Because of its very compact undermoderated core, more than 70% of the fast-fission neutrons immediately emerge into the moderator tank. However, about 25% of these neutrons are reflected as fast and about 18% diffuse as thermal neutrons back into the core. Another 34% are thermalized within this core. Larger negative deviations from this neutron balance will stop the chain reaction.

Another passive safety feature - which is a consequence of the small reactor nominal thermal power of 20MW - is that, in the event of a loss of the external heat sink, the integrated decay heat could be fully absorbed by the large heat capacity of about 700m³ pool water.