ML24215A006

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LLC, Response to Sdaa Audit Question Number A-3.3-4
ML24215A006
Person / Time
Site: 05200050
Issue date: 08/02/2024
From:
NuScale
To:
Office of Nuclear Reactor Regulation
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Response to SDAA Audit Question Question Number: A-3.3-4 Receipt Date: 06/19/2023 Question:

Section 3.3 states that the RW-IIa portions of the RWB have been evaluated for severe and extreme wind loads using the methodology in Section 3.3.1.3 and can withstand severe and extreme winds. The staff noted in Section 3.3 of NuScale DC that the RWB (both Category II and RW-IIa) was evaluated for severe and extreme wind loads. The staff also noted in Table 3.2-1 on page 3.2-7 that RW-IIa portions of the RWB is a below-grade structure, and Category III portion of the RWB is a above-grade structure. Section 3.3.1.1 states that design parameters for severe wind are based on ASCE/SEI 7-05. However, Table 2 of RG 1.143 lists ASCE 7-95 for wind loads in RW-IIa portions of the RWB.

a.

Clarify whether Category III portions of the RWB will be evaluated for the same severe and extreme wind loads to avoid collapse and adversely affect the RW-IIa portions of the RWB.

b.

Explain how wind loads can be applied to the below-grade RW-IIa portions of the RWB.

c.

Address the inconsistency of ASCE code between Section 3.3.1.1 and RG 1.143.

Response

Initial Response:

A. The Seismic Category III portion of the Radioactive Waste Building (RWB) is evaluated for severe and extreme winds to avoid collapse and adverse effects on the RW-IIa portion of the RWB. The responses to audit questions A-3.3-2 and A-3.3-3 provide more detail and changes to SDA Section 3.3.

B. The reactions from the Seismic Category III structure are transmitted into the below-grade RW-IIa structure.

C. SDAA Section 3.3.1.1 is only applicable to RXB and CRB. RWB was erroneously included in this section and is documented in a Condition Report (CR-147594), which NuScale Nonproprietary NuScale Nonproprietary

tracks the correction and evaluation of the wind design parameters for the RW-IIa portion of the RWB.The SC-III portion of the RWB is evaluated for severe wind using ASCE 7-16 and a wind speed of 122 mph. For the applied extreme wind loading on the SC-III superstructure, wind speed is taken from Reg Guide 1.221 (290 mph) as it is more conservative than what is provided in Reg Guide 1.76. Then, the three-fifths criteria from Reg Guide 1.143 Table 2 is implemented to determine the design speed and the external pressure drop applied to the superstructure. The reaction loads from the SC-III structure consider the severe and extreme wind loads, which are then applied to the below-grade RW-IIa structure.

Updated Response:

The updated response contains the markups to Section 3.3. FSAR markups were changed from the original submitted response following the Section 3.3 NRC clarification call on 8/8/2023 and the receipt of Audit Question A-3.3-5.

Markups of the affected changes, as described in the response, are provided below:

NuScale Nonproprietary NuScale Nonproprietary

NuScale Final Safety Analysis Report Wind and Tornado Loadings NuScale US460 SDAA 3.3-1 Draft Revision 2 3.3 Wind and Tornado Loadings Audit Question A-3.3-2 Severe wind, tornado, and hurricane loads impact Seismic Category I (SC-I), Seismic Category II (SC-II) primary load resisting, and Seismic Category RW-IIa structures. The Reactor Building (RXB), Control Building (CRB), and Radioactive Waste Building (RWB) are enclosed structures impacted by severe wind, tornado, and hurricane loadings.The Seismic Category I portions of the Reactor Building (RXB) and Control Building (CRB), as well as the RW-IIa portion of the Radioactive Waste Building (RWB), are evaluated for wind, tornado, and hurricane loads. The three buildings are enclosed structures. The design criteria for evaluating local damage to the Reactor Building and Control Building from tornado and wind is consistent with Regulatory Guide (RG) 1.76, Design-Basis Tornado and Tornado Missiles for Nuclear Power Plants and RG 1.221, Design-Basis Hurricane and Hurricane Missiles for Nuclear Power Plants.

Audit Question A-3.3-2 The RXB is composed of SC-I and SC-II portions. Severe and extreme wind loading is applied to exterior portions of the RXB. Wind loads from severe wind pressure are determined according to Section 3.3.1.1. Wind loads from extreme wind pressure are determined according to Section 3.3.1.2. The design evaluates local and global damage to the RXB consistent with Regulatory Guide (RG) 1.76, Design-Basis Tornado and Tornado Missiles for Nuclear Power Plants and RG 1.221, Design-Basis Hurricane and Hurricane Missiles for Nuclear Power Plants.

Audit Question A-3.3-3 SC-I and SC-II portions of the CRB are exposed to wind loading. The SC-I portion of the CRB is designed and analyzed for the same wind loads as the SC-I portions of the RXB.

The SC-II portion of the CRB is analyzed for the same wind pressures as the SC-I portions with an importance factor of 1.0 but is not analyzed for tornado and hurricane missiles impacts.The RWB is Seismic Category III above grade, with some limited sections categorized as RW-IIa (High Hazard). The RW-IIa portion is analyzed for tornado missile protection per RG 1.143, Design Guidance For Radioactive Waste Management Systems, Structures, and Components Installed in Light-Water-Cooled Nuclear Power Plants.

Audit Question A-3.3.1.1-1 The SC RW-IIa portion of the RWB is analyzed for reactions from the SC-III superstructure from severe and extreme wind. The severe wind loading condition uses the parameters in Section 3.3.1.1 and is consistent with SC-II structures. The extreme wind loading is based on the three-fifths factor from Table 2 of RG 1.143 applied to the maximum tornado and hurricane parameters provided in Section 3.3.1.2, which are more conservative than RG 1.76.The RW-IIa portion of the RWB is designed using the same wind, tornado, and hurricane loads as specified for the Seismic Category I structures.

This approach is consistent with the wind load specified in Table 2 of RG 1.143. The ASCE/SEI 7-05 Standard (Reference 3.3-1) is used for wind loads in this design. Tornado missiles from RG 1.76 are also used.

COL Item 3.3-1:

An applicant that references the NuScale Power Plant US460 standard design will confirm that nearby structures exposed to severe and extreme (tornado

NuScale Final Safety Analysis Report Wind and Tornado Loadings NuScale US460 SDAA 3.3-2 Draft Revision 2 and hurricane) wind loads will not collapse and adversely affect the Seismic Category I portions of the Reactor Building or of the Control Building.

The design complies with General Design Criteria 2 and 4, in that structures, systems, and components are designed to withstand the most severe effects of natural phenomena wind, hurricane, and tornadoes without loss of capability to perform their safety functions. This conformance is achieved by establishing design parameters that are representative of a reasonable number of potential plant site locations in the United States. Design parameters for severe wind loads are provided in Section 3.3.1.1 and design parameters for extreme wind loads are provided in Section 3.3.1.2.

Audit Question A-3.3-5 The RW-IIa portions of the RWB have been evaluated for severe and extreme wind loads using the methodology in Section 3.3.1.3 and can withstand severe and extreme winds.

3.3.1 Wind Loadings 3.3.1.1 Design Parameters for Severe Wind Audit Question A-3.3-5 The design-basis operating wind speed is a 3-second gust at 33 feet above ground for exposure category C. For severe wind analysis, the operating wind speed, Vw, is 190 mph based on ASCE 7-16 (Reference 3.3-2). The wind speed is increased by an importance factor of 1.15 based on ASCE 7-05 (Reference 3.3-1) for SC-I structures and a factor of 1.0 based on Reference 3.3-2 for other structures. These design parameters apply when evaluating severe or extreme wind on enclosed structures categorized as SC-I (portions of RXB and CRB), SC-II primary load resisting (portions of CRB), and SC RW-IIa (portions of RWB). The operating wind speed (Vw) is 190 mph. The wind speed is increased by an importance factor of 1.15 for the design of the Reactor Building, Control Building, and Radioactive Waste Building. These design parameters are based upon Reference 3.3-1.

3.3.1.2 Design Parameters for Extreme Wind (Tornado and Hurricane)

Tornado wind loads include loads caused by the tornado wind pressure, tornado atmospheric pressure change effect, and tornado-generated missile impact.

Hurricane wind loads include loads due to the hurricane wind pressure and hurricane-generated missiles.

Audit Question A-3.3-5 The parameters for the design-basis tornado listed below are more conservative than theconsistent with tornado parameters postulated in RG 1.76:

Maximum tornado wind speed........ 270 mph Translational speed................ 55 mph Maximum rotational speed........... 215 mph Radius of maximum rotational speed... 150 ft

NuScale Final Safety Analysis Report Wind and Tornado Loadings NuScale US460 SDAA 3.3-5 Draft Revision 2 Wm = load from missile impact effect.

3.3.2 References 3.3-1 American Society of Civil Engineers/Structural Engineering Institute, Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-05, Reston, VA.

Audit Question A-3.3.1.1-1 3.3-2 American Society of Civil Engineers (ASCE), Minimum Design Loads and Associated Criteria for Buildings and Other Structures, ASCE 7-16.

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