Niche Waste Streams

Waste streams containing technetium, cesium and strontium pose unique challenges to radioactive waste management. 

Technetium and cesium are both volatile, have isotopes whose half-lives exceed 100,000 years, and are highly mobile in the environment. Consequently they feature heavily in repository performance assessments.  In addition cesium and strontium account for the majority of radiogenic heat generated in fission product wastes.

In this context synrocANSTO has developed a range of waste form solutions that manage the unique risks posed by these waste streams. 

The integration of waste form and process design enables the elimination of volatility concerns during consolidation by the use of hot-isostatic pressing technology. 

The waste forms use extremely durable synroc phases that have demonstrated their ability to incorporate radionuclides and survive in the natural environment over geological timeframes. The resulting matrix achieves maximum waste loadings whilst minimizing associated environmental risks related to off-gas emissions and final repository disposal.   

By overcoming volatility concerns during consolidation, these tailored waste forms also relieve pressure on the off-gas requirements and represent a one-step final immobilization option, resulting in further cost savings. Volatility concerns during consolidation are a major limitation of joule heated vitrification.

These waste forms are designed to be chemically flexible to readily accommodate process impurities and the anticipated compositional variation of the feed stream.  Consolidation options other than hot-isostatic pressing can be used, including sintering and CCIM melting.  

Ceramic waste forms exhibit greater refractory properties than glass. Therefore they can better accommodate radiogenic heating from short-lived cesium and strontium decay without the devitrification problems inherent in glasses, thus permitting higher waste loadings