Inventories and chemical groups

Because models are often updated or replaced, it is difficult to compare risk assessments of different vintage. Models of varying technical sophistication have been used to predict radionuclide release and behavior. 

Note that the elements within a group do not necessarily conform to the usual chemical constituents of the group of the same name. The release behaviors of these elements have usually been found sufficiently similar to be included in the group. Sometimes alternative groupings of the elements are developed to better reflect the evolving understanding of chemistry under accident conditions. 

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