ML071720186

Enclosure 2 Technical Evaluation Report on the Seismic Portion of Browns Ferry Nuclear Plant Unit 1 Individual Plant Examination for External Events

ML071720186
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Site:	Browns Ferry
Issue date:	03/31/2006
From:	Chang T NRC/RES/DFERR/DDERA/MSEB
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Brown Eva, NRR/DORL, 415-2315
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TECHNICAL EVALUATION REPORT ON THE SEISMIC PORTION OF THE BROWNS FERRY NUCLEAR PLANT UNIT 1 INDIVIDUAL PLANT EXAMINATION FOR EXTERNAL EVENTS March 2006 T. Y. Chang Mechanical and Structural Engineering Branch Division of Fuel, Engineering and Radiological Research Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Enclosure 2

1.0 INTRODUCTION

1.1 Purpose In the Commission policy statement on severe accidents in nuclear power plants issued in 1985, the U.S. Nuclear Regulatory Commission (NRC) concluded, based on available information, that existing plants pose no undue risk to the public health and safety and that there is no present basis for immediate action on any regulatory requirements for these plants.

However, the NRC recognized that systematic examinations are beneficial in identifying plant-specific vulnerabilities to severe accidents that could be fixed with low-cost improvements. In 1988, with Generic Letter (GL) 88-20, Individual Plant Examination for Severe Accident Vulnerabilities, the NRC requested that each licensee conduct an individual plant examination (IPE) for internally initiated events including internal flooding. Many Probabilistic Risk Assessments (PRAs) performed in support of the IPEs indicated that, in some instances, the risk from external events could contribute significantly to core damage.

The NRC issued Supplement 4 to GL 88-20, Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities (Reference 1) in April 1991. The supplement requested all licensees to address five external events: seismic events, internal fires, high winds, external flooding, and transportation and nearby facilities accidents. Acceptable methodologies for performing the IPEEE are summarized in NUREG-1407, Procedural and submittal Guidance for the Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities (Reference 2). The objectives of the IPEEE are for each licensee: (1) to develop an appreciation of severe accident behavior; (2) to understand the most likely severe accident sequences that could occur at the licensees plant under full power operating conditions; (3) to gain a qualitative understanding of the overall likelihood of core damage and fission product releases, and (4) if necessary, to reduce the overall likelihood of core damage and radioactive material releases by modifying, where appropriate, hardware and procedures that would help prevent or mitigate severe accidents.

This Technical Evaluation Report documents the result of the NRC staff evaluation of the seismic portion of the IPEEE for Browns Ferry Nuclear Plant Unit 1 (BFN1) submitted by the licensee Tennessee Valley Authority (TVA).

1.2 Background The Browns Ferry Nuclear Plant (BFN) consists of three General Electric (GE) boiling water reactors (BWRs) of the type of BWR/4 and with Mark I containments, each has an electrical output of about 1,100 megawatts. Commercial operation of BFN1 began on August 1, 1974, BFN2 on March 1, 1975, and BFN3 on March 1, 1977. The Browns Ferry site is located on the north shore of Wheeler Lake at river mile 294 in Limestone County in north Alabama. The site is approximately 10 miles southwest of Athens, Alabama, and 10 miles northwest of the center of Decatur, Alabama. For the Browns Ferry project, TVA acts as its own engineer-constructor.

GE designed, fabricated, and supplied the nuclear steam supply system (NSSS) and nuclear fuel for the plant, as well as the turbine generators. GE also provided technical supervision for the installation and startup services of these equipment.

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The Design Basis Earthquake (DBE) of BFN, i.e., the seismic licensing basis for BFN, is defined as follows. The site DBE design ground spectrum is represented by a Housner shaped spectrum anchored to 0.20g Peak Ground Acceleration (PGA). The horizontal PGA corresponds to a value of 0.20g defined at the top of sound rock, whereas the vertical ground motion is defined as two-thirds of the horizontal ground motion. The Operating Basis Earthquake is defined as one-half of the DBE in both the horizontal and vertical directions. All three units of BFN are designated as 0.30g PGA Focused Scope Plants in NUREG-1407 for seismic IPEEE.

For BFN, the response from the TVA to supplement 4 of GL 88-20 came in several parts submitted at different times. Internal fire for BFN2, together with high winds, floods, transportation and other external events for BFN1, BFN2, and BFN3, were submitted to the NRC on July 24, 1995. Subsequently, seismic portion for BFN2 and BFN3 was submitted on July 28, 1996. And finally, internal fire for BFN3 was submitted on July 11, 1997. These submittals have been reviewed by the NRC staff (the staff), and a Staff Evaluation Report (SER) was issued on June 22, 2000. However, because BFN1 has been shut down since March 19, 1985, TVA has identified the seismic and fire portion of the BFN1 IPEEE as a restart issue for BFN1, and they are being handled separately from the IPEEE for BFN2 and BFN3.

The TVA submitted seismic and internal fire IPEEE for BFN1 to the NRC on January 14, 2005 (Reference 3). The staff performed a screening review of the IPEEE submittal to assess the adequacy of information needed. As a result of this review, a Request for Additional Information (RAI) was sent from the staff to the TVA. TVAs response to this RAI was submitted to the NRC on February 2, 2006 (Reference 4). The original submittal of reference 3 provided BFN1 Seismic IPEEE Report as Enclosure 1 (Reference 5) for the seismic IPEEE review. In response to staffs RAI No. 1, TVA also provided in reference 4 additional seismic information needed for BFN1 seismic IPEEE review, which includes: (1) Calculation of Basic Parameters for A46 and Individual Plant Examination of External Events (IPEEE) Seismic Program (Reference 6), (2) Browns Ferry Nuclear Plant Unit 1 USI A-46 Seismic Evaluation Report (Reference 7), (3) USI A-46/Seismic IPEEE Relay Evaluation, Browns Ferry Nuclear Plant Unit 1 (Reference 8), and (4) Seismic-Induced II/I Spray Evaluations at Browns Ferry Nuclear Plant Unit 1 (Reference 9). In addition, in response to the staffs RAI, TVA provided two samples of the High Confidence of Low Probability of Failure (HCLPF) calculation for equipment not screened out (References 10 and 11). This Technical Evaluation Report (TER) documents the result of the NRC staffs technical evaluation of the seismic portion of References 3 and 4, as well as References 5 to 11.

1.3 Licensees IPEEE Process and Licensees Insights Licensees IPEEE Process NUREG 1407 (Reference 2) stated that for seismic IPEEE, the evaluation may be conducted by performing a seismic PRA or a Seismic Margins Assessment (SMA). TVA chose the SMA method proposed by the Electric Power Research Institute (EPRI), as documented in EPRI NP-6041 (Reference 12) for BFN1 seismic IPEEE. The SMA method was designed to demonstrate sufficient margin over the Safe Shutdown Earthquake (SSE) to ensure plant safety and to find any weak link that might limit the plant shutdown capacity to safely withstand a seismic event larger than the SSE or lead to seismically induced core damage.

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Detailed Seismic Review Team (SRT) walkdowns for IPEEE were performed in conjunction with the walkdowns for Unresolved Safety Issue (USI) A-46, Verification of Seismic Adequacy of Equipment in Operating Plants. The walkdowns used the methodology, criteria, and Screening Evaluation Work Sheet (SEWS) documentation forms provided in EPRI NP-6041 and the Generic Implementation Procedure (GIP) developed by the Seismic Qualification Group (SQUG), with enhancement based on EPRI NP-6041.

The SRT identified issues related to anchorage design, maintenance, housekeeping, and seismic interaction that required design change notices (DCNs) or work orders to satisfy SRT field issues. These items will be resolved as part of the USI A-46 program. Several components not screened out were identified for subsequent High Confidence of Low Probability of Failure (HCLPF) evaluation.

The BFN1 SMA was performed following the same approach as used for the BFN2 and BFN3 seismic IPEEE programs. Common system components and BFN1 components that were included in the BFN2 and BFN3 seismic IPEEE programs were re-evaluated only if the item of equipment is located inside of the BFN1 Reactor Building. Other components previously addressed in the BFN2 and BFN3 programs (such as items in the Diesel Generator Buildings and the Intake Pumping Station) were not re-evaluated.

Relay evaluation for BFN1 followed the methodology recommended in the GIP.

Seismic-induced-flooding evaluations were performed based on the results of a recently-completed seismic II/I spray program implemented as part of the BFN1 Restart project.

Specific seismic-induced fire walkdown evaluations were performed as part of the BFN1 SMA.

The BFN1 USI A-46 resolution program is documented in References 7 and 8 for the equipment and relay reviews, respectively. Certain items of equipment were identified as outliers in the USI A-46 program, and the outlier resolution activity for some of these outliers involves work orders and design change notices (DCNs). The BFN1 seismic IPEEE program takes credit for these outlier resolution modifications.

In response to RAI No. 3, which questioned how is the Restart Project seismic review coordinated with the seismic IPEEE/USI A-46 review, TVA responded that the USI A-46 and seismic IPEEE reviews were conducted in parallel with the other ongoing design basis verification programs prior to restart. As a result of performing the USI A-46 and seismic IPEEE reviews in parallel with these other programs, final verification for certain items of equipment was not possible due to ongoing work associated with open Design Change Notice (DCN) packages. To enable final verification, a Punch List was developed to track each item of equipment requiring final verification. The Punch List is documented in Appendix H of Reference 7.

In addition, as documented in a letter from TVA to the NRC dated October 7, 2004, there are two regulatory commitments associated with the USI A-46 reviews:

1. BFN1 USI A-46 outliers will be resolved prior to restart of BFN1.

2. TVA will complete the operations review of the BFN1 USI A-46 verification following BFN1 procedural development and approval, and notify the NRC of the results of that review prior to 3

restart of BFN1.

Licensees Insight

1. Detailed plant walkdowns are considered by TVA as the most-effective and beneficial aspect of the SMA program.

2. For equipment and components not screened out, HCLPF calculations were performed.

None of these equipment and components have HCLPF capacities below 0.30g.

3. One potential seismic-induced fire hazard was identified during the walkdowns. This consisted of unrestrained batteries on the emergency lighting system battery rack in the BFN1 cable spreading room. The batteries lacked end restraints, side restraints, and spacers between the batteries. The concern was that the batteries could fall from the rack during an earthquake and cause sparks. This situation was corrected by using the TVA Problem Evaluation Report (PER) process. PER No. 64143 was issued to address and correct the condition.

4. No low ruggedness relays and no outliers were identified during the relay evaluation.

5. The seismic IPEEE evaluation concluded that BFN1 HCLPF is at least as great as the 0.30g review level earthquake defined as an earthquake having a response spectrum that matches the median (50% Non Exceedance Probability) CR-0098 spectral shape anchored to a peak ground acceleration of 0.30g.

2.0 REVIEW FINDINGS 2.1 IPEEE Format and Methodology Documentation The IPEEE submittal for BFN1 does not follow the format requested in NUREG-1407. The documentation of methodology generally addresses all of the elements of the seismic IPEEE; however, very little detail is provided. Because of the lack of detail, ten RAIs were sent to the TVA to obtain sufficient additional information to complete the review.

Key information relating to development of the review level earthquake (RLE) seismic demand is contained in TVAs responses to the RAI, Calculation of Basic Parameters for A46 and Individual Plant Examination of External Events (IPEEE) Seismic Program (Reference 6). The submittal did not identify any references for details of the HCLPF capacity calculations. The appropriate documentation of HCLPF capacity calculations was provided by TVA in response to RAI No. 8.

2.2 Seismic Review Team (SRT) Selection and Peer Review The SRT is discussed in Section 5.1. The SRT was comprised of TVA personnel and personnel from Facility Risk Consultants, Inc. and other individual consultants. Each walkdown team included a minimum of two Seismic Capability Engineers (SCEs) members who had completed the Seismic Qualification Utility Group (SQUG) Walkdown Screening and Seismic 4

Evaluation training course. In addition, some members also attended the seismic IPEEE training course. SRT qualifications are included as Appendix A to the submittal.

Peer review was not discussed in the submittal. In response to the staff RAI No. 7, TVA provided information on the peer review as follows:

The BFN Unit 1 seismic IPEEE was peer reviewed by Dr. James J. Johnson in conjunction with his peer review of the BFN1 USI A-46 program as documented in Chapter 6 and Appendix G of Browns Ferry Nuclear Plant Unit 1 USI A-46 Seismic Evaluation Report, Rev. 0, dated September 2004 (note from the NRC staff: this is Reference 7 of this Technical Evaluation Report).

The Peer review included the safe shutdown equipment selection, cable tray and conduit raceways, mechanical and electrical equipment for A-46 and seismic IPEEE as an integrated implementation program, and High Confidence of Low Probability of Failure (HCLPF) capacity determination. The scope of the peer review focused on those aspects of the seismic IPEEE program not reviewed previously for the integrated program, and involved in-plant observation, walkdown documentation, and HCLPF calculations for selected components and plant features.

The peer review concluded that The approach and result are consistent with the EPRI NP-6041 and acceptable in response to the NRC Supplement 4 to Generic Letter 88-20 for BFN Unit 1. No major comments were identified in this peer review. Some clarifications were provided by the Seismic Capability Engineers as to the precise meaning of selected sections of the summary report, thereby reaching concurrences on these issues.

The staff judged that the SRT selection and peer review reasonable.

2.3 Seismic Input The seismic input for IPEEE is discussed in Section 4 of the submittal, entitled Seismic Margin Earthquake Demand. The licensee stated that In-structure response spectra (IRS) corresponding to the Review Level Earthquake (RLE) are required for the Seismic Margin Assessment (SMA). For Browns Ferry, the RLE is defined as an earthquake having a response spectrum that matches the median CR-0098 spectral shape anchored to a peak ground acceleration of 0.30g. The IRS for the reactor building, diesel generator building and intake pumping station were obtained from the A-46 spectra using scaling procedures, following the recommendations given in EPRI NP-6041. The details of this scaling are discussed in Section 4.2 of the submittal.

The staff reviewed this Section 4.2 of the submittal and the methodology utilized for scaling appears to be consistent with the recommendation given in EPRI NP-6041 and therefore is judged reasonable.

In RAI No. 2, the staff asked TVA to provide a graph of the RLE spectra used for the SMA. On the same graph also provide the site DBE ground spectra (Housner spectra with 0.20g PGA),

and the USI A-46 spectra. Discuss whether there is any exceedance of DBE or USI A-46 5

spectra over the RLE spectra in the frequency range of interest for BFN Unit 1 systems, structures, and components (SSCs). TVA in return provided information for RAI No. 2. The graphs in the TVA response showed that the IPEEE ground motion response spectrum fully envelopes the DBE ground motion response spectrum. The SQUG GIP Bounding Spectrum was also shown for information. The SQUG GIP Bounding Spectrum fully envelopes both the DBE and the IPEEE spectra.

The staff considers the TVA response to RAI No. 2 reasonable.

2.4 Success Path Selection and Safe Shutdown Equipment List (SSEL)

System Description and Success Path Selection is discussed in Section 3 of the submittal. The discussion is very brief. RAI No. 5 raised two questions on this Section: (1) For the current BFN1 seismic IPEEE, did TVA prepare separate Success Path Logic Diagrams (SPLDs) and Seismic Safe Shutdown Equipment Lists (SSELs) for BFN1 apart from those for BFN2 and BFN3? BFN1 should have its own set of SSELs that are basically different from those for BFN2 and BFN3. If there is common equipment that appears on BFN1 and BFN2 and BFN3, please identify, and (2) Please confirm whether the following function/system match-up for BFN2 and BFN3 also applies for BFN1:The frontline systems selected to achieve the four shutdown functions are: a) control rod drive system (CRD) for reactivity control, b) safety/relief valves (SRVs) for reactor pressure control, c) core spray (CS) and low pressure coolant injection (LPCI) mode of residual heat removal system (RHR) (with reactor pressure vessel depressurization using SRVs) for reactor coolant inventory control, and d) suppression pool cooling mode of RHR for decay heat removal.

TVA in response confirmed that item (2) above is indeed the case. As for item (1), separate SPLDs and SSELs were prepared for BFN1. The SPLDs for BFN1 are the same as those constructed for BFN2 and BFN3. The BFN1 USI A-46 SSEL was expanded to include the additional items of equipment that are evaluated for seismic IPEEE. This includes the items of equipment necessary for primary containment isolation and small LOCA mitigation. There are items of common equipment that appear on BFN1 and BFN2 and BFN3. Appendix B of Browns Ferry Nuclear Plant Unit 1 USI A-46 Seismic Evaluation Report (note from the NRC staff: this is Reference 7 of this Technical Evaluation Report) provides the composite SSEL for BFN1. Common equipment items (also on BFN2 and BFN3 SSEL) are identified with an asterisk following the SSEL number in the 1st column of the IPEEE components are identified with an I entry in the 8th column of the Table (Issue).

The staff reviewed this TVA response and also Appendix B of Reference 7 to this report, and noted that there are a total of 52 components that are categorized as IPEEE components. The staff considers the TVA response to RAI No. 5 reasonable.

However, the staff noted that although the selected equipment in the SSEL seems to provide two success paths for a safe shutdown for both transient and small LOCA conditions, the lack of inclusion of any HPI system (which is the system that responds to an accident condition without any operator intervention), the use of a single train of a system for a success path, and the lack of inclusion of the automatic initiation circuitries for the low pressure systems in the SSEL raise some reliability issues. This selection of success path is judged as a weakness by 6

the staff. The related nonseismic failure and human action issues are discussed in more detail in Section 10.2 of this technical evaluation report.

2.5 Plant Walkdown Approach The plant walkdown approach is described in Sections 5.2, 5.3, and 5.4 of the submittal. The information provided is reasonably comprehensive. Walkdown preparation, pre-screening, screening criteria, and seismic IPEEE walkdowns are addressed. A combined A-46/IPEEE walkdown was conducted following the procedures of the SQUG GIP supplemented by EPRI NP-6041 and NUREG-1407. Screening criteria from Table 2-3 and Table 2-4, and supplemented by Appendix A, of EPRI NP-6041 for 5% damped peak spectral acceleration less than 0.80g were used for BFN1 on the RLE. Walkdown data sheets from the SQUG GIP augmented to include additional review per EPRI NP-6041 were used during the SRT walkdowns.

The walkdowns concentrated on the strength and load path of the equipment as well as function and integrity. The review of equipment anchorage was a prime objective for the walkdown teams. The anchorage evaluation addressed both physical attributes of the anchorage installation and the capacity relative to other success path items as well as the postulated demand at the RLE. The SRT walkdowns also included physical interaction reviews.

The seismic-induced spray program was performed separately, on an area-by-area basis, as part of the BFN1 Restart Project. After the equipment walkdowns were completed, an additional focused seismic-induced fire walkdown was performed on a area-by-area basis.

Suspended systems (conduit, cable trays, ductwork were walked down separately from the seismic IPEEE walkdowns, as part of USI A-46 the BFN1 Restart Project. The control room ceiling was reviewed to identify potential interaction due to falling light fixtures and ceiling panels. To address containment performance, containment penetrations were reviewed and containment isolation valves were added to the SSEL.

Following the completion of the plant A-46/IPEEE walkdowns, SRT members reviewed and categorized components into the following resolution categories:

• Screened out by the SRT based on Table 2-4 of EPRI NP-6041 or A-46 evaluations with factor of safety greater than 2

• Screened out pending resolution of A-46 outliers

• Candidate for HCLPF evaluation identified during walkdown The staff finds the plant walkdown approach for BFN1 complies with those discussed in NUREG-1407 and therefore reasonable.

2.6 Structural Analysis and HCLPF Calculation 2.6.1 Structural Analysis and In-Structure Response Spectra In-Structural Response Spectra (IRS) for the reactor building (RB), diesel generator building (DGB) and intake pumping station (IPS) were obtained from the A-46 spectra using scaling procedures, following the recommendations given in EPRI NP-6041. The procedure used to 7

generate the IRS is described briefly in the submittal. The complete treatment of the subject is presented in Calculation of Basic Parameters for A46 and Individual Plant Examination of External Events (IPEEE) Seismic Program (Reference 6).

The dominant mode scaling procedure described in EPRI NP-6041 is used for BFN1, since the input motion spectra for the A-46 and IPEEE have similar shapes over the relevant range of frequencies. The procedure uses a scale factor for the spectral amplitude change when the input motion is changed.

The predominant frequency of the soil-structure system was estimated as the frequency corresponding to the peak spectral acceleration in the A-46 in-structure response spectra. The damping for the SMA RLE was taken as 7% for the reinforced concrete structures at RB and DGB, and 5% for IPS. The level of damping was estimated as the sum of two parts: (1) damping of 5% for structures founded on rock such as RB and IPS, assuming the structure is not highly stressed at the RLE, and (2) 2% additional damping to reflect the material and radiation damping of the soil for soil-supported structures such as DGB. A damping value of 7% was assumed for RB based on the estimated stress state of the structure at the RLE.

The vertical input ground motion specified for seismic IPEEE is defined as two-thirds of the horizontal motion. Since the vertical A-46 IRS is also defined as two-thirds of the horizontal spectra, the scale factors used to obtain the vertical SMA IRS are the same as for the horizontal case.

The staff judged the BFN1's structural analysis and IRS reasonable.

2.6.2 SSEL HCLPF Calculations Determination of HCLPF capacities is addressed in Sections 5.4 through 5.9 and 6.1 through 6.9 of the submittal. As a result of the screening process, items were selected for HCLPF evaluation. A summary of this screening is presented in Table 6-1 of the submittal. A total of 90 equipment components are addressed in the HCLPF capacity evaluation calculations.

These items identified for HCLPF evaluation were grouped into the following seven categories based on similarity of the equipment and identified controlling failure mode:

Group 1: Anchorage of motor control centers Group 2: Anchorage of instrument racks Group 3: Anchorage of instrumentation/control panels and cabinets Group 4: Anchorage of main control room cabinets Group 5: Anchorage of residual heat removal and containment spray pumps Group 6: Anchorage of residual heat removal heat exchangers Group 7: Anchorage of remote control cabinets The HCLPF capacity evaluations for other categories of equipment such as transformers, low voltage switchgear, battery racks, battery chargers, and the residual heat removal service water pumps were performed under BFN2 and BFN3 seismic IPEEE programs. The SRT reviewed these calculations and concurred with the conclusions that HCLPFs are greater than 0.3g, so no new HCLPF capacity evaluations were performed for these categories of equipment.

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TVA has not discovered any components in BFN1 that have HCLPF capacities below 0.3g.

The staff in RAI No. 8 requested and received copies of HCLPF calculations for MCC (ID No. 1-BDBB-281-0001A) and residual heat removal heat exchanger (ID No. 1-HEX-74-900A). The calculations appear to be reasonable.

In RAI No. 8, ths staff also stated that Flat bottom tanks were identified in many previous seismic IPEEE reviews as components with potential low HCLPFs, but the submittal has no discussion on this. Was the condensate storage tank included in the SSEL? If the condensate tank was not included, please explain why.

TVA responded that the condensate tank was not included in the SSEL. The reactor decay heat removal function is accomplished by relieving steam from the reactor via the lifting of the main steam safety/relief valves (MSRVs) at their respective set points into the suppression pool. The MSRVs could be manually operated by the control room operator to lower reactor pressure so that the low pressure coolant injection (LPCI) mode of residual hear removal (RHR) could be initiated for reactor coolant inventory control. In this mode, the LPCI takes suction from the suppression pool. The decay heat removal would be achieved by placing the RHR system in the suppression pool cooling (SPC) mode of operation. During the SPC mode of RHR, the RHR pump takes suction from and discharges to the suppression pool via the RHR heat exchangers. The service water system would provide the capability to transfer the decay heat from the RHR system to the ultimate heat sink.

The staff finds the explanation to RAI No. 8 reasonable. The condensate storage tank is not included in the SSEL because the high pressure injection (HPI) systems (which include the high pressure coolant injection (HPCI) system and the reactor core isolation cooling (RCIC) system) are not chosen as part of the success path. Both HPCI and RCIC systems initially take water from the condensate storage tank. However, as mentioned at the end of Section 2.4 of this technical evaluation report, the lack of inclusion of any HPI system (which is the system that responds to an accident condition without any operator intervention), the use of a single train of a system for a success path, and the lack of inclusion of the automatic initiation circuitries for the low pressure systems in the SSEL raise some reliability issues. This selection of success path is judged to be a weakness by the staff.

2.7 Soil Evaluation No soil evaluation was conducted for BFN1 because supplement 5 to GL 88-20 removed soil evaluation from the IPEEE scope for most plants.

2.8 Relay Chatter Evaluation Relay chatter evaluation is addressed in Section 7 of the submittal. BFN is identified as a focused scope plant for the 0.30g earthquake by NRC GL 88-20, Supplement 4. NUREG-1407 requests that focused scope plants which are also included as an USI A-46 plant should follow the USI A-46 procedures for relay review of A-46 equipment. If low ruggedness relays are identified during the A-46 review, then an additional low ruggedness relay review should also be performed for IPEEE-only equipment. The EPRI NP-7148-SL (Reference 13) methodology was 9

used in performing BFN1 relay evaluation. In general, the methodology consists of the following steps:

1. Examine the control circuits for the safe shutdown system components.

2. Screen out non-essential relays using systems and circuit evaluation techniques. Also screen out contact devices such as large switches, which are considered not vulnerable to seismic motion and relays considered inherently rugged such as solid state relays.

3. Assess the seismic adequacy of the remaining essential relays.

4. Provide a traceable documentation of the evaluation.

5. For IPEEE additional components, perform a bad actors relay review.

Essential relays and the cabinets housing those essential relays were identified for the seismic capability engineers performing the seismic verification walkdowns and evaluations. The SRT determined in-cabinet amplification factors for use in the relay capacity versus demand screening. The SRT also took appropriate cautions and factors of safety into consideration when evaluating the cabinets housing the essential relays. The cabinets were determined to be acceptable and no modifications were required. Certain additional special evaluation methods were utilized for BFN1. BFN1 equipment common to BFN2 or BFN3 which was evaluated in the prior review for those units, are not reevaluated.

The lead relay chatter reviewer for BFN1 is Mr. Jess Betlack, he was the primary developer of the relay review guidelines for both USI A-46 resolution and seismic IPEEE. The relay chatter evaluation findings were summarized by TVA in the submittal as follows:

• Inherent ruggedness of contact devices, chatter acceptability and seismic adequacy were sufficient to satisfactorily resolve the seismic acceptability of contact devices affecting the USI A-46 Safe Shutdown Equipment List (SSEL) components.

• No outliers were identified in the evaluation.

• No essential relays were found to be low ruggedness (bad actor) relays.

• No operator actions were identified in the evaluation as necessary to correct relay-chatter-caused malfunctions.

• Based on the result of the relay review, BFN1 relays can be assigned a HCLPF capacity exceeding 0.30g.

The staff considers TVAs relay chatter review reasonable.

2.9 Containment Performance Containment performance is discussed in Section 9 of the submittal. NUREG-1407 guidelines for containment performance evaluation is followed. The main objective of the containment evaluation is to identify vulnerabilities that involve early failure of containment functions. This includes consideration of containment integrity, containment isolation, and other containment functions. To this end, TVA stated in the submittal that the emphasis of containment performance for BFN1 is on seismic relay review and containment walkdown results. The containment walkdown consists primarily of inspecting and evaluating unusual conditions or configurations in the drywell and torus, including spatial interactions, unique penetrations (including the post-accident operation of penetration cooling systems), piping hot spots, and items or components bridging the seismic gap between the containment liner and interior 10

structure. Further, BFN1 containment structure is screened for further seismic review based on EPRI NP-6041 (Reference 12).

TVA stated that no unusual conditions or configurations were identified during the containment performance evaluation.

Since TVAs containment performance evaluation is conducted in accordance with the guidelines of NUREG-1407, the staff judged the evaluation reasonable.

2.10 Nonseismic Failures and Human Actions In the submittal, the topic of nonseismic failures and human actions were not specifically addressed.

RAI No. 6 stated that NUREG-1407, in Section 3.2.5.8, indicated that Success paths are chosen based on a screening criterion applied to nonseismic failures and needed human actions. It is important that the failure modes and human actions are clearly identified and have low enough probabilities to not affect the seismic margins evaluation. TVA is asked to provide information as to how this was considered in choosing the success paths and the associated equipment for BFN1 SMA.

In response, TVA stated that in Chapter 2 of Browns Ferry Nuclear Plant Unit 1 USI A-46 Seismic Evaluation Report (Reference 7), it was described that multiple trains were evaluated for each success path, thereby resolving nonseismic failure concerns. The TVA response further stated that:

Human actions are addressed in accordance with the SQUG GIP. The desk top review method will be used by the Operations Department to verify that existing normal, abnormal and emergency operating procedures are adequate to mitigate the postulated transient and that operators could place and maintain the plant in a safe shutdown condition. As documented in TVA letter to the NRC dated October 7, 2004, TVA will complete the operations review of the BFN Unit 1 A-46 verification following BFN Unit 1 procedural development and approval, and notify the NRC of the results of that review prior to restart of BFN Unit 1.

The systems and equipment selected for seismic review in the BFN Unit 1 USI A-46 program are consistent with those selected in the BFN Units 2 and 3 programs, which are those for which normal, abnormal, and emergency operating procedures are available to bring the plant from a normal operating mode to a hot shutdown condition.

The BFN Units 2 and 3 shutdown paths for USI A-46 and seismic IPEEE were reviewed by the BFN Operations staff, and as a result the plant abnormal operating procedure 0-AO1-100-5, Earthquake, was revised to enhance the operator guidance necessary to verify and ensure diesel generator and electrical board operation, as well as identify specific instrumentation with the highest reliability following a seismic event. The operations personnel reviewed the specific actions required and concluded that the actions could be performed in the required amount of time with normally available resources.

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Potential challenges to the operators were explicitly reviewed during validation of the pertinent plant operating procedures related to the FSAR, Chapter 14, Accident Analysis for the LOOP transient and Appendix R evaluations which preceded the A-46 program review. In addition, the potential for local failure of architectural features and the potential for adverse interactions in the vicinity of safe shutdown equipment, where local operator action may be required, were reviewed as part of the BFN Units 2 and 3 A-46 resolution process. There were no seismic or housekeeping issues affecting the control room. Seismic interaction reviews eliminated any concerns with the plant components and structures located in the immediate vicinity of the components which had to be manipulated. Therefore, the potential for physical barriers resulting from equipment or structural earthquake damage which could inhibit operator ability to access plant equipment was considered, and the potential barriers to successful operator performance was eliminated. The BFN Unit 1 A-46 reviews similarly eliminated all seismic interaction concerns.

The staff judged the above response reasonable.

2.11 Seismic-Induced Fires/Floods Seismic induced flood and fire evaluation are addressed in Section 8 of the Seismic IPEEE submittal and also in Section 8.2.1 of the internal fire IPEEE submittal.

IPEEE seismic-induced flood and fire issues relative to BFN1 were addressed during the combined USI A-46/IPEEE equipment walkdowns and other evaluations. The concerns have been addressed in accordance with the guidelines of NUREG-1407.

On seismic-induced flooding, a seismic-induced class II over class I (II/I) spray evaluation program was implemented as part of the BFN1 Restart Project (Reference 9). In-plant screening walkdown evaluations fo seismic II/I spray hazards were performed on an area-by-area basis. A total of 27 designated plant areas were included. The areas encompassed all of the BFN1 reactor building. Other BFN1 plant areas were addressed in previous seismic II/I spray programs for BFN2 and BFN3. Potential outliers identified during the in-plant screening walkdowns were further evaluated which consisted of hand calculations using basic engineering mechanics techniques for simple configurations, and rigorous piping analyses (TPIPE computer program) for more complex piping configurations. A total of 19 outliers were found to have not met the acceptance criteria of TVA Design Criteria BFN-50-7306. Plant modifications were designed and Design Change Notice (DCN) issued to implement the changes so that all of these concerns were resolved. Furthermore, 13 maintenance and/or housekeeping items were also identified for corrective actions. Maintenance work order requests were issued to address these items. The general approach used to eliminate any unacceptable seismic II/I spray interactions at BFN1 is by ensuring that the source has the proper seismic capacity to resist the earthquake and not to result in any possible leakage or spray. To meet the requirements of the SMA, the RLE was used for earthquake input levels. The items which have been screened out by the walkdown, evaluated as acceptable or modified by either a design change or a maintenance order are judged by the SRT to have significant seismic margin such that the HCLPF capacity is greater than the RLE of 0.30g. During the walkdowns, the SRT determined that the controlling component which provides a good indication of the seismic capacity of the non seismic components which could result in a seismic induced flood interaction is the Gland 12

Seal Storage Tank located in the reactor building at elevation 639'. A HCLPF capacity calculation was performed for the Gland Seal Storage Tank and it was determined the HCLPF capacity to be greater than 0.30g. Based on this bounding evaluation, all non-seismic components which could pose a seismic induced flooding also have a HCLPF capacity greater than 0.30g.

The staff finds the above description for seismic-induced internal flood reasonable and acceptable. However, the submittal does not have any discussion regarding seismic-induced external flood. RAI No. 10 raised the question of failure potential of dams upstream of BFN1 and its consequences to BFN1. TVA responded that a similar question was raised by the staff during the review of the BFN2 and BFN3 seismic IPEEE, and has been resolved for all three units of BFN, the argument used was the elevation above sea level for all three units, therefore no further evaluation is needed for BFN1. The staff agrees with this statement.

On seismic-induced internal fire, the discussion appears in both the seismic portion and internal fire portion of the IPEEE submittal. Seismic/fire interactions considered in the BFN1 IPEEE includes: (1) seismic-induced fires, (2) seismic actuation of fire suppression systems, and (3) seismic degradation of fire suppression systems. Walkdowns were performed to identify sources of combustion and possible interactions. One potential seismic-induced fire hazard was identified during the walkdowns. This consisted of unrestrained batteries on the emergency lighting system battery rack in the BFN1 cable spreading room. The batteries lacked end restraints, side restraints, and spacers between the batteries. The concern was that the batteries could fall from the rack during an earthquake and cause sparks. This situation was corrected by using the TVA Problem Evaluation Report (PER) process. PER No. 64143 was issued to address and correct the condition. The submittal stated that no problem was identified.

The staff considers the above discussion on seismic/fire interaction reasonable.

2.12 Coordination with ongoing programs and other seismic issues Other than seismic induced fire/flood evaluation and USI A-46, the submittal does not address coordination of BNF1 IPEEE coordination with ongoing programs and other seismic issues. In NUREG-1407, it requires that coordination with ongoing programs and other seismic issues be described in the IPEEE submittal. In RAI No. 9, this question was raised.

In response to RAI No. 9, TVA provided information regarding the coordination of IPEEE with ongoing programs and other seismic issues. It is summarized below.

USI A-17 System Interactions in Nuclear Power Plants SQUG GIP stated that successful completion of USI A-46 fully addresses, without any other actions, USI A-17 as it applies to seismic spatial interactions. Seismic-induced flooding and fire are addressed in Chapter 8 of the submittal.

USI A-40 Seismic Design Criteria USI A-40 required action is limited to the seismic adequacy of safety related above ground 13

tanks. SQUG GIP stated that successful completion of USI A-46 fully addresses, without any other actions, USI A-40 as it applies to seismic adequacy of tanks and heat exchangers. Also, there are no large above ground flat bottom tanks on the BFN1 SSEL, as described in response to RAI No. 8.

USI A-45 Shutdown Decay Heat Removal Requirements The seismic adequacy of the decay heat removal system is included in the BFN1 seismic IPEEE program. No significant or unique seismic vulnerabilities were identified in the decay heat removal function.

Eastern U.S. Seismicity Issue This issue addresses the likelihood of earthquake events exceeding the seismic design basis for plants. The NRC identified 8 plants at 5 eastern U.S. sites and outliers. BFN is not one of the 5 sites.

GSI-156 Systematic Evaluation Program (SEP)

The SEP included reviews of 11 older operating nuclear power plants. BFN was not a SEP plant.

GSI-172 Multiple System Responses Program (MSRP)

The MSRP identified 21 potential safety issues. The completion of IPE and IPEEE closed all these issues.

Furthermore, in RAI No. 4, the staff raised the question that BFN1 has been out of service since March 1985. Considering the safety-related SSCs in BFN1 have been idle for 20 years, how does TVA ensure that these SSCs will be in working order and will perform their designed safety functions properly, especially under the seismic DBE conditions? Pre-operational tests (if to be performed) and limited IPEEE seismic walkdowns performed may not uncover all the potential seismic problems due to age-related degradation of SSC. Are all these addressed in the BFN1 Restart Project?

TVA responded by stating that concerns raised in RAI No. 4 are being addressed by the following ongoing programs/projects for BFN1:

BFN1 Plant Layup and Preservation Program To protect BFN1 during the extended shutdown, many of the BFN1 systems were placed in the Plant Layup and Preservation Program, while other systems remained in operation to maintain BFN1 in its de-fueled condition or to provide necessary support of the operation of BFN2 and BFN3. For systems placed in the Plant Layup and Preservation Program, internal conditions were controlled and monitored in accordance with that program. For systems that remained in operation, they were maintained in accordance with plant procedures consistent with the operating BFN2 and BFN3.

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BFN1 System/Component Replacement and Refurbishment Program This program is part of the BFN1 Recovery/Restart Project (see below), and also serves to support the BFN license renewal application (also see below). For BFN1, the approach taken by TVA for restart of BFN1 is to return the plant to operation in a condition that would support long-term safe and reliable operation of BFN1, including the anticipated 20-year period following the license renewal. TVA developed a process/methodology, system-by-system, to identify piping and equipment to be inspected/evaluated for integrity and system design criteria, and if needed, to be repaired/replaced. In some cases, TVA decided up front to replace entire piping sections and equipment, rather than expend extensive engineering resources to confirm that the existing piping and equipment was acceptable.

BFN1 Recovery/Restart Project TVA stated that the ongoing BFN1 Recovery/Restart Project is comprehensive in scope and systematic in design. In addition to the BFN1 System/Component Replacement and Refurbishment Program discussed above, other key aspects relative to system seismic capability include:

• Inspection of piping and equipment not slated for replacement or refurbishment at the outset of the project to evaluate piping and equipment condition.

• Modification of BFN1, where appropriate, to address design and operational issues resolved previously for BFN2 and BFN3, and to make BFN1 functionally congruent to BFN2 and BFN3.

• To complete TVA-proposed and NRC-accepted BFN Nuclear Performance Plan (NPP) special programs, which includes: long term torus integrity program, large bore piping and supports program, small bore piping and instrument tubing program, control rod drive insert and withdrawal piping seismic qualification program, drywell steel platform and upper drywell platforms program, miscellaneous steel frames program, cable tray supports program, conduit supports program, HVAC duct supports program, seismic II/I spatial system interactions program, and the restart test program.

• Resolution of outstanding NRC Generic Letters, NRC Bulletins, and other action items not previously completed for BFN1 due to shutdown since 1985.

BFN License Renewal Application To support the BFN license renewal applications, TVA stated that it has performed a system-by-system detailed evaluation of the BFN1 layup conditions and associated aging management review, and provided the NRC staff responsible for license renewal review with the following information: (1) inspection/evaluation methodologies used to verify piping system integrity, (2) piping system refurbishment and replacements, and (3) a discussion of evaluation of the effects of layup on BFN1 structures and supports. This evaluation identified no adverse effects of layup on BFN1 structures and component supports.

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BFN1 Restart Test Program TVA provided this program to the staff in August 2005.

TVA asserts that collectively, the above BFN1 ongoing programs/projects represent a comprehensive effort to inspect, evaluate, repair or replace, and/or modify BFN1 to ensure integrity and capability of SSCs to perform their designed functions, and ensure long term (including the expected 20-year service life for the license renewal) plant reliability.

Accordingly, based on these efforts, TVA is assured that BFN1 SSCs will be capable of performing their designed functions under DBE conditions.

The staff considers the responses from TVA for this Section reasonable.

2.13 Vulnerabilities/plant Improvement No vulnerabilities were identified by TVA as a result of the seismic IPEEE. The term vulnerability is not defined. Several components were identified for subsequent HCLPF evaluation, but none had HCLPF capacities less than 0.30g. In addition, relay evaluation for BFN1 followed the methodology recommended in the SQUG GIP, and did not find any low ruggedness relays or outliers.

However, in Section 10 of the submittal, TVA stated that some plant improvement did take place as a result of the seismic IPEEE process. The SRT identified issues related to anchorage design, maintenance, housekeeping, and seismic interaction that required design change notices (DCNs) or work orders. These items will be resolved as part of the USI A-46 program. One item was observed to be a potential seismic-induced fire hazard as discussed in 2.11 above. A PER was initiated to correct the situation.

In conclusion, TVA stated that seismic IPEEE showed BFN1 HCLPF is at least as great as 0.30g review level earthquake defined as an earthquake having a response spectrum that matches the median (50% Non Exceedance Probability) CR-0098 spectral shape anchored to a peak ground acceleration of 0.30g.

3.0 OVERALL EVALUATION AND CONCLUSIONS The technical information contained in the BFN1 IPEEE submittal (Reference 3) is inadequate for the staff to assess whether TVAs seismic IPEEE has met the objectives described in GL 88-20, supplement 4 and NUREG-1407. Nevertheless, with the additional information provided by TVA in response to the staffs RAI, the staff has sufficient information to conclude that TVA has performed the seismic IPEEE in reasonable conformance with GL 88-20, supplement 4 and NUREG-1407.

As mentioned in the February 2000 Technical Evaluation Report for BFN2 and BFN3 seismic IPEEE, one weakness of the seismic IPEEE is that the success paths selected do not include any high pressure injection system (i.e., RCIC and HPCI). The automatic initiation circuitry of the low pressure systems is also not included in the SSEL. The demands on the depressurization system and operator actions are therefore significant. Since the success path 16

selection and identification of components for the BFN1 seismic IPEEE program were based on the previous BFN2 and BFN3 seismic IPEEE programs, the above-mentioned weakness for BFN2 and BFN3 success paths selection therefore also is a weakness for the BFN1 seismic IPEEE.

4.0 REFERENCES

1. Generic Letter 88-20, Supplement N0. 4, Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities - 10 CFR 50.54(f), U.S. NRC, April 1991.

2. NUREG-1407, Procedural and submittal Guidance for the Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities, U.S. NRC, June 1991.

3. Browns Ferry Nuclear Plant (BFN) Unit 1 - Response to NRC Generic Letter (GL) 88-20, Supplement 4 - Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities - Submittal of Browns Ferry Nuclear Plant Unit 1 Seismic and Internal Fires IPEEE Reports, TVA, January 14, 2005.

4. Browns Ferry nuclear Plant (BFN) Unit 1 - Response to NRC Request for Additional Information Regarding Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities - Submittal of Browns Ferry Nuclear Plant Unit 1 Seismic and Internal Fires IPEEE Reports (TAC No. MC5729), TVA, February 2, 2006.

5. Browns Ferry Nuclear Plant Unit 1 Seismic IPEEE Report, TVA, October 2004.

6. Calculation of Basic Parameters for A46 and Individual Plant Examination of External Events (IPEEE) Seismic Program, Rev. 1, TVA, June 14, 1996.

7. Browns Ferry Nuclear Plant Unit 1 USI A-46 Seismic Evaluation Report, TVA, September 2004.

8. USI A-46/Seismic IPEEE Relay Evaluation, Browns Ferry Nuclear Plant Unit 1, TVA, January 2004.

9. Seismic-Induced II/I Spray Evaluations at Browns Ferry Nuclear Plant Unit 1, Rev. 0, TVA, March 2004.

10. HCLPF Calculations of MCC Anchorage for Seismic IPEEE Program, TVA Calculation No. CDQ1 999 2004 0156, Rev. 0, TVA, June 9, 2004.

11. HCLPF Calculations of RHR Heat Exchanger Anchorage for Seismic IPEEE program, TVA Calculation No. CDQ1 074 2004 0160, Rev. 0, TVA, June 9, 2004.

12. EPRI NP-6041-SL, A Methodology for Assessment of nuclear Power Plant Seismic Margin, Electric Power Research Institute, Rev. 1, August 1991.

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13. EPRI NP-7148-SL, Seismic Ruggedness of Relays, and Addendums, Electric Power Research Institute, August 1991.

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