ML092040006

RAI, Regarding Response to Generic Letter 2004-02 (Tac No. MC4691)

ML092040006
Person / Time
Site:	Kewaunee
Issue date:	08/14/2009
From:	Tam P Plant Licensing Branch III
To:	Heacock D Dominion Energy Kewaunee
Tam P
References
GL-04-002, TAC MC4691
Download: ML092040006 (11)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 August 14, 2009 Mr. David A. Heacock President and Chief Nuclear Officer Dominion Nuclear Dominion Energy Kewaunee, Inc.

Innsbruck Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711

SUBJECT:

KEWAUNEE POWER STATION - REQUEST FOR ADDITIONAL INFORMATION REGARDING RESPONSE TO GENERIC LETTER 2004-02 (TAC NO. MC4691)

Dear Mr. Heacock:

The Nuclear Regulatory Commission (NRC) staff is reviewing the submittals provided by Dominion in response to Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design-Basis Accidents at Pressurized Water Reactors." On June 22,2009, we emailed a draft Request for Additional Information (RAI) (Agencywide Documents Access and Management System Accession No. ML091740641) on your submittals to your staff. On July 14, 2009, the NRC staff discussed the draft RAI with your staff by conference call. Participants in the conference call agreed to delete Question 1.e, and to revise Question 8 of the draft RAI. Enclosed please find the RAI as finalized.

Your staff had proposed that a conference call be held around September 14,2009, when we will discuss your planned responses to the RAI in detail. We will also discuss the schedule for your response to this RAI.

C?;SiZ P~ S. Tam, Senior Project Manager Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-305

Enclosure:

RAI cc w/encls: Distribution via ListServ

KEWAUNEE POWER STATION REQUEST FOR ADDITIONAL INFORMATION SUPPLEMENTAL RESPONSES TO GENERIC lETTER (Gl) 2004-02 DATED 02/29/2008 AND 12/18/2008 A. Break selection

1. Please provide the following additional information regarding the break selection evaluation:

a. the systematic method used in the break selection evaluation,

b. the specific locations of the selected breaks along their respective piping component,

c. specification of which reactor coolant loop contains the pressurizer,

d. justification for not having a reactor vessel nozzle break in the list of break selections.

B. Debris generation/Zone of Influence

2. Please justify adopting the safety evaluation-approved 5.45D zone of influence for calcium silicate insulation for the Thermobestos installed at Kewaunee by comparing the respective jacketing/banding systems to ensure that the Thermobestos is as well-protected as the Ontario Power Generation-tested calcium silicate insulation.

3. Please describe the repairs that were made to the calcium silicate (Thermobestos) and fiberglass insulation systems that justify reducing the amounts of debris generated by these two insulation types. State the zones of influence used for these materials in the updated debris generation evaluation.

Provide the bases and assumptions for the bases for the zones of influence if they differ from those in the staff Safety Evaluation on the Nuclear Energy Institute Guidance Report 04-07.

4. Please verify that all latent debris is assumed to be fines or provide a justification for any different classification. Specify separately the amount of latent particulate and latent fiber assumed in the evaluation.

5. Please identify the amount of TempMat assumed to be initially rendered into fines and the basis for the assumption.

6. Please identify the amount of each type of debris that is considered to erode into fines over the mission time of the strainer. The total amount of TempMat fines was significantly reduced in the updated (12/18/08) supplemental response even though the total amount damaged remained the same between the two responses. This seemed to be due to a smaller erosion percentage. In addition, the staff could not determine the amount of Thermobestos erosion. Please provide a percentage of each material and the total amount (mass or volume) considered to erode, ineludinq basis for the numbers provided.

- 2 C. Debris Characteristics

7. Please state the debris size distribution assumed and the amount of debris in each size category assumed to be generated for the following types of debris and provide a technical basis:

a. Thermobestos (Note that although a 5.45D was adopted for this material from the NEI 04-07 guidance based upon a comparison to calcium silicate insulation, from Table 3.E-1 in the December 18, 2008, supplement, it appeared that the NEI 04-07 guidance was not followed in that calcium silicate should be assumed to be destroyed into 100 percent small fines.

Specifically, some of the Thermobestos debris appeared to have been treated as large pieces.)

b. Fiberglass pipe cover D. Latent debris

8. The staff noted the licensee provided estimates of the mass of latent fiber and particulate. However, only a brief description of the methodology used to estimate the quantity of the latent debris was provided. The staff determined that the methodology was not presented in sufficient detail to judge its adequacy and conservatism. Similarly, the staff noted that although the licensee provided quantitative estimates of the area of tapes, tags, signs and stickers, the procedure used was described insufficiently to jUdge the adequacy and conservatism of the evaluation. The staff also noted that latent debris quantity (11.3 Ibm) is the lowest measured latent debris quantity of any pressurized-water reactor plant (approximately 1/1Oth the median value), even though the containment sampling was performed during a relatively dirty condition with work in progress. The licensee stated that its strainer head loss analysis and testing assume 100 Ibm of latent debris, substantially greater than the 11.3 Ibm measured but staff notes, that many plants (including some with low amounts of fibrous and/or particulate insulation), have measured more than 100 Ibm of latent debris in containment, so staff needs to have confidence that the licensee's sampling method is sufficiently accurate that the 100 Ibm assumed for testing is conservative. Therefore, please describe the surfaces where samples were collected and the number of samples per surface. Please justify that the sample locations were representative of floors, walls, ductwork and equipment surfaces where latent debris could collect. Please summarize the extrapolation/statistical method used to estimate the total latent debris quantity in containment.

E. Debris Transport

9. Insufficient information was provided in the supplemental response to demonstrate that the debris interceptor testing was conducted in a manner that is prototypical of the expected plant condition. If the interceptor tests are not being used to demonstrate adequate strainer performance, please so state, and the additional questions below need not be addressed. If the interceptor tests are being used to demonstrate adequate strainer performance, then please provide the following additional information concerning the debris interceptor testing:

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a. the basis for adding debris with the test pump stopped

b. a description of the procedure for preparing fine debris

c. a discussion as to whether fine and small debris were prepared and weighed separately to determine the quantities used for testing

d. discussion concerning the concentration in the debris slurries prepared for testing and the potential for debris to agglomerate during preparation and addition in a nonprototypical manner

e. description of the debris addition sequence for all types and sizes of debris used in the test. If particulate debris was not included, then please justify not including it in the testing, since it could result in increased flow restriction at the interceptors, leading to greater flow over the tops of the interceptors, consequently increasing downstream transport.

f. description of how far in front of the debris interceptor the debris was added to the test flume and a technical basis

g. description of whether a case considering total blockage at the debris interceptors was considered in the test matrix

h. the technical basis for scaling the debris quantity used for debris interceptor testing to the total debris interceptor area

i. description of the extent to which floating transport was analyzed by the test program, since the debris was likely mixed with water (thereby removing trapped air) prior to the test initiation

j. discussion of any sources of drainage from containment spray, the refueling canal, the pipe rupture, etc., that enter the containment pool near the strainer, and the technical basis for considering the overhead sprays used in the test as representative of the plant condition that would likely involve more concentrated streams of break and spray drainage

k. comparison of the range of velocity and turbulence conditions used for the debris interceptor testing to the computational fluid dynamics calculation for the plant condition and the technical basis for the flow conditions used for the testing I. discussion of the flume width and water level used for flume testing and whether these parameters are representative of the analogous parameters for Kewaunee

m. description of the physical characteristics of the debris interceptors including at a minimum the height of the interceptors, the size of any openings in the interceptors, and the total surface area of the debris interceptors

n. discussion of the specific individual percentages of the fines and of small pieces that transported downstream of the debris interceptors

o. the technical basis for using a 40 percent fines and 25 percent small pieces size distribution for Thermobestos and Okotherm debris. Please further describe the form of the remaining 35 percent of the Thermobestos and Okotherm debris and provide a technical basis for this debris not being considered as transporting to the debris interceptors either in its destroyed form or as eroded fines.

p. description of how the results of the debris interceptor testing are being applied to the Kewaunee strainer performance analysis and identification of the quantities of each type and size of debris assumed to be trapped on the plant debris interceptors.

q. description of the methodology used to determine the differential pressure across the debris interceptors due to debris blockage to ensure structural adequacy.

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r. explanation for why the interceptor tests with less debris added to the flume experienced greater percentages of debris downstream of the interceptor.

10. The supplemental response described erosion testing that was used as a basis for the assumption of 10 percent erosion of fiberglass pipe cover and Temp Mat fibrous debris.

a. Please describe the test facility used and demonstrate the similarity of the flow conditions (velocity and turbulence), chemical conditions, and fibrous material present in the erosion tests to the analogous conditions applicable to the plant condition.

b. Please justify taking credit for any erosion tests conducted at a minimum tumbling velocity if debris settling was credited in the test flume for velocities in excess of this value (e.g., in front of the debris interceptor).

c. Please identify the duration of the erosion tests and describe how the results were extrapolated to the sump mission time.

11. Please identify whether erosion of Thermobestos debris in the containment pool was accounted for in the sump performance analysis. Please state the erosion percentage assumed over a 30-day period and discuss the technical basis for the assumed erosion percentage.

12. Please describe whether/how erosion of debris that settles in the test flume is accounted for in the sump performance evaluation. If this phenomenon was neglected, please estimate the quantity of eroded fines from large and small pieces of fibrous and Thermobestos debris that would result had erosion of the settled debris in the head loss test flume been accounted for and justify the neglect of this material in the head loss testing program. If this eroded debris is not accounted for in a prototypical or conservative manner, then please provide a basis for the conservatism of the analytical debris erosion results given that the analysis significantly underestimates the total quantity of settled debris (when debris that settled in the test flume is considered).

13. Please identify the computational fluid dynamics code used to determine the flow pattern in the containment pool and provide an overview of the simulations run and modeling assumptions. In addition to this general discussion, please also provide the following specific information:

a. description of how the debris interceptors were modeled in the input deck (e.g., as a porous medium, fully blocked, time-dependent modeling, etc.) and how the flow split between the various interceptors was determined.

b. description of the locations where drainage from the break, containment sprays, and any other sources of significant water addition, is assumed to enter the containment pool and how they are modeled in the code.

c. description of the size of the computational domain and boundary conditions in the model.

d. discussion of the main physical models used in the computational fluid dynamics simulation (e.g., turbulence).

e. basis for concluding that the simulations run are bounding with respect to debris transport.

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14. Drainage from the elevation above the containment basement was assumed to reach the containment pool primarily through the south stairwell due to a 2-inch floor collar, weirs, and a toe-rail at the north stairwell. Following a loss-of-coolant accident, if large pieces of debris are able to settle out on this floor elevation, flow to the south stairwell could be partially restricted, resulting in pooling of water and redirection of part of the drainage through the north stairwell that is closer to the containment sump strainer. Please describe how these phenomena were analyzed in the debris transport calculation, how flow to the containment pool was distributed between the north and south stairwells, and whether any hold up of water on this elevation was considered.

15. Please provide contour plots of the velocity and turbulence in the containment pool. Please also provide close-up plots of the velocity and turbulence contours in the region of the strainer and its immediate surroundings. In addition, please provide a table of the head loss test flume (average) velocity as a function of distance from the test strainer and the basis for the velocities chosen. Please identify the turbulence level simulated in the test flume and state the flume width(s) used for testing.

16. Please identify the distance from the strainer at which debris was added to the test flume. Please justify the conservatism or prototypicality of this distance based on the transport analysis results for blowdown, washdown, and pool-fill transport.

17. Please describe how the potential for debris transport in the vicinity of the strainer via floatation was considered in the head loss tests for Kewaunee.

F. Head Loss and Vortexing

18. Please provide the clean strainer head loss (CSHL) methodology for the non strainer portions of the assembly. Please provide the assumptions used for the CSHL calculation.

19. Very little head loss and vortexing information was included in either submittal.

Please provide information on the testing conducted on the strainer including the following, along with other relevant information:

a. Identify the maximum debris head loss measured during testing. Identify the test clean strainer head loss portion of the total separately. Provide the temperature at which the head loss was measured.

b. Provide information that clearly shows how the debris head loss was extrapolated to temperatures other than the test temperature. If plant CSHL was adjusted for temperature, please provide the CSHL at the various temperatures that were considered. Provide the plant CSHL and debris head loss separately for each temperature.

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c. Provide the head loss test methodology including details of the following, for each test:

i. debris introduction sequences ii. if any debris additions, including latent debris surrogate, were made at less than the scaled 100 percent flow rate, provide the flow rate at which the debris was added iii. debris preparation methodology and resulting surrogate size distributions iv. debris characteristics for all debris surrogates used during testing

v. general procedure/steps for conducting the tests vi. description of the test facility vii. description of debris introduction techniques including the debris mixtures and concentration (with respect to water) for each debris addition viii. thin bed incremental amounts of fibrous debris added (theoretical thickness and the basis) and the type(s) of fiber added ix. the amounts (volume or mass) of each size (fine, small, etc.) of all debris that was added to the test flume for each debris addition, and the location of the debris addition with respect to other equipment within the test flume

x. scaling factors xi. flow rates xii. verification that particulate debris surrogate amounts were density corrected so that the required volume of surrogate was used during testing xiii. statement as to whether stirring was used, and if used, whether the stirring affected the debris bed (either by forcing larger debris onto the bed or washing debris from the bed) xiv. the amounts of debris that settled in the test apparatus xv. information that justifies that excessive agglomeration of debris did not occur due to higher than prototypical debris concentrations within the flume or higher than expected concentration during debris addition

20. Please provide a vortexing evaluation including test conditions, assumptions, and their basis. Include any additional vortexing evaluation that was conducted not based.on test observations.

21. Please provide the conditions assumed for the voiding evaluation and their bases. Please include an evaluation for the potential of degasification of the sump fluid as it passes through the debris bed.

22. Please provide the conditions assumed for the evaluation of flashing in the strainer and their bases. Please provide the margin to flashing for each condition considered.

23. Please provide head loss plots for the testing including annotations of relevant steps in the tests.

24. Please provide information on whether the strainer is vented.

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25. Please provide the head loss test termination criteria. Include test data that verifies the criteria were met.

26. Please provide any extrapolation of head loss test results to the plant strainer mission time and the methodology used. Please provide adequate data that the staff can verify that the extrapolation was performed conservatively.

27. Please provide a schematic representation of the test flume that includes relevant measurements and articles within the flume.

28. Please state whether any debris interceptors were included in the head loss testing. If debris interceptors were included in the testing, please provide details of how the debris interceptors are installed in the plant and how the interceptors were installed in the test flume. Please provide adequate details so that the staff can evaluate the prototypicality of the test setup against the plant.

G. Net Positive Suction Head (NPSH)

29. The basis for the stated design flow rates for the residual heat removal (RHR) pumps was not provided. Please provide the methodology and assumptions for the calculation of these flow rates.

30. The basis for the NPSH required for the RHR pumps at the design flow rate was not provided. Please provide the basis for the RHR pump NPSH required, including any assumptions or acceptance criteria used by the pump vendor.

31. The methodology for the calculation of suction line friction head losses for the NPSH calculations was not provided. Please provide the NPSH calculation methodology along with the calculation's assumptions and the bases for these assumptions.

32. Differences between the conditions and assumptions for the small- and large break loss-of-coolant accident cases were not provided. Please provide any differences in conditions for the small- and large-break loss-of-coolant accident cases or demonstrate one case to be limiting.

33. Please discuss the potential for differences between hot-leg and cold-leg injection flow rates and NPSH margins. Alternatively, please demonstrate that the evaluated case is limiting or that other cases are not required at Kewaunee.

34. Please identify the water sources and hold up volumes considered in the minimum water level calculation and provide quantitative values for each hold up volume for the limiting water level for the small- and large-break loss of coolant accident cases.

35. Please identify whether the emergency operating procedures would allow operators to manually operate two trains of RHR in recirculation mode. If this configuration is allowed, quantify its impact on the pumps' NPSH margin. Please provide similar information regarding the operation of the internal containment spray system in recirculation mode.

-8 H. Structural analysis

36. In accordance with the first portion of Section 3.k of the Revised Content Guide for Generic Letter 2004-02 Supplemental Responses, licensees were requested to provide the design code of record used in the structural qualification of their replacement strainer components. The licensee did not provide this information in the supplemental responses. Please provide the applicable code(s) of record for the qualification of the strainer modules, piping, piping supports, Sump B pit cover, Sump B pit maintenance hatch strainer, and any other applicable components.

37. In accordance with the second portion of Section 3.k of the Revised Content Guide for Generic Letter 2004-02 Supplemental Responses, licensees were requested to provide the design margins for the strainer components which were analyzed for structural adequacy. Please provide and summarize, in tabular form, the design margins and or/interaction ratios for the strainer components analyzed for resolution of GL 2004-02.

38. The third portion of item 3.k of the revised content guide for the GL 2004-02 supplemental responses requests that the licensees "Summarize the evaluations performed for dynamic effects such as pipe whip, jet impingement, and missile impacts associated with high-energy line breaks (as applicable)." Please provide a detailed summary along with any additional supporting information regarding the assessment that the strainer modules are not subject to the aforementioned dynamic effects.

39. Figure 4 of the licensee's February 2008, supplemental response, indicates that three debris interceptors were installed as part of Dominion Energy Kewaunee, Inc.'s GL2004-02 resolution efforts. However, these components were not mentioned in Section 3.k of the supplemental response. Please provide additional information regarding the structural adequacy of these components including a description and summary of the structural analyses that were performed to demonstrate the ability of these components to maintain their structural integrity during a design-basis accident.

I. Upstream Effects

40. Please describe the size of the refueling cavity drainline, the minimum flow restriction in this line, and any line losses associated with the drain line. Please also describe the types and quantities of debris that could transport to the refueling cavity, and the basis for concluding that debris blockage or partial blockage will not occur at the cavity drain. The evaluation should account for the potential for some types of debris to remain buoyant following a loss-of-coolant accident, transport toward the cavity drain due to surface currents, and potentially sink on top of the cavity drain as water gradually displaces the air trapped in the debris material's pores. Please quantify the holdup volume assumed for the refueling cavity in the containment pool minimum water level calculation.

- 9 J. Downstream effects/in-vessel

41. The NRC staff considers in-vessel downstream effects to not be fully addressed at Kewanee as well as at other pressurized-water reactors. The licensee's submittal refers to draft WCAP-16793-NP, "Evaluation of Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid."

The NRC staff has not issued a final SE forWCAP 16793-NP. The licensee may demonstrate that in-vessel downstream effects issues are resolved for Kewanee by showing that the licensee's plant conditions are bounded by the final WCAP 16793-NP and the corresponding final NRC staff SE, and by addressing the conditions and limitations in the final SE. The licensee may also resolve this item by demonstrating without reference to WCAP-16793 or the staff SE that in-vessel downstream effects have been addressed at Kewanee. In any event, the licensee should report how it has addressed the in-vessel downstream effects issue within 90 days of issuance of the final NRC staff SE on WCAP-16793.

K. Chemical Effects

42. Please identify and justify all plant-specific refinements made to the WCAP 16530-NP base chemical model predictions and indicate how much each refinement reduced the predicted amount of precipitate compared with the October 2006, analysis. For example, if silicate inhibition was credited, please provide justification. Please provide any relevant bench-top testing and analysis that support reduction of the Kewaunee-specific chemical precipitate loading.

Discuss why the overall plant-specific chemical effects evaluation remains conservative when crediting reductions to the WCAP-1530-NP base chemical model. Additional information concerning staff expectations for the use of plant specific refinements to WCAP-16530 is available in Section 9 of the Chemical Effects Review Guidance available at ML080380214.

43. The licensee's February 29, 2008, supplemental response, states that the minimum pH range calculation assumes end of cycle and minimum boron concentration. Likewise, the maximum pH is based on beginning of cycle maximum boron concentration. The staff would expect the maximum boron concentration to result in the minimum sump pool pH and the minimum boron concentration to result in the maximum sump pool pH. Please explain the basis for the pH calculations with respect to boron concentration at the beginning and end of cycle. Also, please explain if the volume and concentration of sodium hydroxide is adjusted during the operating cycle.

L. Licensing Basis

44. Please describe any surveillance requirements applicable to the emergency core cooling recirculation strainer installed at Kewaunee to ensure that the strainer is not restricted by debris and that there is no evidence of structural distress or abnormal corrosion.

August 14, 2009 Mr. David A. Heacock President and Chief Nuclear Officer Dominion Nuclear Dominion Energy Kewaunee, Inc.

Innsbruck Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711

SUBJECT:

KEWAUNEE POWER STATION - REQUEST FOR ADDITIONAL INFORMATION REGARDING RESPONSE TO GENERIC LETTER 2004-02 (TAC NO. MC4691)

Dear Mr. Heacock:

The Nuclear Regulatory Commission (NRC) staff is reviewing the submittals provided by Dominion in response to Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design-Basis Accidents at Pressurized Water Reactors." On June 22, 2009, we emailed a draft Request for Additional Information (RAI) (Agencywide Documents Access and Management System Accession No. ML091740641) on your submittals to your staff. On July 14, 2009, the NRC staff discussed the draft RAI with your staff by conference call. Participants in the conference call agreed to delete Question 1.e, and to revise Question 8 of the draft RAI. Enclosed please find the RAI as finalized.

Your staff had proposed that a conference call be held around September 1, 2009, when we will discuss your planned responses to the RAI in detail. We will also discuss the schedule for your response to this RAI.

Sincerely, IRAJ Peter S. Tam, Senior Project Manager Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-305

Enclosure:

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