Observations regarding fixed decay constants on the reactivity prediction for the fast fission of U-235

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Delayed neutron precursors have traditionally been represented by six groups. The group yields and decay constants are obtained from nonlinear fits to delayed neutron emission rates obtained experimentally. Each fit to the data produces different set of group decay constants based on the statistical precision of the instruments used and on the time domain used. As a result, standard data libraries contain different sets of group decay constants for each fissionable nuclide based on the nonlinear least squares fit. The group decay constants for thermal and fast fission of the same fissile nuclide are also different. The advantages of using ... continued below

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9 p.

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Loaiza, D. & Haskin, F.E. November 1, 1997.

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  • Loaiza, D. Los Alamos National Lab., NM (United States)
  • Haskin, F.E. New Mexico Univ., Albuquerque, NM (United States). Chemical and Nuclear Engineering Dept.

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Description

Delayed neutron precursors have traditionally been represented by six groups. The group yields and decay constants are obtained from nonlinear fits to delayed neutron emission rates obtained experimentally. Each fit to the data produces different set of group decay constants based on the statistical precision of the instruments used and on the time domain used. As a result, standard data libraries contain different sets of group decay constants for each fissionable nuclide based on the nonlinear least squares fit. The group decay constants for thermal and fast fission of the same fissile nuclide are also different. The advantages of using a single set of decay constants for all isotopes facilitate the analysis to cores that have different type of fissionable materials. This and other advantages have been discussed by several authors. Cahalan and Ott, 1973 developed six group formulations with fixed decay constants for fast fission of 8 different nuclide. A simpler transformation is used in this work to demonstrate that fixed decay constant formulations can easily be developed and differences in reactivity introduced by the transformation are very small. The seven decay constants used for this demonstration are not optimal or recommended in any sense. The selection of a fixed set of decay constants that could be used for all fissionable nuclides and neutron energies appears feasible and is under study, but it is well beyond the scope of this abstract.

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9 p.

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INIS; OSTI as DE97008626

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  • 1997 American Nuclear Society (ANS) winter meeting, Albuquerque, NM (United States), 16-20 Nov 1997

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  • Other: DE97008626
  • Report No.: LA-UR--97-2252
  • Report No.: CONF-971125--
  • Grant Number: W-7405-ENG-36
  • Office of Scientific & Technical Information Report Number: 292842
  • Archival Resource Key: ark:/67531/metadc679054

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • November 1, 1997

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  • July 25, 2015, 2:20 a.m.

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  • Feb. 29, 2016, 10:06 p.m.

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Loaiza, D. & Haskin, F.E. Observations regarding fixed decay constants on the reactivity prediction for the fast fission of U-235, article, November 1, 1997; New Mexico. (digital.library.unt.edu/ark:/67531/metadc679054/: accessed October 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.