Assessment of seismic code case N-411 for application to candu piping

This study addresses in three parts, the applicability and implementation of the Code Case N-411 for seismic analysis of CANDU piping systems. In the first part, a piping model is analyzed using Code Case N-411 dampings. Contributions of different support excitation groups are accounted for using a) enveloping the spectra among groups, b) using multisupport excitation option (MSE) with absolute summation among groups and c) MSE option with SRSS summation. Results from these analyses are compared against those obtained by time history analysis. It is found that Code Case N-411 with SRSS method of combination still maintains conservatism over time history analysis. In the second part, a method of producing the composite N-411 spectra, by interpolation among curves of various dampings together with ±15 percent peak broadening rule, is described. In the third part, a method to extrapolate and generate new spectra from the ones available is given