Abstract: A method of generating a medial mesh of an object. The method first includes obtaining a surface mesh of the object. Define a set of node normal vectors, each having its origin at a node and being directed towards the interior of the object. For each node: select a node normal from the set having their origins at that node; define a sphere wherein a surface of the sphere includes the node and the centre point is positioned at a scalar multiple of the node normal; increment the centre point along the scalar multiple; iterate until the surface of the sphere includes another node or element. The centre point is recorded as a medial point and the diameter as a thickness. The medial mesh is generated from the set of medial points and object thicknesses.

Abstract: A control rod ejection retardation assembly is mounted to a control rod assembly of a nuclear reactor to retard the ejection of the control rod only during an undesired ejection of the control rod while allowing normal control rod movement and "scramming" operation to be drag free and unretarded. The ejection retardation assembly includes a piston assembly mounted to the control rod and having an opening thereto controlled by a ball valve. The piston assembly seals are made loose fitting to allow sufficient fluid flow through the seals to provide unhindered normal control rod movement even with the ball valve sealing the piston assembly opening. During undesired speedy ejection of the control rod, the ball valve seals the opening to prevent fluid flow to the piston assembly retarding piston movement and thereby controlling control rod movement.

Abstract: A typical embodiment of the invention provides a means for selectively inserting and withdrawing one or more fuel rods from a fuel element cellular grid structure. The transverse stubs on one side of a long, thin bar are turned through 90.degree. to extend across the gap between mutually perpendicular grid structure plates. The extreme ends of these stubs engage the adjacent portions of the associated plates that form part of the grid cells. Pressing the stubs against the plate portions through the application of appropriate force in a longitudinal direction relative to the bar deflects the engaged plates through a sufficient distance to enable fuel rods to be inserted into, or withdrawn from, respective cells. After rod insertion, the force applied to the bar is released to enable the plates to relax and engage the fuel rods. The bars are rotated once more through 90.degree. and withdrawn from the grid structure. A similar procedure is employed to withdraw fuel rods from the grid structure.

Abstract: A grid structure for holding a plurality of nuclear fuel rods. The grid structure is of the type having wall means, including rigidly interconnected generally rectangular metal strips, forming a plurality of passageways and adapted to support nuclear fuel rods within some of the passageways. The improvement comprises providing elongated slots intermediate and normal to the longitudinal edges of each of the strips at each intersection of the strips whereby the slots form openings in each corner of each passageway.