The thesis was performed at Forsmarks Kraftgrupp AB in the department of mechanical engineering, FTCM.   Forsmark nuclear power plant has had problems with cracks in some of the control rods which are placed in the reactor at Forsmark 3. To investigate the cause of this, material samples were taken from five of the damaged control rods. This sampling of the rods resulted too short rods to be transported in the shipping container to the interim storage facility for used nuclear fuel in Oskarshamn.   Control rods are crucial components in a nuclear reactor, regulating the reactor effect by blocking or unblocking fuel rods. Control rods which have been in the reactor are always handled under water in order to protect against the radiation they emit.   The task was to design a control rod adapter that extends the control rod so transport can be performed from Forsmark. The goal of the work was a complete set of blueprints so the control rod adapter can be manufactured and mounted on the short control rods and then be transported to the interim storage facility.   The work began with mapping of how control rods normally being handled from the reactor to the interim storage facility. With the mapping as a basis, a requirement specification was made. From the specification and the information from the mapping different concepts were sketched. The concepts were evaluated and improved to a final concept, which was then drawn up with the CAD-program Inventor. Materials for the various features were selected and calculations were performed in calculation-program ANSYS 13.0. Finally, blueprints were produced of the control rod adapter.   The control rod adapter meets the requirement specification. It is easy to mount and has a robust design. A prototype should be manufactured to enable practical testing to verify that the control rod adapter works as planned.