nuclear power plants sited in the vicinity of a large source of water either a sea lake or river are generally cooled by running a large amount of water into the condenser and discharging it back to the original source a few degrees warmer with little or no evaporation this is known as oncethrough cooling the water withdrawal requirements for a nuclear power plant of gw employing this cooling method are about m s which corresponds to billion tonnes of water per year if the water availability is limited heat removal is generally accomplished via evaporation in cooling towers with a recirculating system water passes through the condenser is pumped to the top of the tower and is sprayed downwards to a collection basin while being cooled by an updrought of air in a wet recirculating system about of the water evaporates and must be replaced