Volatile Impurities in the Plutonium Immobilization Ceramic Wasteform Page: 2 of 10
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Savannah River Defense Waste. The development of the phase formation and mineralogy of a tailored
high-alumina ceramic wasteform to immobilize Savannah River Defense Waste was demonstrated by
Morgan et a13. A dissolution study of the tailored alumina wasteform with all of the expected minor
components added suggested that the amorphous phase formed at grain boundaries governed the chemical
durability of the ceramic4. Further experiments indicated that an increase in the phase forming materials
mitigated the effects of the amorphous phase. Concurrently, SYNROC, a titanate ceramic, also was being
developed as a wasteform for nuclear wastes. Buykx et al.6 concluded that an impurity level of less than
three weight percent did not inhibit the formation of the major rad-bearing phases in an alumino-titanate
wasteform with varying quantities of common waste stream impurities. However, a simultaneous increase in
the level of impurities resulted in ceramics with high porosity and unacceptable durability. Lumpkin et al.7,
determined that in SYNROC C (primarily hollandite, zirconolite and perovskite), the addition of impurities
associated with the Savannah River Defense Waste did not strongly affect the partitioning of the uranium
and rare earth elements. In this study, three wasteform compositions, including the baseline composition,
were used to verify the ability of the ceramic wasteform to accommodate impurities.
Approximately 18 of the 50 metric tons of plutonium identified for disposition contain significant quantities
of impurities. A titanate-based ceramic waste form is the chosen option for immobilization of the excess
plutonium. The primary desired phase for the ceramic is a highly substituted pyrochlore, ideally
Cap 89Gdo.22Hfo.23U0.44Puo.22Ti207 with an excess of HfO2 substituted TiO2(ss). Other phases that may
form, depending upon the impurities present, include zirconolite, brannerite, monazite, perovskite and a
silica-based amorphous phase. Table I8 is the relative abundance of the observed phases in the baseline
composition and in the baseline composition with various impurities added.
Table I. Targeted, Observed and Acceptable Ranges of Phase Abundance with Impurities.
Baseline Observed Range Acceptable Range
Mineral Vol. % Vol. % Vol. %
Pyrochlore 80 62 - 90 >50
Brannerite 12 0-22 0-50
Zirconolite 0 0- 25 0-50
Rutile 8 0-16 0-20
Actinide Oxide 0.5 0.04 - 0.6 0-1
Other Minor Phases 0 0 - 6 0-10
(e.g. monazite, perovskite)
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Cozzi, A.D. Volatile Impurities in the Plutonium Immobilization Ceramic Wasteform, article, October 15, 1999; South Carolina. (digital.library.unt.edu/ark:/67531/metadc622583/m1/2/: accessed February 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.