Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in the 1940s, and while there was progress, it wasn't until 2107 that the first commercially available fusion reactor came online.
Modern fusion designs are almost always constriction, though most modern reactors are a cross between magnetic and gravitic constriction. Due to the high energy cost of gravitic constriction, it's much easier to build magnetic constriction reactors and then use gravitic constriction to improve efficency, as opposed to building an entirely gravtically constricted reactor.
There are a lot of misconceptions about how modern fusion works.
While it is possible to lose containment and make the plasma shoot out at impressive velocity, destroying the reactor and anything nearby, fusion reactors don't "explode" in the traditional sense. They can't "go critical"; the meaning with a fusion reactor would be that it was about to lose containment.
It's possible for the plasma of a fusion reactor to irradiate things, but that's the same problem as plasma weapons. Additionally, most of the radiation is alpha and beta radiation, which is fairly safe.
In applications where the ability to start and stop reactors frequently (like on a space craft) is required, small fission based reactors are used to provide enough power for the initial start-up of the fusion reactors. These fission based reactors can also provide emergency backup power, however, they are not designed for continuous operation over months or weeks, more like hours or days.
While considered to be "safe", radioactive byproducts are still a concern, especially in combat scenarios where they may be damaged or destroyed. While mitigations are in place and the reactors used are purpose built, they can still be a hazard to their own crews. While rare, radiation poisoning still occurs.