Experience feedback on the maintenance of nuclear power plant pump rolling bearings

Rolling bearing maintenance in nuclear power plants is not seen as critical. The maintenance programmes only call for monitoring techniques once an evaluation of the consequences in relation to failure risks of the bearings has been carried out and the efficiency of such methods has been validated in a case by case basis. However, in terms of design, we are unhappy with 'under load' operating problems which are characterized by overheating of the bearings which can lead to destruction of the bearing. These problems have, on occasion, been underestimated by the designers. They also appear later on when bearings with 'improved' load capacities appear on the market which, paradoxically, no longer meet the operational requirements of the machines. 'Greasing problems' must also be mentioned. These can arise because of bearing design problems which are difficult to modify on an installed base of machines as EDS's. Another problem is the difficulty of defining a satisfactory optimum in terms of quality, frequency and quantity of greasing on machines operated in very particular conditions. Finally, the drive to optimize maintenance and the desire to reduce the risks attributed to the mixing of different greases entails the standardization of certain practices, notably the choice of lubricants. In this respect, the disparate nature of the nuclear base represents a difficult hurdle to surmount. (authors)