ML24215A020
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Response to SDAA Audit Question Question Number: A-3.5.3-4 Receipt Date: 08/28/2023 Question:
Section 3.5.3.1.3 states equations based on Bruhl are used to calculate the required steel plate.
The SRP 3.5.3 states that the equations presented in Ballistic Perforation Dynamics are acceptable to determine the residual velocity when the first barrier of a multi-element missile barrier is steel. It appears that the applicant uses alternate equations.
- a. Provide Bruhl equations and define all terms used in the equations.
- b. Provide the justification why Bruhl equations are acceptable in the design of composite SC walls to prevent perforation from missile impact.
Response
A. The Bruhl equations used for analyzing the steel plates were presented to and approved by the NRC in TR-0920-71621-P, Building Design and Analysis Methodology for Safety-Related Structures. A pointer to the topical report has been included in Section 3.5.3.1.3 of the SDAA.
B. The methodology implementing the use of Bruhl equations applied to composite SC walls were presented and approved in TR-0920-71621-P.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Missile Protection NuScale US460 SDAA 3.5-12 Draft Revision 2 impact loadings. The barrier design discussed below addresses internal and external missiles.
3.5.3.1 Local Damage Prediction The prediction of local damage in the impact area depends on the basic material of construction of the structure or barrier (i.e., concrete, steel, or composite). The analysis approach for each basic type of material is presented separately. Unless stated otherwise, it is assumed the missile impacts normal to the plane of the wall on a minimum impact area.
3.5.3.1.1 Concrete Barriers Concrete missile barriers are evaluated for effects of missile impact resulting in penetration, perforation, and scabbing of the concrete using the Modified NDRC formulas discussed in Reference 3.5-3 as described in the following paragraphs. Concrete barrier thicknesses calculated using the equations in this section for perforation and scabbing are increased by 20 percent per F7.2.1 and F7.2.2 of ACI 349 (Reference 3.5-4).
Audit Question A-3.5.3-1 Concrete thicknesses to preclude perforationpenetration, perforation, spalling, or scabbing from the design-basis hurricane and tornado pipe and sphere missiles are calculated for the Reactor Building, and Control Building external walls and roof, RW-IIa interior barriers, and 100 foot elevation slab of the Radioactive Waste Building, and RW-IIa portion of the Radioactive Waste Building external walls and roof using the equations below. Interior walls within the RWB identified as missile barriers to protect RW-IIa SSC have been evaluated and provide protection against extreme wind missiles.
Audit Question A-3.5.3-1 Additional design characteristics of the RXB and the CRB, including concrete wall thickness, are in Appendix 3B.2.
3.5.3.1.1.1 Penetration and Spalling Equations The depth of missile penetration, x, is calculated using the following formulas:
- where, x = penetration depth, in.,
x 4KNWd V
1000d
1.8 0.5 for x d---
2.0
=
x KNW V
1000d
1.8 d for x d---
2.0
+
=
NuScale Final Safety Analysis Report Missile Protection NuScale US460 SDAA 3.5-14 Draft Revision 2 minimum steel thickness for a barrier to prevent perforation of the missile if the results are comparable to the Stanford Formula results or if they are validated by penetration testing.
Audit Question A-3.5.3-3 In using the Stanford and BRL formulae for missile perforation, it is assumed the missile impacts normal to the plane of the wall on a minimum impact area and, in the case of reinforced concrete, does not strike the reinforcing. Due to the conservative nature of these assumptions, the minimum thickness required for missile shields is taken as the thickness just perforated. Steel barrier thickness determined by the BRL formula is increased by 25 percent, per Reference 3.5-5. There are no steel missile barriers used in the design.
3.5.3.1.3 Steel-Plate Composite Walls Audit Question A-3.5.3-4 The required steel plate thickness to prevent perforation of SC walls from missile impact is calculated using equations based on Bruhl (Reference 3.5-7). The Bruhl equations used for analyzing the steel plates are presented in detail in the topical report TR-0920-71621-P, Building Design and Analysis Methodology for Safety-Related Structures. A three-step approach is presented based on the failure mechanism described in the reference.
Step 1. Select an initial concrete wall thickness. Tc is the SC wall concrete infill thickness.
Step 2. Compute the weight, WCP, and residual velocity, Vr, of the concrete conical plug dislodged by the missile after penetrating the SC wall.
Step 3. Calculate the required thickness, tp, of the rear steel faceplate to prevent its tearing fracture and thus perforation of the SC wall due to the concrete plug projectile.
3.5.3.2 Overall Damage Prediction For impactive and impulsive loads, the design considers localized and global effects.
The forcing functions to determine the structural responses are Nuclear Engineering and Design, Full-Scale Tornado-Missile Impact Tests, (Reference 3.5-6) for the triangular impulse formulation of the design-basis steel pipe missile. Reference 3.5-5 is used for the design-basis automobile missile. The solid sphere missile is too small to affect structural response of the RXB and the CRB, and is not evaluated for its contribution to overall structural response.
Design for impulsive and impactive loads is in accordance with Reference 3.5-4 for concrete structures and NuScale Topical Report, TR-920-71621, Building