KWU techniques for LWR fuel assembly repair and reconstitution

Although KWU fuel assemblies (FA) have shown an excellent operation record since the early beginnings of commercial nuclear power generation, techniques for FA inspection, FA repair and reconstitution were developed at a very early stage, both for PWRs and BWRs. In all KWU built plant reconstitution equipment is installed in the spent fuel storage pool. For other utilities, KWU can provide its reconstitution technique for PWR assemblies by means of transportable equipment. In addition, an electric discharge machining technique (EDM) is available to be applied to non-KWU fuel assemblies originally not intended to be repairable. The techniques applied for a variety of repair and reconstitution tasks describe such as removal of defective rods, including EC testing, re-conditioning of damaged spacers, and transfer of fuel rods to another skeleton. Some more recent developments are sketched in the following. Spacer springs broken by baffle jetting are a common reason for transfer of rods into a new skeleton. To avoid cost for disposal of the old skeleton, KWU has developed special dummy rods with retractable springs for filling up the damaged rod positions in-situ. The repair and reconstitution equipment not only serves for repair of defective fuel assemblies but is also the key to fuel performance evaluation and future developments by providing access to individual fuel rods. Measurements of fuel rod diameter and oxide thickness are performed in many plants to provide the data base for design and further development. To extend the burnup of pathinder fuel rods, they are transfered from their original assembly to another host assembly. Selected fuel rods are removed at intermediate or final burnup for detailed examinations in hot cells. All techniques have been applied to a large number of PWR and BWR fuel assemblies which were subject to further investigations. (author). 7 refs, 10 figs, 3 tabs