Nuclear research reactors are a cornerstone of European science and technology across multiple fields beyond nuclear engineering, ensuring Europe's competitiveness. In recent years, the closure of several research reactors has not been matched by the commissioning of new facilities, leading to a gap in nuclear-related applications across science, industry, and academia. To combat this decline, the VERONICA (Versatile European Reactor for Neutron Irradiation and nuclear research) project was established. It focuses on developing a framework and, eventually, commissioning a new multipurpose research reactor. The objective of this reactor is versatility: to provide neutron spectra tailored to a wide range of current and future applications.
A facility capable of offering flexible neutron spectrum shaping would significantly benefit material testing, nuclear physics research, and the validation of detectors and computational codes, particularly for emerging technologies such as nuclear fusion, small modular reactors (SMRs), and Generation IV reactors. Additionally, critical applications such as the production of medical isotopes and semiconductor doping would also be supported.
Existing beamline configurations offer limited control over spectrum tailoring, restricting experimental flexibility. The goal is to enhance this flexibility by addressing the inverse problem: Given a specified input flux and a desired output flux, how can we design a material configuration to achieve the targeted spectral transformation? This work presents the initial phase of a computational framework for versatile neutron spectrum shaping, with a focus on constructing a comprehensive database of material transmission matrices under idealized flat-flux conditions.
The database initially focuses on transmission matrices of individual nuclides, with future work extending toward complex materials and mixtures through direct Monte Carlo modeling. The calculations were performed under idealized conditions: a flat neutron spectrum and slab geometry. To increase the usefulness of the database, different material thicknesses and material combinations were also explored. The generated database forms a foundational layer for future inverse design tools, enabling the rapid identification of material configurations capable of reproducing targeted neutron spectra—thermal, epithermal, fast, or hybrid.
Preliminary efforts have also explored different methods for quantitative spectrum comparison, which will be essential for establishing a value function to assess the quality of a solution in matching a target flux. This paper outlines the simulation methodology, initial transmission matrix results, and the conceptual structure of the inverse design workflow. By establishing a data-driven approach, we aim to significantly enhance the flexibility of research reactor facilities in the future.
