The development and evaluation of SYNROC for high-level radioactive waste immobilization

The current status of SYNROC evaluation and development by the Australian Atomic Energy Commission is reviewed. The methods used for the evaluation of leach, irradiation, thermal and mechanical stability of SYNROC are described. A range of tests show that SYNROC is more leach resistant than borosilicate glasses over the temperature range 45-300 deg. C. Because of its excellent stability under hydrothermal leach conditions at 300 deg. C, SYNROC could be used to immobilize and dispose of high-level waste without long periods of engineered storage likely to be necessary for borosilicate waste glass. Accelerated radiation damage testing using fast neutrons has simulated storage times of up to 9x105 years. The results indicate that actinide decay damage is unlikely to cause deleterious effects in SYNROC for at least 2x105 years and, even after much longer times, no great increase in leach rate is expected. SYNROC has been fabricated on a 30 kg scale using 'in-can hot-pressing'. Candidate processes are being evaluated for inclusion in a proposed engineered pilot plant for SYNROC fabrication. (author)