Abstract: Fuel cell lifting systems for nuclear reactors are disclosed. A fuel cell lifting system includes a radiation shield comprising: a first plate defining a first plane and comprising one or more first openings; and a second plate defining a second plane parallel to the first plane and comprising one or more second openings. At least one of the first plate or the second plate is rotatable around an axis perpendicular to the first plane and the second plane. A first opening of the first plate can be aligned with a second opening of the second plate to form a combined opening. A lifting motor is configured to extend and retract a tether through the combined opening of the radiation shield. The tether is attachable to a nuclear fuel cell.

Abstract: Fuel, heat exchangers, and instrumentation for nuclear reactors are disclosed. A nuclear power system includes a plurality of nuclear fuel elements, each of the nuclear fuel elements including an annulus; and a plurality of heat pipes, each of the plurality of heat pipes configured to pass through the annulus of a respective one of the nuclear fuel elements in conductive thermal contact with the respective nuclear fuel element. A nuclear instrumentation module includes an assembly of optical fibers, each optical fiber comprising one or more sensors and configured for removable installation at one of the plurality of heat pipes. A heat exchanger includes a heat pipe including an evaporating region and a condensing region; and a tube bundle configured to wrap around the condensing region of the heat pipe and including one or more adjacent, parallel tubes, each tube forming a helix that is coaxial to the heat pipe.

Abstract: System and methods are disclosed for controlling a nuclear reactor that uses fuel having plutonium-239. The nuclear reactor includes a neutron moderator, such as ZrH1.6, which behaves as an Einstein oscillator and increases the energy of thermal neutrons into the Pu-239 neutron absorption resonance as the temperature of the nuclear reactor increases. A neutron absorbing element with neutron absorption around 0.3 eV is added to the nuclear reactor to suppress any reactivity gain that can occur due to the increase in temperature. The amount of the neutron absorbing element to be added to the nuclear reactor is calculated such that the reactivity gain that may occur at any time during the life of the fuel is suppressed.