Molten salt dynamics in glass melts using millimeter-wave emissivity measurements

A novel application of millimeter-wave radiometry has been made for the first time to non-contact detection and monitoring of molten salt layer formation on a nuclear waste glass melt (without the nuclear waste) in a joule-heated melter, which could eventually be implemented for on-line monitoring in nuclear waste vitrification facilities. The experiments were carried out at a frequency of 137 GHz in the EV-16 melter at Clemson Environmental Technology Laboratory (CETL) with 245 lbs. (111 kG) of glass and a total of 4.2 lbs. (1.9 kG) of added salt. The dynamics of salt layer build up were observed from the initial formation of small drops of about 5 mm diameter or less to larger pools >28 mm cross-section that were coincident with the increase in millimeter-wave surface level fluctuations causing the salt to flow back and forth until a continuous layer was formed. The millimeter-wave emissivity at 137 GHz of DWPF black frit glass melt and molten sodium sulfate salt at 950 °C was determined to be 0.64 ± 0.05 and 0.44 ± 0.05, respectively.