Assessment of dose to man from releases of 99Tc in fresh water systems.

Abstract

The objective of this paper is to evaluate the dose to man from releases of 99Tc in a fresh water system and to identify the biospheric transfer parameters to which the total dose is the most sensitive. Only internal exposure is taken into account, as the external irradiation leads to a negligible dose contribution. Two release modes were considered: continuous (routine) releases and accidental releases. The concentrations in the biospheric compartments subsequent to routine releases were calculated according to International Atomic Energy Agency procedures. For the accidental releases, a more dynamic approach was adopted, especially for the milk and meat compartments. A routine-release scenario typical for the Mol site has been applied, and the biospheric compartment leading to the highest dose contribution was shown to be the irrigated grain. The biospheric transfer parameters to which the first-year doses were the most sensitive consisted mainly of the mass interception factor for grain and the milk transfer factor. The doses in following years were very dependent on the value of the root zone removal rate. The accidental-release scenario resulted in committed dose equivalent that are strongly influenced by the time of year at which the release occurs.