In my understanding of a "real" Fusion Reactor it can not fail in a catastrophic manner as the only thing that could possibly happen is a failure of the magnetic field by a component failure that would result in a more or less catastrophic heat damage to the internal structure. But ther is no chain reaction or something possible that possibly could get out of control.
More of a problem is the neutron radiation! It's quiet simple to "catch" the neutrons but that is one of two problems with actual real fusion reactors, the internal chamber wall is bombarded with neutrons doing severe damage to the internal structure ...
actually they are covered with lithium to create new tritium when bombarded with the neutrons for the reaction to keep up but as the lithium is depleted the chamber components have to be replaced.
And whoever said a fusion reactor would not have produced more energy than used is at fault! There were a almost 5minutes running attempt of a fuision that created waaaayyy more energy than used but there are yet no heat converters installed or used on the real fusion reactors to convert the heat into something usefull.
And by the way running an Tokamak-Fusion-Reactor for pretty much longer is not possible as you have to induct an current into the plasma through a central placed coil to keep the plasma in a torus shape, requireing a constant linear raising current transient trough the coil which is pretty impossible 
a quiet real fusion reactor should only work in a charge pump manner, inputting huge ammount of EU for very limited time, resulting in either a s***load of heat or the equivalent ammount of plasma stored in what way ever 
and maybe some damage when standing close by
PS: to make it more realtistic add platings that need to be replaced now and then (reactor platings from nuclear reactor) and additionally lithium platings. Using lithium platings will eliminate the need of trithium but yield less plasma ... reduced by at least the amount of energy equivalently used to make the trithium by hand ... and probably the platings can be used inside a nuclear reactor, when placed against a fuel rod it will take damage and somehow the resulting trithium has to be collected ... could be a nice combination .... one or more nuclear reactor producing the EU & trithium needed for a fusion run
