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NUCLEAR SAFETY &

SEISMIC RISK MANAGEMENT IN

FRANCE: OVERVIEW

SEPTEMBER 28, 2016, SCIENTIFIC & TECHNICAL SEMINAR AT THE

CANADIAN NUCLEAR SAFETY COMMISSION

| Catherine BERGE-THIERRY,

Seismologist & Seismic Risk Expert at CEA

21 OCTOBRE 2016 | PAGE 1 CEA | 10 AVRIL 2012

CONTENT

1. Introduction

2. Seismology & French Approach to define the seismic hazard

for nuclear facilities

3. French Approach and acceptance criteria for the design and

assessment of nuclear facilities

4. Seismic risk management in light of Fukushima action items

5. The SINAPS@ research project

6. Conclusions et Discussions

| PAGE 2 CEA |SEP., 28th, 2016

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5. THE SINAPS@ RESEARCH PROJECT

21 OCTOBRE 2016

| PAGE 3

CEA | 10 AVRIL 2012

5. THE SINAPS@ RESEARCH PROJECT

5.1. Framework & Motivations of the project (SEISM Institute),

5.2. Objectives, Resources and Partnership

5.3. Scientific Structure

5.4. Synthesis of identified limitations of the current regulatory nuclear practice

5.5. Overview of the 5 scientific work packages

5.6. Focus on some specific key issues

“control point – where is defined the hazard?”

Toward an outcropping bedrock seismic hazard definition

instead of current free field SHA including partially site effects

Non-linear interactions between seismic wave field, soil and

foundations

| PAGE 4 CEA |SEP., 28, 2016

SMIRT-2015

presentation

• NED post- SMIRT-2015

special issue

• Paper accepted for

WCEE2017

TOWARD AN INTEGRATED SEISMIC RISK ASSESSMENT

FOR NUCLEAR SAFETY IMPROVING CURRENT FRENCH

METHODOLOGIES THROUGH THE SINAPS@ RESEARCH

PROJECT

CATHERINE BERGE-THIERRY1, P.Y. BARD2, T. CHARTIER3, R. COTTEREAU4, E.

BERTRAND5, F. LOPEZ-CABALLERO4, D. CLOUTEAU4, S. GRANGE6, S. ERLICHER7, F.

HOLLENDER8, P. KOTRONIS9, M. LANCIERI3, A. LAURENDEAU8, A. LE MAOULT8, N.

MOUSSALLAM10, M. NICOLAS8, F. RAGUENEAU11, J.F.SEMBLAT12 AND F. VOLDOIRE13

1ATOMIC ENERGY COMMISSION (CEA) SENIOR RESEARCHER & SINAPS@ COORDINATOR, FRANCE

2ISTERRE, 3IRSN, 4ECP, 5 CEREMA, 6 INP-GRENOBLE & UJF, 7EGIS, 8CEA, 9ECN, 10AREVA, 11ENS CACHAN,

12IFSTTAR, 13EDF ,

| PAGE 5 Paper 571, Division VII

CEA | 19 JUILLET 2012 | PAGE 6

OUTLINE

Context

SINAPS@ project motivations

Focus on the « Risk Assessment » Work Package 4

In short … WP1, WP2, WP3, WP5 and WP6

Conclusion

CONSULTANCY MEETING EBP PHASE 2

WORKING AREA 2, TASK 2.1. FEB. 22-26TH, 2016

CONTEXT - SEISMIC MARGINS (S.M.)

Several international programs on S.M.

Niigataken Chuetsu Oki, M6,6 EQ 2007 : Kashiwazaki-Kariwa NPP experience

IAEA Karisma benchmark

Extension life duration of NPP’s (subject raised in France since 2009),

2011, Tohoku, M9, EQ & Fukushima accident :

Underestimation of Seismic & Tsumani Hazards

Consequences on French NP’s : Complementary Safety Studies (C.S.S.) (2011-12)

French Nuclear Safety Authority asked all Nuclear Operators to “assess the capacity of the existing NPP to sustain seismic levels higher than the one considered for design and/or during safety reassessment reviews”.

requires to assess the Seismic Margins of existing plants

| PAGE 7

SINAPS@ R&D collaborative project

Early 2012 the French Government published a call to initiate research projects

to improve NP’s Safety regarding internal and external events.

SINAPS@: « Earthquake and Nuclear Plants – Improving and Sustaining Safety »

Main Issue: Identification and propagation of uncertainties (epistemic and aleatory)

on data and methods in the assessment of seismic risk (deterministic

& probabilistic approaches) in moderate to low seismic areas (considering

extreme seismic levels) :

Critical Opinions on the French and International Practices,

Improve Methodologies

Contribute to Seismic Margins Assessment,

& Formulate Recommendations

Strong Partnership ensuring the completeness of skills

13 teams, ~60 researchers/eng., 12PhD’s, 19 post-docs

Full Cost ~13M€, National Funding 5 M€

Sept 2013 – Sept 2018

| PAGE 8


SINAPS@ - 6 WP’S

« WP1 » Seismic Hazard

« WP2 » N.L. Site Effects & SSI

« WP3 » Structural &

SSC’s response

« WP4 » Seismic Risk Assessment

Demonstrative test case:

Kashiwazaki Kariwa NPP site

+ WP 5 BBI & WP 6 Knowledge Dissemination

SINAPS@ : WP4 – RISK ASSESSMENT & KK DEMONSTRATIVE CASE (D.C.)

| PAGE 10

Ground motion parameters devoted to seismic risk assessment

Parameters adapted to the vulnerability analysis, involving SSI.

Simulation and propagation of uncertainties

Statistical meta-models built on best-estimate finite element simulations and sampling techniques,

Performance of Bayesian methods and extreme statistics for fragility curves computing.

Demonstrative numerical case study “Kashiwazaki-Kariwa BWR unit 7”

Objective: “from the fault to probabilistic floor spectra”, including N.L. Site Effect

simulation, N.L. Soil-Structure Interaction, RC N.L. structural behavior.

KK Test case based on:

• Data from the July 16th 2007 Niigata-ken-Chuetsu-Oki earthquake,

• TEPCO measurements available for the former International benchmark KARISMA,

[ near-field natural seismic signals, soil & site geotechnical data, nuclear island structural parameters...]

WP1, WP2 & WP3


First Step : Estimating the Plant Fragility using current tools & practices

as required by French deterministic regulation

uncertainties treated through standard coefficients

• Seismic scenario : Chuetsu Oki 2007 EQ,

• Seismic Level [ Spectral Approach / GMPE(s) …],

• SSI, structural seismic & floor responses [elastic- linear - BEM-FEM]

• Accelerograms selected from Japanese databases.

• Fragility curves computed for 2 SSC’s

• Damage criteria assessed using EPRI simplified approach

Second Step : Re-Assess the Plant Fragility using

state of art knowledge & innovative methods [SINAPS@],

including variabilities and N.L.

propagating uncertainties through probabilistic approaches

• Seismic inputs from a PSHA study, 3D accelerograms from UHS (WP1),

• Use more « realistic » methods including variabilities & uncertainties, N.L., SSI and Site Effects (WP2),

• Use of N.L. structural models provided by (WP3),

• Fragility curves assessed using probabilistic approaches [uncertainties accounted],(WP4).

General 2D stratigraphy [ V. Pavlenko and K. Irikura].

SINAPS@ WP4 – THE KK D.C.

Structural model of RB Unit 7, [Banci and Zentner 2015].

(i) get forward S.M. through identification of key parameters & assumptions

uncertainties treatment & methods used in the whole seismic chain.

KK D.C. (ii) validate and disseminate methodologies for practitioners and structural engineers.

| PAGE 12

WP1 MAIN ISSUES & PROGRESS

«SEISMIC SOURCES CARACTERISATION, GROUND MOTION PREDICTION & UNCERTAINTIES »

French Metropolitan territory

- Diffuse seismicity,

- Uncertainties in meta data of seismic catalogs,

- Difficulty to identify faults and associate deformation rates,

- Poor or lack of knowledge on soil properties (site effects)

(…)

- Which Seismic Scenario ? (Magnitude ? Distance ?)

- Which Maximum magnitude to account for (PSHA) ?

- Large dispersion in Ground motion predictions

(…)

Great Uncertainties Large dispersion in SHA

Major challenges : (i) Analysis of appropriate methods for seismic hazard evaluation vs

seismicity knowledge and the uncertainties.

(ii) Provide to WP2-3-4&5 accurate seismic outputs

Improving Characterization of « French data » & Metadata and their uncertainties;

Sensitivity of methods (probabilistic or deterministic) towards data / assumptions

Hierarchy in data/parameters used in seismic hazard process and evaluation of impact of uncertainties;

Interface between hazard and vulnerability of structures - " relevant indicators « / selection of time series ?

13

PSA

SINAPS@ – WP 1 : S.H. practices & outputs … Probabilistic : UHS IAEA main practice / post-Fukushima Assessments

Gutenberg-Richter Recurrence Characteristic earthquake

Uniform Hazard Spectrum

Prediction of ground motion and variability

13

Small local earthquake

Great regional earthquake

Hz

Prediction of seismic motion = response spectr(a)um

Envelop Spectrum

« Reference earthquake(s) »

Deterministic – scenario Current practice in France

Seismotectonic

Zone

dmin

Seismicity

Fault

WP2, WP3 and WP4 : - Spectra « levels » / Uncertainties

Need of time series (T.S.) … -Methodologies to select T.S. ? - Impact of selected T.S. (natural or

synthtics) on structural response ?

| PAGE 14


NON LINEAR SITE EFFECTS / SOIL-STRUCTURE INTERACTION (1/3)

Objectives of WP2 :

Improvement of current-practice methods defining the input motion at structure base

Based on results obtained from WP1

Including spatial variability of seismic motions

quantification of the effect of uncertainties of various soil materials

Development of new methods

From the fault to the equipment's : including non-linear behaviour and variability

Coupling of the seismic source models, wave propagation, and structural codes

New seismic data acquisition to validate numerical developments

In high seismic activity countries (Japan)

and a European seismic framework (low to moderate) <-> Greek test site

KEY ISSUE: Track & propagate the uncertainties, avoiding double counting from WP1 to WP2 … !

SINAPS@ strategy:

WP1 : providing Hazard at the “Bedrock condition” reference,

WP2: Assess Non-linear effects from the bedrock to the plant foundations, & SSI


NON LINEAR SITE EFFECTS / SOIL-STRUCTURE INTERACTION (2/3)

Argostoli – Greece - Test Site

Vertical and Horizontal accelerometric networks,

Spatial variability/coherency of seismic motions,

Validation in 2D or 3D conditions

3D Spectral Elements Simulation

• Spring 2015 : Release of the Linear Soil behavior,

• To be completed by a kinematic source model, N.L. soil behavior and structural code

• Development of a large-scale non-linear probabilistic model from source to structure

enable to account for variabilities and propagate uncertainties.

•

60*60*30 km3 mesh of Argostoli

Island and the surrounding sea

Test site Argostoli

Seismic network installed in the framework of SINAPS@ after the Argostoli January 26, 2014 M6 EQ

Continuous Data acquisition

Regional model to site effects / spatial variability and SSI studies (data constrained)


SINAPS@ WP 3 STRUCTURAL AND COMPONENTS SEISMIC BEHAVIORS

(3/4) Major challenge : Enhance the modeling relevance regarding the structural vulnerability assessment

(under severe seismic loadings)

Task 1 : Model calibration and Experimental Comparisons

1. Calibrate the dynamic model

2. Estimate the Modeling to Experiment Gap

3. Modeling update

Task 2 : Nonlinear Dynamic behaviours

• Modal superposition,

• Multifiber beams models,

• Plates and shells 2D models,

• Full 3D models,

Task 3: Seismic Isolation – Reinforcement / Design Optimization

Mo

del

s re

du

ctio

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Mu

lti-scales a

na

lysis

Strong interactions

• WP1 : S.H. outputs relevance / time series selections/seismic damage indicators (PhD)

• WP4 : provide relevant structural models from simplified to complex one’s

• All WP : check uncertainties propagation/treatment


SINAPS@ WP 5 BUILDING / BUILDING INTERACTION (BBI)

(3/4)

Objectives: Evaluation and reduction of pounding of existing adjacent nuclear

buildings during earthquakes.

Topic highlighted in French Post-Fukushima C.S.S.

Pounding can create

• Stresses in local areas and collapse

• Floor spectra modification

Work package resources:

• Access to CEA/TAMARIS shaking table facility

• 1 PhD (Sept-2015), 2 scholarships

• 50 man.months

• Ressources for mockup, instrumentation, etc.

Work plan:

• State of the art (2014)

• Design of the experimental setup (2015)

• Preliminary numerical investigation (2015)

• Tests (2016 & 2017)

• Analyses (2017 & 2018)

One of the very few ST study (California)

From A. Le Maoult et al., 2015. Azalée CEA shaking table


SINAPS@ WP 6 TRAINING & KNOWLEDGE DISSEMINATION

(3/4)

Objectives :

• 2 training sessions during the project,

• All topics of Seismic Risk Assessment, particularly for NPs,

• State of the Art of knowledge, data, modelings and methodologies

• Current seismic risk approaches, but also other innovative.

Session 1 Summer School June 2016 (in French)

for Master, Ph D’s, post doctorates &

young researchers/engineers.

http://www.institut-seism.fr/formation/sinaps2016/programme/

Session 2: in 2017 in collaboration with IAEA-ISSC (in English)

for researchers (academic, safety authorities,

technical supports, gov.org., design offices …).

Participation of international experts.






CONCLUSION

SINAPS@ aims

To prioritize parameters and Assess Impact of Uncertainties (data & methods) on all key steps: seismic hazard, site effects, soil-structure interaction, seismic behavior of structures and equipment's,

risk assessment.

To Identify & quantify potential seismic margins

from data / meta data / assumptions/ methods / uncertainties treatment WP4 KK D.C.

To disseminate Knowledge/Practices on Seismic Risk Assessment [2 training sessions 2016 & 2017]

To Formulate Recommendations for future R&D actions and efforts on data acquisition, regulatory

developments and updates

Achieving these goals calls for strong inter-disciplinarity in and between all WP’s

Currently

6 complementary WPs whose experimental & numerical work is now well engaged

~ 60 researchers/engineers involved, 12 PhDs, 19 post-docs already working or beginning soon

Next SINAPS@ progress point during SMIRT24 !


PAPER PUBLISHED SOON IN NUCLEAR ENG. & DESIGN

NED-SINAPS@-2016

Paper which presents, for each step of the seismic risk analysis:

• The state of practice in the French Nuclear Approach,

• The advantages and limits identified from return experience,

• Illustrates the gap with recent R&D results and improvments,

• The specific (on data) or more generic (methods) objectives of SINAPS@.

NED-D-16-00247-Revised-after-review-24-06-2016.pdf






PAPER ACCEPTED FOR THE WCEE2017

WCEE-2017-SINAPS

Paper which presents a practicle application on the Kashiwazaki-Kariwa site.

On the influence of the « control point » where the seismic input (from SHA)

is transferred to the SSI computation,

On soil non-linearity / outcropping bedrock condition

On the use of the equivalent linear method to deconvolve the seismic input

from the surface down to foundations or basement reactor,

Check the impact on the fragilty curves estimates,

A two steps study :

• Initial Phase: «French current practice » (free field seismic input & deconvolution)

• Final phase: defining the seismic motion at the outcropping bedrock,

../../../../SINAPS@-VALO/WCEE-Santiago-Chili-2017/Version-2/Version-Finale/APRES-REVIEW/Paper3553-AfterReview.pdf





GLOBAL SEISMIC RISK ANALYSIS – SINAPS@


SINAPS@ - CASE STUDY


Assumptions: (see KARISMA, IAEA 2010 benchmarck)

Seismic scenario: the 2007 NCOE earthquake (Mag 6.6 / Epicentral dist 16 km),

Reactor building N°7

Soil column: very low Vs30m (250 m/s) at the near surface,

Bedrock found at 167m in depth (Vs30m = 720 m/s)

RB7 model: simplified but including the embedment

Structural behavior : elastic linear

Soil : non linear properties

SSI : equivalent linear method

Linear transfer from structure to equipment

CASE STUDY – SCHEME OF GEOLOGY/ RB7


Simplified scheme of the KK SINAPS@ DC. The RB7 is embedded over 25 m.

Beneath the soil the bedrock is found at ~167 m in depth. Stars indicate location

of different “control points”.

STRUCTURAL RB7 MODEL


CASE 1: SEISMIC INPUT AT THE FREE SURFACE

(STAR 1) – SOFT SOIL VS30=250 m/s


NCOE 2007 scenario (Mw=6,6 and epic.dist. of 16 km), 50 synthetic ground

motions have been generated whose mean response spectrum fits the target

scenario spectrum assessed using the Campbell and Bozorgnia (CB) GMPE).

Figure 6 presents the initial 50 strong motions set.

To increase the seismic inputs number, the “classical engineering scaling”

process is applied on the set (with factors of 0,5, 1, 2, 2.5 and 3).

CASE 1: RECORDED NCOE DATA VS SYNTHETICS


DECONVOLUTION FROM SURFACE TO - 25m (EMBEDMENT FUNDATIONS LEVEL, CONTROL POINT 3


To account for the nonlinear soil behavior, a linear equivalent approach is used

(similar to that used for the original KK benchmark): for each seismic input of the 250

strong motions (amplification factors of 0.5, 1, 2, 2.5 and 3 on initial 50 data), an

iterative procedure is applied assessing the equivalent soil column properties (through

the shear strain, G modulus reduction, damping ratio).

Finally the seismic input at the reactor basement is obtained for every input signal, if

the process converges.

A significant number of seismic signals (among them, especially those coming

from the “scaling process” with factors 2, 2.5 and 3) produced “divergence” in the

linear equivalent deconvolution approach, highlighting the problem related to

the use of the method above its own limitations (usually 0.1% shear strain,

threshold also recommended in [3]) to a soil site which is highly nonlinear in such

acceleration domains. In the following, we consider deconvolution results only

if the maximal soil shear strain does not exceed 0,8% (as done in the IAEA

Karisma benchmark).

CASE 2: SEISMIC INPUT AT THE OUTCROPPING BEDROCK

(STAR 2) - VS30 = 720 m/s THEN DECONVOLUTION TO – 25m


Now 50 seismic signals are generated at the control point 2, at the ground surface for

a bedrock site condition (outcropping bedrock, Vs30=720 m/s) in order to avoid the

“soil non linearity” phenomenon, still fitting the CB2008 GMPE.

Figure 9 : seismic motions re-assessed at the RB7 basement, after the deconvolution.

In the left figure (“case 1”), a large amplitude appears for one of the signal

exhibiting the deconvolution “failure” with such a nonlinear soil using linear

equivalent method. On right, generating the initial seismic input at the outcropping

bedrock (“case 2”) ensures the stability of the deconvolution.

IMPACT ON THE FRAGILITIY CURVES CASES 1 & 2


a “fictive” equipment - resonance frequency postulated at 4 Hz: the failure criterion is

the exceedance of its 5% damped PSA at 4 Hz of a level of acceleration; this is

supposed unknown, and will be explored during the study.

“RB7 – responses sets 1 and 2”, RB basement motions transmitted to the equipment.

Figure 10 presents in ordinates the PSA values corresponding to seismic inputs from

set 1 (triangles) and to set 2 (circles) as function of PGA values at control point 3 - RB

basement at -25 m: the color scale is related to the soil distorsion rate.


Finally, the fragility curves of the equipment have been determined from the 145

structural responses for the set 1 (excluded the 105 runs that do not converge or the soil

shear strain is over 0.8%), and from the 157 inputs of set 2. Theses fragility curves have

been approximated by the cumulative distribution function of a lognormal random

variable.

IMPACT ON THE FRAGILITIY CURVES CASES 1 & 2

CONCLUSIONS OF THE STUDY


This study also illustrates the biases which can be introduced into the fragility

assessment process. The median acceleration of the fragility curve and its

uncertainty (value) are different in case of using set 1 data or set 2, and finally

the case 1 approach (which has to be proscribed) would be not conservative

(Am-set1 systematically higher than Am-set2).

To conduct the full seismic risk analysis, this fragility curve should be convolved to the

seismic hazard curve: this latter step should be necessarily performed by

seismologists at the control point 3 to assure the coherency of the whole process.

Such SHA in depth at the outcropping bedrock site condition is clearly not the

current practice in France (SHA is always performed at the free field level, including

potential site effects, and most of the time SHA is given through response spectra, the

time series selection and generation being sensitive and complex problems).

Without a careful check at each step (and especially analyzing the physical meaning

of incredible high acceleration values resulting from the deconvolution phase -

using a methodology not adapted for such high nonlinear soil behavior) the

fragility curve itself (from set 1) could be considered as “acceptable”, whereas this

study demonstrated its unrealistic and unphysical bases.

Contact

[email protected]

& Consult

http://www.institut-

seism.fr/en/projects/sinaps/

The work carried out under the SINAPS@ project benefited SSRR

French funding managed by the National Research Agency under

the program “Future Investments”

[SINAPS@ reference No. ANR-11-RSNR-0022].

THANKS TO ALL SINAPS@ CONTRIBUTORS

THANK YOU FOR YOUR ATTENTION

mailto:[email protected]



http://www.institut-seism.fr/en/projects/sinaps/




Commissariat à l’énergie atomique et aux énergies alternatives

Centre de Saclay | 91191 Gif-sur-Yvette Cedex

T. +33 (0)1 69 08 66 55

Etablissement public à caractère industriel et commercial |

RCS Paris B 775 685 019 21 OCTOBRE 2016

| PAGE 34

CEA | 10 AVRIL 2012

Catherine BERGE-THIERRY

CEA/DEN/DANS/DM2S

• Seismologist – Seismic Risk Expert Centre de Saclay

[email protected]

• SINAPS@ R&D project coordinator


• SEISM Institute Scientific Director

http://www.institut-seism.fr







http://www.institut-seism.fr/



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