Well basically you need:
- a special type of uran (dunno the exact number now)
- lots of water
- a neutron source
- turbines
- a cooling circuit
Then you put all the water into a big tank with the uran.
The tank must have pipes that leads the water to the turbines and then to the cooling circuit and then back into the main tank.
Now shoot some neutrons at the uran, this will result in a chain reaction and the uran will start shooting around many neutrons with immense energy.
This energy will heat the water so it will evaporate and abet the turbines.
After cooling down it will return into the main tank.
That's just the basics, been a while since we had this at school so there might be mistakes in it.