Radioactive Aerosols of Chernobyl Accident - Aerosols: Measurement, Dosimetry, and Health Effects - page 488

18.9.2 a erosol c oncentration inside tHe “s Helter ”
In the irst years of the work of the “Shelter,” the main cause of aerosol forming was drilling work
inside the structure. Small radioactive particles were present in large amounts in boring liquids, on
the loor, which led to high aerosol concentration.
During the existence of “Shelter,” a large number of aerosol samples were taken in room 207—
the corridor was divided into three sections. After the completion of drilling activity, some of the
boreholes remained open and became channels of intake for air and water from sites with high
concentrations of radionuclides products of the accident. According to the measurements provided
in 2000, the dose rate of gamma-radiation in 207 changed in the range of 0.1-10 mSv/h.
The results of systematic aerosol sampling in room 207/5, taken every 1 h in 1988-1991, were
very signiicant. Figure 18.8 shows variations of summary aerosol alpha-activity. After the bore
equipment was cut out, their concentrations were usually at a level of 0.03 Bq/m 3 , and when the
boring work started it increased by 1-2 or even 3-4 orders of magnitude.
A large amount of dust formed during boring activity, and its deposition on all surfaces was
very substantial even for other types of activity. For example, when the metal platform was cut, the
concentration of alpha-active aerosol increased by 2 orders of magnitude, up to 7 Bq/m 3 . The con-
centration decreased to normal level only 8-10 h after completion of the work.
The secondary long monitoring of radioactive aerosols in room 207/5 took place from November
28 to December 26, 2000, after Chernobyl NPP was closed. During those days, 20 samples were
taken with 2-3 h exposure [44]. As can be seen from Figure 18.9, 137 Cs concentration varies from
0.2 to 20 Bq/m 3 . There was a positive correlation between 137 Cs concentration and long-lived beta-
emitters. During monitoring, some splashes of radioactive aerosol concentration were measured,
but all of them were lower than during the drilling activity.
As can be seen from Figure 18.9, the highest concentration of radioactive aerosols was measured
on December 9. Besides 137 Cs, also 134 Cs, 154 Eu, 155 Eu, 90 Sr, 241 Am, and 60 Co were found in aerosol
samples. Taking radioactive decay into account, the ratio of activities of 134 Cs/ 137 Cs was 0.48, which
is close to the number at the time of the accident [45].

100

11.1988
01.1989
10.1991

10

1

0.1

0.01

1 5 9 13 17 21 25 29

Date

FIGURE 18.8 Concentration of alpha-active aerosols during drilling works in room 207/5 of the “Shelter”

(1988-1991).