A preliminary assessment of salt and radionuclide volatilities in the molten salt processor

We have applied thermodynamic methods to analyze the volatilities of plutonium (Pu), uranium (U), iodine (I), and salts from molten salt processor baths in bench-scale runs conducted by Rockwell International on oxidation of laboratory mixed waste. Good agreement is obtained between calculated and observed volatilities. The volatilizing species of Pu and U have been identified as gaseous PuO2(OH)2 and UO2(OH)2, both with volatilities that are strongly dependent upon temperature, chemical activity of condensed phase Pu and U, and steam pressure. Hence, for example, orders of magnitude reduction can be achieved in Pu and U volatilities by operating the bath at lower temperatures. Iodine is found to volatilize from the bath as gaseous sodium iodide (NaI) but a small portion of the NaI is converted to gaseous I2 during cooldown of the off-gas. Observations by Rockwell of trace amounts of sodium chloride (NaCl) particulates in the off-gas as a result of NaCl volatilization from the bath are confirmed by our calculations. 24 refs., 1 fig., 16 tabs