WURGASSEN TO BE DECOMMISSIONED - CRACKS I N THE NUCLEAR CORE POSE NO THREAT

Cracks in the core shroud have been detected in several boiling water reactor plants in the United States of America, Japan, Taiwan, Switzer land and Sweden. To this date, findings of this type have been made in a total of 23 plants. Also visual inspection of the core shroud of th e Wurgassen Nuclear Power Station revealed cracks during the 1994 revi sion. The cause was found to be intergranular stress corrosion crackin g (SCC) in 1.4550 type austenitic material sensitized by heat treatmen t. Safety assessment indicated cared no impairment of functional relia bility either during normal operation or under accident conditions. Ec onomic and licensing constraints prevented repair of the core shroud a lthough this has been achieved successfully in the United States and i n Japan. Consequently, replacement of the core shroud was prepared in the planning stage, and the feasibility of this step was demonstrated However, the fundamental modernization of the entire plant, which woul d have been necessary in case of replacement of the core shroud, cause d PreussenElektra to decide on decommissioning the Wurgassen plant on economic grounds. This is the first decommissioning decision about a c ommercial nuclear power plant in the old German federal states. Inspec tions of the other German boiling water reactor plants did not result in any indications of cracks in the core shroud ar-ea. The activities listed below were carried out by the following external firms: General Electric Nuclear Energy provided support in visual inspections, takin g samples of materials, conducting ultrasonic measurements to determin e crack depths, calculating residual welding stresses, and performing evaluations of technical safety. Siemens/KWU conducted research into m aterials and manufacturing steps, performed metallographic studies of materials samples. The ABB Reaktor-Voest-Alpine consortium did a feasi bility study of the the exchange of RPV internals in the Wurgassen Nuc lear Power Station.