Release of Neptunium, Plutonium, Uranium and Technetium from the Metallic Waste form from the Electrometallurgical Treat
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RELEASE OF NEPTUNIUM, PLUTONIUM, URANIUM AND TECHNETIUM FROM THE METALLIC WASTE FORM FROM THE ELECTROMETALLURGICAL TREATMENT PROCESS S. G. Johnson, M. Noy, T. DiSanto and T. L. Barber Argonne National Laboratory-West P.O. Box 2528 Idaho Falls, ID 83403 ABSTRACT This waste form is an alloy consisting of stainless steel with 15 wt% zirconium and acts as a host for the immobilization of radioelements that remain with the spent fuel cladding hulls following their treatment using an electrometallurgical treatment process. The results presented here are from 14, 34 and 90-day immersion tests conducted at 90 °C. These tests show that the release of uranium is considerably higher than that of all other major elements present (Fe, Cr, Ni, Zr), but that release of all constituents is comparable to or lower than that for borosilicate glass. INTRODUCTION Argonne National Laboratory is developing an electrometallurgical treatment for spent metallic fuel from the Experimental Breeder Reactor II [1]. A product of this treatment process is a metallic waste form that incorporates the stainless steel cladding hulls, zirconium from the fuel and the fission products that are noble to the process, i.e., Tc, Ru, Pd, Rh, Ag. The nominal composition of this waste form is stainless steel/ 15 wt% zirconium/ 1-4 wt% noble metal fission products/< 11 wt% uranium. The process used to produce the metallic waste form ingots from the cladding hulls is straightforward. Spent fuel is chopped into small segments and placed into an electrorefiner where the fuel is anodically dissolved into a molten salt electrolyte. The hulls, after being removed from the electrorefiner, are introduced to a furnace where the adhering salt from the electrorefiner is distilled off. The hulls are then placed into a crucible and, if necessary, small amounts of trim chemicals are added, such as zirconium or stainless steel, to adjust the composition to match the target range. The casting takes place at 1650 °C with a 2 hour hold. The finished product is an ingot approximately 40 cm in diameter and 10-15 cm thick. The behavior of actinides, specifically, U, Pu, and Np, and also Tc is evaluated using a standardized leach test modeled after American Society of Testing and Materials standard C1220 [2]. The behavior of these elements is of interest in a geologic repository setting. The relatively simple test employed here will not yield sufficient information to effectively model the performance of the metallic waste form in a geologic repository. It will yield, within the limitations of the test conditions used, the relative release behavior of the various elements that make up this multi-phase waste form. This information can then be used to revise the existing model [3]. Readers interested in a discussion of the current corrosion model for the metallic waste form are encouraged to read ref. [3]. The metallic waste form (MWF) is a mixture of two phases of Fe2Zr-type intermetallic and an iron solid solution phase (stainless steel phase), see figure 1. The intermetallic phase a
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