Impact Assessment on the Aquatic Ecosystem in the Vicinity of an Operating Nuclear Power Plant at the Kalpakkam Coastal Site

An inherent problem in electricity generation is that much of the heat produced cannot be converted into electricity and is dissipated in nearby heat sinks, such as lakes, rivers and oceans. In India, such heat rejection to water bodies is governed by legislation from ministry of environment and forests and central and state pollution control boards. New standards for thermal discharge issued by MoE&F in 1998 seem to be very stringent. But in the absence of relevant data for Indian sites appear to be somewhat justified. In order to make a realistic assessment of the impact of thermal discharge on aquatic ecosystems, the Department of Atomic Energy initiated the first major thermal ecological study in the country at two of its operating nuclear power plants, one at a coastal site in Kalpakkam and the other on the banks of river Kali at Kaiga. The 5 years duration co-ordinated research project involved researchers from eight different universities and national laboratories and experts from NIO, NIOT, CECRI, BARC, NPCIL and MoE&F. In view of the fact that the most of the forthcoming nuclear power plants in the country are coastally located, this article discusses the findings of Thermal Ecological Study at Kalpakkam. A major achievement of the study was to map the precise boundaries of the small mixing zone, the region of confluence of the heated water with the recipient water body, wherein the thermal plume effected a ∆T of only 3–5 °C due to rapid inundation and mixing with turbulent sea water. This caused a limited impact on the growth and distribution of the relatively sedentary benthic flora and fauna, though none of the motile forms, including fishes, were affected. Beyond the mixing zone, the life appeared to be as near normal as possible. No change in any physico-chemical parameter was noticed, except for a small expected decrease in dissolved oxygen at the discharge point. At Kalpakkam, position of the mixing zone shifts periodically due to formation of a natural sand bar by sea currents. This allows restoration of parameters, especially temperature to more conducive values and results in recolonization of the previously impacted sites. An ecologically encouraging finding of the study was that the impact was restricted in space and reversible in time. The data generated are expected to aid regulatory agencies in formulation of more appropriate stipulations for thermal discharge and also guide power industry to design eco-friendly technologies in future.