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Recommendations for Using Current Sentinel Location Screening and Assessment Methodologies for License

Renewal Environmental Fatigue Calculations Tiberio García

Iñaki Gorrochategui Ainara Mira

(IDOM) Marta Álvaro

(Tecnatom)

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• Introduction

• Objective

• Identification of sentinel locations

• Assessment of sentinel locations

• Conclusions

Table of contents

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• Introduction

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Introduction Long Term Operation (LTO)

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Long Term Operation

Operation beyond an established time frame defined by, for example, licence term, design, standards, licence and/or regulations (TYPICALLY 30-40 YEARS)

CONTINUE OPERATING UP TO 60 YEARS

INCREASE THE PROFITABILITY OF THE INVESTMENTS

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Introduction Time Limited Ageing Analyses

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SAFE LONG TERM OPERATION

SAFETY ANALYSES

Basic feature of any design

Use assumed time limits

TIME LIMITED AGING ANALYSIS (TLAA)

6 conditions

METAL FATIGUE IS A TLAA

NEEDS TO BE REEVALUATED

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Introduction LTO in Spain

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SPAIN

EEUU

Instruction IS-22

Regulation 10 CFR 54

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Introduction Metal fatigue TLAA: Environmental Assisted Fatigue (EAF)

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NUREG 1800 Rev. 2

Environmental fatigue in Class 1 pressure boundary components is considered a TLAA

As minimum, critical location selected in NUREG/CR-6260

Should be considered additional component locations

SENTINEL LOCATIONS Indicator of the damage accumulated by the EAF effect

LICENSE RENEWAL

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Introduction Metal fatigue TLAA: Environmental Assisted Fatigue (EAF)

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EAF TLAA TWO STEPS

1º SCREENING SENTINEL LOCATIONS

EPRI TR-1024995 METHODOLOGY

2º ASSESSMENT TO JUSTIFY THAT CUF VALUE CONSIDERING

ENVIRONMENTAL EFFECT MEETS ASME REQUIREMENT

CUF = �niNi

< 1m

i=1

THE EFFECT OF THE ENVIRONMENT is taken into account according to:

CUFen = Fen · CUF Fen

SULFUR CONTENT

TEMPERATURE

DISSOLVED OXYGEN

STRAIN RATE

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Introduction Fen formulation

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NUREG 1800 REV. 2 LETS TO USE THE FOLLOWING SET OF FEN FORMULATION:

CARBON STEEL AND LOW ALLOY STEEL

Fen from NUREG/CR-6583 combined with S-N curves from ASME Section III Code.

Fen from NUREG/CR-6909 Appendix A combined with S-N curves from ASME Section III Code or the ones from NUREG/CR-6909.

AUSTENITIC STAINLESS STEEL

Fen from NUREG/CR-5704 combined with S-N curves from ASME Section III Code.

Fen from NUREG/CR-6909 Appendix A combined with S-N curves from this reference.

NICKEL BASED ALLOY

Fen from NUREG/CR-6909 Appendix A combined with S-N curves from this reference.

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•OBJECTIVE

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Objective MAIN ISSUES AND OBJECTIVE

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MAIN ISSUES

FATIGUE ANALYSIS OF CURRENT NPPs

WERE DONE SOME DECADES AGO

HAVE BEEN REVIEWED SEVERAL TIMES

ACCURACY OF AVAILABLE INFORMATION

CANNOT BE ENOUGH

OBJECTIVE

TO PROVIDE SOME RECOMMENDATIONS THAT SOLVE POSSIBLE ISSUES

THAT COULD BE FOUND IN THE RESOLUTION OF EAF TLAA

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Identification of sentinel locations

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Identification of sentinel locations EPRI methodology

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NPP have a different level of detail in their calculations, especially depending on its age.

NPP may have performed modifications during its operating life – Replacement of Steam Generators, Replacement of RPV Head, Uprating, etc

Re-evaluate the stress reports, either in all calculated locations or only in the most limiting ones.

GENERAL APPLICATION

The recommended procedure for identification of sentinel locations applicable to the USA design plants is described in EPRI TR-1024995.

HOWEVER

How to use the general EPRI procedure to REAL SITUATIONS RECOMMENDATIONS

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Identification of sentinel locations ASME vs. NUREG 6909

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1/6 For the selection of sentinel locations NUREG-1800 Rev. 2 offers the possibility of using either NUREG-6583 (CS and LAS) and NUREG-5704 (SS) in combination with original ASME S-N curves, or NUREG-6909.

NUREG 6909 Requires to re-evaluate CUF values according to its own S-N curves

IN MANY CASES, CUF VALUE IS ONLY AVAILABE

IT CANNOT BE RE-EVALUATED

USING NUREG-6583 (CS AND LAS) AND NUREG-5704 (SS) WITH ASME S-N CURVES

IS APPROPIATE FOR THE SCREENING

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If all stress ranges (Salt i) and number of cycles (ni) ARE KNOW

Identification of sentinel locations Nickel based alloys NUREG-6909 re-evaluation

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2/6 FOR NICKEL ALLOYS, ONLY NUREG-6909 CAN BE USED

RE-EVALUATION OF CUF ACCORDING TO NUREG-6909 IS INMEDIATE

CONSERVATIVE ESTIMATION

If all stress ranges (Salt i) and number of cycles (ni) ARE NOT KNOW

𝐂𝐔𝐔𝟔𝟔𝟔𝟔 = 𝟏𝟔 · 𝐂𝐔𝐔𝐎𝐎𝐎𝐎𝐎𝐎𝐎𝐎

SOME CONSIDERATIONS SHALL BE INCLUDED IN THE SCREENING PROCESS

NOTE:

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It can be continued with the screening process

Identification of sentinel locations Common Basis Model

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3/6 EPRI: VERIFICATION OF COMMON BASIS MODEL

AFIRMATIVE

COMMON BASIS STRESS EVALUATION PROCEDURE

To compute an estimated CUF

NEGATIVE

Some limitations for its use

ALTERNATIVE BASED ON KUPPER AND GRAY METHODOLOGY

If all loc. of the system/equipment have been calculated with the

same level of conservatism

If not, loc. with the same type of fatigue calculation must be classified in different groups

TYPES OF FATIGUE CALCULATIONS C.T. Kupper and M.A. Gray, “License Renewal Environmental Fatigue

Screening Application”, PVP 2014-29093. Proceedings of the ASME 2014 Pressure Vessels & Piping Conference. 2014.

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In some combination of thermal zone/material CUF IS NOT CALCULATED at any location in contact with the coolant environment

Identification of sentinel locations Conservative CUF estimation

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4/6

If additionally, CBSEP IS NOT APLICABLE

It is strictly valid for cylindrical and plate

components

It can be evaluated to ASSIGN

CUF 𝑖𝑖 𝑐𝑐𝑖𝑐𝑐𝑐𝑐 𝑒𝑖𝑒𝑖𝑒𝑐𝑖𝑒𝑒𝑖𝑐

CUF𝑤𝑖𝑐𝑤𝑐𝑤𝑐 𝑐𝑐𝑖𝑐𝑐𝑐𝑐𝑒𝑖𝑒𝑖𝑒𝑐𝑖𝑒𝑒𝑖𝑐

If it can be verified that CUF of location that is not in contact with environment is higher

than the rest of locations of thermal zone/material

CUF available Highest CUF value Not in contact with

environment

CUF not available In contact with

environment

NOTE: SOME CONSIDERATIONS SHALL BE INCLUDED IN THE SCREENING PROCESS

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If the CUF has been calculated with NUREG-6909 S-N curve the EPRI criteria can be used.

If the CUF has been calculated multiplying by ten original CUF only the following criteria apply: If in one thermal zone there is one or more nickel based alloy candidate

sentinel location, all of them will directly promote to initial sentinel location.

Only can be applied the technique that establishes that if the sentinel location shows a conservative CUFen value for 40 years lower than 0.8 it could be excluded from the final list of sentinel locations.

Identification of sentinel locations Sentinel locations screening

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5/6 SOME LIMITATIONS SHOULD BE INCLUDED IN “Ranking and sentinel location identification for each material and thermal zone” and “Guidelines for reducing the number of sentinel locations” of EPRI document

DUE TO THESE RECOMMENDATIONS

FOR NICKEL BASED ALLOY LOCATIONS 1

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All of them will directly promote to initial sentinel location. Only can be applied the technique that establishes that if the sentinel location

shows a conservative CUFen value for 40 years lower than 0.8 it could be excluded from the final list of sentinel locations.

Identification of sentinel locations Sentinel locations screening

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5/6 SOME LIMITATIONS SHOULD BE INCLUDED IN “Ranking and sentinel location identification for each material and thermal zone” and “Guidelines for reducing the number of sentinel locations” of EPRI document

DUE TO THESE RECOMMENDATIONS

Locations where the CUF value represents to other ones that are not in contact with the coolant environment

2

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Identification of sentinel locations Component replacement

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6/6 FOR SYSTEMS OR COMPONENTS INSTALLED AFTER THE INITIAL OPERATION OF THE NPP

The following constraints must be introduced in the application of the criteria defined in section “Guidelines for reducing the number of sentinel

locations” of document EPRI TR-1024995

- One sentinel location of a component installed from the start of plant operation CAN COVER one initial sentinel location of other component installed later if the criteria of “Guidelines for reducing the number of sentinel locations” of document EPRI TR-1024995 are accomplished.

VESSEL BODY SENTINEL LOCATION CUFEN= 2.3

VESSEL HEAD WAS CHANGED

VESSEL HEAD SENTINEL LOCATION CUFEN= 1.2

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- One initial sentinel location of a component installed later than the start of plant operation CANNOT COVER one initial sentinel location of other component installed at the beginning of plant operation even if the criteria of “Guidelines for reducing the number of sentinel locations” of document EPRI TR-1024995 are accomplished.

Identification of sentinel locations Component replacement

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6/6 FOR SYSTEMS OR COMPONENTS INSTALLED AFTER THE INITIAL OPERATION OF THE NPP

The following constraints must be introduced in the application of the criteria defined in section “Guidelines for reducing the number of sentinel

locations” of document EPRI TR-1024995

VESSEL HEAD SENTINEL LOCATION CUFEN= 2.3

VESSEL HEAD WAS CHANGED

VESSEL BODY SENTINEL LOCATION CUFEN= 1.2

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•Assessment of sentinel locations

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Assessment of sentinel locations

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ASME vs. NUREG 6909

FOR ASSESSMET PHASE, IT IS PROPOSED NUREG-6909

THREE MAIN REASONS:

Final sentinel locations that result from the screening process usually correspond to locations whose fatigue calculations are detailed in the stress reports, hence, the CUF value can be re-evaluated according to NUREG/CR-6909.

Nickel based alloys are only addressed in NUREG/CR-6909, this document must necessarily be employed for these materials. In order the calculations for all materials (CS, LAS and SS) be consistent it is more appropriate to use the same formulation for all of them.

To be consistent with the position of the NRC about how to consider the effects of the environment in the fatigue design of new reactors.

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Accurate methods to calculate Fen, as integrated method, are difficult

to be used

IN MANY CASES, ESPECIALLY IN OLD PLANTS, THIS

INFORMATION IS NO AVAILABLE

Assessment of sentinel locations Fen calculation

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Depending on the conservatism needed for the assessment of the sentinel locations an increasing degree of accuracy can be necessary in the estimation of the parameters contributing in the calculation of the Fen factor.

START CONSERVATIVE AND SIMPLE APPROACH

Enveloping values of all parameters: temperature, dissolved oxygen, sulphur content and strain rate

IF HIGHER ACCURACY IS NEEDED

Then plant specific values should be used

ALTERNATIVES

RECALCULATION FEM

MONITORING SBF

FLAW TOLERANCE METHOD

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•Conclusions

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Conclusions Recommendation

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SOME RECOMMENDATIONS ARE PROVIDED TO SOLVED SOME ISSUES THAT COULD BE

FOUNDED IN THE RESOLUTION OF EAF TLAA

These recommendations must be taken into account as what they are, that is, only recommendations,

which come from the experience acquired

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Thank you!