ML23082A136
| ML23082A136 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 03/23/2023 |
| From: | James Holloway Virginia Electric & Power Co (VEPCO) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 23-055 | |
| Download: ML23082A136 (1) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 March 23, 2023 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 LICENSE AMENDMENT REQUEST 10 CFR 50.90 Serial No.:
23-055 NRA/GDM:
RO Docket Nos.:
50-280 50-281 License Nos.: DPR-32 DPR-37 NRC APPROVAL OF METHODOLOGY CHANGE AND RECLASSIFICATION OF THE TURBINE BUILDING AS A TORNADO RESISTANT STRUCTURE RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION By letter dated April 14, 2022, [Agencywide Documents Access and Management System (ADAMS) Accession No. ML22104A125], as supplemented by letters dated May 11, 2022 and December 1, 2022 (ADAMS Accession Nos. ML22131A326 and ML22339A137, respectively), Virginia Electric and Power Company (Dominion Energy Virginia) submitted a license amendment request (LAR) for Surry Power Station (SPS) Units 1 and 2 requesting NRC approval of a methodology change and reclassification of the Turbine Building as a tornado resistant structure in the SPS Updated Final Safety Analysis Report (UFSAR). The reclassification is based on using a different methodology and acceptance criteria than those defined for other SPS tornado resistant (i.e., Tornado Criterion "T")
structures. The new methodology and acceptance criteria are considered a change to a method of evaluation and therefore require prior NRC approval pursuant to 10 CFR 50.59(c)(2)(viii).
By email dated February 23, 2023, the NRC provided a follow-up request for additional information (RAI) to facilitate the completion of their technical review of the LAR. The response to the RAI was requested by March 24, 2023. Dominion Energy Virginia's response to the NRC RAI is provided in Attachments 1 and 2.
Serial No.23-055 Docket Nos. 50-280/281 LAR RAI Response Page 2 of 3 If you have any questions or require additional information, please contact Mr. Gary D. Miller at (804) 273-2771.
Respectfully, James E. Holloway Vice President - Nuclear Engineering and Fleet Support Commitments made in this letter: None Attachments:
- 1. Response to NRC Request for Additional Information
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)
COUNTY OF HENRICO
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The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mr. James E. Holloway, who is Vice President - Nuclear Engineering and Fleet Support, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.
2,J Acknowledged before me this _l___ dayof }11a.f'e-h 2023.
My Commission Expires:
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CRAIG D SLY Notary Public Commonwealth of Virginia Reg.# 7518653 2.\\f My Commission Expires December 31, 20_
cc:
U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257 Mr. L. John Klos NRC Project Manager - Surry U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738 Mr. G. Edward Miller NRC Senior Project Manager - North Anna U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Surry Power Station State Health Commissioner Virginia Department of Health James Madison Building - 7th floor 1 09 Governor Street Suite 730 Richmond, VA 23219 Serial No.23-055 Docket Nos. 50-280/281 LAR RAI Response Page 3 of 3 Serial No.23-055 Docket Nos. 50-280/281 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST FOR NRC APPROVAL OF METHODOLOGY CHANGE AND RECLASSIFICATION OF THE TURBINE BUILDING AS A TORNADO RESISTANT STRUCTURE Virginia Electric and Power Company (Dominion Energy Virginia)
Surry Power Station Units 1 and 2
Serial No.23-055 Docket Nos. 50-280/281 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION License Amendment Request for NRC Approval of Methodology Change and Reclassification of the Turbine Building as a Tornado Resistant Structure Surry Power Station Units 1 and 2 NRG COMMENT:
By letter dated April 14, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22104A125), Virginia Electric and Power Company submitted to the U.S. Nuclear Regulatory Commission (NRG), a proposed amendment to the license for Surry Power Station (SPS) Units 1 and 2 regarding the Turbine Building tornado classification.
By letter dated December 1, 2022 (ADAMS Accession No. ML22339A137), you provided additional information in support of this review. The NRG staff has reviewed the information submitted to date and needs additional information to complete its review and approval of the licensee's submittal.
Regulatory Basis:
The U.S. Nuclear Regulatory Commission (NRG) issued construction permits for Surry Power Station (SPS) Units 1 and 2 before May 21, 1971. Consequently, SPS Units 1 and 2 were not subject to the requirements in Title 10 of the Code of Federal Regulations (10 CFR) Part 50, "Domestic Licensing of Production and Utilization Facilities," Appendix A, "General Design Criteria (GDC) for Nuclear Power Plants," see SECY-92-223, "Resolution of Deviations Identified during the Systematic Evaluation Program," dated September 18, 1992 (ADAMS Accession No. ML003763736).
However, the proposed LAR notes that the Turbine Building meets the requirements of SPS UFSAR Sections 1.4.2 and 1.4.40, that are generally consistent with the intent of GOG 2 and GOG 4 in Appendix A to 10 CFR Part 50, respectively.
SPS UFSAR Section 1.4.2, states, in part, that "Those systems and components of reactor facilities that are essential to the prevention of accidents that could affect the public health and safety or to the mitigation of their consequences are designed, fabricated, and erected in accordance with performance standards that enable the facility to withstand, without loss of the capability to protect the public, the additional forces that might be imposed by natural phenomena such as earthquakes, tornadoes, flooding conditions, winds, ice, and other local site effects. The design bases so established reflect (a) appropriate consideration of the most severe of these natural phenomena that have been recorded for the site and the suffounding area, and (b) an appropriate margin for withstanding forces greater than those recorded, in view of uncertainties about the historical data and their suitability as a basis for design. "
Page 1 of 9
Serial No.23-055 Docket Nos. 50-280/281 SPS UFSAR Appendix 14B, states, in part, that The analysis ensures that the Commission's General Design Criterion 4 is met, i.e., that all structures, systems, and components important to safety are designed to accommodate the effects of and are compatible with the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents, including loss-of-coolant accidents (LOCAs). These structures, systems, and components are protected against dynamic effects, including the effects of missiles, pipe whipping, and discharging fluids that may result in equipment failures and from events and conditions outside the nuclear power unit."
Follow-up RA/ 3.3.2.3-1A
Background:
SPS LAR Section 3.3.2.3, "Concrete Evaluation," supplemented by letter dated December 1, 2022 (ADAMS Accession No. ML22339A137), discusses structural analysis results for the equivalent membrane plus bending stress and shear stress in concrete elements. RAJ 3.3.2.3-1 requested the licensee to provide the evaluation of reinforcing steel in the concrete, including the ratio of maximum compressive or tensile strength over the compressive or tensile capacity of the reinforcing steel.
The licensee's response to RAJ 3.3.2.3-1 by letter dated January 25, 2023 (ADAMS Accession No. ML23025A125), indicates its evaluation of the reinforcing steel adjusted the ANSYS computer model of the SPS Turbine Building Steel Superstructure (TBSS) by reducing the concrete flexural stiffness by 75% and reduced the dynamic impact loading discussed in LAR Section 3.3.1.1, "Roof Structure Collapse Scenario." Based on the above, it appears that the licensee used a different approach between the evaluation of reinforcing steel and the evaluation of composite slab concrete elements. The reinforcing steel and composite slab concrete work together as one structural component, so the same evaluation approach would be expected to have been used. The NRG staff has additional questions as the change of evaluation approach, such as the consideration of cracked concrete and reduction of the dynamic impact load, may have a significant impact on the evaluation results of composite slab concrete elements.
Issue:
The licensee's response to RAJ 3.3.2.3-1 states that the ANSYS computer model of the SPS TBSS was adjusted to reflect the more realistic condition of cracked concrete by reducing flexural stiffness by 75%, based on AC/ 318. The NRG staff reviewed the AC/
318-71 code and did not find the provision for reducing flexural stiffness by 75% for cracked concrete.
Page 2 of 9
Serial No.23-055 Docket Nos. 50-280/281 The NRG staff understands the concrete evaluation results presented in LAR Section 3.3.2.3 are based on the original SPS TBSS global and local effects evaluations without the reduction of dynamic impact loading. It is not apparent what dynamic impact loading was reduced in the reinforcing steel evaluation, and how the reduction was justified.
The NRG staff expects the concrete and reinforcing steel to be analyzed in the same fashion, with the same material properties and loading conditions. As such, it is not apparent whether the concrete evaluation results presented previously in LAR Section 3.3.2.3 considered the same assumptions as the steel evaluation provided in the RA/
response (i.e., reduction of flexural stiffness for cracked concrete and the reduced dynamic impact loading).
It is also not apparent how the reduced concrete flexural stiffness and reduced dynamic impact loading impacts the evaluations of steel member stability and joint stresses.
Request:
- 1. Clarify which A CJ 318-71 code provision allows for the reduction of flexural stiffness by 75% for cracked concrete or provide justification and identify a code provision or industry standard or guidance that supports the reduction of the concrete flexural stiffness by 75%.
Dominion Energy Virginia Response ACI 318-71, Section 8.5.3.1 (Reference 6), provides limited guidance on the computation of relative stiffness of reinforced concrete members based on the transformed cracked sections, and states, in part, that "Any reasonable assumptions may be adopted for computing the relative flexure and torsional stiffnesses of columns, walls, floors, and roof systems." This limited guidance remained unchanged until issuance of the 1999 revision of ACI 318. Specifically, Section 10.11.1 of ACI 318-99 (Reference 7) permits the flexural stiffness (E/) of "Flat plates and flat slabs" to be based upon a cracked moment of inertia
(/e,) equal to 0.25 lg, where E represents the modulus of elasticity, and fer, and lg are the cracked and gross moment of inertia of the reinforced concrete section, respectively.
Subsequent revisions of ACI 318 have continued to adopt this specific cracked concrete provision, which is the basis of the 75% reduction in flexural stiffness of reinforced concrete slabs in the analysis of the SPS Turbine Building structure.
The ANSYS software, used in the analysis of the SPS Turbine Building structure, calculates section properties of members, including the moment of inertia, automatically. Therefore, the prescribed 75% reduction in flexural stiffness was implemented in the ANSYS model by reducing the concrete modulus of elasticity to 0.25 E to reflect a reduced stiffness for the cracked concrete (i.e., E le, = 0.25 E 19), and to allow the AN SYS software to automatically compute slab section properties based upon the sectional dimensions.
Page 3 of 9
Serial No.23-055 Docket Nos. 50-280/281 Reducing the concrete modulus of elasticity also reduces the slab shear modulus and axial stiffness and can change the distribution of axial, shear, and flexural stresses within the reinforced concrete slab. Flexure is the main load transfer mechanism by which the slabs transfer the applied gravity loads, as well as loads due to the potential falling roof members, to the supporting steel superstructure. Membrane and in-plane shear stresses in the concrete slabs are primarily developed due to the lateral drift of supporting steel columns under tornado wind loading.
Hence, as confirmed by the analysis results presented in the responses to Questions 3 and 4 below, the 75% reduction in flexural stiffness of the concrete slabs will have an insignificant effect upon the transfer of membrane and shear stresses between the slabs and the supporting steel superstructure.
In summary, the axial, shear, and flexural stresses for concrete and reinforcing steel of the slabs in the SPS Turbine Building are demonstrated to remain within the design strengths of the ACI 318-71 code, whether using E or 0.25 E for the concrete stiffness in the analytical model.
Furthermore, both values of stiffness can be considered "reasonable assumptions" of stiffness as permitted by ACI 318-71 (Reference 6).
- 2. Describe the reduced dynamic impact loading with numeric values that is considered in the reinforcing steel evaluation and provide the basis for this reduction.
Dominion Energy Virginia Response In the original analysis of the SPS Turbine Building (References 1 and 5), the combined weight of the steel members above the operating deck (1,960 kip) and the overhead cranes (841 kip) was applied to the operating deck with a dynamic load factor (DLF) of 2.0 to conservatively account for the dynamic impact that the collapse of the entire roof structure would have upon the rest of the Turbine Building structure. This conservative approach resulted in a total impact live load of 5,602 kip on the operating deck of the Turbine Building.
By letter dated December 1, 2022 (Reference 2), Dominion Energy Virginia provided evidence demonstrating the overhead cranes and their supporting columns and girders are able to withstand a 250-mph tornado wind speed without falling onto the operating deck. This evidence provides the technical basis for reducing the dynamic impact loading on the operating deck. As discussed in the letter, the overhead cranes are not anchored to their rails and are free to roll or slide under tornado wind loading. Hence, the tributary tornado wind reaction at the crane rail elevation of the Turbine Building Steel Superstructure (TBSS) will be limited by the friction force that a single overhead crane can transmit. Therefore, the results of the original analysis of the Turbine Building (References 1 and 5) that assumed full collapse of all roof members are conservative.
During the effort to resolve NRC RAI 3.3.2.3-1 (Reference 3), the conservatism discussed above was removed from the original analysis. The 841-kip weight of the overhead Page 4 of 9
Serial No.23-055 Docket Nos. 50-280/281 cranes and 678-kip weight of the steel columns that do not fall under the applied tornado wind loads were removed from the total weight of the roof members that had been assumed to collapse in the original analysis (References 1 and 5), resulting in a new static collapse roof weight of 1,282 kip. With the DLF of 2.0 applied to this new static roof weight, the new impact live load becomes 2,564 kip, which shows a 54% reduction compared to the impact load in the original analysis (i.e., 5,602 kip). The new impact live load of 2,564 kip was applied to the operating deck to represent a realistic roof collapse load in the evaluation that supports the letter dated January 25, 2023 (Reference 4).
- 3. Clarify whether the original global and local effects evaluations considered the reduction of flexural stiffness for cracked concrete. If the original evaluations did not consider the reduced concrete flexural stiffness, provide the ratio of equivalent membrane plus bending stress over the compressive strength capacity, and the ratio of maximum shear stress over shear strength capacity for concrete elements in the concrete slabs of the operating and mezzanine decks under the same reduced dynamic impact loading and reduced concrete flexural stiffness that was used in the evaluation of the reinforcing steel.
Dominion Energy Virginia Response The original analysis of the SPS Turbine Building (References 1 and 5) did not consider the reduction of the flexural stiffness of the concrete due to cracking. Consideration of larger stiffnesses for reinforced concrete members result in higher stresses, and thus the results of the original analysis are conservative. As discussed in the response to Question 1 above, more recent editions of the ACI code include provisions that more clearly approximate the reduction of the flexural stiffness of reinforced concrete members due to cracking under the applied loads. Reducing the stiffness of the concrete lowers the peak stresses in the concrete. The maximum concrete stresses predicted by the model are located either at sharp corners or where concrete slabs connect to a neighboring steel column. The results of the finite element analysis show large stresses in these locations because they feature a localized discontinuity in the displacement field of the concrete.
Since an elastic material model is used for the concrete, these peak stresses are proportional to the concrete stiffness. Crediting the reduction in stiffness for the highly loaded concrete therefore reduces the stresses.
As further discussed in the response to Question 4 below, the stiffness of the concrete slabs in the Turbine Building will have no appreciable effect upon the resulting stresses in the TBSS. The TBSS does not rely on the stiffness of the concrete slabs to resist tornado wind loads, as the steel slab grillage, acting in concert with the internal and external bracings, transfers lateral wind loads to the structure's foundation.
Under tornado wind loading, axial and shear stresses in the reinforced concrete slabs are primarily driven by the lateral deflections of the steel columns that support the concrete Page 5 of 9
Serial No.23-055 Docket Nos. 50-280/281 slabs. Flexural stresses in the slabs are primarily due to the impact live load of the falling roof structure.
The combined effect of the 75% reduction in flexural stiffness of the concrete slabs and the reduced roof collapse load is demonstrated by comparing the results of the analysis supporting the January 25, 2023 letter (Reference 4) to those of the original analysis of the Turbine Building (Reference 5), prepared to support the LAR (Reference 1 ). The original analysis reported a maximum concrete equivalent membrane plus bending stress of 2995.7 psi. The compressive strength is 3,800 psi, resulting in a stress ratio of 0.79 (Section 3.3.2.3 of Reference 1 and Section 7.3 of Reference 5). The modified analysis, with reduced flexural stiffness for cracked concrete and reduced roof collapse load, results in a maximum concrete equivalent membrane plus bending stress of 1,440 psi, corresponding to a stress ratio of 0.38.
Similarly, the original analysis (Section 3.3.2.3 of Reference 1, modified by Reference 2) reported a maximum concrete shear stress of 406 psi. The shear capacity is 426 psi, resulting in a stress ratio of 0.95. The modified analysis results in a maximum concrete shear stress of 293 psi, leading to a stress ratio of 0.61.
In summary, both modifications to the original analysis methodology to account for reduced concrete stiffness and reduced roof collapse load removed conservatism in the evaluation of the concrete stresses, which resulted in more realistic concrete and reinforcing steel stresses. All the calculated stresses are within the corresponding design strengths based on ACI 318-71. Therefore, the modified methodology for estimation of stresses in concrete and reinforcing steel does not invalidate nor contradict the evaluation of the concrete slabs performed in the original analysis. Rather, it reinforces that the results of the original analysis were conservative.
- 4. Evaluate the impact of the AN SYS computer model change (such as reduced concrete flexural stiffness and reduced dynamic impact loading) on the evaluation results described in LAR Sections 3.3.2.2, "Steel Member Stability" and 3.3.2.4, "Joint Stress Evaluation," and clarify whether previous evaluation results of steel member stability and their joint stresses are still valid to meet the acceptance criteria set in Section 3.3.1.4 of the LAR.
Dominion Energy Virginia Response Analysis results of the modified ANSYS model (i.e., the modified model to include the reduced concrete flexural stiffness and the reduced roof collapse load) show the evaluation of the steel members and joints in the original analysis (References 1 and 5) remains valid. The effect of the modifications on key analysis results of the TBSS are provided in Table 1. As shown, the overall drift, ratio, steel member stresses, and most joint stress ratios from the modified analysis are bounded by those of the original analysis.
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Serial No.23-055 Docket Nos. 50-280/281 All of the changes are very minor, thus indicating the analysis results for steel members are generally insensitive to the modifications made in the model. Note that modifications in the model, which were made to account for reduced concrete flexural stiffness and the reduced roof collapse load, result in redistribution of loads causing some joints to undergo increased loadings. However, as shown in Table 1, the limiting margin corresponding to the maximum bolt tension ratio is only minimally increased. Although individual joint interaction ratios may change because of the modifications in the model, the impact of these changes on the existing capacity margins of steel members are minor as evidenced by comparison of the maximum interaction ratios provided in Table 1. All results of the modified evaluation continue to meet the acceptance criteria established by the original analysis (References 1 and 5).
Table 1. Comparison of the Key Analysis Results for the Original and Modified Models Scope Result Original Modified Change Evaluation Evaluation Building Stability Maximum Operating Floor Lateral 0.70%
0.68%
-0.02%
(LAR, Section 3.3.2.1)
Drift Ratio Steel Member Stability Maximum True Tensile Stress 59.6 ksi 59.5 ksi
-0.1 ksi (LAR, Section 3.3.2.2)
(Axial plus Bending)
(-0.1 %)
Maximum Bolt Shear Ratio 0.78 0.74
-0.04 Joint Stress Evaluation Maximum Bolt Tension Ratio 0.58 0.62
+0.04 (LAR, Section 3.3.2.4)
Maximum Coped Section 0.96 0.95
-0.01 Interaction Since the modified evaluation includes a significant reduction in the roof collapse load applied to the operating deck, the results presented in Table 1 may seem counterintuitive.
However, it is evident from the behavior of the analysis model that lateral deflections of the Turbine Building and the local stability of structural steel members are not sensitive to the weight applied to the operating deck. Therefore, significant reductions in stress results of the modified model are not observed. The reduction of roof collapse load results primarily in the reduction of stresses in the concrete, not the steel. Additionally, the reduced roof collapse load on the operating deck increases the margin to the buckling failure of the supporting columns, but this improved robustness is not evident in the comparison results provided in Table 1.
Page 7 of 9
Serial No.23-055 Docket Nos. 50-280/281
- 5. Clarify any conforming changes in UFSAR Table 15. 2-1 that may be needed to ensure consistency with the TB evaluation.
Dominion Energy Virginia Response The proposed change to SPS UFSAR Section 15.2 and Table 15.2-1 included in the April 14, 2022 LAR (Reference 1) has been revised to ensure consistency with the revised TBSS evaluation.
Specifically, the two additional changes noted below have been incorporated into the proposed UFSAR change and are indicated by revision bars in the right hand margin of the revised UFSAR change included in Attachment 2 of this letter.
- 1. The following bullet is added to the proposed list of bulleted items being included in UFSAR Section 15.2 that distinguish the tornado evaluation of the SPS TB structure from other Tornado Criterion "T structures:
In accordance with AC/ 318-71, the allowable compressive stress limit for the reinforced concrete portions of the SPS TB structure shall not exceed 0. 85 f c-This concrete compressive stress limit applies to the overall (i.e., global) structural response due to the tornado wind effects.
Note: As shown in Attachment 2, the 1st bullet in the INSERT for UFSAR Section 15.2.3 was also changed. The change is editorial and clarifies the basis for material properties consistent with the verbiage in the LAR.
- 2. Note 3 will be modified in the proposed UFSAR change to Table 15.2-1 to reflect the analyzed extent of "building collapse" in the SPS Turbine Building under a 250-mph maximum tornado wind speed, as follows:
- 3. The extent of "building collapse" in the Turbine Building, under a 250-mph maximum tornado wind speed, consists of the failure of the steel roof trusses. The overhead cranes and their supporting steel columns will remain in place. The operating and mezzanine decks will remain stable to provide tornado protection for safe shutdown and non-isolable water source components located below.
Additionally, no damage will occur to any adjacent Tornado Criterion "T" structures or the protected components housed within (e.g., Service Building -
Control House).
Page 8 of 9
References Serial No.23-055 Docket Nos. 50-280/281
- 1. Letter Serial No.21-330, "Virginia Electric and Power Company, Surry Power Station Units 1 and 2, License Amendment Request for NRC Approval of Methodology Change and Reclassification of the Turbine Building as a Tornado Resistant Structure," April 14, 2022, ADAMS Accession No. ML22104A125.
- 2. Letter Serial No.22-333, "Virginia Electric and Power Company, Surry Power Station Units 1 and 2, License Amendment Request for NRC Approval of Methodology Change and Reclassification of the Turbine Building as a Tornado Resistant Structure, Supplemental Information,"
December 1,
- 2022, ADAMS Accession No.
- 3. Email from John Klos (USNRC) to Gary Miller (Dominion), "Formal 43-day RAI Issuance for Surry Turbine Building LAR - due Friday January 27, 2023," December 15, 2022, ADAMS Accession No. ML22349A210.
- 4. Letter Serial No.22-387, "Virginia Electric and Power Company, Surry Power Station Units 1 and 2, License Amendment Request for NRC Approval of Methodology Change and Reclassification of the Turbine Building as a Tornado Resistant Structure, Response to Request for Additional Information," dated January 25, 2023, ADAMS Accession No. ML23025A125.
- 5. MPR Calculation 0114-0126-CALC-001, "Surry Turbine Building Superstructure Evaluation for Tornado Wind Loads," Revision 1.
- 6. ACl-318, "Building Code Requirements for Reinforced Concrete," 1971 Edition.
- 7. ACl-318, "Building Code Requirements for Structural Concrete (ACI 318-99) and Commentary (ACI 318R-99)," 1999 Edition.
Page 9 of 9 Serial No.23-055 Docket Nos. 50-280/281 REVISED MARK-UP OF SPS UNITS 1 AND 2 UFSAR PLANNED CHANGES Virginia Electric and Power Company (Dominion Energy Virginia)
Surry Power Station Units 1 and 2
FOR INFORMATION ONLY SPSUFSAR It is assumed that a tornado could generate either of the following potential missiles:
15.2-4
- 1. Missile equivalent to a wooden utility pole 40 feet long, 12-inch diameter, weighing 50 lb/ft' and traveling in a vertical or horizontal direction at 150 mph.
- 2. Missile equivalent to a 1-ton automobile traveling at 150 mph.
The design assumes maximum wind forces and partial vacuum to occur simultaneously with the impact of either of the missiles singly. Allowable stresses do not exceed 90% of the certified minimum yield strength of the steel, the capacity reduction factor given in Section 15.5.1.2 times the certified minimum yield strength of the reinforcing steel, and 75% of the ultimate strength of the concrete. The allowable stress limits of 0.9 Fy (steel superstructures) and 0.9 fy and 0.75 f'c (reinforced concrete structures) apply to stresses from the overall structural response due to tornado load effects. These stresses are located away from the tornado missile impact zone and outside any yield-line patterns that may develop during the tornado missile impact.
It is noted that the physical configuration of certain plant components does not provide complete physical protection against tornado-generated missiles. The vulnerable surface area for each component was assessed probabilistically using the Tornado Missile Risk Evaluator Methodology (Reference 12) and it was determined that the risk to the plant is acceptably low, such that the additional missile protection need not be provided. Refer to Table 15.2-1 for identification of these components.
15.2.4 Seismic Design Class I structures, systems, and components designed to resist seismic forces are listed in Table 15.2-1. The design is based on two separate seismic criteria: the operating-basis earthquake (OBE) and the design-basis earthquake (DBE), as described in Section 2.5.
The seismic analysis of Class I structures, such as the containment structure, auxiliary building, fuel building, service building (including the control room), and safeguard areas, was based on the modal analysis response spectra technique. Major equipment-supporting structures, such as steam generator supports, reactor coolant pump supports, and pressurizer supports, were treated in an identical manner. Acceleration response spectra for the OBE and DBE are given on Figures 2.5-5 and 2.5-6.
Seismic loading includes the horizontal or vertical responses acceleration or combinations of both where the effects, as measured by the separate acceleration components, of horizontal and vertical accelerations are combined to produce maximum stress intensities, taking into account any potential adverse effect due to phase of the separate accelerations.
Damping factors for the structures, systems, and components are given in Table 15.2-2.
The design of the containment structures is based on ultimate strength design and loading factors as described in Section 15.5.1.2. Maximum allowable stress levels for both the
INSERT - SPS UFSAR Page 15.2-4 The US NRC approved license amendment request [References 14 and 15] which validates an evaluation that demonstrates the Surry Power Station (SPS) Turbine Building (TB) structure is a tornado-resistant structure, evaluated under a different methodology and acceptance criteria than other Tornado Criterion "T" structures at SPS. The following bullet items help to distinguish the tornado evaluation of the SPS TB structure from other Tornado Criterion "T" structures at SPS.
A nonlinear, static, finite element analysis methodology and associated acceptance criteria demonstrates that the TB is a tornado-resistant structure, which provides protection for safe shutdown and non-isolable components located in the basement of the TB during a tornado.
1'tenlittettf ma.tefittl tteeeptttttee efitefitt ttfe l:msed ott ti'l:e fl1"f'li:ett-ble feqttifemettb of A8:ME Boi:lef ttml Pfessurn Vessel Cocle, 8eetion VIII, Division 2, 2010 Eclition eHcl eolumtt s-ttteiliey is ettsea on a 1% mexifflttffl dfift ffltio from A8CE 7 10. Material properties are based on a true-stress, true-strain curve for carbon steel developed based on the method provided in Section VIII, Division 2 of the ASME Boiler and Pressure Vessel Code using the design basis ASTM A36 material strength and properties. Column stability is based on a 1 % maximum drift ratio from ASCE 7-10. The evaluation demonstrates that during a tornado, partial building collapse of the TB structure is expected above the operating deck elevation, but the operating and mezzanine decks will remain stable. The stable operating and mezzanine decks of the TB provides tornado protection for safe shutdown and non-isolable water source components located below in the basement of the TB. Additionally, partial building collapse of the TB structure during a tornado will not damage any adjacent Tornado Criterion "T" structures or the protected components housed within.
The maximum tornado wind speed for the TB is established as 250-mph, which is the sum of a 208-mph rotational component and a 42-mph translational component.
Only local effects of tornado missiles (i.e., penetration) need to be considered for the design of the TB and the 2-foot thick, reinforced concrete slabs at the mezzanine deck elevation, which provide physical tornado missile protection for safe shutdown components located directly below.
For other safe shutdown and non-isolable water source components located in the basement of the TB, where physical tornado missile protection cannot be provided, adequate tornado missile protection is demonstrated via the Tornado Missile Risk Evaluator (TMRE) methodology and designated by the Tornado Criterion "P*" protection classification in SPS UFSAR, Table 15.2-1 (Ref. Revised TMRE & Notebook Analyses, Calculation No. TBD).
Partial differential pressures will not develop during a tornado in a vented structure such as the TB.
In accordance with ACI 318-71, the allowable compressive stress limit for the reinforced concrete portions of the SPS TB structure shall not exceed 0.85 re. This concrete compressive stress limit applies to the overall (i.e., global) structural response due to the tornado wind effects.
FOR INFORMATION ONLY SPS UFSAR 15.2-8
15.2 REFERENCES
- 1. V. C. Gilberton and E. E. Mageanu, Tornadoes, AL4 Technical Reference Guide, TRG 13-2, U.S. Weather Bureau.
- 2. T. W. Singell, Wind Forces on Structures: Forces on Enclosed Structures, Journal of the Structural Division of the ASCE, July 1958.
- 3. Deleted.
- 4. Letter, NRC to Vepco, Serial #85-885, dated December 4, 1985
- 5. ASME Boiler and Pressure Vessel Code,Section III, Division I, Code Case N-411, Alternative Damping Values for Seismic Analysis of Piping Sections, American Society of Mechanical Engineers, 345 E. 4 7th Street, New York, NY 10017, dated September 17, 1984.
- 6. NRC Bulletin No. 88-11: Pressurizer Surge Line Thermal Stratification, USNRC, December 20, 1988.
- 7. Virginia Power Letters Serial Nos. 89-006A dated May 3, 1989 and 89-006B dated November 13, 1989 to United States Nuclear Regulatory Commission.
- 8. Revised report on the Reanalysis of Safety-Related Piping Systems - Surry Power Station, Unit 1, August 1979, by Stone & Webster Engineering Corporation.
- 9. Report on the I.E.Bulletin 79-14, Analysis for As-Built Safety-Related Piping Systems -
Surry Power Station - Unit 2, July 1981, by Ebasco Services, Inc.
- 10. Report on the Reanalysis of Safety-Related Piping Systems - Surry Power Station - Unit 2, Rev. 1, April 1980, by Ebasco Services, Inc.
- 11. Mitsubishi Heavy Industries, LTD., Design Report DG KCS-03-0008, Dominion Generation, Surry Power Station Unit 2, Control Rod Drive Mechanism Design Report, Rev. 3.
- 12. NEI 17-02, Rev. IB, Tornado Missile Risk Evaluator (TMRE), September 2018, as implemented and approved at Shearon Harris Nuclear Power Plant (ML18347A385).
- 13. SWECO 7703, Missile-Barrier Interaction -A Topical Report, Stone & Webster Engineering Corporation, Boston, MA, September 1977
21 -330), "Virginia Electric and Power Company, Surry Power Station Units 1 and 2, Request for NRC Approval of Methodology Change and Reclassification of the Turbine Building as a Tornado Resistant Structure."
Subject:
Surry Power Station, Units l and 2 - Issuance of Amendment Nos. 3XX and 3XX RE: Methodology Change and Reclassification of the Turbine Building as a Tornado Resistant Structure."
FOR INFORMATION ONLY Table 15.2-1 (CONTINUED)
STRUCTURES, SYSTEMS, AND COMPONENTS DESIGNED FOR SEISMIC AND TORNADO CRITERIA (Refer to the equipment classification list (Q-list) for a more comprehensive list of components. See Note 1.)
Earthquake Tornado Item Criterion Criterion Sponsora Note Emergency diesel-generator rooms (continued)
Walls, excluding louvers Roof slab I
Turbine building NA Mechanical Equipment Room-5 Low-level intake structure (Circulating water pump intake structure)
High-level intake structures Seal pits High-level intake canal Fire-pump house Fuel-oil transfer pump vault Boron recovery tank dikes Waste gas & boron recovery pump house
- a. HISTORICAL information, see Note 2.
I I
I I
I I
I I
I rn
~~
T T
T T
NA T
T T
T SW SW SW SW SW SW SW SW By design, building collapse will not damage any Class I structures and components during earthquake, or tornado-resistant structures a.,,_.__,.__,.__,.__,.-..,-...._
components during tomad T for emergency service water cubicle pump only T, no missile protection required T, no missile protection required Engine-driven pump only Vl iv I.....
FOR INFORMATION ONLY Table 15.2-1 (CONTINUED)
STRUCTURES, SYSTEMS, AND COMPONENTS DESIGNED FOR SEISMIC AND TORNADO CRITERIA (Refer to the equipment classification list (Q-list) for a more comprehensive list of components. See Note 1.)
Earthquake Tornado Item Criterion Criterion Sponsora Note Legend W - Westinghouse Electric Corporation.
SW - Stone & Webster Engineering Corporation.
I - Refers to Seismic Class I criteria. All Class I components and structures are designed to resist the operating-basis earthquake within allowable working stresses. A check has been made to determine that failure to function will not occur with a design-basis earthquake.
T - Refers to structures that will not fail during the design tornado.
P - Refers to systems and components that will not fail during the design tornado since they are protected by tornado resistant structures or by being buried underground.
P* - Refers to systems and components that are not provided with complete physical protection from tornado-generated missiles, but have been evaluated using the Tornado Missile Risk Evaluator Methodology (Reference 12) and it has determined that the risk to the plant associated with the partially exposed SSC is sufficiently low such that complete physical protection from tornado-generated missiles need not be provided.
NA - Not applicable.
T+ - Refers to the main structural steel members of the operating and mezzanine decks of the Turbine Building structure, which will remain stable and not collapse during a tornado with a 250-mph maximum wind speed.
C/.l..,,
C/.l
~
C/.l
~
FOR INFORMATION ONLY Table 15.2-1 (CONTINUED)
STRUCTURES, SYSTEMS, AND COMPONENTS DESIGNED FOR SEISMIC AND TORNADO CRITERIA (Refer to the equipment classification list (Q-list) for a more comprehensive list of components. See Note 1.)
Earthquake Tornado Item Criterion Criterion Sponsora Note NOTES:
- 1.
CAUTION, this table shall only be used for the classification of structures. Refer to the PAMS database for the classification of systems and components. A list of structures, systems, and components, like those in Table 15.2-1, was provided as part of the licensing application to permit a determination to be made as to the general suitability of the classification given and the design approach applied. Since the time of original plant licensing, an equipment classification listing (Q-List), was developed and subsequently replaced with a database (PAMS) to provide a more comprehensive and up-to-date list of individual components and their classifications than does this table, which only provides a general list of systems and components. According to the SPS current licensing basis, structures required to withstand the effects of a design basis tornado (Tornado Criterion "T") are also required to be designed to Seismic Category I requirements (Seismic Criterion "I"). Hence, all structures classified as "T" must also be classified as "I", but not necessarily vice versa. The Q-List and PAMS database only provide an input field for the more encompassing Seismic Category I classification for structures and do not provide a separate input field to identify those Seismic Criterion "I" structures that must also meet the Tornado Criterion "T" classification. Hence, SPS UFSAR, Table 15.2-1, was updated to be consistent with the SPS current licensing basis to reflect both the Seismic Criterion "I" and Tornado Criterion "T" classifications for structures at SPS in response to US NRC RIS 2015-06. For the classifications of systems and components at SPS, designed to be functional under Seismic Class I, Seismic Criterion "I", refer to the PAMS database.
- 2. The information in the sponsor column designates the division of responsibility between Westinghouse and Stone & Webster for the original design of listed structures, systems, and components. These designations are considered HISTORICAL and are not intended or expected to be updated for the life of the plant.
- 3. The extent of "building collapse" in the Turbine Building, under a 250-mph maximum tornado wind speed, consists of the failure of aH the steel roof trusses. and their supporting steel eolumns dovvn to the top of the operating deek elevation. The overhead cranes and their supporting steel columns will remain in place. The operating deck and mezzanine decks will remain stable to provide tornado protection for safe shutdown and non-isolable water source components located below. Additionally, no damage will occur to any adjacent Criterion "T" structures or the rotected comr.onents housed within ( e.g., Service B ii in -
o tr I Ho se.
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