Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Out of curiousity

  1. Jan 6, 2010 #1
    Of the typical generation 2 reactor in service today, in percentage terms how much of the energy produced by the reactor is turned into electricity? What about new Generation 3+ reactors (such as the AP 1000)?



    Thanks.
     
  2. jcsd
  3. Jan 6, 2010 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    PWR about 35%
    AGR about 40%
     
  4. Jan 7, 2010 #3
    5% improvement? Doesn't seem like that much on the surface. Of course any improvement in efficiency is welcome.
     
  5. Jan 7, 2010 #4

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    At the temperatures used in a typical PWR the thermal efficiency has been about 32-34% typically. Some plants have had their turbines replaced with more efficient designs and some current PWRs attain ~35-36% thermal efficiency. I believe AREVA expects about 35-36% efficiency with the EPR, while Mitsubishi has mentioned ~37% (although one citation mentioned 39%). I believe the AP1000 is expected to attain ~35% gross efficiency (~33% net if cooling towers are used for cooling).

    British Energy has a comparison. They AGR may achieve up to about 42% thermal efficiency.
    http://www.british-energy.com/documents/Different_types_of_nuclear_power.pdf
     
    Last edited: Jan 7, 2010
  6. Jan 7, 2010 #5
    The thermodynamic efficiency (or plant "heat rate") is determined by the temperatures of the steam and condenser, along with the sophistication of the secondary plant equipment. Since most power reactors produce saturated steam, the efficiency is going to be lower than that obtained by a superheat fossil fired boiler. The exception is the B&W once-through steam generator, which produces a little bit of superheat. That design is not without its own problems.

    Second, remember that the fuel cost in a nuclear unit is a minor contributor to the overall generating cost. That means that improved thermo efficiency does not reduce the cost the way it does for fossil units (where fuel cost is the major contributor to the total cost). Since uranium has no other use, "wasting" a little bit in the "low efficiency" nuclear unit really doesn't matter much.

    Finally, "any improvement in efficiency is welcome" is only true subject to the financial costs associated with the improvement. The power company will do a cost-benefit analysis to determine if they should make improvements in the secondary plant (new feedwater heaters or MSRs; replace/rework the HP and/or LP turbines, etc). For them, it all comes down to dollars & cents.
     
  7. Jan 7, 2010 #6

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    One thing I did always wonder.
    In europe at least, coal fired stations have huge cooling towers even though they are normally on rivers (the only economic way to get 1000s of tons of coal/day). While nuclear stations are almost always built on the coast and use water cooling.

    Originaly the reactors were built on the coast for safety well away from big cities. Or it's a shear coincidence that France built most of it's plants on the north coast facing Britain and Britain built them in the north of England or Scotland.

    Since in both cases you want the maximum cooling to increase the efficency? Is it just that with modern coal stations you don't use cooling towers either, it's just that they were originally built 30-50years when cooling towers were the best solution. Or is it that you don't want the nuclear statiosn to have any more visible impact than is necessary - to reduce public objections.
     
  8. Jan 7, 2010 #7
    The cooling towers are needed when regulations limit the temperature increase between intake and outfall into the river or bay or whatever. Whether the towers are needed depends on local/state/federal regs in place at the time the plant was built/licensed, not so much on whether it's a nuke or a dirt burner.

    Many people think that the nuclear units' remote location was safety consideration (and to some extent that was true in the early 1960s) but don't forget that the fuel is cheap and easy to transport to remote locations. That's certainly not true for coal. So if the grid needs a generator way out in the woods, a nuclear unit fills the bill. Instead of a continuous flow of coal cars on a heavy rail line, all you need is a coupla dozen semi-trucks once a year and a paved road...
     
  9. Jan 7, 2010 #8

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    But you do need reasonable access to build the place and if that were true you would put the coal fired stations on the coast, not inland next to the cities they supplied.

    The cost of building cooling towers is a tiny part of the plant costs so that can't have been a driver for putting them on the coast. France had a problem in the summer when several of it's nukes on rivers had to be shut down because of cooling limits.

    Do they still build cooling towers for modern coal stations? In the UK all new power plants in the last 20years have been gas and relatively small so no need for towers.
     
  10. Jan 7, 2010 #9
    Actually the cooling towers are very expensive.

    I thought it was low water level in the river, but I could be wrong.

    Yes. Well, in the US they do.
     
  11. Jan 7, 2010 #10

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    There's a trade-off. Ideally the plant is closest to the load/demand, which means inland near cities (population centers) in order to avoid transmission losses (and minimize reactance). That requirement has to be balanced with the environment and available heat sinks.

    Another consideration is the requirement for exclusion zones around nuclear power plants. It's much easier to build NPPs in remote areas and not have to deal with evacuation plans of hundreds of thousands or millions of people. Coastal areas (away from ports) tend be remote.

    I believe those plants had cooling towers. They are large structures and do represent a not too insignificant portion of capital cost.

    That depends on the plant capacity. In the US as well, new plants tend to be gas-fired (gas turbine or combined-cycle) of low unit capacity. They have been primarily peaking units, although with inexpensive gas they could be base-load units.

    Some modern coal-fired plants could use coal gasification and incorporate combined cycle to reduce the waste heat load.
     
  12. Jan 7, 2010 #11

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Oh, these towers are amazing bits of engineering they are very thin and contain very little concrete. I assumed they were pretty cheap to build (once you had been doing it for 70years)

    250px-Ferrybridge_power_station.jpg
     
  13. Jan 7, 2010 #12

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    That's a fair amount of steel and concrete, and the cost of those commodities has gone up. In addition, the sap about 2% of the plants thermal efficiency. One has to pump the water and blow the air (force draft).

    Update:

    http://www.world-nuclear-news.org/RS-Cooling_tower_requirement_for_Oyster_Creek-0801104.html
     
    Last edited: Jan 8, 2010
  14. Jan 8, 2010 #13

    mheslep

    User Avatar
    Gold Member

    That additional 5% on a single 1GW(e) reactor will run 25,000 to 50,000 more homes.
     
  15. Jan 8, 2010 #14

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    While getting some improvement from more efficient turbine sets, most nuclear plants are looking at uprates or increases in thermal power - anywhere from 5% to 20% of original design.

    http://www.world-nuclear-news.org/C-Shaw_eyes_US_reactor_uprate_market-0701104.html
     
  16. Jan 9, 2010 #15

    mheslep

    User Avatar
    Gold Member

    Yes I'd seen that - 'uprates'. Essentially ~4 new reactor power equivalents all under the radar of the nuclear critics. That's all to the good, except that I don't care for the double standard at the NRC: immediate approval of uprates, but new reactors or designs are slow walked or ignored forever.
     
  17. Jan 9, 2010 #16

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    The new plants are not being ignored. There's a lot going on behind the scenes.
     
  18. Jan 9, 2010 #17

    mheslep

    User Avatar
    Gold Member

    I'd argue that some of these new designs are being ignored, like the small reactors discussed in this forum, and I'd argue that the main stream new PWR plant proposals are being slow walked. Some ~17 plant proposals submitted - years ago - and not a single plant breaking ground. I saw the FP&L CEO interviewed the other day - he stated the NRC takes about 42 months to review a proposal for a new plant - after which they still can (and do) say no. Compare that to the speed with which uprates go through.
     
  19. Jan 9, 2010 #18

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    The NRC is still working on the certifications - and recircertification of the ABWR, since GNF/Hitachi parted ways with Toshiba. And all parties are working on resolving some issues with the new plants. And the small plants are not forgotten - they just got a late start.
     
  20. Jan 9, 2010 #19
    I've argued in other places that the incredibly long licensing times are the biggest impediment to building new nuclear power plants in the United States. It makes no sense at all that is should take so long to approve a new plant when the designs have already been approved by the NRC.

    As it stands now, the Chinese will have Westinghouse AP1000 reactors up and running before we start construction on our first one. The first one is supposed to go online in 2013.

    BTW the AP1000 has already been uprated from 1175MWe to 1250MWe because of new turbine designs.

    http://www.world-nuclear.org/info/inf63.html" [Broken]
     
    Last edited by a moderator: May 4, 2017
  21. Jan 9, 2010 #20

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    Note that Mitsubishi is supplying the turbines - they are not from the US. Westinghouse exited the large turbine business a while ago.

    Mitsubishi is competing with Toshiba/Westinghouse to sell new NPPs in the US.
     
    Last edited by a moderator: May 4, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook