Currently, building a single tokamak reactor requires pretty much the entire world's annual production of beryllium. When running, said reactor would run through the entire world's supply of tritium in about two months.

That later point means that the reactor needs to not only produce power, but produce it's own fuel... a process that gradually makes the entire reactor radioactive due to neutrons striking and damaging the beryllium enclosure.

Should check out Helion's approach, which makes a lot more sense that others I've seen. Tokamaks are a dead end.