Synroc Derivatives for the Hanford Waste Remediation Task

ABSTRACTThree wt% each of Cs and Tc were mixed with the standard Synroc precursor and the ceramic was formed by hot-pressing. Attempts were made to incorporate the Tc as either metal or Tc 4+, using different redox conditions in processing. Volatile losses of Tc during calcination were < 0.1% in all cases. Short-term Tc leach rates when the Tc was present as a metal alloy were in the order of 10−4 g/m /d at 90°C with frequently changed water, and decreased with increasing leaching time. The valence of the Tc was monitored by X-ray absorption spectroscopy at the drying and calcination stages of the production. The general viability of Synroc/glass composites for immobilising the Hanford HLW sludges is further demonstrated by using further refinements of additive schemes for the inactive “All-blend” formulation and initial studies using the U-containing “All-blend” waste formulation.

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Plutonium and Neptunium Incorporation in Zirconolite

MRS Proceedings ◽

10.1557/proc-465-325 ◽

1996 ◽

Vol 465 ◽

Cited By ~ 18

Author(s):

B. D. Begg ◽

E. R. Vance ◽

R.A Day ◽

M. Hambley ◽

S. D. Conradson

Keyword(s):

Absorption Spectroscopy ◽

Valence State ◽

Charge Compensation ◽

Redox Conditions ◽

X Ray ◽

Compensation Mechanisms ◽

X Ray Absorption

ABSTRACTThe incorporation of Pu and Np in zirconolite (CaZrTi2O7) has been investigated over a range of redox conditions. Zirconolite formulations designed to favour either trivalent or tetravalent Pu and Np were prepared by limiting the amount of charge compensating additives available to maintain electroneutrality. From near-edge X-ray absorption spectroscopy the Pu valence state was found to vary with the processing atmosphere, from completely tetravalent when fired in air, and located on either the Ca or Zr sites, to trivalent, when substituted on the Ca site after annealing in 3.5% H2/N2. Np was predominantly tetravalent over the range of redox conditions examined and was readily incorporated on either of zirconolite's Ca or Zr sites. The charge compensation mechanisms at work in different zirconolites are also discussed.

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Further Studies of Synroc Immobilization of HLW Sludges and Tc for Hanford Tank Waste Remediation

MRS Proceedings ◽

10.1557/proc-506-289 ◽

1997 ◽

Vol 506 ◽

Cited By ~ 4

Author(s):

E.R. Vance ◽

K.P. Hart ◽

M.L. Carter ◽

M.J. Hambley ◽

R.A. Day ◽

...

Keyword(s):

Hot Pressing ◽

Argon Atmosphere ◽

Redox Conditions ◽

Phase Assemblage ◽

Iron Group ◽

Glass Composites ◽

Waste Remediation ◽

Reducing Conditions ◽

Tank Waste

ABSTRACTSynroc/glass composites were designed for simulated Hanford HLW sludges containing U (the current “All-Blend” formulation). The composite contained ∼ 50 wt% of simulated HLW (oxide equivalent), to which ∼ 6, 10, 10, and 24 wt% of CaO, Al2O3, TiO2 and SiO2 were added, and melted under an argon atmosphere at 1350°C. The phase assemblage consisted of zirconolite, perovskite, spinel, nepheline, whitlockite and glass as major phases. Seven-day PCT tests yielded values of < 0. 1 g/m2 for all elements studied. The PCT results were tolerant to changes of ∼ 20% of the inventories of the additives, and to variations in redox conditions.Technetium separated out during decontamination of liquid Hanford wastes can be incorporated as metal in hot-pressed Synroc prepared under reducing conditions, and its leach resistance is good (∼ 10∼3 g/m2/day at 70°C), and can be improved by alloying with iron group metals. With a choice of “neutral” (P(O2) ∼ 10−4 atm., near the Ni/NiO buffer) hot-pressing conditions, Tc can also be incorporated as Tc4+, substituting for Ti4+ in the ceramic phases, and in this form, it should be highly leach resistant also.

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