The importance of deposition for individual and collective doses in connection with routine releases from nuclear power plants

Deposition velocities, vsub(D), and wash-out coefficients 1sub(g), to be used in different velocity- and Pasquill classes in Denmark are estimated. The estimated vsub(D)'s describe the maximum dry deposition possible, as the surface is assumed a perfect absorber in the considerations. The 1sub(g)-values are found corresponding to the average rain intensity, when it rains, within each Pasquill class and apply for materials which dissolve rapidly in water. The estimated parameter values were used as central values in a parameter study as follows: For four different deposition cases and two release heights the committed effective dose equivalent (individual and collective) from a postulated annual routine release to the atmosphere has been calculated. An increase of the deposition parameters by more than one order of magnitude was found to have negegible influence on the total committed effective dose equivalent. However, the choice of deposition parameters was found to be of major importance for the assessment of the surface contamination and thus the radiological consequences of airborne routine releases. (author)