Measurements and Monte Carlo simulations with miniature neutron detectors for flux characterization in the SUR-100 zero power reactor

An advanced neutron detection system for highly localized in-core measurements developed in the Laboratory for Reactor Physics and System Behaviour (LRS) at École polytechnique fédérale de Lausanne (EPFL) it is used to characterize the neutron flux of the SUR 100 zero-power reactor of the Institut für Kernenergetik und Energiesysteme (IKE) operated at the University of Stuttgart. The small size of its experimental channels requires the use of miniature detectors for a proper characterization of the neutron flux profiles, not achievable with conventional detection techniques. An experimental campaign is carried out in the IKE laboratory by means of an academic collaboration established with the EPFL-LRS. Miniature neutron detectors are disposed in different arrangements in order to achieve high spatial resolution measurements of the neutron flux profiles in the experimental channels of the reactor. The detection system is extensively tested in the EPFL facilities as a preparatory activity for the experimental campaign. Part of the work is dedicated to adapt an existing Monte Carlo model of the reactor to the three-dimensional neutron transport code SERPENT2. Neutron transport simulations have been run both before and after the campaign, to prepare the experimental activities and to verify their results with comparisons against the computations. A good level of agreement is found between computational and experimental results, demonstrating the goodness of the converted Monte Carlo model and the excellent acquisition capabilities on small scale of the miniature detectors. In light of the obtained results, an accurate characterization of the thermal neutron flux profiles within the experimental channels of the SUR 100 reactor is achieved.