Dechlorination Apparatus For Treating Chloride Salt Wastes: System Evaluation And Scale-Up

This paper describes an apparatus used to remove chlorine from chloride salt-based nuclear wastes from electrochemical reprocessing and/or chloride-based molten salt reactors (MSRs) through dechlorination by reacting the salts with ammonium dihydrogen phosphate (NH4H2PO4 or ADP) at temperatures up to 600 °C to produce NH4Cl as a byproduct. The benefits of removing the Cl from these salts include 37Cl recovery from Cl-based MSR salts, formation of UCl3 from the NH4Cl, as well as removal of Cl from the salts and conversion of the salt cations to oxides to allow for immobilization in a chemically durable iron phosphate waste form. This generation-2 system is an improvement over the generation-1 system and provides a means for scaling up salt throughput as well as NH4Cl recovery. The generation-2 system includes a five-zone furnace so the temperature of the four-zone gradient furnace can be tailored to control the location of NH4Cl condensation on a four-piece fused quartz off-gas system. Both ADP and NH4Cl decomposition reactions include the production of NH3 and acids (i.e., H3PO4 and HCl, respectively), so careful temperature control is needed during the ADP-salt reactions to maximize the NH4Cl production and minimize NH4Cl decomposition. In two sets of experiments run in the generation-1 and generation-2 apparatuses, NH4Cl yields were ≥5.5-fold higher for the new system compared to the original prototype system and the batch sizes can be ≥2.5-fold higher. In addition, some thermodynamic experiments evaluating the reactions of ADP + KCl as well as decomposition of pure NH4Cl were performed to assess the temperatures of the reactions and identify off-gas products

Synthesis Of Dysprosium Oxychloride (DyOCl)

Dysprosium oxychloride, DyOCl, was synthesized using a simple hydrolysis method with DyCl3·6H2O. X-ray powder diffraction (XRD) data was used to determine the crystal structure. The DyOCl compound is isostructural to the matlockite (PbFCl) crystal structure and crystallizes in the tetragonal P4/nmm (#129) space group. The crystal structure contains the alternating cationic layers of (DyO)n and anionic layers of nCl− along the c-axis. The structural data including unit cell, volume, and density of DyOCl were compared to other rare-earth oxychloride data from the Inorganic Crystal Structure Database (ICSD) and our previous study on TbOCl. Fourier-transform infrared spectroscopy was performed on DyOCl and peaks observed at 543 and 744 cm−1 were attributed to Dy–O and Dy–Cl. Scanning electron microscopy analysis showed irregularly shaped crystals. Hot-stage XRD, thermogravimetry, as well as differential scanning calorimetry coupled to a gas chromatograph and a mass spectrometer (evolved gas analysis) were performed on DyCl3·6H2O to understand the phase transformation to DyOCl (and Dy2O3) as a function of temperature and time at temperature. Graphic Abstract: DyOCl compound with the tetragonal P4/nmm space group is composed of the alternating layers of (DyO)n and nCl− along the c-axis

CHARACTERIZATION OF SODALITE BASED WASTE FORMS FOR IMMOBILIZATION OF 129I

Sodalite was investigated for application in waste forms for immobilization 129I. The goal of this research is to develop a chemically durable glass-bonded sodalite waste form for immobilization of 129I. The study is focused on 1) the synthesis and characterization of iodine-containing sodalite mineral, 2) the synthesis and characterization of glass-bonded iodosodalite waste form, and 3) understanding the formation of sodalite with different anions.Sodalite is a microporous mineral that can incorporate alkali halides within the β-cage. The chemical formula of natural sodalite and iodosodalite are Na8(AlSiO4)6Cl2 and Na8(AlSiO4)6I2 respectively. For 1), the optimal condition for the hydrothermal synthesis of iodosodalite was determined by studying the effects of different process variables including pH, temperature, precursor concentration, Al/Si ratio, aging time, and precursors.For 2), the glass-bonded iodosodalite waste form was synthesized and investigated. The hydrothermally grown iodosodalite powder was mixed with 10 or 20 mass% of the borosilicate glass binders, pressed into pellets, and heat-treated at 650, 750, and 850°C. The iodine quantification and chemical durability test in addition to the standard characterizations were performed to understand the efficiency of the final product as the waste form.For 3), the selectivity of anions for the β-cage was investigated by comparing the experimental and computational results. For the experimental study, the sodalites with mixed anions, including I-, Cl-, and OH-, were synthesized hydrothermally, and the selectivity constant was calculated using the lattice parameter. For the computational study, density functional theory was used to understand the formation of the sodalite with different anions.In addition to this experimental study, background is provided for sodalite, the capture and immobilization of iodine, and the glass ceramic waste form. The appendix section provides general information on the classification of radioactive waste, illustration of various sodalites, and parameters for Rietveld analysis

Synthesis and crystal structure of a neodymium borosilicate, Nd3BSi2O10

A lanthanide borosilicate, trineodymium borosilicate or Nd3BSi2O10, was synthesized using a flux method with LiCl, and its structure was determined from X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA). The structure is composed of layers with [SiO4]4− and [BSiO6]5− anions alternating along the c axis linked by Nd3+ cations between them

Iodine Capture with Metal-Functionalized Polyacrylonitrile Composite Beads Containing Ag⁰, Bi⁰, Cu⁰, or Sn⁰ Particles

The capture of radioiodine from nuclear processes and the mitigation of environmental release are important topic areas of research. Some of the more commonly employed chemisorption-type iodine scavengers reported in the literature are based on metal-exchanged porous sorbents such as Ag-zeolites or metal-functionalized aerogels and xerogels. However, another option is to use zero-valent metals directly that have known high affinities for iodine gas [i.e., I2(g)]. In this study, fine metal particles of Ag0, Bi0, Cu0, and Sn0 were embedded in porous polyacrylonitrile (PAN) substrates at 75 mass% metal loadings within the form of ellipsoidal beads with maximum diameters of ∼2–3 mm. These composite beads showed extremely high iodine loadings that are directly related to the metal particle loadings. The X-ray diffraction (XRD) analyses of Ag0, Bi0, Cu0, and Sn0 particles as well as metal-PAN composite beads reacted with iodine gas at 120 ± 1 °C showed phases of AgI, BiI3, CuI, and SnI4, respectively. For the Ag-PAN, Cu-PAN, and Sn-PAN beads, no other crystalline peaks were observed in XRD for unreacted metal or oxidized metals after 48 h in saturated I2(g) at 120 ± 1 °C, whereas unreacted metallic Bi0 was observed within the Bi-PAN composites. However, after a 72 h exposure at 120 ± 1 °C, both the Bi0 particles and the Bi-PAN composites showed full conversion from Bi0 to BiI3 with XRD. Comparisons between mass uptake data and X-ray absorption spectroscopy were used to better understand the phase distribution of the Bi phases present in the Bi-PAN+I composites. The iodine loadings (mg iodine per g sorbent, or qe) for these materials were 1120 (Ag-Particle), 1382 (Bi-Particle-72h), 1033 (Cu-Particle), 3000 (Sn-Particle), 753 (Ag-PAN), 1012 (Bi-PAN-72h), 1457 (Cu-PAN), and 1669 (Sn-PAN). It is possible that inexpensive sorbents such as these could be deployed to help limit or prevent release of radioiodine to the environment