Many fusion advocates suggest that fusion reactors are safer than fission reactors. For instance, the ITER website states in the Advantages of fusion :

No risk of meltdown: A Fukushima-type nuclear accident is not possible in a tokamak fusion device.

With this and other statements, there is the claim fusion is intrinsically safe and the implication implicit or explicit that fission is intrinsically unsafe.

Below is an evaluation of the true risks for accidents at fusion reactors.

Safety Concerns

Loss of plasma due to disruption

Plasma confinement is not stable and abrupt losses of plasma called "disruptions" take place for a number of reasons. The fast release of the thermal and magnetic energy of the plasma in these disruptions, can put huge mechanical strains on the vacuum vessel. Power fusion reactors will incorporate mitigation systems to dissipate the energy in the plasma without causing damage.

Some critics of fusion think disruptions will be frequent events and significant risks to the mechanical integrity of the reactor

Quenches of superconducting magnets

Safety Analysis 

Some safety analyses of fusion reactors are published in open literature, e. g. Nuclear safety issues for fusion power plants . This particular paper studies many issues and points out areas where more work is needed to properly evaluate risks the concerns.

The paper includes the following conclusions:

  • Disruptions that could lead to a release of magnetic energy need to be better understood, in order to gain a better understanding of the potential risk they pose. 
  • Breeder blankets and their tritium inventories pose a challenge to the design and safety analysis of fusion power stations. 
  • Whilst the hazard potential of a fusion power station is significantly less than that of a fission power station, there is the potential for the release of radioactive materials in accident conditions. 

Nuclear Fission Safety