Characterization of Radioactive Slags (NUREG-1703)

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Publication Information

Manuscript Completed: February 2004
Date Published: October 2004

Prepared by:
L.A. Veblen,^1,2
D. Farthing,²
E. O'Donnell,¹ J.D. Randall¹

¹ Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

²Department of Earth and Planetary Sciences
Johns Hopkins University
Baltimore, MD 21218

Prepared for:
Division of Systems Analysis and Regulatory Effectiveness
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

Slag samples from three humid region sites located in the Eastern United States were studied in detail. Since this investigation is generic in nature, the precise locations of the sites are not identified and are referred to as Sites A, B, and C. Site A's slag was formed from a reprocessed Nb-Ta slag that was ground, leached and deposited in settling ponds which were allowed to evaporate. The resulting material was a "rock like," porous, altered material that resembled a sandstone. Site B was the most intensively studied site and it provided valuable information on the physical and chemical form of the original Nb and Ta slag, as well as the Sn slag that was used as the "ore" material. Site C's slag, although not studied in as much detail as the Site B slag, is physically similar to the Site B slag and both sites had (i) glassy slag and (ii) dense dark slags that ranged from fine grained to very coarsely crystalline. Detailed microanalytical data from Sites B and C provide information regarding the degradation of the radionuclide-bearing phases. Uranium and thorium are present in glass, perovskite, calzirtite, zirconolite, and pyrochlore. Cerium and thorium are present in hibonite. These phases are similar to phases in the proposed high-level radioactive waste form SYNROC. Numerous studies provide experimentally determined solubility and leach rates for these phases. These data provide insight into and bounding values for estimates of slag leach rates. Data reduction and a detailed petrological study provide the necessary information for guidance to the NRC's Office of Nuclear Material Safety and Safeguards for license termination at future decommissioning sites.