Radioecology of cobalt-60 under tropical environmental conditions

Cobalt-60 and cesium-137 released into the near shore environment of a BWR (400 Mwe) nuclear power station at Tarapur, have been found to be readily sorbed by the sedimentary particles. Surveillance over the last two decades showed that beyond 2 km distance north and south from the discharge point concentrations were within background range despite the continued release of controlled low levels of radioactive wastes. Within 1 km of the effluent point of both the nuclides dropped exponentially with time, yielding effective half-lives of 1.5 and 2.0 y against their respective physical half-lives of 5.2 and 30 y. Under laboratory-simulated conditions the sorption-desorption of cesium could be explained in terms of ambient salinity and other environmental parameters. It was, however, not possible to demonstrate similar behaviour for cobalt-60 in laboratory studies. The possible mechanism governing sorption-desorption of both radionuclides under field and laboratory conditions are discussed. (Author)