A fuel assembly for a nuclear reactor having an upstream minor portion defining an upstream end, a main portion, and a downstream minor portion defining a downstream end. Fuel rods extend in a flow interspace permitting a flow of coolant through the fuel assembly in contact with the fuel rods. Two elongated tubes form a respective internal passage extending in parallel with the fuel rods and enclosing a stream of the coolant. Each elongated tube having a bottom, an inlet at the upstream minor portion and an outlet at the downstream minor portion. Each elongated tube having an inlet pipe having an inlet end and an outlet end in the internal passage at a distance from the bottom, thereby forming a space in the internal passage between the outlet end and the bottom.

The invention relates to a process for aiding the detection of migrating bodies within a fuel assembly of a nuclear power plant and more particularly on the anti-debris grid of the lower end piece of said assembly, during which at least one camera is controlled in the direction of said assembly and the stream of images recorded by said at least one camera is directed towards a man-machine interface which comprises at least one screen allowing a first operator to view said stream of video images, characterized in that it comprises a first step of detecting, using an image recognition algorithm, said migrating bodies, as well as at least a second step of alerting said operator if said algorithm has detected the potential presence of at least one migrating body.

A fuel assembly for a nuclear water reactor having an upstream end, a downstream end, and a flow interspace between the upstream and downstream ends. Fuel rods are provided in the flow interspace between the upstream and downstream ends. The flow interspace permits a flow of coolant through the fuel assembly along a flow direction from the upstream end to the downstream end. A filter device is provided to catch debris particles in the flow of coolant. The filter device has a first filter zone for a major part of the flow of coolant, and a second filter zone for a minor part of the flow of coolant. The first filter zone has a first filtering efficiency and the second filter zone has a second filtering efficiency. The second filtering efficiency is higher than the first filtering efficiency.

Debris filters fit in fuel assembly lower tie plates and filter fluids passing therethrough. Filters use a series of adjacent plates with aligned peaks and valleys to create several channels. The plates have small excisions in diamond, triangle, or other debris-catching shapes, such as near a lower portion of the filter where fluid enters the filter. Excisions may alternate around each channel, such as four alternating cut-outs in 90-degree intervals about a channel circumference. Excisions may be sized to entrap smaller debris common in reactor coolant flow and liable for fretting damage to fuel cladding. Multiple vertical stages can be used in filters, with different channels for each stage. Ligaments may hold each stage to the next, potentially with a gap between stages for intermixing. Plates, peaks, valleys, ligaments, and excisions may all be formed in a single stamping operation to eliminate excess or overlapping pieces or extensions.

A method and device is claimed for preventing reverse coolant flow in a BWR Power Reactor. The device comprises a screen that is free to move between a top plate and a bottom plate in a fuel assembly lower tie plate box. Flow holes are formed and aligned in the top plate and in the bottom plate, creating a path for reactor coolant. Disks at a bottom of the screen are aligned with the flow holes in the bottom plate, and are shaped and formed to cover flow holes in the bottom plate. When flow stagnates or reverses, the screen drops causing the disks to rest on the bottom plate blocking downward flow. Upstanding tabs at the top surface of the screen contact the top plate when normal coolant flow is in the upward direction, allowing flow through the flow holes in the top plate.

An improved retention system for retaining fuel rods in a fuel assembly is disclosed. The retention system includes a plurality of first engagement surfaces on the bottom nozzle of a fuel assembly. There is at least one engagement surface for each fuel rod. A second engagement surface is formed on the bottom end plug of each fuel rod. The first and second engagement surfaces are configured for engagement with each other for axially and laterally retaining each fuel rod within the fuel assembly. Debris deflectors may also be provided to deflect debris from coolant channels surrounding the fuel rods.

A filtering arrangement for use in a bottom nozzle of a fuel assembly in a nuclear reactor includes a top surface, a bottom surface, a plurality of vertical wall portions arranged in a generally squared grid-like pattern which extend between the bottom surface and the top surface and define a plurality of non-circular passages extending between the bottom surface and the top surface through the arrangement, and a plurality of first debris filters which are each positioned between the top surface and the bottom surface to generally span across a respective one of the plurality of passages.

Debris filters fit in fuel assembly lower tie plates and filter fluids passing therethrough. Filters use a series of adjacent plates with aligned peaks and valleys to create several channels. The plates have small excisions in diamond, triangle, or other debris-catching shapes, such as near a lower portion of the filter where fluid enters the filter. Excisions may alternate around each channel, such as four alternating cut-outs in 90-degree intervals about a channel circumference. Excisions may be sized to entrap smaller debris common in reactor coolant flow and liable for fretting damage to fuel cladding. Multiple vertical stages can be used in filters, with different channels for each stage. Ligaments may hold each stage to the next, potentially with a gap between stages for intermixing. Plates, peaks, valleys, ligaments, and excisions may all be formed in a single stamping operation to eliminate excess or overlapping pieces or extensions.

A filter for separating particles from a cooling liquid in a nuclear plant is presented. The filter includes at least one passage with an inner surface, an inlet end and an outlet end, wherein the at least one passage is arranged to permit through-flow of the cooling liquid in a main flow direction (MFD) from the inlet end to the outlet end. The inner surface of the at least one passage includes at least one surface section having a structured surface forming a plurality of surface portions facing the main flow direction (MFD) of the cooling liquid and being arranged to catch the particles. Also, a fuel assembly for a nuclear plant, including a filter is presented.

A base portion for use in a bottom nozzle of a fuel assembly in a nuclear reactor includes a top surface, a bottom surface, and a plurality of vertical wall portions arranged in a generally squared grid-like pattern which extend between the bottom surface and the top surface and which define a plurality of non-circular passages passing between the bottom surface and the top surface through the base portion.