The paper describes a case in which with more detailed analysis of the seismic loads and with more elaborated, more accurate model the Main Steam Line of a 1000 MWe class nuclear power plant with BWR has been redesigned. Re-design and re-qualification has resulted in a new piping configuration with significantly reduced number of installed snubbers, and in a more simple support system. The analysis of the piping system has been repeated over twenty years after the original work, whereas the main differences consisted of changes in the piping code and the use of the abundant computational resources available today — besides revision of the earthquake analysis of the buildings. Final recommendation consisted in two suggested configuration change packages. One with a significant reduction in the number of earthquake restraints snubbers) with no need to further analyze elements of the support structure before implementation. A second one with an additional possibility to reduce the number of snubbers, but requiring analysis of piping support structures to see if the higher loads are still allowable or else if a reasonable hardware changes would reinforce structural elements to carry the new load.

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