SEISMIC RE-EVALUATION OF OLDER NPPs...IN EARLY 1990 US NRC INITIATED IPEEE – SSE ONE OF MAJOR EXTERNAL EVENTS 30.11.2011 5 SEISMIC MARGIN REVIEW PROCESS IN MAY 1984 US NRC FORMED

30.11.2011 1

SEISMIC RE-EVALUATION OF OLDER NPPs

L. Pecinka. NRI Rez

IAGE WORKSHOP 2011

30/11/2011 2

CONTENT

SEISMIC MARGIN REVIEW PROCESS

DETAILED DESCRIPTION OF THE SEISMIC REVIEW PROCESS

SEISMIC FRAGILITIES FOR NPP’s

CONCLUSIONS

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HISTORICAL BACKGROUND

SINCE LATE 1970’s SEISMIC RE-EVALUATION HAS CARRIED IN

SEVERAL STAGES AT THE US NRC

IN THE LATE 1970’s AND EARLY 1980’s SEP WAS CARRIED TO

ELEVEN OLDEST NPP’s (CONSTRUCTION PERMITS BETWEEN

1956 – 1967

– DESIGN CRITERIA WERE LESS RIGOROUS THAN THE CRITERIA

SPECIFIED TODAY IN NRC RG AND SRP

– FOCUSED ON REVIEW OF THESE PLANTS WITH THE OBJECTIVE OF

SEISMIC UPGRADING

– KEY ELEMENTS

DETAILED INSPECTION OF THE PLANT

REVIEW OF EXISTING DOCUMENTATION, REPORTS, PLANS AND

CALCULATION

REANALYSIS OF CRITICAL STRUCTURES AND EQUIPMENTS USING LESS

CONSERVATIVE CRITERIA THAN THE SRP FOR GROUND RESPONSE

SPECTRA, DAMPING, DUCTILITY ETC.

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HISTORICAL BACKGROUND – cont. 1

IN THE LATE 1980’s UNRESOLVED SAFETY ISSUE A-46 WAS

INITIATED TO VERIFY THE SEISMIC ADEQUACY OF MECHANICAL

AND ELECTRICAL EQUIPMENT IN MANY OF OLDER PLANTS

(CONSTRUCTION PERMIT APPLICATION BEFORE ABOUT 1972)

IN NOVEMBER 1988 NRC REQUEST THAT EACH LICENSEE

SHALL CONDUCT IPE FOR INTERNALLY INITIATED EVENTS ONLY

IN EARLY 1990 US NRC INITIATED IPEEE – SSE ONE OF MAJOR

EXTERNAL EVENTS

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SEISMIC MARGIN REVIEW PROCESS

IN MAY 1984 US NRC FORMED AN „EXPERT PANEL ON THE

QUANTIFICATION OF SEISMIC MARGIN“

– TECHNICAL GUIDANCE AND ADVISE ON THE SUBJECT OF SEISMIC

MARGINS OF NPP’s

ISSUED REPORTS

– NRC SEISMIC DESIGN MARGINS PROGRAM PLAN

– AN APPROACH TO THE QUANTIFICATION OF SEISMIC MARGINS IN

NPP’s

GENERAL DEFINITION OF „SEISMIC MARGIN“

„SEISMIC MARGIN“ IS EXPRESSED IN TERMS OF THE EARTHQUAKE

MOTION LEVEL THAT COMPROMISES PLANT SAFETY,

SPECIFICALLY LEADING TO MELTING OF THE REACTOR CORE. IN

THIS CONTEXT, MARGIN NEEDS TO BE DEFINED TO WHOLE PLANT.

CAN BE EXTENDED TO ANY PARTICULAR STRUCTURE ETC. WHICH

„COMPROMISING SAFETY“

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DETAILED DESCRIPTION OF THE SEISMIC

MARGIN REVIEW PROCESS

THE SEISMIC MARGIN REVIEW PROCESS IS DIVIDED INTO EIGHT

STEPS

– SELECTION OF THE EARTHQUAKE REVIEW LEVEL

– INITIAL SYSTEMS REVIEW

– INITIAL COMPONENT HCLPF CATEGORIZATION

– FIRST PLANT WALKDOWN

– SYSTEMS MODELLING

– SECOND PLANT WALKDOWN

– SYSTEM MODEL ANALYSIS

– MARGIN EVALUATION FO COMPONENTS AND PLANT

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MARGIN REVIEW PROCESS – cont. 1

SELECTION OF THE EARTHQUAKE REVIEW LEVEL

– THE REVIEW LEVEL SHOULD BE SPECIFIED IN TERMS OF PGA AND

ENOUGH SPECTRAL INFORMATION

– IAEA SPECIFIC SAFETY GUIDE SSG-9 „SEISMIC HAZARDS IN SITE

EVALUATION FOR NUCLEAR INSTALLATIONS (ISSUED 2010)

SHOULD BE USED

– THE CHOICE OF THE REVIEW LEVEL IS A CRITICAL ONE SINCE IT IS

USED AS A BASIS FOR SCREENING OUT OF COMPONENTS

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INITIAL SYSTEM REVIEW. THE GENERAL PROCEDURE IS AS

FOLLOWS

– DEFINE THE INITIATING EVENTS FOR THE FUNCTIONS FOUND TO BE

MOST IMPORTANT (GROUP A) TO SEISMIC INDUCED CORE MELT

– REVIEW THE CONFIGURATION AND OPERATION OF THE PLANT

– DEVELOP SYSTEMIC EVENT TREES FOR THE DEFINED INITIATING

EVENTS

– IDENTIFY SUPPORT SYSTEMS AND COMPONENTS OF GROUP A

– IDENTIFY THE SYSTEMS AND COMPONENTS SUPPORTING THE

OPERATION OF THE SUPPORT SYSTEMS

– DOCUMENT THE SYSTEMS REVIEW RESULTS

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INITIAL COMPONENT HCLPF CATEGORIZATION. TASKS ARE THE FOLLOWING

– GATHER INFORMATION ON THE PLANT AND ITS SYSTEMS AND COMPONENTS

SECTIONS OF FSAR OR OTHER DOCUMENTS THAT DESCRIBE THE SEISMIC DESIGN AND THE SITE SOIL CONDITIONS

PLANT GENERAL ARRANGEMENTS DRAWINGS

LIST OF DRAWINGS

INFORMATION ON AVAILABLE REPORTS

SELECTED STRUCTURE AND FOUNDATION DRAWINGS

SQRT

SELECTED ANCHORAGE DETAILS

DESIGN REPORTS, SELECTED CALCULATIONS

– DETERMINATION OF TARGET AREAS AND STRATEGY FOR THE FIRST VISIT

– START SCREENING OUT BROAD CLASSES OR GROUPS OF COMPONENTS

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FIRST PLANT WALKDOWN: ACTIVITIES ARE

– TO CONFIRM THAT NO WEAKNESSES EXIST IN THE PLANT

STRUCTURES AND EQUIPMENTS THAT WOULD MAKE THEIR HCLPF

LOWER THAT GENERIC VALUE

– TO CONFIRM THE ACCURACY OF SYSTEM DESCRIPTIONS FOUND IN

PLANT DESIGN DOCUMENTS

– TO IDENTIFY ANY SYSTEM INTERACTIONS, SYSTEM DEPENDENCIES

AND PLANT UNIQUE FEATURES NOT ALREADY IDENTIFIED

– TO GATHER INFORMATION ON CERTAIN POTENTIALLY WEAK

COMPONENTS FOR FURTHER HCLPF CALCULATIONS

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SYSTEM MODELLING: THE TASK ARE THE FOLLOWING

– REVIEW THE DEVELOPED EVENT TREE AND REVISE, IF NECESSARY

– DEVELOP FAULT TREES FOR THE SYSTEMS USED IN THE EVENT

TREES

– DOCUMENT THE SYSTEMS MODELLING RESULTS

IN DEVELOPMENT OF FAULT TREES THE FOLLOWING FAILURE

CAUSES SHOULD BE CONSIDERED

– DIRECT SEISMIC FAILURE

– TEST AND MAINTENANCE UNAVAILABILITY

– HUMAN ERRORS

– FAILURES AS A RESULT OF SYSTEM INTERACTIONS

– INTERNAL FLOODINGS

– RANDOM FAILURES

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SECOND PLANT WALKDOWNS: THE OBJECTIVES ARE

– TO OBTAIN ADDITIONAL SPECIFIC INFORMATIONS, I.E. DIMENSIONS,

NUMBER AND SIZE OF ANCHOR BOLTS, SUPPORT DETAILS ETC.

FOR EVALUATING OF THE HCLPF VALUES OF SCREENED IN

COMPONENTS

– TO VERIFY THE SYSTEMS MODELS AND COLLECT ANY ADDITIONAL

NEEDED INFORMATION

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SYSTEM MODEL ANALYSIS: THE OBJECTIVE IS TO ANALYZE

THE EVENT TREES AND FAULT TREES TO DETERMINE THE

BOOLEAN EXPRESSION FOR SAFETY IMPORTANT SYSTEM

FAILURES, ACCIDENT SEQUENCES AND THE AGGREGATION OF

ACCIDENT SEQUENCES THE TASKS TO BE PERFORMED ARE

THE FOLLOWING

– ANALYSE THE FAULT TREES TO DETERMINE THE BOOLEAN

EXPRESSION FOR EACH SAFETY IMPORTANT SYSTEM FAILURE

– DETERMINE THE BOOLEAN EXPRESSION FOR THE SEISMIC

INDUCED CORE MELT ACCIDENT SEQUENCES

– DOCUMENT THE RESULTS OF THE SYSTEM MODEL ANALYSIS

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MARGIN EVALUATION OF COMPONENT AND PLANT: THE

OBJECTIVES OF THE ANALYSIS ARE

– TO ESTIMATE OF HCLPF OF THESE COMPONENTS

– TO ESTIMATE THE HCLPF OF THE PLANT

– FOR HCLPF EVALUATION, TWO ALTERNATIVE APPROACHES ARE

POSSIBLE

CONSEVATIVE DETERMINISTIC FAILURE MARGIN – CDFM

FRAGILITY ANALYSIS METHOD

HCLPF = HIGH CONFIDENTIAL OF LOW PROBABILITY OF

FAILURE

PROBABILITY OF FAILURE IS LESS THEN 5% WITH 95%

CONFIDENCE

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CDFM

– LOAD COMBINATION NORMAL + REVIEW EARTHQUAKE LEVEL (REL)

– GROUND RESPONSE SPECTRUM 84% NON-EXCEEDANCE PROBABILITY,

SITE SPECIFIC SPECTRUM

– DAMPING CONSERVATIVE STRUCTURE 7%

PIPING 5%

CABLE TRAYS 15%

– STRUCTURAL MODEL BEST - ESTIMATE - MEDIAN

– SOIL-STRUCTURE INTERACTION ENVELOPE EXPECTED PARAMETER VARIATION

– MATERIAL STRENGTH 95% EXCEEDANCE ACTUAL STRENGTH

– STATIC CAPACITY EQUATIONS 84% EXCEEDANCE BY TEST DATA OR CODE

EQUATION

– SYSTEM DUCTILITY BETWEEN 1.0 – 1.5

FOR SHEAR WALL STRUCTURE SHOULD NOT

BE LESS THAN 1.3

– FLOOR SPECTRA GENERATION MEDIAN DAMPING VALUE FOR EQUIPMENT

FREQUENCY SHIFTING RATHER THAN PEAK

BROADENING

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HCLPF DERIVATION

CRELNOC

)()( ingRELkC

ingRELHCLPFD

REL

NOC

REL

NOC

NOCREL

C

C

1

5.11Dk

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FRAGILITY ANALYSIS METHOD: IT IS POSSIBLE TO

EXPRESS IT USING THREE PARAMETERS – MEDIAN CAPACITY Am: IS APPROXIMATELY ESTIMATED AS

– LOGARITHMIC STANDARD DEVIATIONS R AND U REPRESENTING,

RESPECTIVELY RANDOMNESS IN THE CAPACITY AND UNCERTAINTY

IN THE MEDIAN VALUE

– FOR CONSERVATIVE ESTIMATION OF HCLPF VALUE WE

CONSERVATIVELY ASSUME

RELbycausedresponsemedian

responseloaddesignnormal

capacitymedian

Am

84.0UR

84.025.0

25.0

65.1

65.1

UR

m

m

fore

A

eAHCLPF

UR

UR

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SEISMIC FRAGILITIES FOR NPP’s RISK

STUDIES

AVAILABLE METHOD TO ESTIMATE SEISMIC RISK

– „ZION METHOD“ DEVELOPED AND APPLIED TO ESTIMATE SEISMIC

RISK AT THE ZION PLANT AND THE INDIAN POINT PLANT

– THE SEISMIC MARGIN RESEARCH PROGRAM DEVELOPED AS NRC

FUNDED RESEARCH PROGRAM AT THE LLNL

THE MAJOR DIFFERENCE IS IN LEVEL OF DETAIL IN SEISMIC

RESPONSE ANALYSIS

KEY ELEMENT: SEISMIC FRAGILITY

SEISMIC FRAGILITY OF A STRUCTURE OR EQUIPMENT IS DEFINED

AS CONDITIONAL FREQUENCY OF ITS FAILURE FOR A GIVEN VALUE

OF THE SEISMIC RESPONSE PARAMETER

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STUDIES - cont. 1

EXAMPLE OF A MOTOR ACTUATED VALVE FAILURE MODES

– FAILURE OF POWER OR CONTROLS TO THE VALVE AS A RESULT

OF SEISMIC CAPACITY OF THE CABLE TRAYS, CONTROL ROOM

AND EMERGENCY POWER

– FAILURE OF THE MOTOR

– BINDING OF THE VALVE DUE TO DISTORTION AND THUS FAILURE

TO OPERATE

– RUPTURE OF THE PRESSURE BOUNDARY

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STUDIES - cont. 2

FRAGILITY MODEL

– GROUND ACCELERATION CAPACITY A IS GIVEN BY

Median ground acceleration capacity

Variables with unit medians lognormally distributed with

logarithmic standard deviations R, U

– WITH PERFECT KNOWLEDGE THE CONDITIONAL FREQUENCY OF

FAILURE IS GIVEN AS

OR

Probability that the is less than for given a

RUAA ~

A~

RU ,

0f

R

Aaf

~/ln

0

R

UQAa

f

1

0

~/ln

Q f f

30.11.2011 21


STUDIES - cont. 3

NUMERICAL EXAMPLE

– INPUT DATA

– THEN FOR „BEST-ESTIMATE“

– OR THE CONDITIONAL FAILURE FREQUENCY AT 5% NON-EXCEEDANCE PROBABILITY

gagA UR 50.0,28.0,30.0,73.0~

014.00 f22

URC

6.0f

Seismic fragility family for a component

28.0

30.0

73.0~

U

R

gA

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STUDIES - cont. 4

DEVELOPMENT OF THE FACTOR OF SAFETY F

EXPRESS GROUND ACCELERATION CAPACITY ABOVE SSE – ASSE

THE FOLLOWING DEFINITION IS USED

SSEAFA

SSEtodueresponseActual

SSEtodueresponseDesign


capacityCalculated

capacityCalculated

capacityActual


componentofcapacityseismicActualF

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STUDIES - cont. 5

FOR SAKE OF SIMPLICITY F IS WRITEN AS

DEFINITION OF THE MEDIAN FACTOR SAFETY




capacityActualF

RCCFFF

SSEAAF /

~~

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STUDIES - cont. 6

STRUCTURES

strength factor

in-elastic absorption factor (ductility)

F

2/122 ...........

~~~~~~~~

SAF

SSSDECMCMSARS

SSSDECMCMSARS

FFFFFFFF

FFFFFFFF

NT

NS

RSS

CF

FFFF

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STUDIES - cont. 7

EQUIPMENT

–

– RATIO OF THE ACCELERATION LEVEL AT WHICH THE EQUIPMENT CEASES TO PERFORM ITS INTENDED FUNCTION TO SEISMIC DESIGN LEVEL

– EQUIPMENT FAILURES CAN BE CLASSIFIED AS FOLLOWS

ELASTIC - ELASTIC BUCKLING IN TANKS WALL

- RELAY CHATTER AND TRIP

- EXCESSIVE BLADE DEFLECTION IN FANS

- SHAFT SEIZURE IN PUMPS

BRITTLE - ANCHOR BOLT FAILURES

- COMPONENT SUPPORT WELD FAILURE

- SHEAR PIN FAILURES

RSRECFFFF

CF

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STUDIES - cont. 8

DUCTILE - PRESSURE BOUNDARY FAILURE OF PIPING

- STRUCTURAL FAILURE OF CABLE TRAYS AND DUCTING

- POLAR CRANE FAILURE

– COMPONENTS OF FRE - qualification method IF DYNAMIC - spectral shape ANALYSIS IS USED - modelling - damping - combination of modal components - combination of earth components

2/1

2

22

22

22

22

N

NTNC

NNTT

NC

TC

NC

CS

NT

NS

CF

component rigidfor13,0

2/11.002.0,0.1~12

UF

30.11.2011 27


STUDIES - cont. 9

– COMPONENTS OF FRE - qualification method

IF SEISMIC - spectral shape

QUALIFICATION - boundary conditions (test versus is used)

- damping

- spectral test method (sine beat or sweep,

complex waveform)

– FRS IS BASED ON RESPONSE CHARACTERISTIC AT THE LOCATION

OF COMPONENT

THE APPLICABLE VARIABLES ARE

- SPECTRAL SHAPE

- DAMPING

- MODELLING

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STUDIES - cont. 10

INFORMATION SOURCES

– SEISMIC QUALIFICATION DESIGN REPORTS

– SEISMIC QUALIFICATION TEST REPORTS

– PLAN SAFETY ANALYSIS REPORTS

– SEISMIC QUALIFICATION REVIEW TEAM (SQRT) SUBMITTALS

– SEISMIC QUALIFICATION REPORT SUMMARIES

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STUDIES - cont. 11

EXAMPLE OF CLASS 2 PIPING RESPONSE FACTORS

Factors

Median

safety factor

Random-ness

R

Uncertainty

U

CAPACITY FACTOR

Piping

Strength

In-elastic energy absorption

Three hinge factor

x

2.24

1.22

0

0.16

0

x

0.16

0.10

Capacity

Supports

Strength x 0 x

In-elastic energy absorption 1.5 0.16 0.16

Capacity

Anchors

Strength x 0 x

In-elastic energy absorption 1.5 0.15 0.15

Piping system minimal x x

Capacity FC value

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STUDIES - cont. 12

Factors Median

safety factor

Random-ness

R

Uncertainty

U

EQUIPMENT RESPONSE FACTOR

Qualification method

Spectral shape

Modelling

Damping

Mode combination

Earthquake component combination

1.0

x

1.00

x

1.0

1.0

0

x

0

x

0.15

0.12

0

x

0.15

x

0

0.10

Combined FRE

Structural Response Factor FRS

task for civil engineers

x

x

x

x denote: shall be calculated

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CONCLUSIONS

THE HISTORY OF THE SEISMIC RE-EVALUATION OF OLDE NPP’s HAS

BEEN PRESENTED

THE CDFM IS SIMPLY METHOD AND NO TIME CONSUMING

SMA ACCORDING US NRC IS EXACT BUT TIME CONSUMING

SEISMIC PRA NEED GENERATION OF FRAGILITY CURVES

– OVER 100 EQUIPMENT ITEMS CAN BE MADE FEASIBLE IN COMMERCIAL PRA

STUDIES

AFTER SOME MODIFICATIONS PRA MAY BE EXTENDED TO

– WIND HAZARD ANALYSIS WIND FRAGILITY ANALYSIS

– EXTERNAL – FLOODING HAZARD ANALYSIS EXTERNAL – FLOODING

FRAGILITY ANALYSIS

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SEISMIC RE-EVALUATION OF OLDER NPPs...IN EARLY 1990 US NRC INITIATED IPEEE – SSE ONE OF MAJOR EXTERNAL EVENTS 30.11.2011 5 SEISMIC MARGIN REVIEW PROCESS IN MAY 1984 US NRC FORMED