0.100kg of a nuclear is converted to energy per day. what is the power produced by this fuel?

This problem is just what everybody likes to see: 
A direct application of  E=mc²  !

If 0.100m kg of matter is converted to energy,
the quantity of energy is

                               E  =  m   c²

                                    = (0.1 kg) · (3 x 10⁸ m/s)²

                                    = (0.1 kg) · (9 x 10¹⁶ m²/s²)

                                    =  (9 x 10¹⁵)   (kg-m/s²)(m)

                                    =  (9 x 10¹⁵)   (Newton)(m)

                                    =  (9 x 10¹⁵)   Joules .

Thatsa lotta energy, Bub !

1 day = 86,400 seconds

                  Power  =  (energy)  /  (time)

                               = (9 x 10¹⁵ joules)  /  (86,400 seconds)

                               =        1.041 x 10¹¹  joules/sec

                               = almost exactly  1 gigawatt  .