Abstract
Drop-on-demand generation is an alternative approach to the traditional
vibrating nozzle used for the production of nuclear fuel microspheres via
the internal gelation method. We integrated a low-cost pneumatic setup and
demonstrated that the drop-on-demand approach has some advantages, such as
low inventory of feed solution (attractive for laboratory-scale research),
improved drop diameter control, reproducibility, scale-up to desired
throughput by simple multiplication of the number of dispensing units, and
simple remote operation. However, limitations on reproducibility and drop
diameter control still exist due to the intrinsic variation of physical
properties, viscosity, and dispensing-tip wettability during the internal
gelation process. These adverse effects can be mitigated, to a certain extent,
by carefully controlling the temperature of the feed as uniformly as possible.
We validated the drop-on-demand generation method by producing solid kernels
of yttrium-stabilized zirconia and soft gel microspheres of iron hydroxide.
In addition, we have measured the diameter change at each principal process
stage. Based on the observed gas entrainment/absorption in the gel spheres,
we conjectured that aging and washing are likely the critical stages
determining the final precision to which microspheres can be made.
Finally, we comment on potential improvements that add robustness to the method
for handling other metal precursors in aqueous solutions.
