Difference(s) between B&W type OTSG and Westinghouse/CE SG's?

[nspunx4]

All of the recent news about SG tube wear at San Onofre has me curious about the differences between the different type's of SG's used in PWR plants? What are the operational challenges of the different type's?

[wlrun3@aol.com]

American PWRs   69 Reactors
     Westinghouse   48
            Two Loop   6
            Three Loop   13
            Four Loop   29
      Combustion Engineering   14
      Babcock  & Wilcox   7

  Westinghouse PWRs all have one SG and one reactor coolant pump per loop. A loop is the pipe path that the reactor coolant follows from the reactor to the SG to the reactor coolant pump and back to the reactor vessel. Westnghouse PWRs have two, three or four loops. The reactor coolant enters and exits the SGs from the bottom and flows through thousands of pencil width tubes upward into the steam generating area and then downward and out of the SG after passing through a 'U' bend at the top of the tubes. This type of SG is called a 'U' tube SG. The steam exits the SG from the top.
  Combustion Engineering PWRs, unlike Westinghouse, all have two reactor coolant pumps per loop and only two SGs. Like the Westinghouse design they are 'U' tube SGs. San Onofre's two PWRs are Combustion Engineering designs. Like the Westinghouse PWRs the steam exits the SG from the top.
  Babcock & Wilcox SG tubes, unlike 'U' tube SGs, are straight and the SG is called a 'once through SG'. The reactor coolant enters the SG from the top, flowing downward as it transfers its heat, and exits from the bottom. The steam exits from the side of the SG. B&W PWRs, like the Combustion Engineering PWRs, all have two reactor coolant pumps per SG and only two SGs.

americannuclearpowerplants.com




 

[nspunx4]

Thank you for that detailed and informative answer. What are the different operational concerns of the different designs as far as normal and transient operation?

By the way wlrun I read the .PDF of "American nuclear power plants" and really enjoyed it. Thank you!

[nspunx4]

I have read that the B&W style Once Through Steam Generators will boil dry quicker than the CE/Westinghouse design. Is this true, and if so how does that effect SOP's and EOP's at B&W Plants vs. CE/Westinghouse plants?

[Fermi2]

Yes true. But outside of curiousity why are you asking?

[nspunx4]

Nuclear power specifically the operations side really interests me. I realize that it is not on the cards for me to ever work at a plant or be a RO but I still try to read and learn as much as I can. My father was a boilermaker and worked on Pilgrim and Seabrook. He is also a steam engineer in conventional plants so i have always had an interest.

The reason I am interested in this specific subject is because I have seen vague mentions in different books (about TMI 2) that the once through steam generator is not as forgiving and I was looking for the scoop from the real world.

[Fermi2]

Feedwater transients are more wicked and tend to take the primary for quite a ride.

[fueldryer]

American PWRs   69 Reactors
     Westinghouse   48
            Two Loop   6
            Three Loop   13
            Four Loop   29
      Combustion Engineering   14
      Babcock  & Wilcox   7

  Westinghouse PWRs all have one SG and one reactor coolant pump per loop. A loop is the pipe path that the reactor coolant follows from the reactor to the SG to the reactor coolant pump and back to the reactor vessel. Westnghouse PWRs have two, three or four loops. The reactor coolant enters and exits the SGs from the bottom and flows through thousands of pencil sized tubes upward into the steam generating area and then downward and out of the SG after passing through a 'U' bend at the top of the tubes. This type of SG is called a 'U' tube SG. The steam exits the SG from the top.
  Combustion Engineering PWRs, unlike Westinghouse, all have two reactor coolant pumps per loop and only two SGs. Like the Westinghouse design they are 'U' tube SGs. San Onofre's two PWRs are Combustion Engineering designs. Like the Westinghouse PWRs the steam exits the SG from the top.
  Babcock & Wilcox SG tubes, unlike 'U' tube SGs, are straight and the SG is called a 'once through SG'. The reactor coolant enters the SG from the top, flowing downward as it transfers its heat, and exits from the bottom. The steam exits from the side of the SG. B&W PWRs, like the Combustion Engineering PWRs, all have two reactor coolant pumps per SG and only two SGs.

americannuclearpowerplants.com


Pencil sized tubes ?

 

[Bradtv]

While I don't know the tube dimensions, the OTSG has something like 15,500 tubes compared to 3000 for a U-tube SG.

Part of an assignment I wrote for school:

The OTSG is a very large, vertical, counter flow, two-phase heat exchanger.  The reactor coolant from the hot leg enters the vessel into a chamber in the top, then filter through tubes extending to a chamber in the bottom of the vessel, where the reactor coolant exits as the cold leg towards the Reactor Coolant Pumps.  There are upper and lower tube support sheets welded to the tubes that prevent reactor coolant from entering the lower pressure shell side.  The feedwater (455 °F) from the secondary side flows into the vessel through feedwater inlets (halfway up the OTSG) and is directed through downcomers towards the bottom, releasing the feedwater into the shell side above the lower tube sheet.  The feedwater continues upward across the tubes, absorbing the energy from the primary side and flashing to steam (535 °F).  As the steam rises, it passes the hotter portion of the tubes and is further heated past saturation.  The superheated steam finally exits the vessel through the steam outlets.  In the event of a feedwater failure, auxiliary (emergency) feedwater enters the vessel through auxiliary feedwater headers located below the upper tube sheets and above the steam outlets. 

There are various regions specified to the OTSG for the secondary system which identify conditions of the feedwater.  These are the Feedwater Heating Region, the Nucleate Boiling Region, the Film Boiling Region and the Superheated Steam Region.  The Feedwater Heating Region occurs from the condenser hot-well to the downcomer in the Steam Generator.  There are holes in the downcommer which allow steam to aspirate into the entering feedwater, bringing the feedwater to saturation temperature.  The Nucleate Boiling Region occurs as the feedwater begins to bubble into vapor on the surface of the tubes.  As those bubbles increase, eventually a film of vapor is created (Film Boiling Region) and the vapor escapes the feedwater.  The Superheated Steam Region is where the vapor quality surpasses zero moisture steam as it passes closer to the hot leg. 

A few resources:
http://www.pdhonline.org/courses/e183/e183content.pdf
ftp://ftp.eia.doe.gov/features/steamgen.pdf
http://www.babcock.com/bwc/nuclear_division/nuclear_sgfeatures.html
http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/100r1.html
http://www.platts.com/IM.Platts.Content/ProductsServices/ConferenceandEvents/2010/pc030/presentations/Michael_Shepherd.pdf

[nspunx4]

That is GREAT! Thank you!

[wlrun3@aol.com]

Bradtv...there should be awards for best forum posts. Well done.

I changed my post from 'pencil sized tubes' to 'pencil width' tubes because I was impressed with the quality of this forum discussion.

[Fermi2]

Bradtv...there should be awards for best forum posts. Well done.

I changed my post from 'pencil sized tubes' to 'pencil width' tubes because I was impressed with the quality of this forum discussion.

Wow you set the bar low...

[thenuttyneutron]

There are holes in the downcommer which allow steam to aspirate into the entering feedwater, bringing the feedwater to saturation temperature. 
 

It is more of an annular gap in the steam generator called the aspirating port located near the FW nozzles.  It uses about 10% of the total steam flow generated in the SG to bring the FW to saturation.

[Bradtv]

If there is incorrect material, I do rely on you folks to correct me.

I may need a "not in the industry" (yet) disclaimer - though is an example of what one may find through information on the internet.