Nuclear capacity definitions

The following definitions for capacity are used in the Global Nuclear Power Tracker.

Nameplate capacity: The maximum gross electrical power, measured in megawatts (MW), that could be continuously maintained throughout a prolonged period of operation under specific ambient reference conditions designated by the manufacturer. The word "nameplate" is used because this capacity is often indicated on a nameplate physically attached to the generator.

Reference net capacity: The maximum electrical power, measured in megawatts (MW), that could be continuously maintained throughout a prolonged period of operation under specific ambient reference conditions designated by the manufacturer, measured at the unit outlet terminals, i.e. after deducting the power taken by unit auxiliaries and the losses in transformers that are considered integral parts of the unit. The “reference” refers to this capacity figure being the net capacity for the reference period. In data sourced from the International Atomic Energy Agency’s Power Reactor Information System (PRIS), the reference period is the most recent year for which data is available, whether that is the current year in the case of operational plants or the last operational year in the case of mothballed or retired plants. For plants under construction, this figure should generally be identical to the Design net capacity.

Design net capacity: The manufacturer’s intended maximum electrical power, measured in megawatts (MW), that could be continuously maintained by the unit throughout a prolonged period of operation under specific ambient reference conditions, measured at the unit outlet terminals, i.e. after deducting the power taken by unit auxiliaries and the losses in transformers that are considered integral parts of the unit. This value need not have ever been routinely achieved during actual operation, and this value does not reflect possible power changes during the lifecycle of the unit’s operation.

Thermal capacity: The reference figure from the manufacturer for the thermal power of the plant, measured in units of megawatt thermal or thermal megawatt (MWt, MWth). The reactor thermal power measures the net heat transferred from the fuel in the nuclear reactor core to the coolant. Different coolant materials are used in different types of nuclear reactors, from ordinary water (AKA light water) to deuterium oxide (AKA heavy water) to a liquid metal such as molten sodium. Heat transferred from the nuclear fuel is ultimately used to drive a turbine connected to a generator, producing electricity.