Debris-retaining trap for a fuel assembly

Abstract

A debris trap is mounted within a bottom nozzle of a fuel assembly so as to capture and retain debris carried by coolant flowing from the lower core plate openings of the nuclear reactor to the fuel assembly. The trap includes a hollow enclosure disposed below the bottom nozzle adapter plate and between the corner legs thereof. The enclosure is composed of upper and lower walls and inwardly inclined side walls which space apart the upper and lower walls and interconnect their peripheries so as to form a debris capturing and retaining chamber within the hollow enclosure. The walls are composed of a material, such as wire mesh screen and/or perforated plate, which is permeable to liquid coolant but impermeable to debris. Openings are defined in the bottom wall of the enclosure aligned with the flow openings of the core plate. Two embodiments of features are provided for capturing debris and diffusing coolant flow within and through the trap. In the preferred embodiment, lower bell mouthed rings are disposed on the lower wall about the respective openings and upper flared diffuser rings attached to corner pieces extend inwardly so as to overlie and align with the respective lower rings and openings. The lower rings prevent reverse movement of debris out of the enclosure through the openings, while the upper rings cause uniform distribution of coolant flow through the bottom nozzle. In the alternative embodiment, lower cylindrical rings on the lower wall about the openings and upper inverted cones on the upper wall and aligned with the lower rings and openings provide these respective functions.