US3147088A - Uranium-tin-zirconium corrosion resistant alloy - Google Patents

Description

United States Patent M 3,147,088 URANIUM-TlN-ZIRCONIUM CORROSION RESISTANT ALLOY Herbert S. Kalish, Jackson Heights, and Henry H. Hausner, New York, N.Y., assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed June 23, 1953, Ser. No. 373,462 8 Claims. (Cl. 29-194) This invention relates to a corrosion resistant alloy. More particularly, it relates to a corrosion resistant alloy of zirconium, uranium and tin.

Fuel elements for nuclear reactors frequently contain uranium. They may also contain zirconium as a diluent. In some reactors, for example, alloys of uranium and zirconium are considered useful for this purpose. The extent of dilution of the fuel with zirconium in these cases is a matter of choice and depends on the power level at which the reactor is to be operated. One of the undesirable characteristics of these alloys is, however, its susceptibility to corrosion particularly at the elevated temperatures which prevail in the reactor. Since these alloys constitute the core of the fuel element and since the core is frequently clad in a corrosion resistant material, such as zirconium, the corrosion resistance might not be considered to be much of a problem. However, this is not entirely true for under optimum conditions it would be desirable to have a core which is entirely corrosion resistant or which at least can withstand a degree of corrosion in those cases in which there might be a break or leak in the cladding material.

An object of this invention is to improve the corrosion resistance of the zirconium uranium alloys.

A further object of this invention is to provide a zirconium uranium fuel element for nuclear reactors which can withstand the corrosive action of water at elevated temperatures.

It is a further object of this invention to provide a fuel element of zirconium uranium alloy which need not be provided with a corrosion resistant cladding material.

It has been found that these objects and other advantages incidental thereto can be obtained by incorporating in the zirconium uranium alloy a small percentage of tin.

Alloys of this type are readily made by powder metallurgical techniques in which the zirconium powder, uranium powder and tin powder are homogeneously mixed in the desired proportions and then pressed and sintered. It has, however, been found that a good corrosion re- "trtant alloy can only be obtained in those cases in which the uranium and tin contents are kept below a certain maximum limit. In the case of uranium this limit is approximately 30% whereas in the case of tin the limit is in the neighborhood of 10%, with the balance of the alloy being zirconium. In those cases in which the percentage of uranium in the alloy exceeds 30%, the tin content is no longer effective in retarding the corrosion of the uranium zirconium alloy and, although experiments have indicated that alloys containing more than 10% of tin are better than alloys which contain no tin at all, they are not as good as those alloys in which the percentage of tin lies within the range of 1 to Alloys of this type can be prepared in somewhat the following manner. The starting materials are preferably 325 mesh zirconium hydride or zirconium, 325 mesh uranium and -325 mesh tin. In the following specific examples the zirconium hydride is used; however, zirconium powder is sometimes preferable. 11.88 parts of zirconium hydride, .63 part of uranium and .25 part by 3,147,088 Patented Sept. 1, 1964 weight of tin making a total of 12.76 parts are preferably tumbled in an inert atmosphere such as, for example, argon for a period of about two hours. The mixture can then be pressed at a pressure of about 50 tons per square inch in a die and then sintered for about 10 hours at approximately 1320" C. which operation is preferably carried out in a vacuum furnace. At the end of this treatment a material should be obtained which has an approximate density of 6.76 grams per cubic centimeter and having a Rockwell A hardness of about 65. Materials prepared in this manner were subjected to a corrosion test by placing the samples in water at 315 C. and then weighing the samples at regular intervals to determine the gain in weight due to oxidation. In making these tests care must be taken since occasionally there may be a loss in weight owing to powdering and falling away of powder. When such tests were carried out and the corrosion rate expressed in milligrams gained or lost per square centimeter of surface exposed per month, the following results were obtained. An alloy consisting of 1% uranium by weight, 0% tin gained 7.44 milligrams per month per square centimeter in a two week test period and had a white powdery coat. By comparison an alloy containing 1% uranium and 2% tin and the balance of 97% zirconium had a corrosion rate of only .08 in the same period. Similar results were obtained when the tin percentage was increased to 3 and 5%. In still other tests which were run with alloys containing 2% uranium, 98% zirconium and no percent of tin, the corrosion rate was found to be about 6.38 in the same period, and the sample exhibited a black and White color and a powdery coat. By comparison a composition of 2% uranium, 1% tin and 97% zirconium showed a corrosion rate of only .16 milligram per square centimeter per month when tested for the same period.

Results, such as expressed above, strikingly show the inhibition of corrosion caused by the addition of a small percentage of tin to a zirconium uranium alloy. Other tests which were made, for example, on a 5% uranium, 3% tin and 92% zirconium alloy showed the corrosion rate upon four weeks exposure to be only .20 milligram. Another sample containing as much as 20% uranium, 5% tin and zirconium showed a rate of only .63 after a two week run. It was, however, found that when an alloy had a uranium content as high as 40%, the balance being 5% tin and 55% zirconium, it began to fall apart and appeared to be a dark grey powder after a two week corrosion test, the sample losing some 10.68 milligrams per centimeter square per month. This is a marked indication that the effect of tin for retarding the corrosion of uranium zirconium alloys starts to fall off before a uranium content of 40% is reached.

The following tabulated data shows the effect of increasing the tin concentration in a 20% uranium alloy with the balance Zirconium.

The following tabulated data was obtained with a 10% uranium alloy when the percent of tin was varied from to 5% 1 D.T-Discontinued test.

In view of its high corrosion resistance this alloy might in some cases be used in the unclad condition in a nuclear reactor. However, in all probability it will in most instances still be clad with either a zirconium or aluminum or stainless steel cladding material, with the corrosion resistance of the alloy being used somewhat in the form of an insurance factor.

While the above description submitted herewith discloses a preferred and practical embodiment of the corrosion resistant alloy of this invention it will be understood that the specific details of construction and arrangement of parts described are by way of illustration and are not to be construed as limiting the scope of the invention.

What is claimed is:

1. A corrosion resistant alloy of uranium, zirconium and tin which contains from about 1 to 30% uranium, from about 1 to tin and the balance zirconium by weight.

2. A corrosion resistant alloy of uranium, tin and zirconium which contains from about 1 to 30% uranium, from about 1 to 5% tin and the balance zirconium by weight.

3. A corrosion resistant alloy of uranium, zirconium and tin which contains approximately 20% uranium, 5% tin and the balance zirconium.

4. A corrosion resistant alloy of uranium, zirconium and tin which contains approximately 10% uranium, 5% tin and the balance zirconium.

5. A clad uranium containing body for a nuclear reactor, the core of which consists essentially of a corrosion resistant alloy of uranium, zirconium and tin which contains from about 1 to 30% uranium, from about 1 to 10% tin and the balance zirconium by weight, and having a metal cladding.

6. A clad uranium containing body for a nuclear reactor, the body consisting of a corrosion resistant alloy of uranium, tin and zirconium which contains from about 1 to 30% uranium, from about 1 to 5% tin and the balance zirconium by weight and the cladding consisting essentially of a corrosion resistant metal.

7. A clad uranium containing body for a nuclear reactor, the core of which consists essentially of a corrosion resistant alloy of uranium, zironium and tin containing approximately 20% uranium, 5% tin and the balance zirconium, and having a metal cladding.

8. A clad uranium containing body for a nuclear reactor, the core of which consists essentially of a corrosion resistant alloy of uranium, Zirconium and tin containing approximately 10% uranium, approximately 5% tin and the balance zirconium, and having a metal cladding.

No references cited.

Claims (2)

1. A CORROSION RESISTANT ALLOY OF URANIUM, ZIRCONIUM AND TIN WHICH CONTAINS FROM ABOUT 1 TO 30% URANIUM, FROM ABOUT 1 TO 10% TIN AND THE BALANCE ZIRCONIUM BY WEIGHT.

5. A CLAD URANIUM CONTAINING BODY FOR A NUCLEAR REACTOR, THE CORE OF WHICH CONSISTS ESSENTIALLY OF A CORROSION RESISTANT ALLOY OF URANIUN, ZIRCONIUM AND TIN WHICH CONTAINS FROM ABOUT 1 TO 30% URANIUM, FROM ABOUT 1 TO 10% TIN AND THE BALANCE ZIRCONIUM BY WEIGHT, AND HAVING A METAL CLADDING.