ML22236A547

NRC Slides for Decommissioning Engagement Panel 8-24-2022 Meeting

ML22236A547
Person / Time
Site:	Diablo Canyon
Issue date:	08/24/2022
From:	Clifford Munson NRC/NRR/DEX
To:
Lee S, NRR/DORL/LPL4
References
Download: ML22236A547 (12)

Text

Current Diablo Canyon Seismic Evaluation Dr. Cliff Munson Senior Level Advisor for Siting U.S.N.R.C

Outline

• Background

• Near Term Task Force Hazard Assessments

• Diablo Canyon Seismic Hazard and Risk Evaluations

• References

NRC Regulations - Safe Shutdown Earthquake

• Nuclear power plant structures, systems and components important to safety are required to be able to withstand effects of natural phenomena such as earthquakes

• Safe shutdown earthquake ground motion (SSE) is the vibratory ground motion for which safetyrelated structures, systems, and components must be designed to remain functional

NRC Regulations for Siting Facilities

• 10 CFR Part 100 - Reactor site criteria including geology and seismology

- Specifies siting investigations and analyses in order to determine Safe Shutdown Earthquake ground motion (SSE)

- Prior to 1997 SSE determined using Deterministic approach

• Ground motion from maximum earthquake used to determine SSE

DCPP Seismic Design Spectra Design Earthquake (1969)

Double Design Earthquake M7.25 at 20 km (1969)

Long Term Seismic Program Margin Analysis (1978)

Hosgri fault M7.2 at 4.5 km (1971)

NRC 2012 Request for Hazard Assessments

• In response to March 11, 2011, Great East Japan earthquake and tsunami NRC requested seismic hazard assessments for all U.S. NPPs

- Request specified use of presentday NRC regulations and guidance to assess hazard

- PG&E submitted its seismic hazard assessment to the NRC in 2015

Current NRC Regulations and Guidance for Seismic Hazards

• Post 1997 Geologic and Seismic siting regulations provided in 10 CFR 100.23

- 100.23 requires determining slip rates for local and regional faults

- 100.23 requires incorporating uncertainty into determining SSE

• Regulatory Guide 1.208 describes performancebased approach to define sitespecific ground motion

- Specifies a Probabilistic approach rather than Deterministic

- Uses riskinformed approach to develop site ground motion that achieves performance goals in standard ASCE 43

DCPP Seismic Hazard Assessment

• PG&E evaluated data from multiple offshore and onshore geophysical and geotechnical investigations to develop

- Seismic source model

- Seismic ground motion model

- Amplification of seismic ground motions due to local soil and rock properties

DCPP Seismic Hazard Assessment

• PG&E developed a detailed seismic source model for the region

- Fault slip rates

- Fault geometries and locations

- Maximum magnitudes for faults

- Multiple fault rupture scenarios

• PG&E developed a seismic ground motion model to assess ground motion amplitudes from multiple faults

- PG&E adjusted the ground motion model to account for the local site effects

DCPP Ground Motion Response Spectrum (GMRS)

DCPP Seismic Risk Evaluation

• Based on the results of the seismic hazard reevaluation PG&E performed a seismic probabilistic risk assessment (PRA)

- Determined seismic fragilities of structures and components

- Performed soilstructure interaction analyses

- Evaluated system accident sequences

- Evaluated containment performance

• Based on its review of the PG&E Seismic PRA, the NRC staff concluded that PG&E followed the appropriate guidance and adequately addressed the effects of the reevaluated hazard on the plant.

References

• Detailed summary of Diablo Canyon Seismic Hazard Assessment is provided in Section 3.3 of NUREG/KM017 ML21344A126

• PG&E Seismic PRA ML18120A201

• NRC Staff Assessment of Seismic PRA ML18254A040