The effect of ZnO and CaO on the hardness and fracture toughness of basic alkali borosilicate glass immobilizing simulated mixed HLW

Vitricfication is a mature treatment method to immobilize HLW and successfully used since 1970's in around 10 countries, after around fifty-year development and research. Some HLW stream, as UK mixed HLW stream, is rich in transition metal, such as Ni, Fe, Cr, etc., which would take an effect on the long term behavior, weakening their physical and chemical properties of HLW glass. Mechanical properties are important factors to the transportation, handling and storage of the HLW glass production, before the waste form will be finally disposed of in deep geologyical formations. In this paper, four glass matrixes immobilizing those types HLW stream were tested and compared. Those glass samples loaded 15% and 20% waste oxide, and adopted ZnO and CaO, respectively. The hardness test results showed that the glass coupons adopted ZnO and CaO with 20% waste loading had the highest hardness value than others, and N15 got the lowest hardness value; at the same time, the fracture toughness gives same trend as hardness test results, except the glass matrixes adopted ZnO and CaO with 20% waste loading. Those results will be contributed to the safety assessment of above glass matrixes' properties and be helpful for the modified vitrification formulation to effective and safety immobilizing the new HLW stream. (authors)