A type of failure of a nuclear reactor in which insufficient heat removal from the reactor core occurs, e.g., due to leakage of cooling water from the primary circuit. The loss of coolant accident could be a potentially harmful event because insufficient heat dissipation can damage, or even melt, the core. Therefore, each reactor is equipped with an emergency core cooling system, or ECCS. Its purpose is to replenish lost coolant, ensure its circulation and sufficient cooling of the core. Other systems ensure that, in the event of a loss of coolant accident, the fission reaction stops as quickly as possible by inserting emergency rods to reduce the amount of heat that needs to be removed from the reactor.