As far as I know, yes.

The experiment was previously filled with water in order to resolve the fluid flow. Water and Sodium have very similar viscous properties so long as you have the temperatures correct. Sodium is also opaque so you can't use lasers and are limited to a combination of ultrasound and flow tomography (basically, backing out the flow from the induced magnetic field), so its somewhat common practice to do a water model of sodium experiments. Lathrop's Water part of the experiment lasted 4ish years? (I think, perhaps between 2 and 4?) because he encountered some interesting hydrodynamic effects. I saw Dr. Lathrop speak at a conference about 3 weeks ago and they were about halfway thru the fill process then, so this article lines up quite nicely with what would have been a reasonable completion time.