ML081270091

Response to NRC Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors

ML081270091
Person / Time
Site:	Catawba
Issue date:	04/30/2008
From:	Morris J R Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-04-002
Download: ML081270091 (15)

Text

JAMES R MORRIS Duke .RoRs Dukery Vice President Catawba Nuclear Station 4800 Concord Road / CNO0 VP York, SC 29745-9635 803 831 4251 803 831 3221 fax April 30, 2008 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION:

Document Control Desk

SUBJECT:

Duke Energy Carolinas, LLC Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413 and 50-414 Response to NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors" On September 13, 2004, the Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2004-02. The GL requested that all pressurized-water reactor (PWR)licensees (1) evaluate the adequacy of the emergency sump recirculation function with respect to potentially adverse effects associated with post-accident debris, and (2)implement any plant modifications determined to be necessary.

By letter dated March 1, 2005, as supplemented by letters dated September 1, 2005, June 28, 2006, and February 29, 2008 Duke Energy Carolinas, LLC (Duke) provided responses to GL 2004-02. As stated by Duke's letter of December 7, 2007, any additional or revised information resulting from the Integrated Prototype (chemical effects) Testing was to be provided as an amended response to GL 2004-02 by April 30, 2008. This extension was approved by the staff in a letter dated December 28, 2007.The purpose of this letter is to provide the amended response to Generic Letter 2004-02 discussed in the February 29, 2008 submittal, as well as a summary level description of Duke's approach to resolution of issues related to Generic Letter 2004-02.The NRC Revised Content Guide for Generic Letter 2004-02 Supplemental Responses, dated November 21, 2007 requested a summary level description of the approach taken to provide reasonable assurance that long-term core cooling is maintained.

Attachment 1 to this letter provides the requested summary.Attachment 2 provides the amended response as discussed in the February 29, 2008 submittal (results of the Integrated Prototype (chemical effects) Testing performed for Catawba and McGuire).At i www. duke-energy.

corn US Nuclear Regulatory Commission April 30, 2008 Page 2 As stated by GL 2004-02 Supplemental Response dated February 29, 2008, Duke agreed to provide additional information related to the NRC staff-requested re-evaluation of downstream effects, to be performed using WCAP-16406, Revision 1, dated August 2007, and the associated NRC SER. The re-evaluation determined that all affected single and multistage pumps, heat exchangers, instrument tubing, valves, spray nozzles and orifices are not expected to fail or become blocked during the 30-day mission time following a LOCA event using the methodologies and acceptance criteria of WCAP-1 6406-P, Revision 1. The wear evaluation of all Emergency Core Cooling and Containment Spray system piping containing recirculated containment sump pool fluid during and after an accident determined that system piping is not expected to fail.under the methodology and acceptance criteria provided in WCAP.-16406-P, Revision 1.In addition, the previous acceptable downstream effects evaluations performed addressing the nuclear fuel and reactor internals have been determined to still be bounding with respect to the new requirements of WCAP-1 6406-P, Revision 1.Consistent with the GL 2004-02 Supplemental Response dated February 29, 2008, the results of the Catawba downstream debris effects evaluations on the critical ECCS/CS components, reactor internals and the nuclear fuel, performed using the guidance of WCAP-16406-P, Revision 1 criteria and the associated NRC SER, demonstrate the currently installed components on Catawba Unit 2 are acceptable for the expected ECCS mission time. Once the modifications in the Spring 2008 Outage (1 EOC1 7) are completed, Unit 1 will also be in full compliance.

Duke understands that the NRC staff will consider this set of additional information and will issue a letter to Duke Energy assessing the overall adequacy of the Catawba Nuclear Station's GL 2004-02 corrective actions.If any questions arise or additional information is needed, please contact A. P. Jackson at (803) 831-3742.Very truly you J Attachments US Nuclear Regulatory Commission April 30, 2008 Page 3 James R. Morris affirms that he is the person who subscribed his name to the foregoing statement, and that all the matters and facts set forth herein are true and correct to the best of his knowledge.

Ja eR. Morris, Vice President, Catawba Nuclear Station Subscribed and sworn to me.IDate Notary Public My commission expires:-71 Z Date US Nuclear Regulatory Commission April 30, 2008 Page 4 xc (with Attachments):

Victor M. McCree (Acting), Region II Administrator U.S. Nuclear Regulatory Commission Sam Nunn Atlanta Federal Center, 23 T85 61 Forsyth St., SW Atlanta, GA 30303-8931 J. F. Stang, Jr., Senior Project Manager (CNS & MNS)U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 8 G9A Rockville, MD 20852-2738 A. T. Sabisch Senior Resident Inspector U. S. Nuclear Regulatory Commission Catawba Nuclear Station S. E. Jenkins, Manager Division of Radioactive Waste Management Bureau of Land and Waste Management Department of Health and Environmental Control 2600 Bull Street Columbia, SC 29201 US Nuclear Regulatory Commission April 30, 2008 Page 5 bxc (with Attachments):

J. R. Morris (CN01VP)J. W. Pitesa (CN01SM)T. M. Hamilton (CNS01SA)R. D. Hart (CN01 RC)R. L. Gill (EC05P)A. P. Jackson (CN01RC)K. L. Ashe (MG01RC)R. S. Lytton (MG05SE)G. A. Bartosch (CN03SE)S. K. Pursley (CN03SE)M. H. Shipley (EC05P)G. D. Robison (EC09E)NCMPA-1 NCEMC PMPA SREC Document Control File 801.01 RGC File ELL-EC050 Attachment 1 Summary of Approach Taken (

Attachment 1 Summary of the Catawba ECCS Sump Strainer Design Validation Process The NRC Revised Content Guide for Generic letter 2004-02 Supplemental Responses, dated November 21, 2007 requested a summary level description of the approach taken to provide reasonable assurance that long-term core cooling is maintained.

The following major activities have been completed in support of GL 2004-02 for Catawba:* Baseline evaluation, performed by Enercon Services, Inc.* Refined evaluation using the guidance of NEI 04-07, completed by Enercon Services, Inc.Downstream effects evaluation using the WCAP-16406-P, Rev.0 methodology.

A re-evaluation using Revision 1 of the WCAP and the associated NRC SER was also completed.

Containment walkdowns using the guidance of NEI 02-01, "Condition Assessment Guidelines:

Debris Sources Inside PWR Containments" The modification process and the plant labeling process have been enhanced relative to GL 2004-02 controls.Replacement of the Microtherm insulation, previously installed on portions of the reactor vessel heads, with RMI.* Installation of a new ECCS sump strainer in Unit 2 (-2000 sq ft).* Removal of interferences and scoping in preparation for the installation of the Unit 1 strainer installation in the Spring of 2008.Replacement of the fiberglass blankets (Nukon) insulation on the bottom bowls of the Unit 1 Steam Generators with reflective metal insulation (RM I). This. replacement removed approximately 400 cubic feet of fibrous insulation of which approximately 280 cubic feet are below the maximum flood level in containment.

Unit 2 does not require a similar modification since RMI insulation is already installed on the bottom SG bowls.Replacement of the existing orifice plates with smaller diameter orifice plates to allow the ECCS throttle valves to be opened greater than currently allowed for flow balancing.

Work on Unit 2 is complete.

Unit 1 requires further modification during the Spring 2008 outage since the initial orifice plate sizing modification was not successful in allowing the throttle valves to be opened the proper amount in order to meet the requirements for the WCAP-1 6406-P, Rev. 1 downstream effects analysis.Completion of the Integrated Prototype Test (IPT) /chemical effects test.The Catawba ECCS sump strainer was initially sized using Enercon Baseline analyses in an attempt to install as large a strainer area as possible in each Containment.

Refined analyses were then performed along with testing to validate the final design. These input activities are listed below. The details of the initial inputs are contained in the February 29, 2008 Duke Response (Enclosures 1 and 2). A description and quantification of the refined inputs is Page 1 of 4 Attachment 1 Summary of the Catawba ECCS Sump Strainer Design Validation Process finalized In Attachment 2 of this letter. Additionally, final ECCS Strainer head loss and ECCS recirculation pump NPSH margins are reported in Attachment 2 of this letter.KEY ELEMENTS The key elements of the design validation process are illustrated on Figure 1.The key elements align with the "NRC Revised Content Guide for Generic Letter 2004-02 Supplemental Responses," dated November 21, 2007.1. Break Selection 2. Debris Generation

3. Latent Debris 4. Debris Transport 5. Head Loss 6. Sump Structural Design 7. Chemical Effects (Post-Accident Environment Determination)

8. Integrated Prototype Testing (IPT)9. Downstream Effects 10.Additional Design Considerations/Modifications CONSERVATISMS The conservatisms in many of the areas are described in the February 29, 2008 submittal related to each of the analyses described above as appropriate.

The IPT takes design inputs from the different analyses and conservatively simulates the environmental conditions of the Containment sump pool over the ECCS mission time. IPT conservative assumptions include: " Using conservatively small strainer areas for determining debris bed thicknesses.

• Providing conservative scaling of debris to both strainer surface area and to containment sump volume to ensure close but conservative chemical concentrations in the test apparatus.

• Applying conservatively high chemical loads to compensate for the brief period when the test could not mimic the elevated post-LOCA temperatures.

• Operating in test startup mode for over 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> at elevated temperatures, ensuring debris bed formation, head loss stabilization, and conservative pool chemistry prior to data acquisition.

Page 2 of 4 Attachment 1 Summary of the Catawba ECCS Sump Strainer Design Validation Process*

• Applying conservatively high aluminum loads as soluble material so that silicate inhibition would not limit the aluminum in the test.Following a temperature profile that exceeds the maximum expected temperatures early in the test to promote excess corrosion products and descends below the minimum temperature late in the test to promote excessive dissolution of potential precipitation products.Providing temperature and flow correction that conservatively decreases the amount of temperature compensation with increasing temperature.

Page 3 of 4 Attachment 1 Summary of Approach Taken Figure 1 Key Elements of the Design Validation Process for the ECCS Sump Strainer Modified sump strainer designed per initial baseline analysis W Key Element Numbers (Refer to Key Element Listing, Attachment 1, Page 2 of 4)Page 4 of 4 Attachment 2 Amended Response to Staff Request for Additional Information

1. 12 Identified on February 9, 2006 Catawba Integrated Prototype (Chemical Effects)Testing Refinements and Conclusions Amended Supplemental Response to Staff Request for Additional Information (RAI) #12 Catawba Nuclear Station Units 1 and 2 Generic Letter 2004-02 Request for Additional Information 12 For your plant-specific environment, provide the maximum projected head loss resulting from chemical effects (a) within the first day following a LOCA, and (b) during the entire ECCS recirculation mission time. If the response to this question will be based on testing that is either planned or in progress, provide an estimated date for providing this information to the NRC.General Note: Duke's Integrated Prototype Test (IPT) for chemical effects was conducted in the fall of 2007 at Wyle Laboratories in Huntsville, Alabama. A description of the design of the IPT and the associated input parameters was submitted in the Catawba GL 2004-02 Supplemental Response dated 2/29/08 (RAI #11). Due to the timeframe and the logistics involved in generating the final test report and supporting documentation, Duke requested and received NRC approval for an extension of the date to submit details of this documentation until April 30, 2008.The original response to RAI #12 in the Catawba GL 2004-02 Supplemental Response dated 2/29/08 indicated that the maximum projected head loss (including chemical effects) across the Catawba ECCS sump strainer, the refined limiting NPSH margins on the ECCS sump recirculation pumps, and supporting information regarding refinements made to the initial ECCS sump strainer sizing evaluations would be provided once the documentation was complete.Those details are provided herein.Catawba Response: Analytical Refinements to Initial Strainer Sizing Evaluation As noted in Catawba's 2/29/08 GL 2004-02 Supplemental Response to RAI #11, Duke's ECCS sump strainer IPT for chemical effects included refinements to the low density fiberglass (LDFG) insulation debris and to the Catawba Computational Fluid Dynamics (CFD) model transport evaluation input parameters to more accurately represent the debris bed on the top-hat strainer module. The specific debris load refinements made to the initial strainer sizing values are listed below: The break Zone of Influence (ZQI) for jacketed Nukon and jacketed Thermal-Wrap fiber insulation was reduced from 17D (as recommended per NEI 04-07 guidance) to 7D, using the methodology outlined in WCAP-16710-P, "Jet Impingement Testing to Determine the Zone of Influence (ZOI) of Min-K and NUKON Insulation for Wolf Creek and Callaway Nuclear Operating Plants", Page 1 of 4 Amended Supplemental Response to Staff Request for Additional Information (RAI) #12 Catawba Nuclear Station Units 1 and 2 Generic Letter 2004-02 dated October 2007. The WCAP methodology in this report was evaluated and determined to apply to Catawba, and as such was implemented.

The refined 7D ZOI changes the limiting break location at Catawba from the "B" Loop Hot Leg to the "B" Loop Crossover Leg. The quantity of fiber transported to the Catawba ECCS sump for the limiting break reported in the .Catawba 2/29/08 submittal reflects the initial 17D fiber load used for sizing the modified ECCS sump strainer.

In addition to this refinement, the quantity of latent fiber existing in Containment was refined using the walkdown sampling guidance described by NEI 04-07'.The CFD model for the Catawba ECCS sump transport analysis was refined to incorporate more realistic sump pool kinetic energy near the crane wall penetration recirculation outfalls.Table 12-1 shows the initial and refined quantities and transport fractions for LDFG at Catawba.Table 12-1 Catawba Fiber Insulation Debris Loads -Limitin Break A ~ 'A Debis:~Y'el iis ~Oibisak Debrise ukoný" and~ Th ni7- >"Q~ ' artity U &Q t rasor Ant S',, ~ sity ihberg la~ss (LDFG) -Generate

~ r~td r~e'tklL'.cion Facio Fines (constituent fibers) 195.5 ft 3 0 ft 3 100% 100% 195.5 ft 3 0 ft Small Pieces (<6" on a Side) 663.0 ft 3 195.0 ft 3 70% 45% 464.1 ft 3 88.3 1 Large Pieces (>6" on a Side) 322.4 ft 3 130.0 ft 3 10% 10% 32.2 ft 3 13.01 Intact Blankets 344.9 ft 3 0 ft 3 0% 0% 0 ft 3 0 ft 3* The break ZOls evaluated include those defined by NEI 04-07 guidance, and also a 7D ZOI refined by WCAP-16710-P for LDFG insulation.

7D ZOI debris quantities represent the tested 7D fiber debris size distribution described in the WCAP-1 6710-P test report. Limiting break is on the "B" Loop Crossove r Leg for the 7D ZOI, and on the "B" Loop Hot Leg for the 17D ZOI.** The refined quantities of fiber at the sump strainer shown do not include a 10% analytical increase accounting for measured latent fiber and other contingencies.

The contribution of fiber fines (constituent fibers) is incorporated into strainer head loss through erosion".Strainer Head Loss, NPSH Margin, and ECCS Strainer Structural Limitations After a LOCA, early in the event the sump pool temperature (and therefore the pool vapor pressure) determines the limiting conditions for operation of the ECCS sump strainer in the recirculation phase. Since the strainer head loss has not yet reached its maximum, the available NPSH margins for the RHR and CS pumps are minimized because the pool temperature is high (and vapor pressure is high).As the event continues and the head loss across the strainer increases over time (i.e., due to chemical effects, increases in pool density and changes in the debris Page 2 of 4 Amended Supplemental Response to Staff Request for Additional Information (RAI) #12 Catawba Nuclear Station Units 1 and 2 Generic Letter 2004-02 bed morphology), the strainer structural margin becomes more limiting, since the NPSH available for the ECCS recirculation pumps increases substantially.

For this reason, the limiting NPSH margins for the RHR and CS pumps exist early in the event, at the time of pump suction realignment to the ECCS sump pool.Maximum Projected Strainer Head Loss The maximum projected head loss across the Catawba ECCS Sump Strainer within the first day following a LOCA is shown in Table 12-2. At this time interval, the sump pool temperature is predicted to be between 120°F and 130°F (maximum safeguards/maximum flowrate).

Table 12-2 Maximum (16,000 gpm) I* Clean strainer head loss The maximum projected head loss across the Catawba ECCS Sump Strainer during the entire ECCS mission time (30 days) is shown in Table 12-3. At this time interval, the sump pool temperature is predicted to be approximately 90 0 F.Table 12-3 Limiting ECCS Sump Recirculation Pump NPSH Margins The Catawba ECCS sump recirculation pump NPSH margins are shown in Table 12-4 and Table 12-5. For conservatism, the limiting NPSH margin is given at the maximum ECCS sump pool temperature of 190'F and the maximum recirculation flow condition.

At the time of pump suction realignment to the ECCS sump pool, page 3 of 4 Amended Supplemental Response to Staff Request for Additional Information (RAI) #12 Catawba Nuclear Station Units 1 and 2 Generic Letter 2004-02 the head loss across the Catawba ECCS sump strainer is conservatively predicted to be 5.4 feet of water.Table 12-4 Limiting NPSH Margin for Catawba Containment Sj R~ecirCUlation Flow SCondition

• NPSH available is referenced to the Catawba ECCS Sump minimum strainer submergence elevation (2 feet, 9 inches submergence) and does not credit containment overpressure.

• • Limiting NPSH occurs when the Sl pumps are aligned to the RCS Hot Legs, with an assumed failure of the "B" train of RHR.Table 12-5* NPSH available is referenced to the Catawba ECCS Sump minimum strainer submergence elevation (2 feet, 9 inches submergence) and does not credit containment overpressure.

• • Limiting NPSH occurs when the Sl pumps are aligned to the RCS Hot Legs, with an assumed failure of the "B" train of RHR.The Catawba ECCS sump strainer meets the ECCS sump recirculation pump NPSH requirements with the predicted debris loading, and, as reported in the 2/29/08 Catawba GL 2004-02 submittal, meets all AISC, AWS, and ASME code allowable stresses at the maximum predicted head loss condition (highest flowrate and lowest temperature).

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