(102e) Effect of Oxygen Bubble Distributions On Rare Earth Precipitates In Molten Salts

Effect of Oxygen Bubble
Distributions on Rare Earth Precipitates in Molten Salts

Ryan W. Bezzant and Supathorn Phongikaroon

University
of Idaho-Idaho Falls

Center for
Advanced Energy Studies

1776 Science Center Dr.

Idaho
Falls, ID 83402

 

Michael F. Simpson

Pyroprocessing Technology Department

Idaho National Laboratory

Idaho Falls, ID 83402

Abstract:

Pyroprocessing technology
has been developed at the Idaho National Laboratory for treating spent nuclear
fuel from Experimental Breeder Reactor-II.  An electrorefiner (ER) is the key
unit operation of this process, recovering uranium metal via anodic dissolution
and electrodeposition at a cathode.  During this process, minor actinides,
fission products and rare earths (RE) form chlorides and accumulate in the LiCl-KCl
eutectic salt.  This results in excess heat generation and other effects which
lower the system efficiency.  To maintain ER performance, it is necessary to
remove contaminated salt and refill with fresh salt.  But this approach is
costly and generates a high waste volume.

Researchers at the Korea
Atomic Energy Research Institute have demonstrated oxygen sparging as an
effective way of separating rare earth chlorides from molten salt to partially
prepare it for reuse.  Rare earth chlorides react with oxygen at high
temperatures.  Rare earth oxides and oxychlorides form and precipitate to the
bottom of the salt container. After the salt cools, the salt can be
mechanically separated from the rare earth fission products.  Aside from a
demonstration of the process, no fundamental aspects of this system are well understood. 

Thus, to gain insight into
physiochemical parameters for systematic scale-up, such as mass transfer rate
and gas holdup fraction, a transparent furnace with an oxygen sparging system
was constructed with the capability of operating under an argon environment at
500 °C.  LiCl-KCl-RECl₃ternary salt was loaded in the quartz crucible to study
the effect of oxygen bubble sizes on rare earth precipitate in the system. A
simple two blade, downward pitch turbine was used for mixing the bubbles in the
medium with a rotational speed varying between 100 and 250 RPM. The oxygen
flowrate was varied between 0.05 L/min and 0.25 L/min.  Oxygen concentration
was detected by an oxygen sensor.  Bubble sizes were captured by using a high
speed digital camera.  Detailed results will be presented and discussed.