The efficiency of a nuclear power plant with a capacity of 800 MW is 20%. Determine the mass of nuclear fuel (Uranium-235) consumed by the power plant. Keep in mind that 200 MeV of energy is released each time the nucleus of Uranus splits.

To solve this problem, we need to follow these steps:

1. First, we need to convert the power plant's capacity from MW to Joules per second. 1 MW = 10^6 W, so 800 MW = 800 * 10^6 W = 8 * 10^8 W = 8 * 10^8 Joules/second.

2. Next, we need to calculate the total energy produced by the power plant in one second. Since the efficiency of the power plant is 20%, the total energy produced is 8 * 10^8 Joules/second / 0.20 = 4 * 10^9 Joules/second.

3. Now, we need to convert the energy released per fission of Uranium-235 from MeV to Joules. 1 MeV = 1.60218 * 10^-13 Joules, so 200 MeV = 200 * 1.60218 * 10^-13 Joules = 3.20436 * 10^-11 Joules.

4. We can now calculate the number of fissions per second. This is the total energy produced divided by the energy per fission, which is 4 * 10^9 Joules/second / 3.20436 * 10^-11 Joules/fission = 1.248 * 10^20 fissions/second.

5. The mass of one atom of Uranium-235 is given by its atomic mass (235 g/mol) divided by Avogadro's number (6.022 * 10^23 atoms/mol), which is 235 g/mol / 6.022 * 10^23 atoms/mol = 3.90 * 10^-25 g/atom.

6. Finally, we can calculate the mass of Uranium-235 consumed per second. This is the number of fissions per second times the mass per atom, which is 1.248 * 10^20 fissions/second * 3.90 * 10^-25 g/atom = 4.87 g/second.

So, the nuclear power plant consumes approximately 4.87 grams of Uranium-235 per second.