[en] The latest release of the VITAMIN-E multigroup cross-section library contains two different versions of neutron cross sections for natural iron, one based on ENDF/B-V MOD-1, and the other on MOD-3. The isotope ⁵⁷Fe has four inelastic-scattering levels below 846 keV, the energy of the first excited state in ⁵⁶Fe. The importance of the new cross sections was investigated by using both VITAMIN-E versions of the iron cross sections in S₈P₃ 174 group ANISN calculations for two Na-Fe shield configurations. In neutron penetration calculations through thick steel regions, ⁵⁷Fe can be 10 times more important than is indicated by its isotopic abundance in natural iron. The 14.4-keV inelastic level of ⁵⁷Fe is sufficiently important that it may be worthwhile to perform a measurement of this cross section to validate the ENDF/B-V MOD-3 value, which was obtained from nuclear model calculations. Shielding analyses were done with iron cross sections predating ENDF/B-V MOD-3 should be reviewed and may need to be revised