The Oil Drum

It's far, far, cheaper to build fast reactors using enriched uranium. The accidental pollution cost of attempting to use old, radioactive, PWR fuel rods is horrendous. The financial cost is almost as bad as the security issues.
Specify helium and you run into availability issues. Argon is a byproduct of nitrogen fixation plants. We aren't going to run out of argon. Helium leaks into and out of everything. And if you are running a fast neutron reactor, thermal absorbtion is not a significant factor for gas coolant. Helium gas does have a lower viscosity and that reduces pumping power.
The good news is that the Chinese government will build sensible systems. They don't care what the political types in America and France will back. If we want to do something dumb, that's our decision.