helium is also a noble and isn't likely to react with much
Wont react but could you contain it in the vesseL? helium is really light, Ie it will raise up and get lost if you dont seal the reaction vessel....
Argon is a much better idea (MIG welding??) its nobel gas (wont react) and its actually heavier than air so (for a reflux under inert atmosphere) you just pump in argon into a side port of the flask and it pushes all the air out the top of the condenser. The argon will sit on the reaction materials shielding them from air.
-AC