ML23054A241

NRR E-mail Capture - Formal Issuance of RAIs for Surry Turbine Building Tornado Reclassification

ML23054A241
Person / Time
Site:	Surry
Issue date:	02/23/2023
From:	Ed Miller Plant Licensing Branch II
To:	Geoffrey Miller Virginia Electric & Power Co (VEPCO)
References
Download: ML23054A241 (4)

Text

From: Ed Miller Sent: Thursday, February 23, 2023 12:32 PM To: Gary D Miller

Subject:

Formal Issuance of RAIs for Surry TB Tornado Reclassification

Gary, 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 (NRC), 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 NRC staff has reviewed the information submitted to-date and needs additional information to complete its review and approval of the licensees submittal. These requests for additional (RAIs) are released formally with a 30-day response period (March 24, 2023) requested.

Regulatory Basis:

The U.S. Nuclear Regulatory Commission (NRC) 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 GDC 2 and GDC 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 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.

SPS UFSAR Appendix 14B, 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.

Follow-up RAI 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. RAI 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 licensees response to RAI 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 NRC 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 licensees response to RAI 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 ACI 318. The NRC staff reviewed the ACI 318-71 code and did not find the provision for reducing flexural stiffness by 75% for cracked concrete.

The NRC 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 NRC 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 RAI 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 ACI 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%.

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.

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.

4. Evaluate the impact of the ANSYS 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.

5. Clarify any conforming changes in UFSAR Table 15.2-1 that may be needed to ensure consistency with the TB evaluation.

Ed Miller (301) 415-2481

Hearing Identifier: NRR_DRMA Email Number: 1957 Mail Envelope Properties (SA1PR09MB748756B5E91567ADE621DFE9E9AB9)

Subject:

Formal Issuance of RAIs for Surry TB Tornado Reclassification Sent Date: 2/23/2023 12:32:10 PM Received Date: 2/23/2023 12:32:00 PM From: Ed Miller Created By: Ed.Miller@nrc.gov Recipients:

"Gary D Miller" <gary.d.miller@dominionenergy.com>

Tracking Status: None Post Office: SA1PR09MB7487.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 7834 2/23/2023 12:32:00 PM Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date: