content: Fuel is hydrogen, the most common element in the universe, and while it's dangerous (explosion in contact with air) the residual is... water.  On the other hand, as far as I remember the residual of the reactor as it is ... it's Helium. One of the most harmless elements in the universe, and also very useful in several industries. Now, if the reactor goes bonkers, it will be a very bad thing... however, leaving behind the initial explosion (shouldn't be even that big), the combustible will be consumed almost instantly and there are no dangerous residuals to worry about. In other words, a fusion reactor is going to be   3000  the safest, greenest (by far), and more efficient (also by far) source of energy. We are talking that if these reactors can be build at reasonable prices and time, we will be seeing one of the biggest revolutions of all time: extremely cheap, unlimited energy. Think about creating drinkable water from the oceans (energy prohibitive today), ridiculously efficient farms in terms of water and pesticides (hell subterranean farms would be viable), long space travel would be viable (if we resolve the gravity and radiation issues) and we could start to unfuck the planet by removing our needs for contaminant fuels, or with advanced methods to destroy our waste and even invert desertification.  I can't find the source, but with this sort of energy, the planet could host 10x the current population without any noticeable impact in life standards. (Other than super packet cities)