Design of a 150-miniature detectors 3D core-mapping system for the CROCUS reactor

Abstract

The present article provides an overview of the design of a three-dimensional (3D) full-core mapping system for the CROCUS reactor, operated at the École polytechnique fédérale de Lausanne (EPFL), Switzerland. The system is composed of 149 miniature neutron detectors distributed within the core double lattice at three main axial levels. The miniature detector technology is based on the optimization of the well-proven coupling of a miniature ZnS:6LiF(Ag) scintillator to a state-of-the-art silicon photomultiplier (SiPM) via jacketed optical fibers. The challenges in the mechanical design, the detector optimization, the core criticality, and the development of the acquisition electronics are strongly interconnected and their combination is addressed in this article. The 3D full-core mapping system is foreseen to be installed in CROCUS in autumn 2021 and it will pave the way for the investigation of 3D dynamic phenomena in nuclear reactor cores.

Ten springs of experiments in CROCUS

“…Thanks to the scalability of MiMi detectors using digital acquisition, a core-mapping array called SAFFRON was developed, licensed, and finally loaded in CROCUS in 2022 [74]. It consists of 149 detectors distributed radially in both inner and outer lattices of CROCUS, and axially on three main levels, i.e.…”

“…With this unique 3D instrumentation we aim at the study of static and dynamic neutron flux maps. For this purpose, each individual MiMi detector was intercalibrated in the CARROUSEL facility, which consists of a PuBe neutron source set in a water tank [75]. First results were obtained for an absolute flux map of CROCUS, i.e.…”

Simultaneous inter-calibration of 160 MiMi neutron detectors

“…The MiMi neutron detectors [4], [5] have been developed at EPFL since 2018 targeting a variety of zero-power reactor applications ranging from the investigation of localized neutronics phenomena in CROCUS, i.e., azimuthal flux dependencies [7] and lateral fuel rod displacements [8], [9], to their application to 3D full-core mapping systems such as SAFFRON [1].…”

“…A crucial upgrade for the extension of the applicability of MiMi detectors to full-core mapping systems was the transition from an analog readout system to a custom-made six-module multi-channel processing electronics system, coupled with FPGA-based digital readout [1]. The combination of the two systems allows the simultaneous processing and acquisition of up to 160 MiMi detector signals.…”

“…HE development of a three-dimensional (3D) full-core mapping system, called SAFFRON [1], was initiated in 2020 for its installation in the core of the CROCUS zero-power research reactor [2], [3] operated at the Ecole Polytechnique de Lausanne (EPFL), Lausanne, Switzerland. SAFFRON consists of 149 miniature and minimalistic (MiMi) neutron detectors [4], [5] distributed at different radial and axial inter-pin locations of the CROCUS core (plus 11 mobile MiMi detectors), the detectors' supporting structure, and custom digital readout electronics.…”