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 secondary shutdown system for a nuclear reactor using melting seal includes a guide pipe located inside the nuclear reactor, a storage container communicating with the guide pipe and storing a neutron absorber therein, a sealing member provided in the storage container and configured to close an outlet of the storage container so that the neutron absorber stored in the storage container is not moved, and a hot wire configured to supply heat to the sealing member, wherein the sealing member is melted by the heat supplied by the hot wire to open the storage container and move the neutron absorber to the guide pipe.

The present invention relates to a nuclear reactor, more precisely a passive safety device applicable to a thermal neutron reactor and a nuclear fuel assembly equipped with the same. The nuclear fuel assembly for a thermal neutron reactor of the present invention includes multiple fuel rods; multiple guide thimbles arranged between the fuel rods; and a passive safety device including neutron absorber parts which are inserted in one or more guide thimbles.

The present invention relates to a nuclear reactor, more precisely a passive safety device applicable to a thermal neutron reactor and a nuclear fuel assembly equipped with the same. The nuclear fuel assembly for a thermal neutron reactor of the present invention includes multiple fuel rods; multiple guide thimbles arranged between the fuel rods; and a passive safety device including neutron absorber parts which are inserted in one or more guide thimbles.

A nuclear power plant having buried buildings that include a containment building housing a nuclear reactor, a power generation building housing turbines, and a nuclear material storage building. A borated cooling water tank is located above the containment building and can gravity feed water thereto through cooling pipes. Steam exhaust pipes extend from the containment building to the bottom of the water tank. A float and valve arrangement provides seawater to keep the water tank at a constant water level. Horizontal tunnels have manually operated hatches to isolate the different buildings from one another. Vertical tunnels have gravity elevators.

A PWR includes a secondary circuit that is normally fluidly isolated from the primary circuit. The secondary circuit includes secondary fluid in a steam generator. In response to detection of a core melt, the secondary circuit is placed in fluidic communication with the primary circuit, so that secondary fluid from the steam generator can flow into the primary circuit and then into the reactor vessel.

One variation of a system includes: a nuclear reactor; a shield arranged about the nuclear reactor; a metallic coolant; and a set of melt seals. The nuclear reactor includes a pressure vessel and nuclear fuel arranged within a lower region of the pressure vessel. The metallic coolant includes a mixture of metals and is configured to: occupy a liquid state within an operating temperature range; occupy an interstitial volume between the nuclear reactor and the shield; and occupy the lower region of the pressure vessel encompassing the nuclear fuel. The set of melt seals are arranged on the pressure vessel and configured to open to enable transfer of a volume of the metallic coolant from the interstitial volume into the lower region of the pressure vessel in response to temperatures within the pressure vessel exceeding the operating temperature range.

A fast nuclear reactor, provided with a protection system for shutdown of the reactor in accidental conditions and comprising shutdown devices that surround the core of the reactor and have an upper volume and a lower volume separated by a septum. The upper volume contains an operating fluid partly facing the active part of the core with neutron reflecting function to facilitate reaching the critical mass of the reactor. The lower volume contains a neutron transparent medium (for example gas) or a neutron absorbing medium (for example boron carbide balls immersed in the primary coolant). Replacement in the volume of the neutron reflecting medium with a neutron transparent or absorbing medium reduces the reactivity of the reactor and causes its shutdown.

One variation of a system includes: a nuclear reactor; a shield arranged about the nuclear reactor; a metallic coolant; and a set of melt seals. The nuclear reactor includes a pressure vessel and nuclear fuel arranged within a lower region of the pressure vessel. The metallic coolant includes a mixture of metals and is configured to: occupy a liquid state within an operating temperature range; occupy an interstitial volume between the nuclear reactor and the shield; and occupy the lower region of the pressure vessel encompassing the nuclear fuel. The set of melt seals are arranged on the pressure vessel and configured to open to enable transfer of a volume of the metallic coolant from the interstitial volume into the lower region of the pressure vessel in response to temperatures within the pressure vessel exceeding the operating temperature range.

A nuclear power system has an open volume between containment vessel and a reactor vessel containing a reactor core. Located in the open volume is a container holding a neutron-absorbing chemical in solid form. The container is configured to release the chemical in solid form directly into the open volume in response to a predetermined temperature and/or a predetermined pressure within the open volume. The released chemical can assist in maintaining the reactor core in a sub-critical state.