Chrompik was used as a cooling mediumfor storage of A1 nuclearpower plant spent fuel assemblies before their transport outside Slovakia. It was found that the main and crucial problem related to thermal treatment of part of Chrompik, denoted as Chrompik III with a specific activity of 137Cs approx. 1×10¹¹ Bq/dm³ (respectively approx. 1×10¹² Bq/dm³ after densification of liquid Chrompik III) is in the long-term drying and follow-up melting with origin glass frit (so called LKU). Thermal treatment process caused a strong evaporation of 137Cs, mainly during vitrification of this mixture (hereinafter referred to as the ‘vitrification mixture’). 137Cs represents a substantial part of radionuclides in this liquid solution. The vitrification process causedthe evaporation of 137Cs, which exceeded limit values according to the Slovak and international standards.

In order to suppress evaporated 137Cs during the melting–vitrification process of Chrompik III implemented by the national decommissioning and waste management organization JAVYS Inc., were in companyVUJE Inc. (both Slovakia) developed novel original additives. These additivesare additions to the vitrification mixture composed with origin glass frit and origin glass. Composition of additives is based on thermal activated (methakaolinite) geopolymer. High efficiency of additives on suppression of 137Cs evaporation, during all process of thermal treatment and first of all melting–vitrification, was observed.

The results at the end of vitrification process showed that the efficiency of retention activity is on the level approx. 99.996% of input value.

Laboratory research was also carried out on the purification of radioactive waste gases and the capture of 137Cs on the surface of natural zeolite grains, containing a natural glassy phase softened at high temperature. It was found, that 137Cs is captured on surface of these softened glassy phase. 

In order to eliminate leaching radionuclide from matrix obtained from the process of vitrification, was for long-term storage proposal the process of additional covering of this matrix with a glass phase with high resistance to water, from example with basalt glass.