Mark A. Williamson

Chemical partitioning technologies for an ATW system

Abstract A roadmap for the development of the technology of an Accelerator Transmutation of Waste (ATW) system was recently submitted to the U.S. Congress by the U.S. Department of Energy. One element of this roadmap was a development plan for the separations technologies that would be required to support an ATW system operating with a sustained feed of 1,450 tonnes of commercial light water reactor spent fuel per year. A Technical Working Group was constituted to identify appropriate separations processes and prepare a plan for their development. The baseline process selected combines aqueous and pyrochemical processes to enable efficient separation of uranium, technetium, iodine, and the transuranic elements from LWR spent fuel in the head-end step. For the recycle of unburned transuranics and newly-generated technetium and iodine from irradiated ATW transmuter assemblies, which were given to be metallic in form, a second and quite different pyrochemical process was identified. The diversity of processing methods was chosen for both technical and economic factors; aqueous methods are deemed to be better suited to large tonnages of commercial oxide spent fuel, while it is considered that pyrochemical processes can be exploited effectively in smaller-scale operations, particularly when the application is to metallic fuels or targets. A six-year technology evaluation and development program is foreseen, by the end of which an informed decision can be made on proceeding with demonstration of the ATW system.

Presence of Li Clusters in Molten LiCl-Li

Molten mixtures of lithium chloride and metallic lithium are of significant interest in various metal oxide reduction processes. These solutions have been reported to exhibit seemingly anomalous physical characteristics that lack a comprehensive explanation. In the current work, the physical chemistry of molten solutions of lithium chloride and metallic lithium, with and without lithium oxide, was investigated using in situ Raman spectroscopy. The Raman spectra obtained from these solutions were in agreement with the previously reported spectrum of the lithium cluster, Li8. This observation is indicative of a nanofluid type colloidal suspension of Li8 in a molten salt matrix. It is suggested that the formation and suspension of lithium clusters in lithium chloride is the cause of various phenomena exhibited by these solutions that were previously unexplainable.

The structure of liquid UO2−x in reducing gas atmospheres

High energy X-ray diffraction experiments performed on hypostoichiometric UO2−x liquids in reducing gas mixtures of 95%Ar:5%CO and 95%Ar:5%H2 are compared to that conducted in a pure Ar atmosphere [Skinner et al., Science 346, 984 (2014)]. The measurements are pertinent to severe accident scenarios at nuclear reactors, where core melts can encounter reducing conditions and further shed light on the oxide chemistry of the low valence states of uranium, particularly U(III), which become stable only at very high temperatures and low oxygen potentials. The radioactive samples were melted by floating small spheres of material using an aerodynamic levitator and heating with a laser beam. In the more reducing environments, a 1.7% shift to lower Q-values is observed in the position of the principal peak of the measured X-ray structure factors, compared to the more oxidizing Ar environment. This corresponds to an equivalent elongation in the U-U nearest neighbor distances and the U-U periodicity. The U-O peak (mod...

Phase Equilibria Studies of the LiCl-KCl-UCl3 System

Abstract Regions of the LiCl-KCl-UCl3 phase diagram used to represent the molten salt compositions generated during the electrorefining of used nuclear fuel were evaluated by studying the LiCl-UCl3 and KCl-UCl3 binary systems and several ternary mixtures. Phase transition temperatures of several binary and ternary mixtures made with LiCl, KCl, and UCl3 were measured by using differential scanning calorimetry. Inductively coupled plasma-atomic emission spectroscopy was used to measure the gross compositions of the salt mixtures and X-ray diffraction (XRD) was used to identify the phases formed after they were thermally cycled and had cooled to room temperature. The LiCl-UCl3 system has a eutectic transition at 763 ± 2 K for a mixture with 25 mol % UCl3. The KCl-UCl3 system has two eutectic transitions, one at 827 ± 3 K and another at 805 ± 4 K for mixtures with 19 mol % UCl3 and 57 mol % UCl3, respectively, and the congruently melting compound K2UCl5 was identified to have formed by XRD. The LiCl-UCl3 and KCl-UCl3 binary phase diagrams were developed and combined with the LiCl-KCl phase diagram to produce a portion of the LiCl-KCl-UCl3 phase diagram. The LiCl-KCl-UCl3 system includes two ternary eutectics, one occurring at 681 ± 6 K for the mixture with 33 mol % UCl3, 42.0 mol % LiCl, and 25 mol % KCl, and the other at 619 ± 1 K for the mixture with 8 mol % UCl3, 50.0 mol % LiCl, and 42 mol % KCl. The evaluation of these phase diagrams provides an improved understanding of the LiCl-KCl-UCl3 systems generated during electrorefining.

Corium lavas: structure and properties of molten UO2-ZrO2 under meltdown conditions

In the exceedingly rare event of nuclear reactor core meltdown, uranium dioxide fuel reacts with Zircaloy cladding to produce eutectic melts which can subsequently be oxidized by coolant/moderator water. Oxidized corium liquids in the xUO2·(100 − x)ZrO2 system were produced via laser melting of UO2-ZrO2 mixtures to temperatures in excess of 3000 K. Contamination was avoided by floating the droplets on a gas stream within an aerodynamic levitator and in-situ high-energy x-ray diffraction experiments allowed structural details to be elucidated. Molecular dynamics simulations well reproduced diffraction and density data, and show less compositional variation in thermal expansion and viscosity than suggested by existing measurements. As such, corium liquids maintain their highly penetrating nature irrespective of the amount of oxidized cladding dissolved in the molten fuel. Metal-oxygen coordination numbers vary with both composition and temperature. The former is due to mismatch in native values, nUO(x = 100) ≈ 7 and nZrO(x = 0) ≈ 6, and the requirement for oxygen site stabilization. The latter provides a thermal expansion mechanism.

Conceptual Design of a Pilot-Scale Pyroprocessing Facility

Abstract Argonne National Laboratory and Merrick & Company developed the conceptual design of a pilot-scale (100 T/year) pyroprocessing facility for the treatment of used fuel generated by commercial light water reactors and subsequent treatment of waste streams generated during the process. The primary purpose of this study was to perform sufficient engineering for the pilot facility conceptual design so that credible capital and operating cost estimates could be developed. Initial safety, safeguards, and security assessments were also completed to provide a detailed evaluation in these areas that can significantly affect both capital and operating costs. Electrorefining-based pyroprocessing resulted in a compact hot-cell facility with few process equipment systems. The process equipment and support systems were estimated to cost

Topological ordering in liquid UO2.

93 million and the facility

Development of an Engineered Producet Storage Concept for the UREX+1 Combined Transuraqnic?Lanthanide Product Streams

305 million for a project total cost of

Determining the Exchange Current Density and Tafel Constant for Uranium in LiCl/KCl Eutectic

398 million. The annual operating cost was estimated at

Application of Voltammetry for Quantitative Analysis of Actinides in Molten Salts

53 million/year. Scaling up to a commercial-scale (400 T/year) was also evaluated and the capital cost was estimated at