A4-3-3 Fragmentation and dispersion of material

It is assumed that the material is fragmented into blocks 0.2. 3 m in diameter and that a layer 1-3 mm thick of each block is pulverized into fragments ranging between 1 pm and 1-3 mm, with a uniform distribution between the two extremes (see Table A4-1). 

If an intermediate case is chosen (e.g. a volume equal to 2.5 m ), a weight of finely fractured material of 5 t is obtained, corresponding to a fraction of about 3 per cent of the total. This percentage agrees with the values estimated, for example, for the Chernobyl accident (Vargo, 2000). 

It is possible to make an assumption, also on the basis of accident data, that the coarser part of the powder produced (from 10 pm to 1 mm), with an overall weight approximately equal to the total one (99 per cent), is deposited over a radius of a few kilometres (2 km are assumed) from the release 

This evaluation is not conservative since the effect of wind is completely disregarded. This effect causes the angular distribution of the particulate to be non-uniform. 

An estimate of the concentration of the deposited radioactivity can be made with the following assumptions  

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