Answer with Explanation:
The relation between power and energy is

Since the nuclear reactor operates at 1200 MW throughout the year thus the energy produced in 1 year equals

Now from the energy mass equivalence we have

where
'c' is the speed of light in free space
Thus equating both the above values we get

Since it is given that 1 kg of mass is 34% effective thus the mass reuired for the reactor is

Thus 1.235 kg of nuclear fuel is reuired for operation.