Fusion can only happen in a controlled environment, not like Chernobyl where it got out of their control. It is not like fission where you have control rods that could blow off in an explosion.
In lab experiments you limit the fuel to burn so you will never get a "Sun" like in Spiderman II. The lasers acts as an ultimate piston and compress and heat the fuel to 100,000,000 degrees for 25 billioneths of a second, consuming all the fuel and ready for more. It is not the heat that is as important as the high energy neutrons that are released to cause fission in u238 in a readctor based on spent fuel.
Eventually maybe there will shrink the whole process, much like the laser in a CD was once huge not fits in your hand. Then it is a process of firing the lasers, burning the Dueterium/Tritium and then pausing to re-load and fire again to the level of energy that is intended to be produce, much like "Mr. Fusion" in "Back to the Future" series. The key is producing more energy then the lasers used to set off the burn, and capturing the energy from the burn. We will get there, some say in a lecture I attended in 20-50 years, not the too distant future.
A safety feature is if you do not reload, the cycle stops right there. No chance of runaway. This is ony one of the many ideas coming from research. It is just so few have paid attention to it because when you think of fusion, you think of the Takomak that can't keep the magnetic field perfect.
We are doing shots every couple of days and even with a D-D reaction, they are getting out neutrons from the success fusion process. It is like air flight. All the scientists back in 1900 said motor powered flight was impossible because at higher air speeds the wing control become unstable. The Wright Brothers didn't care and came up with powered flight. One others saw it could be done. planes started flying everywhere.
One successful fusion is controlled and achieved, and research increases at an exponential rate, you will see them being built around the world.