Provided is a secondary shutdown structure of a nuclear reactor, which uses sliding doors, and more particularly, to a secondary shutdown structure of a nuclear reactor, which uses sliding doors and is capable of shutting down a nuclear reactor reliably with a simple structure without using a boric acid solution.

Provided is a secondary shutdown structure of a nuclear reactor, which uses sliding doors, and more particularly, to a secondary shutdown structure of a nuclear reactor, which uses sliding doors and is capable of shutting down a nuclear reactor reliably with a simple structure without using a boric acid solution.

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 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.

Configurations of molten fuel salt reactors are described that utilize neutron-reflecting coolants or a combination of primary salt coolants and secondary neutron-reflecting coolants. Further configurations are described that circulate liquid neutron-reflecting material around an reactor core to control the neutronics of the reactor. Furthermore, configurations which use the circulating neutron-reflecting material to actively cool the containment vessel are also described.

Methods of controlling the reactivity of a molten salt fission reactor. The molten salt fission reactor comprises a core and a coolant tank (101), the core comprising fuel tubes (103) containing a molten salt fissile fuel, and the coolant tank containing a molten salt coolant (102), wherein the fuel tubes are immersed in the coolant tank. The methods comprise dissolving a neutron absorbing compound in the molten salt coolant, the neutron absorbing compound comprising a halogen and a neutron absorbing element. The first method further comprises reducing the neutron absorbing compound to a salt of the halogen and an insoluble substance comprising the neutron absorbing element, the halogen being fluorine or chlorine, wherein the insoluble substance is not volatile at a temperature of the coolant during operation of the reactor. In the second method the one or more neutron absorbing compounds are chosen such that reduction of the neutron absorbing capacity of the one or more neutron absorbing compounds due to absorption of neutrons compensates for a fall in reactivity of the core in order to control fission rates in the core. Apparatus for implementing the methods are also provided.

Methods of controlling the reactivity of a molten salt fission reactor. The molten salt fission reactor comprises a core and a coolant tank (101), the core comprising fuel tubes (103) containing a molten salt fissile fuel, and the coolant tank containing a molten salt coolant (102), wherein the fuel tubes are immersed in the coolant tank. The methods comprise dissolving a neutron absorbing compound in the molten salt coolant, the neutron absorbing compound comprising a halogen and a neutron absorbing element. The first method further comprises reducing the neutron absorbing compound to a salt of the halogen and an insoluble substance comprising the neutron absorbing element, the halogen being fluorine or chlorine, wherein the insoluble substance is not volatile at a temperature of the coolant during operation of the reactor. In the second method the one or more neutron absorbing compounds are chosen such that reduction of the neutron absorbing capacity of the one or more neutron absorbing compounds due to absorption of neutrons compensates for a fall in reactivity of the core in order to control fission rates in the core. Apparatus for implementing the methods are also provided.

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 boiling water reactor system includes a reactor vessel including a reactor core. A steam line is in communication with the reactor core and a turbine that is connected to an electrical generator. A dry standby liquid control system includes a standby vessel containing dry powder containing boron and including a high pressure water supply in communication with the standby vessel via a first closed valve, wherein the standby vessel is in communication with the reactor vessel via a second closed valve.