Patent Application
20080165912
1. Field of the Invention
The invention is generally related to nuclear fuel rods and more particularly to a clad tube with a rhenium liner that is produced by an electro deposit process.
2. General Background
Numerous materials have been investigated for use as cladding for uranium nitride nuclear fuel. Near the end of the SP-100 space nuclear reactor program clad development was focused on a fuel pin design having a Nb (niobium)-1% Zr (zirconium) outer shell with a rhenium liner. The purpose of this design was two-fold. First was that the 1% Zr would be reduced by the free contaminant oxygen found in the niobium alloy. Second was that the rhenium also provided a boost in creep strength over an unlined Nb-1% Zr tube. The outer niobium alloy was generally a powder metallurgy fabricated tube that typically had trace (˜1,000 ppm) impurities of oxygen. Since lithium was to be the reactor coolant, any free oxygen was scavenged from the clad by the lithium. This led to pitting in the pure niobium material and, ultimately, to clad/fuel failure. It was found that by adding 1% Zr to the niobium, the zirconium would “tie up” the free oxygen such that the lithium could not getter it from the clad and, hence, not form pits in the clad. The inner rhenium liner protects the niobium alloy from chemical attach by the uranium nitride fuel.
The method of manufacture of the tubes during the SP-100 program was not direct and required subsequent forming to achieve a finished product. The basic process was a complicated forming of powder metallurgy rhenium sheet, followed by a multi-step rolling operation to form the rhenium into a tube shape. The tube seam was then EB (electron beam) welded along its length to form a closed tube. The rhenium tube was then slid into a close tolerance fit niobium tube and a specially developed braze/weld performed to join the rhenium and niobium. This resulting clad was then loaded with fuel and seal welded.
The invention addresses the above problems. What is provided is a rhenium lined niobium alloy tube for use as a clad tube for nuclear fuel in a nuclear reactor. The tube is produced by an electro deposit process. A graphite mandrel is placed in the electro deposit chamber as the cathode material. Refined rhenium stock is used as the anode material. The chamber is filled with the chloride electrolyte. The chamber is closed and the electrolyte bath is heated. Current and voltage applied across the anode and cathode cause the rhenium to be deposited on the mandrel. Refined niobium alloy is then used as the anode material and applied over the rhenium on the mandrel to a desired thickness. The part is removed from the chamber and ground to the desired outside diameter. The graphite mandrel is removed from the tube.
For a further understanding of the nature and objects of the present invention reference should be made to the following description, taken in conjunction with the accompanying drawing in which like parts are given like reference numerals, and wherein:
Referring to the drawings,
The process of forming the tube is comprised of several steps.
A graphite mandrel 16, seen in
Rhenium stock 20 is placed in the electro deposit chamber 18 as the anode material. It is preferable to use refined rhenium. The chloride electrolyte 22 is placed in the electro deposit chamber 18. The chamber 18 is sealed and heating elements 24 are used to heat the electrolyte 22 to a desired temperature at less than 800 degrees Celsius. The electrolyte is a non-toxic molten salt mixture. Current and voltage are applied from a power source 26 to the mandrel cathode 16 and the rhenium stock anode 20. This causes the release of rhenium into the electrolyte 22 and the deposition of rhenium on the mandrel cathode 16. The current and voltage is applied until a desired thickness of rhenium is deposited on the mandrel to form the inner liner 12 of rhenium for the clad tube. The mandrel 16 with the rhenium deposited thereon is best seen in
The electrolyte solution 22 is allowed to cool and the mandrel 16 is removed from the electro deposit chamber 18. As seen in
The mandrel 16 may be rotated during the electro deposit process to assist in uniform deposition.
The current and voltage is shut off after the desired layer of niobium alloy is achieved and the chloride electrolyte is allowed to cool. The mandrel 16 is removed from the chamber and the niobium alloy is ground to the final outside diameter. As seen in
An advantage of using this electroforming process to form the clad tube 10 is that it allows the formation of multi-layer products using materials that are not normally suitable for welding together. The process results in an atomic level bonded interface between the differing metal alloys. Another advantage is that the electroforming process is less expensive, faster, and more uniform than the method employed during the SP-100 program. The tubes are more uniform than those produced during the SP-100 program because subsequent forming is not required to achieve the finished product.
Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.
