NOC-AE-13003065, Response to STP-GSI-191-EMCB-RAI-1

Response to STP-GSI-191-EMCB-RAI-1

ML14015A312
Person / Time
Site:	South Texas
Issue date:	12/23/2013
From:	Meier M South Texas
To:	Document Control Desk, NRC Region 4
References
NOC-AE-13003065, TAC MF2400, TAC MF2401
Download: ML14015A312 (7)

Text

Nuclear Operating Company South Texas ProcdtEectric GeneratingStation PO. Box 289 Wadsworth, Texas 77483 V December 23, 2013 NOC-AE-13003065 10 CFR 50.12 10 CFR 50.90 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Response to STP-GSI-191-EMCB-RAI-1 (TAC NOs MF2400 and MF2401)

References:

1. Letter, D. W. Rencurrel, STPNOC, to NRC Document Control Desk, "Revised STP Pilot Submittal and Requests for Exemptions and License Amendment for a Risk-Informed Approach to Resolving Generic Safety Issue (GSI)-191," June 19, 2013, NOC-AE-13002986 (ML131750250)

2. Letter, G. T. Powell, STPNOC, to NRC Document Control Desk, "Supplement 1 to Revised STP Pilot Submittal and Requests for Exemptions and License Amendment for Risk-Informed Approach to Resolving Generic Safety Issue (GSI)-191, " November 13, 2013, NOC-AE-1 3003043 (ML13323A183)

3. E-mail, Matthew Bartlett, NRC, to A. W. Harrison, STP, "Request For Additional Information (RAI) Regarding License Amendment for Risk-Informed Approach to Resolving Generic Safety Issue (GSI) 191 South Texas Nuclear Operating Company (STPNOC) South Texas Project (STP), Units 1 And 2, Docket Nos.

50-498 and 50-499", November 26, 2013 (ML13330B715)

4. Meeting Notes, Mohan C. Thadani, NRC, "Summary of September 13, 2010, Category 1 Meeting, Via Conference Call, with STP Nuclear Operating Company-Discussion Of Draft Responses to Request for Additional Information for Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors",

October 13, 2010 (ML102810345)

ST133797950

NOC-AE-13003065 Page 2 of 3 By email on November 26, 2013, (Reference 3) the NRC staff requested additional information (RAI) regarding the applications in References 1 and 2. The STPNOC response to the RAI is provided in the attachment to this letter.

This response was discussed and found to be acceptable by the NRC staff in a conference call on September 13, 2010. It is documented as RAI-49 in meeting notes dated October 13, 2010 (Reference 4).

There are no regulatory commitments in this letter.

If there are any questions, please contact Ken Taplett at 361-972-8416.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on: 'Q./Og, 3 MMichael . Meier Vice President, Corporate Services awh

Attachment:

Response to STP-GSI-191-EMCB-RAI-1

NOC-AE-1 3003065 Page 3 of 3 cc:

(paper copy) (electronic copy)

Regional Administrator, Region IV Steven P. Frantz, Esquire U. S. Nuclear Regulatory Commission A. H. Gutterman, Esquire 1600 East Lamar Boulevard Morgan, Lewis & Bockius LLP Arlington, TX 76011-4511 Balwant K. Singal Balwant K. Singal Michael Markley Senior Project Manager John Stang U.S. Nuclear Regulatory Commission U. S. Nuclear Regulatory Commission One White Flint North (MS 8 B1) 11555 Rockville Pike John Ragan Rockville, MD 20852 Chris O'Hara Jim von Suskil NRC Resident Inspector NRG South Texas LP U. S. Nuclear Regulatory Commission P. O. Box 289, Mail Code: MN116 Kevin Polio Wadsworth, TX 77483 Richard Pefia City Public Service Jim Collins City of Austin Peter Nemeth Electric Utility Department Crain Caton & James, P.C.

721 Barton Springs Road Austin, TX 78704 C. Mele City of Austin Richard A. Ratliff Robert Free Texas Department of State Health Services

Attachment NOC-AE-1 3003065 Page 1 of 4 Response to STP-GSI-191-EMCB-RAI-1

References:

1. Enclosure to Letter From William H. Ruland, Director, Division of Safety Systems, Office of Nuclear Reactor Regulation, U. S. Nuclear Regulatory Commission, to Anthony Pietrangelo, Vice President, Regulatory Affairs, Nuclear Energy Institute, "Revised Content Guide for Generic Letter 2004-02 Supplemental Responses." November 21, 2007. (ADAMS Accession No. ML073110389)

2. Letter No. NOC-AE-08002372, From David W. Rencurrel, Site Vice President, South Texas Nuclear Operating Company, to U. S. Nuclear Regulatory Commission, Document Control Desk, "Supplement 4 to the Response to Generic Letter 2004-02,"

December 11, 2008. (Accession No. ML083520326)

3. Letter No. NOC-AE-1 3002986, From D. W. Rencurrel, Senior Vice President, Operations, South Texas Nuclear Operating Company, to U. S. Nuclear Regulatory Commission, Document Control Desk, "Revised STP Pilot Submittal and Requests for Exemptions and License Amendment for a Risk-Informed Approach to Resolving Generic Safety Issue (GSI)-191," June 19, 2013. (Accession No. ML13175A211)

4. Letter No. NOC-AE-13003043, From G. T. Powell, Site Vice President, South Texas Nuclear Operating Company, to U. S. Nuclear Regulatory Commission, Document Control Desk, "Supplement 1 to Revised STP Pilot Submittal and Requests for Exemptions and License Amendment for a Risk-Informed Approach to Resolving Generic Safety Issue (GSI)-191," November 13, 2013. (Accession No. ML13323A183)

NRC Question STP-GSI-191-EMCB-RAI-1:

Mechanical and Civil Enqineeringq Branch (EMCB)

Item 3.k of Reference 1 requested licensees to summarize the structural qualification results and design margins for various components of the sump strainer structural assembly. In Reference 2, STPNOC, the licensee, provided a qualitative response regarding the structural analysis without any supporting quantitative data. Additional information is needed regarding actual and allowable stresses and design margins for the various components of the sump strainer structural assembly to clarify the inherent level of conservatism employed in the design. This information was not included in STPNOC submittals (References 3 and 4).

Please summarize the structural qualification results, including the actual and allowable stresses, and design margins for the various components of the sump strainer structural assembly.

Attachment NOC-AE-1 3003065 Page 2 of 4 STP Response:

The strainer assembly is installed using multiple individual strainer modules (20 per sump).

Detailed structural analysis was performed on a single strainer module. The analysis is bounding and applicable to each of the 60 modules. Each sump pit is a 4' x 10' opening, covered by steel cover plates with a plenum box in the middle. The plenum box collects water from all strainer modules and directs the water down into the sump pit. Each strainer module is mounted to angle iron running along the floor. Where suitable floor embedded plates were available, the angle iron was attached to the embedded plates with welded clips. At other locations, the angle iron was welded to anchor plates and attached to the floor with concrete expansion anchors.

The results tabulated below are grouped into 3 categories: 1) strainer module components, 2) sump pit cover (cover plate, plenum box and connecting elements), and 3) floor mounting hardware (angle iron, clips, concrete expansion anchors). In the following tables, the term "Allowable" applies to stress, force per unit length or force, as applicable. The corresponding "Actual" value uses the same units as the "Allowable", to facilitate comparison. Most strainer components are A240, type 304 stainless steel, for which the allowable stress was computed based on a yield stress of either 23.2 ksi at 267 °F or 28.15 ksi at 128 OF. Two separate cases were considered, denoted as cases 1 and 2 in the following tables. The first case corresponds to maximum temperature (267 OF), which occurs early following a LOCA, while debris loading is low and resulting differential pressure is also low. Eventually the sump would experience the maximum debris loading, causing the maximum differential pressure. Because this occurs later, temperatures would have cooled greatly, to 128 OF. In the following tables, Case 1 is the early case (peak temperature, low differential pressure) and Case 2 is the long-term case (low temperature, peak differential pressure). As indicated above, the material properties differ, with Case 1 having the lower yield stress due to higher temperature.

The acronym "IR" stands for Interaction Ratio, which is nominally "Actual" divided by "Allowable". Since seismic loads are present, most components are subject to loads in multiple directions acting simultaneously. Code allowables may be different in different directions. (For example, AISC allows 0.6 fy for major axis bending and 0.75 fy for minor axis bending of plates; the axial allowable is generally lower and dependent on kL/R ratio.) Thus, IR is often not a direct ratio, but instead is the sum of multiple IR components. In cases where IR was computed from the sum of stress components combined using different allowables that are explicitly documented in the calculation, the tables conservatively list total stress and the lowest of the allowables, along with the true IR as reported in the structural calculation. "Actual" and "Allowable" correspond to the higher IR of cases 1 and 2. In cases where the directional stress components were not separated and documented individually in the calculation, only total IR is reported. Whenever IR is one or less, the component meets the stress requirements of the applicable code. Compliance with this requirement is confirmed by the results tabulated below.

Since allowables for safe shutdown earthquake (SSE) are higher than those for operating basis earthquake (OBE), the two cases are listed separately. In each of the following tables, the highest values of IR for SSE and OBE are highlighted in bold.

Attachment NOC-AE-1 3003065 Page 3 of 4 Summary of Structural Analysis Results - - Strainer Module Components Component Seismic IR IR IR Case (1) (2) (max)

External Radial Stiffener OBE 0.74 0.69 0.74 SSE 0.86 0.74 0.86 Tension Rods OBE 0.37 0.32 0.37 SSE 0.40 0.34 0.40 Edge Channels OBE 0.51 0.54 0.54 SSE 0.71 0.71 0.71 Seismic Stiffeners OBE 0.64 0.65 0.65 SSE 0.66 0.63 0.66 Spacers OBE 0.68 0.57 0.68 SSE 0.56 0.48 0.56 Core Tube OBE 0.04 0.04 0.04 SSE 0.05 0.05 0.05 Perforated Plate OBE 0.33 0.45 0.45 SSE 0.53 0.54 0.54 Wire Stiffener (differential pressure only) --- 0.25 0.33 0.33 End Cover OBE 0.40 0.49 0.49 SSE 0.35 0.48 0.48 End Cover Welds OBE 0.41 0.49 0.49 SSE 0.35 0.43 0.43 Weld of External Radial Stiffener to Core Tube OBE 0.19 0.17 0.19 SSE 0.21 0.18 0.21 Weld of External Radial Stiffener to Seismic Stiffener OBE 0.51 0.48 0.51 SSE 0.58 0.52 0.58 Edge Channel Rivets OBE 0.09 0.10 0.10 SSE 0.11 0.12 0.12 Inner Gap Hoop Rivets OBE 0.11 0.12 0.12 SSE 0.14 0.14 0.14 End Cover Rivets OBE 0.00 0.01 0.01 SSE 0.01 0.01 0.01 Module-to-Module Sleeve OBE 0.16 0.14 0.16 SSE 0.20 0.17 0.20 Module-to-Module Latch Connection OBE 0.60 0.62 0.62 SSE 0.92 0.87 0.92 Mounting Pins (standard) OBE 0.32 0.26 0.32 SSE 0.31 0.27 0.31 Mounting Bolts (alternate) OBE 0.20 0.22 0.22 SSE 0.21 0.22 0.22 Clevis Hitch Pins OBE 0.35 0.39 0.39 SSE 0.38 0.39 0.39 External Radial Stiffener Mounting Tabs OBE 0.14 0.14 0.14 SSE 0.15 0.13 0.15 Weld of Radial Arm to End Plate OBE 0.62 0.75 0.75 SSE 0.48 0.56 0.56 CASE 1) Early Conditions - - peak temperature, low differential pressure (low debris)

CASE 2) Late Conditions - - peak differential pressure (max. debris), low temperature

Attachment NOC-AE-1 3003065 Page 4 of 4 Summary of Structural Analysis Results - - Items Spanning Sump Pit Component Seismic Allowable Actual IR IR IR Case (1) (2) (max)

Cover Plate + Angle Iron + Tee OBE 18.6 ksi 7.96 ksi 0.41 0.43 0.43 (combined section) SSE 29.7 ksi 10.23 ksi 0.34 0.34 0.34 Angle Iron + Cover Plate OBE 18.6 ksi 11.85 ksi 0.58 0.64 0.64 (combined section) SSE 29.7 ksi 14.66 ksi 0.48 0.49 0.49 Cover Plate Bolts OBE 24.63 ksi 23.73 ksi 0.76 0.96 0.96 SSE 39.40 ksi 27.83 ksi 0.58 0.71 0.71 Weld connecting T to cover plate OBE 2.11 k/in 1.39 k/in 0.59 0.66 0.66 SSE 3.38 k/in 1.66 k/in 0.46 0.49 0.49 Plenum Box plate panels OBE 21.1 ksi 13.43 ksi 0.51 0.64 0.64 SSE 33.8 ksi 14.94 ksi 0.37 0.44 0.44 Plenum Box + Cover Plate OBE 0.47 0.50 0.50 (combined section) SSE 0.43 0.42 0.43 Plenum Box perimeter angles OBE 0.76 0.86 0.86 SSE 0.63 0.67 0.67 Plenum Box panel welds OBE 2.81 k/in 0.112 k/in 0.03 0.04 0.04 SSE 4.50 k/in 0.125 k/in 0.02 0.03 0.03 Weld between plenum box panels and OBE 2.11 k/in 0.43 k/in 0.18 0.21 0.21 perimeter angles SSE 3.38 k/in 0.51 k/in 0.14 0.15 0.15 Plenum Box Access Cover Bolts OBE 0.18 0.25 0.25 1 SSE 0.13 0.17 0.17 Summary of Structural Analysis Results - - Floor Mounting Hardware Component Seismic Allowable Actual IR IR IR Case (1) (2) (max)

Angle Iron Tracks OBE 13.9 ksi 7.49 ksi 0.54 0.54 0.54 SSE 22.3 ksi 13.64 ksi 0.61 0.58 0.61 Anchor Plates OBE 21.1 ksi 12.72 ksi 0.58 0.60 0.60 SSE 27.8 ksi 20.96 ksi 0.75 0.71 0.75 Weld of Angle Iron to Anchor OBE 1.74 k/in 0.17 k/in 0.10 0.09 0.10 Plate SSE 2.78 k/in 0.28 k/in 0.10 0.09 0.10 Hold Down Bars OBE 13.9 ksi 5.47 ksi 0.36 0.32 0.36 SSE 22.3 ksi 10.03 ksi 0.42 0.36 0.42 Weld of Hold Down Bars to OBE 1.16 k/in 0.46 k/in 0.40 0.35 0.40 Angle Iron Tracks SSE 1.86 k/in 0.88 k/in 0.47 0.41 0.47 Concrete Expansion Anchors SSE 3100 lb Tension = 2028 lb 0.92 0.71 0.92 Shear = 818 lb Standard mounting clips OBE 21.1 ksi 12.41 ksi 0.53 0.59 0.59 SSE 33.8 ksi 16.61 ksi 0.48 0.49 0.49 Welds on standard OBE 2.90 k/in 2.78 k/in 0.96 0.78 0.96 mounting clips SSE 3.71 k/in 3.58 k/in 0.96 0.93 0.96 Alternate (taller) mounting OBE 17.7 ksi 12.41 ksi 0.62 0.70 0.70 clips SSE 28.4 ksi 16.61 ksi 0.56 0.58 0.58 Welds on alternate mounting OBE 2.37 k/in 1.77 k/in 0.74 0.75 0.75 clips SSE 3.18 k/in 2.56 k/in 0.80 0.76 0.80 CASE 1) Early Conditions - - peak temperature, low differential pressure (low debris)

CASE 2) Late Conditions - - peak differential pressure (max. debris), low temperature