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What is the reactor power at Source, Intermediate and Power

  1. May 23, 2016 #1
    hello all, I am trying to determine what the percentage of reactor power will be at each power level range measured by each detector (i.e Source, Intermediate and Power range). All I can seem to find is info in the CPS rate not percent reactor power.
  2. jcsd
  3. May 23, 2016 #2


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    This may be close. It indicatesthe source range goes from a few cps (usually a min of 2 cps) to about 1M cps (M = million), intermediate range from 0 power (100k to 1 M cps), but increasing counts to 1% to 10% reactor power, and power range overlaps up to about 10%, and then is all the way to 100%.


    SRM - A fission-counting device that operates from below the source level to 109 nv, or approximately 10-3 percent of the rated power

    As the reactor power level exceeds the range in which the SRM can count neutron counts individually, a drive mechanism withdraws the detector from the reactor core to a storage location below the active fuel region.

    Then the IRM begins to generate output and is used to control the reactor operation up to approximately 10 percent of the rated reactor power. After the power level exceeds the range of the IRM, it is removed and stored. The IRM is a fission chamber that uses a voltage variance (Campbell) method and operates from 108 to 1.5 x 1013 nv, or approximately 10 percent of the rated reactor power.


    The power range monitor starts at a ~1% and goes up to full power.

    I think the same goes with PWRs, but I can't access several sites that have information in pdf files.
  4. May 27, 2016 #3

    Go to figure 6-3 on page 6-6, this shows the overlap between SRM, IRM, APRM, and also the relationship between neutron counts and rough % power.

    The rule of thumb that BWR licensed operators are taught, is that the IRMs, on range 10 at 100%, are about 40% reactor power. Every down range is a factor of sqrt(10), or in other words, every 2 ranges is 10x). So 100% flux on range 8 = 4% power, and 100% flux on range 6 = 0.4% power. 100% flux on range 4 = 0.04% power. etc

    This is a very rough estimate, but gives a relative range. At any given point in time, your 8 IRMs for a BWR can be as much as 2 ranges apart, based on local core power, burnup of the IRM detector, and calibration/compensator settings.

    The actual % power or counts per second doesn't matter as much in startup and low power operation. Your focus is more on maintaining reactor power steady while you are heating up and bringing steam loads online.

    Once you are in Mode 1 (Power Operation), your SRMs and IRMs don't really matter or count anymore. After a scram, your IRMs are only used to follow the power decrease and to act as a backup method to determine the core is shut down. SRM indications aren't really useful except during pull to critical and core alterations, however they also provide period indications which are useful during all power operations as they are the first indicator of something going snakey in the reactor.
  5. May 28, 2016 #4

    jim hardy

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    Was i surprised to find this old document. It's a "how it works" for Westinghouse PWR.


    Three ovelapping instruments cover the reactor from zero to 200% power.
    They use neutron detectors located a foot or two or three outside the reactor vessel in the ventilating space.
    two are logarithmic , one is linear
    here's their approximate overlap
    Source range indicates counts from a proportional counter tube, ie individual neutrons that strike the detector, from about 1cps to 1 million cps on a logarithmic counts per second meter scale
    Intemediate range indicates current from a small compensated ion chamber just above the source range counter. It indicates DC current not counts, because when count rate gets high enough the pulses run together and become a DC current. When intermediate range is indicating we turn off high voltage to source range so as to not saturate its detector.
    intermediate range indicates current from approximately 10-11 amps to a milliamp on a logarithmic ammeter scale. It reads about a milliamp at full power but with its 8 decade log scale it's not accurate enough for fine control of power.
    Power range is linear and indicates current from a large ion chamber , calibrated to indicate reactor power on a linear scale from 0 to 120% .
    The power range instrument is capable of accurately reporting reactor power to 200% , two special fast response recorders are provided in the control board for "just in case" . Automatic trips will drop the rods long before it gets there.

    Detailed description at that link up above
    and here's the approximate overlap from its page 28
    be aware this chart is approximate, for teaching purposes only.
    But it i think answers your question for Westinghouse PWR's.
    Exact overlap depends on the arrangement of concrete surrounding the reactor and how far outside the vessel each individual detector is positioned.
    So do not expect to find any plant's actual numbers in exact agreement with it. They might differ by nearly a decade.

    Here's a top view of detectors relative to reactor from that PWR manual(well, my annotation should be obvious ).
    Drawings of the actual instruments are there too.

    Reactor Engineer from any individual plant can give you his plant's actual overlap.

    old jim
    Last edited: May 28, 2016
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