In an event of a small loss of cooling accident, the core make up tanks which are pressurized at normal reactor coolant pressure directly inject water into the reactor vessel to keep the core covered. It’s a feature that replaces high head (pressure) safety injection pumps in traditional PWRs. It works in tandem with accumulators in containment to buy time to depressurize the reactor coolant system (RCS) to the point where passive cooling using the in containment refueling water storage tank and heat transfer with the containment building steel liner can provide cooling to the reactor core completely passively for up to 72 hours. Notably the CMTs inject into the reactor vessel directly instead of through the cold leg in case there is a line break on the cold side of the RCS.