A passive reactor cavity cooling system according to the present invention includes: a reactor cavity formed between a reactor vessel and a containment structure enclosing the reactor vessel; a first cooling system to control external air to sequentially pass through an air falling pipe and an air rising pipe provided in the reactor cavity, so that residual heat of a core transferred to the reactor cavity is discharged to the atmosphere; a second cooling system having a water cooling pipe disposed in an inner space of the containment structure or in a wall of the containment structure to discharge the residual heat of the core transferred to the reactor cavity to outside; and a functional conductor having an insulating property in a normal operation temperature range of the reactor and a heat transfer property in an accident occurrence temperature range of the reactor which is a higher temperature environment than the normal operation temperature range, wherein the air falling pipe and the water cooling pipe are disposed behind the air rising pipe with respect to a direction viewed from the reactor vessel, and the functional conductor is disposed between the air falling pipe and the air rising pipe.

A nuclear reactor is designed to couple the load path of the control elements with the reactor core, thus reducing the opportunity for differential movement between the control elements and the reactor core. A cartridge core barrel can be fabricated in a manufacturing facility to include the reactor core, control element supports, and control element drive system. The cartridge core barrel can be mounted to a reactor vessel head, and any movement, such as through seismic forces, transmits an equal direction and magnitude to the control elements and the reactor core, thus inhibiting the opportunity for differential movement.

A nuclear reactor is configured with an intermediate coolant loop for transferring thermal energy from the reactor core for a useful purpose. The intermediate coolant loop includes a bypass flowpath with an air heat exchanger for dumping reactor heat during startup and/or shutdown. A fluidic diode along the bypass flowpath asymmetrically restricts flow across the bypass flowpath, inhibiting flow in a first flow direction during a full power operating condition and allowing a relatively uninhibited flow in a second direction during a startup and/or shut down low power operating condition.

A nuclear reactor is configured with a primary coolant loop for transferring heat away from the nuclear reactor core. In a shutdown event, the primary coolant pump may stop pumping primary coolant through the reactor core, resulting in decay heat buildup within the reactor core. An inertial energy coast down system can store kinetic energy while the nuclear reactor is operating and then release the stored kinetic energy to cause the primary coolant to continue to flow through the nuclear reactor core to remove decay heat. The inertial energy coast down system may include an impeller and a flywheel having a mass. During normal reactor operation, the flowing primary coolant spins up the impeller and flywheel, and upon a shutdown event where the primary coolant pump stops pumping, the flywheel and impeller can cause the primary coolant to continue to flow during a coast down of the flywheel and impeller.

Damper systems selectively reduce coolant fluid flow in nuclear reactor passive cooling systems, including related RVACS. Systems include a damper that blocks the flow in a coolant conduit and is moveable to open, closed, and intermediate positions. The damper blocks the coolant flow when closed to prevent heat loss, vibration, and development of large temperature gradients, and the damper passively opens, to allow full coolant flow, at failure and in transient scenarios. The damper may be moveable by an attachment extending into the coolant channel that holds the damper in a closed position. When a transient occurs, the resulting loss of power and/or overheat causes the attachment to stop holding the damper, which may be driven by gravity, pressure, a spring, or other passive structure into the open position for full coolant flow. A power source and temperature-dependent switch may detect and stop holding the damper closed in such scenarios.

Damper systems selectively reduce coolant fluid flow in nuclear reactor passive cooling systems, including related RVACS. Systems include a damper that blocks the flow in a coolant conduit and is moveable to open, closed, and intermediate positions. The damper blocks the coolant flow when closed to prevent heat loss, vibration, and development of large temperature gradients, and the damper passively opens, to allow full coolant flow, at failure and in transient scenarios. The damper may be moveable by an attachment extending into the coolant channel that holds the damper in a closed position. When a transient occurs, the resulting loss of power and/or overheat causes the attachment to stop holding the damper, which may be driven by gravity, pressure, a spring, or other passive structure into the open position for full coolant flow. A power source and temperature-dependent switch may detect and stop holding the damper closed in such scenarios.

Methods and systems for in-vessel natural circulation alkali metal reactor systems, purification systems, and associated methods are disclosed. A nuclear reactor vessel system includes an inner vessel that defines an inner volume sized to at least partially enclose a reactor. The reactor includes a plurality of nuclear fuel elements at least partially enclosed within a cladding, the reactor being cooled by a liquid metal coolant in a primary coolant loop. A pool of immersing fluid occupies a volume inside the inner vessel. The reactor vessel system includes an outer vessel sized to wholly or substantially enclose the inner vessel. A nuclear reactor power system includes a reactor core including an active fuel region; and a rotatable drum including at least one of a neutron absorbing material, a neutron leakage enhancing material, or a neutron reflecting material, the rotatable drum positioned external to the active fuel region of the reactor core.

Methods and systems for in-vessel natural circulation alkali metal reactor systems, purification systems, and associated methods are disclosed. A nuclear reactor vessel system includes an inner vessel that defines an inner volume sized to at least partially enclose a reactor. The reactor includes a plurality of nuclear fuel elements at least partially enclosed within a cladding, the reactor being cooled by a liquid metal coolant in a primary coolant loop. A pool of immersing fluid occupies a volume inside the inner vessel. The reactor vessel system includes an outer vessel sized to wholly or substantially enclose the inner vessel. A nuclear reactor power system includes a reactor core including an active fuel region; and a rotatable drum including at least one of a neutron absorbing material, a neutron leakage enhancing material, or a neutron reflecting material, the rotatable drum positioned external to the active fuel region of the reactor core.

Designs for a low power, fast spectrum molten fuel nuclear reactor that can be used to advance the understanding of molten salt reactors, their design and their operation are described. Furthermore, the designs described may be adapted to extra-terrestrial use as described herein for use as a low-gravity, moon-, Mars-, or space-based power generator. These low power reactors include a reactor core volume defined by a radial neutron reflector enclosed in a reactor vessel, in which heated fuel salt flows from the reactor core through a duct between the radial neutron reflector and the reactor vessel and back into the reactor core. Heat generated from the fission in the reactor core is transferred from the molten fuel through the reactor vessel to a coolant, in the case of an experimental design, or directly to an extra-terrestrial environment, in the case of an extra-terrestrial design.

A boiling water reactor includes a reactor building, a reactor cavity pool, a primary containment vessel, and a passive containment cooling system. The reactor building includes a top wall defining a penetration therein, a bottom wall, and at least one side wall, which define a chamber. At least a portion of the primary containment vessel is in the chamber. The passive containment cooling system includes a thermal exchange pipe including an outer pipe and an inner pipe. The outer pipe has a first outer pipe end and a second outer pipe end. The first outer pipe end is closed and in the primary containment vessel. The second outer pipe end is open and extends into the reactor cavity pool. The inner pipe has a first inner pipe end and a second inner pipe end, which are open. The second inner pipe end extends into the reactor cavity pool.