Uranium-Molybdenum Alloy for Use in a Prompt-Burst Reactor

A large prompt-burst nuclear reactor, “Super Kukla,” required a core of material that would withstand unusually high stress levels resulting from rapid thermal expansion and inertia loads. An experimental investigation was undertaken to determine the properties of cast uranium—10 wt percent molybdenum alloy under static and dynamic conditions of loading at various temperatures for application in this reactor. Techniques were developed to cast, inspect by radiographic and ultrasonic means, machine, and nickel plate the material. Castings are in the form of rings, 30 in. OD, 18 in. ID, and 2 in. thick. Sound material with carbon content of less than 250 ppm was found to have a static yield strength of approximately 130,000 psi, ultimate strength of 133,000 psi, and elongation of 10 percent at room temperature. Sustained static loads of more than 40,000 psi in a normal atmosphere were found to induce a brittle fracture attributed to stress corrosion. Test specimens subjected to strain rates on the order of 20 in/in/sec withstood stresses of 200,000 psi in the gage region, but usually failed in the threaded ends.