Benchmarking of activation rate in special core in LR-0 reactor

The experiments focused on the determination of activation reaction rates of selected IRDFF materials activated in a well-defined special core assembled in the LR-0 reactor are presented in the paper. The used core is designed and verified for IRDFF library testing by reactivity characterization, fission rates distribution and also neutron spectra measurement at the center of the core. ²³Na(n,2n), ⁷⁵As(n,2n), ⁸⁹Y(n,2n) and ⁹⁰Zr(n,2n) reaction cross sections were measured in this special core. The presented neutron cross sections were derived from experimentally determined reaction rates of irradiated samples of NaF, As₂O₃, Y₂O₃, and ZrO₂. These reaction rates are derived from gamma activities of the activation products of studied activation reactions. Net Peak Areas (NPA) of photons accompanying decay were measured using a semiconductor High Purity Germanium (HPGe) detector. Despite the fact that mentioned reactions have a threshold above 10 MeV, where the neutron spectrum in the special LR-0 core is nearly undistinguishable from ²³⁵U prompt fission neutron spectrum, the measured integral cross sections averaged in LR-0 spectrum were corrected for spectral shift. The obtained values of ²³⁵U spectral average cross section are: (3.84 ± 0.19) μb for ²³Na(n,2n); (0.320 ± 0.015) mb for ⁷⁵As(n,2n); (0.171 ± 0.006) mb for ⁸⁹Y(n,2n); (0.107 ± 0.005) mb for ⁹⁰Zr(n,2n). (authors)