New experiment for measuring the delayed neutron yields of ²³⁸U fission in the range 1 MeV to 19 MeV

¹ CEA, DES, IRESNE, DER, SPRC, LEPh, Cadarache, F-13108 Saint Paul Lez Durance, France
² CEA, DES, IRESNE, DTN, SMTA, LMN, Cadarache, F-13108 Saint Paul Lez Durance, France
³ Institut Laue-Langevin, Grenoble, France
⁴ CEA, DES, IRESNE, DER, SPESI, LEXIC, Cadarache, F-13108 Saint Paul Lez Durance, France
⁵ PTB, Braunschweig, Germany
⁶ GANIL, Caen, France
⁷ CNRS, IN2P3, LP2i, Bordeaux, France
⁸ CNRS, IN2P3, LPSC, Grenoble, France

^* dorian.belverge@cea.fr

Published online: 21 November 2023

Abstract

In nuclear reactors operating in nominal conditions, delayed neutrons (DN) drive the kinetic behavior of the neutron population. Predicting this behavior requires therefore the knowledge of the DN yield per fission, average lifetime, and kinetic of their emission, which is described by precursors groups abundances. Characterizing the uncertainties of these macroscopic data is essential, especially as they are used to design the safety margins of reactors.

Even for major fissile isotopes such as ²³⁵U and ²³⁹Pu, discrepancies still appear between the main nuclear data library. In 2018, CEA launched the ALDEN project (Average Lifetime of DElayed Neutrons), gathering several laboratories (CEA/DES and DRF, CNRS/LPSC, LP2i and LPC Caen, ENSICAEN, and University of Caen). This collaboration aims at producing new precise DN macroscopic data for reactor applications.

Three experimental campaigns were conducted in 2018, 2019 and 2021 on the thermal fission of ²³³U, ²³⁵U and ²³⁹Pu at Institut Laue Langevin in Grenoble (France), giving high quality results. In February 2023, a new campaign was performed at the PTB Ion Accelerator Facility in Braunschweig (Germany), focusing on the fast fission of ²³⁸U. In particular, the DN yield was measured for eight energies between 1.5 and 19 MeV. This paper presents the experimental setup, that was adapted to the new facility and neutron spectrum. The methodology of analysis is also detailed, and some preliminary delayed neutron decay curves are showed.