactive Waste Management Ltd (TREE project).
Review statement
This paper was edited by Giulio G. R. Iovine and reviewed by four anonymous referees.
ReferencesAleksakhin, R. M., Buldakov, L. A., Gubanov, V. A., Drozhko, E. G., Ilyin, L. A.,
Kryshev, I. I., Linge, I. I., Romanov, G. N., Savkin, M. N., Saurov, M. M.,
Tikhomirov, F. A., and Kholina, Yu. B.: Major radiation accidents: consequences and
protective measures, edited by: Ilyin, L. A. and Gubina, V. A.,
Moscow, Publishing House IzdAT, 752 pp., available at: http://elib.biblioatom.ru/text/krupnye-radiatsionnye-avarii_2001/go,0/ (last access: 17 August 2020), 2001.
Begichev, S. N., Borovoy, A. A., Burlakov, E. V., Gavrilov, S. L., Dovbenko,
A. A., Levina, L. A., Markushev, V. M., Marchenko, A. E., Stroganov, A. A., and
Tataurov, A. L.: Preprint IAE-5268/3: Reactor Fuel of Unit 4 of the Chernobyl
NPP (a brief handbook), Kurchatov In st. Atomic Energy, 1990.Beresford, N. A., Gaschak, S., Barnett, C. L., Maksimenko, A., Guliaichenko,
E., Wells, C., and Chaplow, J. S.: A “Reference Site” in the Chernobyl Exclusion
Zone: radionuclide and stable element data, and estimated dose rates
NERC-Environmental Information Data Centre, 10.5285/ae02f4e8-9486-4b47-93ef-e49dd9ddecd4, 2018.Beresford, N. A., Scott, E. M., and Copplestone, D.: Field effects studies in the
Chernobyl Exclusion Zone: Lessons to be learnt, J. Environ. Radioact., 211, 105893,
10.1016/j.jenvrad.2019.01.005, 2019.
Bondar, Yu.: Field studies in the Chernobyl exclusion zone along the
Belarusian border (dosimetric monitoring and soil radiation analysis),
Report of Polesye State Radiation and Ecological Reserve, Belarus, Khoiniki,
2015.
Chaplow, J. S., Beresford, N. A., and Barnett, C. L.: Post-Chernobyl surveys of radiocaesium in soil, vegetation, wildlife and fungi in Great Britain, Earth Syst. Sci. Data, 7, 215–221, https://doi.org/10.5194/essd-7-215-2015, 2015.
Eckerman, K. F. and Ryman, J. C.: External exposure to radionuclides in air,
water, and soil, Federal guidance report No. 12, EPA-402-R-93-081, Oak Ridge
National Laboratory, Tennessee, USA, 238 pp., 1993.Fuller, N., Smith, J. T., and Ford, A. T.: Effects of low-dose ionising radiation
on reproduction and DNA damage in marine and freshwater amphipod
crustaceans. NERC Environmental Information Data Centre, 10.5285/b70afb8f-0a2b-40e6-aecc-ce484256bbfb, 2018.
Gaschak, S. P., Beresford, N. A., Barnett, C. L., Wells, C., Maksimenko, A.,
and Chaplow, J. S.: Radionuclide data for vertebrates in the Chernobyl
Exclusion Zone NERC-Environmental Information Data Centre,
https://doi.org/10.5285/518f88df-bfe7-442e-97ad-922b5aef003a, 2018.
Hilpert, K., Odoj, R., and Nurnberg, H. W.: Mass spectrometric study of the
potential of Al203/Si02 additives for the retention of cesium in coated
particles, Nucl. Technol., 61, 71–77, 1983.
IAEA: International Chernobyl Project: Technical Report, International
Advisory Committee, Vienna, 1991.IAEA: International Chernobyl project, technical report, ISBN 92-0-400192-5, available at: http://www-pub.iaea.org/MTCD/publications/PDF/Pub886_web/Start.pdf (last access: 17 August 2020), 1992.
IAEA: Environmental consequences of the Chernobyl accident and their
remediation: twenty years of experience, Report of the Chernobyl Forum
Expert Group “Environment”, edited by: Anspaugh, L. and Balonov, M., Radiological
assessment reports series, IAEA, STI/PUB/1239, 166 pp., 2006.IAEA: Guidelines on soil and vegetation sampling for radiological
monitoring, Technical Reports Series No. 486, International Atomic Energy
Agency, Vienna, 247 pp., available at: https://www.iaea.org/publications/12219/guidelines-on-soil-and-vegetation-sampling-for-radiological-monitoring (last access: 17 August 2020),
2019.
Izrael, Yu. A., Vakulovsky, S. M., Vetrov, V. A., Petrov, V. N., Rovinsky,
F. Ya., and Stukin, E. D.: Chernobyl: Radioactive Contamination of the
Environment, Gidrometeoizdat publishers, Leningrad, 223 pp., 1990 (in
Russian).
Kashparov, V. A.: Hot Particles at Chernobyl, Environ. Sci. Pollut. R., 10,
21–30, 2003.
Kashparov, V. A., Ivanov, Y. A., Zvarich, S. I., Protsak, V. P., Khomutinin,
Y. V., Kurepin, A. D., and Pazukhin, E. M.: Formation of Hot Particles
During the Chernobyl Nuclear Power Plant Accident, Nucl. Technol., 114,
246–253, 1996.Kashparov, V. A., Lundin, S. M., Zvarich, S. I., Yoschenko, V. I., Levtchuk,
S. E., Khomutinin, Yu. V., Maloshtan, I. N., and Protsak, V. P.: Territory
contamination with the radionuclides representing the fuel component of
Chernobyl fallout, Sci. Total Environ., 317, 105–119,
10.1016/S0048-9697(03)00336-X, 2003.Kashparov, V., Levchuk, S., Zhurba, M., Protsak, V., Khomutinin, Y.,
Beresford, N. A., and Chaplow, J. S.: Spatial datasets of radionuclide
contamination in the Ukrainian Chernobyl Exclusion Zone, NERC-Environmental
Information Data Centre, 10.5285/782ec845-2135-4698-8881-b38823e533bf, 2017.
Kashparov, V., Levchuk, S., Zhurba, M., Protsak, V., Khomutinin, Y., Beresford, N. A., and Chaplow, J. S.: Spatial datasets of radionuclide contamination in the Ukrainian Chernobyl Exclusion Zone, Earth Syst. Sci. Data, 10, 339–353, https://doi.org/10.5194/essd-10-339-2018, 2018.Kashparov, V., Levchuk, S., Zhurba, M., Protsak, V., Beresford, N. A.,
and Chaplow, J. S.: Spatial radionuclide deposition data from the 60 km radial
area around the Chernobyl nuclear power plant, 1987, NERC Environmental
Information Data Centre, 10.5285/a408ac9d-763e-4f4c-ba72-73bc2d1f596d, 2019.Kendrick, P., Barçante, L., Beresford, N. A., Gashchak, S., and Wood, M. D.:
Bird Vocalisation Activity (BiVA) database: annotated soundscapes from the
Chernobyl Exclusion Zone, NERC Environmental Information Data Centre,
10.5285/be5639e9-75e9-4aa3-afdd-65ba80352591,
2018.
Kuriny, V. D., Ivanov, Y. A., Kashparov, V. A., Loschilov, N. A., Protsak,
V. P., Yudin, E. B., Zhurba, M. A., and Parshakov, A. E.: Particle
associated Chernobyl fall-out in the local and intermediate zones, Ann.
Nucl. Energy, 20, 415–420, 1993.Lerebours, A. and Smith, J. T.: Water chemistry of seven lakes in Belarus and
Ukraine 2014 to 2016, NERC Environmental Information Data Centre, 10.5285/b29d8ab8-9aa7-4f63-a03d-4ed176c32bf3, 2019.
Loshchilov, N. A., Kashparov, V. A., Yudin, Y. B., Protsak, V. P., Zhurba,
M. A., and Parshakov, A. E.: Experimental assessment of radioactive fallout
from the Chernobyl accident, Sicurezza e Protezione, 25–26, 46–49, 1991.Muikku, M., Beresford, N. A., Garnier-Leplace, J., Real, A., Sirkka, L.,
Thorne, M., Vandenhove, H., and Willrodt, C.: Sustainability and integration of
radioecology—position paper, J. Radiol. Prot., 38, 152–163, 10.1088/1361-6498/aa9c0b, 2018.
National Report of Ukraine: Twenty-five Years after Chornobyl Accident:
Safety for the Future, Kyiv KIM, 328 p., 2011.Pontillon, Y., Ducros, G., and Malgouyres, P. P.: Behaviour of fission
products under severe PWR accident conditions VERCORS experimental
programme – Part 1: General description of the programme, Nucl.
Eng. Des., 240, 1843–1852, 10.1016/j.nucengdes.2009.06.028, 2010.
Saji, G. A.: scoping study on the environmental releases from the Chernobyl
accident (part I): Fuel particles, American Nuclear Society International
Topical Meeting on Probabilistic Safety Analysis, PSA 05, 685–696, 2005.
Salbu, B., Krekling, T., Oughton, D. H., Ostby, G., Kashparov, V. A., Brand,
T. L., and Day, J. P.: Hot Particles in Accidental Releases from Chernobyl and
Windscale Nuclear Installations, Analyst, 119, 125–130, 1994.
Talerko, N.: Mesoscale modelling of radioactive contamination formation in
Ukraine caused by the Chernobyl accident, J. Env. Radioactivity, 78,
311–329, 2005.
UIAR: The map of the 30-km Chernobyl zone terrestrial density of
contamination with cesium-137 (in 1997), UIAR, Kyiv, Ukraine, 1998.
United Nations Scientific Committee on the Effects of Atomic Radiation,
UNSCEAR, Sources and effects of ionizing radiation, Report to the General
Assembly with Scientific Annexes, volume II, Annex D. Health effects due to
radiation from the Chernobyl accident, United Nations, New York, 178 pp.,
2008.