A nuclear power system includes a reactor vessel that includes a reactor core mounted, the reactor core including nuclear fuel assemblies configured to generate a nuclear fission reaction; a riser positioned above the reactor core; a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation.

A control rod drive system includes a drive assembly and a cage assembly operably coupled to the drive assembly. The cage assembly includes a plurality of drive rods operably engaged with a drive platform, a plurality of guide rods extending through the drive platform, and a control platform releasably coupled to the drive platform via quick release assembly, the control platform configured to have a control rod mounted thereto. A method of control operation of a nuclear reactor includes receiving instructions to adjust operation of the nuclear reactor, moving a control rod relative to a core of the nuclear reactor via rotating one or more drive rods engaged with a drive platform, and releasing a control platform coupled to the control rod from the drive platform.

A control drum assembly may include a control drum and a control assembly coupled to the control drum through a drive shaft. The control drum assembly may also include a cage assembly. The cage assembly may include one or more structural supports and one or more modular platforms coupled to the one or more structural supports. The one or more modular platforms may be configured to support one or more components of the control assembly. The cage assembly may also include a base configured to be coupled to a surface of a core and to locate the cage assembly relative to the core.

A nuclear plant includes a nuclear reactor, a containment structure that at least partially defines a containment environment of the nuclear reactor, and a passive containment cooling system that causes coolant fluid to flow downwards from a coolant reservoir to a bottom of a coolant channel coupled to the containment structure and rise through the coolant channel toward the coolant reservoir due to absorbing heat from the nuclear reactor. A check valve assembly, in fluid communication with the coolant reservoir, selectively enables one-way flow of a containment fluid from the containment environment to the coolant reservoir, based on a pressure at an inlet being equal to or greater than a threshold magnitude. A fusible plug, in fluid communication with the coolant reservoir at a bottom vertical depth below the bottom of the coolant reservoir, enables coolant fluid to flow into the containment structure based on at least partially melting.

A subcritical reactivity monitor that utilizes one or more primarily gamma sensitive (prompt responding) self-powered detector style radiation measurement devices located within the core of a nuclear reactor to determine the amount that the reactor multiplication factor (K.sub.eff) is below the reactivity required to achieve or maintain a self-sustaining nuclear chain reaction. This invention utilizes measured changes in the self-powered detectors' current(s) to allow a reactor operator to measure the value of K.sub.eff at essentially any desired interval while the reactor is shutdown with a K.sub.eff value less than the critical value of 1.0. This invention will enable integration of the output of the value of K.sub.eff directly into the Reactor Protection System, which will enable the elimination of the operational and core design analysis constraint costs associated with the current Boron Dilution Accident prevention methodology and enable automatic control of the Chemical Volume Control System.

A subcritical reactivity monitor that utilizes one or more primarily gamma sensitive (prompt responding) self-powered detector style radiation measurement devices located within the core of a nuclear reactor to determine the amount that the reactor multiplication factor (K.sub.eff) is below the reactivity required to achieve or maintain a self-sustaining nuclear chain reaction. This invention utilizes measured changes in the self-powered detectors' current(s) to allow a reactor operator to measure the value of K.sub.eff at essentially any desired interval while the reactor is shutdown with a K.sub.eff value less than the critical value of 1.0. This invention will enable integration of the output of the value of K.sub.eff directly into the Reactor Protection System, which will enable the elimination of the operational and core design analysis constraint costs associated with the current Boron Dilution Accident prevention methodology and enable automatic control of the Chemical Volume Control System.

A safety method for a reactor including a primary circuit in which a water-based primary fluid is intended to circulate, and a secondary circuit, in which a water-based secondary fluid is intended to circulate, the secondary circuit being hydraulically isolated from the primary circuit and including a steam generator is provided. In the event of a meltdown of the core of the reactor with the formation of a corium bath in a bottom of the vessel: in response to the detection of the formation of a liquid metallic layer at the surface of the corium bath: the method provides for setting the secondary circuit in fluidic communication with the primary circuit so that the secondary fluid follows the primary circuit to flow inside the vessel over the liquid metallic layer of the corium bath.

A system configured to monitor the structural health of reactor vessel internals of a nuclear reactor is disclosed herein. The system includes a memory configured to store historical information associated with past performance of the nuclear reactor, and an anomaly detection subsystem including a control circuit configured to receive a signal from a sensor. The anomaly detection subsystem is configured to determine, via the control circuit, a characteristic of a vibrational response of the reactor vessel internals based, at least in part, on the signal; access, via the control circuit, the historical information stored in the memory; compare, via the control circuit, the determined characteristic to the historical information stored in the memory; and determine, via the control circuit, a condition of the reactor vessel internals based, at least in part, on the comparison of the determined characteristic and the historical information.

A system configured to monitor the structural health of reactor vessel internals of a nuclear reactor is disclosed herein. The system includes a memory configured to store historical information associated with past performance of the nuclear reactor, and an anomaly detection subsystem including a control circuit configured to receive a signal from a sensor. The anomaly detection subsystem is configured to determine, via the control circuit, a characteristic of a vibrational response of the reactor vessel internals based, at least in part, on the signal; access, via the control circuit, the historical information stored in the memory; compare, via the control circuit, the determined characteristic to the historical information stored in the memory; and determine, via the control circuit, a condition of the reactor vessel internals based, at least in part, on the comparison of the determined characteristic and the historical information.

A nuclear reactor control rod drive assembly includes a control rod drive mechanism coupled to a drive shaft and operable to bi-directionally urge the drive shaft through a portion of an inner volume of a reactor vessel at a first force; a control rod manifold coupled to the drive shaft; a plurality of control rods coupled to the control rod manifold, the plurality of control rods adjustable among a plurality of positions within the inner volume of the reactor vessel based on operation of the control rod drive mechanism; and at least one variable strength joint positioned between the control rod drive mechanism and the plurality of control rods.