Reactor Concept

west_cost

Out of curiosity why do reactor companies patent next generation reactors, while there is more than 20 years to build next generation reactors, the time which patents are expired? Are they wasting money?

Astronuc

Which generation? Generation IV? Most of those are being developed by DOE. The reactors themselves are not patented, but certain unique aspects would be at some point.

Normally the fine details are not disclosed in the public domain, but rather, the details are trade secrets. Trade secrets do not generally appear in patents.

west_cost

For example, all the new small reactors such as IRIS, are in a pressure vessel, that water comes from the side (down comer) and pushed up through the reactor, then turn into steam. Nuscale is also designing a same thing almost. This concept of natural circulation can be copied by anyone since it almost looks like BWR. And they don't have to pay a penalty...

Astronuc

IRIS has pumps internal to the RPV. So does mpower's system.
http://www.nrc.gov/reactors/advanced/iris.html

http://www.westinghousenuclear.com/O...rch_areas.shtm (note the research on SiC, in addition to IRIS)

Natural circulation is not as simple it seems. The crud formation potential is an issue, particularly as it affects the hot channel.

west_cost

Thats is true if you are producing a lot of power but what if you don't choose to produce 1000 MW of power?
Also I don't know why Nuscale puts the reactor inside water. (Bouncy effect and a lot of stress on the pressure vessel). Do they count the fact that water hammer might happend inside the pressure vessel?

Astronuc

Either one uses forced convection, or natural convection. Most designs, even small modular reactors, use forced convection. The exact configuration of the pumps and placement in the RPV varies considerably among the various designs.
The NuScale design has no valves in the primary circuit, no pumps either, so no water hammer. The head is sufficient to drive natural convection. Bouyancy of the vessel is not an issue, especially with the core intact. The reactor is inside (surrounded by) water in order to remove LOCA as a concern, or at least minimize it.

west_cost

Do they install a pump inside the RPV?

Astronuc

Who?

The ABWR has pumps in the RPV, but the motors are external to the RPV.

The AP1000 has hot and cold legs, and external steam generators (SGs) like a conventional PWR.
http://www.nrc.gov/reactors/new-reac...rt/ap1000.html

The IRIS has a special type of motor installed within a chamber in the upper head of the RPV
http://www.nrc.gov/reactors/advanced...files/iris.jpg