Abstract: A fuel assembly has a spring detent spacer grid of intersecting strips for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly. A plurality of fuel end caps are peripherally grooved to receive springs projecting from the strips. The end caps are thus captured by springs and debris is wedged and trapped on opposite sides of the strip and against the end caps by pairs of adjacent integral leaves projecting from the stips intermediate and substantially symmetrically arranged about their intersections.

Abstract: A control rod for a nuclear fuel assembly has structures formed of boron carbide mounted inside it. The boron carbide structures are provided deformable members between them which will deform at operating temperatures to accommodate the dimensional increase of the boron carbide structures and reduce the level of deformable stress on the rod cladding.

Abstract: A nuclear fuel assembly having an improved fuel rod of the type having a column of hollow pellets. A plurality of spacer plugs are interposed between proximate pellets at selected elevations along the fuel rod in order to trap pellet debris that would otherwise fall through the passage in the center of the column and accumulate at the bottom of the fuel rod. Thus, an undesirable power peak at the bottom of the fuel rod is avoided. In the preferred embodiment, the plugs are located at the same elevations as the fuel assembly grids, where the local flux is lowest and the effect of the plugs on the power distribution is minimized. The plugs could be made from any material, but graphite or a low enrichment UO.sub.2 pellet are preferred.

Abstract: A nuclear fuel pin has positioned within it material which will decompose to release an oxidizing agent which will react with the cladding of the pin and form a protective oxide film on the internal surface of the cladding.