ML17341A062

NextEra Energy Seabrook Presentation Slides - Seabrook Station ASR Methodology LAR: Structural Deformation - LAR 16-03, Methodology and Responses to Rais D2-D8 - for November 17, 2017, Public Meeting

ML17341A062
Person / Time
Site:	Seabrook
Issue date:	11/17/2017
From:	NextEra Energy Seabrook
To:	Office of Nuclear Reactor Regulation
Poole J, NRR/DORL/LPLI, 415-2048
References
CAC MF8260, EPID L-2016-LLA-0007
Download: ML17341A062 (29)

Text

LAR 16-03 Methodology and Responses to RAIs D2-D8 November 17, 2017 Seabrook Station ASR Methodology LAR:

Structural Deformation

2 The foundation for everything we do are the Values and Core Principles of our Nuclear Excellence Model

3 NextEra Energy Seabrook Ken Browne Licensing Manager Jeff Sobotka Design Engineering Manager Ed Carley Engineering Supervisor Jaclyn Hulbert Engineer - ASR Program Owner Simpson Gumpertz and Heger Dr. Said Bolourchi Senior Principal Dr. Andrew Sarawit Senior Project Manager MPR John Simons General Manager

4 Overview of Methodology Document Provides Analysis and evaluation approach for all Seismic Category I structures and all stages.

Sufficient details provided for consistent application and repeatability for all three stages of analyses.

Acceptance based on meeting the Codes of record as supplemented.

Supplements to the Codes with justifications.

Monitoring parameters and threshold limits.

Actions when ASR deformations approach limits.

Allows knowledgeable structural engineers to implement methodology in a consistent and repeatable manner.

5 ASR Evaluation Process License Amendment Request Methodology Document Structural Analysis &

Evaluation Threshold Limits Stage 1, 2, and 3 analyses Material properties Repeatable process for Stage 1, 2, and 3 analyses Demand calculations Compliant to ACI 318-71 and ASME Code as supplemented Establish design margin for potential future ASR expansion Structures Monitoring Program Monitoring parameters and frequency Trending Action if approaching threshold limits

6 Contents of Methodology Document Characteristics and Measurement of ASR Loads and Load Combinations Analysis Approach Acceptance Criteria ASR Threshold Limits and Monitoring Evaluation for Approaching Threshold limits

7 Loads and Load Combinations Loads and factored load combinations are

- as defined in the current UFSAR and

- supplemented by LAR 16-03 to include ASR loads and load factors.

ASR load factors provide safety margins consistent with the original codes of record.

8 Field Measurements Sustained Loads Cracking Is cracking observed?

Is cracking limit exceeded?

Stiffness reduction due to axial, shear, and/or flexural cracking.

Moment Redistribution Limit to ACI 318-71 8.6 Factored Loads Demand-to-Capacity Ratio Acceptance Criteria Supplement to ACI 318-71 Consideration of ASR loads Code acceptance criteria Shear-friction capacity for members subjected to net compression Acceptable reduction in flexural stiffness Stiffness reduction due to axial and shear cracking Evaluation Stage Three Evaluation Process Correlation of Analysis to Field Observations Threshold Parameters & Limits Expansion In-plane expansion measurements Distribution of ASR Structural deformation measurements Structural cracking Structures Monitoring Program FEA Model Field Observations Concrete Backfill Pressure Stiffness reduction due to ASR expansion of unreinforced backfill Backfill pressure reduction:

No structural cracks/distress Overburden pressure Confinement strength reduction

9 Methodology Document Summary Provides detailed analysis approach for all stages of analyses described in the LAR 16-03.

Allows knowledgeable structural engineers to implement methodology in a consistent and repeatable manner.

10 RAI-D2 Request - Provide a detailed explanation of how the Stage 3 analysis methods will be implemented in a consistent, repeatable manner. Identify deviations from the design code of record.

Response

Methodology Document establishes an approach to perform a Stage 3 analysis in a consistent, repeatable manner.

Supplements to the codes of record Supplement 1 - Consideration of ASR loads Supplement 2 - Code acceptance criteria Supplement 3 - Shear-friction capacity for members subjected to net compression Supplement 4 - Flexural cracked section properties Supplement 5 - Axial and shear cracked section properties UFSAR markup will be revised to reflect these supplements

11 RAI-D3 Request - Explain with sufficient technical detail how the proposed moment redistribution approach meets specific requirements of ACI 318-71.

Response

The Methodology Document limits the use of moment redistribution for all structures to be in accordance with ACI 318-71 Section 8.6.

The CEB evaluation is being revised in accordance with the Methodology Document.

Eliminate the use of moment redistribution.

Consider cracked section properties.

12 RAI-D4 Request - Explain with sufficient technical detail how the "simplified moment redistribution" method is applied.

Response

As discussed in response to RAI-D3 moment redistribution will be limited to ACI 318-71 section 8.6.

The CEB evaluation is being revised without the use of moment redistribution methods. Appendix L of the CEB Evaluation will be superseded. The same structural model and boundary conditions were used in previous analysis.

13 RAI-D5 (a)

Request - Clarify what the threshold factor represents in Stage 3 analyses and how the factor will be determined for future analyses.

Response

Threshold factor is design margin expressed as the amount ASR loads can increase and still meet ACI criteria.

Threshold factor is an output of the evaluation, not an input to the methodology.

A unique threshold factor is calculated for each building based on the available margin.

Used to establish threshold limits for monitored parameters.

This margin is available to account for potential future ASR expansion without reducing the code inherent margin of safety.

Threshold factor may be revised based on further analysis, by using additional inspection and measurement data, and/or using a more refined structural analysis method without reducing the code inherent margin of safety.

14 Request - Explain if there is a limit imposed on the extent of analysis that can be used to modify the demands upon a structure and if this impacts the specification of the threshold factor.

Response

Threshold factor is an output of an evaluation (see RAI-D5(a)).

There is no limit on re-evaluation provided evaluation satisfies ACI Code as supplemented.

Moment redistribution is limited per ACI Code.

Re-evaluations would use additional inspection and measurement data, and/or use a more refined structural analysis method in accordance with the Methodology Document.

Structural modification may be required to reestablish margin.

RAI-D5(b)

15 RAI-D6 Request - Clarify whether the 100-40-40 method will be implemented in equivalent static analyses for ASR-affected structures.

If so, provide the technical basis for using the method in conjunction with equivalent static analysis.

Response

The 100-40-40 method will be deleted from the proposed methodology The CEB evaluation is being revised to use the square-root-of-the-sum of-the-squares (SRSS) method in conjunction with the equivalent static analysis method consistent with the original design calculation approach.

UFSAR markups will be revised to remove references to 100-40-40.

16 RAI-D7(a)

Request - Provide an explanation of how multiple load components (e.g., axial force and moment) are combined to perform code interaction checks.

Response

The Methodology Document only allows the use of SRSS method for calculation of seismic demands.

The CEB evaluation is being revised without the use of the 100-40-40 method.

For conditions with multiple components (e.g., axial force and moment P-M interaction), the Methodology Document requires All components are calculated by the SRSS method.

The SRSS calculated +/-P and +/-M will be used for P-M interaction evaluation.

17 RAI-D7(b)

Request -

Explain why the combination of EO, and He in some cases is less than EO, alone. If the explanation assumes a phase relationship between EO, and He, provide the technical basis for the assumed phase relationship.

Response

For the CEB calculation, the seismic inertia force, EO, and soil pushing the embedded part of the CEB, He, are modeled in-phase.

In-phase modeling maximizes base shear and overturning moment when the static equivalent method and the SRSS responses are used.

The out-of-plane bending response in CEB is influenced by the presence of large penetrations, and location of applied loads including dynamic soil loads. The dynamic soil response and inertial response may counteract each other at limited small locations.

Analyses consider seismic motion in opposite directions. Results at each location are enveloped, therefore the localized areas are covered.

18 RAI-D8 Request - Explain, with sufficient technical detail, how the proposed method of evaluation for ASR-affected structures verifies that the stresses and strains in the concrete and reinforcement remain within elastic limits based on realistic behavior under normal operating (service) load conditions, including ASR load.

Response

Compliance with the ACI Code, as supplemented by the Methodology Document, ensures structures behave elastically, and the rebar and concrete stresses and strains remain within acceptable limits.

19 RAI-D8 Response (continued)

Performed two parametric studies to examine rebar stresses.

Scope 1.

Effect of increasing ASR expansion for member subjected to external load.

2.

Impact of increasing load on ASR-affected member.

Preliminary results for discussion Rebar stresses remain in elastic range for normal operating (service) loads.

Assessed rebar stresses for Seabrook structures.

Scope Structures evaluated to date Preliminary results for discussion Stresses and strains in the Seabrook structures are shown to be within elastic limits under normal operating load conditions (unfactored loads) when ASR loads are considered.

20

-800

-600

-400

-200 0

200 400

-400

-300

-200

-100 0

100 200 300 400 Axial force (kip/ft)

Moment (kip-ft/ft)

P-M interaction Ultimate strength Service stress Case A Case B Case C Case D Case E Case F Case G Case H Case I Case J Case K Case L P-M Combinations Cases Parametric Study 1-Stress in tension rebar of typical 2 ft thick member subjected to P-M and increasing ASR strain Preliminary Resultsverification pending.

21 Parametric Study 1 - Stress in tension rebar of typical 2 ft thick member subjected to P-M and increasing ASR strain Factored load Service load

-10 0

10 20 30 40 50 60 70 0

0.5 1

1.5 2

2.5 Rebar1stress(ksi)

Internal ASR (mm/m)

Case A Case B Case C Case D Case E Case F Internal ASR only fy =60ksi

-10 0

10 20 30 40 50 60 70 0

0.5 1

1.5 2

2.5 Rebar1stress(ksi)

Internal ASR (mm/m)

Case G Case H Case I Case J Case K Case L Internal ASR only fy =60ksi The tensile stress in the rebar increases after ASR expansion is sufficient to close structural cracks around the tensile rebar.

For sections with already high levels of external load (factored level loads), high levels of ASR are needed to cause additional tensile stress in rebar.

Preliminary Resultsverification pending.

22 Parametric Study 2 - Stress in tension rebar of typical 2 ft thick ASR-affected member with increasing moment Self-straining concrete compressive stress effect will unload before rebar tensile stress increases. This is because the concrete section is much stiffer than the steel based on the reinforcement ratio.

Stresses and strains in steel rebar are less than the elastic limits at service load conditions, provided that ASR strain is less than steel yield strain (2 mm/m).

Preliminary Resultsverification pending.

-20 0

20 40 60 0

20 40 60 Rebar 1 stress (ksi)

Moment (kip-ft/ft) 0 mm/m 0.5 mm/m 1 mm/m 1.5 mm/m 2 mm/m Mn 60% Mn

23 Stresses in Seabrook Structure due to Service Load The stresses for the structures that are completed or being completed have been calculated for the following two service load conditions:

in situ condition: D + L + E + To + Sa in situ condition plus operating basis earthquake and potential future ASR expansion up to threshold limit: D + L + E + To + Eo + He + FTHR*Sa For the above realistic unfactored service load combinations, stresses in rebar are below yield, and concrete strains are less than 0.001 and are less than the 0.003 ACI Code maximum usable strain for concrete compression

24 Maximum steel rebar tensile stress and concrete compressive stress for in situ condition: D + L + E + To + Sa Structure Analysis Stage ASR (mm/m)

Component Maximum tensile stress in rebar (ksi)

Maximum compressive stress in concrete (ksi)

Maximum compressive strain in concrete CRMAI 3

0.99 Base Mat 27.8

-0.28

-0.00009 RHR 3

0.75 East exterior wall 47.0

-1.8

-0.00058 CSTE 2

0.43 Tank wall 16.0

-0.66

-0.00018 CEHMS 1

0.72 East wing wall 31.3

-0.78

-0.00025 CEVA 1

0.31 Base slab 32.8

-0.88

-0.00028 CEB 3

0.60 Wall between Mech.

& Elec. Penetration 24.6

-2.19

-0.00065 WPC/PH 2

0.24 North wall 6.5

-0.49

-0.00016 EMH 1

0.25 W13/W15 walls 7.3

-0.03

-0.00001 Preliminary Resultsverification pending.

25 Structure Analysis Stage ASR (mm/m)

Component Maximum tensile stress in rebar (ksi)

Maximum compressive stress in concrete (ksi)

Maximum compressive strain in concrete CRMAI 3

0.99 x 1.4 Base Mat 39.1

-0.37

-0.00012 RHR 3

0.75 x 1.2 East exterior wall 56.5

-2.1

-0.00067 CSTE 2

0.43 x 1.6 Tank wall 26.7

-1.11

-0.00031 CEHMS 1

0.72 x 1.5 East wing wall 41.6

-1.52

-0.00049 CEVA 1

0.31 x 3.0 Base slab 44.0

-1.08

-0.00035 CEB 3

0.60 x 1.3 Wall between Mech.

& Elec. Penetration 44.0

-2.8

-0.00091 WPC/PH 2

0.24 x 1.8 North wall 23.2

-0.85

-0.00027 EMH 1

0.25 x 3.7 W13/W15 walls 26.8

-0.11

-0.00004 Maximum steel rebar tensile stress and concrete compressive stress for in situ condition plus operating basis earthquake and future ASR expansion up to threshold limit:

D + L + E + To + Eo + He + FTHR*Sa Preliminary Resultsverification pending.

26 Summary The Methodology Document provides the approach for performing all three stages of analyses described in the LAR can be implemented in a consistent and repeatable manner by a knowledgeable structural engineer.

Use of moment redistribution for structures will be in accordance with ACI 318-71 Section 8.6.

The 100-40-40 method will not be considered for calculating seismic demands for any Seismic Category I structures at Seabrook. The UFSAR markup will be revised to use the original SRSS methods.

Compliance with the ACI Code, as supplemented by the Methodology Document, ensures structures behave elastically, and the rebar and concrete stresses and strains remain within acceptable limits.

27 Building Deformation Analyses (1 of 2)

Structure Schedule Percent Complete Incorporated to SMP Condensate water storage tank Complete 100%

Complete Containment enclosure building (revision) 4Q2017 80%

Complete

• • 2/2018(Rev1)**

Containment enclosure ventilation area Complete 100%

Complete Containment structure Complete 100%

Complete Equipment hatch missile shield Complete 100%

Complete Control room make-up air intake Complete 100%

Complete Electrical cable tunnels Complete 100%

Complete Pre-action valve building 4Q2017 80%

2/2018 RHR equipment vault Complete 100%

Complete Containment internal structures 4Q2017 90%

2/2018 Main steam and feed water east pipe chase 4Q2017 70%

2/2018 Hydrogen recombiner structure Stage 1 Safety-related electrical duct banks and manholes 1Q2018 80%

4/2018 Stages 2 and 3 Safety-related electrical duct banks and manholes 1Q2018 40%

4/2018 Emergency feedwater pump building 1Q2018 50%

4/2018 Fuel storage building 4Q2017 80%

2/2018 Structures that are/expected to be Stage 3

28 Building Deformation Analyses (2 of 2)

Structure Schedule Percent Complete Incorporated to SMP Control Building Diesel Generator Building 1Q2018 30%

4/2018 Mechanical Penetration Personnel hatch area 1Q2018 40%

4/2018 Main steam and feed water west pipe chase 4Q2017 90%

2/2018 Primary auxiliary building 4Q2017 30%

2/2018 Service water cooling tower incl. switchgear rooms 1Q2018 4/2018 Service water access (inspection) vault 1Q2018 4/2018 Circulating water pumphouse (below el. 21')

Service water pumphouse 2Q2018 7/2018 Piping (RCA) Tunnels 2Q2018 7/2018 Tank farm area 2Q2018 7/2018 Waste processing building 2Q2018 7/2018 Structures that are/expected to be Stage 3

29 Questions?