Intra-pin Reaction Rate Measurements in the CROCUS Experimental Reactor

In response to the need for validating high-fidelity deterministic neutronics solvers capable of providing pin-resolved neutron flux distributions, intra-pin reaction rates measurements were performed in the CROCUS experimental reactor. A specially designed instrumented fuel rod was employed to gather intra-pin data thanks to activation dosimetry techniques. Positioned in the outer region of the reactor core, the rod takes advantage of spaces between the fuel elements to house pre-cut gold disk dosimeters for in-core irradiation. Subsequently, radial and azimuthal sections of the irradiated dosimeters are subjected to activity determination using an HPGe gamma spectrometer to retrieve the ¹⁹⁷ Au(n,γ) ¹⁹⁸ Au reaction rate distribution within the dosimeter. This paper comprehensively describes the setup of the instrumented fuel rod as well as the experimental protocol and planning needed for such measurements. First measured radial and azimuthal intra-pin reaction rate distributions are presented and compared to predictions from the GeN-Foam high-fidelity model of the CROCUS reactor. Additionally, the repeatability of the measurements has been demonstrated, with particular emphasis on the identification of the experimental sources of variability in the measured reaction rates.