Patent Number: 
Section: claims

1. A lower nozzle for use in a nuclear fuel assembly and having an axis, the lower nozzle comprising:a transverse lower tie plate for channeling a coolant through the lower tie plate;a tubular skirt extending axially from a periphery of the lower tie plate, the skirt including sidewalls extending axially downward from the lower tie plate delimiting an axial housing closed at one end by the lower tie plate and open at an opposite end; anda debris filter configured for axial insertion in the housing and snap-fit springs for retaining the debris filter in the axial housing after insertion, the debris filter including a top front face facing the lower tie plate, a bottom front face facing away from the lower tie plate and side faces extending axially downward from the top front face to the bottom front face, the snap-fit springs each being positioned between one of the sidewalls of the tubular skirt and one of the side faces of the debris filter facing said sidewall, the snap-fit springs configured to clamp the debris filter to the tubular skirt and press the debris filter axially towards the lower tie plate after insertion by contacting the sidewalls and the side faces at locations axially between the top front face and the bottom front face. 2. The lower nozzle according to claim 1, wherein the snap-fit springs are configured to transversely center the debris filter in the housing. 3. The lower nozzle according to claim 1, wherein the snap-fit springs are configured to seal gaps between side faces of the debris filter and inner faces of the axial housing. 4. The lower nozzle according to claim 1 wherein each snap-fit spring snap-fits in a corresponding groove. 5. The lower nozzle according to claim 4, wherein each snap-fit spring is fitted to one of a side face of the debris filter and an inner face of the housing, the corresponding groove being provided in the other one of the side face of the debris filter and the inner face of the housing. 6. The lower nozzle according to claim 1, wherein each snap-fit spring is fitted to a side face of the debris filter. 7. The lower nozzle according to claim 1, wherein each snap-fit spring is elongated perpendicularly to the axis and comprises two lateral parts bearing against one of a side face of the debris filter and an inner face of the housing, each snap-fit spring comprising a central part protruding from the one of the side face and the inner face and snap-fitted in a groove formed in the other of the side face and the inner face. 8. The lower nozzle according to claim 1, wherein each snap-fit spring is configured for snap-fitting with bearing transversely on a wall such as to create an axial reaction force having an axial component shifting the debris filter axially towards the lower tie plate. 9. The lower nozzle according to claim 1, wherein each snap-fit spring comprises a flange gripping a side edge of the debris filter for retaining the debris filter axially in the housing. 10. The lower nozzle according to claim 1, wherein the debris filter is maintained at a distance from the lower tie plate. 11. The lower nozzle according to claim 1, wherein the skirt has a shoulder, the snap-fit springs pressing the debris filter axially against the shoulder. 12. A nuclear fuel assembly comprising:a bundle of nuclear fuel rods;an upper nozzle; andthe lower nozzle as recited in claim 1, the nuclear fuel rods extending from the lower nozzle to the upper nozzle. 13. The lower nozzle according to claim 1, wherein the snap-fit springs axially clamp the debris filter to avoid axial movement of the debris filter. 14. The lower nozzle according to claim 1, wherein the snap-fit springs transversely clamp the debris filter. 15. The lower nozzle according to claim 1, wherein the debris filter is in the shape of a plate and has an upper face pressed axially against a shoulder of the lower tie plate owing to the snap-fit springs. 16. A lower nozzle for use in a nuclear fuel assembly and having an axis, the lower nozzle comprising:a transverse lower tie plate for channeling a coolant through the lower tie plate;a tubular skirt extending axially from a periphery of the lower tie plate, the tubular skirt delimiting an axial housing closed at one end by the lower tie plate and open at an opposite end; anda debris filter configured for axial insertion in the housing and snap-fit springs for retaining the debris filter in the axial housing after insertion, the snap-fit springs each including a lateral upper part, a central bulged part below the lateral upper part and a lateral lower part below the central bulged part, the snap-fit springs configured to clamp the debris filter to the tubular skirt by contacting the tubular skirt or the debris filter via the central bulged part so the central bulged parts press the debris filter axially towards the lower tie plate after insertion, the snap-fit springs axially clamping the debris filter to the tubular skirt to avoid axial movement of the debris filter, the snap-fit springs transversely clamping the debris filter to the tubular skirt by contacting the tubular skirt or the debris filter via the central bulged parts, the housing being open at a lower axial end thereof and the debris filter being shifted upwardly by the central bulged parts of the snap-fit springs contacting the tubular skirt or the debris filter. 17. The lower nozzle as recited in claim 16 wherein the lateral upper part and lateral lower part of each of the snap-fit springs contact a respective side face of one of the tubular skirt and the debris filter and each of the central bulged parts extends into a groove in a respective axially extending wall of the other of the tubular skirt and the debris filter. 18. A lower nozzle for use in a nuclear fuel assembly and having an axis, the lower nozzle comprising:a transverse lower tie plate for channeling a coolant through the lower tie plate;a tubular skirt extending axially from a periphery of the lower tie plate, the tubular skirt delimiting an axial housing closed at one end by the lower tie plate and open at an opposite end; anda debris filter configured for axial insertion in the housing and snap-fit springs for retaining the debris filter in the axial housing after insertion, the snap-fit springs each configured to extend into a groove formed in a respective axially extending wall to clamp the debris filter to the tubular skirt and press the debris filter axially towards the lower tie plate after insertion, each snap-fit spring being configured for snap-fitting by bearing transversely on the respective axially extending wall such as to create an axial reaction force having an axial component shifting the debris filter axially towards the lower tie plate, the snap-fit springs axially clamping the debris filter to the tubular skirt to avoid axial movement of the debris filter, the snap-fit springs transversely clamping the debris filter to the tubular skirt, the housing being open at a lower axial end thereof and the debris filter being shifted upwardly by the snap-fit springs, the debris filter being in the shape of a plate and having an upper face pressed axially against a shoulder of the lower tie plate owing to the snap-fit springs. 19. The lower nozzle as recited in claim 18 wherein the snap-fit springs each includes a lateral upper part, a central bulged part below the lateral upper part and a lateral lower part below the central bulged part, the central bulged part protruding transversely away from the lateral lower part and the lateral upper part to extend into the respective groove.