ML100620316
| ML100620316 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 03/10/2010 |
| From: | Orf T Plant Licensing Branch II |
| To: | |
| Orf, T J, NRR/DORL/301-415-2788 | |
| References | |
| GL-04-002, TAC MC4709 | |
| Download: ML100620316 (11) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 10, 2010 LICENSEE: Carolina Power & Light Company FACILITY: H. B. Robinson Steam Electric Plant, Unit 2
SUBJECT:
SUMMARY
OF FEBRUARY 18, 2010, MEETING WITH PROGRESS ENERGY CAROLINAS, INC., ON GENERIC LETTER 2004-02 SUPPLEMENTAL RESPONSE (TAC NO. MC4709)
On February 18, 2010, a Category 1 public meeting was held between the U.S. Nuclear Regulatory Commission (NRC) and representatives of Progress Energy Carolinas, Inc.
(representing Carolina Power & Light Company, the licensee). The meeting was held via a toll-free audio telephone conference call that was available to interested members of the public.
(See meeting notice dated January 29, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML 10019005).) The purpose of the meeting was to discuss remaining issues identified during the NRC staff's review of the H. B. Robinson Steam Electric Plant, Unit 2, Generic Letter 2004-02 Supplemental Responses (ADAMS Accession No. ML083570469). The meeting was intended to provide feedback to the NRC staff on the licensee's plans for resolving the remaining issues, to discuss any points of disagreement, and to discuss the licensee's path forward. A list of attendees is provided as .
The licensee presented the draft responses to requests for additional information (RAls) found in Enclosure 2. These RAls were in response to the licensee's supplemental response to Generic Letter 2004-02.
The NRC staff had no questions with regard to the licensee's responses to RAls 2,5,7, or 8.
As of the meeting, the licensee had not prepared a response to RAI 17.
RAI1/4:
The NRC staff asked if any exceptions had been taken to the baseline methodology as discussed in the Nuclear Energy Institute's Guidance Report 04-07. The NRC staff asked if the model held any fines in the upper containment. The licensee responded that no holdup of fines is credited for the upper containment. The licensee also stated that they would provide additional clarification regarding their transport assumptions and their containment-com partmentalization model.
RA110:
The NRC staff requested clarification of the approach velocity of the strainer. The licensee stated that they would clarify the response to indicate the top-hat strainer tested was slightly shorter than the strainer in the plant.
-2 RA111:
The NRC staff asked what type of surrogates would be used for CalSil in future testing. The licensee responded that they would use powder. They added that they would refer back to the previous response for other surrogates.
RA114:
The NRC staff had few questions regarding this RAI, but planned to have another member of the staff review the chemical effects discussion to determine if previous conclusions remained the same.
RA116:
The NRC staff asked if the conclusions of this RAI response would remain the same after future testing. The licensee responded that it had analyzed for full open throttle valve so having the valve fail open should yield the same results. The licensee will provide additional discussion regarding how having two pumps running with valve failure is more limiting than having one pump running.
Another telephone conference was held to discuss the licensee's updated responses to the above RAls and RAI 17. A separate meeting summary will be issued for that telephone conference.
Members of the public were in attendance. Public Meeting Feedback forms were not received.
Please direct any inquiries to me at 301-415-2788, or tracy.orf@nrc.gov.
Tracy J. Orf, Project Manager Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-261
Enclosures:
- 1. List of Attendees
- 2. Licensee Handout cc w/encls: Distribution via Listserv
LIST OF ATrENDEES FEBRUARY 18, 2010, MEETING WITH PROGRESS ENERGY CAROLINAS, INC.
GENERIC LETrER 2004-02 SUPPLEMENTAL RESPONSE Progress Energy Carolinas, Inc.
Curt Castell, Licensing Supervisor Warren Farmer, Manager of Engineering Avery Jones, Supervisor of Mechanical Design Engineering Wes McGoun, Progress Energy Corporate Engineering Bill Peavyhouse, Superintendent Design Engineering Don Phillips, Mechanical Design Engineering Gil Zigler, Alion Science and Technology Tim Canter, Shearon Harris Steam Electric Plant Billy Jessup, NRR/DE Paul Klein, NRR/DCI John Lehning, NRR/DSS Tracy ort, NRR/DORL Mike Scott, NRR/DSS Stephen Smith, NRR/DSS Duke Energy Tony Jackson Enclosure 1
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Page 1 of7 1 H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO.2 2
3 4 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATON ON THE 5 SUPPLEMENTAL RESPONSE TO NRC GENERIC LETTER 2004-02, "POTENTIAL 6 IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION 7 DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED-WATER REACTORS" 8
9 10 11 By letter dated December 3, 2009, a request for additional information (RAI) regarding the H. B.
12 Robinson Steam Electric Plant (HBRSEP), Unit No.2, response to NRC Generic Letter (GL) 13 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design 14 Basis Accidents at Pressurized-Water Reactors," was provided by the NRC. The following 15 information is provided in response to this RAJ.
16 17 Debris transport 18 19 RAIl&RAI4:
20 21 Provide additional information to justify the credit taken for the retention of small fibrous fines 22 and particulate debris in the upper containment and inactive holdup volumes or provide 23 additional basis to demonstrate that the head loss impact of the debris is insignificant.
24 25 Response:
26 27 The debris quantity and characteristics for blowdown and washdown transport will be 28 recalculated based on the baseline methodology, as described in the Nuclear Energy Institute's 29 (NEI) Guidance Report 04-07, "Pressurized Water Reactor Sump Performance Evaluation 30 Methodology." The head loss testing will be repeated, using the revised debris quantity and 31 methodology consistent with the guidance provided in the report, "NRC Staff Review Guidance 32 Regarding Generic Letter 2004-02 Closure in the Area of Strainer Head Loss and Vortexing, 33 March 2008" (ADAMS Accession No. ML080230038). Therefore, Progress Energy commits to 34 perform additional head loss testing using the revised debris quantity and characteristics. Results 35 of this testing are expected to be submitted by June 30, 2010.
36 37 RAI2:
38 39 Provide additional information in light of the discussion below to justify the assumptions of zero 40 percent erosion and zero percent transport of large pieces of fibrous debris.
41 42 Response:
43 44 Transport of large pieces will be addressed by assuming erosion of the large pieces and including 45 the erosion fines in the head loss test debris mix. Ten percent of the large pieces will be assumed Enclosure 2
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Page 2 of7 1 to erode and deposit on the screens as fines. This is considered reasonable and conservative 2 because the fines in the debris bed are expected to add more to the head loss than large pieces.
3 4 The debris quantity and characteristics will be recalculated, based on the baseline methodology, 5 as described in the NEI Guidance Report 04-07. As previously stated, the head loss testing will 6 be repeated, using the revised debris quantity and methodology consistent with the guidance 7 provided in the report, "NRC Staff Review Guidance Regarding Generic Letter 2004-02 Closure 8 in the Area of Strainer Head Loss and Vortexing, March 2008" (ADAMS Accession No.
9 ML080230038).
10 11 Therefore, Progress Energy commits to perform additional head loss testing using the revised 12 debris quantity and characteristics. Results of this testing are expected to be submitted by 13 June 30, 2010.
14 15 Head Loss and Vortexing 16 17 RAI5 18 19 Provide justification that the debris preparation for the head loss testing resulted in a 20 conservative or prototypic head loss value for limiting plant conditions.
21 22 Response:
23 24 As previously stated, the head loss testing will be repeated, using the revised debris quantity.
25 The debris preparation and introduction for this testing are expected to be consistent with 26 methods previously determined to be acceptable for this type of testing. Therefore, Progress 27 Energy commits to perform additional head loss testing (including thin bed) using the revised 28 debris quantity and methodology consistent with the guidance provided in the report, "NRC Staff 29 Review Guidance Regarding Generic Letter 2004-02 Closure in the Area of Strainer Head Loss 30 and Vortexing, March 2008" (ADAMS Accession No. ML080230038). Results of this testing 31 are expected to be submitted by June 30, 2010.
32 33 RAI7 34 35 Provide information that justifies that any agglomeration of debris did not affect head loss test 36 results nonconservatively.
37 38 Response:
39 40 As previously stated, the head loss testing will be repeated, using the revised debris quantity and 41 methodology consistent with the guidance provided in the report, "NRC Staff Review Guidance 42 Regarding Generic Letter 2004-02 Closure in the Area of Strainer Head Loss and Vortexing, 43 March 2008" (ADAMS Accession No. ML080230038). The debris preparation and introduction 44 for this testing are expected to be consistent with methods previously determined to be 45 acceptable for this type of testing. Therefore, Progress Energy commits to perform additional
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Page 3 of7 1 head loss testing using the revised debris quantity and characteristics. Results of this testing are 2 expected to be submitted by June 30, 2010.
3 4 RAI8 5
6 Provide an evaluation that shows that any settling that occurred resulted in a negligible effect on 7 head loss test results or that the settling was prototypical or conservative compared to the 8 expected plant conditions.
9 10 Response:
11 12 As previously stated, the head loss testing will be repeated, using the revised debris quantity.
13 Therefore, Progress Energy commits to perform additional head loss testing using the revised 14 debris quantity and methodology consistent with the guidance provided in the report, "NRC Staff 15 Review Guidance Regarding Generic Letter 2004-02 Closure in the Area of Strainer Head Loss 16 and Vortexing, March 2008" (ADAMS Accession No. ML080230038). The debris preparation 17 and introduction for this testing are expected to be consistent with methods previously 18 determined to be acceptable for this type of testing. Results of this testing are expected to be 19 submitted by June 30, 2010.
20 21 RAI10 22 23 Provide additional information on the vortex evaluation methodology so that the staff may fully 24 evaluate the ability of the strainer system to prevent the formation of vortices.
25 26 Response:
27 28 In the discussion below, the average velocity through the perforated plate of an individual top hat 29 strainer is referred to as the top hat approach velocity. The average velocity through the 30 perforated plates of the array of individual top hat strainers forming the sump screen is referred 31 to as the screen approach velocity.
32 33 V011ex testing was conducted on horizontal, single top hat modules, with perforated plate 34 diameters of 8 inches and 6 inches, a perforated plate surface area of 9.2 square feet and a cross 35 sectional flow area through the strainer base plate of 0.132 square feet. The water level was set 36 to 3 inches above the top of the perforated plate of the strainers, which is comparable to the RNP 37 minimum design water level. The average top hat approach velocity was increased in this testing 38 from 0.01 feet/second to 0.03 feet/second with no air-entraining vortices detected. Testing was 39 also conducted from 0.04 feet/second to 0.09 feet/second showing that air-entraining vortices 40 could occur at these velocities and were completely eliminated by standard 1.5 inches-thick floor 41 grating installed flush with the surface of the water.
42 43 Based on testing described above, two correlations were derived for flow velocity through the 44 individual top hat base plate and the onset of vortexing. Since the vortexing is driven by the 45 velocity through the base plate of the Top Hat - the area of greatest constriction, greatest fluid 46 acceleration, and therefore lowest pressure in the strainer module ~ the highest flow velocity
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Page 4 of7 1 through the base plate for which no vortexing occurred was considered as a limiting condition 2 and both correlations were based on the limiting base plate velocity.
3 4 One correlation was made by directly relating the limiting base plate velocity to the top hat 5 approach velocity based on the ratio of base plate to perforated plate flow areas. The other 6 correlation determined the limiting Froude number based on the limiting velocity through the top 7 hat base plate and submergence below the water surface. Both correlations were used to 8 calculate the maximum top hat approach velocity for the specific top hats that can be sustained 9 without vortexing. The lower of the two calculated velocities was used. Note the testing was 10 conducted on "single" top hats and the installed top hats are of the "double" design, i.e. similar to 11 two concentric single top hats. The methodology called for determination of the limiting top hat 12 approach velocity based on only the outer annulus base plate and perforated plate areas. The 13 calculated limiting top hat approach velocity is inversely proportional to the perforated plate 14 area. Conservatively, only the outer annulus base plate flow area and the entire perforated plate 15 areas of both the inner and outer annulus were used in determination of the limiting maximum 16 top hat approach velocity. The limiting maximum top hat approach velocity to prevent the onset 17 ofvortexing for the strainer was determined to be 0.0115 feet/second.
18 19 The maximum normalized screen approach velocity with the strainer fully loaded with debris is 20 0.002 feet/second. This is well below the limiting maximum top hat approach velocity of 21 0.0115 feet/second. Therefore, air entrainment due to vortexing is not expected when the 22 strainer is fully loaded and top hat approach velocities converge to normalized screen approach 23 velocities.
24 25 The screens are arranged on a horizontal plenum mounted on the floor with top hat strainers 26 arranged in sets of two (one on either side of the plenum). In addition, there are two plenums, 27 one located inside the crane wall and one located outside the crane wall. The maximum 28 expected top hat approach velocity with clean screens was calculated as 0.017 feet/second at the 29 first set of top hats nearest the sump (i.e., nearest the pump suction) located inside the crane wall.
30 31 The top hat approach velocity at the first set of top hats is above the limiting maximum top hat 32 approach velocity of 0.0115 feet/second. The high top hat approach velocity indicates the 33 potential for vortexing without the use of vortex suppressors. The top hat approach velocities 34 drop off very quickly and the third set of top hats has a maximum top hat approach velocity of 35 only 0.009 feet/second, which is approximately 22% less than the limiting maximum top hat 36 approach velocity. The maximum expected top hat approach velocity, at the first set oftop hats, 37 outside the crane wall is 10% less than the limiting top hat approach velocity. The remaining top 38 hats inside and outside the crane wall are well below the limiting top hat approach velocity.
39 40 To eliminate the concern over air core vortices, vortex suppressors are installed over all of the 41 top hats outside the crane wall and over the first eight sets of top hats inside the crane wall.
42 Inside the crane wall, the eighth set of top hats have a maximum expected top hat approach 43 velocity of only 0.004 feet/second providing a margin to vortexing, without vortex suppressors, 44 of more than a factor of 2.8. Testing showed the vortex suppressors eliminated vortexing with 45 top hat velocities up to the highest tested velocity of 0.09 feet/second, or approximately 5 times 46 the highest top hat approach velocity of 0.017 feet/second.
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Page 5 of7 1
2 RAIll 3
4 Provide the size distribution of the particulate insulation surrogate used during testing.
5 6 Response:
7 8 As previously stated, the head loss testing will be repeated, using the revised debris quantity.
9 Therefore, Progress Energy commits to perform additional head loss testing using the revised 10 debris quantity and methodology consistent with the guidance provided in the report, "NRC Staff 11 Review Guidance Regarding Generic Letter 2004-02 Closure in the Area of Strainer Head Loss 12 and Vortexing, March 2008" (ADAMS Accession No. ML080230038). Particulate insulations 13 and insulation surrogates used during testing are expected to be in powder form, with is 14 consistent with the original testing. Size distribution for particulate insulation and the insulation 15 surrogates used during the repeat testing will be provided with the test results.
16 17 RAIl4 18 19 Provide justification that the debris bed head loss was not limited due to bed shifting or provide 20 an evaluation based on the head loss that could occur should the head loss be limited as 21 described above.
22 23 Response:
24 25 To address the potential for bed shifting, it is expected the chemical effects head loss will not be 26 temperature corrected and the NPSH margin will credit the time delay of chemical precipitate 27 formation based on bench top test results as previously described in the December 17, 2008 RAI 28 response letter. This is similar to the testing and approach used by other utilities. The time delay 29 will allow crediting an additional 10 feet or more ofNPSH available, which will address the bed 30 shifting issue without adversely impacting pump NPSH margin.
31 32 The chemical debris load was assumed to instantaneously fonn on the screens. The debris 33 actually takes time to form, during which the sump will cool to subcooled conditions, i.e. cool to 34 where the vapor pressure is below the minimum pre-accident containment pressure.
35 36 Bench top testing was conducted to determine the timeline for chemical formation in the sump.
37 The tests consisted of a series of temperature controlled and gently stirred beakers. Each beaker 38 was filled with deionized water buffered to a target pH representative of the ECCS sump along 39 with insulation and structural materials found in the containment that may contribute to the 40 formation of chemical precipitates. The amounts of materials were scaled to be representative of 41 the containment sump. Five tests with three replicates of each were conducted. The five tests 42 consisted of a baseline test, tests with reduced levels of Cal-Sil, tests with higher water pH, and a 43 test with a 20% increase in aluminum. Temperatures were controlled over time to mimic post 44 LOCA temperature. The beakers were visually monitored for signs of precipitate formation for 3 45 days. Also, frequent samples were taken for inductively coupled plasma-atomic emission (ICP) 46 analysis.
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Page 6 of7 1
2 At the end of the test, material samples were collected from the beakers and analyzed by 3 scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) for the 4 presence of precipitates. The surface of the insulation fibers exhibited no signs of coatings or 5 adherence of bulk precipitates and the microstructure and EDS spectra of the Cal-Sil samples 6 appeared identical to the un-tested Cal-Sil, indicating no precipitation. EDS spectra of the 7 aluminum samples indicated some areas of corrosion and other areas of surface passivation.
8 Solution transparency, ion concentrations, and debris microstructure provide evidence that 9 minimal or no precipitation will occur in a post-LOCA environment at RNP for temperatures 10 above 11 O°F.
11 12 Based on the post-LOCA containment analysis, the sump pool temperature will be less than 13 190°F after 11.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. At temperatures below 209°F the water will be subcooled compared to 14 the saturation temperature at the minimum pre-accident containment pressure. At 190°F, the 15 corresponding reduction in vapor pressure is 4.5 psi or 10.4 feet of water below the minimum 16 pre-accident containment pressure. A 10.4 feet decrease in vapor pressure will more than offset 17 the 7.4 feet increase (to 10 feet) of head loss through the. The net result is expected to be an 18 increase the debris plus chemical effects NPSH margin by 3.0 feet or more over the previous 19 analysis without adjusting the measured head loss for temperature. In addition, the design 20 differential pressure for the screens is 15 feet. Therefore, allowing the head loss to increase to 21 10 feet will not challenge the structural integrity of the screens.
22 23 The revised analysis and testing is expected to be based on chemical precipitant formation to 24 occur at a sump temperature of 140°F based on bench top testing for HBRSEP, Unit No.2.
25 26 Structural analysis 27 28 RAI17 29 30 Provide an explicit and detailed summary of the quantitative results of the structural design 31 qualification of the different components of the replacement sump strainer structural assembly 32 (including trash racks, if any) under design loads and load combinations; and their comparison to 33 the design code acceptance criteria. This information should include actual stresses, forces, 34 displacements, etc. (as applicable), the component material type, the corresponding code 35 allowables, and interaction ratios for the limiting members of the various structural components 36 of the replacement strainer assembly. Additionally, provide a more detailed list of all the 37 components that were analyzed for structural adequacy, including a description of the 38 components.
39 40 Response:
41 42 [Response being developed].
43 44 45 Net Positive Suction Head 46
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Page 7 of7 1 RAI16 2
3 Please address whether a single failure of a throttle valve to the open position in post-LOCA 4 scenarios during recirculation where throttling credit is taken would result in increased flows 5 through the residual heat removal (RHR) pump(s) that could result in a loss of net positive 6 suction head margin or emergency core cooling system strainer structural limits being exceeded.
7 8 Response:
9 10 The valves are throttled only in the alignment of both RHR pumps operating and providing 11 suction to the High Head SI pumps. This is not the limiting system alignment for determination 12 ofRHR pump NPSH. Incorporating strainer head loss, NPSH margin is 8.8 feet without valve 13 failure and 2.4 feet with a valve failure.
14 15 The screens are designed for a differential pressure of6.5 psi (15 feet). The total head loss 16 across the screen and plenum concurrent with throttle valve failure is 3.5 psi (8.4 feet).
17 Differential pressure across the top hat strainers only, is less. Therefore, structural limits are not 18 challenged as a result of throttle valve failure.
19 20 21 22
' .. ML100620316 NRC-001 OFFICE DORLlLPL2-2/PM DORLlLPL2-2/LA DSS/SSIB/BC DORULPL2-2/BC (A) DORLlLPL2-2/PM SBailey for NAME TOrf CSoia MScott TOrf DBroaddus DATE 3/9/10 3/9/10 3/10/10 03110/10 03/10/10