Fuel assembly bottom nozzle with integral debris trap

In a liquid cooled nuclear reactor having a plurality of fuel assemblies supported on a lower core plate, each of said fuel assemblies and said lower core plate being constructed to allow coolant flow therethrough, said fuel assembly including a plurality of nuclear fuel rods, a plurality of grids axially disposed along and supporting said fuel rods in an organized array, and a plurality of guide thimbles supporting said grids, an improved bottom nozzle disposed adjacent a lowermost one of said grids, supporting said guide thimbles spaced above said lower core plate and adapted to allow flow of liquid coolant into said fuel assembly from said lower core plate, said improved bottom nozzle comprising:

• (a) a housing formed by a plurality of interconnected, upstanding side walls having upper and lower peripheral edges and adapted to rest at said lower peripheral edge thereof upon said lower core plate and spaced at said upper peripheral edge from said lowermost grid;
• (b) a network of interconnected structural members disposed within said housing and extending across said housing between said side walls thereof, said members being connected to said side walls a short distance be1ow said upper peripheral edge of said housing so as to define an open region within said upper portion of said housing above said network of members and below said lowermost grid, said members together defining open space for flow of coolant therethrough to said fuel assembly;
• (c) means supported on said network of members for attaching and anchoring said guide thimbles to said members;
• and
• (d) a trap disposed within said open region and adapted for passage of said guide thimble therethrough to said network of members and the flow of said coolant therethrough for capturing and retaining debris carried by said flowing coolant within said trap to substantially prevent entry of debris into said fuel assembly, said trap including
• (i) a structure disposed upon said network of members and within and extending across said open region of said upper portion of said housing in a path of coolant flow from said core plate through said spaces between said network of members and to said fuel assembly,
• (ii) said structure being composed of a plurality of straps aligned with respect to each other in a crisscross arrangement so as to define a plurality of intersections disposed below and aligned respectively with said fuel rods, said straps defining a plurality of interconnected wall portions which form a multiplicity of cells each being open at opposite ends and defining a central channel extending generally parallel to said path of coolant flow for passage of coolant flow therethrough to said fuel assembly, said wall portions of each cell being defined in oppositely-disposed interconnected pairs thereof, some of said wall portions being common to two adjacent cells, and
• (iii) a plurality of spring-like fingers disposed in each cell and extending into said channel thereof for capturing and retaining within said structure debris carried into said cell by said coolant flowing therethrough, said spring-like fingers being punched out of respective ones of said wall portions of said cell and bent to extend both vertically and horizontally into said channel of said cell and other cells adjacent thereto, one pair of said fingers on one pair of said wall portions in a cell being disposed downstream from and in overlapping relation with another pair of said fingers on another pair of said wall portions in said cell such that a fuel rod cannot enter said cell, said wall portions which are common to two adjacent cells having a pair of said fingers punched out therefrom being located upstream and downstream from one another and extending oppositely into separate ones of said two adjacent cells.