[Animats]

In light-water reactors, the highly radioactive part of the system is very simple. It's a core of metal fuel rods and support structure, some control rods, and water. All the plumbing complexity is external, and it's on water, which isn't hard to handle.

Most of the alternative reactor designs have more going on in the radioactive part of the system, or more difficult working fluids. This usually leads to trouble. Sodium-cooled reactors have sodium fires. Helium-cooled reactors have helium leaks. Pebble bed reactors have pebble jams. (The one in Germany is so jammed it can't be decommissioned.) Molten salt reactors have to pump radioactive molten salt around and run it through a chemical processing plant. In some designs that salt is a fluorine compound. Now you have all the headaches of operating a radioactive chemical plant.

Most power utilities don't want to operate a radioactive chemical plant.

[pjc50]

I wondered what had happened to pebble beds. http://en.wikipedia.org/wiki/AVR_reactor

Most power utilities don't want to operate a radioactive chemical plant

This is a brilliant phrase, thankyou.