Method for controlling heat exchange in a nuclear reactor

A method for controlling heat exchange in a nuclear reactor comprising the steps of:

• circulating a heated liquid through a conduit forming a closed loop extending from a heat exchanger in the nuclear reactor to at least one other heat exchanger immersed in a pool of relatively cold liquid located external of the nuclear reactor;
• confining said at least one other heat exchanger within a container immersed in said pool of liquid, said container having an upper part forming an area surrounding said at least one other heat exchanger and an open lower part through which the liquid of said pool may freely pass;
• forming a passageway in said upper part of said container to permit communication through said passageway from said area surrounding said at least one other heat exchanger and said pool;
• and
• controlling the opening and closing of said passageway such that when the passageway is closed a vapor is formed in said area inhibiting further heat exchange with the heated liquid in the conduit and when the passageway is open heat exchange is maximized.