The importance of plume rise in risk calculations

Various plume rise models are discussed in relation to predictions of the height of rise and radius of a continuous plume as a function of travel time or distance downwind. It is concluded that, if there is no rain, plume rise can give a substantial reduction in the radiation doses likely to be received by people living in some areas downwind of the source. If there is rain, levels of deposited activity are independent of the plume rise so that areas of unacceptably contaminated land are not reduced by taking plume rise into account. If rapid evacuation is possible, however, the accumulated external radiation doses can be much reduced and, some benefits will be seen from plume rise. (U.K.)