The Development and Testing of Synroc C as a High Level Nuclear Waste Form
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THE DEVELOPMENT AND TESTING OF SYNROC C AS A HIGH LEVEL NUCLEAR WASTE FORM
K.D. REEVE, D.M. LEVINS, E.J. RAMM, J.L. WOOLFREY AND W.J. BUYKX Australian Atomic Energy Commission Research Establishment, Sutherland NSW 2232 Australia
ABSTRACT The current status of SYNROC C research and development by the Australian Atomic Energy Commission is reviewed. A non-radioactive fabrication demonstration line designed to produce 10 cm o.d., 90 cm long, cylinders of SYNROC canned in stainless steel by the method of in-can hot pressing is being commissioned. Leach tests are proving the excellent leach resistance of SYNROC. Accelerated radiation damage testing using fast neutrons has simulated storage times of up to 6.7 x 105 years. Thermophysical properties of SYNROC have been measured over the temperature range 20-6500C.
INTRODUCTION SYNROC is a synthetic three-phase titanate ceramic, designed [1] on the basis of known geochemistry, for the immobilization of high level nuclear waste at a 10-20 weight per cent level of addition. Collectively, the three SYNROC phases barium hollandite (BaAl 2 Ti 8 O1 6 ), perovskite (CaTiO3) and zirconolite (CaZrTi207) can take into solid solution nearly all of the components of high level wastes. SYNROC, without or with simulated radwaste ('SYNROC B' and 'SYNROC C' respectively) may be synthesized from the component oxide powders or from their nitrates or other precursors and may be densified readily to a finegrained three-phase ceramic by either hot-pressing or cold pressing and sintering. Research and development on SYNROC commenced at the AAEC Research Establishment, Lucas Heights, in March 1979, in association with a complementary program at the Australian National University (ANU) in Canberra. Progress on the Lucas Heights project was reported at Waste Management '81 [2]. The present paper reviews the current status of the project's four main strands. SYNROC FABRICATION DEVELOPMENT Laboratory Process The laboratory process developed during the first two years of the project has been used to prepare all SYNROC C specimens for leaching tests. Briefly, fine powders of TiO2, A1203, ZrO2, BaC0 3 and CaCO 3 are ball-milled in alcohol with zirconia media, sufficient nitric acid is added to convert the carbonates to nitrates and simulated radwaste is added as a nitrate solution (see Table I). The slurry is spray-dried, calcined in a stream of dry argon - 3.5% hydrogen for 16 h at 11000C, then cooled and remilled. At this stage, 2.0 wt% of fine titanium metal powder is added for additional control of oxygen potential during hot-pressing. Formerly, 0.5 wt% of iron powder was used. Hot-pressing is carried out in graphite dies in which the SYNROC C powder is contained within a nickel or iron capsule separated from the die wall by SYNROC B powder. The standard hot-pressing conditions are 12500C and 13.8 MPa, but lower temperatures, and both lower and higher pressures, have been assessed.
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TABLE I Typical SYNROC C composition Component
wt%
Component
wt%
Component
wt%
TiO2 ZrO2 A12
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