Immobilization of separated Tc and Cs/Sr in Synroc
- ANSTO, Menai, New South Wales (Australia)
In some radwaste applications, such as immobilization of Hanford Tank wastes using vitrification, Tc and Cs/Sr are likely to be separated out from HLW supernates. Simplified Synroc preparations can be devised for the immobilization of separated Tc and Cs/Sr, either together or individually. Under suitably reducing processing conditions, Tc can be immobilized as metal or Tc{sup 4}. The volatility of Tc and Cs/Sr in Synroc processing is very restricted. In Synroc-C, designed for Purex high-level reprocessing wastes, Tc exists as a metal alloy. In air-saturated water, normalized MCC-1 type total differential leach rates at 90 C decreased with leaching time and after 90 days were < 10{sup {minus}4} g/m{sup 2}/d, decreasing by a factor of {approximately} 100 in anoxic conditions. The corresponding results in a pH = 6.1 buffer solution were fairly similar to those in deionized water, but in anoxic conditions, the leach rates were higher in the buffer solution than in the deionized water. A single perovskite phase was loaded with ca 40 wt% of TcO{sub 2} to form CaTc{sub 0.5}Ti{sub 0.5}O{sub 3} by a combination of graphite-die hot-pressing and heating in argon. Rutile, intended to be doped with ca 35 wt% TcO{sub 2}, was fabricated by bellows hot-pressing at 1,200 C; approximately 75% of the Tc formed a solid solution with rutile, but some metallic Tc was also present due to imperfect redox control. Results of both MCC-1 and PCT-type leach tests are presented on a preparation containing 70 wt% hollandite + 20 wt% perovskite + 10 wt% rutile containing about 5 wt% of Cs and Sr respectively. Phase distributions resulting from incorporating Cs and Sr in Synroc-B precursor were studied.
- OSTI ID:
- 264432
- Report Number(s):
- CONF-951155--; ISBN 1-55899-315-0
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CERAMICS
CESIUM
EXPERIMENTAL DATA
HANFORD RESERVATION
HIGH-LEVEL RADIOACTIVE WASTES
HOT PRESSING
LEACHING
LOADING RATE
LOW-LEVEL RADIOACTIVE WASTES
PHASE STUDIES
REMEDIAL ACTION
SEPARATION PROCESSES
STORAGE FACILITIES
STRONTIUM
SYNROC PROCESS
SYNTHETIC ROCKS
TECHNETIUM
VITRIFICATION
WASTE FORMS