Environmental Engineering Reference
In-Depth Information
9
8
7
6
5
Cs-134
Cs-137
Ce-144
4
3
2
1
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
Date of sampling
FIGURE 18.7
AMAD (in μm) of aerosols
134
Cs,
137
Cs, and
144
Ce in 5 km zone around the Chernobyl NPP
in 1986-2002.
More extensive data on the disperse composition of aerosol carriers of radionuclides until April
2002 were obtained by analysis of
137
Cs.
144
Ce disperse composition was measured only until the
end of 1992, when this radionuclide decayed practically completely.
Figure 18.7 shows the value of AMAD of
137
Cs and
144
Ce for all periods of monitoring, where
AMAD is in the range of 3-8 μm. These data are comparable with the data presented in Ref. [38].
It should be noted that in the majority of cases, the sizes of particle carriers of
90
Sr and plutonium
isotopes are the same as for
137
Cs.
From the presented data, it is clear that average AMAD increased from the summer-autumn of
1986 until 1991-1992, after which it became constant until now. It is dificult to ind a reason for
this. The sizes cannot be different from the sizes of nonactive aerosol, which were developed from
resuspension from surfaces of soil, vegetable, roads, buildings, etc., because of natural causes. Such
was the situation in 1992. However, the continuation of activity near the Chernobyl NPP (trans-
portation of soil, transport movement, etc.) led to changes in aerosol concentration and disperse
composition, which was observed frequently [39].
18.8 FOREST FIRES IN THE EXCLUSIVE ZONE
Forest ires taking place on territories polluted with radionuclides are an additional factor of
radiation danger, because under these circumstances aerosol particles that consist of radioactive
substances are formed. Their concentration can substantially exceed what was typical for this site
before the ire. Physicochemical characteristics of aerosols of ire genesis can be different from
“background” aerosols in the atmosphere. Smoke trains are dangerous for people who take care of
the ire, as for people located at great distances from the ire. Transportation of radioactive smoke
leads to a redistribution of radionuclides between “dirty” and “clean” territories.
Nearly 600 different ires were observed from 1993 to 2002 in the 30 km zone of the Chernobyl
NPP. For the irst time, attention was paid to the radiation effects of ires after the hot and dry sum-
mer of 1992 [40]. Then radioactive substances, moving with the smoke trains from Chernobyl, were
observed as far as 500 km in Lithuania [41] and Sweden [42]. Monitoring of the radiation situation
at 30 points in the 30 km zone of Chernobyl showed that even at a distance of 5-10 km from for-
est ires on relatively “clean” territories, the concentration of radioactive aerosols increased up to
10-100 times.
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