Temperature activated passive shutdown device for a nuclear reactor

A nuclear fission reactor comprising:

• a passive thermal shutdown device,
• a criticality safe dump tank, and
• a reactor core containing a fully or partially liquid fissile fuel, which has a free surface
• the passive thermal shutdown device comprising;
• a Pythagorean syphon having inlet within the liquid fissile fuel, an outlet in fluid communication with the criticality safe dump tank;
• such that when the fissile fuel overtops the Pythagorean syphon due to thermal expansion, the fissile fuel flows through the Pythagorean syphon and into the criticality safe dump tank.

A nuclear fission reactor comprising:

• a passive thermal shutdown device, and a reactor core containing fissile fuel, the passive thermal shutdown device comprising;
• a reservoir, the reservoir being in thermal and neutronic communication with the reactor core, and containing a liquid neutron moderator or reflector which has a free surface;
• a Pythagorean syphon having an inlet within the reservoir, an outlet in fluid communication with a drain which leads to a location that is not in neutronic communication with the reactor core;
• such that when the neutron moderator or reflector overtops the syphon due to thermal expansion, the neutron moderator or reflector flows through the Pythagorean syphon and into the drain.