Composite nozzle dam in the steam generator of a nuclear reactor

Abstract

The period of normal shutdown and maintenance for a nuclear power plant can be remarkably shortened when the examination and maintenance of the tubes of a steam generator are simultaneously carried out with refueling. The nozzle dam in a steam generator is a closure to block the flow of coolant from the inlet-outlet nozzles in a steam generator. Recently, the installation and removal operations of the nozzle dam were attempted using a robot rather than the manual operation because of the radioactive hazard. For the operation using the robot the weight of the dam must be reduced because the robot's payload for assembling operations is usually small. In this work, a lighter nozzle dam was designed and manufactured using a carbon-epoxy composite, a glass-epoxy fabric composite, an aluminium plate and honeycomb. The carbon-epoxy composite was used for the main structural material and the honeycomb was used to increase the bending stiffness, while the aluminium plate and the glass-epoxy fabric composite were used to reduce the stress concentration around bolt holes. Also, the variation in mechanical properties of composites with respect to radiation emission was investigated. In order to verify the structural integrity of the nozzle dam installed on the nozzle ring with bolts, the stress analyses of the nozzle dam under hydrostatic pressure were performed using commercial finite-element software and the pressure test was performed. The stiffness of the composite nozzle dam was measured and compared to that obtained by finite-element analysis. (C) 1997 Elsevier Science Ltd.