Ten springs of experiments in CROCUS

Abstract

Around a decade ago, a new team rebuilt experimental research at EPFL’s nuclear facilities, and in particular in the CROCUS nuclear reactor. After a broad investigation and open discussions with colleagues from the nuclear community, a number of experiments and research directions were selected. They range from reactor physics to nuclear data, with a focus on instrumentation. We present here the variety of experiments carried out and how instrumentation has been instrumental in these perspectives. Developments on branching or intrinsic reactor noise were made possible thanks to extensive theoretical investigation coupled with the developments of pulse and current modes neutron detection systems, as well as the LEAF gamma detection array. With regard to modulation or perturbation reactor noise, a study of fuel rods vibration was carried out thanks to the unique COLIBRI in-core fuel rods oscillation device; in the VOID experiments, a method was tested to measure the void coefficient with neutron modulation; in the APRHODITE project, the PISTIL rotating absorber, or absorber of variable strength, was used to determine the zero power reactor transfer function, in order to obtain feedback on kinetics nuclear data, particularly delayed neutrons. On the topic of nuclear data, the PETALE programme consisted on criticality and transmission experiments for the study of stainless steel, using instrumented metal reflectors. New dosimetry methodologies were developed for consistent and complete propagation of uncertainties, which also enabled experiments to be optimized. It will be continued in the HARVEST-X project, and its pile-oscillation program, BLOOM. Last but not least, developments in dosimetry as well as for a novel miniature neutron scintillation technology (MiMi detectors) allowed for interand intrapin (NECTAR) neutron measurements. 160 MiMi detectors have recently been distributed throughout the CROCUS core in a unique 3D detector array called SAFFRON, paving the way for novel high-resolution neutronics.