Seismic Response Analysis and In-Structure Floor Spectra (Task 5) and Seismic Risk Quantification (Task 13): Difference between pages

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===Objective===
===Objective===
The objective of this task is to derive the best-estimate (or median-centered) seismic responses and their variability in the form of structural loads or floor response spectra.  The loads and floor response spectra define the demand for which SSCs are evaluated.
The objective of this task is to quantify CDF and LERF frequency from the SPRA model.   


===Purpose===
===Purpose===
Derivation of these best-estimate loads and floor response spectra and their variabilities are obtained through simulation probabilistic response analysis, by new deterministic analysis with estimated variability, or by scaling of the SSE responses and assigning variability.
This section provides guidance for assembling the results of the seismic hazard analysis, fragility analysis, and seismic sequence models, after they are completed, to estimate the CDF and LERF.


===Guidance===
===Guidance===
The best-estimate seismic demand is determined at the mounting point of each item on the SEL to support fragility calculations.
One approach used in SPRA is to develop a discrete hazard interval model using a PGA-based hazard curve as the base SPRA model quantification.  The modeling approach is illustrated in the following figure.
Seismic demands are calculated by analyzing the dynamic response of structures and equipment to seismic input.  Typically, seismic structure response analysis is first conducted using the input ground motion.  Then, structures are evaluated using structure forces and displacements.  The equipment and systems within the structures are evaluated using in-structure seismic response as input.  Depending on the fragility approach, either realistic or somewhat conservative seismic demands can be developed from the structure and equipment response analyses.


For the separation of variabilities (SOV) fragility approach, median (realistic) seismic demands are calculated using median centered models and analysis parameters.  For the hybrid fragility approach, the response factors and variabilities are used to inform the development of 84% non-exceedance probability (NEP) responses. 


To account for conservatism or non-conservatism in the dynamic analysis methods, structure and equipment response factors are applied to the fragility as lognormally distributed random variables.  The median values of these random variables are used to calculate the median ground acceleration capacity.  Variabilities in the response factors are propagated through the seismic capacity analysis to calculate logarithmic standard deviations for fragilities.  
[[File:13_SPRA_Modeling_Approach.jpg|1000px|thumb|center|Figure 13-1 Graphical depiction of a typical seismic probabilistic risk assessment modeling approach (from EPRI 3002000709)]]
 
The applicable variables used to generate floor spectra are as follows:
 
* Spectral shape
The elements of the analysis are summarized below:
* Ground motion incoherence
* Seismic initiators derived from site-specific probabilistic seismic hazard analysis ([[Seismic Hazard Analysis (Task 6)]])
* Damping
* Seismic accident sequences developed by using a seismic initiating event tree (SIET) and a set of accident sequence event trees from the FPIE PRA ([[Fault Trees and Accident Sequences (Task 11)]])
* Modeling
* Seismic System fault trees ([[Relay Chatter Evaluation (Task 9)]], [[Seismic Fragility Calculations (Task 10)]], [[Fault Trees and Accident Sequences (Task 11)]])
* Mode combination (if mode superposition time history is used)
* Fragility analysis ([[Seismic Fragility Calculations (Task 10)]]) is used to model seismically induced system failure modes in the event tree and fault tree models ([[Fault Trees and Accident Sequences (Task 11)]])
* Soil–structure interaction, including reduction with depth of seismic input
* Crew interface with accident mitigation systems is incorporated into the seismic system fault trees as modified by the fragility analysis ([[Fault Trees and Accident Sequences (Task 11)]], [[Seismic Human Reliability Analysis (Task 12)]])
* Software is used to process this information into a cohesive framework and quantify the models
 
'''Software'''
 
The analytic tools for the development of a quantified model may use the EPRI CAFTA code, augmented by the ACUBE Binary Decision Diagram (BDD) software (or an alternative BDD software).  The CAFTA code is well tested and widely used in various industries and numerous countries. CAFTA is available together with ACUBE, PRAQuant, FRANX and other tools through the EPRI .
 
The SPRA model is typically developed in a modular approach.  Event trees (converted to fault trees), event tree top logic (nodal fault trees), and system-level fault trees are all developed as distinct files.  In addition, the FRANX tool may be used to develop a relational database for linking individual fragility events to existing, modeled basic events.  This modular structure allows individual files to remain manageable and reviewable.  A single-top model used for quantification may be developed by merging the previously described files.  Merging the files into a single-top model is a standard CAFTA modeling technique that is performed by the analyst.
 
The model may be quantified using PRAQuant, from the [https://www.epri.com/search#q=Phoenix%20Architect&t=research&sort=relevancy&f:@typecategory=Software Phoenix Architect software suite].  Also, due to the special circumstances within seismic modeling (for example, overcounting caused by numerous high failure probability events), the ACUBE code, which uses the BDD algorithm, or an alternative software is used in model quantification to obtain a realistic assessment of the total CDF risk metric (or individual accident sequence frequencies as desired).


==Supplemental Guidance==
==Supplemental Guidance==


===Related Element of ASME/PRA Standard===
===Related Element of ASME/PRA Standard===
Part 5, Seismic Fragility Analysis (SFR)
Part 5, Seismic Plant-Response (SPR)


===EPRI Guidance===
===EPRI Guidance===
''Seismic Fragility and Seismic Margin Guidance for Seismic Probabilistic Risk Assessments'' ([https://www.epri.com/research/products/000000003002012994 3002012994]) provides extensive guidance on conducting seismic response analysis.
''Seismic Probabilistic Risk Assessment Implementation Guide'' ([https://www.epri.com/research/products/000000003002000709 3002000709]), Appendix C Section C.2 describes software and quantification algorithms.
 
''Phoenix Architect v2.0 Suite'' ([https://www.epri.com/research/products/000000003002023512 3002023512])


===Other Guidance===
===Other Guidance===
(none noted)
(none noted)

Revision as of 21:25, 27 March 2025

Task Overview

Objective

The objective of this task is to quantify CDF and LERF frequency from the SPRA model.

Purpose

This section provides guidance for assembling the results of the seismic hazard analysis, fragility analysis, and seismic sequence models, after they are completed, to estimate the CDF and LERF.

Guidance

One approach used in SPRA is to develop a discrete hazard interval model using a PGA-based hazard curve as the base SPRA model quantification. The modeling approach is illustrated in the following figure.


Figure 13-1 Graphical depiction of a typical seismic probabilistic risk assessment modeling approach (from EPRI 3002000709)


The elements of the analysis are summarized below:

Software

The analytic tools for the development of a quantified model may use the EPRI CAFTA code, augmented by the ACUBE Binary Decision Diagram (BDD) software (or an alternative BDD software). The CAFTA code is well tested and widely used in various industries and numerous countries. CAFTA is available together with ACUBE, PRAQuant, FRANX and other tools through the EPRI .

The SPRA model is typically developed in a modular approach. Event trees (converted to fault trees), event tree top logic (nodal fault trees), and system-level fault trees are all developed as distinct files. In addition, the FRANX tool may be used to develop a relational database for linking individual fragility events to existing, modeled basic events. This modular structure allows individual files to remain manageable and reviewable. A single-top model used for quantification may be developed by merging the previously described files. Merging the files into a single-top model is a standard CAFTA modeling technique that is performed by the analyst.

The model may be quantified using PRAQuant, from the Phoenix Architect software suite. Also, due to the special circumstances within seismic modeling (for example, overcounting caused by numerous high failure probability events), the ACUBE code, which uses the BDD algorithm, or an alternative software is used in model quantification to obtain a realistic assessment of the total CDF risk metric (or individual accident sequence frequencies as desired).

Supplemental Guidance

Related Element of ASME/PRA Standard

Part 5, Seismic Plant-Response (SPR)

EPRI Guidance

Seismic Probabilistic Risk Assessment Implementation Guide (3002000709), Appendix C Section C.2 describes software and quantification algorithms.

Phoenix Architect v2.0 Suite (3002023512)

Other Guidance

(none noted)

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