ML23100A065

Issuance of Amendment Nos. 310 and 310, Regarding Turbine Building Tornado Classification

ML23100A065
Person / Time
Site:	Surry
Issue date:	04/25/2023
From:	John Klos Plant Licensing Branch II
To:	Stoddard D Virginia Electric & Power Co (VEPCO)
Klos, J
References
EPID L-2022-LLA-0056
Download: ML23100A065 (17)

Text

April 25, 2023 Mr. Daniel G. Stoddard Senior Vice President and Chief Nuclear Officer Innsbrook Technical Center 5000 Dominion Blvd.

Glen Allen, VA 23060-6711

SUBJECT:

SURRY POWER STATION, UNIT NOS. 1 AND 2, ISSUANCE OF AMENDMENT NOS. 310 AND 310 REGARDING TURBINE BUILDING TORNADO CLASSIFICATION (EPID L-2022-LLA-0056)

Dear Mr. Stoddard:

The U.S. Nuclear Regulatory Commission (the Commission) has issued the enclosed Amendment No. 310 to Subsequent Renewed Facility Operating License No. DPR-32 and Amendment No. 310 to Subsequent Renewed Facility Operating License No. DPR-37 for the Surry Power Station, Unit Nos. 1 and 2 (Surry), respectively. The amendments are in response to your application dated April 14, 2022, as supplemented by letters dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023.

These amendments revise the designation of Surrys turbine buildings as tornado-resistant structures, which will be reflected in the Surry Updated Final Safety Analysis Report.

A copy of the related safety evaluation is also enclosed. A Notice of Issuance will be included in the Commissions monthly Federal Register notice.

Sincerely,

/RA/

John Klos, Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-280 and 50-281

Enclosures:

1. Amendment No. 310 to DPR-32

2. Amendment No. 310 to DPR-37

3. Safety Evaluation cc: Listserv

VIRGINIA ELECTRIC AND POWER COMPANY DOCKET NO. 50-280 SURRY POWER STATION, UNIT NO. 1 AMENDMENT TO SUBSEQUENT RENEWED FACILITY OPERATING LICENSE Amendment No. 310 Subsequent Renewed License No. DPR-32

1. The Nuclear Regulatory Commission (NRC, the Commission) has found that:

A. The application for amendment by Virginia Electric and Power Company (the licensee) dated April 14, 2022, as supplemented by letters dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commissions rules and regulations set forth in 10 CFR Chapter I; B. The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public and (ii) that such activities will be conducted in compliance with the Commissions regulations; D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.

Enclosure 1

2. Accordingly, by Amendment No. 310, Subsequent Renewed Facility Operating License No. DPR-32 is hereby amended to authorize revision to the Updated Final Safety Analysis Report of the Surry Power Station as set forth in the licensees application dated April 14, 2022, as supplemented by letters dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023, and evaluated in the NRC staffs safety evaluation enclosed with this amendment.

3. This license amendment is effective as of its date of issuance and shall be implemented within 90 days.

FOR THE NUCLEAR REGULATORY COMMISSION Digitally signed by Glenn Glenn E. E. Miller Date: 2023.04.25 Miller 18:09:50 -04'00' Michael T. Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Date of Issuance: April 25, 2023

VIRGINIA ELECTRIC AND POWER COMPANY DOCKET NO. 50-281 SURRY POWER STATION, UNIT NO. 2 AMENDMENT TO SUBSEQUENT RENEWED FACILITY OPERATING LICENSE Amendment No. 310 Subsequent Renewed License No. DPR-37

1. The Nuclear Regulatory Commission (NRC, the Commission) has found that:

A. The application for amendment by Virginia Electric and Power Company (the licensee) dated April 14, 2022, as supplemented by letters dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commissions rules and regulations set forth in 10 CFR Chapter I; B. The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public and (ii) that such activities will be conducted in compliance with the Commissions regulations; D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.

Enclosure 2

2. Accordingly, by Amendment No. 310, Subsequent Renewed Facility Operating License No. DPR-32 is hereby amended to authorize revision to the Updated Final Safety Analysis Report of the Surry Power Station as set forth in the licensees application dated April 14, 2022, as supplemented by letters dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023, and evaluated in the NRC staffs safety evaluation enclosed with this amendment.

3. This license amendment is effective as of its date of issuance and shall be implemented within 90 days.

FOR THE NUCLEAR REGULATORY COMMISSION Digitally signed by Glenn Glenn E. E. Miller Date: 2023.04.25 Miller 18:10:21 -04'00' Michael T. Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Date of Issuance: April 25, 2023

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 310 TO SUBSEQUENT RENEWED FACILITY OPERATING LICENSE NO. DPR-32 AND AMENDMENT NO. 310 TO SUBSEQUENT RENEWED FACILITY OPERATING LICENSE NO. DPR-37 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION, UNIT NOS. 1 AND 2 DOCKET NOS. 50-280 AND 50-281

1.0 INTRODUCTION

By letter dated April 14, 2022 (Agencywide Documents Access and Management System Accession No. ML22104A125), as supplemented by letters dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023 (ML22131A326, ML22339A137, ML23025A125, and ML23082A136, respectively), Virginia Electric and Power Company (the licensee) submitted to the U.S. Nuclear Regulatory Commission (NRC, the Commission) a license amendment request (LAR) for changes to the Surry Power Station, Unit Nos. 1 and 2 (Surry)

Updated Final Safety Analysis Report (UFSAR) (Revision 54; ML22283A015). The requested changes would revise the designation of Surrys turbine buildings as a tornado-resistant structures called T+ which is lower than the current T rating, which would be reflected in the Surry UFSAR.

The supplements dated May 11, 2022, December 1, 2022, January 25, 2023, and March 23, 2023, provided additional information that clarified the application, did not expand the scope of the application as originally noticed, and did not change the NRC staffs original proposed no significant hazards consideration determination as published in the Federal Register on July 15, 2022 (87 FR 42510).

2.0 REGULATORY EVALUATION

2.1 Regulatory Requirements and Guidance Enclosure 3

The NRC issued construction permits for Surry before May 21, 1971. Consequently, Surry was 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 (ML003763736)). The conclusion was that Surry met the intent of the GDC published in 1967 (draft GDCs). In its LAR, the licensee stated that Surry UFSAR Section 1.4.2, Performance Standards, Section 1.4.40, Missile Protection, Section 2.2.2.1, Tornadoes, and Section 15.2.3, Tornado Criteria, meet the intent of GDC 2, Design bases for protection against natural phenomena, and GDC 4, Environmental and dynamic effects design bases.

Surry 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 surrounding 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.

Surry UFSAR Appendix 14B.1.1 states, in part, that:

The analysis ensures that the Commissions 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.

The regulatory requirements and guidance applicable to the LAR are listed below.

Regulations Appendix A to 10 CFR Part 50, GDC 2, requires that structures, systems, and components important to safety be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions.

Appendix A to 10 CFR Part 50, GDC 4, requires that structures, systems, and components important to safety be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents, including loss-of-coolant accidents.

Guidance NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR [Light-Water Reactor] Edition, Section 19.2, Review of Risk Information Used to Support Permanent Plant-Specific Changes to the Licensing Basis: General Guidance, dated June 2007 (ML071700658), provides general guidance to the NRC staff for evaluating the technical basis for proposed risk-informed changes.

Regulatory Guide 1.76, Revision 1, Design-Basis Tornado and Tornado Missiles for Nuclear Power Plants, dated March 2007 (ML070360253), provides licensees with guidance that the NRC staff considers acceptable for use in selecting the design-basis tornado and design-basis tornado-generated missiles that a nuclear power plant should be designed to withstand to prevent undue risk to the health and safety of the public.

NUREG/CR-4461, Revision 2, Tornado Climatology of the Contiguous United States, dated February 2007 (ML070810400), examines the implications of switching from the Fujita Scale to the Enhanced Fujita Scale on design wind speed estimates for tornadoes.

3.0 TECHNICAL EVALUATION

3.1 Turbine Building Background The Surry turbine building (TB) houses the steam turbines and main generators, as well as other auxiliary equipment and piping systems. The TB contains safety-related equipment mainly in the basement level, and its north side shares a common wall with a portion of the service building which also houses safety-related equipment.

The TB is a steel-framed structure with the lower portions of the exterior walls constructed of masonry and the upper portions constructed of uninsulated metal siding. The structural framing of the TB consists primarily of a steel superstructure (i.e., the turbine building steel superstructure (TBSS)) that supports several concrete slabs at various elevations. The roof is metal decking covered with insulation and membrane roofing. The operating floor is reinforced concrete supported on steel framing at elevation 58 feet 6 inches. The mezzanine level and platforms are steel framed with metal floor grating at elevation 29 feet 6 inches; the basement floor level is at elevation 9 feet 6 inches. The TB is not currently designated as a Seismic Category I or Tornado Criterion T structure.

In the LAR, the licensee proposed to designate the TB as a tornado-resistant structure in the Surry UFSAR under a different methodology and acceptance criteria than those defined for the other Surry tornado-resistant (i.e., Tornado Criterion T) structures, and proposed to use a maximum tornado wind speed of 250 miles per hour (mph) for the TB. It proposes to call the new designation T+.

3.2 Structural Evaluation of the Turbine Building Steel Superstructure 3.2.1 Background of the TBSS Analysis The licensee performed structural analyses of the TBSS under the wind speed of 150 mph and under the tornado wind speed of 250 mph using a three-dimensional (3-D) nonlinear finite element model. The NRC staffs evaluations of the licensees analysis methods and results are summarized in the following sections.

3.2.2 Methods of Structural Analysis for the TBSS 3.2.2.1 Roof Structure Collapse Scenario In Section 3.3.1.1, Roof Structure Collapse Scenario, of the LAR, the licensee performed the original global evaluations of the Surry TBSS with the Surry TB overhead cranes externally anchored to their crane rails within the end bays of the TB. This evaluation concluded that the TBSS roof structure portion of the steel frame above the operating floor at elevation 58 feet 6 inches would collapse during the postulated tornado wind event (i.e., 250 mph wind speed). The licensee considered the impact of the falling roof structure onto the operating deck slab by adding a distributed weight across the operating floor with a dynamic load factor of two (2) applied to the entire weight of the roof structure and both overhead cranes.

The licensee also performed separate evaluations on the local effects of the fallen Surry TB overhead cranes externally anchored to their crane rails within the end bays of the TB. The local effect evaluation concluded that the end bays of the TBSS would sustain severe local damage from falling TB overhead cranes, but progressive collapse would not extend beyond the adjacent interior columns due to the redundancy of the Surry TBSS [structure/structural members?]. Similarly, the licensee considered the same approach by removing the damaged members of the end bays from the computer model and concurrently applying their dead loads, impact live load, and governing wind load to the remaining portions of the Surry TBSS. In addition, the licensee conducted walkdowns to the Surry TB, and found that the TB overhead cranes were not externally anchored as detailed on plant drawings, but instead were free to roll or slide on their crane rails when exposed to the governing east-west tornado winds. Since the TB overhead cranes are free to roll or slide, they cannot exert their full tributary wind reactions to the Surry TBSS that were calculated in the original global and local effects evaluations.

The licensee estimated the force of 97.7 kips (1 kips = 1000 pounds-force) per crane to tributary tornado crane rail reactions, that will sufficiently reduce the tornado wind bending stresses associated with a 250 mph tornado wind speed in the supporting columns of the Surry TBSS to allow the supporting columns to remain stable under tornado wind speeds well above 250 mph.

Therefore, the operating deck of the Surry TBSS under the current unanchored condition of the TB overhead cranes will not experience the dead load and dynamic impact effects from falling cranes, crane rails, and columns that were included in the original global and local effects evaluations.

In its supplements dated December 1, 2022 and March 23, 2023, the licensee stated that its evaluation adjusted the ANSYS computer model of the Surry TBSS by reducing the concrete flexural stiffness by 75 percent and reducing the dynamic impact loading. In its adjusted evaluation, the licensee removed 841 kips weight of the overhead cranes and 678 kips weight of the steel columns because it demonstrated that the cranes and steel columns would not fall in a tornado event. The TB overhead cranes are free to move during a tornado event and so the only load applied to the TBSS at the crane level would be limited to the friction force, and this would not be large enough to fail the supporting steel columns above the operating deck. The new impact live load of 2564 kips, along with a dynamic load factor of two (2), was applied to the operating deck.

The NRC staff reviewed the original Surry TBSS global and local effects evaluations and the licensees supplemental information, as well as the licensees responses to staff requests for additional information (RAIs), and finds removing the weights of the overhead cranes and their supporting steel columns above the operating deck and applying live loading (2564 kip) of the

collapsed roof members with a dynamic load factor of two (2) acceptable because it reflects a realistic roof structure collapse condition, i.e., that there is reasonable assurance that the Surry TB overhead cranes in their current unanchored condition and their supporting steel columns will not fall under the maximum tornado wind speed of 250 mph.

3.2.2.2 Finite Element Modeling Approach In its supplement dated December 1, 2022, the licensee described a 3-D finite element model of the TBSS using an ANSYS finite element computer program. During an NRC staff regulatory audit (ML22313A159), the staff noted that the steel beams and columns are modeled using 2-node, 3-D beam elements, that concrete elements are modeled using 3-node and 4-node shell elements, and that steel and concrete connections are modeled using 3-D spring elements with translational and rotational degrees of freedom. The staff also noted that nonlinear static finite analyses include P-Delta effects based on guidance provided in American Society of Civil Engineers (ASCE)/Structural Engineering Institute (SEI) 7-10, Minimum Design Loads for Buildings and Other Structures.

The licensee proposed to use nonlinear material properties by using a true-stress, true-strain curve for carbon steel based on a method provided in Section VIII, Division 2 of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and by using the design basis American Society for Testing and Materials (ASTM) A36, Standard Specification for Carbon Structural Steel, 2004, material strength and properties. During the NRC staffs audit, the staff reviewed the true-stress, true-strain curve for carbon steel and confirmed that it was developed based on the equations in ASME Boiler and Pressure Vessel Code Section VIII, Division 2, 2010 Edition.

The NRC staff finds the licensees use of nonlinear material properties for carbon steel and the design basis ASTM A36 material strength and properties acceptable because this realistically represents the stress-strain behavior of the ASTM A36 carbon steel comprising the structural framing of the TBSS.

3.2.2.3 Applied Loads In Section 3.3.1.3, Applied Loads, of the LAR and in its supplement dated December 1, 2022, the licensee described two (2) loading conditions (including roof uplifts) for the TBSS.

The first loading condition addressed loads due to the 150 mph wind applied on the entire external TB, whichbased on the Surry current licensing basiswill create a scenario where metal siding will blow off of the TB.

The second loading condition addressed tornado wind loads at 250 mph wind speed applied on exposed structural steel members and equipment. The licensee concluded that the loads due to the 250-mph tornado wind case, with siding removed, are more limiting and bound the loads from the 150-mph wind case with the siding intact.

During the NRC staffs regulatory audit, the staff also reviewed Surry UFSAR Section 15.2.3, and finds that the wind load calculations are acceptable because they are calculated based on the equivalent wind load pressure formula found in Surry UFSAR Section 15.2.3.

3.2.3 TBSS Structural Analysis and Acceptance Criteria In Section 3.3.1.4, Acceptance Criteria, of the LAR and in its supplement dated December 1, 2022, the licensee described the acceptance criteria for the Surry TB mezzanine and operating decks to remain stable for a 250 mph tornado wind speed. The following sections discuss the adequacy of the identified acceptance criteria and whether the structural analyses successfully meet the criteria.

3.2.3.1 Lateral Drift Acceptance Criteria and Building Stability In Section 3.3.1.4 of the LAR, the licensee confirmed that the steel superstructure is considered to remain stable and not collapse if the lateral drift of the operating floor is less than 1 percent of the operating floor height. The NRC staff finds this acceptance criterion acceptable because it is consistent with the allowable drift ratio of 1 percent based on guidance provided in ASCE/SEI 7-10. During the staffs regulatory audit, the NRC staff reviewed the TBSS analysis results and found that the maximum lateral drift ratio of the operating floor slab at elevation 58 feet 6 inches is less than the acceptable drift ratio of 1 percent. Therefore, the NRC staff concludes that the lateral drift of the operating floor is within the allowable drift provided in ASCE/SEI 7-10.

In Section 3.3.2.1, Building Stability, of the LAR, as supplemented by letters dated December 1, 2022, January 25, 2023, and March 23, 2023, the licensee responded to NRC staff RAIs regarding the lateral load resisting system of the TB. Specifically, the turbine pedestals are large, heavily reinforced concrete pedestals that extend from the TB foundation to the operating deck. The turbine pedestals provide significant lateral load support for the TBSS once the existing construction gaps between the pedestals and the operating or mezzanine decks are closed. During the NRC staffs regulatory audit, the staff noted that the finite element model of the TBSS included the turbine pedestals using node-to-node contact elements which incorporate a gap. The turbine pedestals are considered rigid elements and fixed in all degrees of freedom at base during the analysis. This information and the lateral drift information demonstrate that the acceptance criterion is acceptable and that it is successfully met.

3.2.3.2 Steel Members Acceptance Criteria and Stability In Section 3.3.1.4 of the LAR and in its supplement dated December 1, 2022, the licensee described the acceptance criteria for TB steel members to ensure that these steel members are within their ultimate strength design limit.

Structural steel members are evaluated based on their material (i.e., A36 carbon steel) behavior and by comparing their maximum principal strain to the minimum elongation of the carbon steel (per the ASTM A36 standard). The NRC staff evaluated this alternative acceptance criterion and finds it acceptable because the staff noted that the steel members of the TB were originally designed based on American Institute of Steel Construction (AISC), Steel Construction Manual, 6th edition. In that, the allowable stresses and strengths defined in building codes and standards, such as AISC 6th edition, would not be predictive of the ultimate capacity of structures right before collapse. Additionally, the element stress levels of the TBSS structural steel membersat the tornado wind speed of 250 mphare likely to go beyond what is typically allowable by applicable industry building codes and standards such as AISC.

Therefore, the allowable stresses and strengths defined in AISC 6th edition cannot be used for the design of TB steel members at the tornado wind speed of 250 mph. The staff also noted that the proposed acceptance criterion is developed based on material properties and the behavior

of carbon steel per the ASTM A36 standard, and represents realistic material behavior of the steel members of the TB during a tornado event. Additionally, in the LAR, the licensee stated that the alternative acceptance criterion was applied and that the evaluation documented geometric nonlinearities due to large deflection and P-Delta effects and plasticity in the finite element model. The staff finds this acceptable because they are consistent with the AISC/SEI 7-10 recommendations.

In Section 3.3.2.2, Steel Member Stability, of the LAR, the licensee described the maximum combined true tensile stress (i.e., axial plus bending) in steel beams to be 59.6 ksi (one thousand pounds per square inch). That value is equivalent to a true strain of approximately 0.097 inch/inch using the stress-strain curve for A36 carbon steel based on the method provided in Section VIII, Division 2 of the ASME Boiler and Pressure Vessel Code, and the allowable elongation of ASTM A36 is 0.2 inch/inch based on ASTM A36 material strength and properties.

The NRC staff noted that the maximum strain ratio (actual/allowable) for the steel beam is 0.485, therefore, the staff finds this acceptable because the maximum actual strain is less than the allowable strain. In addition, in the LAR, the licensee described the maximum stresses in the TB columns for the east-wind, limiting case which were found to be smaller than their ultimate strength design limit. Finally, the licensees responses to staff RAIs in the supplements dated January 25 and March 23, 2023, stated that the modified steel member stresses are bounded by those of the original analyses and that all of the steel member stress changes are minor.

Therefore, the staff concludes that both steel beams and columns of the TBSS are acceptable to the criterion of ultimate strength design limits of ASCI/SEI 7-10.

3.2.3.3 Composite Reinforced Concrete Acceptance Criteria and Concrete Evaluation In Section 3.3.1.4 of the LAR, the licensee described the acceptance criteria that composite reinforced concrete stresses are limited to the concrete compressive strength, and that their shear stresses are also evaluated. In its supplement dated January 25, 2023, the licensee stated the acceptance criterion for reinforcing steel is that reinforcing steel stresses are within the allowable stress limits of American Concrete Institute (ACI) 318-71, Building Code Requirements for Reinforced Concrete, 1975. Therefore, the acceptance criteria for the composite reinforced concrete and reinforcing steel are acceptable, as they meet the criteria of ACI 318-71.

In its supplements dated January 25 and March 23, 2023, the licensee responded to NRC staff RAIs and stated that the licensee considered the factor of cracked concrete in the Surry ANSYS computer model by reducing flexural stiffness by 75 percent, which is based on ACI 318-71. The licensee also stated that the dynamic impacting loading was also reduced because the TB overhead cranes and supporting columns will not fall until tornado wind speed on the TB exceeds the maximum tornado wind speed of 250 mph. The licensee also evaluated reinforcing rebar stresses in the concrete slabs of the operating and mezzanine decks of the Surry TBSS and re-evaluated the impact of concrete flexural stiffness reduction and dynamic impacting loading reduction on the concrete analyses.

During the NRC staffs review of the licensees RAI responses, the staff found that ACI 318-71, Section 8.5.3.1, related to stiffness, provides limited guidance on the computation of relative stiffness of reinforced concrete members based on the transformed cracked sections. However, ACI 318-99, Building Code Requirements for Structural Concrete and Commentary, 1999 edition and the subsequent ACI 318 codes permit the flexural stiffness reduction of cracked concrete by 75 percent. Therefore, the reduction of the concrete flexural stiffness by 75 percent

in the licensees ANSYS computer model of the Surry TBSS is acceptable. The staff also finds all the reinforcing steel in the concrete slabs of the operating and mezzanine decks of the Surry TBSS acceptable because all reinforcing steel stresses, compressive and tensile, are within the allowable stress limits of ACI 318-71. The staff further reviewed the modified concrete analysis results and finds that the equivalent membrane plus bending stress in concrete elements for the east-wind, limiting case is below the compressive strength with a stress ratio of 0.38, and the maximum concrete shear stress is below the shear strength with a shear stress ratio of 0.61.

Therefore, they are acceptable.

3.2.3.4 Connections Acceptance Criteria and Joint Stress Evaluation In Section 3.3.1.4 of the LAR, the licensee described that the acceptance criteria for bolt evaluations are based on AISC 6th and 7th editions, and that the acceptance criteria of coped members connections evaluations are based on the 15th edition of the AISC. These are recognized industry consensus standards; therefore, they are acceptable.

In Section 3.3.2.4, Joint Stress Evaluation, of the LAR, the license discussed the evaluation of connections based on the guidance provided in AISC 15th edition and the evaluations of bolt tensile and shear strengths as well as their interaction based on the guidance provided in AISC 6th and 7th editions. The licensee also stated that the maximum interaction ratio from the coped section, bolt shear, and bolt tension analysis are 0.96, 0.78, and 0.58, respectively, while considering the effect of the limiting wind load from the east wind. In addition, in its supplements dated January 25 and March 23, 2023, the licensee stated that the modified joint stress ratios are bounded by those of the original analyses and that all of the joint stress ratio changes are minor. Therefore, the NRC staff concludes that all joints of steel connections are acceptable.

3.2.4 TBSS Structural Evaluation Regulatory Summary Based on the above, the NRC staff finds that the operating and mezzanine decks will remain stable under the maximum 250 mph tornado wind speed, because analysis results of the Surry TBSS demonstrated that all the acceptance criteria are acceptable based on industry standards, and that all those criteria have been documented by the licensee and have been met. Further, based on these findings, the staff concludes that there is reasonable assurance that the requirements of GDC 2 and GDC 4 will continue to be met. Therefore, the staff finds the proposed change acceptable.

3.3 Technical Evaluation for Maximum Tornado Wind Speed In the LAR, the licensee stated that the proposed change requests approval to designate the turbine buildings as tornado-resistant structures in the Surry UFSAR under a different methodology and acceptance criteria than those defined for the other tornado-resistant structures in the UFSAR. Specifically, the UFSAR would be revised to change the existing Tornado Criterion N/A classification for the turbine building in UFSAR Table 15.2-1, Structures, Systems, and Components Designed for Seismic and Tornado Criteria, to a new Tornado Criterion T+ classification. The proposed methodology and acceptance criteria include the use of a maximum tornado wind speed of 250 mph. The licensee stated that a maximum tornado wind speed of 250 mph will preserve the design margin and assure acceptable levels of protection for the health and safety of the public.

Regulatory Guide 1.76, Revision 1, provides licensees with guidance that the NRC staff considers acceptable for use in selecting the design-basis tornado and design-basis tornado-

generated missiles that a nuclear power plant should be designed to withstand to prevent undue risk to the health and safety of the public. This guidance is based on NUREG/CR-4461, Revision 2, which examines the implications of switching from the Fujita Scale to the Enhanced Fujita Scale on design wind speed estimates for tornadoes. Regulatory Guide 1.76, Table 1, Design-Basis Tornado Characteristics, specifies a maximum wind speed of 200 mph for region II, which is where Surry is located. From NUREG/CR-4461, Table 6-1, Tornado Wind Speed Estimates for United States Nuclear Power Plant Sites, a maximum wind speed of 200 mph corresponds to a frequency of approximately 1E-7 per year for Surry.

The NRC staff finds that a maximum tornado wind speed of 250 mph is acceptable because it is greater than the maximum wind speed of 200 mph for Surry. In Regulatory Guide 1.76, the frequency of occurrence of tornados with wind speeds greater than 250 mph is less than 1E-7 per year based on the information in NUREG/CR-4461. Based on these findings, the staff concludes that there is reasonable assurance that the requirements of GDC 2 will continue to be met. Therefore, the staff finds the proposed change acceptable.

3.4 Technical Evaluation of Risk Insights This LAR is not a risk-informed application because the licensee did not provide a quantitative risk assessment and the NRC staff did not review the licensees probabilistic risk assessment models to determine their technical acceptability as a basis to support the LAR.

The NRC staff determined that special circumstances, as discussed in NUREG-0800, Section 19.2, which would have necessitated additional risk information to be provided, did not exist for the proposed change.

In its supplement dated December 1, 2022, the licensee provided a qualitative risk assessment and summarized the key risk insights associated with the LAR. The NRC staff considered the licensees risk insights in the deterministic review of the LAR.

In the qualitative risk assessment, the licensee stated that a major tornado (i.e., a tornado with wind speeds above the proposed maximum tornado wind speed of 250 mph) is likely to cause a plant transient and a loss of offsite power (LOOP). Based on these two initiating events, the licensee identified six condensate system valves (three for each unit) and four main feedwater pumps (two for each unit) that are considered by this evaluation.

The six condensate system valves were identified for LOOP events because they are in the flow path used to provide extended auxiliary feedwater (AFW) inventory to the emergency condensate storage tank (ECST) after the initial eight hours of AFW inventory in the ECST is depleted. The licensee stated that the operator actions to refill the ECST from the condensate storage tank (CST) occur by manipulating two of these valves (1-CN-150 for Unit No. 1 or 2-CN-150 for Unit No. 2) and these actions are proceduralized. The licensee also explained that the performance of this procedure would not be impacted by the tornado postulated in the LAR because operators would not need to manipulate these valves for eight hours, which provides sufficient time for operators to find an alternative path to these valves if the primary path was obstructed. Finally, the licensee stated that the plant has additional sources of long-term AFW available from the firewater system and the tornado missile-protected emergency condensate makeup tanks if the CST is impacted by tornado missiles.

The four main feedwater pumps were identified for plant transients where the control rods fail to insert, leading to an anticipated transient without scram (ATWS) event that requires main

feedwater for secondary heat removal. The licensee stated that the tornado postulated in the LAR would likely cause a LOOP, which would render the main feedwater pumps inoperable and unavailable for use if an ATWS occurs. The NRC staffs review determined that the frequency of the tornado postulated in the LAR leading to a LOOP and subsequent ATWS does not impact this application.

In the qualitative risk assessment, the licensee stated that there are circulating water system and service water system valves and piping in the turbine building that are risk significant for the LAR because they are potential sources of flooding in the turbine building basement that could impact equipment in the emergency switchgear room. The licensee stated that these circulating water system and service water system valves and piping would not be adversely impacted by the postulated roof collapse scenario because they are protected by the structure above them or can be successfully isolated before flood propagation.

The NRC staff reviewed the licensees qualitative risk assessment and summary of risk insights.

Based on its review, the staff finds that (1) the licensee appropriately identified the dominant risk scenarios for the proposed change, (2) the risk from the dominant scenarios is either appropriately managed by the licensees existing procedures or does not impact this application, and (3) the postulated roof collapse scenario would not damage risk significant safe shutdown equipment in the turbine building basement. Therefore, the staff concludes that the licensees risk insights support the proposed change. Based on these findings, the staff concludes that there is reasonable assurance that the requirements of GDC 2 and GDC 4 will continue to be met. Therefore, the staff finds the proposed change acceptable.

3.4 Technical Evaluation of Tornado Missile Analysis The licensee stated that the combined effect of tornado missiles and wind loads will not lead to global collapse of the turbine building or adversely impact the safe shutdown and unisolable water source components in the turbine building basement and the adjacent service building.

The licensee provided a justification based, in part, on the presence of physical protection against the local effects (i.e., penetration) of tornado missiles for some safe shutdown and unisolable water source components. The licensee provided a discussion of its evaluation of tornado missile impacts for the remaining safe shutdown and unisolable water source components.

The NRC staffs review finds that the decoupling of tornado missile effects from tornado wind loads is acceptable for this application because the licensees separate analysis sufficiently addresses the impact of tornado missiles for this application. Based on these findings, the staff concludes that there is reasonable assurance that the requirements of GDC 2 and GDC 4 will continue to be met. Therefore, the staff finds the proposed change acceptable.

4.0 STATE CONSULTATION

In accordance with the Commissions regulations, the Commonwealth of Virginia official was notified of the proposed issuance of the amendments on April 8, 2023. On April 10, 2023, the official confirmed that the Commonwealth of Virginia had no comments (ML23107A221).

5.0 ENVIRONMENTAL CONSIDERATION

The amendments change requirements with respect to installation or use of facility components located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined

that the amendments involve no significant increase in the amounts and no significant change in the types of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration published in the Federal Register on July 15, 2022 (87 FR 42510), and there has been no public comment on such finding. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

6.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) there is reasonable assurance that such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributors: George Wang Steven Alferink De Wu Jason White Date: April 25, 2023

ML23100A065 OFFICE DORL/LPL2-1/PM DORL/LPL2-1/LA DEX/ESEB/BC DRA/APLC/BC NAME JKlos KGoldstein ITseng SVasavada DATE 04/06/2023 04/11/2023 03/30/2023 01/30/2023 OFFICE DEX/EXHB/BC OGC DORL/LPL2-1/BC DORL/LPL2-1/PM NAME BHayes JWachutka MMarkley (EMiller For) JKlos DATE 01/19/2023 04/18/23 04/25/2023 04/25/2023