## Abstract

Delayed neutron group constants, i.e. decay constants and relative abundances, are important data in reactor kinetics calculations. Due to the current inconsistencies occurring in the time description of delayed neutron emission and the lack of covariance data in ENDF evaluated files, we propose a method to derive a set of eight group relative abundances for the thermal fission of ^{235}U and fast fission of ^{238}U, based on a two-step approach. The former considers summation calculations using the JEFF-3.1.1 evaluated fission yields and the ENDF/B-VII.l neutron emission probabilities and half-lives, to evaluate a first set of delayed neutron abundances. Covariances are estimated from a Monte-Carlo approach, sampling the parameters according to their uncertainties. The latter step is to consider two independent measurements of the zero power transfer function using both neutron noise and reactivity modulation techniques. A Bayesian approach was applied, with the microscopic approach used as a prior estimation of the group constants and related covariances and applying the integral data assimilation technique to account for the feedback of the reactor experiments. These data were compared to the evaluated ones from the JEFF-3.3 (Keepin 8-group expanded), ENDF/B-VIII.0β4 (Brady and England) and JENDL-4.0 (Keepin 6-group) libraries, to compute dynamic reactivity and associated uncertainty of various LWR core benchmarks loaded with U fuel, covering ^{235}U enrichments from 2 to 20%.

Original language | English |
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Title of host publication | International Conference on Physics of Reactors, PHYSOR 2018 |

Subtitle of host publication | Reactor Physics Paving the Way Towards More Efficient Systems |

Publisher | Sociedad Nuclear Mexicana, A.C. |

Pages | 951-965 |

Number of pages | 15 |

ISBN (Electronic) | 9781713808510 |

State | Published - 1 Jan 2018 |

Event | 2018 International Conference on Physics of Reactors: Reactor Physics Paving the Way Towards More Efficient Systems, PHYSOR 2018 - Cancun, Mexico Duration: 22 Apr 2018 → 26 Apr 2018 |

### Publication series

Name | International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems |
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Volume | Part F168384-2 |

### Conference

Conference | 2018 International Conference on Physics of Reactors: Reactor Physics Paving the Way Towards More Efficient Systems, PHYSOR 2018 |
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Country/Territory | Mexico |

City | Cancun |

Period | 22/04/18 → 26/04/18 |

## Keywords

- Delayed neutron relative abundances
- Inhour equation
- Reactor experiments
- Summation calculations

## ASJC Scopus subject areas

- Nuclear Energy and Engineering
- Nuclear and High Energy Physics
- Radiation
- Safety, Risk, Reliability and Quality

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