response to request for additional information · with additional guidance provided in regulatory...

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Non-Proprietary

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION

APR1400 Design Certification

Korea Electric Power Corporation / Korea Hydro & Nuclear Power

Docket No. 52-046

RAI No.: 208-8245

SRP Section: 03.08.03 – Concrete and Steel Internal Structures of Steel or Concrete Containments

Application Section: 03.08.03

Date of RAI Issue: 09/14/2015

Question No. 03.08.03-1

10 CFR 50.55a and Appendix A to 10 CFR Part 50, General Design Criteria (GDC) 1, 2, 4, 16 and 50, provide the regulatory requirements for the design of structures including the in-containment refueling water storage tank (IRWST). Standard Review Plan (SRP) 3.8.3, Section II discusses the loads and load combinations normally applicable to internal concrete structures, particularly the IRWST, with emphasis on the extent of compliance with American Concrete Institute (ACI) 349-01, “Code Requirements for Nuclear Safety Related Concrete Structures,” with additional guidance provided in Regulatory Guide 1.142.

In DCD Tier 2, Section 3.8.3.1.8, “In-Containment Refueling Water Storage Tank,” the applicant stated that, “The design of the IRWST considers pressurization as a result of the reactor containment building systems design basis accident.” The applicant further stated in Appendix 3.8A, Section 3.8A.1.4.3.1.3, “Structural Design Summary,” report that, “The hydrodynamic pressure load, which is generated by the expulsion of air in the pilot-operated safety relief valve (POSRV) discharge, is applied to the wall and bottom slab of the IRWST through the two spargers.” The staff noted that additional information is needed in order to better understand the hydrodynamic pressure loads that are being considered for the analysis and design of the IRWST. Per 10 CFR 50.55a, Appendix A to 10 CFR Part 50, GDCs 1, 2, 4, 16 and 50; and SRP 3.8.3, the applicant is requested to provide additional information that fully describes the hydrodynamic pressure loads that are being considered in the analysis and design of the IRWST. The additional information should include a description, as to:

a. How the pressure transient (including the steady state portion) for a single sparger activation was developed (a figure of this load over time should be provided).

b. What cases of activation of the spargers may occur, i.e., one sparger alone, two spargers simultaneously, and/or some lag between the two activations.

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Non-Proprietary

TS

c. How the total pressure transients on the walls and floor were developed based on the cases identified in item (b) above (a figure showing the pressure distributions on the walls and floor should be provided).

d. How the dynamic impact factor, discussed in DCD Section 3.8A.1.4.3.1.3, was determined, and explain why applying this as a static load is considered conservative.

Response

a. Pressure load on the IRWST due to actuation of POSRVs is governed by the air bubble dynamics during the discharge of air present in the piping. The largest hydrodynamic loads on the IRWST are dependent on the pressure and frequency of the air bubble formed during the air clearing phase

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Non-Proprietary

TS Based on the method developed by ABB-Atom and applied to the System 80+, scaling factors for the APR1400 design are developed as follows:

The hydrodynamic loads during the water and the steady steam discharge phases are bounded by that of the air discharge phase. The steam bubble oscillation issues can be neglected since discharged steam is fully condensed in the IRWST subcooled water.

Figure 1 shows the pressure-time history from the sparger test performed to verify the performance of the APR1400 sparger.

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TS

TS

Figure 1 Pressure Transient for APR1400 POSRV Sparger

b. Following a postulated POSRV actuation, air inside the PORSR discharge piping is discharged into the IRWST water through all spargers connected to discharge piping simultaneously, i.e., multiple spargers are activated on POSRV actuation.

For multiple spargers actuation, the air in each sparger is assumed to be discharged in the form of a bubble and each air bubble causes loads on the submerged IRWST wall boundaries independently. The bubbles from all activated spargers are assumed to simultaneously enter the IRWST pool. The hydrodynamic load at a location of interest is obtained by the combination of individual load from each sparger using SRSS (Square Root of the Sum of Squares) method.

The SRSS approach provides a simple conservative representation of the effects of bubble phase differences on the combined load without requiring a detailed mechanistic model for the bubble formation process. The phase differences are attributed to the key bubble formation parameters (e.g., valve actuation, opening time, line length, etc.). The combined load is further limited to no greater than the maximum individual air bubble source pressure.

The combined pressure load considering activation of all POSRV spargers for APR1400 is expressed as follows:

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Non-Proprietary

TS

c. The hydrodynamic loads are the short transient pressure time histories at frequencies ranging from 4 Hz to 14 Hz. In the structural analysis for containment internal structure design, the maximum pressure value of the total pressure transient is conservatively obtained by applying a dynamic impact factor, and is considered as a static load. The maximum pressure value, which considers the dynamic impact factor, is distributed on the walls and floor in accordance with locations distances from spargers. Two spargers are located at Az. 90o (West Direction) and Az. 180o (North Direction), and the spatial distribution is expressed as a normalized factor. Figure 2 shows pressure distributions on the walls and the floor.

Figure 2 Pressure Distribution of Hydrodynamic Loads

d. The hydrodynamic load due to POSRV discharge is transient and normally the load experienced by the IRWST returns to ambient conditions in a short period of time. In the analytical procedure of fast load transients, the transient load can be simplified by introducing a dynamic load factor. It transforms a dynamic peak load into a static load with the same effect on the structure. And in the case of an idealized triangle-shaped wave load, the dynamic load factor approaches its boundary limit of 2 (refer to Chapter 2 of “Introduction to Structural Dynamics”, by John M. Biggs). Therefore, considering that the hydrodynamic load due to POSRV discharge is a short transient, and the shape of the pressure transient is a sine-curve (similar to triangle), the equivalent static load, with the application of a dynamic load factor, is conservative compared to the transient dynamic load.

Impact on DCD

There is no impact on the DCD.

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Non-Proprietary

Impact on PRA

There is no impact on the PRA.

Impact on Technical Specifications

There is no impact on the Technical Specifications.

Impact on Technical/Topical/Environmental Reports

There is no impact on any Technical, Topical, or Environmental Report.

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Docket No. 52-046

RAI No.: 208-8245

SRP Section: 03.08.03 - Concrete and Steel Internal Structures of Steel or Concrete Containment

Application Section:



10 CFR Part 50.65 provides the regulatory requirements for monitoring the effectiveness of maintenance of the containment internal structures (CIS). Standard Review Plan (SRP) 3.8.3, Section II.7, provides guidance for testing and examining the preservice, in-service, and repair/replacement requirements of containment internal structures. DCD Tier 2, Section 3.8.3.7, “Testing and Inservice Inspection Requirements,” refers to DCD Section 3.8.4.7, “Testing and Inservice Inspection Requirements,” which describes the testing and in-service requirements for other seismic Category I structures.

The staff reviewed DCD Section 3.8.4.7 and noted that the applicant did not identify and discuss the requirements for monitory the effectiveness of maintenance of the CIS and other structures, specifically, the requirements of 10 CFR 50.65 and the supplemental guidance of Regulatory Guide 1.160, “Monitoring the Effectiveness of Maintenance and Nuclear Power Plants.” Per 10 CFR 50.65 and SRP 3.8.3, the staff is requesting the applicant to include this information in the DCD.

Response

The requirements for monitoring seismic Category I structures will be added to DCD Tier 2, Section 3.8.4.7.

Impact on DCD

DCD Section 3.8.4.7 will be revised as indicated on the attached markup.

Impact on PRA


Non-Proprietary

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Non-Proprietary

APR1400 DCD TIER 2

3.8-80

Erection tolerances, in general, are in accordance with the referenced design code. Where special tolerances that influence the erection of equipment are required, they are indicated on the design drawings.

3.8.4.6.3 Special Construction Techniques

No special construction techniques are used in the construction of other seismic Category I structures.

The corrosion protection of the auxiliary building reinforcing steel is provided by an adequate cover of high-quality concrete over the reinforcing bar. Unless the concrete is penetrated by chloride or sulfide ions, the reinforcing bar remains passive and will not corrode.

Slabs in the auxiliary building are constructed using metal deck and steel beams that support metal deck and concrete slab during construction. Steel beams are connected to shear walls or concrete beams. This method allows concrete slabs to be constructed without shorings and forms.

The COL applicant is to determine construction techniques to minimize the effects of thermal expansion and contraction due to hydration heat, which could result in cracking (COL 3.8(4)).

Testing and Inservice Inspection Requirements 3.8.4.7

There is no testing or in-service surveillance beyond the quality control tests performed during construction, which is in accordance with ACI 349, AISC N690, or ANSI N45.2.5, in accordance with NRC RG 1.127 and NUMARC 93-01.

However, the COL applicant is to monitor the safety and serviceability of seismic Category I structures during the operation of the plant, and appropriate maintenance will be provided as necessary (COL 3.8(5)).

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RAI 208-8245 - Question 03.08.03-2 Attachment (1/1)Non-Proprietary

Monitoring of seismic Category I structures is performed in accordance with RG 1.160.

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Docket No. 52-046

RAI No.: 208-8245





Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50, provides the regulatory requirements for the design of the containment internal structures. Standard Review Plan (SRP) 3.8.3, Section II discusses the loads and load combinations normally applicable to containment internal structures, with emphasis on the extent of compliance with American Concrete Institute (ACI) 349-01, “Code Requirements for Nuclear Safety Related Concrete Structures,” with additional guidance provided in Regulatory Guide 1.142, and ANSI/AISC N690-1994, “Specification for the Design, Fabrication and Erection of Steel Safety- Related Structures for Nuclear Facilities,” including Supplement 2 .

APR1400 DCD Tier 2, Section 3.8.3.3, “Loads and Load Combinations,” indicates that the typical loads and load combinations used for the internal structures are detailed in Section 3.8.4.3. Then it lists loads that the internal structures are designed for. A comparison of these loads listed in DCD Section 3.8.3.3 with those of DCD Section 3.8.4.3 shows that some loads are not included like operating pressure loads, construction loads, and internal flooding. Per Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50, and SRP 3.8.3, the applicant is requested to confirm that all applicable loads described in DCD Section 3.8.4.3 are used for internal structures, or explain why not. This issue of consideration of all applicable loads also applies to the list of loads identified in DCD Section 3.8.3.4.1 – Analysis Procedures.

In addition, DCD Appendix 3.8A.1.4.3.1.2, “Load Combinations Considered,” identifies load combinations that are critical for the analysis and design of the primary shield wall (PSW). It is not clear to the staff whether only these load combinations were evaluated or all load combinations were evaluated, and only these were critical. This should be explained. In addition, there are some loads that are not included in these critical load combinations such as Ro in load combination labelled a. and c., Ra in load combination b., and Ra, Yj, Ym, and Yf in load combination d. This should be explained. The applicant is also requested to address the above items for the other containment internal structures (e.g., IRWST and SSW).

Non-Proprietary

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Response

All loads described in DCD Section 3.8.4.3 are not used for the design of internal structures, but the appropriate loads for the design of internal structures are considered. DCD Section 3.8.3.3 will be revised to state hydrostatic and dynamic loads are applicable loads used for the design of the IRWST, as indicated on the attached markup.

Based on the design experience of Shin-Kori 3&4, the load combinations present in DCD Appendix 3.8A.1.4.3.1.2 were the most critical for the design of the primary shield wall (PSW). The maximum moment and shear force for the design of the PSW are due to these of all load combinations. The reinforcement of the PSW is determined by the maximum moment and shear force. Therefore, other load combinations in Table 3.8-9A are not evaluated for APR1400.

Ro and Ra are considered as the dead load (D) in the analysis. So, Ro and Ra are included in D. Also, there is no Ro and Ra at the primary shield wall (PSW). Based on the ACI 349 Appendix C, impactive and impulsive effects are treated separately because of the nature of the effects as well as the response characteristics of the structural members subjected to these loads. Yj and Ym act on the local area of the internal structures. So, Yj and Ym are evaluated with the design margin of the arranged reinforcement in the local area after design with load combinations. For the containment internal structures, Yf is offset by acting equally on both sides of the internal wall. So, Yf is not included in the load combination. The above discussion regarding Yj,Ym, and Yf are also applicable to the other containment internal structures (e.g., IRWST and SSW).

Impact on DCD

DCD Section 3.8.3.3 will be revised as indicated on the attached markup.

Impact on PRA






Non-Proprietary

APR1400 DCD TIER 2

3.8-52

3.8.3.1.11 Interior Concrete Fill Slab

The interior concrete fill slab is located on the surface of liner plate of the reactor containment building basemat for protection of pressure boundary structures.

3.8.3.1.12 Polar Crane Supports

A large capacity of polar crane is supported by brackets installed in the containment shell, and the bracket is a steel structure consisting of cantilever beam.

Applicable Codes, Standards, and Specifications 3.8.3.2

The following codes, standards, and specifications are applied to the design of internal concrete and steel structures.

3.8.3.2.1 Design Codes and Standards

The design codes, standards, and regulations are listed in Table 3.8-1.

3.8.3.2.2 NRC Regulatory Guides

Conformance to each NRC RG is described in Section 1.9. The NRC RGs applicable to the design of the concrete and steel structures are 1.60, 1.61, 1.92, 1.122, 1.142, and 1.199 (References 22 through 27).

3.8.3.2.3 Industry Standards

Nationally recognized industry standards, such as those published by ASTM, will be used whenever possible to describe material properties, testing procedures, and fabrications and construction methods.

Loads and Load Combinations 3.8.3.3

The typical loads and load combinations used for the internal structures are detailed in Subsection 3.8.4.3.

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described

APR1400 DCD TIER 2

3.8-53

The internal structures are designed for the following loads:

a. Dead load

b. Equipment operating loads and other live loads

c. Pipe reactions

d. Seismic load

e. Internal missiles (the internal structure is designed to withstand internal missiles, as described in Section 3.5)

f. Pipe rupture jet impingement

g. Compartment accident pressure

h. The greatest pipe rupture loads from (1) pipe breaks not eliminated by leak-before-break, (2) the largest through-wall leakage crack in a high-energy line (minimum 37.9 L/min (10 gpm)), whether or not consideration of dynamic effects is eliminated by leak-before-break for the line, or (3) the largest leak from another leak source, such as a valve or pump seal.

i. Operating and accident temperatures

Seismic Category I concrete structures are designed for impulsive and impactive loads in accordance with the ACI 349 Code, and special provisions of Appendix C of the same code, with exceptions given in NRC RG 1.142. Impactive and impulsive loads are considered concurrent with seismic and other loads (i.e., dead and live loads) in determining the load resistance of structural elements.

Subcompartment pressure loads are the result of postulated high-energy pipe ruptures. In determining an appropriate equivalent static load for Yr, Yj, and Ym, elasto-plastic behavior is acceptable with appropriate ductility ratios, provided excessive deflections do not result in loss of function of any safety-related system.

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j. Hydrostatic and dynamic loads (IRWST)

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Docket No. 52-046

RAI No.: 208-8245





10 CFR 50.55a and Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50, provide the regulatory requirements for the design of the containment internal structures. Standard Review Plan (SRP) 3.8.3, Section II specifies analysis and design procedures normally applicable to internal concrete structures, with emphasis on the extent of compliance with American Concrete Institute (ACI) 349-01, “Code Requirements for Nuclear Safety Related Concrete Structures,” with additional guidance provided in Regulatory Guide 1.142, and ANSI/AISC N690-1994, “Specification for the Design, Fabrication and Erection of Steel Safety- Related Structures for Nuclear Facilities,” including Supplement 2.

APR1400 DCD Tier 2, Section 3.8.3.4, “Design and Analysis Procedures,” states, “The thermal stress analysis is carried out by inputting the normal operating thermal load into the corresponding FEM for the internal structure.” In reviewing this section, the staff noted that no description about accidental thermal loads - loads generated by a postulated pipe break - was provided. Per 10 CFR 50.55a; Appendix A to 10 CFR Part 50, General Design Criteria1, 2, 4, 16 and 50; and SRP 3.8.3, the applicant is requested to confirm that accident thermal loads were considered; and describe how the accident thermal loads were evaluated in the analysis and design of the internal structures.

Response

Equivalent linear temperature profile of normal operating conditions represent the limiting temperature profile for all plant conditions. Therefore, normal operating thermal loads were considered for containment internal structure design instead of accident thermal loads. Figure 1, below, compares normal operating thermal loads and accident thermal loads.

According to ACI 349, the actual non-linear temperature distribution can be converted to an equivalent linear temperature distribution for use in design of concrete structures. In the containment internal structure, the equivalent linear temperature profile for normal operating

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conditions is more severe than those of the accident conditions since the temperature difference between the inside and the outside surface of the containment internal structure during accident conditions is negligibly small. Figure 1 shows the example of differential temperatures for normal operating conditions and accident conditions.

(a) Normal Operating Condition (b) Accident Condition

Figure 1 Example of Temperature Profile

Impact on DCD


Impact on PRA






Inside Outside Outside Inside

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Docket No. 52-046

RAI No.: 208-8245





10 CFR 50.55a and Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50, provide the regulatory requirements for the design of the containment internal structures. Standard Review Plan (SRP) 3.8.3, Section II specifies analysis and design procedures normally applicable to internal concrete structures, with emphasis on the extent of compliance with American Concrete Institute (ACI) 349-01, “Code Requirements for Nuclear Safety Related Concrete Structures,” with additional guidance provided in Regulatory Guide 1.142, and ANSI/AISC N690-1994, “Specification for the Design, Fabrication and Erection of Steel Safety- Related Structures for Nuclear Facilities,” including Supplement 2.

DCD Tier 2, Section 3.8A.1.4.3.1.3, “Analysis Methods and Results”

a. APR1400 DCD Tier 2, Section 3.8A.1.4.3.1.3 describes the analysis methods and results for the containment internal concrete structures. It states that, “Operating concrete floor slabs are modeled to mass in a finite element model (FEM), such as slabs between the SSWs and containment shell.” Per 10 CFR 50.55a; Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50; and SRP 3.8.3, the applicant is requested to clarify if this meant to say that the operating floor slabs between the secondary shield walls (SSWs) and the containment shell are included as masses in the FEM. If this is the case, then explain why it is acceptable to decouple these slabs from the overall FEM analysis of the internal structures and how is the analysis and design for such subelements performed for all of the various loadings.

b. Additionally, DCD Section 3.8A.1.4.3.1.3 indicates that fifty percent of the weights and equipment weights on the floor between the containment shell and the SSW are assumed to be distributed to the containment shell and the SSW, respectively. This implies that there is a connection between the containment internal floors and the containment. Per 10 CFR 50.55a; Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50; and SRP 3.8.3, the applicant is requested to explain in what

Non-Proprietary

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directions (radial, tangential, and/or vertical) are the connections made and the details of how they are designed. Also, identify the gap provided between the containment and the floor slabs/connections to prevent impact/interaction and describe how the relative displacements between the containment and the floor slabs/connections from all loads including thermal and seismic were determined to demonstrate the gap is adequate.

c. This DCD Section also indicates that Figure 3.8A-23 shows the full FEM for the containment internal structures and Figure 3.8A-24 shows the solid element model (PSW, IRWST, and fill concrete), shell element model (SSW), and beam element model (RCS). The staff notes that part (b) of Figure 3.8A-24, which is labelled Shell Element Model (SSW), does not show the shell elements of the SSW. The applicant is requested to clarify why not.

d. DCD Section 3.8A.1.4.3.1.3 states that, “An equivalent uniform temperature gradient is input directly in the ANSYS model at the appropriate nodes. The temperature profiles during normal operating condition are more severe than those of the accident condition, thus represent the limiting temperature for all the plant conditions.” Per 10 CFR 50.55a; Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50; and SRP 3.8.3, the applicant is requested to provide the technical basis for this conclusion.

Response

a. Operating floor slabs between the secondary shield walls (SSWs) and the containment shell are included as masses in the FEM. The decoupling criteria in SRP 3.7.2 allow decoupling if the mass ratio of the substructure is less than 0.1 but above 0.01 (0.01

mass ratio (Rm) 0.1), and if the frequency ratio of the substructure is less than 0.8 or

above 1.25 (frequency ratio (Rf) 0.8 or 1.25 frequency ratio (Rf)). The Rm for concrete slabs and internal structure is .051 and the fundamental frequencies of the concrete slabs are lower than 18.7 Hz which is .80 of the dominant frequency of internal structures. Thus, internal structures and operating concrete slabs may be decoupled.

Regarding the analysis and design of subelements, the concrete slabs at elevations 114'-0", 136'-6", and 156'-0" between secondary shield wall and containment wall are structurally analyzed using the FE (Finite Element) analysis program GTSTRUDL. A separate analysis model simulating each floor level is prepared and evaluated for each specified design load condition. The span direction for concrete slabs is considered in determining the tributary areas. To incorporate the proper vertical seismic load on each slab, slab self-weights and attachment loads are multiplied by the peak acceleration of slab response spectra at each elevation. The equivalent-static loads are determined by multiplying the structure, equipment, or component masses by an acceleration equal to 1.5 times the peak acceleration. The thickness of the slab is generally determined by the requirements of radiation shielding, missile protection, and structural integrity. Based on the enveloped results of FE analysis, the slab reinforcements are determined for flexure and out-of-plane shear in accordance with ACI 349.

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b. The floors are supported by structural steel beams which span the secondary shield wall and the containment wall. Each end of the steel beams have a fixed connection at the secondary shield wall and a sliding connection at the containment wall. The fixed connection is composed of a beam seat, a bumper, and a web angle connection. The beam seat supports vertical load, the bumper supports shear load, and the web angle connection supports vertical and axial load. The sliding connection at the containment wall is composed of a beam seat, a bumper, and a gap between the end of the steel beam and the containment wall to allow radial displacements due to seismic and thermal loads. The gap between the end of the steel beam and the containment wall is 1 5/8” (1.625”) which is larger than the maximum displacement of 1.58” (containment wall displacement by earthquake, thermal displacement, displacement by post-tensioning, and installation tolerance). Based on the results of FE analysis of containment shell & dome, containment wall displacements by earthquake and post-tensioning are determined. Thermal displacement is thermal expansion of steel beam in RCB under design basis accident condition of LOCA. Installation tolerance is also determined according to tolerances on structural steel fabrication. In addition to the gap between the end of the steel beam and the containment wall, the gap between the edge of concrete floors and the containment wall is 2”. Therefore, the gap is adequate to allow the relative displacements between the containment internal floors and the containment wall.

c. Part (b) of Figure 3.8A-24 shows the solid element model of the PSW, the IRWST, and the fill concrete due to an editorial error. To show the shell element model of the SSW, part (b) of Figure 3.8A-24 will be revised as indicated on the attached markup.

d. According to ACI 349, the actual non-linear temperature distribution can be converted to an equivalent linear temperature distribution for use in design of concrete structures. In containment internal structure, the equivalent linear temperature profiles of normal operating condition is more severe than those of the accident condition. A detailed explanation is provided in KHNP’s response to RAI 208-8245, Question 03.08.03-4.

Impact on DCD

DCD Tier 2, Section 3.8A.1.4.3.1.3 and Figure 3.8A-24, part (b) will be revised as indicated on the attached markup.

Impact on PRA






Non-Proprietary

APR1400 DCD TIER 2

3.8A-19

d. Abnormal/extreme: 1.0D + 1.0Lh + 1.0L + 1.0Pa + 1.0Ta + 1.0Yr + 1.0Es

3.8A.1.4.3.1.3 Analysis Methods and Results

The containment internal concrete structures are interconnected at various elevations. Significant lateral loads from the reactor coolant system (RCS) supports are applied at several elevations. In order to properly account for the load distribution in structures, an overall structural model representing containment internal concrete structures is prepared. Operating concrete floor slabs are modeled to mass in a finite element model (FEM), such as slabs between the SSWs and containment shell.

The ANSYS program is used to perform structural analysis using the containment internal structure full model. The FEM consists of a total of 50,496 nodes. The numbers of shell, solid, and beam elements are 5,522, 41,689, and 827, respectively. The following containment internal structures are included in the analysis model:

Solid Elements

a. PSW

b. IRWST and fill concrete

Shell Elements

a. SSW

b. Refueling pool wall and slab

c. Pressurizer (PZR) enclosure wall and slab

d. Steam generator (SG) enclosure wall

e. Operating floor slab between SSW and refueling pool wall

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between the SSWs and containment shell are included as masses in the finite element model (FEM).

Non-Proprietary

APR1400 DCD TIER 2

3.8A-111

(a) Solid Element Model (PSW, IRWST, and Fill Concrete)

(b) Shell Element Model (SSW)

(c) Beam Element Model (RCS)

Figure 3.8A-24 Solid, Shell, and Beam Element Model for RCB Internal Structure

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Docket No. 52-046

RAI No.: 208-8245





10 CFR 50.55a and Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50, provide the regulatory requirements for the design of the containment internal structures. Standard Review Plan (SRP) 3.8.3, Section II specifies analysis and design procedures normally applicable to internal concrete structures, with emphasis on the extent of compliance with American Concrete Institute (ACI) 349-01, “Code Requirements for Nuclear Safety Related Concrete Structures,” with additional guidance provided in Regulatory Guide 1.142.

APR1400 DCD Tier 2, Section 3.8A.1.4.3.1.3, “Analysis Methods and Results,” describes analysis parameters used for the in-structure refueling water storage tank (IRWST) in the containment internal structure FEM. It indicates that the damping ratio for water in the IRWST or refueling pool is the same as that for reinforced concrete structures: the seismic response of water is only considered as impulsive (rigid) mode for structural analysis. Per 10 CFR 50.55a; Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50; and SRP 3.8.3, the applicant is requested to explain why the damping ratio for water is included in the model unless the water is included using finite elements to represent the water. If so, then describe the methodology for representing the water as finite elements.

Based on the above statement from DCD Section 3.8A.1.4.3.1.3, explain why only the impulsive (rigid) mode is considered in the analysis. To enable the staff to fully understand how water in pools are evaluated to design the pool walls and slabs, the applicant is also requested to provide a full description of how water in the various pools is modeled in the FEM and how member forces are determined to design the walls and floors of the pools. Also, explain if the approach followed the methodology presented in ASCE 4-98 Section 3.5.4, or what alternative methods were used, and the basis for those methods.

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03.08.03-6 - 2 / 2 KEPCO/KHNP

Response

1. In the IRWST analysis, the water is not included using finite elements to represent the water. The water is only considered as mass, and the damping ratio for the IRWST is equal to the value used for reinforced concrete structures. DCD Section 3.8A.1.4.3.1.3 will be revised as shown in the attached markup to clarify the value used for the damping ratio.

2. The hydrodynamic pressure in the IRWST which results from seismic excitation can be considered as impulsive and convective modes depending on the depth, simultaneously, but not in phase with each other. The impulsive pressure is associated with inertial force produced by acceleration of the wall, and the convective pressure is produced by the oscillations of the fluid. The impulsive mode primarily acts to stress the wall, whereas the convective mode acts primarily to uplift the wall. The sloshing due to the convective mode could increase and decrease the fluid pressure on the wall and the fluid pressure due to the sloshing effect is smaller than that due to the impulsive effect. Therefore, considering the impulsive mode over the water level is more conservative than considering both impulsive and convective modes.

3. There are two water tanks in the RCB, the IRWST and the refueling pool. Water is not in both tanks simultaneously. The hydrostatic pressure loads are applied as surface pressure on the IRWST and refueling pool walls and bottom slabs. For the hydrodynamic pressure, a mass calculated in accordance with ASCE 4-98, Section 3.5.4 is applied to the IRWST and refueling pool, and then a response spectrum analysis was performed. Member forces and stresses for design were computed using modal combinations (SRSS) in accordance with Regulatory Guide 1.92.

4. In the IRWST analysis, the methodology presented in ASCE 4-98, Section 3.5.4 was used.

Impact on DCD

DCD Section 3.8A.1.4.3.1.3 will be revised as indicated on the attached markup.

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Non-Proprietary

APR1400 DCD TIER 2

3.8A-21

c. SG compartment – SG blowdown nozzle

d. PZR compartment – PZR spray nozzle

e. PZR compartment – POSRV nozzle

f. PZR spray valve room – PZR spray line

Branch line pipe break (BLPB) loads are dynamic reactions caused by the combined effects of branch line nozzle reactions or thrust due to pipe break, jet impingement on RCS equipment, or subcompartment pressure effects on RCS equipment. The RCS support reactions due to BLPB are applied as nodal forces at the support locations.

The hydrodynamic pressure load, which is generated by the expulsion of air in the pilot-operated safety relief valve (POSRV) discharge, is applied to the wall and bottom slab of the IRWST through the two spargers. For the hydrodynamic pressure load, by multiplying the dynamic impact factor (DIF), the maximum pressure is conservatively considered as the static load in the analysis. In addition, the normalized factor is considered for the spatial distribution due to the location of spargers.

The seismic analysis for structures is performed using response spectrum analysis. A 7 percent damping ratio for reinforced concrete structures (SSE) and 3 percent damping ratio for the RCS model are used. In addition, the damping ratio for water in the IRWST or refueling pool is the same as that for reinforced concrete structures: the seismic response of water is only considered as impulsive (rigid) mode for structural analysis. Figure 3.8A-5 (a) and (c) show the in-structure response spectrum (ISRS) of the SSE level at El. 78 ft 0 in with 3 percent and 7 percent damping.

Three sections are selected in the PSW as critical sections. Each section is thinnest in the directions of north, south, and east. The design forces and moments for PSW critical sections are presented in the Table 3.8A-18. Table 3.8A-22 presents the margins of safety of rebar stress in the primary shield wall. The margin of safety is the ratio of allowable stress and actual stress.

Rev. 0

Non-Proprietary

03.08.03-7 - 1 / 2 KEPCO/KHNP




Docket No. 52-046

RAI No.: 208-8245





10 CFR 50.55a and Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50, provide the regulatory requirements for the design of the containment internal structures. Standard Review Plan (SRP) 3.8.3, Section II specifies analysis and design procedures normally applicable to internal concrete structures, with emphasis on the extent of compliance with American Concrete Institute (ACI) 349-01, “Code Requirements for Nuclear Safety Related Concrete Structures,” with additional guidance provided in Regulatory Guide 1.142.

APR1400 DCD Tier 2, Section 3.8.3.1.11, “Interior Concrete Fill Slab,” and Appendix 3.8A.1.4.3, “Internal Structures,” indicate that the containment internal structures include concrete fill located on the surface of the liner plate of the reactor containment building basemat for protection of the pressure boundary structures. The staff notes that this concrete fill also provides support to the containment internal structures. Therefore, per 10 CFR 50.55a; Appendix A to 10 CFR Part 50, General Design Criteria 1, 2, 4, 16 and 50; and SRP 3.8.3, the staff requests the applicant to explain if the concrete fill is reinforced concrete. If not, then explain how the structural adequacy of the concrete fill is demonstrated. In addition, describe the connection details of the concrete fill to the reactor containment basemat to demonstrate its capability to withstand the various loads including seismic.

Response

The concrete fill slab is not considered to be a structural member, but is reinforced. The reinforcement of the concrete fill slab is conservatively based on the maximum moment of the secondary shield wall (SSW), as well as the minimum amount of reinforcement needed for cracking considerations. The concrete fill slab is not connected to the basemat, but the reinforcement of the SSW is connected to the basemat through the concrete fill slab. The maximum moment of the SSW is considered along with various other design loads including seismic.

Non-Proprietary

03.08.03-7 - 2 / 2 KEPCO/KHNP

Impact on DCD


Impact on PRA






Non-Proprietary

response to request for additional information · with additional guidance provided in regulatory...

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