A breeder reactor on the Caspian
On the desert coast of the Caspian Sea stands the decommissioned BN-350 reactor, the world's first commercial-scale fast breeder reactor. Construction began in 1964, with the plant connecting to the grid and beginning commercial operation on July 16, 1973. Located in the city of Aktau (formerly Shevchenko), the reactor had a dual purpose that was important for the city's existence. It generated electricity—up to 135 MWe—and also powered the world's only industrial-scale nuclear desalination facility.
This system provided water, producing up to 120,000 cubic meters of fresh water daily for the city. The reactor itself was a liquid-metal fast breeder reactor, using liquid sodium as a coolant in its primary and secondary loops. This advanced design allowed it to "breed" more fissile material than it consumed and also produced plutonium. The reactor operated for over 25 years, exceeding its planned 20-year lifespan before the government of Kazakhstan decided to shut it down on April 22, 1999.
An accidental warm-water ecosystem
The plant's cooling system created an unintended and unique ecological side effect. To cool its tertiary water-steam loop, the facility drew in cold water from the Caspian Sea and discharged it at a higher temperature. This outflow of warm water created a stable, artificially heated microclimate in the immediate coastal area, preventing the water from freezing or dropping to the typical low winter temperatures of the temperate Caspian Sea.
This thermal plume allowed a non-native tropical fish species, the Mozambique tilapia (Oreochromis mossambicus), to establish a self-sustaining population. Native to southeastern Africa, this tilapia is a robust, adaptable cichlid, but it cannot survive cold temperatures. The consistently warm effluent from the BN-350 reactor provided a year-round refuge, allowing this tropical species to thrive thousands of kilometers from its native habitat. Tropical species colonizing the warm water discharge zones of power plants have been observed globally. When the Aktau reactor was decommissioned in 1999, this artificial heat source was switched off. The thermal refuge vanished, and the local water temperatures returned to their natural state, leading to the collapse of the isolated tilapia population which could not survive the Caspian winter.