ML083080350

Request for Additional Information (RAI) Regarding Supplemental Responses to Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized

ML083080350
Person / Time
Site:	McGuire, Mcguire
Issue date:	11/18/2008
From:	Stang J Plant Licensing Branch II
To:	Brandi Hamilton Duke Energy Carolinas
Thompson Jon, NRR/DORL/LPL 2-1, 415-1119
References
TAC MC4692, TAC MC4693
Download: ML083080350 (12)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 18, 2008 Mr. Bruce H. Hamilton Vice President McGuire Nuclear Station Duke Energy Carolinas, LLC 12700 Hagers Ferry Road Huntersville, NC 28078 SUB..IECT:

MCGUIRE NUCLEAR STATION, UNITS 1 AND 2, REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING SUPPLEMENTAL RESPONSES TO GENERIC LETTER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS" (TAC NOS.

MC4692 AND MC4693)

Dear Mr. Hamilton:

By letters dated February 28,2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML080730131) and April 30, 2008 (ADAMS Accession No. ML081280488), Duke Energy Carolinas. LLC (the licensee) submitted a supplemental response to Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors," for the McGuire Nuclear Station, Units 1 and 2 (McGUire). The U.S. Nuclear Regulatory Commission (NRC) has reviewed the licensee's submittals. The process involved detailed review by a team of approximately 10 NRC staff subject matter experts, with a focus on the review areas described in the NRC staff's revised "Content Guide for Generic Letter 2004-02 Supplemental Responses" sent by letter dated November 21, 2007 (ADAMS Accession No. ML073110389). Based on these reviews, the NRC staff has determined that additional information is needed in order to conclude there is reasonable assurance that GL 2004-02 has been satisfactorily addressed for McGuire. The enclosed document describes this request for additional information (RAI).

The NRC staff requests that the licensee respond to this RAI within 90 days of the date of this letter. However, the NRC staff would like to receive only one response letter for all RAI questions with exceptions stated below. If the licensee concludes that more than 90 days are required to respond to this RAI, then the licensee should request additional time and include a basis for why the extension is needed.

If the licensee concludes, based on its review of the RAI, that additional corrective actions are needed for GL 2004-02, the licensee should request additional time to complete such corrective actions as needed. Criteria for such extension requests are contained in SECY-06-0078 (ADAMS Accession No. ML053620174), and examples of previous requests and approvals can be found on the NRC's sump performance website, located at:

http://www.nrc.gov/reactors/operating/ops-experience/pwr-sump-performance.html.

B. Hamilton

- 2 Any extension request should also include results of contingency planning that will result in near term identification and implementation of any and all modifications needed to fully address GL 2004-02. The NRC staff strongly suggests that the licensee discuss such plans with them before formally transmitting an extension request.

The exception to the above response timeline is RAI question 31 contained in the enclosure.

The NRC staff considers in-vessel downstream effects to not be fully addressed at McGuire, as well as at other pressurized water reactors. The licensee's submittal refers to Topical Report (TR) WCAP-16793-I\\lP, Revision 0, "Evaluation of Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid" (ADAMS Accession No. ML071580139). At this time, the NRC staff has not issued a final Safety Evaluation (SE) for TR WCAP-16793-NP.

In the future, the licensee may demonstrate that in-vessel downstream effects issues are resolved for McGuire by showing that McGuire plant conditions are bounded by the approach described in TR WCAP-16793-NP, after the TR's approval, and by addressing the conditions and limitations described in the final NRC staff's SE for the approved version of this TR. The licensee may also resolve RAI question 31, without reference to the approved version of TR WCAP-16793-NP and the associated conditions and limitations described in the final NRC staff's SE for this TR, by demonstrating that in-vessel downstream effects have been addressed at McGuire. The specific issues raised in RAI question 31 should be addressed regardless of the approach the licensee chooses to take.

The licensee should report how it has addressed the in-vessel downstream effects issue and the associated RAI referenced above within 90 days of issuance of the final NRC staff's SE for TR WCAP-16793-I\\lP. The I\\lRC staff is currently developing a Regulatory Issue Summary to inform licensees of the NRC staff's expectations and plans regarding resolution of this remaining aspect of Generic Safety Issue 191, "Assessment of Debris Accumulation on PWR Sump Performance."

Sincerely,

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':i i\\i Jo n Stang, Senior ~roject Manager Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-369 and 50-370

Enclosure:

Request for Additional Information cc w/encl: Distribution Via ListServ

REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING SUPPLEMENTAL RESPONSES TO GENERIC LETTER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURllED WATER REACTORS" MCGUIRE NUCLEAR STATION, UNITS 1 AND 2

1.

Please state whether the testing identified in the test report WCAP-1671 O-P, "Jet Impingement Testing to Determine the lone of Influence (lOI) of Min-K and Nukon Insulation for Wolf Creek and Callaway Nuclear Operating Plants," was specific to the McGuire Nuclear Station, Units 1 and 2, (McGuire) insulation systems. If not, please provide information that compares the McGuire encapsulation and jacketing systems structures with the systems that were used in the testing, showing that the testing conservatively or prototypically bounded potential damage to the insulation materials.

2.

Considering that the McGuire debris generation analysis diverged from the approved guidance contained in NEI 04-07, "Pressurized Water Reactor Sump Performance Evaluation Methodology," Revision 0, please provide details on the testing conducted that justified the lOI reductions for jacketed Nukon. The information should include the jacket materials used in the testing, geometries and sizes of the targets and jet nozzle, and materials used for jackets installed in the plant. Please provide information that compares the mechanical configuration and sizes of the test targets and jets, and the potential targets and two-phase jets in the plant. Please provide an evaluation of how any differences in jet/target sizing and jet impingement angle affect the ability of the insulation system to resist damage from jet impingement. Please state whether the testing described in test report WCAP-1671 O-P was bounding for the McGuire insulation systems. If not, please provide information that compares the McGuire encapsulation and jacketing systems structure with the system that was used in the testing, showing that the testing conservatively or prototypically bounded potential damage to the insulation materials.

3.

Please clarify if unjacketed Nukon is present in the McGuire containment and, if so, please state whether the 170 lOI was used instead of the 70 lOI. Please provide the resultant debris quantities for unjacketed I\\lukon. (Section 3(b)(2) of the supplemental response sent by letter dated February 28, 2008, stated that unjacketed Nukon was present within the evaluated lOis. The supplemental response further stated that test report WCAP-1671 O-P demonstrates a refined 70 lOI for jacketed Nukon insulation, but was silent with respect to how unjacketed Nukon was handled with respect to lOI reduction from 170 to 70.)

4.

Please state whether or not the break location selection was revisited when the lOI for fibrous insulation was changed from 170 to 70. If break selections were not revisited, please provide the rationale for not doing so. If the break selections were revisited, please provide the top four breaks in terms of debris generation for the 70 lOI. (The Enclosure

- 2 supplemental response sent by letter dated February 28, 2008, indicates only that the break locations already identified for a 170 lOI were reassessed for debris quantity generation and confirmed not to have changed relative ranking.)

5.

Provide information that compares the ability of the McGuire fibrous jacketing system and the test report WCAP-1671 O-p-tested jacketing system to resist steam jet damage.

Please provide information that demonstrates that the McGuire jacketing is at least as structurally robust as the jacketing that was subjected to the test report WCAP-1671 O-P steam jet impingement testing.

6.

Please provide information that verifies that test report WCAP-1671 O-P testing used to justify a lOI reduction from 170 to 70 for jacketed fiber insulation was conducted prototypically or conservatively. Include information on nozzle size, target size, and the various test configurations Get to target distance and relative angle, location of jacket seams, etc) conducted to show that the testing was prototypical or conservative.

7.

Please provide the fibrous size distribution (including debris amounts determined) for the debris generation calculation based on the 70 lOI.

8.

Please provide details regarding the tags and labels equipment qualifications and engineering judgments used as basis for reduction of tag and label quantities which were originally assumed to fail and reach the sump. Provide the technical basis for the conclusion that tags and labels outside the crane wall in lower containment are capable of withstanding post-Ioss-of-coolant accident (post-LOCA) conditions. Justify the application of the Institute of Electrical and Electronics Engineers (IEEE) Standard 323-1974, "IEEE Standard for Qualifying Class 1 E Equipment for Nuclear Power Generating Stations," in qualifying Electromark labels for a post-LOCA environment.

9.

Please provide the technical basis for the latent fiber and particulate total mass calculation. Include a description of surface types sampled, the number of samples per surface type, the accuracy of the mass measurement, the method of computing the densities for specific areas, and the extrapolation to the scale of containment.

10.

Please provide the details of the methodology used for the tag and label refinement evaluation. Provide details of the equipment qualifications and engineering judgments used as basis for reduction of tag and label quantities which are assumed to fail and reach the sump.

11.

Please provide the technical basis for the assumption of 10-percent erosion of fibrous debris in the containment pool. If testing was performed, please demonstrate the similarity of the flow conditions, chemical conditions, and fiberglass material present in the test or tests versus the conditions expected in the McGuire containment pool.

12.

Please provide the results of the array testing conducted at the Alion Science and Technology Corporation and the Integrated Prototype Test (IPT) testing conducted at Wyle Laboratories. For the IPT testing, in addition to head loss values, please provide the results as a function of time. Provide a thorough description of the methodology used to combine the two test results to determine the final head loss for the strainer

- 3 debris bed. If a correlation was developed to determine head loss, provide the correlation along with the assumptions and bases used in the development of the correlation.

13.

The conditions under which vortex testing was conducted for McGuire, and the plant conditions for which the testing was being conducted, are not clear from the available documentation. Based on the information provided to date, the NRC staff has been unable to determine what conditions resulted in vortex formation and whether the modifications made to eliminate vortices were tested under conditions that conservatively represented those expected in the plant post-LOCA. Vortex testing was conducted at 3-inch submergence (as stated in the Duke Energy Carolinas (Duke) response to RAI question 39 in Enclosure 1 to the supplemental response dated February 28, 2008), which is greater than the expected 2-inch minimum submergence for a small break loss-of-coolant accident (SBLOCA) (as stated in Section 3(f)(2) of of the supplemental response). Note that Duke further states in its response to RAI question 39 in Enclosure 1 that the minimum submergence for the strainer is expected to be "at least" 2 inches and separately that it is "about" 4 inches (Enclosure 1, pages 35-36). Enclosure 2, Section 3(f)(2), also states that the strainer is submerged by at least 2 inches while Enclosure 2, Section 3(f)(3), states that the grating is submerged by at least 2 inches. Enclosure 2, Section 3(f)(3), also states that the testing was performed with a "few inches" of submergence. This set of disparate strainer submergence values does not provide a coherent description of the test conditions., Section 3(f)(3), states that the testing was conducted at velocities between 0.01 tt/sec and 0.09 tt/sec, while the maximum approach velocity for the strainer is 0.052 tt/sec, The response does not provide a basis for the 0.052 ft/sec, other than the expected maximum approach velocity is greater than nominal by about a factor of 2 (Enclosure 1, pages 35-36), and does not clearly state that testing at or above 0.052 tt/sec did not result in vortices.

Please provide information that describes the conditions expected in the plant and those present during testing, including the following information:

a. Please clarify what the actual minimum submergence for the strainer is expected to be in the plant.

b. If different evaluations for vortexing were conducted for SBLOCAs and large break loss-of-coolant accidents (LBLOCAs), please provide details for each evaluation.

c. Please provide the basis for the maximum approach velocity.

d. Please provide a quantitative value for the approach velocity during which vortices were observed to form when no vortex suppressors were installed.

e. Please provide a quantitative value for the submergence level at which the testing was conducted with no vortex suppressors installed. If the level changed (e.g between SBLOCA and LBLOCA tests), please provide the test conditions for each test.

- 4

f. Please provide information for testing that was conducted with the vortex suppression grating in place, including the minimum submergence and maximum approach velocities that were present when vortices did not occur.

g. Provide a quantitative value for the vortex suppressor submergence in the reactor plant. If some suppressors are installed at different elevations than others, provide the submergence level for each location.

14.

Please provide a response to the question from the revised NRC Content Guide sent by letter dated November 21, 2007, relating to Enclosure 2 of the supplemental response dated February 28,2008, Section 3(f)(5), regarding the ability of the strainer to accommodate the maximum potential debris volume. This response should apply specifically to the McGuire strainer and not be a general answer (as is found in, Section 3(f)(5)). The McGuire response to Enclosure 1, RAI question 40, sends the reader to Enclosure 2, Sections 3(f) and 3(0) to find this information. The information is contained in neither location.

15.

Please provide information that verifies that the debris preparation and introduction methods used during the array test and IPT were prototypical or conservative with respect to the transport evaluation for the plant. In general, protocols for fibrous debris preparation result in debris that is coarser than predicted by the plant-specific transport calculation. In addition, the NRC staff has noted that debris introduction frequently results in agglomeration of debris such that it may not transport to the strainer prototypically or create a prototypical debris bed. Both of these issues can result in non conservative head loss values during testing.

16.

Please provide information on the 'flowfields in the array test. The NRC staff is concerned that non-prototypical debris distribution may have occurred during testing caused by stirring of the tank. The stirring can result in the transport of debris that would otherwise not transport, or result in washing debris from the strainer screen surfaces.

Either of these phenomena can result in reduced (non-conservative) head loss values during testing.

17.

Please provide debris preparation and introduction information similar to that requested in this enclosure, RAI question 15, for the testing that was used to justify that a thin bed would not form on a top hat strainer. Note that for thin bed testing, the NRC staff considers it prototypical or conservative for fine fiber to arrive at the strainer prior to less transportable debris. Overly coarse debris preparation or non-prototypical introduction to the flume may non-conservatively affect the potential for thin bed formation.

18.

Please provide the criteria used to judge that differential pressure-induced effects (e.g.,

boreholes) did not occur during testing.

19.

Please provide the scaling parameters used for calculation of debris quantities and strainer approach velocities used during testing. State whether the scaling accounted for strainer areas blocked by miscellaneous debris such as labels and tape.

- 5

20.

Please provide information on whether the amount of coatings surrogate was adjusted for the volume difference created by the difference in density between the surrogate material and the potential debris in the plant.

21.

Please discuss the NRC staff's observation that in the IPT the flow was non prototypically directed at the top hat strainer in a direction parallel to the strainer long axis. Please address whether this non-prototypical 'flow direction could result in a non prototypical formation of debris on the top hat strainer.

22.

Please provide the clean strainer head loss for McGuire Unit 2 (only the clean strainer head loss for McGuire Unit 1 was provided).

23.

The supplemental response stated that the total head loss across the McGuire Emergency Core Cooling System Sump strainer (clean strainer head loss plus debris bed head loss) was conservatively predicted to be 9.8 ft at switchover to sump recirculation. No explanation was provided as to how this value was derived. It appears that the licensee is taking credit for time-dependency in head loss, since the 30-day value is 15.7 ft. Please provide the time-dependent results and calculation methodology for determining net positive suction head margin throughout the 30-day mission time.

24.

Please provide the types and amounts of debris added to each test (Array and IPT).

Include information on introduction sequence. Please provide relevant test parameters such as temperature, debris introduction times, and flow rate for the Array and IPT tests.

25.

Please provide information on the amounts of debris that settled during testing for each test (IPT, Array, and Thin Bed). Note that Enclosure 1, response to RAI question 37, states that near-field settling was not credited during testing. However, the NRC staff observed significant settling during the IPT. Please provide a quantitative evaluation of how this settling affected head losses for each test. Please state whether this settling is prototypical of plant conditions and provide a basis for the conclusion.

26.

Please provide verification that the unqualified epoxy coatings at McGuire are similar to the coatings used in the Electric Power Research Institute's analysis of original equipment manufacturer coatings. Also, are plant records maintained for the unqualified coatings in order to track quantities and composition?

27.

Please clarify the discrepancy in quantitative values for unqualified epoxy coatings debris in Enclosure 2 to the supplemental response dated February 28, 2008, response to Section 3(e)(6), Tables 3E6-1 and 3H6-2.

28.

Please identify and describe the main features of any procedures that comprise containment cleanliness practices.

29.

Please provide the technical basis for the conclusion that all labels are capable of withstanding post-LOCA conditions in containment except inside the crane wall in lower containment.

30.

The revised "Content Guide for Generic Letter 2004-02 Supplemental Responses," sent by letter dated November 21, 2007, Section 3k, requests a summary of structural

- 6 qualification design margins for the various components of the sump strainer structural assembly. This summary should include interaction ratios and/or design margins for structural members, welds, concrete anchorages, and connection bolts as applicable.

Please provide this information.

31.

The NRC staff considers in-vessel downstream effects to not be fully addressed at McGuire as well as at other pressurized-water reactors. The supplemental response for McGuire refers to the evaluation methods of Section 9 of Topical Report (TR)

WCAP-16406-P, Revision 1, "Evaluation of Downstream Sump Debris Effects in Support of GS-191" for in-vessel downstream evaluations and makes reference to a comparison of plant-specific parameters to those evaluated in TR WCAP-16793-NP, Revision 0, "Evaluation ot Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid." The NRC staff has not issued a final Safety Evaluation (SE) for TR WCAP-16793-NP. The licensee may demonstrate that in-vessel downstream effects issues are resolved for McGuire by showing that the licensee's plant conditions are bounded by the final TR WCAP-16793-NP and the corresponding final NRC staff's SE, and by addressing the conditions and limitations in the final SE. The licensee may also resolve this item by demonstrating without reference to TR WCAP-16793 or the NRC staff's SE that in-vessel downstream effects have been addressed at McGuire. 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's SE on TR WCAP-16793. The NRC staff is developing a Regulatory Issue Summary to inform the industry of the NRC staff's expectations and plans regarding resolution of this remaining aspect of GSI-191.

32.

Please discuss why the IPT provided a representative debris bed on the top-hat strainer module for filtering chemical precipitates. The NRC staff observed the debris addition video and concluded that the fibrous debris introduced into the test tank was more agglomerated than what may arrive at the strainer under post-LOCA How conditions in the plant. Please discuss whether the amount of bare strainer area observed in the test representative of what is expected to occur with the plant strainer array if a LBLOCA were to occur. The use of chemical effects test results derived from a test which formed a non-prototypically partially clean screen fiber bed would not be appropriate.

Any extension request should also include results of contingency planning that will result in near term identification and implementation of any and all modifications needed to fully address GL 2004-02. The NRC staff strongly suggests that the licensee discuss such plans with them before formally transmitting an extension request.

The exception to the above response timeline is RAI question 31 contained in the enclosure.

The NRC staff considers in-vessel downstream effects to not be fully addressed at McGuire, as well as at other pressurized water reactors. The licensee's submittal refers to Topical Report (TR) WCAP-16793-NP, Revision 0, "Evaluation of Long-Term Cooling Considering Particulate, Fibrous, and Chemical Debris in the Recirculating Fluid" (ADAMS Accession No. ML071580139). At this time, the NRC staff has not issued a final Safety Evaluation (SE) for TR WCAP-16793-NP.

In the future, the licensee may demonstrate that in-vessel downstream effects issues are resolved for McGuire by showing that McGuire plant conditions are bounded by the approach described in TR WCAP-16793-NP, after the TR's approval, and by addressing the conditions and limitations described in the final NRC staff's SE for the approved version of this TR. The licensee may also resolve RAI question 31, without reference to the approved version of TR WCAP-16793-NP and the associated conditions and limitations described in the final NRC staff's SE for this TR, by demonstrating that in-vessel downstream effects have been addressed at McGuire. The specific issues raised in RAI question 31 should be addressed regardless of the approach the licensee chooses to take.

The licensee should report how it has addressed the in-vessel downstream effects issue and the associated RAI referenced above within 90 days of issuance of the final NRC staff's SE for TR WCAP-16793-NP. The NRC staff is currently developing a Regulatory Issue Summary to inform licensees of the NRC staff's expectations and plans regarding resolution of this remaining aspect of Generic Safety Issue 191, "Assessment of Debris Accumulation on PWR Sump Performance."

Sincerely, IRAI John Stang, Senior Project Manager Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-369 and 50-370

Enclosure:

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