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SEISMIC HAZARD ASSESSMENT AND ITS IMPACT ON NPP DESIGN

IAEA Technical Meeting – July 6 to 9, 2010Vienna

Philippe Monette

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TABLE OF CONTENT

• Generic design basis for Generation 3 reactors• Confronting the reality…• PSHA

- Basic elements- Concerns

• Consequences for New Build• The way forward ??

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GENERIC DESIGN BASIS FOR GEN 3 REACTORS• Utility requirements established in the 1990s• URD (EPRI) :- Standard, certified design should be based on generic, broad band spectra in accordance with Reg. Guide 1.60 and anchored at 0.3g PGA = CSDRS

- Site-specific Ground Motion Response Spectra = GMRS (SSE)- Seismic margin to be demonstrated for 1.67 x CSDRS (0,5g PGA)

• EUR Vol 2 Chap 4 Rev.C- Standard design based on generic, broad band spectra defined by 3 spectral shapes (H, M, S) and anchored at 0.25g PGA (horizontal) = DBE

- Seismic margin to be demonstrated for 1.4 x SSE- Site specific Ground Motion Response Spectra = SSE

EUR SPECTRA ANCHORED AT 0,25G

Nota: Spectra meant to envelope most sites in EUR member countries

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GENERIC DESIGN BASIS FOR GEN 3 REACTORS• Vendors have produced standard designs (certified designs in thecase of US) reflecting the EUR and URD

Reactor Seismic Design Basis CommentAP1000 0,3g PGA; modified RG 1.60

spectrumCSDRS

EPR 0,25g PGA; EUR spectra (H,M,S) 0,3g for USEPR and STD EPRVVER-1000 0,25g PGACANDU 6 0,2g PGA; CSA spectrum (Gen 2)ATMEA1 0,3g PGA; modified RG 1.60

spectrumAPR 1400 0,3g PGA

CONFRONTING THE REALITY…• PEGASOS: a first-of-a-kind PSHA in the heart of Europe• NCO Earthquake - July 2007 • US: the High Frequency Ground Motion issue• European SHA map

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PEGASOS

21 04 09 8TITLE OF THE PRESENTATIONKASHIWAZAKI-KARIWA NPP 16 JULY 2007

K-KJULY 2007

THE HIGH FREQUENCY GROUND MOTION ISSUE21 04 09 10TITLE OF THE PRESENTATION

NORTH ANNAESP

KRŠKO NPP1989 EARTHQUAKE

SEISMIC MAP

4/9/2010 COM

PARISON OF ATM

EA 1

WITH COM

PETITOR D

ESIGNS

13Seismic Hazard Map of Europe & Mediterranea

475 yrs Return Period

INTERMEDIATE CONCLUSIONS• EQ > Dbasis may occur• E Design margin• Older SHA estimates too low; newer estimates too high?• Many regions > STD Design

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PROBABILISTIC SEISMIC HAZARD ASSESSMENT• Recognition of large uncertainties in SHA chain

• Logic trees and scenario weighting• Aggregated seismic hazard curves at various confidence levels• Mean frequency curve dictates the seismic design input

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SEISMIC HAZARD CURVES1E-02

200 400 600 800 1000

ANNU

AL P

ROBA

BILI

TY O

F EX

CEED

ANCE

median15th percentile85th percentile

1E-03

1E-04

1E-05

1E-06

1E-08

1E-090

mean

ACCELERATION (cm/sec2)

1E-07

PROBABILISTIC SEISMIC HAZARD ASSESSMENT• Concerns expressed over the build-up of uncertainty

- Large uncertainties result in the CDF density function being extremely flat (i.e. at various confidence levels, there is a spread of several orders of magnitude)

• Concern over the slope of the mean hazard curve- No asymptotic value (= no maximum credible earthquake)- Very very large earthquakes at very very low probabilities impact the PSA results !!

• Concern over the aggregation and blending into a single UHS- Distinct earthquakes (e.g. near field/small magnitude vs far field/large magintude) produce

quite distinctive effects

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THE CONSEQUENCES FOR NEW BUILD• WARNING: The SSE level is on the rise ! (for new sites as well as for existing sites)

• Beyond-SSE levels pose a threat to the PSA objectives

• Big challenge to Standard Designs in moderate to high seismicityregions !

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EXISTING PLANTS21 04 09 19TITLE OF THE PRESENTATION

Design

Reevaluation / SMA

NEW PLANTS21 04 09 20TITLE OF THE PRESENTATION

Design

Seismic Margin / Seismic PSA

10-4

to10-5

/r.yr

10-5

to10-7

/r.yr

THE WAY FORWARD… ??21 04 09 21TITLE OF THE PRESENTATION

THE WAY FORWARD… ??21 04 09 22TITLE OF THE PRESENTATION

THE WAY FORWARD… ??21 04 09 23TITLE OF THE PRESENTATION

THE WAY FORWARD… ??21 04 09 24TITLE OF THE PRESENTATION

CONCLUSIONS• SHA is a critical component of site selection and characterization, even for moderate seismicity sites

• Large uncertainties can lead to a lot of variability in the SHA results and therefore in the SSE level

• Many moderate-to-high seismicity sites are candidate for new build � need for expanding the NPP seismic design capability of key reactor technologies

• Continuous improvement is needed in order to refine and stabilize the SHA methods, seismic response analysis methods, etc.

• Incremental cost of incremental safety can be very high !!!

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THANK YOU !!

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BACK-UP SLIDES

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