[235] Extending the life of an evaporator vessel through testing, inspection, modelling and analysis

Assessment of ageing nuclear plants and subsequent lifetime extension poses a significant challenge to plant managers. This is particularly the case for vessels supporting fuel reprocessing operations, where the challenge of operating and working conditions, ie high radiation, is combined with a lack of access for conventional inspection and repair techniques.
This case study focuses on Evaporator C, a strategically important vessel required to support Sellafield Ltd’s hazard reduction strategy. The work involved ultrasonic thickness inspections, modelling and simulation, structural and statistical analysis, along with corrosion studies (including the use of large-scale test-rigs). This paper also provides a brief history of plant operations and the assurance required to ensure safe continued operations.
This work has led to an improved operational life for Evaporator C through better understanding of the corrosivity of active liquors, heat transfer characteristics and structural integrity of the vessel, resulting in changed operational procedures and enhancing confidence that operations can continue safely. Consequently, Evaporator C successfully completed missions in excess of its planned life, while a new evaporator, Evaporator D, was being commissioned. The extended lifetime of Evaporator C has enabled it to be kept as a reserve now that Evaporator D is in active service.