you should make the walls of the fuel rods bigger, fuel can leak through if it's only 1 pixel thick
you could use polonium too, but you'd need to have a pile of it at a negative tmp, so you can clone from the pile as a way to refuel. you'd also need a special command for the polonium to make more than a tiny amount of heat, as it melts at around 300C without any commands
ath's so cool man +100000 but it miss a button for all rod up or all rod down
you can use the mix tool for better terrain
How to Use first, press the reaction on button Second, raise all the control rods all the way up. Third, if it's over 200 degrees, lower the control rod. Fourth, if the temperature is low, adjust the number of control rods appropriately. You have to control the control rod precisely.