The efficiencies of nuclear power plants are less then those of fossil fuel plants are les then those of fossil fuel plants. Why?

The efficiency of an engine measures the amount of energy that we can extract from that engine. In the nuclear power plant, there is a large loss of energy when the energy extract from the nuclear reaction. But in the case fossil fuel plant the energy loss is very less as compared to nuclear power plant, since it is a natural process. As the extract energy is more in the case of fossil fuel plant than the nuclear power plant, therefore the efficiency of nuclear power plants are less than those of fossil-fuel plants