Abstract: The present invention, in one form, is a natural circulation reactor having, in one embodiment, a layer of high aluminate cement concrete disposed between an uninsulated steel liner and a prestressed concrete reactor vessel. The prestressed concrete reactor vessel includes a concrete shell having a cavity therein. The steel liner is positioned in the cavity and spaced from the concrete shell so that an insulating chamber is formed between the steel liner and the concrete shell. The insulating chamber is filled with high aluminate cement concrete which is configured to substantially insulate the concrete shell from the steel liner and to transfer loads such as pressure from the liner to the concrete shell.

Abstract: A nuclear reactor having a pressure vessel which is open at the top. The open top of the pressure vessel is closed by a steel dome. A containment, which is open at the top, extends upward from and is joined to the top of the pressure vessel and has an open containment head at the top thereof. The open top of the containment is closed by a steel dome, thereby forming a containment well bounded laterally by the containment, on the bottom by the vessel closure and on the top by the containment closure. The pressure vessel can be a steel-lined prestressed concrete vessel, while the containment is formed by an extension of the prestressed concrete vessel. Alternatively, the pressure vessel and the containment are parts of a unitary steel vessel. Isolation valves are installed on each penetration pipeline to isolate the system in the event of a loss-of-coolant accident.

Abstract: A satellite heat removal means can be embodied as an original nuclear system feature but is especially adapted to be retrofitted to an existing nuclear reactor system to serve optionally to supplement heat removal from the system nuclear reactor containment upon happening of a LOCA, and to assume all system containment drywell venting in the event reactor core meltdown results in breach of the containment floor structure separating the containment drywell and wetwell space which breach would deprive the containment of a space to which a non-condensable fraction of LOCA generated heated fluid in the containment could be vented, cooled and stored. The satellite heat removal means includes a structural external of but preferably situated alongside the nuclear reactor containment. A heat exchanger surrounded by a pool of cooling water is located in an upper chamber of the structure while a pool of water is present in a lower chamber of the structure.

Abstract: A nuclear system of the type which includes a containment wherein a nuclear reactor pressure vessel is located has a suppression pool to which steam can be vented so that it will condense and reduce the pressure in the pressure vessel upon the happening of an accident such as loss of reactor coolant or a steam pipe failure. Steam also can be vented directly to the containment space to further reduce pressure in the reactor. When reactor pressure is lowered to a certain pressure value, a gravity supply of water from an elevated pool of water will have a sufficient head to flow against the pressure in the reactor and into the reactor to submerge the fuel rods in the reactor. One or more isolation condensers are submerged in a large supply of water this supply being elevated some distance above the pressure vessel. At least one isolation condenser has inlet thereto communicated to an open entry conduit disposed in the containment.

Abstract: A nuclear reactor complex includes fusible plugs to prevent water from a wetwell from flowing into a drywell including the reactor vessel. In case the core overheats and molten corium falls to the drywell floor, the heat from the corium melts the fusible plugs and water floods the drywell. The water inhibits a corium-concrete reaction, minimizing pressure increase within the drywell and thus the chances of radioactive materials being released into the environment.

Abstract: A method and arrangement for operating a boiling water nuclear reactor and fuel assembly designs for such reactor wherein the reactor is operated with uniquely located control rods that serve the primary functions of power shaping and reactivity control. A second and separate distinct group of control rods is withdrawn when the reactor is at power and the control rods of this group serve the primary function of reactor shutdown. The design of the fuel assemblies and the selected patterns of fuel assemblies and control rods make the separation of control functions feasible. The power shaping and reactivity control control rods are located in low power regions of the core designated control cells. The design of the fuel is such that the control rods of the control cells may remain in fixed positions in these cells during the operating cycle until withdrawal for burnup reactivity compensation.

Abstract: A control for a power source which includes nuclear fuel interspersed with thermionic converters, including a power regulator that maintains a substantially constant output voltage to a variable load, and a control circuit that drives a neutron flux regulator in accordance with the current supplied to the power regulator and the neutron flux density in the region of the converters. The control circuit generates a control signal which is the difference between the neutron flux density and a linear function of the current, and which drives the neutron regulator in a direction to decrease or increase the neutron flux according to the polarity of the control signal.