each second, a nuclear power plant generates 2100 mj of heat energy from nuclear reactions in the reactor's core. this energy is used to boil water and produce high-pressure steam at 390 ∘c. the steam spins a turbine, which produces 700 mw of electric power, then the steam is condensed and the water is cooled to 40 ∘c before starting the cycle again. what is the plant's actual efficiency?