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. {sup 23}Na(n,2n), {sup 75}As(n,2n), {sup 89}Y(n,2n) and {sup 90}Zr(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, As{sub 2}O{sub 3}, Y{sub 2}O{sub 3}, and ZrO{sub 2}. 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 {sup 235}U prompt fission neutron spectrum, the measured integral cross sections averaged in LR-0 spectrum were corrected for spectral shift. The obtained values of {sup 235}U spectral average cross section are: (3.84 ± 0.19) μb for {sup 23}Na(n,2n); (0.320 ± 0.015) mb for {sup 75}As(n,2n); (0.171 ± 0.006) mb for {sup 89}Y(n,2n); (0.107 ± 0.005) mb for {sup 90}Zr(n,2n). (authors)