FITNESS FOR SERVICE EVALUATION OF CLASS 1 PIPING COMPONENT

ABSTRACT
This paper summarizes the methodology, procedure, and results of a fitness for service assessment performed for one CANDU outlet feeder in accordance with the COG FFSG Appendix E (Evaluation of Thinned Regions) Level 3. A wall thickness of 80% of the pressure-based thickness of the corresponding straight pipe is conservatively considered uniformly distributed along both tight radius bends. Plastic collapse load analyses are performed to address the pressure loading alone (E-6) and the bending moment plus coincident pressure loading (E-9). The crack initiation potential (E-10) is addressed by calculating the cumulative fatigue usage factor (Thermal & Seismic).
This paper highlights the major modelling and analysis details with particular emphasis on the challenges that cut feeder models would face when dealing with the seismic load. These challenges are handled using a full length feeder model and the results from both approaches are compared. It is demonstrated that the cut feeder model for this particular feeder is more conservative compared to the corresponding full length feeder model. As such, it is expected that the full length feeder model would have a significant potential in handling the seismic issues with CANDU feeder pipes. However, more analysis work is needed to confirm and support the findings of this paper in a more general sense.