Thermal Cycling Tests on U-10 W/o Mo for the Ornl Fast Burst Reactor PDF Download

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One of the uncertainties concerning the use of uranium-10 wt.% molybdenum in the ORNL Fast Burst Reactor is the thermal-cycling behavior of this alloy. Accordingly, an experimental program was undertaken to determine whether transformation or distortion of gamma-phase uranium--10 wt.% molybdenum can occur during simulated fast-burstreactor thermal cycling, and, should transformation occur, to establish the thermal cycling behavior of partially transformed uranium- - 10 wt.% molybdenum. Specimens were prepared by vacuum casting pins in coated- graphite molds, homogenizing the castings at 1650 deg F for 24 hr, and centerless grinding and cutting to 0.158-in. diameter by 1.5 in. long. The pins were sealed in evacuated Vycor tubes, heated rapidly both above and below the gamma- transformation temperature. and then cooled slowly to simulate reactor thermal cycling. Measurements of the time required to initiate transformation by conventional isothermal methods were employed to insure that the alloy material behaved as indicated in the literature. Observation of changes in appearance, dimensions, density, resistivity, and metallographic structure were used to obtain the desired information. It was found that thermal cycling did not cause growth or distortion of either gamma-phase or partially transformed uranium-- 10 wt.% molybdenum pins. Transformation of gamma phase to alpha + delta was not initiated by thermal cycling below the equilibrium gamma-transition temperature. (auth).