ML12352A385

San Onofre Nuclear Generating Station, Units 2 and 3- Licensee Slides for 12/18/12 Public Meeting (TAC No. ME9727)

ML12352A385
Person / Time
Site:	San Onofre
Issue date:	12/18/2012
From:	Southern California Edison Co
To:	Plant Licensing Branch IV
Hall J R
References
TAC ME9727
Download: ML12352A385 (50)

Text

SONGS EXCELLENCE 2012 Public Meeting with the Nuclear Regulatory Commission Technical Meeting December 18, 2012 SONGS EXCELLENCE 2012 We operate San Onofre Nuclear Generating Station (SONGS) safely and reliably to the highest standards to protect the health and safety of the public and our employees We will not restart either Unit 2 or Unit 3 until we and the NRC are satisfied it is safe to do Southern California Edison Commitment 2 SONGS EXCELLENCE 2012 with Nuclear Regulatory Commission (NRC) staff with a focus on the Operational Assessments (OA) Discuss response plans for the Requests for Additional Information (RAIs). Confirm scope and understanding of each request 3 SONGS EXCELLENCE 2012 INTRODUCTIONS 4 SONGS EXCELLENCE 2012 Unit 2 Return To Service Strategy Power Reduction to 70% oSignificantly reduces fluid velocities: less energy causing tubes to vibrate oSignificantly reduces void fraction: better damping oPrevents Fluid Elastic Instability (FEI) Preventive Plugging of Tubes oTubes most susceptible to FEI at 100% power Multiple independently developed Operational Assessments Short Operating Interval oFive month window is significantly shorter than analysis allows o100% tube inspection during mid-cycle outage 5 SONGS EXCELLENCE 2012 Unit 2 Return to Service Operational Assessments Required by SONGS Technical Specifications, Steam Generator (SG) Program and Industry Guidelines meet structural and leakage integrity during the operating period prior to next planned inspection Southern California Edison (SCE) commissioned three independently developed Tube-To-Tube Wear Operational Assessments oAREVA oIntertek oWestinghouse (WEC) 6 SONGS EXCELLENCE 2012 Three Independent TTW Operational Assessments Although only one OA is required, SCE used several approaches in a parallel effort to evaluate the new wear mechanism SCE used both probabilistic and deterministic methods The conservative RTS plan is supported by the results of the three independent OAs 7 SONGS EXCELLENCE 2012 Three Independent TTW Operational Assessments AREVA Support Effectiveness oDeterministic analysis indicates FEI will not occur at 70% power oAnalysis of margin using a probabilistic method that models physics of TTW oMargin evaluation produces results consistent with SIPC Intertek - Current OA Methodologies oProbabilistic method provides empirical insights into the prediction of instability and resulting TTW growth rates oConservatively assumes instability occurs during operation Westinghouse Tube Proximity oEvaluates potential for FEI mechanism at 70% power using tube support conditions determined from inspection data including future wear oBased on independent analysis of TTW cause and eddy current data 8 SONGS EXCELLENCE 2012 NRC Requests for Additional Information NRC to SCE, dated Nov. 30, 2012, SONGS Draft RAIs 1 14 NRC to SCE, dated Dec. 10, 2012, SONGS Draft RAIs 15 - 31 9 SONGS EXCELLENCE 2012 NRC Requests for Additional Information RAIs requesting discussion of methodologies RAIs requesting additional information including details of analysis RAIs requesting clarification of information provided in the Return to Service report 10 SONGS EXCELLENCE 2012 METHODOLOGY RAIS 11 SONGS EXCELLENCE 2012 RAI 3 Intertek OA Definition of Wear Index NRC RAI: Reference 4, describe the sensitivity of the results in Figure 5-4 to If alternate definitions significantly affect the results, what is the justification for the definition being used Response Plan: Discuss the approaches to the wear index that were examined: oTube wear at AVBs versus TTW oTube wear at TSPs versus TTW oTube wear at AVBs and TSPs treated as independent parameters oTube wear as the summation of AVB and TSP Provide the evaluation of each approach and the justification for the wear index used in the OA 12 SONGS EXCELLENCE 2012 RAI 4 Intertek OA Wear Index Definition NRC RAI: the depths of 2-sided wear flaws at a given AVB intersection? If not, explain Response Plan: Explain the wear index is based on bobbin Discuss how the wear index is correlated to the presence or absence of tube-to-tube wear and its application in the OA model Explain the change in wear index will depend on the Anti-Vibration Bar (AVB) / Tube Support Plate (TSP) growth rates which are traditionally based on bobbin data SCE will provide the justification for the bobbin-based wear index used in the OA 13 SONGS EXCELLENCE 2012 RAI 2 Intertek OA Tube-To-Tube (TTW) Growth Rates NRC RAI: Operational Assessment in Attachment 6, Appendix C (Reference 4), pages 3-2 and 4-12, appears to state that tube-to-tube wear (TTW) growth rates are based on the maximum TTW depths observed in Unit 3 at EOC 16 divided by the first Unit 3 operating period (0.926 years at power). Provide justification for the conservatism of this Response Plan: Explain the determination of TTW growth rates was based on 0.926 years at 100% power in conjunction with a set of conservative assumptions to provide a conservative wear rate model for Unit 2 Provide discussion of how the Unit 3 wear rates were benchmarked and the justification for this approach 14 SONGS EXCELLENCE 2012 RAI 5 Intertek OA Non-detected Tube Support Wear NRC RAI: Reference 4, third paragraph from the bottom of page 4-3, why is non-detected wear only assigned to no degradation detected (NDD) tubes and not to NDD tube/AVB intersections in tubes with detected wear at other intersections Response Plan: Explain how the OA does assign non-detected wear to both populations Explain how the two tube populations were assigned differently. Explain how NDD tubes with at least a bobbin exam and the tubes with detected wear with at least a bobbin and a rotating coil examination were handled Provide the basis for the methods and assumptions used to account for non-detected wear in the OA 15 SONGS EXCELLENCE 2012 RAI 6 Intertek OA Tube-To-Wear Probability of Detection NRC RAI: Reference 4, page 4-5, it seems that depths of undetected flaws are assumed to be associated with probability of detection (POD) < 0.05. Why is this conservative? Is there a possibility that some undetected flaws may be associated with higher values of POD Response Plan: Provide discussion of likelihood of significant undetected wear greater than 5% POD level Explain the treatment of undetected wear at supports and tube-to-tube contact Provide basis for the approach used in the OA 16 SONGS EXCELLENCE 2012 RAI 10 Primary to Secondary Leakage 17 NRC RAI: Technical Specification (TS) 3.4.13.d allows 150 gallons per day primary to secondary leakage. The Return to Service Report (Enclosure 2 of Reference reactor coolant leak has been modified to require plant Operators to commence a reactor shutdown upon a valid indication of a primary-to-secondary SG tube This procedure change requires earlier initiation of operator actions in response to a potential SG tube leakthis mean that a reactor shutdown would be commenced upon any valid indication of primary to secondary leakage? Provide a description of the action levels in the procedure. Discuss any additional actions, planned or taken, such as simulator testing, operator training, and/or any evaluations to assess potential impacts of the revised procedure SONGS EXCELLENCE 2012 RAI 10 Primary to Secondary Leakage (cont.) 18 Response Plan: Provide the action levels and leakage threshold for plant shutdown in the revised Abnormal Operating Instruction (AOI) and description of action levels Discuss the plant response to leakage indications below that threshold, the process used to conclude a valid indication of leakage is present and the decision making process for shutdown. The Operational Decision Making (ODM) process will be described in greater detail in the response to RAI 16 Discuss actions planned or taken including operator classroom and simulator training, lessons learned from the Unit 3 shutdown, and simulations performed to assess the effectiveness the AOI and operator response SONGS EXCELLENCE 2012 RAI 16 RCS Activity Limit NRC RAI: 1, Section 9.3, page 50 Provide additional information concerning applied if the proposed criterion is exceeded. Provide the procedural action From Reference 1, Section 9.3: plant procedure for chemical control of primary plant and related systems has been modified to require action if the specific activity of the reactor coolant Dose Equivalent (DE) Iodine (I-131) exceeds the normal range of 0.5 /gm, which is one-half of the TS Limit of 1.0 /gm. In the event that the normal range is exceeded, Operations is required to initiate the Operational Decision Making process to evaluate continued plant operation 19 SONGS EXCELLENCE 2012 RAI 16 RCS Activity Limit (cont.) Response Plan: Provide description of the new administrative limit for this activity Discuss criteria for notification of on shift Operators to initiate Operational Decision Making (ODM) process Discuss ODM process and procedure 20 SONGS EXCELLENCE 2012 RAI 17 Reactor Coolant Leakage Procedure NRC RAI: Reference 1, Section 9.4.1, page 50 Provide the procedural action levels/statements. From Reference 1, Section 9.4.1: The plant operating procedure for responding to a reactor coolant leak has been modified to require plant Operators to commence a reactor shutdown upon a valid indication of a primary-to-secondary SG tube leak at a level less initiation of operator actions in response to a potential SG tube leak. Response Plan: This RAI appears to request the same information that will be provided in response to RAI 10 21 SONGS EXCELLENCE 2012 RAI 18 VLPMS Upgrade NRC RAI: 1, Section 11.1, page 52 SCE proposes to upgrade the vibration and loose parts monitoring system (VLPMS) as a defense-in-depth measure to enhance plant monitoring capability to facilitate early detection of a steam generator tube leak and ensure immediate and appropriate plant operator and management response Response Plan: Clarify the upgrade is not a new system and it is not designed to monitor steam generator thermal hydraulic parameters Clarify VLPMS upgrade is intended to provide additional capability for secondary side acoustic signals. The upgrade will improve historical reviews of acoustic signals Describe the capabilities of the upgraded system and the procedural actions for its use 22 SONGS EXCELLENCE 2012 RAI 19 Smart Signal NRC RAI: 1, Section 11.2, page 52 Provide additional details on how the GE Smart Signal System will be used in the context of tube-to-tube wear and/or the circumstances associated with tube-to-tube wear. What information/data will the system be evaluating? For what purpose Response Plan: Describe the smart signal system (including the data evaluated) to monitor historical plant process data as a backward looking tool to assist in the investigation of tube-to-tube wear 23 SONGS EXCELLENCE 2012 RAI 27 MHI Hydrodynamic Force Effects on Contact Forces NRC RAI: -2 (307 of 474) MHI concludes, in part, that the tube-to-AVB gaps in the center columns increase due to hydrodynamic pressure by [ ] when the manufacturing tolerance dispersion is not taken into account. MHI also concludes that the gap increase due to hydrodynamic pressure is small when the manufacturing tolerance dispersion is taken into account. Discuss whether this latter finding may simply reflect the hydrodynamic pressures acting to relieve the tube-to-AVB contact forces caused by the manufacturing tolerance dispersion, such that the gaps are relatively unchanged relative to the case were the hydrodynamic pressure is not considered. Reference 6, Appendix 9, -specific mention of whether the calculated tube-to-AVB contact forces directly considered the effect of the hydrodynamic effect on tube-to-tube contact forces, correct, explain how the resulting contact forces are conservative 24 SONGS EXCELLENCE 2012 RAI 27 MHI Hydrodynamic Force Effects on Contact Forces (cont.) Response Plan: Describe the analyses used to determine the significance of hydrodynamic forces in the contact force analysis Discuss the findings from these analyses which conclude these forces do not have a significant effect on contact force Discuss influence of hydrodynamic forces on contact forces and resulting probability of fluid-elastic instability 25 SONGS EXCELLENCE 2012 ADDITIONAL INFORMATION AND ANALYSIS RAIS 26 SONGS EXCELLENCE 2012 RAI 7 Intertek OA Active Wear Locations NRC RAI: -How determined Response Plan: The definition is implemented in the NDD tubes Discuss the cumulative distribution functions (CDFs) for assigning active wear locations within the NDD tube population 27 SONGS EXCELLENCE 2012 RAI 8 Intertek OA Tube Wear at AVB Locations NRC RAI: -observed that the number of AVB supports that develop wear in the second cycle of operation can increase dependent on the number of worn AVB indications at the beginning of the second cycle. These data were used in the OA to add AVB Provide a more complete description of the model used to add AVB locations that will develop wear during the second cycle. Confirm that this model applies to both the 560 tubes with existing tube support wear and the 1350 NDD tubes Response Plan: Describe the method used to establish the number of additional (predicted to occur during Cycle 17) wear locations in the population of tubes with existing tube support wear The method used for the population of NDD tubes will be described in the response to RAI 7 28 SONGS EXCELLENCE 2012 RAI 9 Intertek OA Benchmarks NRC RAI: is stated in Reference 4, at the top of page 4-9 that the simulation results of the bench marking process are shown in Figure 4-6. Provide additional detail on what Figure 4-6 is showing and how it relates to the benchmarking process. As part of Response Plan: The Unit 2 TTW initiation model will be explained and how it was developed from Unit 3 TTW wear data. This involved a benchmarking process to use the Unit 3 data to predict the actual Unit 2 NDE results Further explanation will be provided to clarify the meaning of the data shown in Figure 4-6 and what it represents from the benchmarking process 29 SONGS EXCELLENCE 2012 RAI 22 AREVA OA Explanation of Contact Force Distribution Calculation Terms NRC RAI: 3, page 57 of 129, first full paragraph beginning with the words - individual run of the quarter model as a single Monte Carlo trial for contact However, the staff was unable to ascertain from the subsequent discussion exactly what was done as an alternative? Nor was the staff able to discern this from Reference 6, Appendix 9. Provide or cite by reference a more complete description of how the cumulative distributions of contact forces were determined. For What How were zones employed in order to provide a more practical approach? Are all tubes in a given zone assumed to have the same initial clearances, final clearances, and contact forces? Do all AVB #5 in a zone have the same cumulative distribution of contact forces? Is a Monte Carlo performed for each zone 30 SONGS EXCELLENCE 2012 RAI 22 AREVA OA Explanation of Contact Force Distribution Calculation Terms (cont.) Response Plan: Provide an expanded description of how the cumulative distributions of contact forces between tubes and AVBs were determined The defined Changes in cumulative distributions of contact forces from zone to zone will be explained 31 SONGS EXCELLENCE 2012 RAI 23 AREVA OA Provide Figures for U2 Steam Generator 88 and U3 Steam Generator 88 NRC RAI: 3 Provide figures similar to Figures 6-19 and 6-20 for Unit 3, SG E-088, and Unit 2, SG E-088 Response Plan The figures will be provided 32 SONGS EXCELLENCE 2012 RAI 25 AREVA OA Dents in Agreement with High Contact Forces NRC RAI: 3, page 59 of 129 There is a statement in the last paragraph that Provide or show this comparison Response Plan The evaluation supporting this statement will be provided 33 SONGS EXCELLENCE 2012 RAI 31 Effect of Non-Pressure Loads - Condition Monitoring NRC RAI: References 7 and 8 (specifically, in Section 7.2 of Reference 7 and in Section 8.0 of Generator Management Program: Steam part, to assess the most limiting structural integrity performance criteria (e.g., the more limiting structural limit determined from (a) the three times the normal operating differential pressure criterion or (b) the safety factor of 1.2 on combined primary loads and 1.0 on axial secondary load criterion). In some cases, it appears that the limits in the Integrity Assessment Guidelines may have been based on specific tests and plant data. Please discuss whether you have confirmed the applicability of the limits in the Integrity Assessment Guidelines (in particular, those related to when non-pressure loads need to be considered) to the SONGS replacement steam generators Response Plan: The response will compare each type of degradation found in the SGs to the criteria found in the Integrity Assessment Guidelines, including the applicability of non-pressure loads 34 SONGS EXCELLENCE 2012 RAI 26 AREVA OA Provide Details of Wear Growth Model NRC RAI: Provide additional details of the wear growth model at the tube supports. Were cumulative probability functions of observed wear rates constructed and randomly sampled when developing the contact force probability distributions at each intersection? Was total gap at each intersection (prior to applying temperature and allowing the model to settle, leading to the development of contact forces) assumed to be the sum of the manufacturing gap and the maximum wear depth Response Plan Full details of incorporating wear at AVB locations into the contact force calculations will be provided. Wear locations, wear depths as a function of time, and gap inputs to the contact force model will be discussed 35 SONGS EXCELLENCE 2012 RAI 28 Westinghouse OA Growth Rate of Unit 3 TTW NRC RAI: What is the estimated growth rate of the tube-to-tube wear in steam generator 3E0-88, tube R106C78? Describe how it was Response Plan: Explain tube-to-tube wear rates (including tube 3E088, R106C78) were not calculated for tubes in Unit 3 Explain that in-plane instability was evaluated by benchmarking TTW in Unit 3 tubes: oDetermined that in-plane instability would occur at a number of tubes including this tube oEstimates of tube-to-tube wear rates were not necessary for this evaluation 36 SONGS EXCELLENCE 2012 RAI 29 Westinghouse OA Case 78 NRC RAI: -12 and 2-13 Provide similar figures for Case 78 (all Response Plan: Explain Case 78 for all AVBs ineffective at 70% Power was calculated as part of the Westinghouse (WEC) OA. The figures were not included in the WEC OA since no tubes in Unit 2 have Case 78 support conditions The figures will be provided in response to this RAI 37 SONGS EXCELLENCE 2012 RAI 1 3 x Normal Operating Pressure Differential NRC RAI: reports the 3 times normal operating pressure differential as being 4290 psi for 100% power conditions. This is the same value assumed in the Condition Monitoring Assessment provided in Attachment 2. This value is significantly higher than the values ranging from 3972-3975 psi for 100% power reported in Attachment 6, Appendices B, C, and D (References 3-5). Describe the reason for the differences Response Plan: Each report uses the value of 3xNOPD appropriate to actual (Condition Monitoring) or RTS (Operational Assessment) Reactor Coolant System (RCS) and steam generator (SG) operating conditions that are appropriate to that assessment (Temperatures, Power and SG Secondary Side Pressure) 38 SONGS EXCELLENCE 2012 RAI 1 3 x Normal Operating Pressure Differential (cont.) Response Plan: SCE will provide a table listing the RCS and SG parameters used for each report and the basis for the value of 3xNOPD used Following completion of the last cycle of operation, the reactor pressure vessel head was replaced and RCS operating assessment of the impact of the temperature increase on Fluid Elastic Instability will be provided 39 SONGS EXCELLENCE 2012 RAI 15 Retainer bar wear NRC RAI: Reference 1, Section 8.3.2, page 48 How will the continued integrity of the non-stabilized, preventively-plugged tubes adjacent to the retainer bars be unable to cause damage to adjacent tubes Response Plan: Provide a discussion of wear mechanism of tubes adjacent to retainer bars Provide a description of stabilizer deployment to ensure integrity of tubes adjacent to retainer bars 40 SONGS EXCELLENCE 2012 RAI 11 Safety Analysis for Operation at 70% Power NRC RAI: assessment should focus on the cycle safety analysis and establish whether operation at and evaluations have been performed to conclude operation at 70% power for an extended period of time is safe. The evaluation should also demonstrate that the existing Technical Specifications, including limiting conditions for operation and surveillance Response Plan: Provide summary of impact evaluations performed for extended operation at 70% power on reactor core design and safety analysis Provide table summarizing impact assessment of reload and UFSAR Chapter 15 safety analyses Provide table summarizing impact assessment of core design and monitoring technical specification surveillance requirements Discuss conclusions of safety analysis methodology, safety analyses, radiological dose consequences, and applicability of Technical Specifications, on extended operation at 70% power 41 SONGS EXCELLENCE 2012 RAI 12 RCS and Secondary Flow Uncertainty NRC RAI: measuring reactor coolant flow. Please provide a detailed evaluation of RCS flow uncertainty, identify how RCS flow uncertainty is affected by operation at 70% power, and discuss the overall treatment of the RCS flow uncertainty, actual and indicated, in the context of the remaining safety analyses. Provide Response Plan: Provide discussion of detailed RCS flow uncertainty evaluation including how it is affected by operation at 70% power Provide discussion of the treatment of RCS flow uncertainty in the context of safety analyses and RCS flow limit requirements of T.S. 3.4.1 Provide discussions of secondary flow uncertainty evaluations performed for main steam flow, main feedwater flow, and SG blowdown flow parameters 42 SONGS EXCELLENCE 2012 RAI 13 ECCS Analysis NRC RAI: generator heat transfer characteristics, which could affect the performance of the plant under postulated loss of coolant accident conditions. Please explain how the existing ECCS analysis accounts for these changes, and how considerable steam generator tube plugging has been addressed in the ECCS evaluation. Provide the ECCS evaluation that will apply to the planned operating cycle Response Plan: Provide discussion of the impact evaluation performed for Replacement Steam Generators on ECCS performance analysis Provide discussion of the major changes in the planned operating cycle (Unit 2 Cycle 17) and the evaluations performed for their impacts on ECCS performance analysis 43 SONGS EXCELLENCE 2012 RAI 14 Calculation Dispositions NRC RAI: planned reduced-power operation Response Plan: The summary dispositions of the calculations pertinent to each of the evaluations covered under RAIs #11-13 will be included in their respective responses Provide summary of the impacts of reduced-power operation on the Westinghouse/CE plant protection system setpoints including RCP Low-Flow Trip, NR steam generator water level indication and control, and validation of control systems Provide summary of RCS internals analysis at reduced-power operation 44 SONGS EXCELLENCE 2012 CLARIFICATION OF RETURN TO SERVICE REPORT RAIS 45 SONGS EXCELLENCE 2012 RAI 20 AREVA OA Tube Support Clearance NRC RAI: 3, page 17 of 129, refers to tube-to-support design clearance of 2 mils diametral. Confirm that this is the nominal diametral clearance under ambient conditions, or clarify the statement otherwise Response Plan Explain the design nominal clearance between tubes and AVBs is based on ambient conditions 46 SONGS EXCELLENCE 2012 RAI 21 AREVA OA Plugged Tubes Considered in Thermal/Hydraulic and Stability Ratio Analysis NRC RAI: local thermal/hydraulic (TH) conditions upon returning to power and have been included in the stability ratio calculations. The staff interprets this to mean the effect of the plugged tubes on the calculated thermal/hydraulic conditions were considered in the stability ratio calculations and that the stability ratio calculations included the plugged (and stabilized) tubes. Is this correct? Clarify, if not Response Plan Explain the correct 47 SONGS EXCELLENCE 2012 RAI 24 AREVA OA Clarify Wording Pertaining to Figure 6-20 NRC RAI: and 10 near row 27 have sporadic dents in the vicinity of the noses of AVBs 1, Provide further clarification relative to the discussion of Figure 6-20 Response Plan The sentence will be clarified and explained 48 SONGS EXCELLENCE 2012 RAI 30 Percentage of Tube Wear vs. Maximum Interstitial Velocity NRC RAI: -2 Provide similar figure for maximum interstitial velocities Response Plan: A similar figure will be provided for maximum interstitial velocities for SONGS RSGs 49 SONGS EXCELLENCE 2012 There is no timeline on safety 50