Mass Spectrographic Determination of Hydrogen Thermally Evolved from Uranium and Uranium Alloys G. L. Powell and J. B. Condon Union Carbide Corporation, Nuclear Division, Oak Ridge Y - 1 2 Plant, Oak Ridge, Tenn. 37830
A hot-extraction, high-vacuum technique using massspectrographic detection has been used to determine the hydrogen content in uranium metal and uranium alloys. The time dependence of the evolution of hydrogen from the bulk metal and that from surface contamination was sufficiently different to resolve these two components. During the transient temperature portion of the analysis the hydrogen evolution rate from various uranium alloys was strongly influenced by the solubility of hydrogen in the alloy. Hydrogen due to sample surface contamination was approximately 0.5 weight-parts-per-million (wppm) which limited the lower limit of detection for bulk hydrogen to 0.05 wppm. Diffusion coefficients for hydrogen in uranium alloys were determined from hydrogen evolution rate data.
This report describes a set of experiments necessary for the development of a procedure to be used for routine determinations of hydrogen in uranium and two uranium alloys over the range of 0.05 wppm to 100 wppm. These experiments demonstrate t h a t the method for time resolving hydrogen evolved from the sample bulk from t h a t due to surface contamination reported for tungsten-nickel-iron alloys ( 1 ) is applicable to a large number of metals and alloys provided the unique properties of each metal or alloy are properly characterized. Uranium metal readily absorbs hydrogen as interstitial solute a t elevated temperatures, and upon cooling the metal to room temperature, this hydrogen precipitates within the metal as uranium trihydride (2, 3). I t has been reported t h a t 0.5 weight-parts-per-million (wppm) hydrogen in uranium shifts the ductile-brittle transition for the metal from room temperature to approximately 100 "C ( 4 ) ; thus, trace quantities of hydrogen can significantly alter the mechanical properties of uranium. Trace amounts of hydrogen may also affect the mechanical properties of uranium alloys, particularly those alloys containing elements from Groups IVB and VB of the Periodic Table since these elements should tend to increase the hydrogen affinity of the alloy relative to that for pure uranium. In order to determine the effects of trace amounts of hydrogen on the mechanical properties of uranium and uranium alloys, precise determinations of hydrogen in the bulk metal below the 1 wppm level are required. Below the 1 wppm level, the hydrogen due to sample surface contamination contributes significantly to the total amount of hydrogen thermally extracted from a uranium sample.
EXPERIMENTAL The instrument used for the hydrogen analyses was that described by Condon e t al. ( 5 ) .The operational mode of the instru(1) G .L. Powell, Anal. Chem.,'44, 2357 (1972). (2) M . W . Mallett and M. J. Trzeciak, Amer. SOC. Metals, Trans. Quart., 50,981 (1 958). ( 3 ) J. 6. Condon and E. A. Larson, J . Chem. Phys., 59,855 (1973). (4) W. D. Davis, "Effect of Hydrogen on the Ductility of Uranium," U.S. A t . Energy Comm. Rep., KAPL-1548, Knolls Atomic Power Laboratory, pp. 50-67, ( 1 956). (5) J. 6. Condon, R. A. Strehlow, and G . L. Powell, Anal. Chem., 43, 1448 (1971).
ment as well as the method for determining the time-temperature profile of a typical sample during analysis was the same as that reported for tungsten-nickel-iron alloys ( I ) . A nominally 1.5-gram sample a t room temperature was dropped into an evacuated quartz furnace maintained a t a fixed temperature, usually 900 "C. The rate of evolution of hydrogen from the sample and the total amount of hydrogen evolved from the sample in micrograms were displayed on a two-channel recorder in real time. The samples used were taken from uranium metal, uranium0.75% titanium alloy (to be referred to as U-Ti alloy) and uranium-7.570 niobium-2.570 zirconium alloy (U-Nb-Zr alloy) (all percentages are by weight). Except for the alloying elements and hydrogen, the total of all other elements (impurities) in these alloys was
