What is capacity (40 MW, 100 MW) of a reactor?
Watt (abbreviation W) is the unit of power, the rate at which energy is produced (or consumed). The letter M stands for mega, which means a million. MW therefore means mega-watts, i.e. a million watts. The capacity of a reactor is generally specified in megawatts of electrical power as MWe, if it produces electricity. The reactors at Narora and other reactors like them have a capacity of 220 MWe. If a reactor does not produce electricity (and sometimes, in some contexts, even if does) the capacity of a reactor may be stated in heat (or thermal) power it produces as MWt. The Cirus reactor has a capacity of 40 MWt and Dhurva (another research reactor at BARC) 100 MWt.
