HONEY: High-Resolution Reactor Kinetics experiments in the CROCUS reactor

¹ École polytechnique fédérale de Lausanne (EPFL), Switzerland
² Université Paris-Saclay, CEA Service d’Etudes des Réacteurs et de Mathématiques Appliquées, France
³ Autorité de sûreté nucléaire et de radioprotection (ASNR), France

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Published online: 6 November 2025

Abstract

This work presents high-resolution kinetic experiments in the CROCUS reactor, where control rod movements are monitored with unprecedented spatial detail using SAFFRON, a novel 3D detection system composed of 160 miniature detectors. These experiments are part of the HONEY (High-resolution Online Neutronics Experiments for dYnamics) program, a series of experimental campaigns developed through a collaboration between CEA (France), ASNR (France) and EPFL (Switzerland). The program is carried out in the CROCUS reactor, operated at EPFL, and aims to advance our understanding of reactor kinetics by investigating fission chain reactions, with particular emphasis on neutron clustering phenomena. As a stepping stone toward this goal, HONEY is devoted to improve the predictive capabilities of simulation tools under dynamic scenarios. The first campaign included global measurements of the reactor kinetic response using two reference fission chambers and, more importantly, it leveraged the high spatial resolution of SAFFRON. This array-type detection system, originally developed as part of a doctoral program at EPFL and supported by the H2020 CORTEX project, is specifically designed to investigate local neutron flux variations, which are of particular interest close to regions where perturbations are introduced. The results from the first campaign were used to validate the reactor kinetics capabilities of TRIPOLI-4, a high-fidelity Monte Carlo particle-transport code developed at CEA. HONEY offers a unique validation framework by combining global measurements with high-resolution local data, enabling detailed spatial assessments of dynamic reactor behavior and paving the way towards a thorough evaluation of how well computational models reproduce local phenomena.