Abstract: A pressurized water reactor fuel assembly with a guide tube and a method for producing a guide tube for control elements are provided. Such guide tubes in pressurized water nuclear reactors which are composed of zirconium alloys (zircaloy-2 and zircaloy-4) show sharp radiation-induced growth in the axial direction at the commencement of their use in the reactor core. The sharp initial growth of the tubes is compensated by an inherent contraction of the tubes. For this purpose, the guide tubes are given internal stresses which are reduced by tube contraction as a result of a radiation-induced supply of energy. During production, guide tubes which are too short are first produced and subsequently lengthened by at least 0.3% to a final dimension in a last production step. In order to lengthen the tube, it may be stretched on a straightening bench.

Abstract: In order to avoid uncontrolled secondary damage to a fuel rod, in particular a fuel rod being formed of Zircaloy and having a liner on the inside, in which the secondary damage may be generated by coolant that enters the fuel rod in the event of primary damage, a nucleus is deliberately provided in a cladding tube. The nucleus, although passivated in an undamaged fuel rod and not impeding the serviceability of the fuel rod, is activated by coolant which enters the fuel rod in the event of primary damage or by hydrogen or other reaction products produced in reactions of the coolant in the interior of the fuel rod and results in a small-area perforation. This prevents an aggressive atmosphere, which may result in unintentional large-area secondary damage at other points, from accumulating in the cladding tube after primary damage.