Accurate measurements of delayed neutron data for reactor applications: methodology and application to 235U(nth,f)

Pierre Leconte; Dorian Belverge; David Bernard; Abdelhazize Chebboubi; Grégoire Kessedjian; Daniela Foligno; Benoit Geslot; Alix Sardet; Pierre Casoli; Timothée Kooyman; Alexandra Pépino; Christophe Domergue; Diane Doré; Xavier Ledoux; Ludovic Mathieu; Olivier Méplan; Annick Billebaud; Benjamin Cheymol; Nathalie Marie; François-René Lecolley; Jean-Luc Lecouey; Ulli Koester; Torsten Solder; Paolo Mutti

doi:10.1140/epja/s10050-024-01402-7

2023 Impact factor 2.6

Hadrons and Nuclei

Open Access

Eur. Phys. J. A (2024) 60: 197
https://doi.org/10.1140/epja/s10050-024-01402-7

Regular Article - Experimental Physics

Accurate measurements of delayed neutron data for reactor applications: methodology and application to ²³⁵U(n_th,f)

Pierre Leconte¹^a, Dorian Belverge¹, David Bernard¹, Abdelhazize Chebboubi¹, Grégoire Kessedjian¹, Daniela Foligno¹, Benoit Geslot², Alix Sardet², Pierre Casoli², Timothée Kooyman², Alexandra Pépino³, Christophe Domergue³, Diane Doré⁴, Xavier Ledoux⁵, Ludovic Mathieu⁶, Olivier Méplan⁷, Annick Billebaud⁷, Benjamin Cheymol⁷, Nathalie Marie⁸, François-René Lecolley⁸, Jean-Luc Lecouey⁸, Ulli Koester⁹, Torsten Solder⁹ and Paolo Mutti⁹

¹ DES/IRESNE/DER/SPRC/LEPh, CEA Cadarache, 13108, Saint Paul Lez Durance Cedex, France
² DES/IRESNE/DER/SPESI/LP2E, CEA Cadarache, 13108, Saint Paul Lez Durance Cedex, France
³ DES/IRESNE/DER/SPESI/LDCI, CEA Cadarache, 13108, Saint Paul Lez Durance Cedex, France
⁴ DRF/IRFU/DPhN/LEARN, CEA Saclay, 13108, Saint Paul Lez Durance Cedex, France
⁵ Grand Accélérateur National d’Ions Lourds, CEA/DRF, CNRS/IN2P3, B.P. 55027, 14076, Caen, France
⁶ LP2I, Université de Bordeaux, 19 Chemin du Solarium, 33175, Gradignan Cedex, France
⁷ LPSC, 53 Avenue Des Martyrs, 38000, Grenoble, France
⁸ LPC Caen, 6 Boulevard du Maréchal Juin, 14000, Caen, France
⁹ Institut Laue-Langevin, 38042, Grenoble, France

^a pierre.leconte@cea.fr

Received: 31 October 2023
Accepted: 1 August 2024
Published online: 3 October 2024

Abstract

Large inconsistencies still exist in nuclear data libraries regarding the kinetic parameters of delayed neutron (DN) precursors. As an example, there is a 17% gap between ENDF-B/VIII.0 and JEFF-3.3 on the average lifetime T_1/2 of DN precursors from thermal fission of ²³⁵U. This parameter is of major importance for reactivity predictions of nuclear reactors in nominal or accidental configurations. In this context, CEA is actively participating to the ALDEN project (Average number and Lifetime of DElayed Neutrons) which aims at providing the nuclear data community with new data sets of DN from thermal and fast neutron induced fission of various actinides. A dedicated experimental setup was designed and optimized for that purpose and is presented in this paper. It consists of a “long counter” detector containing 16 proportional counters filled with ³He, embedded in a high density polyethylene matrix. The detector surrounds a fissile target prepared in the form of a miniature fission chamber, containing a few hundreds of micro-grams of fissile material. This set-up is connected to fast and efficient neutron shutters that can produce step-irradiations of variable durations. The equations driving the DN counting following step-irradiations of the fissile target are established and discussed in the perspective of DN yield or group parameter measurement. A comprehensive analysis of the different steps of data reduction is detailed: dead time characterization, Region of Interest (ROI) determination, absolute and relative efficiency calibration, fission rate estimation, irradiation time and background determination, DN decay curve production and physical parameter fitting. Following a prototype experiment performed in 2018 at the PF1b cold neutron beam line of Institute Laue Langevin (ILL, Grenoble, France), we discuss here the analysis of two campaigns occurring in 2019 and 2021 in which significant improvements were achieved in terms of background minimization, counting statistics and fission rate determination. The achievements of this work are the measurement of the delayed neutron emission per fission for the thermal neutron induced fission of ²³⁵U, estimated at (1.625 ± 0.010) % and the group parameters leading to an estimated lifetime of $T_{1 / 2}$ ${T}_{1/2}$ = (8.87 ± 0.10) s. Those results are consistent with the values recommended by the IAEA/CRP work and they come with reduced uncertainties compared with previously published results.

© The Author(s) 2024

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