Abstract: A method for replacing bolts on core components of nuclear reactors includes machining away a bolt fastened at an installation site in a core component as well as the entire fastening of the bolt with an electroerosion machine. Machined-away bolt material is removed and caught with a filter. The bolt is then ejected from the core component with a closed force system. The installation site of the bolt is remachined with an accurate fit and a new bolt is subsequently inserted. An apparatus for replacing bolts on core components of nuclear reactors includes rails. An auxiliary platform is supported on the rails on both sides of a reactor pressure vessel. An auxiliary crane is disposed on the auxiliary platform and adjustable transverse to the rails. A tool carrier is guided on the auxiliary platform and suspended from the auxiliary crane. A tool is disposed on the tool carrier for replacing bolts on core components.