ML11158A045

Responses to Requests for Additional Information Related to NRC Generic Letter 2004-02, Potential Impact of Debris Blockage During Design Basis Accidents at Pressurized-Water Reactors.

ML11158A045
Person / Time
Site:	Sequoyah
Issue date:	06/02/2011
From:	Krich R M Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-04-002
Download: ML11158A045 (26)

Text

Tennessee Valley Authority 1101 Market Street, LP 3R Chattanooga, Tennessee 37402-2801 R. M. Krich Vice President Nuclear Licensing June 2, 2011 10 CFR 50.54(f)ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Facility Operating License Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 50-328

Subject:

Responses to Requests for Additional Information Related to NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage During Design Basis Accidents at Pressurized-Water Reactors"

References:

1. NRC letter to TVA, "Sequoyah Nuclear Plant, Units 1 and 2 -Request for Additional Information Regarding Generic Letter 2004-002, 'Potential Impact of Debris Blockage During Design-Basis Accident at Pressurized Water Reactors' (TAC Nos. MC4717 and MC4718)," dated October 14, 2009 2. TVA letter to NRC, "Draft Responses to Requests for Additional Information Related to NRC Generic Letter 2004-02, 'Potential Impact of Debris Blockage During Design-Basis Accidents at Pressurized-Water Reactors,"'

dated June 3, 2010 In the Reference 1 letter, the NRC requested additional information regarding the containment emergency sump strainer testing conducted in early 2006 for the Sequoyah Nuclear Plant (SQN), Units 1 and 2. The Tennessee Valley Authority (TVA)provided draft responses to the NRC's Requests for Additional Information (RAIs) for SQN, Units 1 and 2 on June 3, 2010 (Reference

2) citing the plans for full scale testing to be conducted during the summer of 2010. In August 2010, full scale testing of the SQN, Units 1 and 2, containment sump strainers was completed.

printed on recycled paper U.S. Nuclear Regulatory Commission Page 2 June 2, 2011 The Enclosure to this letter provides the final responses to the NRC RAIs considering the results of that testing. Within the Enclosure are several Attachments.

Attachment 3 contains information that AREVA, NP considers to be proprietary in nature and subsequently, pursuant to 10 CFR 2.390, "Public inspection, exemptions, requests for withholding," paragraph (a)(4), TVA requests that such information be withheld from public disclosure.

Attachment 4 contains the affidavit from AREVA, NP supporting this request. Due to the extent of proprietary information in Attachment 3, a non-proprietary version of Attachment 3, with proprietary material removed, would not be usable and has not been provided.There are no commitments contained in this letter. If you have any questions, please contact Dan Green at 423-751-8423.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 2nd day of June, 2011.Respectfully, R. M. Krich

Enclosure:

Responses to Requests for Additional Information Related to Sequoyah Nuclear Plant, Units 1 and 2, Containment Emergency Sump Strainer Testing cc (Enclosure):

NRC Regional Administrator

-Region II NRC Senior Resident Inspector

-Sequoyah Nuclear Plant ENCLOSURE RESPONSES TO REQUESTS FOR ADDITIONAL INFORMATION RELATED TO SEQUOYAH NUCLEAR PLANT, UNITS I AND 2, CONTAINMENT EMERGENCY SUMP STRAINER TESTING E-1 Responses to Requests for Additional Information related to Sequoyah Nuclear Plant, Units 1 and 2, Containment Emergency Sump Strainer Testing The following Request for Additional Information (RAI) responses address those RAIs as sent by the NRC to the Tennessee Valley Authority in "Sequoyah Nuclear Plant, Units 1 and 2 -Request for Additional Information Regarding Generic Letter 2004-02, 'Potential Impact of Debris Blockage During Design-Basis Accidents at Pressurized-Water Reactors' (TAC Nos.MC4717 and MC4718)," dated October 14, 2009.Please note that the RAIs were primarily developed based on the Sequoyah Nuclear Plant (SQN) strainer performance head loss testing conducted in early 2006 and prior to the guidance provided in a letter from NRC to Nuclear Energy Institute, "Revised Guidance for Review of Final Licensee Responses to Generic Letter 2004-02, 'Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors,"'

dated March 28, 2008. Therefore, many of the NRC concerns associated with the small flume testing protocol are addressed by the full scale retest of the strainer head loss. The retest was performed at Alden Research Laboratory (Alden) during the week of August 2, 2010 using the test tank test facility.Head Loss and Vortexing RAI 1 The staff requested that the licensee provide the test protocol used for head loss testing and a justification that shows the aspects of the testing were conservative or prototypical.

The licensee's response did not fully address the issues as discussed below.RAI 1A The staff requested that the licensee provide information that justified that addition of debris to the test flume prior to the starting of the recirculation pump resulted in realistic or conservative test conditions.

In response to this RAI, the licensee described the test methodology in greater detail than in the original supplemental response.

The licensee stated that the debris (mixed with water) was added to the flume with the water level at about 6 inches. The debris was added 3 to 15 feet (ft) from the strainer, which was intended to minimize agglomeration and maximize transport.

Reflective metallic insulation (RMI) was added first in an attempt to prevent it from impeding transport of other debris. The flume was then filled using overhead nozzles intended to keep the debris mixture in suspension.

The debris was also manually stirred prior to starting the recirculation pump. The staff believes that these test methods resulted in nonconservative head loss for the same reasons documented in the Watts Bar Audit Report (ADAMS Accession No. ML062120469).

The licensee should provide additional information that shows that the head loss determined by the testing was prototypical or realistic or the licensee should retest using prototypical or conservative procedures.

E-2 Response The debris head loss testing discussed in prior TVA submittals was performed in December 2005 to support installation of the advanced design containment strainers in both Sequoyah units prior to December 2007. As this testing was performed prior to the NRC guidance for head loss testing published in March 2008, certain aspects of the original testing were not consistent with the test guidelines.

Based on the issues raised by the staff concerning the original "small flume" test protocol used in 2005, TVA conducted additional strainer head loss testing in 2010 using an alternate test protocol designed to provide conservative debris blockage results. The 2010 testing employed a "test tank" protocol which is outlined in Attachment

1. The "test tank" protocol contains a number of elements (see Attachment

2) which are designed to address the overall concerns with the "small flume" testing. With respect to the issue raised by RAI 1A, the "test tank" protocol included the following elements for the conservative introduction and suspension of debris.* The test tank was filled with water and maintained at a prototypical strainer submergence level for the duration of the test.* The tank was composed of two distinct sections leading to the test strainer module: an upstream high-energy mixing section and a middle debris suspension section. The upstream mixing section included high agitation and mixing. The middle suspension section included turbulence adequate to prevent settling without disturbing the formation of debris beds.* Turbulent energy and flow conditions were established in the upstream section by mechanical mixers which took suction near the top of the tank and discharged downwards toward the floor. Turbulent conditions in the mixing section were established by the upward injection of water jets from a perforated floor panel.* Debris was added to the tank through an injection hopper that discharged below the water line upstream of the mechanical mixers with the strainer operating at the design-basis flow rate.* Based on a separate transport test, RMI did not transport to the sump strainer.

RMI debris was conservatively not included in the debris mix in the test tank to eliminate potential for debris entrapment or creation of open spaces on the strainer.The test report (Attachment

3) contains additional details on the introduction and suspension of debris (as well as the other aspects of concern outlined in the following responses to RAIs 1 B through 1E).RAI 1B The staff requested that the licensee provide information that justified that the concentration of debris in the test flume did not result in excessive agglomeration and settling of debris during the head loss testing. The licensee stated that the heavier debris was added to the test flume prior to the lighter debris. This would result in less likelihood of the lighter debris being trapped by the heavier. In addition, the licensee conducted a test where all of the debris was added at or near the test strainer module. The staff considers these points are valid for the aspects stated except that stirring the debris could allow the larger debris to trap some of the smaller E-3 debris that was previously on top of it. Also, agglomeration of debris can occur with a single type of debris and may not depend on relative density.For example, the staff has observed agglomeration of apparently fine fibrous debris into clumps that behave as single large pieces rather than individual fibers. In this example, dumping an agglomerated mass of fiber onto the screen would not be expected to have the same effect on head loss as allowing the individual fibers to transport and collect on the strainer, as would be more likely in the plant. The staff believes that the test methodology used resulted in a nonconservative head loss because the debris preparation and addition practices, higher than prototypical debris concentration, lower than prototypical flume flow rates, and addition of debris prior to starting the recirculation pump have been observed in testing for other plants to contribute to non-prototypical agglomeration and settling of debris. The licensee should provide additional information that shows that the head loss determined by the testing was prototypical or realistic, or the licensee should retest using prototypical or conservative procedures.

Response With respect to the issue raised by RAI 1 B, the "test tank" protocol included the following elements for prevention of debris agglomeration and settling during the testing.* The test tank was filled with water to the design-basis water level and maintained during the duration of the test.* Fine fiber was shredded to achieve the same form of fines as discussed in NUREG/CR-6885, "Screen Penetration Test Report." The fine fibers were then sufficiently diluted such that no clumps were observed.* The debris was introduced into the test tank only after the start of the recirculation pump and the designed flow rate had been established.

Debris was sequenced with the most transportable debris introduced first followed by the next most transportable, and so on, until all debris was sequenced into the test tank.* Debris was mixed with heated water with a ratio of 5 parts water to 1 part debris to ensure the debris did not agglomerate.

• A trash pump was utilized to inject the debris into the test tank below the water surface to ensure there was no air entrainment during debris introduction.

RAI IC The staff requested information regarding the fibrous debris preparation and introduction with respect to prototypical sizing (transport and bed formation), including justification that the testing was performed prototypically or conservatively.

The licensee, in the response to RAI 1. C, stated that finely shredded NUKONTM was used as a surrogate for latent fiber. However, the term finely shredded has little quantitative information associated with it. During staff observations of testing (prior to 2008) at Alden labs, it was noted that the fibrous debris used in the testing was larger than considered prototypical. (The licensee's testing was performed at Alden Labs prior to December 31, 2007.) The staff considers fibers in size classes 1-3 as defined in section 3 of NUREG/CR-6808 to be adequate as a surrogate for fine fiber. Use of larger debris sizes would result in nonconservative test results. The licensee also stated that E-4 the fibers were mixed with water prior to introduction to the flume. The response does not provide an adequate description of the concentration of fibrous debris in the test nor compare it with what would be expected in the plant. The staff could not determine that the concentration of debris added to the flume was justified.

The licensee should show that the debris preparation and introduction methods resulted in a test head loss that was prototypical or conservative.

Response With respect to the issue raised by RAI 1 C, the "test tank" protocol included the following elements for the preparation of fibrous debris used for the testing.* All debris was prepared in accordance with Performance Contracting, Inc. Technical Document Number SFSS-TD-2007-004, "Sure-Flow Suction Strainer -Testing Debris Preparation and Surrogates."" Shredded Nukon fines were use for fiber debris simulation.

The fiber fines were shredded to achieve the form discussed in NUREG/CR-6885, "Screen Penetration Test Report."* The fine fibers were sufficiently mixed/diluted such that no clumps were visible prior to introduction into the test tank." Thin bed testing was conservatively performed with a fiber debris load sufficient to form a uniform thin bed on the surface of the strainer (which bounds the design basis fiber load).RAI 1D The staff requested information regarding the test flume velocity and turbulence.

The licensee provided the calculated flume velocity and flume turbulence.

However, these were not compared to the plant condition.

It was noted that the flume velocity is much lower (by factors of about 2 to 10 times) than velocities used by other plants that attempt to model the flow in the near field of the strainer.

In addition, the licensee confirmed that the Reynolds number (Re) for the flume was in the transitioning regime. Although it was not discussed in the response, the staff believes that the plant Re, due to significantly higher temperatures, larger hydraulic diameter, and higher flow velocities, is almost certainly in fully turbulent region, with an estimated Re likely more than one order of magnitude higher than the flume condition.

Thus, even setting aside the concerns on debris preparation, sequencing, etc., from strictly a flow perspective, it is almost certain that the transport of fine debris in the test flume underrepresented the plant condition.

Because adequate agitation to maintain debris suspended was not provided throughout the test and the flume velocity was likely nonconservative, it is probable that the head loss was affected nonconservatively.

The licensee should provide additional information that justifies that the test was conducted using prototypical or conservative procedures or should perform additional testing using prototypical or conservative procedures.

E-5 Response With respect to the issue raised by RAI 1 D, the "test tank" protocol included the following elements for conservative debris suspension during the testing." The tank was composed of two distinct sections leading to the test strainer module: an upstream high-energy mixing section and a middle debris suspension section. The upstream mixing section included high agitation and mixing. The middle suspension section included turbulence adequate to prevent settling without disturbing the formation of debris beds.* Turbulent energy and flow conditions were established in the upstream section by mechanical mixers which took suction near the top of the tank and discharged downwards toward the floor. Turbulent conditions in the mixing section were established by the upward injection of water jets from a perforated floor panel.* The change in protocol conservatively maintained debris in a suspended condition for transport.

RAI 1E The staff requested the licensee to quantify any near-field settling that occurred during the test.The licensee stated that test 6, which placed all debris on or in the immediate vicinity of the strainer, accounted for any near-field effects that could have altered the outcomes of the other tests. Because the head loss from test 6 was slightly higher than the other test head losses, it was selected as the limiting debris head loss. However, placing debris directly onto a strainer is not likely to result in a conservative or even realistic head loss. Based on staff observations of similar tests, tests 1-5 probably had considerable near-field settlement.

The licensee should provide additional information that justifies that the test was conducted using prototypical or conservative procedures, or should perform additional testing using prototypical or conservative procedures.

Response With respect to the issue raised by RAI 1 E, the "test tank" protocol included the following elements to conservatively eliminate near-field settling effects during the testing.* The tank was composed of two distinct sections leading to the test strainer module: an upstream high-energy mixing section and a middle debris suspension section. The upstream mixing section included high agitation and mixing. The middle suspension section included turbulence adequate to prevent settling without disturbing the formation of debris beds." Turbulent energy and flow conditions were established in the upstream section by mechanical mixers which took suction near the top of the tank and discharged downwards toward the floor. Turbulent conditions in the mixing section were established by the upward injection of water jets from a perforated floor panel.E-6

• The change in protocol conservatively maintained debris in a suspended condition for transport such that near-field settling did not occur.RAI 1F The staff requested that the licensee provide additional information regarding test scaling, including debris amounts and strainer flow velocity.

The licensee provided the scaling for flow and debris amounts. The scaling was based on the ratio of flow areas between the plant strainer and the test strainer.

This scaling factor was applied to both the flow rate and the debris quantities.

However, the scaling factor generally includes a term for the miscellaneous debris assumed in the design basis for the strainer.

Had the miscellaneous debris term of 850 ft 2 (multiplied by the 0. 75 factor) been included in the scaling, the flow rate and debris amounts would have been considerably higher. The licensee did adjust the scaling factor by subtracting about 70 ft 2 from the plant strainer area, but the adjustment should have been 637 ft 2 based on the licensee's calculated miscellaneous debris area. The licensee should justify the use of the lower area assigned to miscellaneous materials.

Response Scaling of the debris quantities and test flow rate(s) for the "tank test" protocol was performed based on the ratio of the surface area of the test strainer module to that of the as-installed plant strainer surface area. To ensure the scaling ratio was conservative, the as-installed strainer area was reduced by 200 ft 2 when the ratio was calculated.

Prior to the debris blockage testing, a separate transportability test was performed to evaluate that potential for miscellaneous debris transport to the sump strainers.

The transportability test was performed using a large flume arrangement to determine the minimum flow velocity at which transport occurs. Transport velocities from flume test were compared to the debris blockage flow velocities to determine need to include miscellaneous debris types in the "test tank" testing. The transport testing confirmed that the miscellaneous debris types do not transport for "test tank" velocities.

Based on these results, the scaling ratio was established as conservative.

RAI 1G The staff requested additional information on how partial submergence of the strainer affects the scaling of flow and debris amounts. The licensee stated that the test program was based on a large break loss-of-coolant accident (LOCA) that would result in a fully submerged strainer, and that scaling for a partially submerged strainer was not considered.

Because a small break LOCA would probably result in a lower debris load, this might be considered acceptable.

However, the critical debris component for this strainer is the latent fiber, which could be present for both large and small break LOCAs in an equal amount. Based on the response to RAI 3 (minimum pool submergence

= 9.06 ft), it appears that the design of the strainer did not account for the possibility of partial submergence.

However, the licensee did recognize that partial submergence was possible for a small break LOCA in its supplemental response, section 3.f. 2.The licensee should provide information that justifies that the strainer will perform adequately under partially submerged conditions considering the reduced strainer area available for debris deposition.

E-7 Response The NRC requested TVA provide additional information for SQN that demonstrates adequate sump performance during a small break loss-of-coolant accident (SBLOCA).

The NRC concern is that the tall sump strainers will be partially submerged when the ESF pumps begin to take suction from the sump. This condition could result in less water flowing through the strainers than is being drawn by the Engineered Safety Feature (ESF) pumps and cause a loss of Emergency Core Cooling System (ECCS) and/or Containment Spray (CS).Per the SQN ESF design, ECCS and CS pump suctions are initially aligned to the Refueling Water Storage Tank (RWST). ECCS pumps are aligned to the sump on RWST low level and the CS pumps are aligned to the sump on RWST Io-lo level. CS actuates on high-high containment pressure (2 psig). Containment Air Return Fans force the steam and hot air in the lower compartment through the ice condenser.

As a result, steam is condensed, hot air is cooled, and the ice melts. Containment design channels all water from CS and steam condensation ice melt back to the sump.For a SBLOCA, the break flow is small enough that the high head ECCS pumps maintain pressurizer level. ECCS pumps provide additional water to the Reactor Coolant System (RCS)to maintain a constant RCS water volume as the RCS cools. RCS pressure remains above the Cold Leg Accumulator (CLA) pressure.

This prevents CLA and Low Head Safety Injection (LHSI) injection.

A break could be located such that the liquid portion of break flow is contained inside the reactor cavity (does not fill sump). (This break location is not a design basis accident (DBA) location as it is not in the hot or cold leg pipe. In addition, this break would not generate debris that could be transported to the sump.) CS actuates for even the smallest breaks due to the buildup of steam and hot air in the lower compartment of containment.

The original SBLOCA sump level calculation for SQN used only a portion of the water available in the RWST between the RWST minimum full level and RWST low level. It assumes the reactor cavity is filled prior to RWST low level. This only occurs if CS does not actuate. It did not account for the contribution to sump water volume from steam condensing and ice melting.The revised SBLOCA sump level calculation more accurately determines the water available in the RWST between RWST minimum full and RWST low level. Adverse instrument errors are still included.

The additional water added to containment is 35,000 gallons.The revised SBLOCA sump level calculation accounts for the time dependent filling of the reactor cavity, based on the size of the SBLOCA. This change results in less water in the reactor cavity at RWST low level and more water in the sump. The calculation determines a lower bound on the amount of ice that would be melted by steam from the break. The amount of steam released from the break is based on saturated conditions at an RCS pressure of 600 psia, CLA pressure.

The released steam is assumed to condense on the ice and flow to the sump as saturated water at a containment pressure of 16.4 psia. This is the lowest containment pressure that containment spray would be in operation.

The melt water from the ice is also assumed to flow to the sump as saturated water at a containment pressure of 16.4 psia. This minimizes the amount of ice that is melted. The ice melt predicted by this method is low compared to better estimate modeling of the ice condenser by TVA's version of CONTEMPT.E-8 The revised SBLOCA sump level calculation explicitly evaluated the following breaks inside the reactor cavity:* 100 gpm -this is just above the size break that would be considered a LOCA (i.e., greater than normal makeup capability).

• 1200 gpm -this is a bounding flow rate for one-train of ECCS when RCS remains pressurized above the CLA pressure.* 2500 gpm -this is a bounding flow rate for 2-trains of ECCS when RCS remains pressurized above the CLA pressure.* Breaks larger than 2500 gpm cannot be maintained above the CLA injection pressure.CLA injection increases the water volume in containment.

From the revised SBLOCA sump level calculation it is determined that about 1.12 gallon of water flows to the sump for every gallon removed from the RWST. One CS pump in operation results in a higher sump level than two CS pumps in operation because of reduced holdup of RWST water in the refueling canal and more ice melt due to the longer time it takes to drain the RWST to low level.At the time the ECCS pumps align to the sump with two containment spray pump operating and the limiting 100 gpm break, the sump water level is 5.73 ft. This results in 4.36 ft of the strainers 6 ft possible wetted height being submerged.

Full submergence of the tall strainers occurs < 4.7 minutes after RWST low level due to continued operation of the CS pumps with their suctions aligned to the RWST. Due to low sump flow rate and short time period, no significant debris accumulation occurs prior to full submergence.

When CS pump suctions are aligned to the sump, the sump water level is 8.5 ft or 1 ft above the top of the tall strainers.

Given the reduced ECCS flow rates associated with the SBLOCA condition (i.e., no LHSI flow) this level provides greater strainer head margin than the comparable 9.06 ft minimum level for the large break LOCA scenario.Based on revised level calculation, strainers are fully submerged for long term SBLOCA sump recirculation.

RAI 4 The staff requested that the licensee provide a basis for the statement that a thin bed cannot form on the strainer, considering the design basis debris loading and strainer size. The licensee responded that, although slightly more than 1/8-inch of fiber is available for thin bed formation, under expected plant conditions, non-uniform accumulation would occur, leading to large portions of clean area. The licensee stated that this effect was observed during strainer testing.The staff did not consider the licensee's strainer testing to have been performed in a prototypical manner and, despite the addition of extra fiber, does not have confidence that a thin bed would not form on the plant strainers.

Strainers manufactured by Performance Contracting Incorporated are designed to encourage uniform debris bed accumulation, and testing performed at Alden Research Laboratory for U.S. pressurized water reactors using the revised protocol has indicated that uniform beds can be formed with relatively small quantities of fiber (precise amounts are unquantifiable due to settling).

Strainer testing for other plants has also E-9 shown that debris beds thinner than 1/8-inch can lead to significant head losses. This again leads the staff to conclude that the licensee has not demonstrated a thin bed of debris is precluded for the design basis debris loading. The licensee should provide additional information that justifies that the thin bed testing was conducted using prototypical or conservative procedures, or should perform additional testing using prototypical or conservative procedures.

Response As part of the "test tank" protocol previously discussed, a conservative thin bed test was conducted.

The test involved particulate, chemical and fiber debris with the fiber debris load conservatively increased above the design basis load to a volume sufficient for formation of a uniform fiber bed over the exposed surface area of the tested strainer.

During this test, debris was introduced in the following manner.* Particulate debris was added in three batches.* Fibrous debris was added in small batches with sufficient fiber to create a 1/1 6-inch fibrous thin bed for the first two fiber batch introductions.

A fixed time period between fiber batch introductions was established to allow the head loss across the strainer to stabilize.

• Chemical batches were introduced to the test tank after all particulate and fibrous debris was placed in the test tank.At the end of the testing, the strainer was observed to have particulate and fibrous debris fully covering the top cap and top plate of the strainer module. Other areas of the strainer were observed to have particulate debris partially covering them. A uniform thin bed did not form during the test.Attachment 3 contains additional details on the thin bed test.RAI5 The staff requested that the licensee provide an evaluation of the performance of the strainer under partially submerged conditions.

The licensee stated that, for a fully submerged strainer, vortex formation would be precluded due to the size of the perforations (0. 095 inches) on the surface of the strainer.

The RAI response further stated that for a partially submerged strainer operating at a flow rate of 12,900 gallons per minute (gpm), a minimum sump level of 4.18 ft is required to prevent drawing the core tube level down to the level of the flow channel that connects the strainers to the emergency core cooling system suction. The minimum sump level was stated to be 5.04 ft. The response to the RAI did not state further assumptions or inputs for this calculation.

It was not clear that the calculation considered whether a vortex could form within the core tube. The flow rate for the calculation was stated to be 12,900 gpm, but the design flow rate for the strainer is somewhat less than this so this input should be conservative.(Note that the response to RAI 6 states that the maximum flow rate is 18,750 gpm, but this appears to be an error. This should be verified to ensure that the evaluation was performed for limiting conditions.

It also appears that small break LOCA flow rates would be significantly lower based on the initial supplemental response.)

The RAI response also stated that E-10 numerous strainer qualification tests had been conducted for both fully and partially submerged strainers with acceptable results. However, these tests were not shown to be applicable or bounding for SQN. The strainer for the SQN test appeared to be very short (about three disks high), so it was not clear that a partially submerged test could have been conducted during the SQN testing. Further details of the calculations and testing performed for the partially submerged condition are needed. The licensee should provide information that justifies that the strainer will perform adequately under partially submerged conditions considering the reduced area for debris deposition on the strainer surface and other considerations contained in Regulatory Guide 1.82, Rev. 3.Response As discussed in detail in the response to RAI 1G, the original sump level calculation which established partial strainer submergence for small break LOCA conditions was reviewed and was determined to be overly conservative.

A revised small break LOCA sump level calculation was performed which removed some of the conservatism from the level calculation.

Specifically, the revised calculation credited 1) additional water inventory available from the RWST, 2) water inventory from ice condenser ice melt and 3) additional inventory based on reactor cavity fill characteristics.

The revised calculation established that the "short stack" strainers are fully submerged and the "tall stack" strainers are approximately 70 percent submerged at the time of ECCS swapover to the containment sump. Full submergence of the"tall stack" strainers occurs < 4.7 minutes later due to continued injection of the CS pumps from the RWST. At the time of CS pump alignment to the sump, the sump water level is 8.5 ft or 1 ft above the top of the "tall stack" strainers.

Based on revised level calculation, strainers are fully submerged for long term small break LOCA sump recirculation.

As such, flashing across the strainers under partial submergence conditions is precluded.

RAI 6 The staff requested that the licensee provide an evaluation that shows that flashing across or within the strainer will not occur. The response to this RAI addressed only the large break LOCA case where the minimum strainer submergence is 1.91 ft. A more limiting case could be the small break LOCA case with lower strainer submergence.

Flashing across a partially submerged strainer may be prevented due to equalization of the pressure both inside and outside of the strainer and also internal to the core tube during partial submergence.

However, once the strainer is fully submerged, head loss may result in flashing if the fluid is close to saturation.

It was noted that the maximum design post-LOCA pool temperature is 190'F. If atmospheric pressure is maintained within the containment, this may provide adequate subcooling such that flashing is prevented.

More realistically, the licensee could determine conservative margins to flashing by crediting the minimum predicted containment pressure and maximum sump temperature at various times throughout the event. The licensee should provide information that justifies that flashing will not occur for all postulated LOCA scenarios.

Response As discussed in detail in the response to RAI 1G, the original sump level calculation which established partial strainer submergence for SBLOCA conditions was reviewed and was determined to be overly conservative.

A revised SBLOCA sump level calculation was performed which removed some of the conservatism from the level calculation.

Specifically, the revised calculation credited 1) additional water inventory available from the RWST, 2) water inventory from ice condenser ice melt and 3) additional inventory based on reactor cavity fill E-11 characteristics.

The revised calculation established that the "short stack" strainers are fully submerged and the "tall stack" strainers are approximately 70 percent submerged at the time of ECCS swapover to the containment sump. Full submergence of the "tall stack" strainers occurs< 4.7 minutes later due to continued injection of the CS pumps from the RWST. At the time of CS pump alignment to the sump, the sump water level is 8.5 ft or 1 ft above the top of the "tall stack" strainers.

Given the reduced ECCS flow rates associated with the SBLOCA condition (i.e., no LHSI flow) this level provides greater strainer head margin than the comparable 9.06 ft minimum level for the large break LOCA scenario.

Based on the minimum calculated water levels (and the fact that minimum containment pressurization and sump inventory temperature reductions are conservatively ignored), flashing is precluded across the strainers.

Chemical Effects RAI 9 The February 2009 SQN supplemental response concludes that detailed chemical effects evaluations are not necessary due to the lack of a fiber bed on the strainer surface. The staff accepts that maintaining sufficient bare strainer area will mitigate potential chemical effects on the sump strainer.

Staff guidance provided in a March 28, 2008, letter (ADAMS Accession No.ML080380214) states, "Plants that plan to credit bare strainer area and perform a simplified chemical effect evaluation should demonstrate, for the maximum debris generation transport break that the screen design allows for chemical precipitates to pass unimpeded due to the excess available bare strainer area. For the purpose of this simplified analysis, strainer area with a very thin layer of debris that covers the strainer flow area is considered to be different from bare strainer area." However, the bare strainer argument is contingent on NRC staff agreeing that a filtering fiber bed will not form on the entire strainer surface and the staff has not agreed that a filtering bed will not form for SQN. Therefore, unless the NRC staff is able to accept the maintenance of sufficient bare strainer area through the RAI resolution process, please address chemical effects on an alternate basis.Response As discussed in the response to RAI 4, a conservative thin bed formation test was performed using the "test tank" protocol.

The test evaluated a "beyond design basis" fiber debris load of sufficient volume to determine if a uniform fiber bed would form on the strainer surface. The results of the thin bed test established that a thin bed did not form for the tested conditions.

Based on these results, a detailed chemical effects evaluation was not performed.

E-1 2 ATTACHMENT 1 TEST TANK PROTOCOL Al-1 TEST TANK PROTOCOL The following steps provide a general approach used with Sequoyah Nuclear Plant, Unit 1 and Unit 2, test tank strainer testing.1. VERIFY that the tank, strainer, piping, and test equipment have been set up in accordance with test set up procedure.

2. PREPARE the debris according to the following steps unless otherwise indicated by the Test Engineer.Note: The non-chemical debris has been prepared by Performance Consulting, Inc.(PCI) in accordance with PCI Technical Document No. SFSS-TD-2007-004,"Sure-Flow Suction Strainer -Testing Debris Preparation and Surrogates," and shipped to ALDEN. Changes to this document implemented in the test plan or test(s) shall be documented in the Test Plan with justification, as applicable.

3. WEIGH the non-chemical debris dry in accordance with the quantities specified in the debris allocation tables.4. ALLOCATE debris into equal amounts into multiple 5-gallon buckets filling each bucket with no more than 1/6 full of debris. This procedure applies to all fiber and particulate debris.5. COMBINE each batch of the non-chemical debris with water and store for introduction into the test tank in mixing containers.

The debris may be "mixed" with hot water (-1 20 0 F) to help remove trapped air from fibrous debris. Use the following steps to mix the debris: a. DILUTE the debris with hot water (-120 0 F) to an approximate ratio of 5 parts water to 1 part debris (by volume).b. MIX the debris and heated city water in mixing containers.

c. If needed, FURTHER dilute the debris to ensure there is no agglomeration.

6. PREPARE the chemical debris in accordance with chemical debris procedure.

7. FILL the test tank with city water and heat to -120°F unless specified by the Test Engineer to the target water level (typically the minimum water level for Emergency Core Cooling System recirculation or equivalent).

8. DOCUMENT the recirculation water level in the test tank of all tests and manually verify sump strainer submergence depth (if applicable).

Note 1: Strainer water level should be below the desired water level to allow for displacement due to diluted debris.A1-2 Note 2: If the water level is lowered, ensure that the temperature probe and thermal control switch remain submerged.

9. BEGIN performing downstream sampling.Document Sample Rate 10. START the test tank recirculation pump and maintain the minimum target flow rate.11. MEASURE and RECORD the pH of test tank water.12. OBSERVE the strainer area for vortexing.

13. OBSERVE tank mixing energy and confirm applicability to hinder near field settling.14. RECORD the following data at approximately 2 to 5 minute intervals.

NOTE that a computer data acquisition automatically records data at approximately 10 second intervals:

• Flow rate* Water temperature

• Differential pressure across the strainer module* Observations of vortexing at the surface of water near strainer (as specified by the Test Engineer)* Observations of bore hole formation (as specified by the Test Engineer)* Additional appropriate information

15. FILL test tank injection hopper with bypass water from the test loop.16. START debris addition trash pump at slow flow. Allow the pump to run for 5 minutes to equilibrate water level in tank.17. ADJUST trash pump drive frequency accordingly to maintain hopper water level approximately 1" above the tapered floor section and -12" below the overflow section.18. RE-MIX the debris with a paddle mixer, or a paint mixer connected to an electric drill (or equivalent).

Note: Additional dilution may be needed to prevent agglomeration.

19. INSERT all of the particulate debris into the pumping receptacle in the order prescribed in the debris allocation table.a. MAINTAIN the water level in the hopper by adjusting the trash pump drive frequency, or cycling the recirculation valve on/off. Water level should be approximately 1" above the tapered floor section and -12" below the overflow section.b. OBSERVE any floating debris on the water surface of the hopper. REMOVE floating debris using the following steps: i. SKIM water surface with a pool skimmer and place debris into a container.

A1-3 ii. DILUTE the debris with hot water (120 0 F) to an approximate ratio of 5 parts water to 1 part debris (by volume).iii. MIX the debris and heated city water in the mixing container.

iv. INSERT re-mixed debris into debris injection hopper.20. RINSE the bucket(s) with heated city water to ensure that all of the debris has been introduced into the test tank.21. INSERT the fibrous debris into the pumping receptacle in the order prescribed in the debris allocation table.Note: Repeat Steps 19a and 19b as required.22. DISASSEMBLE the trash pump to ensure all debris has been transferred to the test tank, if debris is present in the trash pump, perform the following steps: a. DOCUMENT and RINSE any trapped debris into a container.

b. DILUTE the debris with hot water (120'F) to an approximate ratio of 5 parts water to 1 part debris (by volume).c. MIX the debris and heated water in mixing containers.

d. INSERT diluted debris directly to the test tank.23. MAINTAIN the recirculation flow rate and MONITOR the head loss across the test strainer for at least 5 test tank turnovers after 100% of the non-chemical debris has been placed into the test tank.24. MEASURE and RECORD the pH of test tank water.25. OBSERVE the strainer area for vortexing and the formation of bore holes.26. Carefully/slowly INSERT the chemical debris through a debris introduction downcomer into the test tank unless otherwise specified by the Test Engineer.Note 1: For tests which require more than one chemical surrogate (i.e., Calcium Phosphate and Aluminum Oxyhydroxide), a minimum of one (1) test tank turnover should be allowed between introduction of each chemical precipitate into the test tank.Note 2: Be sure the water level is managed by the overflow system.Note 3: MEASURE and RECORD the pH of the test tank water when approximately 25%, 50%, 75%, and 100% of the chemical debris has been added.27. RINSE and FLUSH the chemical debris storage tanks and lines to ensure that 100% of the chemical debris has been introduced into the test tank.A1-4

28. MAINTAIN the recirculation flow rate and MONITOR the head loss across the test strainer for at least 15 test tank turnovers after rinsing and flushing the chemical debris storage tanks and lines.29. RUN the test until the change in head loss is less than 1% in 30 minutes unless directed otherwise by the Test Engineer.

The Test Engineer has the discretion to continue the test, if experimental observation necessitates.

30. After the termination criteria are met, REDUCE the flow to the Small Break LOCA flow.Note: Multiple flow rates may be evaluated as determined by the Test Engineer.31. MAINTAIN the recirculation flow rate and MONITOR the head loss across the test strainer for at least one (1) test tank turnover.

Note that the head loss should decrease.If the head loss fluctuates and does not stabilize, bore holes may have formed through the debris bed.32. OBSERVE the area above the strainer for vortexing.

RECORD head loss observations.

33. SLOWLY decrease the test tank water level enough to expose the top core tube plate.Note: A reduction in water level may not be performed as determined by the Test Engineer.34. MAINTAIN the recirculation flow rate and MONITOR the area above the strainer for vortexing.

MONITOR the head loss across the test strainer for at least 5 test tank turnovers and until the change in head loss is less than 1% in 30 minutes unless otherwise directed by the Test Engineer.35. OBSERVE the area above the strainer for vortexing.

36. TERMINATE the test once all observations of the head loss are deemed acceptable unless directed otherwise by the Test Engineer.Al-5 ATTACHMENT 2 TEST TANK PROTOCOL DESIGN FEATURES A2-1 TEST TANK PROTOCOL DESIGN FEATURES 1. Approach Velocity USNRC Position: Justify that the weighted average approach velocity calculation is conservative.

TVA Approach: The "test tank" protocol does not rely on a weighted average approach velocity to simulate actual plant approach velocities.

The protocol has been designed to establish turbulent conditions which conservatively keep debris suspended during testing for maximum transportability and to preclude near-field settling.

Turbulent test conditions eliminate the need for modeling of strainer approach velocities to establish localized fluid conditions.

2. Flume Turbulence USNRC Position: Justify the test flume turbulence levels are bounding of plant containment turbulence levels.TVA Approach: The "test tank" turbulence does not simulate the containment turbulence.

The test protocol has been designed instead to ensure sufficient turbulence to keep debris in suspension to maximize debris transport.

3. Alternate Break Location to Bound Approach Velocity USNRC Position: Justify that the break associated with the maximum debris load is more conservative than an alternate break location in terms of debris transport characteristics and bounding flume velocities.

TVA Approach: The "test tank" protocol is designed to maintain maximum debris suspension through the establishment of turbulent fluid conditions.

The debris suspension capabilities of the protocol bound all variations in actual plant conditions resulting from changes in assumed break location.

Limiting debris blockage head losses will result from testing of the maximum debris load using the test tank protocol.A2-2

4. Effects of Sources of Water Draining Into Recirculation Pool From Above USNRC Position: Demonstrate that there are no sources of water falling from above that could introduce additional turbulence in the approach flow stream used to define the test flume configuration or show that they are conservatively represented in the test flume configuration/operation.

TVA Approach: The "test tank" does not simulate the strainer approach velocities or turbulence.

It is conservatively designed to keep the debris suspended for the duration of the test without disturbing the debris bed that forms on the test strainer.

The need to model external turbulence in the flow stream is obviated by the turbulent test conditions.

5. Fiber Erosion in Test Flume USNRC Position: Debris introduced as transportable in the test flume and found to settle would erode over the mission time of the post-Loss of Coolant Accident response.Therefore some accounting of the erosion of flume settled debris must be made.TVA Approach: The "test tank" protocol precludes debris settling within the test tank. Turbulence in the test tank maintains debris suspension for transport to the strainer such that erosion of flume settled debris will not occur.6. Debris Concentration on Introduction USNRC Position: The concentration of debris upon introduction is important to eliminate non-prototypical agglomeration in the introduction vessel.TVA Approach: The debris was mixed with water with a minimum dilution of 5 parts water to 1 part debris constituent.

The debris was introduced to the test tank via a trash pump and discharge pipe to ensure the debris is mixed as it enters the tank. The discharge pipe was below the surface of the test tank water to ensure air is not entrained in the debris mixture as it enters the tank.The debris dilution rates conservatively followed the March 2008 NRC test guidance.

Debris introduction was documented in the report along with photos and/or videos taken during the test to validate no significant agglomeration of debris occurred prior to introduction.

A2-3 ATTACHMENT 4 AREVA AFFIDAVIT Attached is the affidavit supporting the request to withhold proprietary information (included in Attachment

3) from public disclosure.

A4-1 AFFIDAVIT COMMONWEALTH OF VIRGINIA )) SS.CITY OF LYNCHBURG

)1. My name is Gayle F. Elliott. I am Manager, Product Licensing, for AREVA NP Inc. (AREVA NP) and as such I am authorized to execute this Affidavit.

2. I am familiar with the criteria applied by AREVA NP to determine whether certain AREVA NP information is proprietary.

I am familiar with the policies established by AREVA NP to ensure the proper application of these criteria.3. I am familiar with the AREVA NP information contained in 66-9144025-000,"Watts Bar Unit I ECCS Strainer Performance Test Report," and 66-9144028-000, "Sequoyah Unit I and Unit 2 ECCS Strainer Performance Test Report," and referred to herein as"Documents." Information contained in these Documents has been classified by AREVA NP as proprietary in accordance with the policies established by AREVA NP for the control and protection of proprietary and confidential information.

4. These Documents contain information of a proprietary and confidential nature and is of the type customarily held in confidence by AREVA NP and not made available to the public. Based on my experience, I am aware that other companies regard information of the kind contained in these Documents as proprietary and confidential.

5. These Documents have been made available to the U.S. Nuclear Regulatory Commission in confidence with the request that the information contained in these Documents be withheld from public disclosure.

The request for withholding of proprietary information is made in accordance with 10 CFR 2.390. The information for which withholding from disclosure is requested qualifies under 10 CFR 2.390(a)(4) "Trade secrets and commercial or financial information." 6. The following criteria are customarily applied by AREVA NP to determine whether information should be classified as proprietary: (a) The information reveals details of AREVA NP's research and development plans and programs or their results.(b) Use of the information by a competitor would permit the competitor to significantly reduce its expenditures, in time or resources, to design, produce, or market a similar product or service.(c) The information includes test data or analytical techniques concerning a process, methodology, or component, the application of which results in a competitive advantage for AREVA NP.(d) The information reveals certain distinguishing aspects of a process, methodology, or component, the exclusive use of which provides a competitive advantage for AREVA NP in product optimization or marketability.(e) The information is vital to a competitive advantage held by AREVA NP, would be helpful to competitors to AREVA NP, and would likely cause substantial harm to the competitive position of AREVA NP.The information in these Documents is considered proprietary for the reasons set forth in paragraphs 6(b) and 6(c) above.7. In accordance with AREVA NP's policies governing the protection and control of information, proprietary information contained in these Documents have been made available, on a limited basis, to others outside AREVA NP only as required and under suitable agreement providing for nondisclosure and limited use of the information.

8. AREVA NP policy requires that proprietary information be kept in a secured file or area and distributed on a need-to-know basis.

9. The foregoing statements are true and correct to the best of my knowledge, information, and belief.SUBSCRIBED before me this ?A__._day of J fXL 2011.Sherry L. McFaden NOTARY PUBLIC, COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES: 10131/14 Reg. # 7079129 SHERRY L. MOFAIDEN Notary. Public -Commonwealth.of Virginia-- ~7079129[My Commission Expires Oct 31. 204