Appendix CRF - Part 3 - Northamptonshire County Council

3.3 Covering soil material thickness
NOT PROTECTIVELY MARKED
Following on from the scenario outlined in Section 3.1, the contact dose rate from high
density (2 g/cm 3 ) contaminated soil and rubble containing 200 Bq/g 60 Co at a density of
2 g/cm 3 covered by uncontaminated soil of various thickness was determined to find a
relationship between the shielding material thickness and dose rate. The density of the
covering soil material was taken as 1 g/cm 3 , which presented the worst case in section
3.1. Figure 1 and Table 3 show the relationship between dose and soil material
thickness.
Dose Rate (uSv/hr)
20
18
16
14
12
10
8
6
4
2
0
25 35 45 55 65 75 85
Soil thickness (cm)
Figure 1: The relationship between soil thickness and contact dose rate for soil and
rubble contaminated by 60 Co isotopes resulting in a uniform activity of 200 Bq/g
Soil Thickness (cm) Dose Rate (Sv/hr)
30 18.35
35 13.78
40 10.39
45 7.84
50 5.93
55 4.49
60 3.40
65 2.58
70 1.96
75 1.48
Table 3: Tabulated data for Figure 1
These data show that to get a dose rate of 10 Sv/hr, the soil material must be at least
40cm thick, and to get a dose rate of 2.5 Sv/hr, the soil material must be at least
65cm thick [3].
WS010001/ENRMF/CONSAPPCRF 713
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