Cooling towers - Indirect cooling towers

From the 1970s onwards, the construction of several high-powered power plants in France represented a major technological advance that is still recognized today.

Nuclear power plants, as well as conventional thermal power plants, involve considerable heat exchange in relation to their power output - up to 1,300 MW for a nuclear reactor. Assuming an average efficiency of 33%, the heat rejected by a reactor is therefore a maximum of 2,600 MW.

To remove this amount of heat, a first solution was to use river water cooling. For a nuclear power plant with 4 900 MW reactors, the total water flow required for cooling to 6 K (ΔT permissible for this type of application) is around 35 m³/s per reactor, i.e. 140 m³/s in total.

Unfortunately, it is almost always impossible to envisage this type of cooling without the risk of overheating river water. For example, with a total installed electrical capacity of 11,600 MW along the Loire, the total flow of cooling water to be drawn from the river would be 450 m³/s, which is higher than its normal average flow.

Other cooling solutions were therefore considered, such as the use of seawater or air, the two most important cold sinks in the surrounding environment. Because of the constraints involved in locating and using seawater, atmospheric coolants are currently the most widely used for high-power cooling. To ensure safe operation, those used to cool nuclear power plants are of the indirect type, with confinement to the secondary cooling circuit. Between lost-water cooling and wet atmospheric coolant, the most widespread system, water savings are estimated at 90% of total circulating water. In fact, the additional river water required to compensate for the quantity of water evaporated is of the order of 2 to 4 m³/s for a 900 MW reactor.

In this dossier, we will describe high-power indirect atmospheric coolers, also commonly referred to as indirect cooling towers:

• operating principle ;

• the state of the art ;

• design and construction principles ;

• advice on commissioning and operation.

For other types of atmospheric refrigerants, please refer to [BE 8 940] "Atmospheric refrigerants, direct dry air coolers" and