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A Revised ANS Standard for Decay Heat from Fission Products

Virgil E. Schrock

Nuclear Technology

Volume 46 / Number 2 / December 1979 / Pages 323-331


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Heating from the decay of radioactive nuclides in shutdown reactors plays an important role in the safety evaluation of nuclear power plants. Although there are many other important uses for this information, the need for more accurate data for the analysis of hypothetical reactor accident scenarios has been the main impetus for recent research activity that has led to a major revision of the Draft American Nuclear Society 5.1 Standard, “Decay Energy Release Rates Following Shutdown of Uranium Fueled Reactors” (published in 1971). The 1978 revised standard, titled “Decay Heat Power in Light Water Reactors,” is based on new experiments and summation calculations. Very accurate determination of the decay heat is now possible for light water reactors, especially within the first 101 s after shutdown, where the influence of neutron capture in fission products may be treated as a small correction to the idealized zero capture case. The new standard accounts for differences among fuel nuclides. It covers cooling times to 109 s, but provides only an “upper bound” on the capture correction in the interval from 104 to 109 s.

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