Uranium Metal Reaction Behavior in Water, Sludge, and Grout Matrices

Abstract

This report was originally published in September 2008. In May 2009, it was discovered that, in the introductory paragraphs of Section 2.1, the units for the reaction enthalpy of uranium metal with water to form uranium dioxide and hydrogen and the reaction enthalpy of hydrogen with oxygen to form water were incorrectly given as kcal/mole rather than kJ/mole. This version of the report, Revision 1, corrects the units for both enthalpies to kJ/mole. Other small editorial changes also were made.iii SummaryThis report summarizes information and data on the reaction behavior of uranium metal in water, in water-saturated simulated and genuine K Basin sludge, and in grout matrices. This information and data are used to establish the technical basis for metallic uranium reaction behavior for the K Basin Sludge Treatment Project (STP). The specific objective of this report is to consolidate the various sources of information into a concise document to serve as a high-level reference and road map for customers, regulators, and interested parties outside the STP (e.g., external reviewers, other DOE sites) to clearly understand the current basis for the corrosion of uranium metal in water, sludge, and grout.The generation of hydrogen gas through oxidation/corrosion of uranium metal by its reaction with water can potentially create a flammable atmosphere during sludge handling, grouting, or subsequent transport and storage operations. Consequently, a thorough understanding of the uranium metal content and its reaction behavior, both in sludge and in grouted sludge matrices, is essential to the process designs and for management of sludge. Results of studies of this reaction and its characteristics have been reported in the technical literature for over 60 years. More focused studies of the reaction in simulated and genuine K Basin sludge and in grout matrices have been conducted in the past 10 years. The outcomes of these studies, provided in the present review, show that: The reaction of uranium metal with anoxic liquid water is highly exothermic and produces stoichiometric uranium dioxide (UO 2 ) and hydrogen. The reaction apparently proceeds through a uranium hydride intermediate that can sequester part of the hydrogen during the initial reaction. The corrosion reaction occurs isotropically such that the uranium particle size decreases at a constant rate at a given temperature. Based on a survey of 32 studies giving 128 data points, the corrosion rate follows an Arrhenius dependence on temperature (i.e., the logarithm of the rate is proportional to the inverse absolute temperature) from at least 24°C to 350°C. The rate law was adopted for the STP. A 95% confidence level on the predicted rate is plus/minus about a factor of three. The STP rate law is essentially the same as used in the application to license the Yucca Mountain repository. Dissolved oxygen inhibits the reaction of uranium metal with liquid water, but the more rapid anoxic reaction can follow the lower oxic rates at times that are difficult to predict...

Becquerelite mineral phase: crystal structure and thermodynamic and mechanical stability by using periodic DFT

“…21,22 Becquerelite phase has been observed as alteration product of spent fuel in cooling basins at the Hanford, Washington site. [23][24][25][26] A contaminant release model 23 was developed to evaluate the release of uranium and other contaminants in the residual sludge of Hanford waste tanks based on the experimental results of waterleaching, selective extractions, empirical solubility measurements, thermodynamic modeling and solid phase characterization. These studies highlighted the importance of the availability of accurate thermodynamic data for the secondary phases of spent nuclear fuel as becquerelite.…”

Evaluation of Settler Tank Thermal Stability during Solidification and Disposition to ERDF

“…This reaction is highly exothermic (ΔH reaction, 298 = -513.2 kJ/mole of uranium) and continues under anoxic conditions at practically the same rate (i.e., largely within a factor of ±3 of the nominal rate) irrespective of whether the uranium metal is in liquid water, saturated water vapor, wet sludge, or even within grout over wide varieties of grout composition or dryness (Delegard and Schmidt 2009). The corrosion rates of non-irradiated uranium metal observed in liquid water and grout (mostly Portland cement but also magnesium phosphate) systems are shown in Figure 5.1.…”

“…Uranium metal corrodes in anoxic liquid water according to the following reaction to form flammable hydrogen gas, H 2 , and uranium dioxide, UO 2 (Delegard and Schmidt 2009):…”

“…Therefore, for most of the modeling cases, the uranium surface area is conservatively assumed to remain constant. This approach is not unreasonable, since reaction rates in a bed of uranium particles remain essentially constant during the time period when the first ~70 mass% of a bed of uranium metal particles are consumed (Delegard and Schmidt 2009;Schmidt et al 2003;and Appendix G of Schmidt and Sexton 2009). In most of the cases modeled, conditions of thermal instability or thermal runaway, if reached, occurred within a period of days.…”

“…Uranium Metal Corrosion Rate Data in Liquid Water and in BNFL Portland Cement Grouts and PNNL Portland Cement and Magnesium Phosphate Grouts(Delegard and Schmidt 2009) …”