Closure of NRC Evaluation of BTP 5-3 to Estimate TNDT ... · Background • January 30, 2014 – AREVA letter with an attached PVP paper (PVP2014-28897) claims that Position 1.1(4)

Closure of NRC Evaluation of BTP 5-3 to EstimateTNDT, RTNDT(u), and Upper-Shelf Energy

Simon C. F. Sheng Sara LyonsSenior Materials Engineer Reliability And Risk AnalystNRR/DE/EVIB NRR/DRA/[email protected] [email protected]

NRC-Industry Annual Materials Information Exchange MeetingMay 23-25, 2017Rockville, Maryland, USA

Background

• January 30, 2014 – AREVA letter with an attached PVP paper (PVP2014-28897) claims that Position 1.1(4) regarding RTNDTof BTP 5-3 is sometimes non-conservative for A508-2 forgings.

• June 4, 2014; February 19, 2015; June 2, 2015; and January 19, 2016 – NRC and industry each updated its assessments of all BTP 5-3 positions regarding TNDT, RTNDT, and USE in the NRC/EPRI annual materials issue information exchange meeting.

• September 23, 2015 – EPRI and PWROG provided MRP-401 (BWRVIP-287) and PWROG-15003-NP for information.

• NRC closure memo dated 4/11/2017 (ML16364A285).2

BTP 5-3 Evaluation Objectives

• Assess the potential impact on safety due to the issues raised by AREVA.

• Evaluate the ways to account for the BTP 5-3 non-conservatism under the current deterministic framework.

• Perform risk-informed evaluation to justify revision/non-revision.

3

BTP 5-3 Positions B1.1(1) and B1.1(2) Regarding TNDT

Under the current framework based on Margin:

Margin = 2(σi2 + σΔ

2)1/2

The NRC staff’s approach: Determine σi considering (1) the σ from the database of estimated and true TNDT values, and (2) the σ from the database of estimated and true “Charpy parameter” based on the Charpy V-notch Curve.Reference: NRC TLR-RES/DE/CIB-2014-011 (ML15268A086).

Conclusion: An acceptable approach is to use a σi of 20° in the margin calculation if the TNDT determined by Position B1.1(1) or B1.1(2) is the RTNDT. 4

BTP 5-3 Position B1.1(3) Regarding Charpy Parameter


The NRC staff’s approach: (1) Determine σi considering the σ from the database of estimated and true “parameter” based on the Charpy V-notch Curve, or (2) determine a new “mean” and σi from the same database.References: MRP-401 (BWRVIP-287) and NRC TLR-RES/DE/CIB-2014-011 (ML15268A086).

Conclusion: An acceptable approach is (1) to use a σiof 20°F in the margin calculation for plates and non-Rotterdam forgings and 60°F for Rotterdam forgings, or (2) to use a mean and σi based on a regression analysis. 5

BTP 5-3 Position 1.1(4) Regarding RTNDT Based on Charpy Data at a Single Temperature


The NRC staff’s approach: Determine σi considering the σ from the database of estimated and true RTNDT.Reference: NRC TLR-RES/DE/CIB-2014-011 (ML15268A086).

Conclusion: An acceptable approach is to use a σi of 0°F in the margin calculation for plates and 30°F for forgings.

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BTP 5-3 Position 1.2 Regarding USE

Under the current framework based on 65% of the longitudinal USE:

The NRC staff’s approach: Reexamine NRC regulations on USE for guidance on establishing generic USE values. References: (1) MRP-401 (BWRVIP-287), (2) NRC TLR-RES/DE/CIB-2014-011 (ML15268A086), and (3) the June 25, 1990 memo from C.Z. Serpan (RES) to C.Y. Cheng (NRR).

Conclusion: No revision is needed because Ref. 3 evaluated and accepted the current position, and NRC did not automatically use the mean ± 2σ approach to derive generic values for material properties important to RPV evaluations.

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Risk-Informed Evaluation to Justify Revision/No Revision

Objective: to determine whether implementation of the deterministic margin meets the NRC criteria for new regulations.1. Pressurized thermal shock (PTS) evaluation for 72 EFPYs:

The NRC staff’s approach:Use past probabilistic fracture mechanics (PFM) results• Select plants based on margin adjusted RTPTS values.• Apply current licensing basis (CLB) material information with CLB

fluence extrapolated to 72 EFPYs.• Add extra margin in RTPL to account for BTP 5-3 non-

conservatism. Reference: NUREG-1874, especially Fig.3.12 (ML070860156).

8


The PTS evaluation for 72 EFPYs:The NRC staff’s PFM results:

Conclusion: Small change in TWCF values suggests no revision. DRA proceeded risk-informed evaluation to completion.

9

Plant Name Initial RTNDTAdjustment (∆)

TWCF w/o BTP 5-3 Non-

conservatism

TWCF with BTP 5-3 Non-

conservatism

Change in TWCF Values

IP-2(plate)

18.5 °F (1x ∆) 3.16x10-9 9.00x10-9 5.84x10-9

37 °F (2x ∆) 2.46x10-8 2.14x10-8

Palisades(plate)

18.5 °F (1x ∆) 2.67x10-10 8.51x10-10 5.84x10-10

37 °F (2x ∆) 2.58x10-9 2.31x10-9

WB-1(forging)

90.7 °F (1x ∆) 6.59x10-16 2.87x10-12 2.87x10-12

136 °F (1.5x ∆) 7.70x10-11 7.70x10-11

NA-1(forging)

90.7 °F (1x ∆) 2.52x10-14 3.00x10-12 2.97x10-12

136 °F (1.5x∆) 7.81x10-11 7.81x10-11


2. Pressure temperature (P-T) limit evaluation for 72 EFPYs:

The NRC staff’s approach:Perform PFM analyses (no past results could be used)• Define bounding PWR and BWR plants based on RVID2

information.• Apply RVID2 material information with 32 EFPY fluence

extrapolated to 72 EFPYs.• Use P-T limit transients and actual transients.• Specify a σi of 20°F in the PFM input for plates and non-

Rotterdam forgings and 60°F for Rotterdam forgings to account for BTP 5-3 non-conservatism.

Reference: NRC memo dated 12/22/2016 from RES to NRR (ML16357A271). 10


Pressure temperature (P-T) limit evaluation for 72 EFPYs:

The NRC staff’s PFM results (actual transient):

11

ReactorType

LoadingCondition

Material Type

Considerationof BTP 5-3

Non-conservatism

Conditional Probability of Failure, CPF

Frequency ofLoading

Condition, F(events/yr)

TWCF= CPF x F

(/yr)

PWRActual

Cooldown

Plate

No 4.9×10-7 1.0 (a) 4.9×10-7

Yes 6.3×10-7 1.0 (a) 6.3×10-7

Rotterdam Forging

No 8.8×10-9 1.0 (a)8.8×10-9

Yes 2.2×10-7 1.0 (a)2.2×10-7

BWRs

100°F/hour Cooldown Following Saturation

Curve Plate

No 1.5×10-7 1.0 (a) 1.5×10-7

Yes 2.6×10-7 1.0 (a) 2.6×10-7

No 0.0×10+00 1.0 (a)0.0×10+00Plant

Procedure Leak Test Yes 9.0×10-15 1.0 (a)

9.0×10-15


Pressure temperature (P-T) limit evaluation for 72 EFPYs:

The NRC staff’s PFM results (actual transient):- Continued from Slide 11

Note: The BWR results for 40°F/hour leak test are much higher. However, they are still two orders of magnitude lower than 1x10-6.

Conclusion: Small change in TWCF values suggests no revision. DRA proceeded risk-informed evaluation to completion.

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Risk-Informed EvaluationDefine Regulatory Framework

• 10 CR 50.109 Backfitting: Imposition of a different regulatory staff position

• Safety Goal Screening per the Regulatory Analysis Guidelines in NUREG/BR-0058, Rev. 4:

Risk-Informed EvaluationFive Principles

Maintains Sufficient

Safety Margins

Performance-Measurement

Strategies Used to Monitor Change

Meets Current

Regulations

Consistent with

Defense-in-Depth Philosophy

Integrated Decision Making

Acceptably Small

Increases in CDF (if any)

Risk-Informed Decision Making

Risk-Informed EvaluationMeets Current Regulations

• The BTP 5-3 issue relates to a non-conservatism in the current staff position

• The staff’s analyses justifies the current guidance based on an extremely small change in predicted TWCF estimates

Risk-Informed EvaluationDefense-in-Depth

• There is no change in plant design or operations

• Changes to the robustness of the RPV is minimal, given existing:– RPV surveillance programs– ISI programs for flaw detection

Risk-Informed EvaluationSafety Margins

• Staff assessment demonstrated that:– PTS events are associated with

an extremely small risk of RPV failure– RPVs exposed to the P-T limit

transient are associated with an extremely small risk of RPV failure

Risk-Informed EvaluationAcceptable Increase in Risk

• Conservative risk estimate:LERF = CDF = TWCF

•

• PTS evaluation and P-T Limit evaluation resulted in ΔCDF estimates well below 1E-6/RY

Risk-Informed EvaluationPerformance Measurement

• ISI programs are sufficient to identify any future need to revisit this assessment

• No change is proposed

• 40 years of operating experience for U.S. fleet of plants which applied BTP 5-3 to their RPV plates and forgings

Conclusion, Impact on Operating Plants, and Next Step

Closure Memo Conclusion:The change-in-risk associated with not pursuing a backfitrelated to the BTP 5-3 non-conservatism for PTS and P-T limits is consistent with the guidance in NUREG/BR-0058.

Positions in BTP 5-3 can still be used in PTS and P-T limits evaluations up to 72 EFPYs.

Impact on Operating Plants:None for 72 EFPYs.

Next Step:Formal processing of the BTP 5-3 revision by NRO.

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Documents

Closure of NRC Evaluation of BTP 5-3 to Estimate TNDT ... · Background • January 30, 2014 – AREVA letter with an attached PVP paper (PVP2014-28897) claims that Position 1.1(4)