I dont know if this has been suggested yet but... Heavy water is x10 times more dense then water, so if you use that to surround your nuclear reactor with it, it could resit heat more, and have a shorter cool time.
Recpie
Heavy water:
Gives 2 pieces of heavy water
I would bet quite a lot that heavy water is not THAT much heavier. 1-2 extra neutrons isn't much to the weight of the H2O molecule...
Edit: Wikipedia says 11% heavier ... Did you confuse it with Deuterium? (Heavy hydrogen)
Edit2: But W/E, given how cheap water cells are there would be no reason NOT to upgrade them, which is bad 
1. No, imbalanced.
2. No, Heavy Water isn't exactly a better coolant then water itself.
