Hi,
You definitely would need triple redundancy for your main circulating pumps and a scavenging system to draw/push the gas phase away from heating surface.

Without the above and depending on what temperature you are operating at, a 1 or 2 second coolant circulation outage could result in a catastrophic heating surface failure.

One thing of interest is that with the correct setup, a continuous generation of steam at the Critical Point (221 bar and 705F) may be able to be achieved, along with the large increases in thermal efficiency.

As you are probably aware, it does away with both latent heat of vaporisation and the latent of the condensation, but current materials and technology do not allow this at present.

BTW it would increase power station efficiency to well above 90%, and that would mean a lot less fuel burnt.

>http://science.nasa.gov/headlines/y2001/ast07sep_2.htm