Environmental Engineering Reference
In-Depth Information
In July-September of 1986, in some of the rooms of the third block, the aerosol concentration
(400-1000 Bq/m
3
) was not lower than at the same period near the destroyed reactor.
Before building the roof of the “Shelter,” it was necessary to ensure the necessity of reconstruc-
tion and connecting up the iltration station, which was common for the third and fourth blocks. For
this purpose, in August and September of 1986, 11 air samples were taken from a height of 10-30 m
above the reactor [22].
Analysis of samples shows that aerosol concentrations (
C
) consisted of gamma-radiation
nuclides and were stable and their values usually did not exceed limit permissible numbers. Short-
lived radionuclides were not found in the samples, which proved that no chain reaction was in
the fragments of the fuel; the values of
C
for alpha-active aerosols were in good correlation with
C
for gamma-radiation (
C
of the last was 5,006,200 times higher). By measuring
242
Cm activity on
aerosol particles, assessments were provided for
C
of
239
Pu. It was shown that the aerosol concentra-
tion of
239
Pu was in the range of 0.1-0.9 Bq/m
3
and was usually higher than the limit permissible
value. Despite the fact that at the end of August
131
I had to be decayed, in one of the samples it
was found completely in the gaseous form (0.6 Bq/m
3
). Small amounts of Ru (2%-5%) were also
in the gaseous form; AMAD values of aerosol consisting of isotopes of Ce, Cs, Zr, and Nb were
the same (1.06 ± 0.08 μm) (September 10, 1986). There were slightly smaller sizes of particles for
Ru (0.84 ± 0.08 μm), but according to one measurement it was dificult to judge the difference. The
absence of diversity of isotopes by particle sizes showed that the temperature in the higher layer of
the destroyed reactor was close to the temperature of outdoor air. The next day, particle sizes were
higher (AMAD = 1.7 ± 0.1 μm) and sizes of Ru were the same as for other isotopes.
During the same period, samples were taken 1 m above the earth's surface around 300 m from
the destroyed reactor. The aerosol concentrations were on average an order of magnitude lower than
near the reactor. Assessment showed that the contribution of aerosols from the reactor to aerosol
concentration near the earth's surface was not more than a few percent.
Important information about the physicochemical forms of radioactive aerosols, sampled near
the surface not far from the destroyed reactor, was obtained by analysis of radionuclide composi-
tion. Radionuclides that made the larger contribution in the summary gamma-radiation of samples
can be divided into two groups.
In the irst group are refractory nuclides Zr, Nb, La, and Ce, which despite the high temperature
during the accident remained in the destroyed fourth block. The second group—
103
Ru,
106
Ru,
134
Cs,
137
Cs—includes volatile compounds, which condensed on aerosol particles in the air.
From the data in Figure 18.5, we can see that the contribution of Ru and Cs in samples of 20-22,
25-26, and 30-31 of August, 1986 did not exceed 20%; therefore, on these days, the contribution of
fuel aerosol was highest.
The sample of September 2 was different. Here, the contribution of Ru and Cs was near 65%. It
has been mentioned very often in the literature [23-25] that the radiation of some highly radioactive
particles sampled even at a great distance from Chernobyl consisted of a large portion of Ru. On
other days there was a mixture of fuel and condensation particles in the atmosphere.
Only in October-November 1986, when a substantial portion near the destroyed reactor was
cleaned up from radioactive fallout, sealed by gravel, sand, and concrete, aerosol concentra-
tions decreased by an order of magnitude and reached relative levels, which were observed in
July-September of 1986.
18.6 GASEOUS COMPONENTS I, TE, AND RU IN THE ATMOSPHERE
The products of the Chernobyl accident in the atmosphere were not only included in aerosols but
also in the form of gases. During the sampling in May 1986, both aerosol and gas compounds such
as I, Te, and Ru were measured. For the detection of gases, multilayer ilter material SFM-I, con-
sisting of an aerosol layer, upper facing ilter material, and two sorption layers, was used. The ratio
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