DELAYED NEUTRON DATA FOR FAST-REACTOR ANALYSIS

The delayed neutron precursor decay curves which result from a pulse of fissions of the isotopes **2**3**8U, **2**3**5U, **2**3**8U, **2**3**2Th, **2**3**9Pu, **2**4**0Pu, **2**4**1Pu, and **2**4**2Pu are consistently fit to a single set of six isotope-independent decay constants. When delayed neutron yields based on a single set of group decay constants are employed in reactor transient analysis, it becomes possible to introduce macroscopic precursor production cross sections for each of the delayed neutron groups. The newly fitted data are tested by the analysis of a typical fast reactor transient; the analysis shows that the utilization of the new data in comparison to the use of original data results in an insignificantly small deviation, while permitting a considerable reduction of calculational effort.