In a nuclear power plant, energy is produced by fission of radioactive elements. Radioactive fuels include unstable isotopes of elements like uranium and thorium. When a radioactive element undergoes a fission reaction the mass of the end-products is less than the mass of the atoms that react. The relation e = m*c^2 gives the energy e that is equivalent to mass m where c is the speed of light.
It is not possible to determine the mass of radioactive material consumed from the information provided. If an assumption can be made that the power plant has an efficiency of 100% and the energy released is equivalent to the decrease in mass of the fuel, the decrease in mass can be determined.
As the power plant produces 1600 MW, the energy produced in a day is 1600*10^6*24*3600 = 1.3824*10^14 J. Using the mass-energy equivalence equation `m = e/c^2` . `c ~~ 3*10^8` m/s
This gives m = 1.536*10^-3 g
A reduction in mass of 1.536*10^-3 g of the radioactive substance results is involved if 1600 MW of energy is produced for a day.