The immobilisation of HLW requires the formation of an insoluble, solid waste form that will remain stable for many thousands of years. In general borosilicate glass has been chosen as the medium for dealing with separated HLW.  

• The stability of ancient glass for thousands of years highlights the suitability of borosilicate glass as a matrix material. This type of process, referred to as vitrification.  

• Most HLW, other than spent fuel itself, arises in a liquid form from the reprocessing of spent fuel. This HLW comprises highly-radioactive fission products and some transuranic elements with long-lived radioactivity.  
• To allow incorporation into the glass matrix the waste is initially calcined (dried) to a granular powder.  
• The product is then incorporated into molten glass, poured into a robust stainless steel canister about 1.3 metres high, and allowed to cool, forming a solid matrix. The containers are then welded closed and are ready for storage and final disposal. 
• India is one of the few countries to have mastered the technology of vitrification. Over the years BARC has developed the technology for vitrification of HLW.  
• India has a unique distinction of having operating vitrification plant at Tarapur and Trombay.   

• In our existing plant at Trombay vitrification process is essentially batch operation consisting of heating and fusing of pre-concentrated waste and glass forming additives and is carried out in melters based on induction heating. 

Source: The Hindu