Question

Why do nuclear power plants use fission instead of fusion?

Scientists have not yet gotten a fusion reaction to happen on Earth.
Per gram of fuel, fission releases more energy than fusion.
The energy from fusion cannot yet be converted to electricity.
Fusion requires conditions that use too much energy to maintain.

Answer 1

Short answer: Because fission is a mature, controllable, and economically practical way to make steady heat for electricity today. Fusion is physically possible and releases more energy per kilogram of fuel, but building a sustained, net‑energy, practical power plant faces hard physics and engineering challenges that haven’t yet been solved for commercial electricity generation.

Now to the four statements you listed:

1) "Scientists have not yet gotten a fusion reaction to happen on Earth." — False (misleading).
- Fusion reactions have been produced on Earth many times: in hydrogen bombs and in laboratory experiments (tokamaks, stellarators, inertial‑confinement facilities, etc.). What has not yet been achieved at power‑plant scale is sustained, practical net energy gain (a commercial reactor that produces more usable electricity than it consumes over its operating cycle).

2) "Per gram of fuel, fission releases more energy than fusion." — False.
- Fusion (e.g., deuterium–tritium) releases substantially more energy per kilogram of fuel than uranium fission. Rough numbers: D–T fusion ≈ 3.4×10^14 J/kg, while U‑235 fission is ≈ 8×10^13 J/kg. Fusion wins on energy per mass.

3) "The energy from fusion cannot yet be converted to electricity." — False (misleading).
- Heat from fusion can in principle be converted to electricity by conventional thermal cycles (steam turbines) or by direct conversion concepts. The real problem is we haven’t yet built a fusion device that produces a sustained, convenient source of surplus heat that can drive turbines continuously and economically. Conversion itself is not the fundamental obstacle.

4) "Fusion requires conditions that use too much energy to maintain." — Largely true (and the key practical issue).
- Achieving and holding the extreme temperatures and pressures needed for controlled fusion (and confining the hot plasma) currently requires huge input energy and very difficult engineering. Most experiments still produce less usable energy than they consume (i.e., Q < 1 for the whole system). Materials, neutron damage, tritium breeding and handling, and cost also add major hurdles.

Bottom line: fusion is scientifically real and very attractive on paper (abundant fuel, high energy density, low long‑lived radioactive waste), but controlled, economically viable fusion power plants are not yet achievable with present technology. That’s why today's nuclear plants use fission. Research continues and there has been steady progress, but commercial fusion power remains a future prospect.