Regulatory application of seismic experience data for nuclear power plants in the United States

On the basis of its review and evaluation (Reference 3) of the SQUG GIP (Reference 2) and on the basis of the differences between current seismic qualification requirements and the criteria and procedures provided in the GIP, the NRC staff does not consider the USI A-46 methodology given in the GIP to be a 'seismic qualification' procedure. Rather, the staff considers the GIP methodology to be a seismic adequacy verification procedure, which was developed on the basis of generic equipment earthquake experience data, supplemented by generic equipment test data. The implementation of the GIP approach for USI A-46 plants provides safety enhancement, in certain aspects, beyond the original licensing bases. Therefore, the GIP methodology is an acceptable evaluation method, for USI A-46 plants only, to verify the seismic adequacy of the safe-shutdown equipment installed in the NPPs in the United States. With the new development in the experience-based approach for seismic qualification of equipment currently underway in the U.S. nuclear industry, there is a potential for future regulatory application of an experience-based approach as a seismic qualification method for certain selected equipment installed in NPPs in the United States. However, industry's use of the experience-based approach will be dependent on the submittal and staff approval of this approach. (J.P.N.)