ML102810345

9/13/2010 Summary of Conference Call with STP Nuclear Operating Company to Discuss Request for Additional Information Responses for South Texas Project, Units 1 and 2 on Generic Letter 2004-02 (TAC Nos. MC4719 and MC4720)

ML102810345
Person / Time
Site:	South Texas
Issue date:	10/13/2010
From:	Thadani M Plant Licensing Branch IV
To:	South Texas
Thadani, M C, NRR/DORL/LP4, 415-1476
References
TAC MC4719, TAC MC4720, GL-04-002
Download: ML102810345 (60)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 13, 2010 LICENSEE: STP Nuclear Operating Company FACILITIES: South Texas Project, Units 1 and 2

SUMMARY

OF SEPTEMER 13, 2010, CATEGORY 1 MEETING, VIA CONFERENCE CALL, WITH STP NUCLEAR OPERATING COMPANY DISCUSSION OF DRAFT RESPONSES TO REQUEST FOR ADDITIONAL INFORMATION FOR GENERIC LErrER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED-WATER REACTORS" (TAC NOS.

MC4719 AND MC4720)

On September 13,2010, U.S. Nuclear Regulatory Commission (NRC) staff held a public meeting with the representatives of STP Nuclear Operating Company (STPNOC, the licensee),

at NRC Headquarters, One White Flint North, 11555 Rockville Pike, Rockville, Maryland. The purpose of the meeting was to discuss the licensee's proposed responses to the NRC staff's request for additional information (RAI) for South Texas Project (STP), Units 1 and 2, dated December 23, 2009 (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML093410607).

A list of meeting participants is provided in Enclosure 1. At this meeting, the licensee summarized the information for its proposed responses. The questions and the licensee's RAI responses discussed at the meeting are summarized in Enclosure 2.

Based on the conference call meeting discussions, representatives of the NRC staff and STPNOC concluded the following.

• The status of the NRC staff's RAI questions numbered 11, 15, 17, 21, 23, 27, 32, 35, 38, 39-42, and 46-50, is summarized below. A description of these questions is contained in Enclosure 2. The initial RAI questions were described in the NRC staff's RAI dated December 23, 2009.

• The licensee has stated that some RAI questions, not listed below, will be discussed in future separate responses pending resolution of the ongoing Commission deliberations on Generic Safety Issue 191, "Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance."

-2 Status of Licensee's Draft Responses to RAls provided in Enclosure 2 RAI No.

11 The NRC staff stated that the licensee's response to this question, as written, is acceptable (Enclosure 2).

15 The NRC staff suggested the licensee add a discussion of open areas on 19-foot elevation, including the percentage of total flow area and size and number of openings. The staff also suggested the license evaluate the impact of these areas on washdown of large pieces. The staff suggested that the licensee update its response to reflect the planned 4-category size distribution.

17 The NRC staff requested the licensee to address the 3-train flow in the head-loss test flume.

21 The NRC staff suggested the licensee add additional discussion of the obstacles in steam generator compartments that would inhibit large-piece blowdown to the upper containment and suggested additional details be provided concerning the solid floor, grating, and open area in the annulus to aid in determining washdown of this material. The staff expressed the view that a 0% assumption of debris flows to upper containment is difficult to demonstrate and suggested that the licensee may benefit from showing that small amounts might blowout and get trapped in intervening areas.

23 The NRC staff noted that the licensee's response did not address linkage between the analytical transport evaluation and the strainer head-loss test debris addition distance. The NRC staff suggested that the licensee add a discussion of how representative modeling of washdown and pool fill would affect the debris addition distance in strainer head-loss testing. The NRC staff noted this issue may be resolved generally through NRC staff-vendor discussions.

The NRC staff suggested the licensee provide the basis for assuming secondary shield-wall doors would remain closed under loss-of-coolant accident (LOCA) loading conditions or the basis for concluding that open doors would not significantly affect analytical or flume test debris transport. The NRC staff suggested that the licensee add additional detail concerning "non-significant" shield wall penetrations.

-3 Status of Licensee's Draft Responses to RAls provided in Enclosure 2 RAI No.

27 The NRC staff stated that vortexing is not likely to be an issue for PCI strainers. The NRC staff suggested that it may be worthwhile for the licensee to remove its draft response and simply state (assuming true) that testing, to date, for STP and other plants shows that vortexes will not occur for conditions bounding the STP conditions. The staff acknowledges that adequate testing has been performed to support this conclusion. Removal of the analytical discussion would render the Froude number issue moot.

32 The NRC staff stated that the licensee's response was acceptable, as written.

35 The NRC staff acknowledged that the basic premise of the licensee's response is likely to be valid in that debris would sink such that it would not accumulate on top of the strainer. The NRC staff suggested that the licensee provide updated debris amounts consistent with its planned revised debris generating and transport evaluations.

38 The NRC staff suggested that the licensee reference its RAI 40 response, which discusses the method for calculating a 2-train flow rate. The NRC staff also suggested the licensee show that pump lineups used for startup surveillance bound all post-LOCA conditions.

39 The NRC staff stated that the licensee's response was acceptable, as written (Enclosure 2).

40, 41 The NRC staff stated that the licensee's response was acceptable, as written (Enclosure 2). The NRC suggested that the licensee provide the basis for selection of the net positive suction head (NPSH) value.

42 The NRC staff suggested that the licensee evaluate the 3-train NPSH margin to determine which is limiting. The NRC staff also suggested that the licensee revise its discussion on turning off redundant pumps to be consistent with configurations allowed by the licensee's procedures.

46 The NRC staff stated that the licensee needs to better justify the basis for concluding the Keeler and Long test results adequately characterize the unqualified epoxies in the plant.

47 Resolution of this item is dependent on resolution of RAI 46 above.

-4 Status of Licensee's Draft Responses to RAls provided in Enclosure 2 RAI No.

48 The NRC staff stated that the licensee's response was acceptable, as written. The NRC staff stated that if the licensee substantially reduces its latent material quantity assumption, the cleaning method could be important in maintaining a valid licensing basis.

49 The NRC staff stated that the licensee's response was acceptable, as written (Enclosure 2).

50 The NRC staff stated that the licensee's response was acceptable, as written (Enclosure 2).

The licensee stated that it will consider its path forward regarding additional submittal timing, and plans to let the NRC staff know of its plans by November 1, 2010.

The NRC staff suggested that the licensee reach an agreement with the staff on its RAI responses before retesting the sump model. . Of the RAls discussed during this call, the licensee indicated that responses to RAls 15,17,21,23,27,35,38,41,42,46, and 47 may be resubmitted in draft before being finalized, so that the NRC staff can verify that the responses are acceptable.

There were no members of the public present to comment. Also, no Public Meeting Feedback forms were received for this meeting.

If there are any questions, please direct them to me at (301) 415-1476 or e-mail at mohan.thadani@ nrc.gov.

Sincerely, Mohan C. Thadani, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosures:

1. List of Attendees

2. Draft Partial Responses to NRC Request for Additional Information.

cc w/encls: Distribution via Listserv

LIST OF ATTENDEES u.S. NUCLEAR REGULATORY COMMISSION MEETING VIA CONFERENCE CALL WITH STP NUCLEAR OPERATING COMPANY September 13, 2010 Name Affiliation Michael Scott NRC/NRR John Lehning NRC/NRR Steven Smith NRC/NRR Matthew Yoder NRC/NRR Emma Wong NRC/NRR Mohan Thadani NRC/NRR Wayne Harrison STPNOC Mike Berg STPNOC Richard Kersey STPNOC Wes Shulz STPNOC Jamie Paul STPNOC Enclosure 1

SOUTH TEXAS PROJECT SUPPLEMENTAL RESPONSE TO GL 2004-02 EMERGENCY SUMP PERFORMANCE RESPONSES TO REQUEST FOR ADDITIONAL INFORMATION JULY 2010 INDEX RAI# Page # Response Comment RAI# Page # Response Comment Now Now or or Later Later 1 2 Later PWROGZOI 27 28 Now PCI 2 2 Later PWROGZOI 28 33 Later PCI 3 3 Later PWROGZOI 29 33 Later PCI 4 3 Later PWROGZOI 30 33 Later PCIIAreva 5 4 Later PWROGZOI 31 33 Later PCI 6 4 Later PWROGZOI 32 34 Now STPNOC 7 5 Later PWROGZOI 33 35 Later PCI 8 5 Later PWROGZOI 34 35 Later PCI 9 6 Later PWROGZOI 35 36 Now STPNOC 10 6 Later PWROGZOI 36 37 Later STPNOC 11 7 Now STPNOC 37 37 Later STPNOC 12 8 Later PWROGZOI 38 38 Now STPNOC 13 8 Later PCI 39 39 Now STPNOC 14 8 Later Alion 40 42 Now STPNOC 15 9 Now Alion 41 43 Now STPNOC 16 13 Later Alion 42 44 Now STPNOC 17 14 Now Alion 43 45 Later STPNOC 18 17 Later Alion 44 45 Later Westinghouse 19 17 Later PCI 45 45 Later Westinghouse 20 18 Later Alion 46 46 Now Westinghouse Alion 21 19 Now Alion 47 47 Now Alion 22 21 Later Alion 48 48 Now STPNOC 23 22 Now Alion 49 49 Now STPNOC 24 27 Later PCI/Alden 50 53 Now STPNOC 25 27 Later Alion 51 54 Later PWROGLTC PCI/Alden I 26 27 Later PCI 52 54 Later PCIIAreva NOW = (5 Y2 Alion + Y2 Westinghouse + 1 PCI + 11 STPNOC) = 18 Page 1 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010 Enclosure 2

A. Debris Generation/Zone of Influence (ZOI)

Please respond to the following questions on debris generation testing. Note that the Pressurized-Water Reactor Owners Group (PWROG) is planning to respond to some of these issues generically. The licensee will be expected to respond to all of them. To the extent NRC staff accepts the PWROG's generic resolution, the licensee's request for additional information (RAI) responses may refer to the resolution document as appropriate, while adding site-specific information as needed.

RAI#1 Although American National Standards Institute (ANSI)/American Nuclear Society (ANS) standard 58-2 1988, "Design Basis for Protection of Light Water Nuclear Power Plants Against Effects of Postulated Pipe Rupture," predicts higher jet centerline stagnation pressures associated with higher levels of subcooling, it is not intuitive that this would necessarily correspond to a generally conservative debris generation result. Please justify the initial debris generation test temperature and pressure with respect to the plant-specific reactor coolant system (RCS) conditions, specifically the plant hot-and cold-leg operating conditions. If ZOI reductions are also being applied to lines connecting to the pressurizer, then please also discuss the temperature and pressure conditions in these lines. Please describe the results of any tests conducted at alternate temperatures and pressures to assess the variance in the destructiveness of the test jet to the initial test condition specifications.

Response to RAI #1 Later RAI#2 Please describe the jacketing/insulation systems used in at South Texas Project (STP), Units 1 and 2, for which ZOI reduction is sought and compare those systems to the jacketing/insulation systems that were tested demonstrating that the tested jacketing/insulation system adequately represent the plant jacketing/insulation system. The description should include differences in the jacketing and banding systems used for piping and other components for which the test results are applied, potentially including steam generators, pressurizers, reactor coolant pumps, etc. At a minimum, the following areas should be addressed:

a. Please describe how the characteristic failure dimensions of the tested jacketing/insulation compared with the effective diameter of the jet at the axial placement of the target. The characteristic failure dimensions are based on the primary failure mechanisms of the jacketing system (e.g., for a stainless steel jacket held in place by three latches where all three latches must fail for the jacket to fail, then all three latches must be effectively impacted by the pressure for which the ZOI is calculated). Applying test results to a ZOI based on a centerline pressure for relatively low LID nozzle to target spacing would be non-conservative with respect to impacting the entire target with the calculated pressure.

b. Please explain whether the insulation and jacketing system used in the testing was of the same general manufacture and manufacturing process as the insulation used in the plant. If not, please explain what steps were taken to ensure that the general strength of the insulation system tested was conservative with respect to the plant insulation. For example, it is known that there were generally two very different processes used to manufacture calcium silicate whereby one type readily dissolved in water but the other type dissolves much more slowly. Such manufacturing differences could also become apparent in debris generation testing, as well.

Page 2 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

c. Please provide results of an evaluation of scaling the strength of the jacketing or encapsulation systems to the tests. For example, a latching system on a 30-inch pipe within a ZOI could be stressed much more than a latching system on a lO-inch pipe in a scaled ZOI test. If the latches used in the testing and the plants are the same, the latches in the testing could be significantly under-stressed. If a prototypically sized target were impacted by an undersized jet, it would similarly be under-stressed. Evaluations of banding, jacketing, rivets, screws, etc., should be made. For example, scaling the strength of the jacketing was discussed in the Ontario Power Generation report, "Jet Impact Tests -Preliminary Results and Their Application, N-REP-34320-10000," dated April 18, 2001 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML020290085), on calcium silicate debris generation testing.

Response to RAI #2 Later RAI#3 There are relatively large uncertainties associated with calculating jet stagnation pressures and ZOls for both the test and the plant conditions based on the models used in the WCAP reports. Please describe the steps taken to ensure that the calculations resulted in conservative estimates of these values. Please provide the inputs for these calculations and describe the sources of the inputs.

Response to RAI #3 Later RAI#4 Please describe the procedure and assumptions for using the ANSI!ANS-58-2-1988 standard to calculate the test jet stagnation pressures at specific locations downrange from the test nozzle. As part of this description, please address the following points.

a. In WCAP-16710-P, "Jet Impingement Testing to Determine the Zone ofInfluence (ZOI) of Min-K and NUKON Insulation, for Wolf Creek and Callaway Nuclear Operating Plants," please explain why the analysis was based on the initial condition of 530 degrees Fahrenheit CF) whereas the initial test temperature was specified as 550 OF.

b. Please explain whether the water subcooling used in the analysis was that of the initial tank temperature or the temperature of the water in the pipe next to the rupture disk. Test data indicated that the water in the piping had cooled below that of the test tank.

c. The break mass flow rate is a key input to the ANSIIANS-58-2-1988 standard. Please explain how the associated debris generation test mass flow rate was determined. If the experimental volumetric flow was used, then explain how the mass flow was calculated from the volumetric flow given the considerations of potential two-phase flow and temperature-dependent water and vapor densities. If the mass flow was analytically determined, then describe the analytical method used to calculate the mass flow rate.

d. Noting the extremely rapid decrease in nozzle pressure and flow rate illustrated in the test plots in the first tenths of a second, please explain how the transient behavior was considered in the application of the ANSI!ANS-58-2-1988 standard. Specifically, please explain whether the inputs to the standard represented the initial conditions or the conditions after the first extremely rapid transient (e.g., say at one tenth of a second).

Page 3 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

e. Given the extreme initial transient behavior of the jet, please justify the use of the steady-state ANSI!ANS-58-2-1988 standard jet expansion model to determine the jet centerline stagnation pressures rather than experimentally measuring the pressures.

Response to RAI #4 Later RAI#5 Please describe the procedure used to calculate the isobar volumes used in determining the equivalent spherical ZOI radii using the ANSI!ANS-58-2-1988 standard. Please include discussions of the following points.

a. Please provide the assumed plant-specific RCS temperatures and pressures and break sizes used in the calculation. Please note that the isobar volumes would be different for a hot-leg break than for a cold-leg break since the degree of subcooling is a direct input to the ANSI!ANS-58-2-1988 standard and which affects the diameter of the jet. Also, please note that an under-calculated isobar volume would result in an under-calculated ZOI radius.

b. Please describe the calculational method used to estimate the plant-specific and break-specific mass flow rate for the postulated plant loss-of-coolant accident (LOCA), which was used as input to the standard for calculating isobar volumes.

c. Given that the degree of subcooling is an input parameter to the ANSI!ANS-58-21988 standard and that this parameter affects the pressure isobar volumes, please describe the steps taken to ensure that the isobar volumes conservatively match the plant-specific postulated LOCA degree of subcooling for the plant debris generation break selections. Please explain whether multiple break conditions were calculated to ensure a conservative specification of the ZOI radii.

Response to RAI #5 Later RAI#6 Please provide a detailed description of the test apparatus, specifically including the piping from the pressurized test tank to the exit nozzle including the rupture disk system. Please also address the following related points:

a. Based on the temperature traces in the test reports, it is apparent that the fluid near the nozzle was colder than the bulk test temperature. Please explain how the fact that the fluid near the nozzle was colder than the bulk fluid was accounted for in the evaluations.

b. Please explain how the hydraulic resistance of the test pIpmg which affected the test flow characteristics was evaluated with respect to a postulated plant-specific LOCA break flow, where such piping flow resistance would not be present.

c. Please provide the specified rupture differential pressure of the rupture disks.

Response to RAI #6 Later Page 4 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAI#7 WCAP-16710-P discusses the shock wave resulting from the instantaneous rupture of piping. Please address the following points regarding the shock wave:

a. Please describe results of analysis or parametric testing conducted to get an idea of the sensitivity ofthe potential to form a shock wave at different thermal-hydraulic conditions. Please state and justify whether temperatures and pressures prototypical of PWR hot legs were considered.

b. Please explain whether the initial lower temperature of the fluid near the test nozzle was taken into consideration in the evaluation, and if not, why not. Specifically, please explain and justify whether the damage potential was assessed as a function of the degree of subcooling in the test initial conditions.

c. Please provide the basis for scaling a shock wave from the reduced-scale nozzle opening area tested to the break opening area for a limiting rupture in the actual plant piping.

d. Please compare how the effect of a shock wave was scaled with distance for both the test nozzle, and compare that with the expected plant condition.

Response to RAI #7 Later RAI#8 Please provide the basis for concluding that a jet impact on piping insulation with a 45 degree seam orientation is a limiting condition for the destruction of insulation installed on steam generators, pressurizers, reactor coolant pumps, and other non-piping components in the containment. For instance, considering a break near the steam generator nozzle, once insulation panels on the steam generator directly adjacent to the break are destroyed, the LOCA jet could impact additional insulation panels on the steam generator from an exposed end, potentially causing damage at significantly larger distances than for the insulation configuration on piping that was tested. Furthermore, it is not clear that the banding and latching mechanisms of the insulation panels on a steam generator or other RCS components provide the same measure of protection against a LOCA jet as those of the piping insulation that was tested.

Although WCAP-1671O-P asserts that ajet at WolfCreek or Callaway cannot directly impact the steam generator, but will flow parallel to it, it seems that some damage to the steam generator insulation could occur near the break, with the parallel flow then jetting under the surviving insulation, perhaps to a much greater extent than predicted by the testing. Similar damage could occur to other component insulation.

Please provide a technical basis to demonstrate that the test results for piping insulation are prototypical or conservative of the degree of damage that would occur to insulation on steam generators and other non piping components in the containment.

Response to RAI #8 Later Page 5 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAI#9 Some piping oriented axially with respect to the break location (including the ruptured pipe itself) could have insulation stripped off near the break. Once this insulation is stripped away, succeeding segments of insulation would have one open end exposed directly to the LOCA jet, which appears to be a more vulnerable configuration than the configuration tested by Westinghouse. As a result, damage would seemingly be capable of propagating along an axially-oriented pipe significantly beyond the distances calculated by Westinghouse. Please provide a technical basis to demonstrate that the reduced ZOIs calculated for the piping configuration tested are prototypical or conservative with respect to the degree of damage that could occur to insulation on piping lines oriented axially with respect to the break location.

Response to RAI #9 Later RAI #10 WCAP-16710-P noted damage to the cloth blankets that cover the fiberglass insulation, in some cases resulting in the release of fiberglass. The tears in the cloth covering were attributed to the steel jacket or the test fixture and not the steam/water jet. Please justify the assumption that damage that occurs to the target during the test would not be likely to occur in the plant. Please explain whether the potential for damage to plant insulation from similar conditions was considered. For example, the test fixture could represent a piping component or support, or other nearby structural member. The insulation jacketing is obviously representative of itself. Please provide the basis for the statement in the WCAP that damage similar to that which occurred to the end pieces would not be expected to occur in the plant. It is likely that a break in the plant will result in a much more chaotic condition than that which occurred in testing.

Therefore, it would be more likely for the insulation to be damaged by either the jacketing or other objects nearby Response to RAI #10 Later Page 6 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #11 Please provide infonnation that justifies that the Marinite insulation is protected by the plate such that damage outside of 20 is not expected. Please provide infonnation on the failure mode of the insulation and describe whether it is destroyed by the LOCA jet or whether it can be crushed by piping following a break. Alternately, please provide infonnation that shows that all Marinite that is installed in the general vicinity of the break is considered to be rendered into debris by the transient.

Response to RAI #11 Per the original plant design, the only Marinite (calcium silicate) insulation inside containment was installed on the Reactor Vessel nozzles. STPNOC has replaced all of the Marinite insulation with NUKON fiberglass insulation. This has been accomplished for Unit 1 during the fall 2009 refueling outage and for Unit 2 during the spring 2010 refueling outage.

Page 70f54 STP Draft Sump RAJ Responses Rev A 7-20-2010

B. Debris Characteristics RAI #12 The analysis assumption of 60 percent small fines and 40 percent large pieces for low-density fiberglass within a 5D ZOI is inconsistent with the Figure 11-2 of NRC staffs safety evaluation (SE), dated December 6, 2004 (ADAMS Accession No. ML043280641), on NEI 04-07, which considers past air jet testing and indicates that the fraction of small fines should be assumed to reach 100 percent at jet pressures in the vicinity of 18-19 pounds per square inch (psi). At 5D, the jet pressure is close to 30 psi, which significantly exceeds this threshold. Furthermore, the licensee's assumption that the size distribution for debris in a range of 5D to 7D is 100 percent intact blankets also appears not to be inconsistent with existing destruction testing data. These assumptions for low-density fiberglass debris size distributions appear to be based on the recent Westinghouse/Wyle ZOI testing discussed in WCAP 1671O-P. However, that testing was not designed to provide size distribution information. Furthermore, given the assumption that insulation between 5D and 7D is 100 percent intact pieces that do not transport or erode, the licensee has effectively assumed a 5D ZOI rather than a 7D ZOI for low-density fiberglass.

Also, it appears from the testing done by Westinghouse/Wyle for Arkansas Nuclear One (Entergy Operations, Inc. letter dated February 28, 2008, ADAMS Accession No. ML080710544), some damage was seen for Thermal Wrap even at 12D and at 7D. Considering that testing, please explain STP's treatment of Thermal Wrap with a 5D ZOI. Please describe the details of the jacketing and banding that support the same ZOI for both Nukon and Thermal Wrap for STP that is based on the Wolf Creek/Callaway testing. Please provide a detailed summary of the testing that was done, the similarity analysis for the insulation design, and a basis for the testing or other source of the debris distribution percentages that were assumed and why it is representative of the plant condition.

Response to RAI #12 Later RAI #13 Please clarify what percentage of the small fines distribution represents fines and what percentage represents small pieces, and how the split between fines and small pieces was determined when preparing debris for head loss testing. This information is needed because the distribution of debris between the fine and small piece size categories has a significant impact on the measured strainer head loss, particularly for a strainer test that credits debris settlement.

Response to RAI #13 Later C. Debris Transport RAI #14 The December 11, 2008, supplemental response states on page 14 that 5 percent of small pieces of fiber are assumed to be trapped on wetted surfaces in congested areas due to changes in flow direction during blowdown. Please clarify whether this assumption is still part of the analysis, given that STP is now assuming a three-category size distribution for low-density fiberglass. If so, then please justify any assumption regarding this debris remaining trapped against a wetted vertical surface for any significant period of time.

Response to RAI #14 Later Page 8 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAI #15 The December 11, 2008, supplemental response states on page 16 that one refinement to the 2004 NRC SE in the transport calculation for STP was that holdup of small pieces of fiberglass was assumed at each level of grating that washdown flow passed through. In addition, zero percent washdown of large pieces of fiberglass was assumed. Please provide the following additional information as a basis for these assumptions:

a. Please describe the extent and continuity of the grating below the limiting break locations, and provide the percentage of the cross-sectional area below these breaks where grating is installed.

b. Please provide adequate basis to justify that 40 to 50 percent of small pieces of debris will be held up on grating. Although results from the Drywell Debris Transport Study (DOTS) were cited in the supplemental response, based on the 30-minute duration of the cited tests, the DOTS recommendation was that no retention credit should be allowed for debris fragments that are smaller than openings in floor grating. Based on the information provided in the supplemental response, the NRC staff notes that the duration of spray operation at STP is not certain but could be significantly longer than 30 minutes (e.g.,

hours or days).

Furthermore, the staff also notes that a fraction of the debris held up on gratings could be exposed to concentrated streams of run-off flow (as opposed to fine spray droplets), which could further increase the tendency for erosion and washdown beyond what was observed in the DOTS results for the spray cases.

c. Please state whether and how the assumptions concerning capture of small pieces of fiberglass on gratings during washdown are currently credited in the STP transport analysis that consider a three category size distribution for low-density fiberglass debris.

Page 90f54 STP Draft Sump RAI Responses Rev A 7-20-2010

Response to RAI #15 Figure 15-1 shows a cross-section view of the region related to the limiting Loop C Hot Leg break. The region in which the break is postulated to occur is separated from the recirculation pool by a concrete floor and grating at elevation 19'-0".

LB-LOCA IN LOOP C HOT LEG ELEVATION 19' - 0" EMERGENCY SUMPS Figure 15 Cross-section of Region of Loop C Hot Leg Break Page 10 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

The floor area (green section) at elevation 19'-0" is shown in Figure 15-2. The total area is 4982.4 square feet.

FLOOR AREA 4982.4 sa FT Figure 15 Floor Area at Elevation 19'-0" Grating at elevation 19'-0" is shown in Figure 15-3. There are two larger sections at the 12 and 6 o'clock positions and six smaller regions within the hexagonal area. The total area comprised of grating is 636.00 square feet. Therefore, the portion of the floor area comprised of grating at elevation 19'-0" is 12.8%.

LARGER GRATED AREA (QTY 2)

SMALLER GRATED AREA (QTY6)

Figure 15 Grating at Elevation 19'-0" Page 11 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

Response to RAI 15b:

Using the 3-category (Small Fines, Large Pieces and Intact Blankets) size distribution assumed for fiber debris in the latest (Revision 3) version of the STP Debris Transport calculation, there is no Small Pieces category and consequently there is no use of 40-50% holdup on grating of Small Pieces of fiber debris.

Response to RAI 15c:

Using the 3-category (Small Fines, Large Pieces and Intact Blankets) size distribution assumed for fiber debris in the latest (Revision 3) version of the STP Debris Transport calculation, there is no Small Pieces category and consequently there is no use of any assumptions concerning capture of Small Pieces of fiberglass on gratings during washdown.

Reference:

ALiON-CAL-STPEGS-2916-005 Revision: 3, Document

Title:

GSI-191 Containment Recirculation Sump Evaluation: CFD Transport Analysis.

Page 120[54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #16 The December 11, 2008, supplemental response states on page 8 that a three-category size distribution is used for low-density fiberglass debris including small fines, large pieces and intact blankets. However, the discussion of debris transport refers in a number of places to small pieces of fiberglass (e.g., page 14, page 16, table 14, etc.). Please clarify whether these statements have been updated to reflect the revised debris size distribution on page 8.

Response to RAI #16 Later Page 13 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAI #17 Please provide the basis for considering a transport case with two sumps operating as the limiting condition for debris transport. Although debris would be distributed to an extra strainer, the staff observed that a design-basis case with three sumps operating would likely experience increased debris transport to the strainers in the analysis, and also in the head loss testing that credited substantial debris settlement using a flow rate based on the operation of two sumps. The increased debris transport associated with this conditlon may be more significant than the offsetting potential for additional debris sharing with a third strainer.

Response to RAI #17 The latest (Revision 3) version of the STP Debris Transport calculation indicates that for the (2 pump) condition that was analyzed, the Turbulent Kinetic Energy (TKE) and velocity conditions warranted assuming that recirculation transport fraction of fine fiber, Curled Paint Chips, Marinite (note - has been removed), Microtherm, Epoxy, Alkyd, IOl, Baked Enamel and Dirt/Dust would be 100%. For these debris types, the increase in flow from a transport case with three sumps operating would result in no increase in recirculation transport. It would however reduce the amount of debris that is accumulated at each active sump by some amount.

Large fiberglass pieces and large intact fiberglass blankets do not reach the recirculation pool because they are prevented from doing so by structural floor and grating. Since they don't reach the recirculation pool, an increase in recirculation pool flow from a transport case with three sumps operating would result in no change in their transport - they are unaffected.

The recirculation transport fractions for Small Paint Chips and Large Paint Chips for the governing case, i.e., Hot Leg (Case 1) break, based upon transport analysis for Cases 1 and 2

[3] are 0%. This is because although there are areas of the recirculation pool with su'fficient TKE and velocity conditions to result in suspension and transport, these regions do not reach the strainers. The potential impact of three-sump operation is discussed below.

The recirculation transport fraction for Fine Paint Chips for Cases 1 and 2 is 41 %. This transport fraction is based upon the size of the region where Fine Paint Chips occur in regions of sufficient TKE and velocity conditions to result in suspension and transport. The potential impact of three-sump operation is discussed below.

An upper bound estimate of the increase in Small Paint Chips and Large Paint Chips transport due to the increase in pool recirculation velocity that would occur with three sumps in operation can be derived by assuming that for the Hot Leg (Case 1) break, all chips outside the Reactor Cavity transport to the sump. Making this assumption increases the transport fraction sum in the unqualified coatings outside the lOI debris transport logic tree for Case 1 from 0.482 to 1.0.

The same approach for the (Case 2) Reactor Cavity break case results in the same change in the recirculation transport fraction sum, from 0.482 to 1.0. Note that unqualified coatings outside the lOI comprise only a portion of the total non-fiber debris loading.

Page 14 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

The increase in total Case 1 particulate quantity from an assumed increase in transport fraction sum for unqualified coatings outside the ZOI from 0.482 to 1.0 is illustrated in Table 17-1, from 2256.8 Ibm to 2412.5 Ibm. The percent increase in total particulate quantity is 7%.

Table 17 Case-1 2- S ump versus 3S- ump o perafIon Pa rt'ICU IateTranspo rt Q uantTlies 2-sump 3-sump Break Case 1, Total 2-sump operation 3-sump operation Loop C hot leg Generated operation transport operation transport transport quantity, transport quantity, Ibm fractions Ibm fractions Ibm Microtherm Ibm 64.5 0.947 61.1 0.947 61.1 Marinite Ibm 0 0 0.0 0.000 0.0 Qualified Coatings in ZOI Epoxy 23 0.947 21.8 0.947 21.8 IOZ 553 0.947 523.7 0.947 523.7 Polyamide Primer 10 0.947 9.5 0.947 9.5 Unqualified Coatings Epoxy inside Rx Cavity 1714 0 0.0 0 0.0 Epoxy outside Rx Cavity 294 0.482 141.7 1.000 294.0 Alkyds 247 1.000 247.0 1.000 247.0 IOZ 843 1.000 843.0 1.000 843.0 Baked Enamel 268 1.000 268.0 1.000 268.0 Latent Debris Dust & Dirt 170 0.83 141.1 0.850 144.5 Total: 2256.8 2412.5

% Increase: 1.07 Page 15 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

The increase in total Case 2 particulate quantity from an assumed increase in transport fraction sum for unqualified coatings outside the lOI from 0.482 to 1.0 is illustrated in Table 17-2, from 3745.5 Ibm to 3901.2 Ibm. The percent increase in total particulate quantity is 4%.

Tabl e 172- - Case-228 - ump versus 38 - ump o'pera f Ion Part'ICU IateTranspo rt Q uanfflies 2-sump 3-sump 2-sump operation 3-sump operation Total operation transport operation transport Break Case 2, Generated, transport quantity, transport quantity, Reactor Cavity Ibm fractions Ibm fractions Ibm Microtherm Ibm 13.5 0.947 12.8 0.947 12.8 Marinite Ibm 220.4 0.830 182.9 0.830 182.9 Quali'fied Coatings in ZOI Epoxy 23 0.830 19.1 0.830 19.1 IOl 553 0.830 459.0 0.830 459.0 Polyamide Primer 10 0.830 8.3 0.830 8.3 Unqualified Coatings Epoxy inside Rx Cavity 1714 0.830 1422.6 0.830 1422.6 Epoxy outside Rx Cavity 294 0.482 141.7 1.000 294.0 Alkyds 247 1.000 247.0 1.000 247.0 IOl 843 1.000 843.0 1.000 843.0 Baked Enamel 268 1.000 268.0 1.000 268.0 Latent Debris Dust & Dirt 170 0.83 141.1 0.850 144.5 Total: 3745.5 3901.2

% Increase: 1.04 3-sump operation results in no increase in fiber loading and less than 10% increase in particulate loading. However 3-sump operation would increase the strainer area available for debris capture by 50%. Therefore, debris load definition based upon 2-sump operation provides a bounding condition for strainer testing debris load definition.

Page 16 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAI #18 Please provide a description of any testing performed to support the assumption of 10 percent erosion of fibrous debris pieces in the containment pool. Please specifically include the following information:

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 provide specific justification 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.

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

Response to RAI #18 Later RAI #19 The supplemental response, dated December 11, 2008, indicates that a significant percentage of small fines of low-density fiberglass were assumed to transport to the strainers (i.e., 95 percent). In addition, no large debris pieces were assumed to enter the containment pool. These analytical assumptions minimized the quantity of settled small and large pieces of fiberglass that were analytically assumed to erode in the containment pool. However, for the strainer head loss testing conducted by Performance Contracting, Inc.

(PCI), the NRC staff considers it likely that a significant fraction of small pieces that were analytically considered transportable actually settled in the test flume, rather than transporting to the test strainer. The head loss testing did not model the erosion of this debris. The licensee's consideration of debris erosion, therefore, appears to be non-conservative, because neither the analysis nor the head loss testing accounted for the erosion of debris that settled during the head loss testing. Please estimate the quantity of eroded fines from small pieces of fiberglass 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.

Response to RAI #19 Later Page 17 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAI#20 For a number of cases, the supplemental response stated that 17 percent of the latent debris was assumed to be captured in inactive holdup volumes in containment (Le., inactive cavities and the inactive sump).

For an additional case (i.e., Case 2), a similar treatment was applied to Marinite and coatings debris.

The NRC staffs SE on NEI 04-07 recommended that no more than 15 percent holdup in inactive volumes be assumed unless a pool-fill transport analysis was performed similar to the staffs sample calculation in Appendix IV to the SE. Please provide adequate justification for the assumption concerning the holdup of latent debris in inactive sump pool volumes.

Response to RAI #20 Later Page 18 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #21 Please provide the technical basis for concluding that no large debris pieces will be blown into upper containment. Please include a description of the extent and continuity of the grating above the limiting break locations, and provide a fraction of the cross-sectional area above these breaks where grating is installed.

Response to RAI #21 The technical basis for concluding that no large debris pieces will be blown into upper containment is that transport to upper containment will be prevented by grating and other obstructions.

The cross-section area of the Steam Generator compartment above break is shown in Figure 21-1. The total area (shown in green) is 3,206.4 square feet.

Figure 21 Cross-Section Area of Steam Generator Compartment above Loop C Hot Leg Break Page 19 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

Figure 21-2 shows the grating and obstructions above the Loop C Hot Leg break location, i.e., at elevation 37'-3".

Figure 21 Grating and Obstructions above Loop C Hot Leg Break The total area of gratings and obstructions is 2,964.6 square feet. The portion of the area above the break that comprises grating and obstructions is 92.5% of the total area.

Page 20 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #22 Please provide additional information concerning the following debris transport assumptions regarding failed coatings debris:

a. A basis for the zero percent transport fraction for epoxy coating debris inside the reactor cavity for breaks that do not occur within the reactor cavity.

b. A description of the methodology for determining the transport fraction for failed epoxy coatings outside the reactor cavity, for which transport percentages from 41 to 48 percent were calculated for various scenarios.

Response to RAI #22 Later Page 21 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAI #23 No transport of small or large pieces of debris was assumed to occur during the pool fill phase of the event, but justification for this assumption was not provided. The NRC staff expects that velocities in some parts of typical containment pools could well exceed the transport metric for debris in these categories during the pool-fill phase of transport. Flow conditions during the pool-fill phase of the LOCA were not considered by the testing, nor was the potential for some types of debris to enter a non-quiescent containment pool closer than 45 feet from the strainer due to the effects of blowdown, washdown, and pool-fill transport. The lack of modeling of these transport aspects of the head loss testing appeared to result in a non-prototypical reduction in the quantity of debris reaching the test strainer. Please provide the technical basis for not explicitly modeling transport modes other than recirculation transport, considering the following points:

a. As shown in Appendix III of the NRC staffs SE on NEI 04-07, containment pool velocity and turbulence values during fill up may exceed those during recirculation, due to the shallowness of the pool.

b. The pool-fill phase will tend to move debris from inside the secondary shield wall into the outer annulus away from the break location and nearer to the recirculation sump strainers.

c. Representatively modeling the washdown of some fraction of the debris nearer the strainer than 45 feet would be expected to increase the quantity of debris transported to the strainer and the measured head loss.

d. If credit was taken for the four openings in the secondary shield wall being raised above the containment pool floor level in making this determination, then please provide a description of any other flow paths through the secondary shield wall through which these debris types might transport during the pool fill phase.

Response to RAI #23 With respect to the concern that "No transport of small or large pieces of debris was assumed to occur during the pool fill phase of the event, but justification for this assumption was not provided", it is noted that STP implemented a 3-category (Small Fines, Large Pieces and Intact Blankets) size fiber distribution in the Debris Transport calculation. The Small Fines category consolidated the two (Fines and Small Pieces) categories into one category, and in the current Debris Transport calculation it is assumed that all fiber within the Small Fines category is fines.

Transport of Small Fines, (i.e., fines), that was blown down into lower containment is explicitly addressed during the pool fill-up phase. A small portion of fines blown down into lower containment is shown to transport to inactive cavities and sump strainers. The rest of the fines blown down into lower containment is explicitly treated in recirculation transport analysis and of this portion, 100% is considered to transport to the sump strainers.

All of the Small Fines, (i.e., fines), debris that is blown down into upper containment is assumed to wash down to the recirculation pool and none of this washed-down debris is considered to be captured in inactive cavities.

The overall result is that approximately 95% of fines is considered to transport to the sumps.

Page 22 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

Likewise, for latent debris, with the exception of the portion that is shown to transport to inactive cavities during the fill-up phase, all latent debris is considered to transport to the sumps.

In the case of transport of unqualified coatings debris outside the ZOI, pool fill-up phase transport is not applicable because destruction of unqualified coatings debris outside the ZOI is conservatively considered to occur after pool fill-up has occurred. Therefore none of the unqualified coatings debris outside the ZOI is assumed to reach inactive cavities, resulting in 100% availability for recirculation transport depending upon the recirculation flow conditions in the pool. Transport of unqualified coatings debris outside the ZOI is therefore not affected, i.e.,

not reduced or prevented in any way, by pool fill-up and hence is effectively defined in the recirculation phase.

The reason that transport of large pieces is assumed to not occur during the pool fill phase is that large pieces do not transport to the recirculation pool elevation; large pieces remain at the elevation of the break, Le., elevation 19'-0". Therefore, since there is no large debris at the recirculation pool elevation, pool fill-up phase transport of large pieces at the recirculation pool elevation is not applicable.

Response to RAI 23a:

The Debris Transport calculation states that during pool fill-up, the flow of water would transport insulation debris from the break location to all areas of the recirculation pool. Some of the debris could be transported to inactive areas of the pool. Some of the debris could also be transported directly to the sump strainers as the emergency sump cavities are filled.

Further, the Debris Transport calculation states that as water pours onto the containment floor, it would initially flow in shallow, high velocity sheets. This sheeting action would cause insulation debris that may not transport easily during recirculation flow to be scattered around the containment floor. As the water level rises, debris would preferentially be swept to cavities below the containment floor elevation, e.g., like the normal sump and the emergency sumps.

The vent holes in the secondary shield wall are raised 18-inches off the floor. Therefore the water level would have to rise high enough for flow to pass through the vent holes before filling the cavities outside the secondary shield wall. The cavities considered for pool fill up transport include the containment sump, the elevator pit, and the three ECCS sumps. Other potentially inactive areas where debris could .be held up including the secondary normal sump were conservatively assumed to be negligible and were not credited. It should be noted that as a result of the assumed uniform debris distribution during the fill-up phase, overall fine fiber and particulate debris transport fractions are approximately 95%.

Page 23 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

Response to RAI 23b:

Figure 23-1 shows a plan view of the STP lower containment where the recirculation pool will exist after fill-up (CAD model). There are no significant openings in the secondary shield wall between the inside and outside of the secondary containment at this level, except for vent holes in the secondary shield wall, which are raised 18-inches off the floor. There are two closed doors in the Secondary Shield wall that have a flow path under the door in the gap between the door bottom and the floor. The opening in the wall for the door is 3'-6" wide. The gap between the floor and the bottom of the door is less than 1 inch. (See Figure 23-3). Therefore, there is negligible floor-level flow path that will allow debris to move from inside the secondary shield wall into the outer annulus.

Figure 23 Plan View of the STP Lower Containment Page 24 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

Figure 23-3 Two Closed Doors (North and South sides) in the Secondary Shield Page 25 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

Response to RAI 23c:

Figure 23-4 shows significant features that were modeled in the Debris Transport calculation.

Among these are washdown and spray locations, including those in proximity to the sumps.

Washdown of all debris, not just debris near the sumps, is considered in the transport model that determines how much debris transports to the sump.

Modeled Wash Spray Regions Combined Case 4b Bre ak Flow with Spray Flow Combined Case 1 and Case 5 Break Flow with Spray Flow Modeled Sump Mass Sinks Modeled Direct Spray Regions Figure 23 Significant Features Modeled in the Debris Transport Calculation Response to RAI 23d:

The Debris Transport calculation took into consideration that the four openings in the secondary shield wall are raised 18-inches above the containment pool floor level. As shown in Figure 23 2 and discussed in the response to RAI 23b, other than the four openings in the secondary shield there are no significant flow paths that allow debris to move from inside the secondary shield wall during the pool fill phase.

Reference:

ALiON-CAL-STPEGS-2916-005 Revision: 3, Document

Title:

GSI-191 Containment Recirculation Sump Evaluation: CFD Transport Analysis Page 26 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAI #24 Please provide plots of velocity and turbulence contours in the containment pool that include the entire pool and which are based on the computational fluid dynamics model used in the debris transport analysis. Please also provide close-up plots of the velocity and turbulence contours in the region of the strainer and its immediate surroundings from the computational fluid dynamics model that was used to determine the flume velocities and turbulence levels for head loss testing. In addition, please provide a table of the head loss test flume (average) velocity as a function of distance from the test strainer. Please indicate which plant strainer is being modeled in the head loss test.

Response to RAI #24 Later RAI #25 Please discuss any sources of drainage that enter the containment pool near the containment sump strainers (i.e., within the range of distances modeled in the head loss test flume, e.g., 45 feet). Please identify whether the drainage would occur in a dispersed form (e.g., droplets) or a concentrated form (e.g.,

streams of water running off of surfaces). Please discuss how these sources of drainage are modeled in the test flume to create a prototypical level of turbulence in the test flume.

Response to RAI #25 Later RAI #26 Please identify any debris quantities added to the test flume prior to starting the test pump for the head loss tests and provide a technical basis for adding this debris prior to starting the test pump.

Response to RAI #26 Later Page 27 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

D. Head Loss and Vortexing RAJ #27 Please provide the vortex test conditions and observations. Page 50 of the supplemental response dated December 11,2008, stated that the Froude (Fr) number was limited to < 0.25, but on page 38 it was stated that the Fr # = 0.459. Please explain this apparent discrepancy.

Response to RAI #27 The Froude number is limited to a value of < 0.25 for RG 1.82 Revision 3 PWR sump designs and conditions. It does not directly apply to strainer designs. Accordingly, the new STP Sure Flow Suction Strainer configuration is such that the guidance provided in the subject RG does not really apply since the STP new strainer configuration is more related to the guidance provided for BWRs, since the subject replacement strainer takes the place of the PWR sump.

PCI Technical Document No. SFSS-TD-2007-003, Sure-Flow Suction Strainer Vortex Issues addresses the 'use' of BWR guidance to evaluate the new Sure-Flow Suction Strainers as well as a summary of the methodology and assumptions utilized in the design and technical application of the PCI technology as it relates to the issues of vortex formation and potential subsequent air ingestion. The subject PCI document has been previously sent to the Staff in support of GL 2004-02 Licensee responses. PCI submitted the subject document as a "proprietary & confidential" document in accordance with 10 CFR Part 2.390.

The subject methodology described in PCI Technical Document No. SFSS-TD-2007-003 is utilized as the basis for PCI Technical Document No. TDI-6005-07, Vortex, Air Ingestion & Void Fraction, South Texas Project Units 1 & 2 and addresses vortex formation and subsequent air ingestion associated with the strainer. The subject calculation provides the specific methodology, basis, and assumptions for evaluating STP with regard to the subject issues.

The post-LOCA containment water level (i.e., minimum water level) at the initiation of ECCS/CSS recirculation for the STP SBLOCA is Elevation -8'-10.5" (2'-4.5" or 28.5" water depth). The minimum strainer submergence was conservatively determined using the maximum elevation of the 'top' of the partially submerged strainer along with the minimum post-SBLOCA containment water level. The maximum elevation of the 'top' of the partially SUbmerged strainer is determined as that portion of the strainer height submerged plus the height of the strainer

'supports' off of the containment floor. The top of the STP strainer module is 27-7/8" (i.e., 2.32')

above the containment floor (EI. -11 '-3") or Elevation -11.25'. Accordingly, the minimum post LOCA containment water level would theoretically be 5/8" (i.e., 0.05') above the top of the strainer module based on the SBLOCA conditions.

For the STP LBLOCA, the post-LOCA containment water level (i.e., minimum water level) at the initiation of ECCS/CSS recirculation is Elevation -8'-1" (3'-2" or 38" water depth). The minimum strainer submergence was conservatively determined using the maximum elevation of the 'top' of the partially submerged strainer along with the minimum post-LBLOCA containment water level. The maximum elevation of the 'top' of the partially submerged strainer is determined as that portion of the strainer height submerged plus the height of the strainer 'supports' off of the containment floor. The top of the STP strainer module is 27-7/8" (I.e., 2.32') above the containment floor (EI. -11 '-3") or Elevation -11.25'. Accordingly, the minimum post-LOCA Page 28 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

containment water level would theoretically be 10-1/8" (i.e., 0.844') above the top of the strainer module based on the LBLOCA conditions.

The PCI Sure-Flow Suction Strainer technology has been extensively tested with regard to the issues of vortex formation and air ingestion. Testing has been performed by PCI and independently at the Fairbanks-Morse Pump Company (FMPC), the Alden Research Laboratory (ARL), and the Electric Power Research Institute's (EPRI) Charlotte NDE Center. The subject testing has been performed on both generic and Licensee specific basis for both pressurized water reactor (PWR) and boiling water reactor (BWR) nuclear power plants in vertical and horizontal strainer orientation configurations as well partially (i.e., small break LOCA (SBLOCA) and flood-up/rising water scenarios) and fully submerged post-LOCA conditions. In no case has sustained vortex formation been observed during the multitude of strainer tests that would result in subsequent air ingestion.

Analytical analysis of vortex formation for a specific component such as the PCI Sure-Flow Suction Strainer for STP is not really possible. Based upon the technical literature search that was performed by PCI and in discussions with known experts from various organizations such as the Alden Research Laboratory, it is abundantly apparent that the issues associated with vortex formation and the associated issue of air ingestion are both difficult to prove or analyze in an analytical manner. The available vortex literature that does exist is almost entirely based on empirical evidence associated with very large high volume intake structures - the study of vortex mitigation and suppression is based on experimental research. The literature search was primarily from sources and examples sited in various technical publications from academia, research laboratories, government agencies, pump vendors, and design engineering firms with respect to the mechanisms of vortex suppression.

It should be noted that the literature search did not identify or produce any documentation that substantiated the phenomena associated with or the possibility of a vortex "penetrating" a perforated plate vortex suppressor. That being said, the available literature does provide both generic and specific information that can be readily and practically applied to a PWR sump strainer installation to preclude vortex formation and subsequent air ingestion. PCI has utilized the information contained in the technical literature during the development and design of the Sure-Flow Suction Strainer for both PWR and BWR applications. These same design principles are applied to and integrated in the design of the STP strainer.

The PCI Sure-Flow Suction Strainer has a unique and patented suction flow control device (SFCD) integral to the strainer. It is known as the core tube. The primary function of the SFCD technology is to provide uniform flow to the entire Sure-Flow Suction Strainer which directly results in overall decreased head loss and the prevention of vortex formation. The design of the SFCD is one of a series of defense-in-depth vortex suppressor design features (i.e., various redundant vortex suppression devices - combination of perforated plate, parallel disk plates, disk wire "grills", and the module external structural bracing) to assure that vortex formation does not occur and subsequently air is not ingested. The SFCD technology is described in PCI Technical Document Number SSFS-TD-2007-002, Suction Flow Control Device (SFCD)

Principles and Clean Strainer Head Loss Design Procedures. The subject PCI document has been previously sent to the Staff in support of GL 2004-02 Licensee responses. PCI submitted the subject document as a "proprietary & confidential" document in accordance with 10 CFR Part 2.390.

Page 29 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

In order to mitigate or suppress a vortex, different measures can be taken. One of the most efficient ways is to ensure that the water head above the pump inlet is greater than the critical submergence head. However, this situation may not be possible, since in many cases the head may be affected by the strainer debris loading/head loss, is not constant, and can vary during the operation of the pump over its design basis conditions. This is the specific case associated with the operation of the STP ECCS and CSS pumps post-LOCA following initiation of recirculation. Therefore, other means or combinations thereof to avoid or reduce free vortex flows are required. There are three (3) possible means or categories that can eliminate and suppress surface vortices. They are as follows:

1. elongation of fluid flow streamlines between the pump inlet and the free water surface,

2. elimination of approach flow velocity non-uniformity (i.e., uniform approach velocity), and

3. use of special vortex suppression device(s)

The regulatory requirements, actually guidance with regard to the specific issue of vortex formation and the related issue of air ingestion are addressed in various sections of RG 1.82, Revision 3.

In RG 1.82, Revision 3, specifically Table A-6 guidance is provided with regard to vortex suppression. The subject table specifies that standard 1.5" or deeper floor grating (e.g., 4" x 4" opening) or its equivalent has the capability to suppress the formation of a vortex with at least 6" of submergence. The USNRC carried out a number of tests regarding vortex suppressors at the Alden Research Laboratory (ARL) to arrive at the information summarized in Table A-6. Table A-6 is based upon the significant testing and evaluation that was performed by ARL under contract to the USNRC with respect to the issue of ECCS sump performance, vortex formation, and vortex suppression. The activities performed by ARL are documented in USNRC NUREG/CR-2772 and -2761 and are supported by USNRC NUREG/CR-2758, -2759, and 2760.

Even though the subject NUREG/CRs dealt specifically with the issue of vortex formation and suppression in an ECCS sump, the conclusions are also relevant to the PCI Sure-Flow Suction Strainer for STP. The perforated plate that surrounds 100% of the PCI Sure-Flow Suction Strainer core tube is equivalent to (actually exceeds) the floor grating recommended and specified in RG 1.82 Revision 3 and NUREG/CR-2772 and -2761, and therefore has the capability to completely suppress the formation of a vortex and preclude subsequent air ingestion.

In addition, RG 1.82, Revision 3 provides further guidance with respect to air ingestion in Table A-6 and specific guidelines for selected vortex suppressors. The guidance is divided into two (2) categories; (1) cubic and non-cubic suppressors surrounding the pump inlet within the sump, and (2) horizontally oriented grating covering the entire sump. It should be noted that the subject Table has the following NOTE: Tests of these types of vortex suppressors at Alden Research Laboratory have demonstrated their capability to reduce air ingestion to zero even under the most adverse conditions simulated (emphasis added).

Even though the PCI Sure-Flow Suction Strainers do not employ the specific use of grating in their design, they do utilize a combination of perforated plates, parallel disk plates, disk wire "grills", module external structural bracing, and the resultant tortuous strainer internal flow path Page 30 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

that is more than equal to the singular vortex prevention capabilities of the grating.

Furthermore, the PCI Sure-Flow Suction Strainers satisfy not one, but both guidance categories as delineated in RG 1.82, Revision 3, specifically Table A-6.

The PCI Sure-Flow Suction Strainer assembly for PWRs is comprised of either vertically or horizontally oriented strainer modules each containing a plant specific number of strainer module disks. The disks are a nominal 5/8" thick (i.e., nominal %" internal thickness) and are separated 1" from each adjacent disk. The interior of the disks contain rectangular wire stiffeners for support, configured as a "sandwich" made up of three (3) layers of wires - 7 gauge, 8 gauge, and 7 gauge, respectively. The disks are completely covered with perforated plate having plant specific sized holes. The end disk of a module is separated approximately 5" from the end disk of an adjacent module. The 5" space between adjacent modules is covered with a solid sheet metal "collar" to seal the module-to-module separation opening. Each of the modules has plant specific structural cross-bracing on the exterior surfaces of each module.

Based on the design configuration of the PCI Sure-Flow Suction Strainer assembly, the largest opening for water to enter into the sump is through the perforated plate holes. The size of the perforated plate holes by themselves would preclude the formation of a vortex, since a compressible air column would be competing for the same space opening (i.e., perforated plate hole opening) as the non-compressible water entering the strainer. Therefore, the non compressible water would preclude the entry of the compressible air column. In the case of all the PCI Sure-Flow Suction Strainer design, the largest perforated plate hole opening is only 0.095", which is only 75% of the 0.125" hole openings that were tested by ARL for the USNRC as documented in NUREG/CR-2772 and -2761. It should also be noted that the strainer perforated plate hole openings are significantly smaller than the large openings associated with the recommend grating (i.e., 1.5" thick x 4" x 4") vortex suppressor design as recommended and specified in RG 1.82 Revision 3, NUREG/CR-2772 and -2761.

However, in the highly unlikely event that a series of "mini-vortices" combined in the interior of a disk to form a vortex, the combination of the wire stiffener "sandwich", the physical closeness of.

the disk perforated plates (i.e., nominal %" internal thickness), and the small openings and passages that direct (i.e., tortuous path) the flow of water to the strainer core tube would further preclude the formation of a vortex in either the core tUbe or the sump.

With regard to category (1) cubic and non-cubic suppressors as discussed in RG 1.82 Revision 3, the PCI suction strainer design "surrounds" the core tube (i.e., cubic suppressor) with a combination of perforated plate, parallel disk plates, internal disk wire "grills", and module external structural bracing. This results in not one (1), but four (4) separate vortex suppressing devices that would prevent both external and internal vortex formation and potential re formation.

In addition, the PCI Sure-Flow Suction Strainer assemblies as designed and installed completely cover the existing PWR sump (i.e., ECCS and CSS pump inlets). Therefore, the strainer assembly could also be considered to be a non-cubic suppressor as well.

Finally, since the strainer assembly covers the entire sump, it can be concluded and as previously discussed, the PCI Sure-Flow Suction Strainer assembly configuration is more than equal to the vortex prevention capabilities of a single 'layer' of horizontally oriented grating due to its "defense-in-depth" multiple vortex suppressors. This is based on the physical configuration of the PCI Sure-Flow Suction Strainer assembly which incorporates a Page 31 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

combination of perforated plate, parallel disk plates, internal disk wire "grills", and module external structural bracing that results in both the tortuous strainer fluid flow path (i.e., the strainer module core tubes with staggered holes would offer even a more torturous flow path and resistance to circulation, making a coherent core vortex including air-drawing vortices unsustainable.), and significant extension of the fluid streamlines (i.e., free water surface to pump inlet) due to the convoluted extended external and internal strainer surface area.

In conclusion, the PCI Sure-Flow Strainer design incorporates all three (3) recognized and recommended means for vortex elimination and suppression:

1. Long flow path from water surface through the PCI Sure-Flow Strainer, plenum, sump, and ECCS pump inlet piping,

2. PCI Sure-Flow Strainer suction flow control device (SFCD) technology - the 'core tube' provides uniform approach velocity to all strainer modules - something that no other strainer design can provide, and

3. PCI Sure-Flow Strainer design utilizes a combination of recognized 'defense in depth' multiple vortex suppression devices - perforated plate, parallel disk plates, disk grill wires, core tube slots, module external bracing, and the resultant tortuous strainer internal flow path - all providing more than the single grating vortex suppressor recommended in RG 1.82 Revision 3.

Based on the above discussion and supporting references, there is considerable and reasonable test, analytical and empirical data that demonstrates that the STP Sure-Flow Suction Strainer will not promote or support vortex formation, but will in fact suppress the formation of a vortex. Accordingly, air ingestion is also precluded, since there is no mechanism to draw air into the ECCS and CSS pumps' suction.

Based on PCl's results for calculation TDI-6005-07, Vortex, Air Ingestion & Void Fraction, South Texas Project Units 1 & 2, the fact that vortex formation was not observed during the STP Large Flume Test at ARL, and the response to this RAI, vortex formation and subsequent potential air ingestion are not issues for the Design Basis LBLOCA or for the SBLOCA scenario. For both the Design Basis LBLOCA and the SBLOCA scenario, the STP Sure-Flow Suction Strainer by design and supported by a multitude of tests does not promote vortex formation and subsequent air ingestion.

RAI #27

REFERENCES:

27.1 PCI Technical Document Number SSFS-TD-2007-002, Suction Flow Control Device (SFCD) Principles and Clean Strainer Head Loss Design Procedures 27.2 TDI-6005-07, Vortex, Air Ingestion & Void Fraction, South Texas Project Units1&2 27.3 RG 1.82, Revision 3 27.4 NUREG/CR-2772 27.5 NUREG/CR-2761 27.6 NUREG/CR-2758 27.7 NUREG/CR-2759 27.8 NUREG/CR-2760 27.9 PCI Technical Document No. SFSS-TD-2007-003, Sure-Flow Suction Strainer Vortex Issues Page 32 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAJ #28 Please provide debris sizing, amount of each debris size for each size category, and basis for the distribution chosen for the debris surrogates added to the head loss testing (similar to what was provided in the February 29, 2008, submittal that referred to an earlier test protocol no longer credited by the licensee). As discussed in the "NRC Staff - lOReview Guidance Regarding Generic Letter 2004-02 Closure in the Area of Strainer Head Loss and Vortexing," dated March 2008 (ADAMS Accession No. ML080230038), and in Appendix II of the NRC staffs SE on NEJ 04-07, the debris should be categorized into distinct sizes including fine debris in order to ensure that the test was conducted in a manner that realistically modeled transport of the debris. Please state what categorization was used and justify any method chosen that is not consistent with the NRC staffs SE and guidance.

Response to RAI #28 Later RAJ #29 Please justify that the debris addition sequence did not non-conservatively affect the ability of more transportable debris to reach the strainer. The supplemental response dated December 11, 2008, indicated that some fine fibrous debris was added after less transportable debris and that coating chips were added in the first debris addition batch. The addition of less transportable debris prior to more transportable debris is likely to result in the entrapment of some debris that might otherwise reach the strainer.

Response to RAI #29 Later RAJ #30 Please provide the head loss plots for the testing including annotation of significant events during the test.

Please include the portion of the plot that shows the flow sweeps that were performed to determine whether boreholes were present in the debris bed.

Response to RAI #30 Later RAJ #31 Please provide the design maximum head loss and the basis for the maximum. It appeared that the structural limit may provide the maximum allowable head loss. Verify that the structural pressure limit of 5.71 feet is not exceeded during any phase of the LOCA response. Please provide head loss at lowest postulated sump temperature and compare it to the structural limit. State whether clean strainer head loss counts against the structural limit, or if only debris head loss needs to be considered. Page 51 of the supplemental response dated December 11, 2008, states that the total strainer head loss is 6.504 feet at 171°F. It is unclear whether this includes the clean strainer head loss. The debris head loss will increase as temperature decreases. Please provide the outcome of extrapolations of the head loss test results to various temperatures required for head loss considerations.

Response to RAI #31 Later Page 33 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAI #32 Please provide information on whether the strainer is vented. The supplemental response dated December 11, 2008, states that the strainer will be fully submerged, but the response did not address whether there are vent paths above the submerged water level. If the strainer is vented, please justify that the strainer will function adequately in the vented configuration considering that the available driving head across the strainer is caused only by the elevation difference between the water upstream and downstream of the strainer.

Response to RAI #32 The emergency sump strainers are not vented.

Page 34 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAI #33 The supplemental response dated December 11, 2008, stated on page 53 that containment accident pressure was not credited to prevent flashing across the strainer. However, the tested head loss is much greater than the stated strainer submergence (l0 inches for large break LOCA and 0.5 inches for a small break LOCA). The sump temperature is greater than 212 of at switchover to recirculation. Therefore, some containment pressure is likely required to prevent flashing. Please provide the margin to flashing and the assumptions for the calculation.

Response to RAI #33 Later RAI #34 In addition to flashing, the potential for deaeration of the coolant as it passes through the debris bed should be considered. Please provide an evaluation of the potential for deaeration of the fluid as it passes through the debris bed and strainer and whether any entrained gasses could reach the pump suction. If entrained gasses can reach the pump suction, please evaluate how the net positive suction head required (NPSHr) for the pump could be affected as described in NRC Regulatory Guide 1.82, Revision 3, "Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident," Appendix A (ADAMS Accession No. ML03314034).

Response to RAI #34 Later Page 35 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #35 Please address the potential for t10ating debris to collect on top of strainer during a small break LOCA and thus provide a potential air-entrainment pathway to the interior of the strainer.

Response to RAI #35 For the SBLOCA case, the potential for floating debris to collect on top of the strainer and provide an air-entrainment pathway is rather small. The only portion of the post-LOCA debris load that could potentially remain buoyant is the low density fiber glass (LDFG) insulation. The amount of fiberglass insulation debris that is generated by the SBLOCA and transported to the sump area is very small compared to the design basis case (1.05 fe vs. 226.4 fe). Industry testing has shown that this type of debris becomes saturated and sinks very quickly in hot water.

During testing of the prototype strainer module with cold water (50°F), there was a considerable amount of floating debris but no observed air ingestion with a submergence of 'Y2 in.

Subsequent testing with hot water (120°F), did not yield any floating fiberglass insulation debris.

Since there was no air ingestion with floating debris with minimal submergence for the cold water test and since the much hotter temperature water expected for the post-LOCA condition will minimize floating debris, this precludes any opportunity for an artificial vent to form between the strainer and the surface of the water.

Page 36 of 54 SIP Draft Sump RAJ Responses Rev A 7-20-2010

RAJ #36 On page 21 of the December 11, 2008, supplemental response, one of the strainers (Strainer A) appears to be located near a region where runoff from spray drainage enters the containment pool. Given that the submergence of the strainers is minimal for the small break LOCA case (0.5 inches), please provide a technical basis for concluding that drainage of spray water near the strainer surface will not result in splashing and surface disturbances that would cause unacceptable air entrainment into the strainers and emergency core cooling system (ECCS) and containment spray pumps.

Response to RAI #36 Later E. Net Positive Suction Head (NPSH)

RAI #37 Please provide NPSH margin results for low head safety injection, high head safety injection and containment spray pumps, for the large break LOCA and small break LOCA cases, under conditions of hot-leg recirculation.

Response to RAI #37 Later Page 37 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #38 As requested in NRC's November 2007 content guide, please describe the methodology and assumptions used to compute the limiting pump flow rates for all pumps taking suction from the ECCS sumps Response to RAI #38 Each of the 3 emergency sumps supplies water to the respective Containment Spray Pump, Low Head Safety Injection Pump, and High Head Safety Injection Pump for that Train.

The CS Pumps discharge to a common ring header piping arrangement. The CS Pump flow used for the NPSH evaluation is based on 2 CS Pumps operating which yields a higher flow per pump than if all 3 CS pumps were operating and discharging to the common ring headers.

The flow rates used for the Low Head and High Head Safety Injection Pumps are the maximum values given in the Technical Specifications.

Page 38 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAI #39 As requested in the NRC's content guide, please provide the volumes of the water sources that contribute to the formation of the containment pool for the limiting minimum containment water level. Please include a specific discussion of both the large and small break LOCA cases. In particular, for small break LOCA cases, the accumulators and RCS volumes may not contribute to containment pool formation because the RCS pressure may remain too high for accumulator injection and because ECCS injection may result in the refill of the RCS with cooler water, even including the pressurizer steam space for a limiting break near the top ofthe pressurizer.

Response to RAI #39 The limiting minimum containment water level is determined using the following methodology:

1. A correlation was developed for the relationship between containment water level and the containment volume as a function of elevation using information from existing STP calculations.

The correlation between containment volume and water level developed in the Water Level Calculation assumes equalization of water level between all areas of containment at the (-)11 '-3" elevation including internal compartments (e.g., incore instrument room, reactor cavity and elevator shaft). The volume inside the accumulator skirts is only credited as a displacement volume for the small break LOCA case in which the water level does not reach the service way openings preventing this volume from filling. The correlation also includes all volumes below the

(-)11 '-3" elevation (e.g., elevator shaft, normal sump, secondary normal sump, emergency sumps, incore instrument room sump and drain lines).

2. The quantity of water added to containment from the Refueling Water Storage Tank, Sl Accumulators, and the Reactor Coolant System was determined for each of the breaks considered.

3. The quantity of water diverted from the containment sump was determined. The following effects were considered:

• Steam holdup in the containment atmosphere

• Additional mass of water that must be added to the RCS due to the increase in the water density at the lower sump water temperature versus the RCS temperature prior to the LOCA

• Water volume required to fill the RCS steam space as condensation occurs

• Condensation on containment surfaces

• Water volume required to fill the Safety Injection and Containment Spray Piping that is empty prior to the LOCA

• Water in transit from the Containment Spray nozzles and the break location to the Containment Sump

• ECCS leakage outside of containment

• Miscellaneous hold-up volumes throughout containment

4. Given the net mass of water added to the containment floor based on items 2 and 3 listed above, the post-LOCA containment water level was then calculated using the correlation developed in item 1.

Page 39 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

The potential sources of water that were considered in the determination of the minimum pool level are as follows:

• The minimum RWST volume supplied to the RCS and RCB is 360,000 gal. This is a conservative safety limit for minimum injection volume. It does not include an allowance for transfer to recirculation (Switchover volume) of 12,400 gal.

• There are three SI accumulators that each has a minimum volume of 8800 gal (1176.4 cu ft). Consideration of instrument inaccuracies, instrument span, operating margins, and tank tolerances gives a minimum volume of 1172.4 cu ft per accumulator.

• The Pressurizer minimum volume was conservatively assumed to be 25%. The total volume is 2100 cu ft. Using 3% increase for thermal expansion and calculation uncertainty gives 2163 cu ft. This yields a minimum volume of 540.7 cu ft.

• The RCS cold volume with Pressurizer 25% is 12963.3 cu ft. Three percent is added for thermal expansion to give 13352.2 cu ft.

A Small Break LOCA may not result in rapid depressurization of the RCS after the break.

During the RCS depressurization and cool down, the SI Accumulators may be isolated. For the SBLOCA water level determination, it is conservatively assumed that the SI Accumulators will be isolated before the RCS pressure drops below the nitrogen cover pressure of the accumulators. The water volume from the SI Accumulators will not be credited as a source that will reach the containment sump during a SBLOCA.

The holdup of water in the RCS depends upon the break location and the time after the break.

The amount of water that contributes to the pool volume will vary. The holdup within the RCS is summarized below:

Page 40 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RCS HOLDUP FOR VARIOUS SCENARIOS LarQe Break LOCA SurQe Line LOCA Small Break LOCA CS and SI RPV is filled to top RCS is filled For all cases, the Switehover of the hot leg and including loop and entire RCS cold leg piping surge piping (including the entire (3265.9 eu ft). Loop (6515.1 eu ft). Pressurizer) will be and surge line pipes Steam Generators completely full.

are filled (1892 eu are filled to the ft), Steam break elevation Generators and (2616.2 eLi ft).

Pressurizer are Pressurizer 2163 eu empty ft) is empty. Holdup volume:

14974.4 eu ft Holdup volume: Holdup volume: Spill volume:

5158 eu ft 9131.3 eu ft 0.0 eu ft Spill volume: Spill volume:

8195 eu ft 4220.9 eu ft Long Term- Entire RCS Entire RCS For all cases, the Sprays Suspended (14,974.4 eu ft) is (14,974.4 eu ft) is entire RCS filled, including filled, except for the (including the entire Steam Generators Pressurizer (2163 Pressurizer) will be and 100% ofthe eu ft) which is empty completely full.

Pressurizer Holdup volume: Holdup volume: Holdup volume:

14974.4 eu ft 12811.4 eu ft 14974.4 eu ft Spill volume: Spill volume: Spill volume:

0.0 eu ft 540.7 eu ft 0.0 eu ft Page 41 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #40 As requested in the NRC's content guide, please identify the methodology and any computer codes used to perform the suction piping friction loss calculations to determine the loss coefficients.

Response to RAI #40 The suction piping and fitting friction head losses are based on standard industry methodologies using Crane Technical Paper 410 and Cameron Hydraulic Data. The maximum pump flow rates were used. No computer codes were utilized for the calculations.

Page 42 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAJ #41 As requested in the NRC's content guide, please state the criterion and methodology used by the pump vendor to determine the NPSHr for all pumps taking suction from the ECCS sumps.

Response to RAI #41 The CS and Sl Pumps are vertical motor-driven pumps, each sitting in an individual barrel.

These vertical multi-stage pumps have independent NPSH requirements at the first impeller and at the suction nozzle.

The NPSH required at the first impeller is provided by the manufacturer's design of the pump can. The design for the pumps provides for the NPSH requirement at the first impeller to be met by the inherent design configuration of the pump. The design calls for a distance of 15 ft in this barrel between the suction nozzle centerline and the pump first-stage impeller. The 15-ft liquid head in the pump barrel thus inherently satisfies the 15ft NPSH requirement at the first impeller which is conservative based upon pump testing by the vendor (Pacific Pumps).

The minimum required NPSH at the slJction nozzle centerline is equal to the velocity head plus one half of the suction nozzle (pipe) diameter expressed in feet. This criterion was given by the pump vendor (Pacific Pumps)

Page 43 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAJ #42 Please provide the basis for considering the two-train NPSH results (based on the failure of one diesel generator) to be the limiting single failure. The NRC staff noted that other cases exist, such as the operation of three trains (no single failure), or the operation of a single train (which is permitted by the emergency operating procedures through operator actions to shut off redundant pumps). Please provide the NPSH results for these other cases and the basis for considering the two-sump case as limiting with respect to NPSH margin.

Response to RAI #42 The design basis for STP is to have a minimum of 2 out of the 3 Trains of ECCS and CS to be used for accident mitigation. Containment analyses consider operation of either two or three ECCS and CS trains at time of accident initiation. This is stated in the licensing basis (UFSAR Section 6.2.1 and 6.3.1). For 3 Train operation, the design basis debris loading will be split among the 3 sumps; and each of the 3 operating sump strainers will have a debris loading per sump that is less than the design case with 2 sumps in operation. Consequently the debris head loss will be less per sump strainer which will have a positive effect on the NPSH margin.

Use of only a single Train is not part of the design and licensing basis. The emergency operating procedures allow containment spray, high head safety injection, and low head safety injection pumps to be secured manually if certain specific criteria are met and permission from the Technical Support Center is obtained. However, the emergency operating procedures do call for 2 low head safety injection pumps to be operating. One low head pump is aligned for cold leg recirculation and the other is switched from cold leg to hot leg recirculation after a certain time post-LOCA. Thus 2 sumps would be in operation to supply the respective low head pump of the 2 in operation. If any containment spray pumps and/or high head safety injection pumps are secured then there would be less flow through the sump strainer which would result in less debris head loss and there also would be less piping friction loss. This would have a positive effect on the NPSH margin.

The 2 operating sump case is the limiting case for NPSH margin.

Page 44 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAI #43 Please state whether the NPSH results on page 58 of the December 11, 2008, supplementary response include debris bed and clean strainer head loss. If these additional loss terms are included in the results, then please provide NPSH margin results that do not include these terms, per the definition of NPSH margin in Regulatory Guide 1.82.

Response to RAI #43 Later RAI #44 Please identify the volume of holdup assumed for the refueling canal and provide further information that justifies that the refueling canal drains cannot become fully or partially blocked such that additional hold up could occur, or the extent to which hold up could occur. STP has the potential to generate hundreds of cubic feet of fiber, as well as miscellaneous debris and other materials. It is not clear from the information provided in the supplemental responses that the existing design of the drains is sufficient to keep small and large pieces of debris from plugging the drains for the refueling canal. In particular, it is not clear why large pieces of debris (e.g., fibrous, miscellaneous, etc.) cannot be transported to the upper containment through blowdown or other transport processes. If debris larger than or similar to the size of the drain line ends up in the refueling cavity, it is not clear that temporary floatation and transport by surface currents to the drains would not provide a credible mechanism for blocking the drain lines. In a like manner, several small pieces of debris may be capable of causing partial or complete blockage of the drain lines as well.

Response to RAJ #44 Later F. Coatings Evaluation RAI #45 In accordance with the NRC staffs "Revised Content Guide for Generic Letter 2004-02 Supplemental Responses," dated November 21, 2007 (ADAMS Accession No. ML073110389), please provide the specific types of qualified coatings used in containment and the substrates on which they were applied.

Also, please justify how the WCAP-16568-P testing is applicable to the qualified coatings at STP.

Response to RAI #45 Later Page 45 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

RAJ #46 The Keeler and Long report 06-0413, "Design Basis Accident Testing of Coating Samples from Unit 1 Containment, TXU Comanche Peak SES," dated April 13, 2006 (ADAMS Accession No. ML070230390), referenced in the licensee's supplemental response, only applies to degraded qualified epoxies and not original equipment manufacturer epoxy coatings. Please clarify the definition of unqualified epoxy coatings at STP, since unqualified epoxy coatings may be considered to be degraded qualified coatings and/or original equipment manufacturer coatings, and that the unqualified epoxies used at STP are similar to the coating systems tested by Keeler and Long.

Response to RAI #46 The definition of a DBA Qualified coating used at STP is:

DBA Qualified Coating System - A coating system used inside reactor containment that can be attested to having passed the required laboratory testing, including irradiation and simulated Design Basis Accident (DBA), and has adequate quality documentation to support its use as DBA qualified. This applies to all coating systems, epoxy or otherwise, that are used inside the reactor containment building.

Any coating that does not satisfy the above definition is classified as an unqualified coating.

The results of unqualified epoxy testing by Keeler and Long were considered by the industry to be generically representative of epoxy with IOZ primer coatings occurring in plants such as STP.

Page 46 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAJ #47 Please clarify/justify the use of unqualified epoxy coating debris in chip form in head loss testing given that a continuous debris bed appears to form during testing. From the NRC review guidance and SE, if there is a bed present, all coating debris should be treated as particulate and assume to transport to the sump, unless proper justification and/or data are provided.

Response to RAI #47 The STP Debris Generation calculation states that unqualified epoxy coating outside the lOI will fail as chips. The determination that unqualified epoxy coating debris that is generated outside the lOI will fail in the form of chips is based upon reference to laboratory testing results that are documented in Alion Report No. ALiON-LAB-REP-TXU-4464-02, TXU Paint Chip Characterization", Revision O.

The properties of the chips examined in ALiON-LAB-REP-TXU-4464-02 were found to be consistent with those of Phenoline 305 and Carboline Cl-11, i.e., comprised of two layers, IOl and epoxy. The properties of the materials characterized in ALiON-LAB-REP-TXU-4464-02 are consistent with the 2-layer composition described in the STP Debris Generation calculation for unqualified coatings outside the lOI, of which the epoxy component is expected to fail as chips.

Page 47 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

G. Debris Source Term RAI #48 The supplemental response dated December 11, 2008, provides a three-sentence summary of how the containment is kept clean. Please provide a more detailed description of the containment foreign material control programs for STP, including reference to procedural requirements and brief description of methods used to clean or maintain cleanliness.

Response to RAI #48 During normal operation (Modes 1 to 4), STPNOC uses a procedure to maintain containment integrity with respect to potential sump debris sources. This procedure provides for a visual inspection of the affected areas within containment at the completion of each containment entry when containment integrity is established to verify no loose debris is present which could be transported to the emergency sump and cause restriction of pump suction during LOCA conditions. Work crews are briefed by Operations to emphasize the importance of maintaining containment cleanliness. During this brief, Operations reviews the work scope of the activity and travel paths inside containment to ensure cleanliness standards are met. Workers are to promptly inform the Control Room if any potential debris items are found.

During outages, STPNOC maintains containment cleanliness by adherence to the housekeeping procedure and the foreign material exclusion control procedure. Containment cleanliness is monitored and encouraged by the reactor containment building coordinators and the work supervisors for all work activities that occur during the outage. Worker training includes an emphasis on containment cleanliness. Outage newsletters, handbooks, signs, site wide messages, etc. are all used to convey an expectation of containment cleanliness. Areas of the containment have been designated to be "owned" by certain STPNOC managers to help ensure cleanliness is maintained and that the area is properly cleaned up at the end of the outage.

Prior to containment closeout at the end of the outage, the building coordinators oversee the cleanup of the containment work areas. Dedicated work crews are assigned to assist in this activity. Identified potential debris is cleaned or removed, as necessary. When temporary scaffolds are taken down, the scaffold procedure calls for inspection of the items and removal of any tape before storage.

Prior to entry into Mode 4 at the end of the outage, Operations performs a surveillance procedure to verify containment cleanliness. This procedure contains an extensive checklist detailing all areas of containment that must be inspected for cleanliness prior to plant startup after each outage. Visual inspections are performed by teams typically led by Senior Reactor Operators.

Page 48 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

H. Structural analysis RAI #49 The supplemental responses contain very limited information detailing the results of the structural analyses performed to demonstrate the structural integrity of the replacement sump strainers at STP. The responses provide only a brief qualitative statement of the results without any supporting quantitative data summarizing the results of the analyses as requested in the second portion of item 3.k of the NRC staffs March 2008 revised content guide for the GL 2004-02 supplemental responses. Please provide the actual and allowable stresses and show the design margins for the strainers and all associated welds and components.

Response to RAI #49 The strainer assembly is installed using multiple individual strainer modules (20 per sump).

Detailed structural analysis was performed on a single strainer module. The analysis is bounding and applicable to each of the 60 modules. Each sump pit is a 4' x 10' opening, covered by steel cover plates with a plenum box in the middle. The plenum box collects water from all strainer modules and directs the water down into the sump pit. Each strainer module is mounted to angle iron running along the floor. Where suitable floor embedded plates were available, the angle iron was attached to the embedded plates with welded clips. At other locations, the angle iron was welded to anchor plates and attached to the floor with concrete expansion anchors.

The results tabulated below are grouped into 3 categories: 1) strainer module components, 2) sump pit cover (cover plate, plenum box and connecting elements), and 3) floor mounting hardware (angle iron, clips, concrete expansion anchors). In the following tables, the term "Allowable" applies to stress, force per unit length or force, as applicable. The corresponding "Actual" value uses the same units as the "Allowable", to facilitate comparison. Most strainer components are A240, type 304 stainless steel, for which the allowable stress was computed based on a yield stress of either 23.2 ksi at 267 of or 28.15 ksi at 128 of. Two separate cases were considered, denoted as cases 1 and 2 in the following tables. The first case corresponds to maximum temperature (267 OF), which occurs early following a LOCA, while debris loading is low and resulting differential pressure is also low. Eventually the sump would experience the maximum debris loading, causing the maximum differential pressure. Because this occurs later, temperatures would have cooled greatly, to 128 of. In the following tables, Case 1 is the early case (peak temperature, low differential pressure) and Case 2 is the long-term case (low temperature, peak differential pressure). As indicated above, the material properties differ, with Case 1 having the lower yield stress due to higher temperature.

Page 49 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

The acronym "IR" stands for Interaction Ratio, which is nominally "Actual" divided by "Allowable". Since seismic loads are present, most components are subject to loads in multiple directions acting simultaneously. Code allowables may be different in different directions. (For example, AISC allows 0.6 fy for major axis bending and 0.75 fy for minor axis bending of plates; the axial allowable is generally lower and dependent on kUR ratio.) Thus, IR is often not a direct ratio, but instead is the sum of multiple IR components. In cases where IR was computed from the sum of stress components combined using different allowables that are explicitly documented in the calculation, the tables conservatively list total stress and the lowest of the allowables, along with the true IR as reported in the structural calculation. "Actual" and "Allowable" correspond to the higher IR of cases 1 and 2. In cases where the directional stress components were not separated and documented individually in the calculation, only total IR is reported. Whenever IR is one or less, the component meets the stress requirements of the applicable code. Compliance with this requirement is confirmed by the results tabulated below.

Page 50 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

Summary of Structural Analysis Results - - Strainer Module Components Component Seismic IR IR IR Case (1) (2) (max)

External Radial Stiffener ODE 0.74 0.69 0.74 SSE 0.86 0.74 0.86 Tension Rods aBE 0.37 0.32 0.37 SSE 0.40 0.34 0.40 Edge Channels aBE 0.51 0.54 0.54 SSE 0.71 0.71 0.71 Seismic Stiffeners aBE 0.64 0.65 0.65 SSE 0.66 0.63 0.66 Spacers aBE 0.68 0.57 0.68 SSE 0.56 0.48 0.56 Core Tube aBE 0.04 0.04 0.04 SSE 0.05 0.05 0.05 Perforated Plate aBE 0.33 0.45 0.45 SSE 0.53 0.54 0.54 Wire Stiffener (differential pressure only) - - 0.25 0.33 0.33 End Cover aBE 0.40 0.49 0.49 SSE 0.35 0.48 0.48 End Cover Welds aBE 0.41 0.49 0.49 SSE 0.35 0.43 0.43 Weld of External Radial Stiffener to Core Tube aBE 0.19 0.17 0.19 SSE 0.21 0.18 0.21 Weld of External Radial Stiffener to Seismic Stiffener aBE 0.51 0.48 0.51 SSE 0.58 0.52 0.58 Edge Channel Rivets aBE 0.09 0.10 0.10 SSE 0.11 0.12 0.12 Inner Gap Hoop Rivets aBE 0.11 0.12 0.12 SSE 0.14 0.14 0.14 End Cover Rivets aBE 0.00 0.01 0.01 SSE 0.01 0.01 0.01 Module-to-Module Sleeve aBE 0.16 0.14 0.16 SSE 0.20 0.17 0.20 Module-to-Modu1e Latch Connection aBE 0.60 0.62 0.62 SSE 0.92 0.87 0.92 Mounting Pins (standard) aBE 0.32 0.26 0.32 SSE 0.31 0.27 0.31 Mounting Bolts (alternate) aBE 0.20 0.22 0.22 SSE 0.21 0.22 0.22 Clevis Hitch Pins aBE 0.35 0.39 0.39 SSE 0.38 0.39 0.39 External Radial Stiffener Mounting Tabs aBE 0.14 0.14 0.14 SSE 0.15 0.13 0.15 Weld of Radial Arm to End Plate aBE 0.62 0.75 0.75 SSE 0.48 0.56 0.56 CASE 1) Early Conditions - - peak temperature, low differential pressure (low debris)

CASE 2) Late Conditions - - peak differential pressure (max. debris), low temperature Page 51 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

Summary of Structural Analysis Results - - Items Spanning Sump Pit Component Seismic Allowable Actual IR IR IR Case (1) (2) (max)

Cover Plate + Angle Iron + Tee aBE 18.6 ksi 7.96 ksi 0.41 0.43 0.43 (combined section) SSE 29.7 ksi 10.23 ksi 0.34 0.34 0.34 Angle Iron + Cover Plate aBE 18.6 ksi 11.85 ksi 0.58 0.64 0.64 (combined section) SSE 29.7 ksi 14.66ksi 0.48 0.49 0.49 Cover Plate Bolts OBE 24.63 ksi 23.73 ksi 0.76 0.96 0.96 SSE 39.40 ksi 27.83 ksi 0.58 0.71 0.71 Weld connecting T to cover plate aBE 2.11 k/in 1.39 k/in 0.59 0.66 0.66 SSE 3.38 k/in 1.66 k/in 0.46 0.49 0.49 Plenum Box plate panels aBE 21.1 ksi 13.43 ksi 0.51 0.64 0.64 SSE 33.8 ksi 14.94 ksi 0.37 0.44 0.44 Plenum Box + Cover Plate aBE 0.47 0.50 0.50 (combined section) SSE 0.43 0.42 0.43 Plenum Box perimeter angles aBE 0.76 0.86 0.86 SSE 0.63 0.67 0.67 Plenum Box panel welds aBE 2.81 k/in 0.112 k/in 0.03 0.04 0.04 SSE 4.50 k/in 0.125 k/in 0.02 0.03 0.03 Weld between plenum box panels and aBE 2.11 k/in 0.43 k/in 0.18 0.21 0.21 perimeter angles SSE 3.38 k/in 0.51 k/in 0.14 0.15 0.15 Plenum Box Access Cover Bolts aBE 0.18 0.25 0.25 SSE 0.13 0.17 0.17 Summary of Structural Analysis Results - - Floor Mounting Hardware Component Seismic Allowable Actual IR IR IR Case (1) (2) (max)

Angle Iron Tracks aBE 13.9 ksi 7.49 ksi 0.54 0.54 0.54 SSE 22.3 ksi 13.64 ksi 0.61 0.58 0.61 Anchor Plates aBE 21.1 ksi 12.72 ksi 0.58 0.60 0.60 SSE 27.8 ksi 20.96 ksi 0.75 0.71 0.75 Weld of Angle Iron to Anchor Plate aBE 1.74 k/in 0.17 k/in 0.10 0.09 0.10 SSE 2.78 k/in 0.28 k/in 0.10 0.09 0.10 Hold Down Bars aBE 13.9 ksi 5.47 ksi 0.36 0.32 0.36 SSE 22.3 ksi 10.03 ksi 0.42 0.36 0.42 Weld of Hold Down Bars to Angle aBE 1.16 k/in 0.46 k/in 0.40 0.35 0.40 Iron Tracks SSE 1.86 k/in 0.88 k/in 0.47 0.41 0.47 Concrete Expansion Anchors SSE 3100lb Tension = 2028 Ib 0.92 0.71 0.92 Shear = 8181b Standard mounting clips aBE 21.1 ksi 12.41 ksi 0.53 0.59 0.59 SSE 33.8 ksi 16.61 ksi 0.48 0.49 0.49 Welds on standard mounting clips OBE 2.90 k/in 2.78 k/in 0.96 0.78 0.96 SSE 3.71 k/in 3.58 k/in 0.96 0.93 0.96 Alternate (taller) mounting clips aBE 17.7 ksi 12.41 ksi 0.62 0.70 0.70 SSE 28.4 ksi 16.61 ksi 0.56 0.58 0.58 Welds on alternate mounting clips aBE 2.37 k/in 1.77 k/in 0.74 0.75 0.75 SSE 3.18 k/in 2.56 k/in 0.80 0.76 0.80 CASE 1) Early Conditions - - peak temperature, low differential pressure (low debris)

CASE 2) Late Conditions - - peak differential pressure (max. debris), low temperature Page 52 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

RAJ #50 Item 3.k.3 of the revised content guide for the GL 2004-02 supplemental responses requests that the licensee "Summarize the evaluations performed for dynamic effects such as pipe whip, jet impingement, and missile impacts associated with high-energy line breaks (as applicable)." The STP initial and final supplemental responses state that no evaluations were performed with regards to the effects that high energy line breaks may have on the strainers. They also state that while the high head safety injection lines are within the vicinity of the strainers, there is no need to perform an evaluation on these lines since the lines are "used for accident mitigation and are not assumed to be the accident initiator." The NRC staff considers that this is not an adequate justification for exempting the lines from an evaluation. Please provide a more detailed synopsis of where the lines are located with respect to the replacement strainers, whether breaks are postulated on these lines in accordance with the licensing basis, or justify technically why no breaks need to be postulated (e.g., are there normally closed isolation valves or is the piping otherwise only pressurized during accident mitigation?).

Response to RAI #50 The high head safety injection lines are located directly above the emergency sump strainers.

The vertical separation is less than 5 ft. However, this piping is only pressurized during accident mitigation. Thus these lines are not considered for evaluation as a postulated location for a high energy line break accident.

Page 53 of 54 STP Draft Sump RAJ Responses Rev A 7-20-2010

1. Downstream effects/in-vessel RAI #51 The NRC staff does not consider in-vessel downstream effects to be fully addressed at STP as well as at other pressurized-water reactors. STP'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 safety evaluation (SE) for WCAP-16793-NP. The licensee may demonstrate that in-vessel downstream effects issues are resolved for STP 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 NRC staff SE that in-vessel downstream effects have been addressed at STP. 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.

Response to RAI #51 STPNOC will submit a report for this issue within 90 days of issuance of the final NRC Staff SE on WCAP-16793.

J. Chemical Effects RAI #52 The licensee performed integrated head loss testing in a flume by adding chemical precipitates after other non-chemical debris. The NRC staff questions the transport of the calcium phosphate precipitate during the test since the plant's trisodium phosphate basket location relative to the sump strainers varies and in some cases may be less than the distance from the precipitate introduction point to the strainer section in the test flume. The staff also questions if fibrous debris settlement within the narrow cross section of the test flume may create a pile of fiber that filters the calcium phosphate precipitate in a non-conservative manner since this precipitate settles more rapidly than the aluminum based precipitate. Given this concern, please justify why the head loss testing was appropriate in terms of calcium phosphate precipitate transport to the test strainer.

Response to RAI #52 Later Page 54 of 54 STP Draft Sump RAI Responses Rev A 7-20-2010

- 4 Status of Licensee's Draft Responses to RAls provided in Enclosure 2 RAI No.

48 The NRC staff stated that the licensee's response was acceptable, as written. The NRC staff stated that if the licensee substantially reduces its latent material quantity assumption, the cleaning method could be important in maintaining a valid licensing basis.

49 The NRC staff stated that the licensee's response was acceptable, as written (Enclosure 2).

50 The NRC staff stated that the licensee's response was acceptable, as written (Enclosure 2).

The licensee will consider its path forward regarding additional submittal timing, and plans to let the NRC staff know of its plans by November 1, 2010.

. The NRC staff suggested that the licensee reach an agreement with the staff on its RAI responses before retesting the sump model. Of the RAls discussed during this call, the licensee indicated that responses to RAls 15, 17, 21, 23, 27, 35, 38, 41, 42, 46, and 47 may be resubmitted in draft before being finalized, so that the NRC staff can verify that the responses are acceptable.

There were no members of the public present to comment. Also, no Public Meeting Feedback forms were received for this meeting.

Ifthere are any questions, please direct them to me at (301) 415-1476 or e-mail at mohan.thadani@ nrc.gov.

Sincerely, IRA by N.Kalyanam fori Mohan C. Thadani, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosures:

1. List of Attendees

2. Draft Partial Responses to NRC Request for Additional Information.

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