Passive containment cooling system for a nuclear reactor

A method for operating a passive containment cooling system for a nuclear reactor, the method comprising:

• directing a flow of a coolant fluid downwards out of a lower region of a coolant reservoir via a coolant supply conduit according to gravity to a bottom of a coolant channel that extends vertically along a containment structure that at least partially defines a containment environment in which the nuclear reactor is located;
• causing the coolant fluid to rise through the coolant channel from the bottom of the coolant channel toward an upper region of the coolant reservoir via a top of the coolant channel according to a change in buoyancy of the coolant fluid based on the coolant fluid absorbing heat rejected from the nuclear reactor in the containment environment via at least the containment structure;
• and
• selectively enabling a one-way flow of a containment fluid, from the containment environment to the coolant reservoir through the coolant channel via a first check valve assembly and the coolant channel, the first check valve assembly at a first vertical depth below a top surface of the coolant fluid in the coolant reservoir, the first check valve assembly in fluid communication with the coolant reservoir through the coolant channel and in fluid communication with the containment environment, wherein the selectively enabling is based on one or more check valves of the first check valve assembly opening in response to a pressure at an inlet of the one or more check valves being equal to or greater than a first threshold magnitude, the first threshold magnitude at least partially corresponding to a hydrostatic pressure of the coolant fluid at an outlet of the first check valve assembly at the first vertical depth.