This thesis focuses on the analysis and reproduction of integral experiments for validating stainless-steel nuclear data, through two complementary programs conducted in the CROCUS zero-power reactor at EPFL. These programs are the semi-integral PETALE program, which includes criticality and transmission experiments with heavy reflectors, and the hybrid pile-oscillation program BLOOM. Both belong to HARVEST X, an EPFL coordinated initiative to reproduce, extend, and cross-validate experiments for stainless-steel and its Fe-Ni-Cr components. The main application concerns heavy reflectors in light-water reactors, with broader relevance to reactor pressure vessel fluence, Generation IV designs (especially fast reactors), and fusion systems. With PETALE, the aim is to deliver benchmark-quality results, including comprehensive covariance data and reduced risks of elemental compensation in alloys using pure elemental reflectors. A further goal is to provide feedback on modern nuclear data libraries, notably JEFF-3.3 and the newly released JEFF-4.0, and to prepare for data assimilation. To achieve these objectives, a new dosimetry analysis framework was developed, enabling the quantification of correlations among its 480 activation dosimetry measurements. This approach supports robust estimation of C/E ratios and their renormalization, including full covariance propagation, without ad hoc assumptions. High-resolution modelling with JEFF-3.3 and JEFF-4.0 confirms improved iron data in the fast neutron range. Trends observed in C/Es with JEFF 3.3 - front-to-back reflector differences of 5.7 % at ~2 MeV and 6.5 % at ~3.6 MeV - are reduced to below 1% with JEFF-4.0. Overall, stainless-steel performance improves as well, although the new chromium and nickel evaluations perform less favorably. These results highlight the need for careful treatment of alloys with reduced iron concentrations compared to typical light water reactor grades. Preliminary assimilation attempts with JEFF-3.3 covariance data suggest a 4-8% increase of the 56Fe inelastic cross section would improve agreement with fast-range observations. The BLOOM program was designed and carried out to complement PETALE, focusing on pile-oscillation experiments. Conducted in 2024, it involved 45 samples oscillated using a dedicated experimental channel, the SAFFRON array, and current mode-operated fission chambers. The measured reactivity worth have uncertainties as low as 0.015 pcm, the theoretical pile-noise limit. Local flux perturbations of ~10% (up to 30%) were measured with relative uncertainties of 0.1-1% (down to 0.05%). Simulations of 30 oscillations using Serpent2 and the black-body exact perturbation method yield complementary results to PETALE's transmission data. Chromium sample results improve with JEFF-4.0 (C/E are +1%, +3.5% previously), whereas nickel results slightly degrade (+1% bias vs. <0.5%). The next step of HARVEST-X involves the ongoing benchmarking of PETALE within ICSBEP. Additional experimental follow-ups are planned, notably the accelerator-based GRAPE campaign. Further oscillations and analysis are also in preparation for BLOOM, including validation using local signals, and higher reactor power oscillations to improve precision. Complete data assimilation studies for dedicated applications are still to be performed, in collaboration with the Paul Scherrer Institute.