Vitrification is the technology used worldwide for treating high-level radioactive waste (HLW) and some forms of low-activity radioactive waste (LAW). This is an immobilization process in which the waste is melted, incorporated in a borosilicate glass matrix and cast into steel canisters for subsequent deposition in underground repositories.

GSI’s processes are based on geological concepts which can be applied to other glass or mineral-based technologies in order to enhance their waste loadings (the amount of waste incorporated in a given volume of the final immobilization product). In addition, our technologies are cleantech, significantly reducing the volume of the treated waste that is sent to interim storage and final underground repositories.

GSI has developed three different processes for enhanced immobilization of radioactive waste. Of these, GSI-2000 is the most applicable to active vitrification plants as it can be implemented in existing facilities requiring modifications only to the process ingredients. GSI-2000 can also be implemented with other vitrification technologies such as GeoMelt Bulk Vitrification. GSI’s Mineral Encapsulation expertise can be used to enhance mineral-based technologies such as Fluidized Bed Steam Reforming. Although GSI is currently targeting radioactive waste, our technologies are also suitable for other hazardous materials.


  • Novel glass compositions enabling vitrification with higher waste loadings
  • Liquid-fed ceramic melter technology – can be deployed in active processing plants
  • Satisfies processing and product quality requirements for currently operational vitrification facilities

The GSI-2000 series are processes for formulating glass for enhanced vitrification performance, with significantly improved waste loadings. GSI-2000 is adjusted to fit specific waste compositions and is suitable for both HLW and high alkaline LAW. The GSI-2000 glass is structured to resemble natural glass. Consequently the GSI-2000 glass is more stable and facilitates higher waste loadings than standard vitrified glass. GSI-2000 has been applied to several waste compositions and has shown significantly improved waste loading performances (refer to Cost Savings).

Mineral Encapsulation

  • High waste loadings achieved
  • Waste form has greater stability than borosilicate glass
  • Improved compatibility between treated waste form and host rock in repository
  • Final waste form: immobilizing minerals enclosed within natural glass
  • In-canister process
  • Single-step heating (~1150°C) and cooling procedure
Mineral Encapsulation is an alternative technology to vitrification, in which HLW is encapsulated within a mineral and a surrounding rock matrix. This provides four barriers against leaching and diffusion of the radioactive waste once buried in the geological repository:

Barrier 1 involves integrating the HLW in an immobilizing mineral.
Barrier 2 protects the immobilizing mineral with a 30-50 micron non-radioactive mineral layer of the same composition as the immobilizing mineral. (A 30 micron covering provides approximately 200,000 years protection and a 50 micron covering provides protection for approximately 1 million years).
Barrier 3 is formed by surrounding the above in a rock matrix, in which more HLW is incorporated.
Barrier 4 - The composition of the surrounding rock matrix is identical to the rock found in the repository. Any ground water that may reach the immobilized waste hundreds of meters below ground will have approached chemical equilibrium with components of the rock-covering of the encapsulated waste product. Thus, the ground water will be almost non-reactive to the treated waste product.

GSI has tested this process specifically for immobilizing lanthanoid and actinoid elements. Due to high viscosity, Mineral Encapsulation is an in-canister process (heated and cooled in its final canister) and is not suitable for liquid-fed ceramic melters used for standard vitrification.

Solid Waste Ceramic Immobilization (SWCI)

  • High waste loadings achieved
  • Suitable for solid waste
  • Final waste form: immobilizing minerals enclosed within durable ceramic
  • In-canister process
Both GSI-2000 and Mineral Encapsulation immobilize liquid HLW. For solid HLW (calcine), GSI has developed Solid Waste Ceramic Immobilization (SWCI). In this technology, the HLW is almost fully crystallized and forms immobilizing minerals. The final waste form is a dense ceramic containing the immobilizing minerals. This is an in-canister process, with a one-stage heating (~1150°C) and cooling process. GSI has demonstrated SWCI for several waste compositions achieving waste loadings of 80% and greater.