High volume reduction and group separation of simulated fission products by cold crucible

An advanced technology of SHTM (Super High Temperature Treatment Method) using an induction cold crucible for the treatment of fission products generated after the reprocessing of spent fuel is proposed as the future stage of the current vitrification. Without adding any glass materials, 2 000 g of simulated fission products consisting of 23 elements, including lanthanides oxides simulating highly active nuclides and corrosion products, together with the minimum amount of reducing agent were inductively heated up to 2000degC, followed by melting and solidification in a convergent type cold wall crucible. Internal diameter of the crucible, applied electric power and the frequency was 100 mm, less than 100 kW and 25 kHz, respectively. As a result, highly volume-reduced materials, approximately 1/20 of the current vitrification, was obtained. Platinum metal group, such as palladium and ruthenium, got together in the center and bottom of the crucible, surrounded with the titanium oxides immobilizing lanthanides elements. Validity of the process concept was confirmed experimentally. A cylindrical mathematical model with three phases coupled with electromagnetic field, heat conduction and mass balance has been developed to get better understanding of SHTM. The model predicts the presence of critical value of magnetic flux density and the initial dimension of the pre-treated fission products that triggers the whole melting of the fission products in the crucible surrounded with the cold wall. Reaction free layer of fission products plays an important role for the melting. There exits an optimal intensity of the magnetic flux density sustaining high temperature of the material near the cold wall. (author)