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

IF 2.6 3区 物理与天体物理 Q2 PHYSICS, NUCLEAR The European Physical Journal A Pub Date : 2024-10-03 DOI:10.1140/epja/s10050-024-01402-7
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
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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 T1/2 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 \({T}_{1/2}\) = (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.

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反应堆应用延迟中子数据的精确测量:235U(nth,f)的方法和应用
核资料库中有关延迟中子(DN)前体动力学参数的数据仍然存在很大的不一致。例如,ENDF-B/VIII.0 和 JEFF-3.3 在 235U 热裂变产生的 DN 前体的平均寿命 T1/2 上就存在 17% 的差距。这一参数对于核反应堆在额定配置或意外配置下的反应性预测具有重要意义。在此背景下,法国原子能委员会积极参与了 ALDEN 项目(叠加中子的平均数量和寿命),该项目旨在为核数据界提供来自各种锕系元素热裂变和快中子诱导裂变的 DN 的新数据集。本文介绍了为此设计和优化的专用实验装置。它由一个 "长计数器 "探测器组成,其中包含 16 个填充有 3He 的比例计数器,并嵌入一个高密度聚乙烯基体中。探测器周围环绕着一个以微型裂变室形式制备的裂变靶,其中含有几百微克的裂变材料。该装置与快速高效的中子快门相连,可以产生持续时间可变的阶跃辐照。在对裂变目标进行阶跃辐照后,建立了 DN 计数驱动方程,并从 DN 产率或群参数测量的角度进行了讨论。详细分析了数据还原的不同步骤:死区时间特征、感兴趣区(ROI)确定、绝对和相对效率校准、裂变率估计、辐照时间和背景确定、DN衰变曲线生成和物理参数拟合。继 2018 年在 Laue Langevin 研究所(ILL,法国格勒诺布尔)的 PF1b 冷中子束线上进行原型实验之后,我们在此讨论对 2019 年和 2021 年进行的两次活动的分析,这两次活动在背景最小化、计数统计和裂变率确定方面取得了显著改进。这项工作的成果是测量了235U热中子诱发裂变的每次裂变的延迟中子发射率,估计为(1.625 ± 0.010)%,并测量了组参数,得出估计寿命为\({T}_{1/2}\) = (8.87 ± 0.10) s。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
The European Physical Journal A
The European Physical Journal A 物理-物理:核物理
CiteScore
5.00
自引率
18.50%
发文量
216
审稿时长
3-8 weeks
期刊介绍: Hadron Physics Hadron Structure Hadron Spectroscopy Hadronic and Electroweak Interactions of Hadrons Nonperturbative Approaches to QCD Phenomenological Approaches to Hadron Physics Nuclear and Quark Matter Heavy-Ion Collisions Phase Diagram of the Strong Interaction Hard Probes Quark-Gluon Plasma and Hadronic Matter Relativistic Transport and Hydrodynamics Compact Stars Nuclear Physics Nuclear Structure and Reactions Few-Body Systems Radioactive Beams Electroweak Interactions Nuclear Astrophysics Article Categories Letters (Open Access) Regular Articles New Tools and Techniques Reviews.
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