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RELAP fuel rod-coolant response modeling

  1. Jul 7, 2014 #1
    I am a beginner with the use of relap. So this might be a bit silly. I am studying the heat transfer between a fuel rod and a single channel of coolant. One of the inputs for the heat structure is the direct moderator heating multiplier. What is that and how do I find its value?

    Thanks. Any help or advice will be greatly appreciated.
  2. jcsd
  3. Jul 8, 2014 #2


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    I presume that is the fraction of heat delivered directly to the coolant, i.e. from neutrons and gamma rays. This is generally a constant only dependent on reactor type. For PWR's we use 97.4% for fraction of heat generated in the fuel (moderator would thus be 2.6%).
  4. Jul 8, 2014 #3
    Thanks QuantumPion ! :)
  5. Jul 8, 2014 #4
    I know for CANDU's we normally use a value of 92.5% heat-to-fuel/energy released. It is interesting that it is so much lower than PWR's. Presumably this is because LWRs have a higher ratio of fuel in the core.
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