Abstract: An improved grid structure is provided for a nuclear reactor fuel assembly whose sole purpose is to promote a crossflow mixing of the coolant through the fuel assembly rather than the support of the fuel rods. The grid straps form an egg-crate configuration creating cell openings for receiving the fuel rods. Associated with each cell opening is at least one coolant flow mixing vane that projects over the cell opening and four dimple protrusions which are open to the flow of coolant therethrough. The dimple protrusions extend into the cell opening to a further extent than the mixing vane so as to prevent damaging impact of the fuel rod with a vane upon transverse movement of the fuel rod across the cell opening. In reducing the pressure drop of the coolant flow through the assembly, the height of the inner grid straps is substantially less than the height of the outer border strap.

Abstract: Described herein is a composite nuclear fuel rod cladding tube which includes two concentric layers of zirconium base alloys metallurgically bonded to each other. The outer layer is composed of a conventional zirconium base alloy having high strength and excellent aqueous corrosion resistance. The inner layer is composed of a second zirconium base alloy containing about 0.2 to 0.6 wt. % tin, about 0.03 to 0.11 wt. % iron and up to about 350 ppm oxygen. This second alloy while also having excellent aqueous corrosion resistance, is further characterized by the ability to prevent the propagation of cracks initiated during reactor operation due to pellet-cladding interaction.

Abstract: The present invention pertains to zirconium base alloys containing about 0.1 to 0.6 weight percent tin; about 0.07 to 0.24 weight percent iron; about 0.05 to 0.15 weight percent chromium; and up to about 0.05 weight percent nickel. The balance of the alloy is zirconium with incidental impurities. The levels of the incidental impurity, oxygen, is controlled to a level of less than about 350 ppm. These alloys have been designed to minimize the adverse effects of pellet-clad interaction, when they are used as a liner bonded to the inside surface of water reactor nuclear fuel cladding. Specific cladding and fuel element designs according to the present invention are described.

Abstract: An improved nuclear fuel assembly includes a plurality of elongated water tubes arranged in a cross-like pattern spaced among a plurality of fuel rods for providing individual, spaced-apart coolant-moderator water flow paths lengthwise through the assembly. Some of the water tubes also function as tie rods interconnecting upper and lower tie plates of the fuel assembly.

Abstract: An improved nuclear fuel rod comprising a tubular metallic cladding containing a plurality of nuclear fuel pellets has a plurality of ceramic wafers therein, each of which wafers being disposed between a major portion of adjacent fuel pellets. The ceramic wafers are formed from a sintered mixture of natural or depleted uranium dioxide and 1-8 percent by weight gadolinium oxide. The wafers are of a diameter substantially the same as that of the fuel pellets and have a thickness of between 10-100 mils. The wafers freeze out harmful fission products released by the fuel pellets and minimize or prevent pellet-clad interaction failures, while also providing flexibility in power shaping in the reactor system.

Abstract: Apparatus comprising a two layered composite with an internal core of zirconium or zirconium alloy which retains tritium, and an adherent nickel outer layer which acts as a protective and selective window for passage of the tritium.