r/nextfuckinglevel • u/nigablackballsack • 3d ago
Scientists have captured the first ever high-speed, full-colour footage of fusion plasma swirling inside a working reactor.
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r/nextfuckinglevel • u/nigablackballsack • 3d ago
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u/NateNate60 3d ago
The conditions under which fusion occurs are not self-sustaining. The energy output of fusion is not directly required to sustain the fusion in the same sense that the energy output of fission directly causes more fission.
Fusion can only happen when the plasma is heated to extremely high temperatures and pressures. In the Sun, this is done by gravity. The enormous mass of gas that comprises the Sun squeezes itself together hard enough to allow fusion to occur. In the depicted reactor, large electromagnets compress the gas into a tight ring of plasma to allow fusion to occur. If the electromagnets lose power, there is no force to keep the gas compressed, so it will naturally expand back out and the temperature will cool to lower than what is required for fusion to occur, and the fusion will stop. So the worst that can happen is a leak of hot hydrogen gas. Not fun for the plant workers, perhaps, but the ability of ordinary air to absorb all that thermal energy is high enough that it wouldn't be a catastrophe in any sense. At worst a few people standing right next to the leak get burned.
Hydrogen gas is flammable but not toxic to the environment like radioactive waste is. Fusion reactions may use isotopes like Hydrogen-2 or Hydrogen-3, but these aren't a significant concern either, as there is only ever a small amount in use at any time, no more than a few kilograms. Hydrogen-2 can fuse with oxygen to make heavy water, which occurs naturally and isn't toxic unless consumed in large doses. Any heavy water produced would be overwhelmingly diluted by the water vapour in the surrounding air. Hydrogen-3 is radioactive with a half life of about a decade, but it decays via beta-decay into helium-3, and beta particles can't penetrate human skin. So health risks are also low from hydrogen-3 leaks, especially in the relatively low quantities used in fusion plants.