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Comparison
Fusion vs Fission Safety
Fission needs active safety systems to manage a chain reaction and decay heat; fusion fails safe by physics — no runaway, no meltdown, no evacuation zone.
- Fission
- Chain reaction + decay heat; active safety
- Fusion
- No chain reaction; fails safe
- Meltdown
- Fission risk / fusion: none
- Evacuation zone
- Fission requires / fusion: none
Both are "nuclear," but their safety physics is opposite. Fission sustains a chain reaction that must be actively controlled, and its fuel keeps generating decay heat after shutdown — the failure that requires emergency cooling and drives evacuation planning. Fusion has neither.
| Dimension | Fusion / Fission |
|---|---|
| Reaction control | Fails safe (stops on disturbance) / active control required |
| Decay heat | None / significant post-shutdown |
| Meltdown | Impossible / must be engineered against |
| Evacuation zone | None / required |
A fusion plasma holds only seconds of fuel and extinguishes on any loss of input. The real fusion hazards — magnet energy, tritium, activation — are engineering-controlled, not accident-scale, and a low-neutron design keeps activation small. See is fusion power safe?