Characterization of a Ceramic Waste Form Encapsulating Radioactive Electrorefiner Salt
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Argonne National Laboratory has developed a ceramic waste form to immobilize radioactive waste salt produced during the electrometallurgical treatment of spent fuel. The first ceramic waste forms that immobilize the radioactive waste salt have been produced. This study presents the first results from electron microscopy and durability testing of a ceramic waste form produced from that radioactive electrorefiner salt. The waste form consists of two primary phases: sodalite and glass. The sodalite phase appears to incorporate most of the alkali and alkaline earth fission products. Other fission products (rare earths and yttrium) tend to form a separate phase and are frequently associated with the actinides, which form mixed oxides. Seven-day leach test results are also presented. INTRODUCTION
Argonne National Laboratory processes EBR-II spent fuel by an electrometallurgical treatment [1]. This treatment creates a radioactive salt waste stream containing transuranics and fission products. To immobilize the radioactive salt, a ceramic waste form has been developed [2-3]. The ceramic waste form (CWF) is produced by blending salt and zeolite 4A at approximately 773 K resulting in a salt loading of about 10.5 wt%. A composition of the electrorefiner salt incorporated into the waste form is given in Table I. The salt-loaded zeolite is then mixed with glass (in a weight ratio of 3:1) and hot isostatically pressed to obtain a consolidated, durable waste form. The maximum temperature and pressure within the hot isostatic press were 1123 K and 100 MPa. For the CWF, the uranium content is 0.5 wt% while the plutonium content is 0.02 wt% and neodymium, the dominant rare earth, is 0.05 wt%. Table I. Measured Composition of Electrorefiner Salt Incorporated in the Ceramic Waste Form. Element Measured wt % Element Measured wt % Li 5.87 La 0.21 Na 1.9 Ce 0.42 K 21.3 Pr 0.21 Cs 0.66 Nd 0.70 Sr 0.15 Sm 0.21 Ba 0.25 Np 0.0265 Y 0.12 UT 7.207 Fe 0.066 Put 0.291 C!1 57.63 tlsotopic compositions are approximately 60% "•U, 40% 738U and 99% ... Pu, rest 24°Pu and 238 Pu.
tCalculated assuming anionic composition is 100% CI and standard chloride stoichiometries for
all elements (3 chlorides for all rare earths and actinides). Analyses for iodide and bromide were not performed but are expected to be 350 ptg/g and 45 jgg/g, respectively. 577 Mat. Res. Soc. Symp. Proc. Vol. 608 0 2000 Materials Research Society
EXPERIMENTAL Both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed. The SEM was done with a Zeiss DSM 960A scanning electron microscope
(Thornwood, NY).
Energy dispersive and wavelength dispersive x-ray spectroscopy
(EDS/WDS) was done by interfacing the detectors and instrumentation of the microscope to an Oxford ISIS series 300 x-ray analysis system, software version 3.2, and the Oxford software Winspec, version 1.3 (Oxford, UK). The TEM was performed with a JEOL 2010 transmission electron microscope (Peabody, MA) operated at 200 kV, and equipped with a LaB 6 filament and EDS detector. Th
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