Two decades of excellent AGR circulator operating performance at AVR Juelich

During the twenty years' operation period there were only a few events connected with circulator operation, which were of interest. In 1970 the frequency convertor was modernized: The mercury-vapor rectifier was replaced by thyristors. In 1974 the helium core outlet temperature was increased from 850 to 950 deg. C. In 1977 after 72,000 operating hours a leak of about 3 mm2 occurred in a superheater pipe in the steam generator. As a consequence 27 t of water penetrated into the primary system. Also the circulators were flooded to half their height. After drying and final revision of the reactor and its auxiliary systems, due to negligence one of the cooling water seals in the oil system had not been properly tightened. Thus there was a water ingress into the bearing oil followed by a temperature rise in one circulator bearing. Consequential damage was prevented by immediate shutdown. Disassembly of the circulator and replacement of the bearings supplied valuable information about the handling of contaminated circulator parts. Incidentally, it was stated when the bearing had been disassembled that the state of the bearing would probably have permitted further operation without exchange. In 1980 the AVR was adapted to the new safety requirements. The helium circulators including the oil systems and the electrical systems were not involved in this process. In the report about general operating experience the operating parameters are discussed in detail. An outlook is given on the further operating mode of the plant. Based on a record of 115,000 operating hours of the circulators, it can be said even today that a service-free operation of the circulators in gas-cooled reactors will be possible for several decades. 5 refs, 10 figs