Formation Of Uranium Hydride Research Articles

Uranium hydride corrosion. I New insights into the Condon-Kirkpatrick model of uranium hydride formation rate

An analytic solution to the uranium hydride formation rate equation of Condon and Kirkpatrick (CK) has been developed, which is directly solved via algebraic operations and requires only gaseous hydrogen (H2) pressure and temperature as inputs. The solution does not depend on the specific functional forms of the hydriding and dehydriding rate constants, nor of key physical parameters. A modified form of the CK model has also been developed, where replacement of the hydrogen solubility function results in an improved fit to published experimental data as H2 pressure decreases toward the corrosion threshold value.

Mechanism of surface uranium hydride formation during corrosion of uranium

Uranium is widely used in the nuclear industry and it is well known that uranium hydride, UH3, forms when uranium is exposed to air. The associated volume change during this transition can cause the surface region to crack, compromising structural integrity. Here, hydriding regions beneath hydride surface craters are studied by secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Our results indicate that strain transition regions exist, which are induced by hydrogen with a certain thickness between hydride craters and the uranium bulk. The SIMS and XPS results suggest that hydrogen exists covalently with uranium and oxygen in these transition regions. A micro-scale induction period model based on the transition region and previous hydriding models is developed. Within the so-called micro-scale induction period, hydrogen diffuses and accumulates at particular sites before reaching the critical concentration required to form stoichiometric UH3 in the transition regions.

Kinetics of the reaction between water and uranium hydride prepared under conditions relevant to uranium storage

The formation of uranium hydride (UH3) during storage of uranium metal poses a hazard owing to its potentially pyrophoric behaviour that affects handling procedures during uranium storage, decommissioning legacy facilities and waste immobilisation. Partial oxidation of UH3 by water significantly reduces its reactivity, which impacts on safety assessments. New measurements of the rate of UH3 hydrolysis are presented for a range of hydrolysis temperatures, UH3 preparation temperatures and under both aqueous and water vapour conditions. The hydrolysis reaction has an initial rapid phase, characterised by consumption of at least 5% of the UH3 and a rapid decrease in the reaction rate. During the second stage of the reaction the reaction rate decreases more slowly with reaction extent and depends strongly on the temperature at which the UH3 was prepared. Evidence suggests that this is, at least in part, caused by the faster reaction of α-UH3 compared with β-UH3. In the final phase the reaction rate decreases to a very low value at 70%–90% reaction extent. The dependence of the reaction kinetics on the temperature of UH3 formation has significant implications for predicting the ignition properties of UH3 and its stability during storage and handling.

Formation and physical properties of uranium hydride under conditions relevant to metallic fuel and nuclear waste storage

The formation of uranium hydride is recognised as a hazard during the storage of uranium metal owing to its potentially pyrophoric properties. This study has assessed the influence of water vapour on the potential for uranium hydride to form at low temperatures and shows that it increases the duration of the induction period but does not necessarily prevent uranium hydride formation and also does not significantly change the reaction rate with hydrogen. It is further shown that the α-UH3 fraction in the uranium hydride gradually increases at decreasing temperatures and is likely to be the dominant phase formed under typical storage conditions. Particle morphology and specific surface area of uranium hydride prepared between 30 °C and 200 °C have also been characterised but show only modest variation compared with the phase composition.

The effects of metal surface geometry on the formation of uranium hydride

The present work examines the effect of surface geometry on the reaction between hydrogen gas and uranium metal, forming uranium hydride (UH3), a pyrophoric compound of significance to the civil nuclear industry. Hydride formation was initiated on uranium samples that had been patterned with a focused ion beam instrument to form surface arrays of triangular prisms and pillars with differing apex angles. Post reaction analysis indicated preferential hydride formation at the apex of these features. Additionally, once hydride formation had commenced the observed growth rate on the prisms appeared to accelerate in comparison to the rate exhibited on the surrounding surface.

Comparison of laser ablation, electrothermal vaporization and solution nebulization for the determination of radionuclides in liquid samples by inductively coupled plasma mass spectrometry

The performance of solution nebulization (SN), electrothermal vaporization (ETV) and laser ablation (LA) of dried micro-droplets as sample introduction systems for ICP-MS are compared for the determination of several radionuclides in digested biological tissue, nearshore sea-water and river water. Samples were subjected to a Ca3(PO4)2 co-precipitation preconcentration prior to analysis. Each introduction system possesses unique advantages and disadvantages. ETV accommodates samples having higher dissolved solids content; consequently, for SN and LA, sample concentrates require additional dilution by 50- and 10-fold, respectively. ETV and LA achieved similar sensitivities and limits of detection, the latter ranging from 0.017 to 0.029 pg ml−1. Although SN provides the best precision (2% RSD versus 7 and 8% for ETV and LA, respectively), formation of uranium hydride can be reduced at least 100-fold using LA of dried micro-droplets of samples. The accuracy of the method was validated by determination of U and Th in NIST SRM 1566b Oyster Tissue, NRC CRM CASS-4 Nearshore Seawater and SLRS-4 Riverine Water and via spike recoveries for Pu.

Uranium Hydride Formation Study as Observed by Scanning Surface Potential Imaging

AbstractUranium is an extremely important material for commercial and military applications (i.e. nuclear power, nuclear weapons, conventional weapons, and armor systems) and, like a number of other materials, is vulnerable to corrosion by environmental gases that affect their properties, leading to component degradation, shortened lifetimes and materials failure. For uranium this is particularly true in the case of corrosion by hydrogen. A fundamental understanding of the corrosion process at the nucleation stage is of critical importance. The goal of this work is to study the role of common chemical impurities in uranium with initiation sites for the formation of destructive hydride blisters. Samples were implanted with various ions, annealed under vacuum at 200°C, than exposed to one atm of ultra-pure hydrogen. Scanning force microscopy surface potential imaging was used to characterize the structure and corresponding electrical properties of polycrystalline uranium surfaces that resulted from the implantation of different suspect atoms after exposure to hydrogen gas. Surface potential images revealed features related to different oxide structures and hydride spots/blisters as well as other features not obvious in the corresponding topograph. In the surface potential images, blisters appear as bright (higher potential) features in sharp contrast to the uranium oxide background. Often a possible inclusion was observed in the center of a blister. Blister formation did not appear to correlate with implantation of any specific specie, however, distinct differences were seen between implanted and non implanted sides of the same sample.

Preventing uranium hydride formation in standard uranium samples for determination of239Pu by ICP-MS

UH+ interference poses considerable difficulties for the determination of 239Pu in samples with high uranium content. A new approach for reducing this interference was developed. Substitution of water with heavy water (D2O) as a solvent in uranium standard solution eliminated the major source of UH+ ions and reduced the UH+/U+ ratio from a typical value of 1.33 × 10−5 to a very low value of 2.60 × 10−7. The method allows the determination of low levels of 239Pu in samples containing 106 fold excess of uranium. The detection limit for 239Pu in a sample containing 10 ppm of uranium was determined as 0.58 ± 0.03 ppt. A kinetic isotope effect of ca. 1.4 was observed for the reaction of U+ with hydrogen (H) compared with the reaction with deuterium (D). The magnitude of this effect is in agreement with the value calculated based on the collision theory.

The initial kinetics of uranium hydride formation studied by a hot-stage microscope technique

The initial stages of the formation of uranium trihydride on the surface of uranium samples reacted with gaseous hydrogen (about 1.5 atm) were studied utilizing a hot-stage microscope. The nucleation and growth processes of the product hydride were continuously monitored with a television camera and were recorded on a videotape. The formation kinetics and the morphological characteristics of the developing hydride phase are discussed. A comparison with the kinetic results obtained in the more advanced bulk hydriding stage is made.

The oxidation behaviour of uranium in air at 50–300°C

The oxidation behaviour of adjusted uranium in air at 1 atm pressure has been examined at 50–300°C, with emphasis on the influence of water vapour at concentrations up to 3×10 4 vpm. The work also covered the effects of prior irradiation of the metal. Temperature had the most pronounced effect and increased the rate of oxidation by a factor of over 10 6 from 50 to 300°C. Water vapour also increased the attack at 100–200°C by up to a factor of 7.5, but was without significant influence at 50, 75 and 300°C. The enhanced attack could be explained by the incorporation of hydroxyl ions in the oxide lattice or by the transitory formation of uranium hydride. Support for the latter explanation was provided by tests in wet air with defected cans containing uranium powder, where oxidant access was limited. The influence of irradiation, to a burn-up of 5600 MWd/t, was governed mainly by the magnitude of the associated swelling. It only became significant for the most swollen (17–21%) material examined, when it increased the attack by factors from 4–90. The mechanism involved the break-up of the uranium surface during oxidation.

Differential Gas Analysis Method -Apparatus and Its Applications-

This apparatus was developed to study the solid-state reactions and physico-chemical changes involving absorption or evolution of gases, and structurally consists of a modified gas effluent analysis equipment and a high-precision gas mixer. The new apparatus is more useful in the fields of inorganic chemistry, organic chemistry, metallurgy, etc. than a conventional EGA equipment.The sample is heated or cooled at the constant rate in a mixed flow of two or more different gases such as He-O2, He-CO2, Ar-H2, etc. The changes in the composition of the gas passing through the reactor due to the decomposition or the gas-solid reaction are detected with high sensitivity by a thermal conductivity detector. The sample weight required for the usual measurement is 5∼50 mg. It is applicable to the range from room temperature to 1600°C and the gas flow of any mixing ratio (200: 1∼1: 200). Although the limits of determination are affected by the operating conditions, an evolution or absoption of 0.01-0.0001 ml of oxygen by the sample in the He-O2 mixture can be detected.This paper describes the following reactions as the applications of this apparatus: reduction of vanadium pentaoxide by hydrogen, thermal decomposition of calcium oxalate monohydrate, oxidation and reduction of iron oxide, formation and decarbonation of calcite, and hydrogenation and formation of uranium hydride.

Hydrogen embrittlement in uranium

Metallographic and mechanical observations of uranium and uranium thermally charged to contain 1.25 ppm to 15 ppm hydrogen are reported. The results have shown that the formation of uranium hydride precipitates is a primary source of embrittlement in uranium-hydrogen alloys and that maximum embrittlement occurs in alloys containing approximately 2.5 ppm hydrogen. The influence of strain rate (2.6 × 10 −2/ sec to 1.3 × 10 −5/ sec) and grain size (0.0075 mm to 0.180 mm) on the fracture stress of thermally charged uranium-hydrogen alloys is also reported. In uranium, cathodically charged to contain uranium hydride precipitates, the embrittlement was shown to be sensitive to the orientation of the precipitates to the tensile axis.

Uranium + water reaction. Part 1.—Kinetics, products and mechanism

The effects of temperature, relative humidity and pH on the rate of the uranium + water reaction have been studied. Linear rates of corrosion and hydrogen evolution are obtained at different temperatures and the derived activation energies vary from 12 to 17 kcal mole–1 depending on the batch of uranium. Hydrogen has no effect on the reaction. The products of the reaction have been investigated under varying conditions of temperature and relative humidity. Parallel studies have been made of the uranium hydride + water system. The data are consistent with an oxide product UO2.06±0.02, containing 2–9% uranium hydride in a protected form. A reaction mechanism is proposed, involving OH– ion diffusion and formation of uranium hydride as a partial intermediate. It is suggested that the rate-controlling step is diffusion of water through fine capillaries to the oxide surface.

The Heats of Formation of Uranium Hydride, Uranium Deuteride and Uranium Tritide at 25°1

The Heats of Formation of Uranium Hydride, Uranium Deuteride and Uranium Tritide at 25°¹

Formation of Uranium Hydride

The formation of uranium hydride (UH3) by the action of hydrogen on massive uranium metal between the temperatures 150° and 375° C. has been described by Burke1.