Buckling evaluation of System 80+trademark containment

The System 80+trademark containment may be subjected to compressive forces which could cause it to become unstable. The stability of the containment shell under prescribed loading combinations was investigated with two analysis levels: axisymmetric and three dimensional. An axisymmetric shell model, including additional mass to account for penetrations and the spray header system, was analyzed using BOSOR4 and BOSOR5 finite difference codes. Loading combinations with pressure, temperature, self weight, and seismic satisfied the American Society of Mechanical Engineers (ASME) stress allowables. The buckling assessment was performed using the worst meridian assumption, including material nonlinearities and a sinusoidal axisymmetric imperfection. The minimum factor of safety for Service Level C was 2.35. A SSE seismic margin of 2.91 was calculated. The ABAQUS finite element code was selected for the three dimensional analysis and tested with classical and BOSOR solutions. The maximum structural response was computed using response spectrum analysis and six potential buckling regions were identified. A set of equivalent static loads was determined for each of the six regions to regenerate the maximum SRSS stress resultants. For each region, combined loads were increased until an instability was detected. A minimum factor of safety of 1.91 was predicted, which does not satisfy ASME Section NE3222.1 or Regulatory Guide 1.57. Code Case N-284 is satisfied. The analysis is conservative primarily because the SRSS 10% method provides a conservative estimate of modal coupling