Experience and status on primary system components after 15 years of operation in the nuclear power plant obrigheim

Abstract

At Obrigheim the first large pressurized light water reactor built in Germany is operating with a nominal power of 345 MW. Since the beginning of electricity production in later 1968 the nuclear power plant Obrigheim (KWO) has proved a reliable, a safe and also an economical operation with a high availability (83%) over 15 years.KWO has shown that it is possible to prove and maintain the safety and reliability of the primary components on the basis of the present regulations and safety requirements. This was achieved by careful maintenance and by applying improved non-destructive test methodsThe reactor pressure vessel with one circumferential weld near the core could be qualified for future operation by means of inservice inspection, irradiation programs, and by implementation of technical changes for normal as well as for abnormal conditions. To maintain the reliability of the steam generators, extensive eddycurrent testing of the tubes has been performed every year. In order to reduce the corrosive attack on the tubes the secondary water chemistry was controlled very sensitively by minimizing the leakage through the condensor and by using all volatile treatment. The intergranular corrosion of the tubes above the tube sheet could be reduced strongly; but an increasing number of small leakages occurred in the tube sheet region. 458 tubes had been plugged in the old steam generators before they were replaced in 1983 by new ones.In summary it can be stated that the continuous effort to maintain a high quality status of the components is responsible for the high operation availability of the plant.