Composition optimization of iron phosphate glasses for radioactive sludge

Takebe, Hiromichi*; Kitamura, Naoto*; Amamoto, Ippei; Kobayashi, Hidekazu ; Mitamura, Naoki*; Tsuzuki, Tatsuya*

The great amount of water used for cooling the stricken power reactors at Fukushima Dai-ichi following the earthquake and tsunami on March 11, 2011 has resulted in the accumulation of the remaining water. The water is subsequently contaminated by fission products and some other radioactive substances. The initial treatment to remove the radioactive substances from the cooling water again produced a secondary radioactive waste, the sludge. Iron phosphate glass powder/frit and main component of raw materials for simulated sludge, e.g., barium sulfate and potassium nickel ferrocyanide with various concentrations, were mixed for melting batch. The temperature required for the formation of homogeneous melt was determined by the direct observation of sample decomposition and melting processes on the thermocouple filament through a microscope. The mixtures for bulk glasses were melted in air using platinum crucibles. The quenched glass samples consisted mainly of oxide constituents due to the decomposition of the sludge components during heating and melting processes. Characteristic temperatures of glass transition, Tg, and onset of crystallization, Tx, was determined by differential thermal analysis. Thermal stability against crystallization for the glass samples was evaluated by the temperature difference between Tx and Tg. Water durability was determined by the weight change per a specific surface area after immersion test in hot water at 120C for 72 hours based on MCC-2 static leaching method. Phosphate network species and chemical bonding were characterized by Raman spectroscopy. Glass composition melted with the stimulated sludge components is optimized in terms of both thermal stability and water durability with the characterization of O/P molar ratio.