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New Technic.al -Basis for Et.imination.-of BWR RPV Circumferential Wel:d lnspectio·ns (BVVRVIP-329) [ C~©$ed ~e$$~(0)ITil]

Wayne Lunceford ·and Nathan Palm EPRI, BWRVIP

NRC Public Meeting May 29, 2019

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Agenda

• Objectives ·

• PFM Evaluation ·Summary

- PFM Approach

_; Safety Goals

- Sensitivity Calculations

- Results and lmple·mentation

• Detailed Discussion Topics

• Planned Next Steps

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· Objectives

• The objectives of this work are: . .

- To identify the -combinations of RTMAX for plate an·d axial and circumfere-ntiaLwelds that wiH ensure a total through-w.all cracking frequency (T.WCF) < lE-6 yr-1 for the RPV beltline materials and a TWCF <

- lE-7 yr-1 for the beltline circumferentialw.elds during a postulated, low · temperature isothermal pressure transient in BWR RPVs, and

- To assess whether these safety goals are satisfied for RPVs in the BWR fleet during the po_stulated transientthrough· an ao:..year operating interval~

· •Compliance with these safety goals provides a continui:ng basis to·· obtain_ relief from the examinations of the circumferential welds· and demonstrate·s that axial welds have adequate margins against failure for the RPVs in the U.S. BWR fleet.

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. p·f M Approa~h

• f\pply PFM evaluation procedures and acceptance criteria consistent with those currently deemed acceptable by NRC.

· • Perform sensitivity studies to address uncertainty in cladding thic.kness, flaw di.stributions ·and v.essel geometry

• Define a set .of limiting vessel g.eometry, cladding, and flaw· conditions

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• Where ap·plicable, surveUla.nce results presented in BWRVIP-l35, · Rev. 3 .were used to ·assess the change in material toughness from · .. irradiation· (~T30).

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•· Perform PFM analyses to determine the com·binations of RTMAX · for ·plate and axial and __ circumferential welds that will ensure the regulatory risk goals are maintained at the end of ·any .specified· operati:ng interval. ·

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Revisions to the PFM Evaluatio-n Procedure and Acceptance Criteria (1 of 2)

Variable Changes Compared toBWRVIP-05

Safety goal for all · [[

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circumferential EPRI Proprietary Information

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beltline welds

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Computational [[

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·. Revisions- to the PFM· Evaluation Procedure and · Acceptance Criteria (2 of 2)

Variable Changes Compared to BWRVIP-05 [[

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Revised Safety Goals

Pl P2 AWl AW2 AW3

....__ CWl ....__ CWl >--

P4 PS AW4 AWS AW6

....__ CW2 - CW2 -AW7 AW8 AW9

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• FAVOR calculates conditional probability of

failure (CPF} based on contributions from axial

welds (AW}, circumferential welds (CW} and plate (P}

• TWCFrotal = CPFrotal x F where:

- TWCF: Thru-Wall Cracking Frequency

- CPF: Conditional Probability of Failure

(CPFrotal = CPFAw + CPFcw + CPFp)

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- F: Event Frequency EPRI Proprietary Information ]]

• Two safety goals defined:

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Sensitivity Variables and-Calculations Contains EPRI Proprietary Information

• Sensiti:vity calculations were performed to d·etermine the vessel·

dimensions (wall thickness and radius) that produced the largest value of CPF:

~ Vessel·wall Jhickness [[

- Cladding thickness [[

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- Depth of a small inner surface circumferential flaw [[ · · . - · · · · . Content Deleted _

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- Cladding stress free·temperature [[ Content Deleted

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. Vessel Geometry and PFM-Evaluation Variab.les - ____________ ___.

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Data pointsrepresent ·. -­- various combinations

. of vessel wall ' thickness, vessel·

radius, cladding _ thickness, suifa~e flaw

' depth, and cladding . · stress free

temperature included . 'in.the sen_sitivity study

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Combinations of. RT MAX for Plates and Axial and Circu111ferential Welds that Correspond to Vari<>us

·_ Values ·of CPF1ota1

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· Contains EPRI - . -. Vessel Specific RTMAx Calculation· Proprietary Information ·

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. • To- assess the usefulnes.s of the selected safety -goals to be applied by_ BWRs _to 'obtain relief from circumferential weld examination for 80 _ · years or more, confirmatory vessel specific calculati.ons were performed

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• Vessel specific mean inner surface· reference temperature, RTMAx, for-_ the 1:imiti.ng plate. and ax.ial and circumferential welds in the vessel

- RT MAX= _RT NDT(U) + 8T30 . . ' . - RTNDT(U) __ ·. initial (uni-rradiated_) RTNDT from ASME NB-2331 or other acceptable· - methods -- · ·

- 8T30 = CF x FF · . . .

- CF_= chemistry factor from RG 1.99 Rev. 2 or BWRVIP-135 Rev; 3

- FF= fluence factor from RG 1.99 Rev. 2. -_ . _ .. _ _ _ _ _

• Projected-limiting- beltline materials at the end of an 8Q--year operating -. interval [[-

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· Compar_ison of Allowa:ble RTMAX Combinations with · . Contains EPRI . .

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.Projected Combinations at the .end of an 80-year · .___ _ _,______;_______. Operating Interval

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' Analysis Conservatisms

• The·,PFM results have been obta,ined using·a number of. conservative assumptions, including: ~. a transient pressure and temperature that bound values used in previous . industry and NRC evaluations . . . . ,

- a beltline geometry that bounds the vessels in the BWR fleet . ' . . .

- assuming that all axial beltline welds in the vessel h.ave the maximum allowable RT MAxfor the axial weld

- assuming that all plates and circumferential welds''in the· vessel have the . ·larger of the maximum allowable RTMAX for the plate circumferential weld·

- using calculated values of CPF that are conservat,ive and ,account for. · uncertainties in the computational procedure.

• These conservative assumptions provide added assurance that · there are substantial margins against failure during the postulated, low temperature isothermal pressure transient for the reactor pressure vessels in the U.S. BWR fleet. -.. ·

----------

Z / 7 ~ F~ mplementation Template

• Verification of Vessel Dimensions

Contains EPRI Proprietary Information

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__ . Oh:nension _ . _ __ Lower Limit U er Lirnit _ _ Reactor Vessel_ Inside Radius to CBMI, in. (mm} _

Base Metal Wall Thickness, in. (mm) · Radius / thickness· _ Cladding Thi.cknes·s, in. (mm.) _ .

• Verification of Acceptable RT MAX

'

Parameter ' r

I 1 .. - .

Umiting Plate

Content Deleted EPRI Proprietary Information

.Limiting Circumferential

Weld

Limiting Axial Weld

11

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_ Heat I Lot Identification Nu~ber _ r-· .............. --- .. ·- :· --------- .... .. .............. :r ----- ... --- ---- -.. - ---- -.. , . .. ......... - .. .. --- ...... ....... ·- - .. .. · 1

Copper Content (wt. %) ..

Nickel Conte91t _(wt.%) _

Chemistry Factor (CFJ (°F) _ ..

_ EOI Neutron Fluence (f) (n/cm2)

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-- -_ -·- - .~ - .-- -·· ·:·

- R,:-NDT(U) (°F) .. -

.. EOI ART NDT (°F) , ;:·.· ·- -.-- --- · .. - - - ~---. ··-- ,-.... ~. -. -- -·- -·· - . ---- - -·-·- -- ·· --- ----- - ·1r ·- ·- - ·· -·-- --- ·--- -- - ---- - --

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EPRI Proprietary Information _ Limiting RTMAX (°F) _ · '. [[I ·- ' I '

EOI RTMAX < Limiting RT MAx?·_ y /N Y/N Y/N

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· Summary and_ C:onclusions Contains EPRI · . Proprietary Information

. . ' . . . . .

• The results from the PFM analyses were used to define the combinations of -RT MAX for plate and aXial and circumferential welds that

· ensure t·he total TWCF < lE-6 yr-1 for the RP\/ beltli'ne and the T·WC.Fcw <. lE-7 yr-1 for circumferential beltline welds in BWR reactor pressure · vessels during a postulated low temperature isothe·rmal pressure ·transient.

. . . . . . . . . . . . . .

• Application of these results provide BWR owners -with a contin·uing basis. to justify relief from examination of circumf~rentialweJds, an_d the· capability to demonstrate acceptable.integrity for axial welds for RPVs in the U.S BW·R fleet ..

• The results from this work indicate that ail the Vessels in the U~S. BWR. . ' . . . ' '

fleet have TWCF < 1E~6 yr-1 with substantial margin ·at the end of an

80-year operating inte·rval;· [[ Content Del.eted .

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· Topics to·r Detailed Discussio_n -_

- • -Isothermal Pressure Tra_nsient

- · • Flaw Distri:butions

• Clad_ding Stress_ Free Temperature · ·

•·Limiting Vessel Geometry

• Additional Sensitivity Analyses . .

• PFM Results Convergence

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· • Sensitivity calculations were preformed to determine the· difference in· • • • • • • • • r • •

CPF forthree different fabrication and associated flaw conditions .. [[

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Shop: 98% SAW, 2% repair

Field: 98% SMAW, 2% repair

Blend: 97% SAW, 1% SMAW, 2% repair

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· Cladding Stress Free Temperature (1 /2) Contains EPRI

Proprietary Information

• The difference between the thermal expansion coefficients for the ferritic and._ stainless steels can pr.oduce a significant residual _· stress gradi-entat the interface between: the stainlesssteel

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cladding and the ferriticsteel base rnetal

• The stres.s free temp.erat.ure (SFT) is the temperature at which the residual stress at the clad to base metal interface (CBMI) is zero

. . ' . . . . . . .

- As the operating .temperature decreases below the SFT, the value of the applied stress intensity, ·K1, for a small .inner surface flaw Jncreases · .

- At temperatures near room temperature, the K1 values can produce a -substantial increase in the potential for the extension of small inner surface flaws nearthe CBML

• Sensitivity studies to determine limiting geometry (Jater slides) also evaluated FAVOR SFT input values ra-nging from· · [[ Content Deleted - E-PRI Proprietary Information · · ]]

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Cladding Stress Free ·TemperQture (2/2J · Contains EPRI , Proprietary Information

·._ . • :Sensiti_vity study results indicate that there is not a significant · · effe.ctofthe input variable values on CPF for a specified wall.

. . . ' .

··thickness __ .·. . .

• The value ofthe SFT used to determine limiting RT MAX values Was · selected based- on a·pplicability to circumferential inner surface

flaws···. [[ .

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, . LimitingVessel Geometry .P!;::..i::1~~~ation

• U.S. BWR· RV beJtline dimensions evaluated . • SerisitivitY study performed to determine combination of fifl"liting . · • dime.n·sidns

• Cladding thicknesses .used i:n the serisitivity study encompa_ss the · mid~to h.igh range of cladding thicknesses typically used in light water reactors in the U.S ..

.•• Sensitivity stucfies performed .at RTfvlAX :values so· that calculated CPF values would be in the tange of [[ .

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• As prev.iously.discussed, a range of SFT values was :also cor,si'd_ered · · .·

• Sensitivity study results indjcatedthat a nEPR1~1~:~~t~i~~~~rrnationn.··· provides limiting CPF values- and was therefore used to determi·ne allowable RTMAx combinations

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· Limiting Vess.el Geometry - Sensitivity Study • -Results.

ID lnner:Radius Base Metal

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SFT CPF

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· Verification of ·RTMAx Limits . Contains EPRI

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· •Additi_ona:I sensitivity calcul·atJons performed to demonstrate that· . : . . . · . · · · · · · . . C · · ·t ·t D ·1 t ·a . ·.. . . . . . . . ·. ·. . . . . . on en e e e .· . . . ' , ' ', , , , ' ,., , , , ]]

· the allowable RTMAx·l1m1ts defrned using the [[ El?RIPrdprietary Information.·.• ·.

, are a:ppropriate for the populatio:n of vesselsin the'BWR fleet •

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• ResultS confirm that the new RT MAX limits Will ensure the defined safety ·goa Is

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· · . Additio,nal Sensitivity Analyses

. . .

• S-ensitivity analyses performed to d:emonstrate that: . . . . . . . . .

- Any combination ·of variable values of that results -in the.same RTMAX will provide approxima:telythe same CPF. . . .

.- Application· o·f the. allowable RTMAX limits is not restricted by-the variable ·. values u.sed to com.pute RT MAX

. . . .

· • Sens:itiVity analyses: performed to evaluate the impact of changes . . . . ·. In:

- Material chemistry (Cu,· Ni, Mn, P)

- Initial RT NDT. (RTNDT(u))

· """" EFPY

. - CoolantTemperature

• Results show Httle change to CPF from. variations in combination of inputs used to calculate RT MAX

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PFM Results Convergen·ce · Contains EPRI . Pmprietary Information

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Summ,ary and Conclusions

> ' :". ' ·-~ ' -© 2019' Ele"ctric ·Power Research lilstitute; lnc . .-AII rights ·r:f:_s·erved. - __ , ____ .. · ..... - ·-·-----· -··-··-···· ··-----~- ---·--·-

---···· -.-·--·;·--~r----. - ' E~1211 ELECTRIC POWER . · I ,- . RESEARCH INSTITUTE

.• PFM results obtained using late-st techn·iques and s·afety goals . provide for an alternativetothe axial weld RrNDT limit in BWRVIP~74-A ·and NUREG~1800, Revision 2

. . . - . -

• Significantmargin exists between the r1ew RTMAX Hmits and the .. expected values for the BWH fleet · · ·

. . .· ' - . . ' ' . . . . . .

• ·Se.nsitivity·ana·lyses have demonstrated the accuracy and appropriateness of the RT rviAx limits

/ / / fi

.Next.Steps-.

• Work will be: pu.blished in an EPRI report

- BWRVIP-32-9: BWR Vessel andlnternals Program: Updated Probabilistic . ·. .

Fracture.Mecha'nics Analysis.forBWR RPV Welds to Address Extended Ope'rations

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• BWRVlP intends to submit BWRVIP-329' for NRC review a-nd _a·pproval hi th'.e2nd half of 2019.

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