ML22277A601

Issuance of Amendment No. 304 Revising the Design Basis for the Shield Building Containment Structure

ML22277A601
Person / Time
Site:	Davis Besse
Issue date:	10/14/2022
From:	Blake Purnell Plant Licensing Branch III
To:	Tony Brown Energy Harbor Nuclear Corp
Purnell B
References
EPID L-2022-LLA-0003
Download: ML22277A601 (15)

Text

October 14, 2022 Mr. Terry J. Brown Site Vice President Energy Harbor Nuclear Corp.

Mail Stop P-DB-3080 5501 North State Route 2 Oak Harbor, OH 43449-9760

SUBJECT:

DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 - ISSUANCE OF AMENDMENT NO. 304 REVISING THE DESIGN BASIS FOR THE SHIELD BUILDING CONTAINMENT STRUCTURE (EPID L-2022-LLA-0003)

Dear Mr. Brown:

The U.S. Nuclear Regulatory Commission (NRC, the Commission) has issued the enclosed Amendment No. 304 to Renewed Facility Operating License No. NPF-3 for the Davis-Besse Nuclear Power Station, Unit No. 1. The amendment is in response to the Energy Harbor Nuclear Corp. application dated January 3, 2022 (Agencywide Documents Access and Management System Accession No. ML22003A147), as supplemented by letter dated May 12, 2022 (ML22132A196). The amendment revises the design basis for the facility to allow laminar concrete cracking of a limited width in the outer reinforcement layer of the shield building containment structure.

A copy of the NRC staffs Safety Evaluation is also enclosed. The Notice of Issuance will be included in the Commissions monthly Federal Register notice.

Sincerely,

/RA/

Blake Purnell, Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346

Enclosures:

1. Amendment No. 304 to NPF-3

2. Safety Evaluation cc: Listserv

ENERGY HARBOR NUCLEAR CORP.

AND ENERGY HARBOR NUCLEAR GENERATION LLC DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 AMENDMENT TO RENEWED FACILITY OPERATING LICENSE DOCKET NO. 50-346 Amendment No. 304 Renewed License No. NPF-3

1. The U.S. Nuclear Regulatory Commission (the Commission) has found that:

A. The application for amendment filed by Energy Harbor Nuclear Corp. dated January 3, 2022, as supplemented by letter dated May 12, 2022, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commissions rules and regulations set forth in 10 CFR Chapter I; B. The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commissions regulations; D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.

Enclosure 1

2. Accordingly, the license is amended by changes to the Updated Final Safety Analysis Report, as described in the application dated January 3, 2022, and the supplement dated May 12, 2022.

3. This license amendment is effective as of the date of its issuance and shall be implemented within 60 days of the date of issuance.

FOR THE NUCLEAR REGULATORY COMMISSION Digitally signed by Robert Robert F. F. Kuntz Date: 2022.10.14 Kuntz 12:57:09 -04'00' Nancy L. Salgado, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Date of Issuance: October 14, 2022

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 304 TO RENEWED FACILITY OPERATING LICENSE NO. NPF-3 ENERGY HARBOR NUCLEAR CORP.

ENERGY HARBOR NUCLEAR GENERATION LLC DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NO. 50-346

1.0 INTRODUCTION

By application dated January 3, 2022 (Agencywide Documents Access and Management System Accession No. ML22003A147), as supplemented by letter dated May 12, 2022 (ML22132A196), Energy Harbor Nuclear Corp. (Energy Harbor, the licensee) submitted a license amendment request (LAR) for Davis-Besse Nuclear Power Station, Unit No. 1 (Davis-Besse). The proposed amendment would revise the design basis for the facility to allow laminar concrete cracking of a limited width in the outer reinforcement layer of the shield building containment structure.

The supplemental letter dated May 12, 2022, was in response to a U.S. Nuclear Regulatory Commission (NRC, the Commission) staff request for additional information dated April 22, 2022 (ML22112A109). The supplemental letter provided additional information that clarified the application, did not expand the scope of the application as originally noticed, and did not change the NRC staffs original proposed no significant hazards consideration determination as published in the Federal Register on March 22, 2022 (87 FR 16252).

2.0 REGULATORY EVALUATION

2.1 Background

Information regarding the Davis-Besse containment structures, including the design basis for the shield building, is provided in section 3.8.2 (ML20302A282) of the Davis-Besse Updated Final Safety Analysis Report (UFSAR), Revision 33. The containment for the station consists of three basic structures: a steel containment vessel, a reinforced concrete shield building, and the internal structures. The containment vessel is a low-leakage steel structure designed to withstand a postulated loss-of-coolant accident and to confine a postulated release of radioactive material. The shield building is a reinforced concrete structure of right cylinder configuration with a shallow dome roof. The shield building completely encloses the containment vessel, the personnel access openings, the equipment hatch, and that portion of all Enclosure 2

penetrations that are associated with primary containment. An annular space is provided between the steel containment vessel and the shield building. The design of the shield building provides for (1) biological shielding, (2) controlled release of the annulus atmosphere under accident condition, and (3) environmental protection of the containment vessel. With the exception of the concrete under the containment vessel, there are no structural ties between the containment vessel and the shield building above the foundation slab. Above the foundation slab, there is freedom for differential movement between the containment vessel and the shield building.

The shield building was designed in accordance with American Concrete Institute (ACI) 307-69, Specification for the Design and Construction of Reinforced Concrete Chimneys, and checked by the ultimate strength design method in accordance with ACI 318-63, Building Code Requirements for Reinforced Concrete. Load combinations specified in ACI 307-69 provide the design basis of the shield building. Section 3.8.2.2.2 of the Davis-Besse UFSAR, Revision 33, states, in part, that [a]dequate reinforcing is placed in the concrete walls, dome, and foundation to control cracking due to concrete shrinkage and temperature gradients. However, the LAR states that the ACI codes do not specify allowable limits or discuss the acceptability of laminar concrete cracking in regard to structural behavior or capacity of the shield building.

Section 2.3 of the LAR states, in part, that laminar cracking in the plane of the outer reinforcement mat of the shield building was observed in 2011. As part of the shield building monitoring program at Davis-Besse, the licensee monitors for extent and width of concrete cracking, as well as visible change of material properties and loss of material for both concrete and rebar in areas of laminar concrete cracking. The LAR also states that [t]he intent of Energy Harbor is to repair areas of laminar cracking. However, some areas where laminar cracking has been observed have limited access for repair. Laminar cracks in these areas, less than or equal to 0.050 inches, would not be immediately repaired; however, these areas would continue to be part of the monitoring program.

2.2 Description of the Proposed Changes The licensee proposed to revise the design and licensing bases for the Davis-Besse shield building though a revision to the Davis-Besse UFSAR, as described in attachment 2 to the LAR.

Section 2.4 of the LAR states, in part, that [t]he proposed change will update the UFSAR with a statement that laminar concrete cracks with widths less than or equal to 0.050 inches in the outer reinforcement layer of the shield building are acceptable in the design bases without explicit consideration in the analysis. The UFSAR would also be revised to state that laminar cracking greater that 0.050 inches in width is to be repaired.

The licensees basis for this revision to the Davis-Besse UFSAR is provided in Bechtel Power Corporation (Bechtel) Technical Report (TR) 25884-000-30R-C01R-00002, Revision 000, Incorporating Laminar Cracks of up to 0.050 Inch in the Design Basis of the Davis-Besse Shield Building (the TR), which is included as attachment 1 to the LAR. The TR concludes that crack widths of up to 0.050 inches in the outer reinforcement layer of the shield building have no adverse impact on the capacity of the reinforcing bars (rebars) to perform their intended function, ensuring shield building structural adequacy. The TR also concludes that the composite action of the shell, overall structural response, and serviceability and durability of the shield building are not adversely impacted with laminar concrete cracking of up to 0.050 inches in the outer reinforcement layer.

2.3 Regulatory Requirements and Guidance On July 11, 1967, the Atomic Energy Commission published a revised and expanded set of 70 draft general design criteria (GDC) for public comment in the Federal Register (32 FR 10213). On February 20, 1971, the Atomic Energy Commission published in the Federal Register (36 FR 3255) a final rule that added appendix A (the final GDC) to 10 CFR part 50, which was amended on July 7, 1971 (36 FR 12733). Differences between the 1967 draft GDC and the final GDC include a consolidation from 70 to 64 criteria.

The construction permit for Davis-Besse was issued on March 24, 1971, and the operating license for Davis-Besse was issued on April 22, 1977. Davis-Besse was designed and constructed in accordance with the 1967 draft GDC. However, the Final Safety Analysis Report provided as part of the application for the Davis-Besse operating license describes the facilitys conformance with the final GDC, as amended on July 7, 1971. Section 3.0, Design Criteria -

Structures, Systems and Components, of the NRC safety evaluation report (NUREG-0136; ML19319B839) related to the Davis-Besse operating license application describes the NRC staffs evaluation of the facilitys conformance with the GDC. The NRC safety evaluation report concludes that the plant design conformed to the intent of the final GDC, as amended on July 7, 1971.

The NRC staff considered the following GDC in its review of the LAR, which the licensee stated are applicable to the LAR:

GDC 1, Quality standards and records, which states, in part, that structures, systems, and components (SSCs) important to safety shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be performed. Where generally recognized codes and standards are used, they shall be identified and evaluated to determine their applicability, adequacy, and sufficiency and shall be supplemented or modified as necessary to assure a quality product in keeping with the required safety function.

GDC 2, Design bases for protection against natural phenomena, which states, in part, that SSCs important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions.

GDC 4, Environmental and dynamic effects design bases, which states, in part, that SSCs important to safety shall be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents, including loss-of-coolant accidents.

These SSCs shall be appropriately protected against dynamic effects, including the effects of missiles, pipe whipping, and discharging fluids, that may result from equipment failures and from events and conditions outside the nuclear power unit.

The regulations in appendix B, Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants, to 10 CFR part 50 establish the quality assurance (QA) requirements for the design, fabrication, construction, and testing of the SSCs for nuclear power plants. The pertinent requirements of appendix B apply to all activities affecting the safety-related functions of those SSCs. The NRC staff considered the following appendix B criteria in its review of the LAR:

Criterion III, Design Control, which states, in part, that the design control measures shall provide for verifying or checking the adequacy of design, such as by the performance of design reviews, by the use of alternate or simplified calculational methods, or by the performance of a suitable testing program.

Criterion XI, Test Control, which states, in part, that a test program shall be established to assure that all testing required to demonstrate that SSCs will perform satisfactorily in service is identified and performed in accordance with written test procedures which incorporate the requirements and acceptance limits contained in applicable design documents. In addition, test results shall be documented and evaluated to assure that test requirements have been satisfied.

As discussed in section 2.1 of this safety evaluation, the Davis-Besse shield building was designed in accordance with ACI 307-69, and checked by the ultimate strength design method in accordance with ACI 318-63. Load combinations specified in ACI 307-69 provide the design basis of the shield building.

3.0 TECHNICAL EVALUATION

3.1 Licensees Technical Information This section of the safety evaluation provides a summary of the TR provided by the licensee in attachment 1 to the LAR. No NRC staff findings or conclusions are included in this section.

The TR states that a laminar crack was observed on October 10, 2011, in the vicinity of a temporary opening that was being created in the cylindrical wall of the shield building for the reactor pressure vessel head replacement at Davis-Besse. The crack was in the plane of the main outer rebar mat. During the original investigation by the licensee, crack widths were determined using core bore samples. The cracks were established to be tight, with crack widths of less than 0.010 inches in most cases (with one reading of 0.013 inches). Since the original investigation, some of these cracks have propagated and/or widened.

Further investigations and examinations were carried out by the licensee using impulse response (IR) scanning and core bores taken from the areas with laminar crack indications. The observations indicated that the laminar cracking is in line with the outer mat of the main cylindrical reinforcing. The licensee conducted a root cause analysis of the condition, and concluded that these cracks had been present in the shield building for a long time with no adverse impact on the shield buildings structural integrity and safety function. As part of the initial technical acceptance of the shield building, a crack monitoring program was instituted.

This periodic monitoring program uses a combination of IR scanning and core bores to evaluate the condition of the building and to identify any changes in the crack configuration.

The TR notes that the data from the crack monitoring program in 2013 and 2014 indicated no significant change in crack widths and no indications of any crack propagation from the initial observations. The data from the crack monitoring program in 2015 indicated that there was an increase in the crack widths at some core bore locations, with a maximum crack width of approximately 0.016 inches observed at one location, but no indication of any crack propagation beyond the initially identified areas. The observations from 2016 indicated that crack widths at most locations were greater than the corresponding 2015 readings, with the maximum crack width exceeding 0.050 inches. Cracking was also observed in core bores that had no prior crack indications. Since the 2016 observations were significantly different than previous observations,

an independent verification of the plant crack measuring procedure was carried out by an outside contractor, Construction Technology Laboratories (CTL).

The TR states that a comparison of the data collected by plant personnel with that collected by CTL, for the same crack locations using similar techniques, generally produced comparable results. However, there were some exceptions where CTL results indicated greater crack widths at some locations. In summary, the TR found that the independent review by CTL verified the plant procedure for crack width measurements and confirmed that crack widths exceeded 0.050 inches at some locations. The crack monitoring program observations from 2017 to present indicate a continued trend of propagation in both crack width and extent of cracking. The TR states that each years findings are documented and evaluated to establish the continued operability of the Davis-Besse shield building.

The TR notes that since the laminar cracking is located along the plane of the reinforcement, the capacity of the reinforcing bars has the greatest potential to be affected by the laminar cracking. The limiting component of this effect was determined to be at the lap splices, where the laminar cracking has the potential to cause slippage and prevent the reinforcing bar from developing its full capacity. The TR discusses the three-phase experimental test program that was conducted to investigate the effects of the laminar cracking and a potential repair method.

Based on the results of the Phase I, II, and III test programs summarized below, the TR concluded that the Davis-Besse shield building rebar lap splices will safely reach the full design basis load capacity with laminar cracks widths of up to 0.050 inches.

Phase I Test Program and Results The Phase I test program was conducted at Purdue University and the University of Kansas in 2012. The TR states that the Phase I test program was developed to evaluate the effect of laminar cracking, with crack widths on the order of 0.010 inches, on the load carrying capacity of rebar, especially at the rebar splices. Twelve girder test specimens were developed with reinforcement details similar to the reinforcement in the Davis-Besse shield building.

Specifically, six specimens used #11 rebar with 79-inch splices and the other six specimens used #11 rebar with 120-inch splices. The tests were conservatively designed to have concrete compressive strengths at the time of the tests that were less than the compressive strength of the concrete in the Davis-Besse shield building. The results of the Phase I test program indicated that laminar cracking with widths up to 0.015 inches had no impact on the capacity of the rebar or the rebar splices.

The observations and conclusions from the Phase I test program were used to perform the initial structural design evaluation of the shield building and to demonstrate compliance with applicable codes of record and regulatory requirements. The TR states that the Phase I testing at the University of Kansas produced similar results as the testing at Purdue University.

However, the University of Kansas test results were not included in the TR because testing at the University of Kansas was not continued beyond Phase I.

Phase II Test Program and Results The TR states that a Phase II test program was conducted at Purdue University in 2016 to estimate the maximum width of laminar cracks that would not impact the load carrying capacity of the rebar splices. The main goal of the Phase II test program was to help establish the structural adequacy of the shield building for crack widths observed during periodic monitoring that may not be covered by the conclusions from the Phase I test program.

The TR states that based on the results of the Phase I tests, six girder test specimens using #11 rebar with 79-inch splices were tested in Phase II. The geometry of the specimens, the test setup, and the testing procedure used were similar to those used in the Phase I test program.

All test specimens demonstrated a capability to maintain strength with an increase in deflection beyond yield. The maximum crack width during initial loading reached 0.054 inches, with a steel stress in the reinforcement of 74 kilopounds per square inch (ksi). The developed reinforcement stress was greater than the rebar yield strength of 65 ksi. The TR states that the Phase II results demonstrate that the load carrying capacity of the lap splices is not impacted for crack widths up to 0.054 inches.

Phase III Test Program and Results As some of the laminar crack observations for the Davis-Besse shield building exceeded the bounding crack width limit recommended by the Phase II test program, the TR states that a Phase III test program was designed and conducted at Purdue University in 2017. The TR states that the purpose of the Phase III test program was to investigate the effect of post-installed anchors on the load carrying capacity of the rebar lap splices. This was to evaluate the adequacy of the anchor system as a potential repair mechanism for the shield building at locations where the laminar crack width exceeded 0.050 inches. Although post-installed anchors were not used as a repair option at Davis-Besse, the Phase III test program included reference samples without anchors that included unconfined rebar splices.

Similar to the Phase II test program, the Phase III test program focused on #11 rebar with 79-inch lap splices, which was identified as the critical configuration for the Davis-Besse shield building. The test specimens had the same cross sections and materials as the specimens used for previous tests. The TR states that test results from specimens without anchors confirmed the results from beam tests in Phase I and Phase II indicating that laminar cracks with widths of up to 0.050 inches did not affect the ability of the lap splice to develop yielding in the spliced bars.

Overall Structural Response Section 5.0, Overall Structural Response, of the TR states:

The test results show that the outer circumferential rebar maintains its full design capacity with the presence of laminar cracks with widths up to 0.050 [inches].

Additionally, review of the load-deflection behavior of the specimens in all three test programs does not indicate any significant change in the reloading stiffness of specimens after introduction of the laminar cracks with widths exceeding 0.050 [inches].

The controlling load combinations for the design of the Shield Building involve the design basis safe shutdown earthquake, for which the Shield Building will behave like a cantilever where most of the forces are transferred through in-plane shear and axial membrane forces and very little through out-of-plane bending of the shell. The laminar cracking has no impact on in-plane stiffness of the cylindrical shell, which will resist most of the applicable seismic loads. For thermal and tornado loads that produce hoop tension and moment, the existence of laminar cracking does not change the concrete section behavior since the concrete shell is already assumed to be cracked through-thickness. The applicable tension forces are primarily resisted by the hoop reinforcement, which are able to maintain their design function with crack widths up to 0.050 [inches]

per the testing. Therefore, it is concluded that no changes need to be made to the analytical model in order to account for the effect of laminar cracking on stiffness of the Shield Building.

Based on above discussion, it can be safely concluded that the effect of laminar cracking on the overall stiffness, dynamic characteristics and performance of the Shield Building is negligible.

Long-Term Durability The TR states that the service life of the Davis-Besse shield building can be affected by the nature, extent, and width of cracking present on the surface of the building that may provide a path for moisture penetration resulting in rebar corrosion. The monitoring program has found indications of rebar corrosion at the locations of maximum laminar crack widths. To address this, the TR states that a repair program has been implemented at Davis-Besse. The repair program requires the removal and replacement of concrete in areas of cracking exceeding 0.050 inches in width, with or without signs of corrosion. The repair program involves the chipping of concrete and rebar removal/replacement (as required) to a larger extent than depicted in the latest IR scans. Additionally, a passive cathodic protection program is implemented to mitigate and prevent rebar corrosion after a repair is completed. The TR states that the periodic monitoring program will continue to verify that the implemented measures are effective in ensuring that there is no further rebar corrosion and that there are no pathways for moisture infiltration. Therefore, the TR concludes that the long-term durability of the shield building is not adversely affected with laminar crack widths of up to 0.050 inches.

3.2 NRC Staff Evaluation The Davis-Besse shield building is a nuclear safety-related, seismic Class 1 structure important to safety and designed to remain functional in the event of a safe shutdown earthquake. The original analysis and design of the shield building did not consider laminar cracks in the wall of the shield building. Therefore, it is necessary for the licensee to ensure that the original design basis strength and stiffness for the shield building is still valid with the presence of laminar cracks in the wall. It is also necessary for the licensee to ensure the long-term durability of the shield building because the laminar cracks may provide a path for moisture to penetrate to the steel reinforcing bars and cause corrosion. Finally, in order to support the licensees assurances, the design and test controls for the test program conducted to support the Davis-Besse shield building design-basis change must meet the NRCs QA requirements, as applicable.

3.2.1 Strength of the Shield Building The Davis-Besse shield building is a reinforced concrete structure. The design uses steel reinforcing bars to take the tensile stress and concrete to take the compressive stress for all sections of the building. The design basis for steel rebar is the available stress value at the steel yielding point; the design basis for concrete is its compressive strength. Due to construction necessity, steel reinforcing bars are required to lap together (splice) at some locations to provide continuity of force transfer from one bar to the next spliced bar through the concrete bond within the length of the splice. However, if the splice length is too short, full transfer of force from one bar to the next spliced bar may not be possible. If the laminar cracks were to occur at or near the splice location, the strength of the concrete bond may be degraded and unable to transfer the full force from one bar to the next spliced bar.

For the test programs discussed above, the reinforcement design for the test girders was conservative for the purpose of the testing when compared to the Davis-Besse shield building reinforcement details. The concrete compressive strengths for the test girders was lower than the compressive strength of the concrete in the Davis-Besse shield building wall. It has been established through testing that the bond strength of concrete is proportional to the compressive strength of the concrete. This means that the concrete bond strength of the test girders was less than the concrete bond strength of the Davis-Besse shield building. Therefore, the NRC staff finds the design of the Phase I, II, and III test programs to be acceptable because the test specimens used a conservative concrete compressive strength and reinforcement design.

The NRC staff reviewed the test data on the reinforcement stress attained at the splice ends when the splice failed. For the Phase I test program, the maximum reinforcement stress attained at the ends of the 120-inch splices (girders A1 through A6) ranged from 77 to 80 ksi, and the maximum reinforcement stress attained at the ends of the 79-inch splices (girders B1 through B6) ranged from 69 to 72 ksi. These results are all greater than the 66 ksi yield stress of the steel rebar used in the Phase I test program. For the Phase II test program, stresses developed in the reinforcement at the ends of the 79-inch splices ranged from 73 to 75 ksi in the six test girders. These results were also all greater than the 65 ksi yield stress of the steel rebar used in the Phase II test program. The NRC staff noted that all test specimens demonstrated a definite capability to maintain strength with increase in deflection beyond yield. In addition, the strength of the test specimens did not vary significantly with the maximum load applied during the initial loading. For the Phase III test program, the test results indicate that if the existing laminar crack does not exceed 0.050 inches, then the splices of three test girders developed a minimum tensile stress of 67 ksi and a maximum tensile stress of 80 ksi. The yield stress of the steel rebar used in the Phase III test program was 67 ksi.

Based on the test results for the 21 girders, the NRC staff determined that the yield stress of the reinforcing bars in the outer reinforcement layer of the Davis-Besse shield building could be fully transferred from one bar to the next spliced bar if the laminar concrete crack width does not exceed 0.050 inches. Since the test design was conservative with respect to the Davis-Besse shield building and since the test results indicate that laminar cracks less than 0.050 inches in width do not impact rebar strength, the NRC staff finds that the strength of the shield building will be maintained if laminar concrete cracking in the outer reinforcement layer does not exceed 0.050 inches in width.

3.2.2 Stiffness of the Shield Building The NRC staff reviewed the Phase I test program data on the measured load-deflection relationships at mid-span of the 12 test girders. The NRC staff found that the overall behavior of test girders A1, A4, A5, and A6 that were loaded, unloaded, and reloaded to failure differed very little from those of A2 and A3 that were continuously loaded to failure (see TR figure 7). The NRC staff also found that the overall behavior of test girders B2, B3, B5, and B6 that were loaded, unloaded, and reloaded to failure differed very little from those of B1 and B4 that were continuously loaded to failure (see TR figure 8). Differences between the load-deflection responses of initially uncracked and pre-cracked girders were found to be negligible. The NRC staff noted that this implies that the stiffness of the specimens and, therefore, the Davis-Besse shield building were not adversely affected by the laminar cracks with widths on the order of 0.010 inches.

The NRC staff also reviewed the Phase II test program data on the measured load-deflection relationships at mid-span of the six test girders (see TR figure 14). For the Phase II test program, four test girders were loaded to a deflection of 0.4 inches and two test girders were loaded to a deflection of 0.5 inches during the initial loading. This amount of deflection was beyond the steel yielding. The girders loaded to a deflection of 0.5 inches had laminar crack widths greater than that of girders with the initial deflection at 0.4 inches. The test girders were then unloaded and then loaded to failure. The NRC staff noted that the combined test data on the measured load-deflection relationships at mid-span of these test girders are almost the same regardless of the initial load deflection. This means that the stiffness behavior of the test specimens is independent of the maximum crack widths generated in the initial loading and unloading, which implies that the stiffness of the Davis-Besse shield building is not adversely affected by the laminar crack widths even beyond steel yielding. Therefore, the NRC staff finds that laminar concrete cracking in the outer reinforcement layer of the shield building with crack widths up to 0.050 inches will have a negligible effect on the stiffness of the shield building.

3.2.3 Long-Term Durability of the Shield Building The Davis-Besse shield building monitoring program is described in section 18.1.43 (ML20302A313) of the Davis-Besse UFSAR, Revision 33. The LAR states that this program monitors for extent and width of concrete cracking, as well as visible change of material properties and loss of material for both concrete and rebar in areas of laminar concrete cracking. The licensee stated that the shield building monitoring program has found evidence of rebar corrosion at the locations of maximum laminar crack widths. To address this, the licensee stated that a repair program has been implemented, which requires the removal and replacement of concrete in areas of cracking exceeding 0.050 inches regardless of indications of corrosion. The repair program involves the chipping of concrete and rebar removal/replacement (as required) to a larger extent than depicted in the latest IR scans.

Additionally, a passive cathodic protection program is implemented to mitigate and prevent rebar corrosion after a repair is completed. As part of its LAR, the licensee proposed to revise the UFSAR to state that laminar cracking greater that 0.050 inches in width is to be repaired.

Based on the above, the NRC staff finds that the shield building monitoring program will continue to verify that the implemented measures are effective in ensuring that there is no further rebar corrosion and that there are no pathways for moisture infiltration. The NRC staff also finds that the licensees monitoring and repair programs described in the LAR and the UFSAR, as amended, provide reasonable assurance that the licensee will ensure the long-term durability of the Davis-Besse shield building, and that the shield building will not be adversely affected by laminar cracking in the outer reinforcement layer with crack widths up to 0.050 inches.

3.2.4 Quality Assurance The NRC staff reviewed the information in the LAR, as supplemented, regarding the QA activities associated with the test program conducted to support the Davis-Besse shield building design-basis change. Specifically, the NRC staff focused on the measures used to verify the adequacy of the design inputs and testing, which are described in the appendices to the TR for each phase of the test program. In addition, the supplemental letter dated May 12, 2022, states, in part, that:

Phase I and II were performed under Bechtel Quality Assurance/Quality Control (QA/QC) oversight under their 10 CFR 50, Appendix B program. This included

subject matter expert review and approval of test procedures, calibration/

certification of equipment, verification of materials (Certified Mill Test Reports and Concrete Mix documentation), and post-testing evaluation. Phase III provided similar verification measures, but as it was exploratory/non-safety, full QA/QC requirements were not required. However, based on the measures taken and the consistency of results, the Phase III was included as alternate and confirmatory test data.

The NRC staff has previously found that Bechtels QA program meets 10 CFR part 50, appendix B. Based on the review of the QA information in the TR and the supplemental letter dated May 12, 2022, the NRC staff found that design control measures to verify or check the adequacy of design inputs were provided and that test controls were in place to ensure that all required testing was performed to demonstrate that the shield building will perform satisfactorily in service. Therefore, the NRC staff has reasonable assurance that the design and test controls for the test program conducted to support the Davis-Besse shield building design-basis change met Criteria III and XI of 10 CFR part 50, appendix B, as applicable.

3.2.5 Technical Conclusion The licensee proposed, in part, to revise the Davis-Besse UFSAR to state that: The Shield Building is to be analyzed per licensing and design basis codes (ACI 318-63 and 307-69) and methodology without the need to explicitly consider laminar cracking up to 0.050 [inches] in the analysis. Laminar cracking greater than 0.050 [inches] is to be repaired. As discussed above, the NRC staff found that the strength and stiffness of the shield building will be maintained if laminar concrete cracking in the outer reinforcement layer does not exceed 0.050 inches in width. The NRC staff also found that the licensees monitoring and repair programs provide reasonable assurance that the licensee will ensure the long-term durability of the shield building.

Finally, the NRC staff found that the design and test controls for the test program conducted to support the Davis-Besse shield building design-basis change meet the NRCs QA requirements, as applicable.

Based on these findings, the NRC staff determined that the capability of the shield building design to withstand the effects of natural phenomena and to accommodate the effects of and to be compatible with the environmental conditions would not be affected. In addition, the NRC staff determined that SSCs important to safety, including the shield building, would continue to be adequately protected against dynamic effects that may result from equipment failures and from events and conditions outside the nuclear power unit. Therefore, the NRC staff concludes that GDC 1, 2, and 4 would continue to be satisfied with the proposed changes to the shield building design basis.

4.0 STATE CONSULTATION

In accordance with the Commissions regulations, the Ohio State official was notified on September 26, 2022, of the proposed issuance of the amendment. The State official had no comments.

5.0 ENVIRONMENTAL CONSIDERATION

The amendment changes requirements with respect to the installation or use of facility components located within the restricted area as defined in 10 CFR part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts and no

significant change in the types of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding, which was published in the Federal Register on March 22, 2022 (87 FR 16252), that the amendment involves no significant hazards consideration, and there has been no public comment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

6.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) there is reasonable assurance that such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributors: John Ma, NRR Frankie Vega, NRR Date: October 14, 2022

ML22277A601 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/ESEB/B(A)

NAME BPurnell SRohrer BLehman DATE 10/5/22 10/5/22 9/21/22 OFFICE NRR/DRO/IQVB/BC OGC - NLO NRR/DORL/LPL3/BC NAME KKavanagh JWachutka NSalgado (RKuntz for)

DATE 6/6/22 10/12/22 10/14/22 OFFICE NRR/DORL/LPL3/PM NAME BPurnell DATE 10/14/22