37
entire hemisphere in which the explosion was conducted. In addition to nuclear
explosions, global uranium deposition on the Earth’s surface is associated with accidents of artificial satellites equipped with nuclear and nuclear-isotope sources of
energy. For example, the crash of the Soviet Cosmos-954 satellite in 1978 led to the
release of several kilograms of uranium into the atmosphere (Bocharov 1995).
The level of global deposition of radionuclides on the Earth’s surface depends on
the geographical latitude. On the territory of Belarus, located at significant distances
from the nuclear test sites, global fallout as a result of nuclear weapons tests had no
significant effect on the content and isotopic composition of uranium in soils.
A large-scale study of the soils of Belarus on the content of uranium was carried
out in the 1970–1980s of the twentieth century. Data on the
238
U content in the soil
cover obtained as a result of this study are presented in the work (Shagalova 1986;
Gurskiy and Loseva 1989). According to these data, the content of natural uranium
in Belarusian soils is within 1 × 10
−5
–3.5 × 10
−4
wt. %. The author (Shagalova 1986)
distinguishes five groups of soils according to the level of
238
U: high (more than
2.0 × 10
−4
), elevated ((1.5–2.0) × 10
−4
), medium ((1.0–1.5) × 10
−4
), reduced ((0.5–
1.0) × 10
−4
), and low (less than 0.5 × 10
−4
wt. %) uranium content. Depending on
the type of soil, the uranium content varies widely. The lowest level of uranium
((1–8) × 10
−5
wt. %) was found in peat-bog soils of the upper and transitional types
and the most of all ((1.6–3.5) × 10
−4
wt. %) in alluvial sod-gley loamy soils.
At present, the main amount of technogenic uranium in Belarus is connected
with the accident at the Chernobyl nuclear power plant (ChNPP). Prior to the accident, the IV block of the Chernobyl NPP worked 865 days. It consisted of 1654 fuel
assemblies. Most of the assemblies were first-load cassettes with a burn-out of
11–15 MW day kg
−1
U. In the active zone, there was also fresh fuel. The mass of
uranium in the cassette was 114.7 kg, and the total mass of the fuel loaded into the
reactor was 190.2 tons with an average burning depth of 10.3 MW day kg
−1
U
(IAEA 1988).
There were two main stages of the Chernobyl accident. In the first stage, which
lasted only a few minutes, as a result of significant overheating, nuclear fuel in the
reactor underwent fragmentation. There was an explosive release of radioactive
products from the reactor to a height of up to 2000 m (IAEA 1988). Many authors
believe that at this stage some of the radioactive products got to the upper atmosphere and even to the stratosphere, which led to contamination of almost the entire
Northern Hemisphere (Hirose et al. 1994). A composition of the radioactive products of this trace completely corresponded to the composition of the fuel of the IV
block at the time of the accident. At this stage, the fuel was dispersed without melting and oxidation (Borovoy et al. 1990).
In the second stage of the accident, graphite burned after heating up the active
zone, and in less than a day, the temperature reached the level, at which the release
of radionuclides began. At this stage of the accident, fractionation of radionuclides
took place. At the beginning of the second stage, volatile products were ejected, and
then radionuclides were released on the combustion products and together with the
fuel matrix. The high temperature in the second stage of the accident contributed to
the partial oxidation of uranium dioxide and removal from the active zone of Cs, I,
Uranium and Its Distribution in Typical Belarusian Soils
entire hemisphere in which the explosion was conducted. In addition to nuclear
explosions, global uranium deposition on the Earth’s surface is associated with accidents of artificial satellites equipped with nuclear and nuclear-isotope sources of
energy. For example, the crash of the Soviet Cosmos-954 satellite in 1978 led to the
release of several kilograms of uranium into the atmosphere (Bocharov 1995).
The level of global deposition of radionuclides on the Earth’s surface depends on
the geographical latitude. On the territory of Belarus, located at significant distances
from the nuclear test sites, global fallout as a result of nuclear weapons tests had no
significant effect on the content and isotopic composition of uranium in soils.
A large-scale study of the soils of Belarus on the content of uranium was carried
out in the 1970–1980s of the twentieth century. Data on the
238
U content in the soil
cover obtained as a result of this study are presented in the work (Shagalova 1986;
Gurskiy and Loseva 1989). According to these data, the content of natural uranium
in Belarusian soils is within 1 × 10
−5
–3.5 × 10
−4
wt. %. The author (Shagalova 1986)
distinguishes five groups of soils according to the level of
238
U: high (more than
2.0 × 10
−4
), elevated ((1.5–2.0) × 10
−4
), medium ((1.0–1.5) × 10
−4
), reduced ((0.5–
1.0) × 10
−4
), and low (less than 0.5 × 10
−4
wt. %) uranium content. Depending on
the type of soil, the uranium content varies widely. The lowest level of uranium
((1–8) × 10
−5
wt. %) was found in peat-bog soils of the upper and transitional types
and the most of all ((1.6–3.5) × 10
−4
wt. %) in alluvial sod-gley loamy soils.
At present, the main amount of technogenic uranium in Belarus is connected
with the accident at the Chernobyl nuclear power plant (ChNPP). Prior to the accident, the IV block of the Chernobyl NPP worked 865 days. It consisted of 1654 fuel
assemblies. Most of the assemblies were first-load cassettes with a burn-out of
11–15 MW day kg
−1
U. In the active zone, there was also fresh fuel. The mass of
uranium in the cassette was 114.7 kg, and the total mass of the fuel loaded into the
reactor was 190.2 tons with an average burning depth of 10.3 MW day kg
−1
U
(IAEA 1988).
There were two main stages of the Chernobyl accident. In the first stage, which
lasted only a few minutes, as a result of significant overheating, nuclear fuel in the
reactor underwent fragmentation. There was an explosive release of radioactive
products from the reactor to a height of up to 2000 m (IAEA 1988). Many authors
believe that at this stage some of the radioactive products got to the upper atmosphere and even to the stratosphere, which led to contamination of almost the entire
Northern Hemisphere (Hirose et al. 1994). A composition of the radioactive products of this trace completely corresponded to the composition of the fuel of the IV
block at the time of the accident. At this stage, the fuel was dispersed without melting and oxidation (Borovoy et al. 1990).
In the second stage of the accident, graphite burned after heating up the active
zone, and in less than a day, the temperature reached the level, at which the release
of radionuclides began. At this stage of the accident, fractionation of radionuclides
took place. At the beginning of the second stage, volatile products were ejected, and
then radionuclides were released on the combustion products and together with the
fuel matrix. The high temperature in the second stage of the accident contributed to
the partial oxidation of uranium dioxide and removal from the active zone of Cs, I,
Uranium and Its Distribution in Typical Belarusian Soils