Environmental Engineering Reference
In-Depth Information
Radioactive aerosol concentration growth was caused by a sublimation of light volatile
137
Cs
from the iring zone. It was found experimentally that the growth of concentration at a distance
of some kilometers from the ire was more than 2 orders of magnitude. Assessments show that
if the density of pollution of the surface is 7 Ci/km
2
(2.6 × 10
5
Bq/m
2
) in the case of a ire close
to the earth's surface, the concentration of radioactive Cs can exceed the limit permissible
values [40].
A study that was provided in the framework of the experimental ire in 1993 suggested that
137
Cs
concentration increased 1000 times, particle size distribution was bimodal (75% AMAD > 10 μm,
25% AMAD = 0.4 μm), and the water-soluble form of Cs increased by 38% [41]. It should be noted
that the primary radioactive fallout of the accident contained 99% of Cs in nonsoluble chemical
form. This means that ires are responsible not just for concentration growth. We have a new sub-
micrometer compound of spectra size of particles much more dangerous from the point of view
of dosimetry of internal irradiation. The amount of water-soluble Cs becomes more substantial.
Ultraine components of aerosol make a substantial contribution in remote transfer. For example,
137
Cs concentration in Vilnius (Lithuania) during the ire of 1992 increased 100 times [41].
18.9 AEROSOLS OF THE “SHELTER”
The object “Shelter” is the aggregate of structures that sealed radioactive sources outside the active
zone of the reactor of the fourth block after the accident. It was completed by November 30, 1986.
As a result, a unique system was created, comprising already destroyed and rebuilt constructions,
which make it generally stable without any guarantee for the destruction of some of its elements.
“Shelter” is a temporary construction for the localization of nuclear fuel and radioactive materials.
“Shelter” was connected with engineer communications and was equipped with devices for
fuel diagnostics, neutron sorption solutions, dust suppression, contraire lines, etc., which present a
complex of the security of “Shelter” [43].
Years of operation of “Shelter” showed that the goal of the “Shelter” building was correct. Still,
the dificult conditions under which it was built did not allow the construction of a truly hermetic
structure. There are cracks, apertures, and technological openings for cables and pipe-lines in the
structure. Natural ventilation of “Shelter” takes place through the ventilation tube in the third and
fourth blocks.
For characterization of “Shelter” as a source of radioactive aerosols and assessment of its inlu-
ence on environment, the following information is required: (1) mechanism of formation of aerosols
inside “Shelter”; (2) physicochemical characteristics of aerosol particles in different parts of the
object; and (3) values and dynamics of ejection of aerosols in the free atmosphere.
18.9.1 t
yPes
oF
a
erosols
At the present time, radioactive aerosols of “Shelter” are formed from dust, present in its compart-
ments (the concentration of uranium in dust is assessed as 5-10 t [2]), and from fuel-containing
materials (FCMs). FCM is destroyed due to radioactive decay, strong ields of radiation, variations
of humidity and air temperature, and also building activity and drilling work.
During the observation period, two types of radioactive aerosols were found in the “Shelter.”
First, aerosols of disperse origin consist of particles of irradiated fuel and, usually, with only small
amounts of volatile isotopes of Cs, Ru, Te, I. Second, condensation aerosols were formed due to the
absorption of these and other radionuclides on the particle carriers.
The fuel particles also consist of two groups. To the irst group belong large particles (average
diameter near 30 μm), consisting of grains of UO
2
. To the second group belong smaller (diameter
some micrometers) particles, formed after graphite burning, fuel oxidation, and its partial melting.
These particles consist of small amounts of fragmental radionuclides, especially Cs.
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