Core barrel is a cylindrical support structure in reactor internals in PWR (Pressurized Water Reactor) plants and a baffle-former assembly and fuel assemblies are placed in it. Barrel former bolts fasten a baffle-former assembly to Core barrel. Core barrel and Barrel former bolts are exposed to relatively high neutron irradiation due to their proximity to fuel assemblies. In order to properly manage the structural integrity of these parts against the degradation caused by neutron irradiation, inspection and evaluation guidelines was established in around 2000. Since then, the guidelines have been updated incorporating such knowledge as operating experience and research results. In this paper, the history of the guidelines including the current activities is overviewed.