ML061020313

Generic Letter 2004-02 - Potential Impact of Debris Blockage on Emergency Recirculation During Design-Basis Accidents at Pressurized Water Reactors - Response to Request for Additional Information

ML061020313
Person / Time
Site:	Sequoyah
Issue date:	04/11/2006
From:	Pace P L Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-04-002, TAC MC4717, TAC MC4718
Download: ML061020313 (18)

Text

April 11, 2006

10 CFR 50.54(f)

U. S. Nuclear Regulatory Commission

ATTN: Document Control Desk

Washington, D.C. 20555-0001

Gentlemen: In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328

SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 - GENERIC LETTER 2004 POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY

RECIRCULATION DURING DESIGN-BASIS ACCIDENTS AT PRESSURIZED

WATER REACTORS - RESPONSE TO REQUEST FOR ADDITIONAL

INFORMATION (TAC NOS. MC4717 AND MC4718)

The purpose of this letter is to provide TVA responses to NRC's request for additional information (RAI) for SQN dated

February 10, 2006. The responses to this RAI supplements

TVA letters dated March 7, July 21, and September 1, 2005, concerning NRC's generic letter.

The enclosure provides the TVA responses for SQN. Please

direct questions concerning this issue to J. D. Smith at

(423) 843-6672.

I declare under penalty of perjury that the foregoing is

true and correct. Executed on this 11th day of April 2006.

Sincerely, Original signed by James D. Smith for:

P. L. Pace

Manager, Site Licensing and

Industry Affairs

Enclosure

cc: See Page 2 U.S. Nuclear Regulatory Commission Page 2 April 11, 2006

cc (Enclosure):

Mr. Edgar D. Hux

94 Ridgetree Lane

Marietta, Georgia 30068

Mr. Douglas V. Pickett, Senior Project Manager

U.S. Nuclear Regulatory Commission

Mail Stop 08G-9a

One White Flint North

11555 Rockville Pike

Rockville, Maryland 20852-2739

Mr. William T. Russell

400 Plantation Lane

Stevensville, Maryland 21666

E-1 ENCLOSURE SEQUOYAH NUCLEAR PLANT (SQN)

UNITS 1 AND 2 GENERIC LETTER 2004-02 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION

The following provides TVA's response to NRC's request for

additional information letter dated February 10, 2006 concerning

Generic Letter 2004-02.

Plant Materials

1. (Not applicable).

2. Identify the amounts (i.e., surface area) of the following materials that are:

(a) submerged in the containment pool following a loss-of-coolant accident (LOCA),

(b) in the containment spray zone following a LOCA:

- aluminum

- zinc (from galvanized steel and from inorganic zinc coatings) - copper

- carbon steel not coated

- uncoated concrete Compare the amounts of these materials in the submerged and

spray zones at your plant relative to the scaled amounts of

these materials used in the Nuclear Regulatory Commission (NRC) nuclear industry jointly-sponsored Integrated Chemical

Effects Tests (ICET) (e.g., 5x the amount of uncoated carbon

steel assumed for the ICETs).

TVA Response 2 The following quantities of materials are present in the SQN

containment

Aluminum - 887 ft 2 Submerged - 200 ft 2 Zinc - 957,893 ft 2 Submerged - 71,592 ft 2 Copper - 26,000 ft 2 Submerged - 26,000 ft 2 Carbon Steel - 373,120 ft 2 Submerged - 74,624 ft 2 Uncoated Concrete - 78,586 ft 2 Submerged - 7,859 ft 2

E-2 The ICET totals for aluminum and copper were 45 and 7.4 times the SQN amount respectively. SQN has 1.3 times the

zinc of the ICET tests. The ICET test used an exposed

concrete area of 12,630 ft 2 all submerged. The ICET value is 0.2 times the SQN value. The ICET value for carbon steel

is small compared to SQN. The actual surface area used for

scaling was not provided in the test plan, or the Test 1 or

5 test report. The surface to volume ratio at SQN is 60

times the ICET value although much of that number is above

the sump and not subject to containment spray. Examples of

this are all of the steam generator shells, the pressurizer, and the upper parts of the reactor vessel. These quantities

are representative of the entire containment, not just the

quantities either in the sump or subject to spray. As an

example, the zinc values include ice baskets and inorganic

zinc paint on the containment shell. Neither of these is in

the sump pool or subjected to containment spray.

3. Identify the amount (surface area) and material (e.g., aluminum) for any scaffolding stored in containment.

Indicate the amount, if any, that would be submerged in the

containment pool following a LOCA. Clarify if scaffolding

material was included in the response to Question 2.

TVA Response 3 There is a provision to store some scaffolding in containment that is either submerged in the sump or subject

to containment spray. The total light-metal inventory

associated with the stored scaffolding is approximately

615 ft 2 of zinc. This inventory is included in the total zinc inventory discussed in the response to Question 2.

All other scaffold type structures present in the lower

compartment are considered to be permanent plant features

and are also included in the response to Question 2.

4. Provide the type and amount of any metallic paints or non-stainless steel insulation jacketing (not included in the

response to Question 2) that would be either submerged or

subjected to containment spray.

TVA Response 4 There are no paints or non-stainless steel insulation

jackets not included in the response to Question 2.

Containment Pool Chemistry

5. Provide the expected containment pool pH during the emergency core cooling system (ECCS) recirculation mission

time following a LOCA at the beginning of the fuel cycle and

at the end of the fuel cycle. Identify any key assumptions.

E-3 TVA Response 5 The expected sump pH is between 8.0 and 8.4 for a LOCA at any time during the fuel cycle. The sump pH range includes

conditions for the beginning and end of core life, the

minimum and maximum quantities of boron and buffering agent

in the reactor coolant system (RCS), the accumulators, the

refueling water storage tank, and the ice condenser. The

range also includes the maximum and minimum water and ice

volumes. The temperature variation of the RWST and

accumulators was included in developing this range.

6. For the ICET environment that is the most similar to your plant conditions, compare the expected containment pool

conditions to the ICET conditions for the following items:

boron concentration, buffering agent concentration, and pH.

Identify any other significant differences between the ICET

environment and the expected plant-specific environment.

TVA Response 6 ICET 5 is the test most representative of the SQN

environment. The boron concentration in the test is 2800

parts per million (ppm) versus a plant concentration of 2500 to 2700 ppm.

The buffer is sodium tetraborate with a weight range of 11,070 to 13,284 pounds. The weight range is based on the amount of ice assumed to be in the ice condenser

(2,225,880 to 2,671,056 pounds). The test pH ranged from 8.0 to 8.5 and the plant pH (8.0 to 8.40) is essentially identical. The amount of aluminum is much higher in ICET 5

than is present in the plant. Since this is the predominant

precipitant, this is significant. The other significant

difference is that the ICET temperature is much higher than

the SQN post-LOCA temperature. ICET 5 showed concentrations

of dissolved aluminum of 55 milligrams per liter (mg/l) and

calcium of 35 mg/l. A correlation developed by Westinghouse

from separate effects precipitation test data (WCAP-16530)

showed a total of 9.6 mg/l for the precipitants at SQN based on the total weight of the precipitants. The precipitants

predicted by the Westinghouse correlations were composed

mainly of NaAlSi 3 O 8 with a small amount of AlOOH.

7. For a large-break LOCA (LBLOCA), provide the time until ECCS external recirculation initiation and the associated pool

temperature and pool volume. Provide estimated pool

temperature and pool volume 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after a LBLOCA.

Identify the assumptions used for these estimates.

E-4 TVA Response 7 The minimum time for the start of residual heat removal (RHR) recirculation from the sump is approximately

485 seconds or 8.1 minutes. This is the time assuming both

emergency core cooling system (ECCS) and containment spray

trains are running. The pool volume is 59,487 ft 3 with a temperature of 177.5 o F. The pool volume at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is 72,425 ft 3 with a pool temperature of 132.3 o F. The sump temperature is based on single train operation with the

maximum ultimate heat sink temperature and highest refueling

water storage tank temperature. The minimum refueling

water storage tank (RWST) injected volume was used.

Plant-Specific Chemical Effects

8. Discuss your overall strategy to evaluate potential chemical effects including demonstrating that, with chemical effects

considered, there is sufficient net positive suction head

margin available during the ECCS mission time. Provide an

estimated date with milestones for the completion of all

chemical effects evaluations.

TVA Response 8 TVA included concentrations of chemical precipitants in head

loss testing performed for the advanced design containment

sump strainers that significantly bound the concentrations present in the SQN post-LOCA sump inventory. For the

purpose of the test, TVA used quantities of aluminum oxides

and calcium carbonate corresponding to 90 mg/l. Both of

these materials are insoluble in water at the temperature of

the test loop. The advanced sump strainer design included a

10 percent (%) increase in required strainer area to accommodate anticipated chemical effects. The testing confirmed that the strainer area is sufficiently large that

a fiber bed cannot form. Chemical precipitants are not a

head loss contributor when there is not a fiber bed.

Further, the quantity of chemical precipitants is very small

compared to the total quantity of particulate debris

evaluated and tested based on the debris generation

calculations. Thus the head loss is not sensitive to the

quantity of chemical precipitants present. Based on these

considerations, the 10% increase in advanced design strainer

flow area to accommodate the chemical effects of the post-

LOCA sump recirculation inventory is considered to be

adequate. TVA has completed all actions associated with chemical effects evaluations accordingly.

E-5 9. Identify, if applicable, any plans to remove certain materials from the containment building and/or to make a

change from the existing chemicals that buffer containment

pool pH following a LOCA.

TVA Response 9 TVA already uses a buffer (sodium tetraborate) that is one of the alternative buffering materials being considered by

the industry. There is no need to remove any materials from

the containment to deal with chemical effects at SQN.

10. If bench-top testing is being used to inform plant specific head loss testing, indicate how the bench-top test

parameters (e.g., buffering agent concentrations, pH, materials, etc.) compare to your plant conditions. Describe

your plans for addressing uncertainties related to head loss

from chemical effects including, but not limited to, use of

chemical surrogates, scaling of sample size and test

durations. Discuss how it will be determined that

allowances made for chemical effects are conservative.

TVA Response 10 See the response to Question 8.

Plant Environment Specific

11. Provide a detailed description of any testing that has been or will be performed as part of a plant-specific chemical

effects assessment. Identify the vendor, if applicable, that will be performing the testing. Identify the

environment (e.g., borated water at pH 9, deionized water, tap water) and test temperature for any plant-specific head

loss or transport tests. Discuss how any differences

between these test environments and your plant containment

pool conditions could affect the behavior of chemical

surrogates. Discuss the criteria that will be used to

demonstrate that chemical surrogates produced for testing (e.g., head loss, flume) behave in a similar manner

physically and chemically as in the ICET environment and

plant containment pool environment.

TVA Response 11 TVA has not performed and does not anticipate performing

plant specific chemical effects tests. TVA has performed

plant specific head loss tests for the advanced design

containment sump strainer design. These tests were

performed by AREVA and did include consideration of chemical

precipitants in the recirculation inventory as discussed in E-6 the response to Question 8

. The test environment was a flume test using tap water at cold temperatures. The chemicals included in the test inventory were chemically

inert at the test temperatures and behaved similar to other particulate debris in the inventory

. Because no fiber bed can form on the SQN sump screen as the result of the amount of screen area available compared with the available fiber, chemical precipitants do not impact head loss in a manner

any different than other particulate debris.

As indicated in the response to Question 8, testing confirmed that the

advanced design strainer head loss is not sensitive to the

quantity of chemical precipitants present for the SQN post-

LOCA sump recirculation inventory.

12. For your plant-specific environment, provide the maximum projected head loss resulting from chemical effects (a)

within the first day following a LOCA, and (b) during the

entire ECCS recirculation mission time. If the response to

this question will be based on testing that is either

planned or in progress, provide an estimated date for

providing this information to the NRC.

TVA Response 12 The testing done for SQN did not provide a separate effect

evaluation of the head loss due to chemical effects. The

total head loss was minimal for all debris. Given the low

quantities of chemical precipitants and that no fiber bed is

present to act as a filter it is judged that the maximum

head loss due to chemical effects at the end of the first

day is zero. Similarly, the maximum head loss due to

chemical effects at any time during the 30 days following a

LOCA is judged to be zero.

ICET 1 and ICET 5 Plants

13. Results from the ICET #1 environment and the ICET #5 environment showed chemical products appeared to form as the

test solution cooled from the constant 140 o F test temperature. Discuss how these results are being considered

in your evaluation of chemical effects and downstream

effects. TVA Response 13 The quantities of materials used in the SQN tests were based

on the amounts of dissolved material present in ICET 5.

The ICET 5 test report did not provide quantities of

precipitants formed. Using data from the Westinghouse

Owner's Group (WOG) Chemical Effects Tests, a quantification

of the precipitants generated when the sump cooled to E-7 approximately 70 o F was made. The quantities of chemical precipitant surrogates used in the flume tests were 9 times

greater than would be seen in the plant. These quantities

then contributed to the head loss measured and in the

quantities of material that was carried through the strainer

and would impact a downstream effects evaluation.

Trisodium Phosphate Plants

14. (Not applicable).

15. (Not applicable).

Additional Chemical Effects Questions

16. (Not applicable).

17. (Not applicable).

18. (Not applicable).

19. (Not applicable).

20. (Not applicable).

21. (Not applicable).

22. (Not applicable).

23. (Not applicable).

24. (Not applicable).

Coatings Generic - All Plants

25. Describe how your coatings assessment was used to identify degraded qualified/acceptable coatings and determine the

amount of debris that will result from these coatings. This

should include how the assessment technique(s) demonstrates

that qualified/acceptable coatings remain in compliance with

plant licensing requirements for design basis accident (DBA)

performance. If current examination techniques cannot

demonstrate the coatings' ability to meet plant licensing

requirements for DBA performance, licensees should describe

an augmented testing and inspection program that provides

assurance that the qualified/acceptable coatings continue to

meet DBA performance requirements. Alternately, assume all

containment coatings fail and describe the potential for

this debris to transport to the sump.

E-8 TVA Response 25 TVA performed head loss testing assuming all coatings failed

whether qualified or not. The head loss from the strainer

for this test condition was similar to the head loss based

on a 10 diameter (D) ZOI for qualified coatings and is a

small fraction of the net positive suction head (NSPH)

available. Thus, no further assessment of the condition of

coatings in the plant is needed.

Plant Specific

26. (Not applicable).

27. (Not applicable).

28. (Not applicable).

29. (Not applicable).

30. The NRC staff's safety evaluation (SE) addresses two distinct scenarios for formation of a fiber bed on the sump

screen surface. For a thin bed case, the SE states that all

coatings debris should be treated as particulate and assumes

100% transport to the sump screen. For the case in which no

thin bed is formed, the staff's SE states that the coatings

debris should be sized based on plant-specific analyses for

debris generated from within the zone of influence (ZOI) and

from outside the ZOI, or that a default chip size equivalent

to the area of the sump screen openings should be used (Section 3.4.3.6). Describe how your coatings debris

characteristics are modeled to account for your plant-

specific fiber bed (i.e. thin bed or no thin bed). If your

analysis considers both a thin bed and a non-thin bed case, discuss the coatings debris characteristics assumed for each

case. If your analysis deviates from the coatings debris

characteristics described in the staff-approved methodology

above, provide justification to support your assumptions.

TVA Response 30 The SQN advanced design containment sump strainer has been

designed to preclude the formation of a fiber bed (thin or

thick) for post accident sump recirculation operation. To

confirm this design objective, a series of flow

transport/blockage tests were performed. The design basis

test case was performed with all failed coatings simulated

as 10 micron particles. This test was intended to maximize

small particulate transport to the sump screen and serve as E-9 a limiting case for thin bed blockage effects. Upon confirmation that the strainer design will preclude thin bed

formation, additional tests were performed to evaluate other

sump blockage mechanisms. These tests included 1) the

limiting failed coating size for maximum strainer blockage (i.e., the size of the failed coatings in this case were

approximately 1/8" square and 5 mils thick and were

considered small enough to maximize transport and large enough to maximize strainer blockage); 2) the maximum coating inventory (i.e., the coating quantities for phenolic

and inorganic zinc coatings were increased to reflect the

total amount of qualified and unqualified coatings inside

containment); and 3) the maximum latent debris inventory (i.e., the quantity of assumed latent dust and dirt was

increased by an order of magnitude to bound latent debris

effects). There was very little change in measured head

loss in all cases. The head loss difference between the

particulate cases and the chip cases was less than 0.05 feet. 31. Your submittal indicated that you had taken samples for latent debris in your containment, but did not provide any

details regarding the number, type, and location of samples.

Please provide these details.

TVA Response 31 A quantitative latent debris walkdown was performed at SQN.

This walkdown was an as found at the start of the refueling

outage. There had been no special containment cleaning.

The walkdown involved the collection of debris samples from

31 locations inside the reactor containment building

selected to provide a representative sample of the latent

debris preset in the containment building. The sample

collection area for each location varied in size from 1 ft 2 to 70 ft 2. The samples collected were analyzed for both quantity and type of debris. The latent debris from the

sampled areas was then projected for the entire containment

building based on the total amount of surfaces similar to

those surveyed.

The walkdown found small quantities of particulate debris such as rust, paint, and dust. The

quantity found would scale to a total containment quantity

of 24.5 pounds. Only a few latent fibers were found. The

latent particulate quantities are insignificant compared to

the paint debris. TVA used the NEI latent debris recommendation of 200 pounds total and 12.5 ft 3 of fiber to design and test the SQN advanced containment sump strainers.

This assumption is extremely conservative compared to the results of the SQN walkdown.

E-10 32. How will your containment cleanliness and foreign material exclusion (FME) programs assure that latent debris in

containment will be controlled and monitored to be

maintained below the amounts and characterization assumed in

the ECCS strainer design? In particular, what is planned

for areas/components that are normally inaccessible or not

normally cleaned (containment crane rails, cable trays, main

steam/feedwater piping, tops of steam generators, etc.)?

TVA Response 32 Procedures are in place to inspect and clean the

containment. These were the procedures in place when the

latent debris walkdown was performed. Given that the

quantities of material found were either insignificant (fibers) or overwhelmed by break generated debris (particulates), no special inspections are planned or can be

warranted given the extra dose to personnel and that there

is no safety benefit.

33. Will latent debris sampling become an ongoing program?

TVA Response 33 Latent debris sampling will not be an ongoing program. See

the response to Question 31 for more details.

34. Based on the low amount of fibrous debris from other sources, has the potential for the "thin bed effect" from

Latent fiber only been evaluated? If so, what were the

results? TVA Response 34 Yes. The strainer is sized such that a thin bed cannot

form. A latent fiber quantity of 12.5 ft 3 is too small to form a thin bed on a flat screen the size of the SQN

strainer much less for an advanced screen design.

35. You indicated that you would be evaluating downstream effects in accordance with WCAP-16406-P. The NRC is currently

involved in discussions with the WOG to address

questions/concerns regarding this WCAP on a generic basis, and some of these discussions may resolve issues related to

your particular station. The following issues have the

potential for generic resolution; however, if a generic

resolution cannot be obtained, plant-specific resolution

will be required. As such, formal RAIs will not be issued

on these topics at this time, but may be needed in the E-11 future. It is expected that your final evaluation response will specifically address those portions of the WCAP used, their applicability, and exceptions taken to the WCAP. For

your information, topics under ongoing discussion include:

a. Wear rates of pump-wetted materials and the effect of wear on component operation

b. Settling of debris in low flow areas downstream of the strainer or credit for filtering leading to a change in

fluid composition

c. Volume of debris injected into the reactor vessel and core region

d. Debris types and properties

e. Contribution of in-vessel velocity profile to the formation of a debris bed or clog

f. Fluid and metal component temperature impact

g. Gravitational and temperature gradients

h. Debris and boron precipitation effects

i. ECCS injection paths

j. Core bypass design features

k. Radiation and chemical considerations

l. Debris adhesion to solid surfaces

m. Thermodynamic properties of coolant TVA Response 35 No response is required at this time.

36. Your response to GL 2004-02 question (d) (viii) indicated that an active strainer design will not be used, but does

not mention any consideration of any other active approaches (i.e., backflushing). Was an active approach considered as

a potential strategy or backup for addressing any issues?

TVA Response 36 The SQN strainer showed a head loss of approximately 0.03

feet for a case where all coatings were assumed to fail and

all debris fell directly on the strainer. This compares to

an available NPSH of about 17 feet. No additional active

features were needed.

37. The NRC staff's SE discusses a "systematic approach" to the break selection process where an initial break location is

selected at a convenient location (such as the terminal end

of the piping) and break locations would be evaluated at 5-

foot intervals in order to evaluate all break locations.

For each break location, all phases of the accident scenario

are evaluated. It is not clear that you have applied such

an approach. Please discuss the limiting break locations

evaluated and how they were selected.

E-12 TVA Response 37 The inside diameters of the primary RCS pipes are 29 inches

for the hot legs, 27.5 inches for the cold legs, and 31

inches for the crossover legs. A break in one of the 31-

inch crossover legs would create the largest ZOI. However, depending on the exact location of various types of

insulation, a break in the smaller hot or cold legs could

result in the generation of a larger quantity of debris.

Therefore, to analyze this scenario, the worst case break

location and corresponding debris generation was considered

for all 4 loops. Iterations were performed which showed the

limiting break location to be the 31-inch crossover leg

pipe. Then, a 28.6D ZOI was used for all materials except

qualified coatings. A 26D zone of influence was used for

all materials except paint. A 10D zone of influence was

used for paint in the base case. Subsequently, TVA assumed

all coatings failed, thus the minimum zone of influence is

26D. The volume of the lower compartment is 280,000 ft

3. The volume of the sphere for a 26D zone is 1,690,000 ft

3. The limiting break was a crossover leg double ended rupture.

This pipe has an inside diameter of 31 inches. This

results in a sphere diameter of almost 68 feet. The

distance from the outside of the biological shield wall

around the reactor vessel to the crane wall is approximately

31 feet. Moving a break at 5-foot intervals along the pipe

does not result in a different ZOI. Thus, where the break

is located on the pipe has absolutely no impact on how much

debris is generated.

38. Were secondary side breaks (e.g., main steam, feedwater) considered in the break selection analyses? Would these

breaks rely on ECCS sump recirculation?

TVA Response 38 No secondary side breaks require sump recirculation for

mitigation. Thus, they did not need to be considered in the

evaluation.

39. The staff SE refers to Regulatory Guide 1.82 which lists considerations for determining the limiting break location (staff position 1.3.2.3). Please discuss how these

considerations were evaluated as part of the Sequoyah break

selection analyses.

TVA Response 39 TVA used the following criteria to determine limiting break

locations.

E-13 Break 1: Largest Potential for Debris Generation

The largest quantity of insulation in containment is located

in the RCS loops near each of the steam generators (SG) and

reactor coolant pumps (RCPs). Due to the size of the

primary RCS loop piping and the quantity of insulation in

close proximity to these pipes, a double-ended guillotine

break of one of the primary loop pipes presents the limiting

case for SBLOCAs and LBLOCAs at SQN. The inside diameters

of the primary RCS pipes are 29 inches for the hot legs, 27.5 inches for the cold legs, and 31 inches for the

crossover legs. Clearly, a break in one of the 31-inch

crossover legs would create the largest ZOI. However, depending on the exact location of various types of

insulation, a break in the smaller hot or cold legs could

result in the generation of a larger quantity of debris.

Therefore, to analyze this scenario, the worst case break

location and corresponding debris generation was considered

for all 4 loops.

Break 2: Two or More Types of Debris

All of the breaks discussed above encompass this break

scenario since reflective metallic insulation (RMI) and

coatings are the only debris present in the lower

compartment.

Break 3: Most Direct Path to the Sump

Given the sump location, all breaks in the lower compartment

proper have a direct path to the sump. Since the ECCS

recirculation sump is in close proximity to the RCS piping

in Loop 4, a break in this loop would have the most direct

path to the sump.

Break 4: Largest Particulate to Insulation Ratio

RMI, latent particles, and coatings are the only debris

present inside the crane wall in the lower compartment. RMI

does not transport as easily as particulates and is not a

major factor in developing head loss. The latent particulate

source is independent of break location. The limiting break

is the one that produces the most coatings debris. A

thorough analysis has shown that a break in each of the

crossover legs near the SG nozzle yields the most coating

debris. Small break LOCAs do not produce a large quantity

of debris.

E-14 Break 5: Potential Formation of the Thin-Bed Effect

SQN has no fibrous material in containment that is a

potential debris source for the sump. The sump strainer

area is large enough that there is not enough fiber in

containment to form a thin bed on a flat screen of this

size, much less an advances strainer design. As such, this

criteria does not affect the break selection process.

40. The licensee did not provide information on the details of the debris characteristics (debris size distribution)

assumptions other than to state that the Nuclear Energy

Institute (NEI) and SE methodologies were applied. Please

provide a description of the assumptions applied in these

evaluations and include a discussion of the technical

justification for deviations from the SE-approved

methodology.

TVA Response 40 TVA did not deviate from the SE-approved methodology.

Stainless steel RMI was assumed to fail as 75% small pieces

and 25% large pieces. Particulate debris was assumed to be

10 micron particles. No large particulate debris was

postulated. Coatings which were assumed to fail as "chips" were assumed to be 1/8 inch in diameter and 5 mils thick. The latent fiber debris was assumed to all be individual fibers.

41. Has debris settling upstream of the sump strainer (i.e., the near-field effect) been credited or will it be credited in

testing used to support the sizing or analytical design

basis of the proposed replacement strainers? In the case

that settling was credited for either of these purposes, estimate the fraction of debris that settled and describe

the analyses that were performed to correlate the scaled

flow conditions and any surrogate debris in the test flume

with the actual flow conditions and debris types in the

plant's containment pool.

TVA Response 41 No.

42. Are there any vents or other penetrations through the strainer control surfaces which connect the volume internal

to the strainer to the containment atmosphere above the

containment minimum water level? In this case, dependent

upon the containment pool height and strainer and sump

geometries, the presence of the vent line or penetration E-15 could prevent a water seal over the entire strainer surface from ever forming; or else this seal could be lost once the

head loss across the debris bed exceeds a certain criterion, such as the submergence depth of the vent line or

penetration. According to Appendix A to Regulatory Guide

1.82, Revision 3, without a water seal across the entire

strainer surface, the strainer should not be considered to

be "fully submerged." Therefore, if applicable, explain

what sump strainer failure criteria are being applied for

the "vented sump" scenario described above.

TVA Response 42 There are no vents between the sump and the containment

atmosphere when recirculation from the sump is initiated

after a design basis accident.

43. What is the minimum strainer submergence during the postulated LOCA? At the time that the re-circulation

starts, most of the strainer surface is expected to be

clean, and the strainer surface close to the pump suction

line may experience higher fluid flow than the rest of the

strainer. Has any analysis been done to evaluate the

possibility of vortex formation close to the pump suction

line and possible air ingestion into the ECCS pumps? In

addition, has any analysis or test been performed to

evaluate the possible accumulation of buoyant debris on top

of the strainer, which may cause the formation of an air

flow path directly through the strainer surface and reduce

the effectiveness of the strainer?

TVA Response 43 The minimum strainer submergence for the limiting LOCA is

9.06 feet at initiation of ECCS switchover to sump recirculation. This rapidly increases to 13.22 feet minimum pool height at containment spray (CS) switchover and remains

at this height for long-term operation in the recirculation mode. The potential for vortex formation at the SQN sump was extensively reviewed by the NRC as part of initial plant licensing. TVA performed a number of tests to support

initial plant licensing that conclusively demonstrated that

no vortex would form. Specifically, the sump design at SQN

showed no air drawing vortex with a pool level of 2.5 feet above the floor for ECCS operation and 5 feet above the

floor for CS operation.

No intermittent surface swirls from supports were demonstrated to exist with a pool level

greater than 8 feet. The water level in the lower

compartment was raised to 13 feet to provide a quiescent

pool surface even with flow rates several times the maximum

ECCS rate. Notwithstanding that, the center line of the E-16 cross over leg where it is close to the sump strainer is over 8 feet below the pool surface. There is no possible way for a break at this location to entrain air into the

sump.

The only potentially buoyant debris present in the sump pool

post-LOCA is the latent fiber. The top of the sump strainer

is over 5 feet below the pool surface and there is very limited fiber. It is physically impossible for these fibers

to form an air flow path to the sump.

44. The September 2005 GL response noted that the licensee analyzed the debris transport based on the methodology

described in the NEI guidance report "Pressurized Water

Reactor Sump Performance Evaluation Methodology," NEI 04-07, for refined analyses as supplemented by the NRC's safety

evaluation, as well as the refined methodologies suggested

by the SE in Appendices III, IV, and VI. Please identify

and justify if any exception to either the NEI 04-07 or SE

method was taken, or confirm that no exception was taken.

TVA Response 44 TVA did not calculate a thin bed head loss as the screens

were designed with sufficient surface area to preclude the

formation of a thin bed given the amount of fiber assumed in

the analysis. Walkdown data showed that there is not enough

fiber present to form a thin bed on the current screen.