Refueling of a nuclear reactor (40) includes removing a fuel assembly (10). The removal method includes lowering a lifting tool (80) of a crane (44) onto a top of the fuel assembly. The lowered lifting tool including a plurality of downwardly extending elements (82) that surround and vertically overlap a portion (74) of a control rod assembly (70) extending above the top of the fuel assembly. The downwardly extending elements are locked with corresponding mating features (26) at the top of the fuel assembly to connect the lifting tool with the fuel assembly. The connected fuel assembly is moved into a spent fuel pool (42) using the crane, and the lifting tool is disconnected from the top of the fuel assembly by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.

A system for refueling a nuclear reactor is provided. The system includes a lower reactor vessel with a plurality of fuel rods and a plurality of control rods disposed therein, the lower reactor vessel further comprising an upper flange. An upper reactor vessel is provided which encloses a steam generator and a pressurizer, the upper reactor vessel further comprising a lower flange that matingly engages the upper flange of the lower reactor vessel. A transporter surrounds an outer surface of the upper reactor vessel, wherein the transporter is configured to translate the upper reactor vessel vertically toward and away from the lower reactor vessel and also to translate the upper reactor vessel horizontally toward or away from alignment with the lower reactor vessel.

Refueling of a nuclear reactor (40) includes removing a fuel assembly (10). The removal method includes lowering a lifting tool (80) of a crane (44) onto a top of the fuel assembly. The lowered lifting tool including a plurality of downwardly extending elements (82) that surround and vertically overlap a portion (74) of a control rod assembly (70) extending above the top of the fuel assembly. The downwardly extending elements are locked with corresponding mating features (26) at the top of the fuel assembly to connect the lifting tool with the fuel assembly. The connected fuel assembly is moved into a spent fuel pool (42) using the crane, and the lifting tool is disconnected from the top of the fuel assembly by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.

A method for calculating a PCI margin associated with a loading pattern of a nuclear reactor including a core into which fuel assemblies are loaded according to the loading pattern is implemented by an electronic system. The fuel assemblies include fuel rods each including fuel pellets of nuclear fuel and a cladding surrounding the pellets. This method includes calculating (100) a reference principal PCI margin for a reference loading pattern of the fuel assemblies in the core; calculating (110) a reference secondary PCI margin for the reference pattern; calculating (120) a modified secondary PCI margin for a modified loading pattern of the fuel assemblies in the core, and calculating (130) a modified principal PCI margin for the modified pattern, depending on a comparison of the modified secondary PCI margin with the reference secondary PCI margin.

Provided herein is a small modular nuclear reactor plant that can comprise a reactor core comprising a primary sodium comprising cool primary sodium flow and heated primary sodium flow. Heated primary sodium flow can enter one or more IHXs where heated primary sodium exchanges heat with secondary sodium flowing through at least one intermediate sodium loop. Intermediate sodium loop can comprise secondary sodium flow that can transport heat to energy conversion portion via a heat exchanger. Energy conversion portion can comprise a bypass valve. Bypass valve can bypass an energy conversion working fluid (such as S-CO2) away from a turbine during periods of adjustment as discussed herein. The plant may comprise passive load following features along with the ability to provide cogeneration heat.

The generation of a nuclear core loading distribution includes receiving a reactor core parameter distribution associated with a state of a reference nuclear reactor core, generating an initial fuel loading distribution for a simulated beginning-of-cycle (BOC) nuclear reactor core, selecting an initial set of positions for a set of regions within the simulated BOC core, generating an initial set of fuel design parameter values utilizing a design variable of each of the regions, calculating a reactor core parameter distribution of the simulated BOC core utilizing the generated initial set of fuel design parameter values associated with the set of regions located at the initial set of positions of the simulated BOC core and generating a loading distribution by performing a perturbation process on the set of regions of the simulated BOC core to determine a subsequent set of positions for the set of regions within the simulated BOC core.

A method for preparing to reload a fast nuclear reactor with heavy liquid metal coolant includes extracting a reactor plug and extracting a removable reactor block. The method includes installing handling equipment to form an unloading path under radiation safety conditions. The reactor plug is extracted from the reactor monoblock housing and transported to a plug shaft. The removable reactor block is extracted from the reactor monoblock housing and transported to a block shaft for later disassembly.

Fuel bundles for a nuclear reactor are described and illustrated, and in some cases include fuel elements each having a fissile content of .sup.235U between about 0.9 wt % .sup.235U and 5.0 wt % .sup.235U, and wherein at least one of the fuel elements is a poisoned low-enriched uranium fuel element including a neutron poison in a concentration greater than about 5.0 vol %.

A method of operating a nuclear fission reactor, the reactor comprising a reactor core, and a coolant tank containing coolant, the reactor core comprising an array of fuel assemblies arranged in generally parallel rows, each fuel assembly comprising one or more fuel tubes containing fissile fuel. For each row of the array, one or more spent fuel assemblies are removed from the array at a second end of the row, fuel assemblies are moved along the row from a first end to the second end; and one or more fuel assemblies are introduced to the array at the first end of the row. Each fuel assembly remains within a single row while the fuel assembly is within the array. At least the fuel-filled portions of the fuel tubes of each fuel assembly are immersed in the coolant while the fuel assembly is within the array.

Refueling of a nuclear reactor (40) includes removing a fuel assembly (10). The removal method includes lowering a lifting tool (80) of a crane (44) onto a top of the fuel assembly. The lowered lifting tool including a plurality of downwardly extending elements (82) that surround and vertically overlap a portion (74) of a control rod assembly (70) extending above the top of the fuel assembly. The downwardly extending elements are locked with corresponding mating features (26) at the top of the fuel assembly to connect the lifting tool with the fuel assembly. The connected fuel assembly is moved into a spent fuel pool (42) using the crane, and the lifting tool is disconnected from the top of the fuel assembly by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.