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Wide-area decontamination

The experience gained in the remediation projects has provided valuable input in terms of developing fast and efficient approaches to assessing the relative distribution of radioactivity (or dose rate) in any remediation area. Integration of electronic maps, geographical information (land use, etc.) and measured radiometric data has worked well. Figures 7 and 8 show examples of thedose-rate reductions achieved by use of wide-area decontamination. Dose-rate reduction based on average dose rates in each land use compartment is between 40% and 80% for Figure 7 and between 30% and 80% for Figure 8.

In terms of estimated annual dose reduction to less than the initial evacuation level of 20 mSv, this has been demonstrated for areas with annual doses of 20 - 30 mSv before decontamination. However, this goal could not be assured for areas exceeding 40 mSv before decontamination. In the case of highly contaminated agricultural and residential areas, the annual dose was decreased by 70 %, but could not be reduced to below 50 mSv. In general, the fractional reduction was smaller in areas of relatively initial low contamination, compared with more highly contaminated areas.

 

Impact of decontamination on measured dose rates

Figure 7. Impact of decontamination on measured dose rates

 

An example showing

Figure 8. An example showing the impact of decontamination on measured dose rates (17ha site). The data for outside the decontamination target area may reflect reduction in the long-range gamma flux contribution from within the cleanup area.