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8 Comments

  1. I wonder how wind farm output is doing right now? I guess we won’t know since their don’t post up-to-date readings of power output.

    1. Jason – all generators in Ontario Canada are required to post their output numbers. Here is the table for July 9, 2010
      http://reports.ieso.ca/public/GenOutputCapability/PUB_GenOutputCapability_20100709_v25.xml
      There is a new xml file put up every hour each day. You can find an archive list at
      http://reports.ieso.ca/public/GenOutputCapability/
      So far, I have not found any similar sites in the US except for the one published by Bonneville Power Authority at http://www.transmission.bpa.gov/Business/Operations/Wind/baltwg.aspx
      It looks like a big breeze just blew in last night after about four days of less than 20% output.

      1. Thanks for the link, I’ve actually been searching for something like that for a long time.

  2. Rod – your readers may also like to know that many (if not all) of the reactors slightly below 100% are in the midst of a ‘coast-down’. This means their performance allowed them to get the maximum use from their fuel. The fissile U-235 that remains is not enough to sustain 100% and they will enter their planned rufuelling outages when demand comes down (with the temperatures) this autumn.

    1. Interesting. Never knew that.
      I would have imagined that the end of a cycle would be somewhat dramatic (in that once k < 1, in any state of the core with all rods out, multiplication would cease entirely in every state of the core), but I forgot about the negative temperature coefficient. So, I’m guessing that the coast-down begins once you start being unable to maintain k >= 1 at full operating temperature with all rods out. The reactor operating temperature then slowly drops as the core has less and less reactivity, so as to maintain k >= 1. Since there’s consequently less ?T between the turbine inlet temperature and the condenser, the plant slowly produces less output, until the end of cycle in the fall, when it’s time to refuel, and the plant is entirely shut down.
      Is this explanation right?

      1. @Dave – though I have never operated a commercial nuclear plant, I would bet that you are right on the money there.
        One thing that is completely different about nuclear reactor cores is that “running out of gas” is a very slow and fuzzy process that does not have a sharp end point like it does for other thermal plants. The full explanations can require numerous credit hours in reactor physics and thermodynamics, but you have done a great summary for a light water reactor with a negative temperature coefficient of reactivity that is feeding a steam plant secondary.

      2. You’re correct Dave, as Rod said. Also remember that some of the reactors are BWRs (with the cardinal sin of sins in PWRs and Navy Subs… boiling in the core). BWR operation is significantly effected by a ‘void coefficient of reactivity’ that is typically an order of magnitude greater than the temperature coefficient. Think if it this way; with k<1, less fission, less energy, less voids, less fast and thermal neutron leakage, positive reactivity, k=1.

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