Estimation of Covariances on Prompt Fission Neutron Spectra and Impact of the PFNS Model on the Vessel Fluence

• Published in: EPJ Web of Conferences Vol. 106; p. 4012
• Main Authors: Berge, Léonie, Litaize, Olivier, Serot, Olivier, Archier, Pascal, Jean, Cyrille De Saint, Pénéliau, Yannick, Regnier, David
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Les Ulis EDP Sciences 01.01.2016
• Subjects: Computer simulation; Covariance; Covariance matrix; Fission; Fluence; Mathematical models; Monte Carlo simulation; Neutron spectra; Nuclear fission; Pressurized water reactors; Thermal neutrons; Uncertainty; Vessels
• ISBN: 9782759819294; 2759819299
• ISSN: 2100-014X; 2101-6275; 2100-014X
• DOI: 10.1051/epjconf/201610604012

As the need for precise handling of nuclear data covariances grows ever stronger, no information about covariances of prompt fission neutron spectra (PFNS) are available in the evaluated library JEFF-3.2, although present in ENDF/B-VII.1 and JENDL-4.0 libraries for the main fissile isotopes. The aim of this work is to provide an estimation of covariance matrices related to PFNS, in the frame of some commonly used models for the evaluated files, such as the Maxwellian spectrum, the Watt spectrum, or the Madland-Nix spectrum. The evaluation of PFNS through these models involves an adjustment of model parameters to available experimental data, and the calculation of the spectrum variance-covariance matrix arising from experimental uncertainties. We present the results for thermal neutron induced fission of 235U. The systematic experimental uncertainties are propagated via the marginalization technique available in the CONRAD code. They are of great influence on the final covariance matrix, and therefore, on the spectrum uncertainty band width. In addition to this covariance estimation work, we have also investigated the importance on a reactor calculation of the fission spectrum model choice. A study of the vessel fluence depending on the PFNS model is presented. This is done through the propagation of neutrons emitted from a fission source in a simplified PWR using the TRIPOLI-4® code. This last study includes thermal fission spectra from the FIFRELIN Monte-Carlo code dedicated to the simulation of prompt particles emission during fission.