9.1 Overview

This section is intended to provide the reader with information about the future use of the CEUS-SSC model for purposes of PSHA. Much of the guidance provided in this section is pragmatic and aimed at assisting the user such that the subsequent calculational process is optimized but the accuracy of the SSC model is maintained. The CEUS-SSC model was developed within the framework of a SSHAC Level 3 process, and all the required steps were taken to implement the letter and the spirit of the SSHAC guidelines (Budnitz et al., 1997). Chapter 2 describes those process steps in some detail. A key step in achieving this goal has been the careful consideration of alternative data, models, and methods, and-using the hazard-informed approach discussed in Section the center, body, and range of technically defensible interpretations into the SSC model. In this sense, the SSC model has been “optimized” to include only those assessments that capture present knowledge and uncertainties and are believed to be significant to hazard. Once this level of uncertainty treatment was reached, there was no further attempt to optimize or reduce the complexity of the model for purposes of subsequent calculational efficiency.

The CEUS-SSC model is a regional model, developed explicitly to calculate seismic hazard at nuclear facilities. For site-specific applications-consistent with the applicable regulatory guidance for the nuclear facility of interest-local data sets will need to be reviewed and possible site-specific refinements made to the model to account for local information. This could include consideration of local geologic structures or local seismic sources that were not considered in this regional SSC model. In addition, the SSC model will need to be paired with a comparable ground-motion characterization (GMC) model to perform hazard calculations. The SSC model was developed with due consideration of the likely types of information that would be needed for these GMC models (see Section 5.4). For example, each seismic source is characterized by its style of faulting and likely future rupture geometries.

The end product of the SSHAC process-and the deliverable for PSHA calculations-is the hazard input document (HID), which is discussed below in Section 9.2 and is provided in Appendix H. Instructions for implementing the HID are given in Section 9.3, with an eye toward simplifications that can be made for future applications without sacrificing accuracy. Section 9.4 discusses approaches to define the level of precision incorporated into a hazard analysis. The purpose of this analysis is to identify the changes in hazard that can be considered significant. One application of this concept would be to provide a basis for assessing whether future changes to the model would lead to significant changes in hazard, which in turn would require that the model be updated.

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