ML24215A007
| ML24215A007 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
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| References | |
| LO-169995 | |
| Download: ML24215A007 (1) | |
Text
Response to SDAA Audit Question Question Number: A-3.3-7 Receipt Date: 11/20/2023 Question:
Related to Audit Issues A-3.3-5 and A-3.3-6:
FSAR Section 3.3 markups in the NuScale response to audit item A-3.3-5 state that 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. FSAR Section 3.3 markups also state that the severe wind loading condition uses the parameters in Section 3.3.1.1 and is consistent with SC-II structures. COL item 3.3-1 considers II/I issue to confirm that nearby structures exposed to severe and extreme (tornado and hurricane) wind loads will not collapse and adversely affect the Seismic Category I portions of the Reactor Building or of the Control Building. Therefore, wind loads for SC-II buildings are not in the scope of the NRC staffs review per SRP.
In addition, FSAR Section 3.3.1.1 markups state that the wind speed is increased by an importance factor of 1.15 based on ASCE 7-05 for SC-1 structures and a factor of 1.0 based on reference 3.3-2 (i.e. ASCE/SEI 7-16) 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). It appears that the applicant uses an importance factor of 1.0 based on ASCE/SE 7-16 for the above ground RW-IIa portion of RWB. Table 2 in RG 1.143 indicates wind category III for RW-IIa. Table 6-1 in ASCE/SE 7-05 indicates that the wind importance factor is 1.15 for category III.
SRP acceptance criteria in SRPs 3.3.1 and 3.3.2 also indicates that the wind importance factor is 1.15.
Equation 6-15 in the NuScale SDAA Section 3.3.1.3 is taken from ASCE/SE 7-05 to determine velocity pressure. The importance factor taken from ASCE/SE 7-16 is not acceptable because:
- 1) ASCE/SE 7-16 uses different methodology to calculate wind loads; and 2) mixed use of different ASCE editions for importance factor is not allowed. The above ground RW-IIa is NuScale Nonproprietary NuScale Nonproprietary
subject to severe and extreme wind loads. Table 2 in RG 1.143 indicates the wind category III for RW-IIa. Table 6-1 in ASCE/SE 7-05 indicates that the wind importance factor is 1.15 for category III. SRP acceptance criteria in SRPs 3.3.1 and 3.3.2 also indicates that the wind importance factor is 1.15.
- 1. Clarify and correct the importance factor and its ASCE code edition used for the RWB, and provide justification for the importance factor used for the above ground RW-IIa portion of the RWB if the importance factor is not 1.15.
- 2. Consider deletion of SC-II primary load resisting and severe wind loading condition uses the parameters in Section 3.3.1.1 and is consistent with SC-II structures described in Sections 3.3 and 3.3.1.1 markups.
- 3. Update FSAR accordingly.
Response
1:The RW-IIa portion of the RWB is analyzed to 190 mph wind speed. This speed is based on ASCE 7-16 and the pressure is applied to the SC-III structure using ASCE 7-16 methodology (also applied to the RW-IIa above grade portions). The reactions from the SC-III structure are applied to the RW-IIa structure through point load reactions at the column base locations.
Based on the Regulatory Guide 1.143 Table 2, the RW-IIa should be designed to ASCE 7-95 category III structure (wind speed 150 mph and an importance factor of 1.15).
Based on SRP 3.3.1 which identifies ASCE 7-05 which would render the same wind speed and importance factor as ASCE 7-95.
Therefore, the criteria described in both SRP 3.3.1 and RG 1.143 would render a maximum wind speed of 150 mph and an importance factor of 1.15. NuScale acknowledges that requirement and has imposed a more rigorous wind pressure on the building than that described in ASCE 7-95 and ASCE 7-05.
NuScale Nonproprietary NuScale Nonproprietary
NuScales Application of wind pressure:
The operating wind speed used is 190 mph, which is consistent with ASCE 7-16 for enveloping the majority of the continental US (excluding minor regions such as Dade County, Florida). Wind speeds from ASCE 7-16 are determined based on the chapter 16 wind maps specific to Risk Category III buildings (keeping the building classification consistent with previous ASCE codes and regulatory guidance). ASCE 7-16 does not utilize an importance factor; therefore, no importance factor was used.
When determining the wind pressure with both code revisions, ASCE 7-16 yields a higher wind pressure despite not applying an importance factor. Since ASCE 7-16 yields a higher wind pressure, the code creates lower strength factors in chapter 2 for wind loading. Since ASCE 7-05 yields a lower wind pressure, the code creates a higher strength factor in chapter 2 for wind loading compared to that of ASCE 7-16.
NuScale conservatively uses both the higher critical wind pressure and the higher load factors by applying ASCE 7-16 methodology for loading (higher wind pressure) while designing the RW-IIa structure per ACI 349-13. Since ACI 349-13 load combinations (Section 9.2.1 of ACI 318-08) are compatible with ASCE 7-05 load combinations (Section 2.3.2), the final results conservatively bound ASCE 7-05. Therefore the methodology used by NuScale still satisfies the requirements of ASCE 7-05 despite no importance factor.
Wind pressure:
ASCE 7-05 wind pressure (Eq. 6-15):
qz = 0.00256 x Kz x Kzt x Kd x V2 05 x I I = importance factor = 1.15 V05 = 150 mph ASCE 7-16 wind pressure (Eq. 26.10-1):
qz = 0.00256 x Kz x Kzt x Kd x V2 16 x Ke Ke = elevation factor NuScale Nonproprietary NuScale Nonproprietary
V16 = 190 mph Kz, Kzt, Kd, are the same in both wind pressure equations.
Solving with the assumption Kz = Kzt = Kd = 1, ASCE 7-05 wind pressure:
qz = 0.00256 x 1502 x 1.15 = 66.24 lb/ft2 ASCE 7-16 wind pressure:
qz = 0.00256 x 1902 x 1 = 92.42 lb/ft2 )
ASCE 7-16 produces the higher wind pressure.
Load combinations:
ASCE 7-05 load combinations (Section 2.3.2):
- 1. 1.4 (D + F)
- 2. 1.4 (D + F + T) + 1.6 (L + H) + 0.5 (Lr or S or R)
- 3. 1.2 D + 1.6 (Lr or S or R) + (L or 0.8 W)
- 4. 1.2 D + 1.6 W + L + 0.5 (Lr or S or R)
- 5. 1.2 D+ 1.0 E + L + 0.2 S
- 6. 0.9 D + 1.6 W + 1.6 H
- 7. 0.9 D + 1.0 E + 1.6 H ASCE 7-16 load combinations (Section 2.3.1):
- 1. 1.4 D
- 2. 1.2 D + 1.6 L + 0.5 (Lr or S or R)
- 3. 1.2 D + 1.6 (Lr or S or R) + (L or 0.5 W)
- 4. 1.2 D + 1.0 W + L + 0.5 (Lr or S or R)
- 5. 0.9 D + 1.0 W NuScale Nonproprietary NuScale Nonproprietary
The SDAA has been updated to clarify that the design requirement of both SRP 3.3.1 and RG 1.143 is 150 mph with an importance factor of 1.15 and that NuScale has applied the loads in a more rigorous approach which includes 190 mph wind speed, derived from ASCE 7-16, as it results in a more conservative approach with a higher wind pressure being incorporated into the analysis.
- 2. Updated 3.3.1.1 markup has been included to incorporate the staff requested deletion of reference to SC-II is attached to this question.
- 3. SDAA Section 3.3.1.1 FSAR updates have been attached to this response.
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, Audit Question A-3.3-7 Severe wind, tornado, and hurricane loads impact Seismic Category I (SC-I) and 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, Audit Question A-3.3-7 The RXB and CRB are 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, Audit Question A-3.3-7 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, Audit Question A-3.3-7 The RW-IIa portions of the RWB are analyzed for reactions from the SC-III structure from severe and extreme wind as well as the above grade exterior RW-IIa wall. The severe wind loading condition uses the parameters in Section 3.3.1.1. 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 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
NuScale Final Safety Analysis Report Wind and Tornado Loadings NuScale US460 SDAA 3.3-2 Draft Revision 2 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, Audit Question A-3.3-7 The design-basis operating wind speed is a 3-second gust at 33 feet above ground for exposure category C. For severe wind analysis on SC-I structures, 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. For RW-IIa structures, Regulatory Guide 1.143 table 2 states the RW-IIa structures should be evaluated to ASCE 7-95, category III structure. ASCE 7-95 along with these parameters would render a wind speed of 150 mph and an importance factor or 1.15. This requirement is incorporated into the analysis by applying the more conservative wind loading by using a wind speed of 190 mph and pressure from ASCE 7-16.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 Pressure drop..................... 1.6 psi Rate of pressure drop............... 0.9 psi/sec
NuScale Final Safety Analysis Report Wind and Tornado Loadings NuScale US460 SDAA 3.3-3 Draft Revision 2 For tornadoes, Vw is the resultant of the maximum rotational speed and the translational speed.
The wind speed for the design-basis hurricane is the highest wind speed postulated in Regulatory Position 1 of RG 1.221, which occurs in Figure 2 of the RG:
Maximum hurricane wind speed....... 290 mph Section 3.5 describes hurricane and tornado wind-generated missiles.
3.3.1.3 Determination of Wind Forces The maximum wind velocities for severe winds and for tornado and hurricane winds are converted into pressure-induced forces (qz) based on the applicable maximum wind speed (Vw) and applied to structures.
Wind forces are determined in conformance with Reference 3.3-1, Equation 6-15, as follows:
Audit Question A-3.3-7 qz = 0.00256 Kz Kzt Kd Vw 2 I (lb/ft2) ASCE 7-05 Audit Question A-3.3-7 qz = 0.00256 Kz Kzt Kd Ke Vw 2 ASCE 7-16
- where, Kz =
velocity pressure exposure coefficient evaluated at height z, as defined in Reference 3.3-1, Table 6-3, but not less than 0.87, Height z is the building height.
For tornadoes, wind speed is not assumed to vary with height.
Kzt =
topographic factor equal to 1.0, Kd =
wind directionality factor equal to 1.0, Audit Question A-3.3-7 Ke =
ground elevation factor equal to 1.0, Vw =
maximum wind speed, and I
=
importance factor equal to 1.15 for the Reactor Building, Control Building, and Radioactive Waste Building.
NuScale Final Safety Analysis Report Wind and Tornado Loadings NuScale US460 SDAA 3.3-4 Draft Revision 2 Audit Question A-3.3-7 Design wind pressures and extreme wind pressures on the Reactor Building, Control Building, and RW-IIa portion of the Radioactive Waste Building are determined in conformance with Reference 3.3-1, Equation 6-17 and Reference 3.3-2, Equation 27.3-1:
p = qGCp - qi (GCpi) (lb/ft2)
- where, G
=
gust factor equal to 0.85, Cp =
external pressure coefficient equal to 1.0, GCpi = internal pressure coefficient equal to 0.18 for severe and hurricane winds, q
=
velocity pressure, and qi = internal velocity pressure.
3.3.1.4 Combination of Forces After tornado wind effects, Ww, atmospheric pressure change effects, Wp, and missile impact effects, Wm, are determined, the combined effect is determined.
The method for combining these effects and establishing the total tornado load on a structure is:
Wt = Wp Wt = Ww + 0.5 Wp + Wm Where:
Wt = total tornado load Ww = load from wind effect Wp = load from atmospheric pressure change effect, which is the pressure drop from Section 3.3.1.2.
Wm = load from missile impact effect The most adverse of the above combinations is used.
After hurricane wind effects, WW, and missile impact effects, Wm, are determined, the combined effect is determined. The method of combining these effects and establishing the total hurricane load on a structure is: