Passive safety features of some recent fusion designs

The presence and effectiveness of passive safety features in six recent U.S. fusion designs are reviewed, namely the Compact Ignition Tokamak (CIT), Tokamak Ignition/Burn Experimental Reactor (TIBER), Tokamak Power Systems Study (TPSS), two TITAN reverse Field Pinch (RFP) designs, and the Advanced Safe Pool Immersed Reactor (ASPIRE). The safety assurance level for these designs range from true inherent safety to requiring active safety systems. Much progress has been made, so that most designs appear to achieve some level of passive safety, intermediate between inherent safety and needing active systems. Key factors include material choice, cooling geometry and neutron wall loading. Advantages in one factor can compensate for disadvantages in another. For example, with selection of a pool geometry, the neutron wall loading may be safely increased. Consideration of investment protection is included with the safety assessments but is quite limited because of the difficulty of assessing what damage can be repaired