Environmental Engineering Reference
In-Depth Information
10
5
10
4
10
3
10
2
10
1
10
0
10
-1
10
-2
28
10
22
3
15
27
9
21
2
April
May
June
July
August
FIGURE 18.2
Concentration of the sum of beta-active aerosols over Chernobyl NPP in April-August 1986.
Sampling from aircraft AN-24.
Table 18.2 presents the distribution of radionuclides in aerosols that were sampled above the destroyed
reactor of the fourth block of Chernobyl NPP in April-May 1986 from helicopter Mi-8 [7], and air-
craft An-30 [1], and An-24 [9].
As we can see from the Table 18.2 data, the composition of the ejection changed strongly not
only day by day, but also during the same day (see the results of measurements on May 8, 14-16).
Figure 18.3 presents the dynamics of changes in aerosol concentration of
95
Zr,
95
Nb,
103
Ru,
106
Ru,
131
I,
134
Cs,
137
Cs,
140
La,
140
Ba, and
141
Ce sampling from An-24 aircraft 200-300 m above the
destroyed reactor on May 8-19, 1986. This period can be described as the beginning of systematical
decreasing of ejection of radioactive substances from the destroyed reactor. At this time, the burn-
ing of graphite was stopped, and the temperature in breakdown began to gradually decrease. Still,
the concentrations measured on May 8 and 16 (some thousands of Bq/m
3
) were comparable with the
concentrations measured on May 4 and 5 (see Figure 18.2).
Usually, the radioactive composition of aerosols did not correspond to the composition of irradi-
ated fuel at the moment of reactor explosion. For example, on May 8 and 19, volatile radioactive
nuclides I, Ru, and Te were measured. On other days, the main contribution to the summary samples
of gamma-radiation was made by refractory radionuclides Zr, Nb, and Ce.
Such variations of the ratio of the activities of nuclides in every sample were similar for the
aerosols sampled above the territory of Belarus and Russia, which were close to Chernobyl NPP
from the north and northeast, and from the research ship in the Atlantic Ocean at the beginning
of May [9].
It is also possible to form an opinion about the composition of primary aerosols based on the
fallout, which were sampled in a 30 km zone around the atomic station. Almost 90% of the particles
were fragments of irradiated nuclear fuel. It consisted of two groups of fuel particles. The composi-
tion of one of them was identical to the composition of fuel elements at the moment of the accident.
These particles were formed under heat explosion of the reactor. 85% of the activity of the second
group consists of refractory
144
Ce. The quantity of radionuclides of
95
Zr and
95
Nb was larger than in
irradiation fuel at the moment of the accident, but Cs and Ru were substantially lower. Among the
particles, there were some radioactive microparticles that were displaced on a nonradioactive car-
rier [10]. Radioactive particles of condensation origin have, mainly, nuclides of Cs and Ru [11]. At a
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