Document: NUREG-0800
Document ID: 83897b75-c615-4927-a67e-da531e7cb01a
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A354.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Draft Revision 4 - December 2012 ISG-01 and also recognize that their application to licensing activities is rather limited to date. In addition, there are no field tests available to confirm the extent to which the incoherent free field ground motion reduces the structural response in terms of in- structure response spectra and member forces. Therefore, it is reasonable to place a limit on the reductions due to incoherency at this time. The staff will reconsider the limit when more information and associated data become available to better quantify the in- structure response reductions due to ground motion incoherency effects. The EPRI performed analytical studies which formed the basis for the staff’s guidance in DC/COL-ISG-01. These studies compared coherent ISRS results to incoherent ISRS results, based on the NRC-accepted coherency function. The structural model used has stick model representations of the AP1000 steel containment vessel, shield building, and containment internal structures, sitting on a large basemat. Review of the comparisons indicated that the ISRS are generally similar up to about 10 Hz. Above 10 Hz, there is generally a gradually increasing difference. Above 30 Hz, differences as high as 40-50% can be observed. The staff has accepted this level of reductions on a case-by-case review along with independent confirmatory analysis. Based on the uncertainties associated with the coherency function described above and the limited experience in its implementation to date, the staff has determined that it is reasonable to impose limits on the maximum acceptable reductions between coherent results and incoherent results. These reductions generally are in line with the EPRI studies. It should be noted that the proposed criteria allows for larger ISRS reductions than the specified limits if sufficient technical information is provided to support the larger reductions. The staff reviews and accepts the technical justifications for larger reductions