A hybrid pile oscillator experiment in the Minerve reactor

Highlights: • Hybrid oscillation technique in Minerve reactor for cross sections measurements. • Newly developed high sensitivity miniature fission chambers. • Local and global perturbations allow to disentangle capture and scattering effects. - Abstract: Pile oscillator techniques are powerful methods to measure small reactivity worth of material of interest for nuclear data improvement. In the Minerve reactor, operated by CEA Cadarache, experiments are being held using a reactivity oscillator method based on the measurement of the global reactivity perturbation associated to samples motion in the core center. The technique has recently been extended by introducing new miniature fission chambers close to the oscillation location, in order to measure local neutron flux perturbations. New detectors and associated acquisition systems were developed for that purpose by CEA. First results are presented and discussed in this paper. Data processing techniques are presented in details which demonstrate that global and local perturbations can be unraveled. Experiments also demonstrate that measuring the local flux depression around oscillated samples indeed provide valuable information regarding partial cross sections. The preliminary results are found to be very sensitive to capture cross section at the expense of scattering cross section, making the technique very useful to measure small capture effects of highly scattering samples and improve nuclear data knowledge, as foreseen in the future CEA's ZEPHYR critical facility to be built in Cadarache around 2026.