Kernreaktorbrennstabbündel mit als unterer Befestigungsplatte ausgeführter Filter

The lower tie plate grid (16) for a nuclear fuel assembly (10) comprises an upper grid portion (28) and lower grid portion (26). A support means including portions (26,28) supports the fuel rods (12) above the lower tie plate grid (16). The support means comprises laterally spaced bosses (36) sized for receiving the lower ends of the fuel rods (12). Bosses (36) have portions extending upwards from the lower grid portion (26). The supporting means also includes webs (38) interconnecting the bosses (36) and having portions extending upwards from the lower grid portion (26) to define with the boss portions, flow spaces (40). The flow spaces (40) are defined in the upper grid portion (28), extending from the lower grid portion (26), and opening through an upper surface of the lower tie plate grid (16). The bosses (36) are cylindrical and have vertical centrelines arranged at the corners of square matrices with the webs (38) extending linearly between the bosses (36) along sides of the square matrices. Convex portions of the bosses (36) extend between perpendicularly orientated webs of each matrix. The bosses (36) and webs (38) have lower boss and web portions, respectively, in the lower grid portion (26). The lower grid portion (26) includes lower openings (46) extending through the portion (26). The openings (46) are defined in part by the lower boss and lower web portions. Openings (46) open into the flow spaces (40) for sepg. debris from a coolant flowing through the grid portion (26) into the flow spaces (40) between the upper boss and upper web portions. Each lower opening (46) is defined in part by projections (44) extending laterally from the lower boss portions or the lower web portions towards a central region of the lower opening and terminating short of the central region.