ML091200364

License Handouts Provided During Category 1 Meeting with the Donald C. Cook Nuclear Plant to Discuss Draft Request for Additional Information Associated with GL 2004-02

ML091200364
Person / Time
Site:	Cook
Issue date:	08/26/2009
From:	Plant Licensing Branch III
To:
beltz T, NRR/DORL/LPL3-1, 301-415-3049
Shared Package
ML091200377	List: ML091200364
References
GL-04-002, TAC MC4679, TAC MC4680
Download: ML091200364 (58)

Text

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DRAFT Margins and Conservatisms Evaluation 1

Introduction The purpose of this evaluation is to demonstrate how the Cook Nuclear Plant ECCS is conservatively designed and operated with respect to the requirements of 10 CFR 50.46 following completion of the corrective actions associated with the resolution of GL 2004-02 (GSI-191).

2 Design Basis Event Scenarios 2.1 q-Iie CNP iceflcondenser containment consists of four uniquely defined and s~p'-~rated vol~'m~s: 1) upper containment, 2) ice condenser, 3)*lower containment,

~

I and f4) reg,qtorJcavity. Refer to the February 29, 2008 Supplemental Response, Attachm~~t.4, Figures A4-2 through A4-10 for illustrations of various views of lower containment and a plan view of upper containment.

The upper containment area (Figure A4-2), which does not contain any high energy piping, is physically separated from the lower compartment by the divider barrier and the ice condenser, The ice condenser forms an approximate 300 0 arc around containment between the containment wall and the crane wall. The ice condenser has 24 paired doors in the lower containment area that will open following a pipe break allowing for

- 1

suppression of the initial pressure surge in containment. There are also doors just above the ice bed and at the top of the ice condenser section to allow steam and non-condensable gases to vent to the upper containment volume.

The lower containment volume contains both the loop compartment inside the crane wall and the annulus area between the crane wall and the containment wall.

The crane wall that separates these two regions is three feet thick. There are ventilation openings in the crane wall which are above the maximum flood elevation of containment. These ventilation openings provide for the supply of cooled air to the loop compartment from the contain~nt lower ventilation units, and also provide a relief path for the mass and energy, release from a HELB for short term containment subcompartment pressurization considerations. Within the loop compartment above nominal elevation<~8~ft'\\. are the SG and PZR enclosures. These enclosures utilize the crarf~wall as o~ part of the enclosure with cylindrical concrete walls forming t~~St of the e~~sures. Each of these enclosures has a concrete roof, the tO~Of.~hiCh is at norTi~al elevation 695 ft.

The cylindrical wall sections and tilert.

~CUi. divider barrier of?Comprise a portion separating the lower containmen rom the ~er containmept.'\\. The loop compartment is surrounded on is,outside A~f}t e r by the c~>wall.

The primary shield wall and refueling cav&V-walls an on the inside perimeter of the loop compartment. The nominal distanM~e primary shield wall to the crane wall varies from 22 to ~~.... The nominaLcistance from the crane wall to the containment wall is 13 ft.

All pO:

break LOCAs for which sump recirculation would be required

~JafeCf Ypipe would ta ~lace within the loop compartment, which is the area inside the crane wall, or in the reactor cavity. For an LBLOCA, once water level in the loop compartment exceeds approximately 4 in. during the injection phase, debris laden water would begin to flow through the main strainer into the recirculation sump.

When the level in the recirculation sump reaches slightly above floor level (598 ft 9 3/8 in. elevation), strained water from the recirculation sump would begin to flow through the waterway toward the remote strainer. Initially, this would only fill the waterway until the water level reaches approximately 8 1/2 in. above the floor, the height of the lowest set of strainer elements in the remote strainer. When the loop compartment water level exceeds this height, strained water would begin

- 2

back-flowing out of the remote strainer. A significant quantity of debris laden fluid would be transported to the main strainer, partially loading it with debris. During this pool fill (injection) phase, the calculated maximum reverse flow rate is approximately 6400 gpm.

Debris laden water would also flow from inside the loop compartment to the debris interceptor installed to protect the 10 in. diameter flow holes through the overflow wall. This flow into the area between the overflow wall and the curb at the annulus side of the crane wall opening would continue until the level reached approximately 12 in. above the floor. This is the height~f.the curb on the annulus side of the overflow wall area. By the time this lev~~1'achedJ water flow out of the remote strainer would have been established.

I (approximately 18 to 20 minutes after the With recirculation flow established, the reverse flow through the remote strainer will cease. Water will then flow into the sump through both the main strainer and through the remote strainer and waterway.

Since a pipe break requiring recirculation would not occur in the annulus, the debris that would be available to the remote strainer would be the debris that was transported from the loop compartment to the annulus region from the initial blowdown, the debris that was transported to the annulus region through the overflow wall flow holes during pool fill, and latent debris resident in the annulus prior to the event. As a result, the

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remote strainer would be essentially debris free at the beginning of recirculation.

Due to the waterway head loss, the preferential flow path would be through the main strainer until the main strainer became substantially blocked by debris. The division of flow between the main and remote strainers would therefore be a function of the head loss through the associated strainer and the waterway.

For the DEGB, water level in lower containment would decrease from the level that existed at the beginning of recirculation flow (7.7 ft) until the minimum water level of 5.9 ft above the floor (604 ft 7 in.) is reached. For the DGBS, a minimum water level of approximately 5.6 ft above the floor (6~~4! ~9 in.) is reached. These decreases in water level are the result of a conserva Ivery assumed minimum ice melt and the flow into the lower reactor ca~via the ex-core nuclear instrumentation position device sleeves in th~~af9~hield wall. For the 2 in.

line break, a minimum water level of approxim.e!.my 5.1((if!l2ove the floor (603 ft 11 in.) is reached.

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DRAFT Figure 1 General Arrangement of Recirculation Sump Vent 000

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3 Debris Generation I Zone of Influence 3.1 Methodology

a. The insulation debris sources were determined through extensive walkdowns to be different between CNP Unit 1 and Unit 2. The insulation debris sources for Unit 2 were determined to be bounding for both units and were used as the input for analysis and testing. The total quantity of Cal-Sil insulation in Unit 2 that could be subjected to a LOCA jet is about 60%~greater than that in Unit 1.

3.2 Key Conservatisms I Margins

b.

Latent Debris 4.1 Methodology

a. The quantity of latent debris to be considered for contributing to strainer head loss was conservatively established at 200 Ibs in containment, with 15%

assumed to be fibrous.

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b. The contribution of latent debris on vertical surfaces was conservatively assumed to be 30 Ibs.

c. 104 latent debris samples were taken in Unit 1 during separate outages and 80 samples were taken in Unit 2 during separate outages. The samples were all taken in areas that are not routinely cleaned as part of containment closeout activities or had some accumulation of oily residue (below RCPs, on polar crane rails).

4.2 Key Conservatisms I Margins

a. The calculated quantity of latent debris wasA eterrnined to be 161.72 Ibs for Unit 1 and 117.26 Ibs for Unit 2. This represen~~rgin of 38.28 Ibs for Unit 1 and 82.74 Ibs for Unit 2. The assum~c{Ua Mfity,<.of 200 Ibs represents a 5

5.1 23.7% increase for Unit 1 and a 70.6%Jncrease for lJiiit'2..

b.

c.

a.

Th~~istransport methodology utilized as-built containment information to modelJlow paths and significant obstructions to flow within lower containment.

b.

The debris transport methodology modeled the main and remote strainers and determined the flow split between the two strainers as a function of head loss through the system. The methodology also modeled the flow path through the flood-up overflow wall holes and the surrounding structural features.

c.

Additional information regarding the debris transport methodology is contained within the February 29, 2008 and August 29, 2008 Supplemental Responses to GL 2004-02.

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5.2 Key Conservatisms I Margins

a. Debris in the sump pool would not transport to the reactor cavity, an inactive volume, while it was filling through the nuclear instrumentation detector positioning device penetrations.

b. The debris transport methodology established transport fractions that resulted in greater than 100% of the debris source available for transport to the strainers. These were the values that were used fgrtStJainer head loss testing.

The materials and quantities are provided below.

Debris Source

c.

d.

e.

g.

The debris transport analysis conservatively did not consider the debris interceptor installed at the flood-up overflow wall flow openings as a debris limiting device for those fines and other debris sources that would be capable of being transported to the remote strainer. In other words, no credit was taken for the filtering capability of the debris interceptor (01) and the RMI bed that would exist at the DI.

h.

The debris transport analysis conservatively modeled the vertical face of the DI as being fully blocked during recirculation transport. The effect of this was to

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6 maxrrmze the velocity of the pool water passing through the design 6 inch opening at the top of the 01 increasing the transportability of the debris sources in the pool.

i.

The debris transport analysis conservatively maximized the effects of water sources entering the containment pool to increase the turbulence of the pool which led to greater transport fractions for the debris sources.

j.

The debris transport analysis conservatively neglected the capture of fibrous and particulate debris by the significant quantity of cQl!lponents that exist in the annulus including the debris.gates that exist oll.G1th"er side of the approach 6.1 area to the remote strainer.

k.

a.

I o"'aetermme tnemuanntv of un'tJlta.lified coatings in containment, two separate The second was to perform more extensive walkdowns of containment to catalog the unqualified coatings that exist in containment. This effort completed following the strainer testing that was performed.

b. For qualified coatings that would be subjected to a LOCA jet, an extensive CAD model of containment was developed that included the structural elements that exist. The debris generation analysis overlaid the ZOI sphere

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onto the model which then calculated the affected areas of concrete and steel surfaces.

c. All OEM unqualified coatings outside of the coatings ZOI were assumed to fail initially as paint chips with a thickness equivalent to the original coating thickness. The EPRI report for OEM coating failures documented autoclave DBA tests of non-irradiated and irradiated unqualified OEM coatings that demonstrated that the majority of the failures were as chips.

The debris generation analysis assumed that OEM coatings failed as 83 micron particles.

6.2 Key Conservatisms I Margins

a.

d. The non-OEM unqualified coatings outside the ZOI have the same failure rate as the OEM coatings outside the ZOI (100%). Since the non-OEM unqualified coatings are not applied to a correctly prepared substrate, it is expected that these coatings would fail as chips of various sizes. Therefore, the non-OEM unqualified epoxy and alkyd coatings outside the ZOI were assumed to fail with chip sizes of 10% (250 - 500 microns), 80% (500 - 1000 microns), and 10%

(1000 - 4000 microns). Autoclave testing (Keeler & Long Report 06-0413, DBA Testing of Coatings Samples for Comanche Peak) indicates that paint

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chips would be generated in sizes larger than 4000 microns which shows that the distribution used in this calculation is conservative.

e.

The cold galvanizing coating used at CNP is an organic zinc material. For determination of debris transport and ultimately strainer head loss testing, the cold galvanizing compound was conservatively assumed to fail as 10 micron particles.

f.

The conservatively calculated unqualified coatings quantities within containment are as follows:

g.

h.

In su~~ry~ t~e ccr~ervat~vely detemiinedquan.tities of unqual!fiedc?ati~gs. th~~ were assumed 'tofvji~Be available for transport at time zero of recirculation IS SignifIcantly greater tha1i,tfi~l guantities that exist. This represents a significant conservatism in that the increase~qtantity of particulate increases strainer head loss and increases the potential for wear and blockage of downstream components. Additional conservatism exists through the use of a ZOI of 5D for qualified coatings in lieu of the 4D recommended by the test report, and the assumption that unqualified coatings will principally fail as small particulate.

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7 Head Loss and Vortexing 7.1 Methodology

a. Head loss testing was performed by the strainer vendor, CCI, at their facilities in Winterthur, Switzerland. All testing was witnessed by a CNP representative.

b. Due to the unique installed strainer configuration for CNP, the debris only strainer head loss testing was performed using a dual sided strainer assembly with the test pool configured to provide equivale~tll:face areas for the main and remote strainer and locations to introduce t l].~a..I?iJopriate debris quantities to each strainer section.

c.

d. Since the strainer head los connects the remote strainer t~m performed to establish an overall configuration.

e.

f.

g.

d to ensure that air would not be drawn into One of the; ' ~ignificant margins established during strainer head loss testing

.was the i!JClu!ion of a 50% increase in strainer system head loss to address u ~certajnties l that could exist as

• a result of debris distribution, test

~t~odofcMy, or other factors.

b.

Margin is also available in the strainer system head loss values as a result of normalizing the results to 68°F (20°C). The margin exists in that at the initiation of recirculation, the containment pool water temperature is at a maximum of 190°F with temperature ultimately decreasing to approximately 100°F. With containment pool temperature at 100°F, the strainer system head loss would be about 30% less than it would be at the normalized value of 68°F.

c.

Significant margin is also available as a result of the conservative total debris quantities that were used for testing as compared to the quantities that would

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be available for transport to the strainers. Considering the margins discussed in Sections 3, 4, 5, and 6 of this evaluation, the expected head loss through the strainer system would be significantly reduced due to the reduction in fibrous and particulate debris that would be at the strainers. The table below provides a comparison of the as-tested values (conservative) and the as-expected (realistic) values for debris quantities.

DEGB Debris Type Units I Test Margin Quantity 0.002 7.41582 13.125 7.33

.057 0.0456 0.0273 0.026 0.000236 0.00022 0.0021 0.002 13.2116 7.40382 A5"~n~PF§een from the i~formatj~~ in the preceding table, the~e is significant marg ~Detween the debris quantities that were used for strainer head loss testing and the actual quantity of debris in containment that would be expected to be available to the strainers during an actual LOCA event. This margin could be further increased by considering the relative absence of fibers within the latent debris inside containment, as discussed in Section 4 of this evaluation.

d. As discussed in Section 8 of this evaluation, the flow rate assumed for testing was approximately 1000 gpm greater than the conservatively determined maximum flow rates for both trains of ECCS and CTS taking suction from the

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8 recirculation sump. This 7% reduction in flow represents an approximate 20%

reduction in head loss across the strainer.

e. The strainer system head loss analysis conservatively assumed the water level in containment was at its minimum water level at the time of maximum head loss. For the bounding DEGB case, the containment water level at the time of maximum head loss (16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br />) would be approximately 6.1 ft. This provides an additional allowable head loss of 0.1 ft. For the bounding DGBS case, the containment water level at the time of maximum head loss (23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />) would be approximately 6 ft. This provides an additional ~allowable head loss of approximately 0.18 ft.

f.

g.

NPSH 8.1 Methodology

a. In the 1998 to 1999 time frame, CNP performed a complete reanalysis of containment water level. The analysis performed considered all parameters that would minimize the quantity of water available in the containment pool, including those that would minimize ice melt and minimize displacement.

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8.2 Key Conservatisms I Margins

a. The containment minimum water level analysis did not consider the increase in water level that would occur if the equipment that occupies the lower containment volume was considered. This would increase the water level at the initiation of recirculation and during recirculation by at least 2.2 in.

b. For the small break analysis, the assumed maximum RCS cooldown rate of 100°F/hr was used. This minimized the energy discharged into containment

c.

thus decreasing ice melt.

d.

The lake water temperature was ass(J"'mec to be 33°F, increasing the cooling of CTS during recirculation, increaS~Qtitr effectiveness at r~-¥ing energy from the containment atmosphere. r.~~Jting in reduced ice melt.

e.

f.

g.

k.

The....1Jow rate assumed for recirculation flow was approximately 1000 gpm greater than the conservatively modeled maximum flow rate for two train ECCS and CTS operation.

This represents an approximate 7% reduction in flow through the strainer system.

I.

For the SBLOCA, conservative values were established for the quantity of water remaining within the RCS and not available for sump water inventory.

m. The NPSH analysis assumed a minimum water level of 601.5 ft recirculation sump, which provides a minimum NPSH margin of 9.2 ft.

in the

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9 In summary, these conservatisms minimized the driving head for flow through the recirculation sump strainers by minimizing the containment water level, maximized the demand on strainer head loss through establishment of flow rates in excess of those calculated for worst case system operation, and minimized the NPSH available to the ECCS and CTS pumps.

Downstream Effects - Ex-Vessel 9.1 Methodology

a.

9.2 Key Conservatisms I Margins

a.

b.

c.

The downstream effects wear evaluation considered that approximately 28.5%

~L t~tal coJd l9.11~an~zin.g compound would pass through the re~irculation sump stramers(Thls IS Significantly greater than the less than 2% failure of the cold gal~~pizI6g"'com po und that was identified through DBA testing.

f.

As described in Section 7 of this evaluation, the use of more realistic values for the debris quantities in containment demonstrate additional conservatism for the methodology that was used for the ex-vessel downstream effects analysis.

In summary, these conservatisms maximized the potential for blockage and wear of components downstream of the recirculation sump strainers, including consideration of the pumps being at their MOL and at the end of plant life wear point.

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10 Downstream Effects - In-Vessel 10.1 Methodology

a. The methodology that was used for performing the in-vessel downstream effects analysis was per WCAP-16793 with consideration of staff comments on that document, including the letter from the NRC to NEI. Additionally, as more questions were raised about the adequacy of the proposed methodology, the PWROG undertook additional testing to determin~~if~uel assembly blockage could occur.

Earlier this year, the PWROG profJdeCl informal results to the NRC and licensees. The PWROG also p~~:cr the threshold criteria for fibrous and particulate debris below which J~jJir~k~ g e was demonstrated by 10.2 Key Conservatisms I Margins 11 11.1 testing to not be problematic.

a.

CCl's MFTL facility using the 11.2 Key Coh$§ rvatisms I Margins

a.

The CCI chemical effects testing determined a maximum increase in head loss across an established debris bed of 53%. CNP increased this to 70% for the entire recirculation sump strainer system for both the DEGB and DGBS to provide additional margin for uncertainty.

b.

The chemical effects testing performed at CCI established a debris bed for the main strainer only which is expected to be the most heavily laden with debris.

This provides conservatism in that for this strainer, the head loss will be greater

- 17

than that for the remote strainer since a higher head loss is indicative of less available flow area through the strainer and a more highly compacted debris bed. With less available flow area, chemical precipitates will more readily block flow through the strainer bed, resulting in a higher head loss increase as a result of the chemical effects.

c. Additional conservatism exists with chemical effects as a result of the debris source term margins and conservatisms discussed in Section 7 of this evaluation.

If testing were to be performed with the more realistic debris quantities, the impact of the chemical precipit ~ t~s~ would be significantly reduced.

d.

Conservatism exists as a result of normaliziri'ff lne 1:hemical effects test results to 68°F. This is below the expected low t(rap~ra~ r:~of 100°F in the RCS and containment pool.

e.

f.

g.

In summary, tne.l cnemical effects testing that was performed has demonstrated that CNP will be able to ~ mitigate the consequences of a LOCA considering the inputs and methodologies that were used to establish bounding conditions for determination of the impacts.

- 18

12 Upstream Effects 12.1 Methodology

a. The methodology that was used for performing the upstream effects analysis was to consider all required flow paths that will either return water from upper containment to the containment pool, or will provide the necessary flow path to the main and remote strainers in lower containment.

13 12.2 Key Conservatisms I Margins

a.

13.1

c. The strainer structural analysis also considered the different phases of the event including temperature and pulse pressure from the failure of the pressurizer surge line, as well as the flow effects on the strainer system, and seismic effects.

13.2 Key Conservatisms I Margins

a. Use of the code of record provides conservatism within the code itself.

- 19

15

b. The values of the margins for structural analysis were provided in the February 29, 2008 and August 29, 2008 Supplemental Responses to GL 2004-02.

In summary, the strainer structural analysis provides margin to design allowable stresses which ensures that the strainer system will perform its function as long as is necessary following an event which requires its use.

14 Debris Source Term 14.1 Methodology

a.

14.2 Key Actions Taken

a.

b.

As diSCUSSed~~~cration, CNP has demonstrated that significant quantifiable margins and conservatitms tjave been established as part of the success path for resolving GL 2004-02 and GSI~9. GNP has also performed extensive analysis and testing, along with significant changes to the plant, to ensure that the EGGS system will meet the requirements of 10 CFR 50.46 following a LOCA. The same testing and analysis also ensures the GTS system will function to remove containment heat and radioactive iodine from the containment atmosphere for the necessary period following an accident.

- 20

DRAFT REQUESTS FOR ADDITIONAL INFORMATION DONALD C. COOK NUCLEAR PLANT, UNITS 1 AND 2 SUPPLEMENTAL RESPONSES TO GENERIC LETTER (GL) 2004-02 Debris GenerationlZone of Influence

1.

Response

Response:

2.

As described, in the ~ ijeb ru a ry 29, 2008 Supplemental Response, the jet ir:gpingement te~n1 g determined the effects of a direct jet impinging on the target at~rial. As inlta led in the plant, due to the small size of the CNP containments, th~~iS signJ.fic ~t congestion surrounding the target materials with very few excep 12>JlS#~iS will result in deflected jets at the targets. For the Marinite board testing. r~sfated in the Supplemental Response, the failure mode was the deformation of the simply supported cable tray section on which the board was mounted. For the label testing the jet size was very closely matched to the size of the labels. For the ArmaflexlRubatex tests the jet was intentionally directed toward the openings of the jacketing to maximize the forces acting on the material to determine if failure would occur. The single jacket tests demonstrated that failure would occur. For the tape tests the jet was again directed in the direction of the laps of tape to induce the greatest impact on the material. Since these tests were not attempting to determine the destruction of large quantities of materials, the use of a 2.45 in. diameter jet is judged to be reasonable and acceptable.

- 21

Debris Characteristics

3.

a) Describe the scaling process used to apply the results of the debris generation testing of the Marinite, Armaflex, fire barrier tape, and other materials to the plant condition. In particular, the staff noted that the size of the nozzle (2.45 inches) used for the testing resulted in a significantly smaller jet than would be created by a large-break LOCA. As a result, large test targets may only have been exposed to the peak pressure at the jet centerline over a limited area due to the radial decay of the jet pressure.

Thus, a significant area of the target material could have been exposed to much lower jet pressures than this peak pressure. This effect could be sigl]ific'Gnt, not only with respect to ablation of base material by the impinging jet, bU!A4!iolfo applying the total force necessary to rip off insulationjacketing or break insu/~t[o!1;bl!Jdjng.

Response: See the response to RAI 2 above.

Response

4.

ebruary 29, 2008 Supplemental Response,

5.

Based uoon discTissions,witmma'ifiifacturefS:of calcium silicate, the staff understands that Response: The material,used for erosion testing was the specific material that is installed in the CNP co~t~ents within potential lOIs (Thermo Gold 12). The OPG testing that is referenced was performed with Thermo Gold 12. This was confirmed through discussion with one of the individuals from OPG that was involved with the testing.

Debris Transport

6.

In the D. C. Cook debris transport analysis, both the total quantity of transported debris and the distribution of this transported debris to the main and remote strainers have an impact on the final system head loss.

- 22

Please describe the basis for considering the Loop 4 break to be bounding, not only from the standpoint of transporting the greatest total amount of debris, but also from the standpoint of the degree of uniformity in the debris distribution between the main and remote strainers.

Response :

7.

a.

and debris

'haDpear-to lack adequate basis,

- 23

0 20 40 60 80 1

Main Strainer Open Area Ratio (%)

100 90 c~

80 t;

.5 e 70 tr.

C 60

• S

~

50..,

c:.o =

E 40 30

--s.

tt:

20

~ e t:

10 0,

s~ers. Thisi~~ ost evident when looking ~t the t~tal debris transp~rt factor f~r thos~at resulted In a value greater than 1 with 1 bemg the total quantity of debns availa l:)l~;~9f;rh"bse debris sources that had a total debris transport factor less than 1, the ~a~~)ipp roa ch was applied resulting in debris transport factors greater than would exist' for a single strainer approach design.

Refer also to the discussion provided in Sections 5 and 7 of the Margins and Conservatisms Evaluation.

b.

To deterrfii~n exact~split of debris between the main and remote strainers would have requireo a.~sub~ta~~tial number of iterative tests followed by analysis followed by tests follo ".i~t;I \\by a ~aIY\\is, etc. The debris transport analysis factored in this 4pcertainty Wh ~mCletermining the debris distribution between the main and remote

c. Water draining into the containment pool during the fill-up phase is clean. Such a condition is not realistic, and the time dependence of blowdown, washdown, and pool-fill-up transport modes is not well known and can vary significantly from one accident scenario to the next.

For this reason, conservatively estimating time dependent debris transport is very challenging.

- 24

As a result of these observations, the staff does not consider the flow and debris distributions to the main and remote strainers (including the time-dependent transport modeling used to determine these distributions) to be adequately justified.

The measured flow rates to the main and remote strainers in the large scale tank tests performed at Control Components Inc. (GGI) further provide support to the staffs view that the fraction of flow and debris transport to the main strainer were overestimated by the transport analysis.

Since non-uniformity of the flow and debris loading tends to reduce the overall system head loss, this overestimate of flow and debris transport to the main strainer appears non-conservative.

Please provide adequate justification to support the abo ~e4s;umptions used to support the determination of flow and debris transport to the maimana remote strainers.

Response

8.

a.

b.

c. The b asis¥1IJj1si~g a velocity.of 0.4 ft/s, since calcium silicate piec~s larg~r than those testeqXI.e., In the large piece category) would not transport at this vetocny.

Response: A higher velocity will result in a greater probability for erosion to occur.

d. The basis for considering the turbulence conditions prototypical or conservative, since defining a limiting condition for turbulence is difficult given that a variety of conditions may exist throughout the containment pool at different times following a LOGA.

- 25

9.

Please identify the basis for the assumed calcium silicate tumbling transport velocity metrics for small pieces (0.33 ft/s) and large pieces (0.52 ft/s).

NUREG/CR-6772 identifies the incipient tumbling velocity of 0.25 ftis for small pieces of calcium silicate.

Response: Specific testing was performed by ALiON to establish both incipient tumbling and tumbling velocities. The test report that documents the results of this test is ALlON REP-LAB-2532-81, Testing to evaluate the Settling and Tumbling velocities of Cal Sil Insulation Debris. This is an ALIGN proprietary document. The following has been excerpted from the test report:

The Cal-Sil insulation samples were tested in the TrBifsjjort Flume under uniform flow conditions. The assembly shown in Figure 2.6 w1[used. An internal channel was inserted in the Transport Flume to reduce t e ross sectional area from 21.5X24 in2 to 12.25X24 in2 to achieve a highe.ft,1elocity a ~a particular flow rate. A flow distributor and flow straightener were used to achieve ' : aminar and unidifecffonalflow.

10.

Please"provide justification that the debris introduction methods used during head loss testing r~(!jtefl inJJfutdtypical or conservative head loss results.

Response: The introduction of the debris directly in front of the strainer prevented settling of v

any debris before it could reach the strainer. Additionally, following testing and drain down of the test loop, there appeared to be a fairly even distribution of fine debris in the strainer pockets.

A prototypical debris loading would have had significantly greater debris loading in the lower pockets. It is judged that the results obtained during the testing were conservative.

Refer also to the information provided in Sections 5 and 7 of the Margins and Conservatisms Evaluation.

11.

The submittal stated that the fibrous debris was shredded, and then blasted with a water jet to render it into fine debris. The submittal stated that the fibrous debris was verified to

- 26

be less than 10 mm in size. It is not clear that the debris was easily suspendable which is the primary consideration for fine fibrous debris. In addition, the submittal did not state the extent to which the fibrous debris was diluted. Therefore, agglomeration of debris could have occurred resulting in non-prototypical debris bed formation and non conservative head losses.

Please provide information that shows that the debris preparation and introduction methods used during head loss testing were conducive to prototypical debris arrival at the strainer and resulted in prototypical or conservative head loss results, or evaluate the effects of the non-prototypical debris on the head loss results.

Response: The overall methodology for determination of strai !JJr.f. ~ead loss was conservative in that debris quantities significantly in excess of.,df:1os e?tpat exist in the plant were used for the testing. The debris preparatio~an~ d~Ii~(.Y was performed as a homogeneous mixture that was well prepj!~ ~ preven t~gglomeration, which is not ~rototypical, but is con~ervative. j}jf,er ~Iso to the ~nforruation provided in Sections 5 and 7 of the Margms and C.onservatlsms Evaluatlo ~

12.

nlie..;g iCtu~s ooeing referred to are those of the chemical effects testing that mo~e iecl~e ~maT~l.t!~iner only to determine a chemical effects ?ump-u,P factor.

DUring the ~~L testll1Q,.there was no "pool-fill" sequence for debrisaddition. The inclusion of Ftflll! in ~grra i ne r test is prototypical as there will be a significant quantity of RMJ\\debris' 'generated during an event which will transport and

§l~~um u l a te a~ ~llg in the main strainer. Due.to the very.Iow fiber that exists at C~~he test~~ "Jhat was p~rformed conservatively d~termlned th.e head ~~ss that woulq,:be developed. If testing had been performed with the debris quantities that actually~i~t )n'containment, the resulting head loss would have been significantly lower. Ag'~jn, refer to the information provided in Sections 5 and 7 of the Margins and Conservatisrns Evaluation.

13.

During head loss testing the flow rate was started at 60% of the maximum flow. The flow rate was then increased to 80%, then to 100% along with debris additions to the same percentages. It is not clear why flow was not maintained at 100% for the entire test.

Please provide the basis for increasing the flow rate during the beginning of the test and provide information that verifies that this practice did not result in non-conservative head loss results. Adding debris with the flow rate below 100% is likely non-conservative due to lower bed compression, and therefore, head loss. The following provides additional

- 27

details on the staff concerns. Forming the bed at reduced flow (60% of debris added at 60% flow), as was done in the large scale extended duration head loss tests, does not appearjustified unless a reduced water level is also simulated that could help model the building of the bed from the base of the strainer to its top at a higher approach velocity.

The staff also questions whether the addition of 60% of the debris during fill up can be justified, and notes that this overestimates the licensee's calculations.

For the large scale event sequence testing, the concern is even more substantial, with 100% of the debris being added at flows representing between 38 and 50% of the scaled plant flow rates. The staff is concerned that the time-dependence of the debris arrival sequence in the plant is not known with confidence, and adding all of th~~ebris at less than 100% of the design flow is non-conservative, unrealistic, and ultlm~/y leads to lower bed compression and lower debris bed head loss than a mOl~"~Ofservative methodology that is better aligned with the expected plant behavior. The"$taff questions whether the time based addition of debris for the main strainer (L~cfctd~gJ.tfle "pool-fill" transported material first) has an adequate technical basillJAlt appears 't~b~ based on arbitrary transport assumptions. Debris addition in this,maDf1er may lead t() \\a)s~atified bed that is non-repr~sentative of,the expecte~plant co1f§fiion. Sin,ce the wale9.h.~ght in the te.st tank durmg the pool-fill aebris eadition ~ot prototy~al, the local afJprc;ach velocity during bed formation was not representeC!.l.l!.C(curately y.lJ1il the actual p)anl~water level

14.

reached the water level modeled in the test.

Please address these concerns.

Response

Please"p.lovide the results of the similar tests run for each flow scenario and provide an Response: The tesf' results requested in this RAI were provided in the February 29, 2008 Supplemental Response, Section 3.f.

evaluatid'rii dOfJ1parilo,lof the results.

15.

During the chemical effects testing, non-chemical head losses were significantly greater than large scale non-chemical head loss testing with a similar debris mixture.

a) Please provide an explanation for this behavior and evaluate how a higher non chemical debris head loss could affect the calculated bump-up factor.

- 28

Response: The MFTL chemical effects test was performed with the main strainer only with the debris load for that strainer. The head loss for the main strainer is greater than the remote strainer which is indicative of a dense and compacted debris bed. Applying chemical precipitates to this condition will result in a more significant increase in strainer head loss since there are less available flow paths through the debris bed than there would be with a strainer with less debris.

b) Provide a justification that the chemical test head loss should not be applied directly to the net positive suction head evaluation.

Response

16.

17.

18. dfrfgfe head loss crl7:ifts for tHe c hemical effects testing show a large rapid increase in head losilmmediately f8i/~ing non~h e mical debris addition. The increase is followed by an l#r'qJfJcJiate decreas ~~\\read 7'fks to a significantly lower value, then a slower decrease are added (see pages 303 and 304).

This behavior is unti f¢hemical preci/5.itates

~

aut-nti unexpected.

a) Please p~~lall explanation for the rapid increase and decrease in head loss that occurred duringilfiis testing.

Response: The non-prototypical addition of debris to the test loop (significant quantities in a relatively short period of time) initially results in a head loss from the near term blockage of the strainer assembly.

As the debris circulates, the debris bed transforms from a film effect to a compacted bed. Due to the debris constituents used during CNP testing, there is insufficient fiber to maintain a tightly interlaced debris bed. Holes will open up in the bed allowing flow through the bed.

- 29

b} Provide justification that the chemical precipitates were added at a time such that a prototypical or conservative bump-up factor would be calculated. The staff considers that adding chemicals when baseline head loss is continuing to decrease could result in a non-conservative bump-up factor.

Response: The primary driver for the decreasing head loss was the increasing temperature within the test loop. Refer to the February 29, 2008 Supplemental Response to GL 2004-02, Section 3.0.13, Figures 3013a-1 and 3013a-2 on pages 303 and 304.

Additionally, the values for head loss were normalized to 68°F for both debris only head loss and chemical effects head loss.

19.

The submittal stat~d that t~~ design maximum head 10SJ!.~B.ft for a large-b:ea.k ~OCA based on the available dnvmg head of water at th~/!l~on sump. This timl: was based on NUREG-CR-680B guidance that head loss~hould n~ceed ;/z of the strainer height (or in this case submergence above theJ!.ottom of the tt;pig;r). A slightly lower limn for the debris generation break size was a/sffi.-!tsted. There wa~ *no limit proviaeo for the small-break LOCA and no calculation ol,,1Otential head losses a~iated with a small Addr~Jn your resP9,[ $e whether the scaling back of this head loss result based on the reduc1!1hlow rate cail'lb1J justified because flow rate determination in the large scale tank was ba;rl{jy(timat~1YJon arbitrary assumptions made during the transport analysis. In actuality, th~1Jis~i~'pancy in flow rate for this test indicates that too little debris was assumed to traTz.r;!ort to the remote strainer (versus the main strainer) and that a higher flow rate would occur at the main strainer, presumably with slightly less debris. In other words, it is a non-converged solution.

Response: Please refer to the responses previously provided regarding flow splits, debris transport, and conservatisms and margins that exist.

Also, the flow rate determination for the large scale testing was not based on debris transport assumptions. The basis for the statement was intended to show that the debris loading for the main strainer in the large scale test was similar to the debris loading for the main strainer in the MFTL. It was not intended to provide justification for break.

Response

20.

- 30

debris quantities, but that there was minor difference in the calculated main strainer head loss from the large scale test and the directly measured main strainer head loss from the MFTL test.

Coatings Evaluation

21.

In the submittal, non-original equipment manufacturer alkyds and epoxies fail as chips in accordance with Keeler and Long Report No. 06-0413. The Keeler and Long report is only applicable to degraded qualified epoxies and not unqualified epoxies or alkyds.

Response

22.

equipment The alkyd was Rustoleum with an

23.

Based upon the information provided in the response, it appears that the potential exists for a break location to be submerged by the water in the containment pool, potentially resulting in a flow path for unfiltered pool water to enter the reactor vessel.

The centerline for the reactor inlet nozzle is at 614 ft elevetion. The maximum containment pool water level is also 614 ft elevation.

a) Please address whether the potential for debris bypass into the reactor vessel through this pathway has been analyzed.

- 31

Response: The maximum, conservatively predicted water level for containment is just below the 614 ft elevation. The analysis that determines this water level is biased in the opposite direction of the analysis that determines the minimum water level in containment.

One of the most significant conservatisms in the maximum water level analysis is the quantity of ice assumed to be in the ice condenser. Several additional conservatisms are included within this analysis which further increases the water level in containment, such as containment pool temperature, available volume from the RWST, RCS, and Accumulators, and the quantity of items that can displace water.

Considering just the difference in /ice mass results in an approximate decrease in water level between 6 in~t 2) and 1 ft (Unit 1).

Additionally, by the time the maximum water leve1: l~~ched, there will be little to no debris remaining in the containment pool du~<<qi1~~fi,ltration of the recirculation sump strainers.

b) Are there any adverse debris effects from

Response

NPSH

24.

a)'\\EJease provide information 1nat justifies that the sump pool level calculations resTJlt~.jn realistic ot '9gnservative levels for the large-and small-break LOCAs.

Response: The~upplem~ntal response statement was strictly referring to the large break scenafiQ.¥

,9yYgmali breaks, the ana~~sis considered. the effects of cooldown, refill, and delaYE;t,dJlaccumulator volume additions as a function of RCS pressure. Refer to the following description of the water level analysis.

The current licensing basis containment sump inventory analysis was performed using the MAAP4 code version 4.0.4.1 (FAI, 1999).

The MAAP4 code calculates the behavior of and interactions between the ECCS, RCS and containment following a postulated accident. Consequently, the pred icted containment sump inventory reflects time-dependent mass and energy inputs from ECCS/containment spray injection and recirculation, ice melt, RCS holdup, accumulator injection, and water flow between containment compartments. The Cook Nuclear Plant reactor

- 32

coolant system is represented as a typical Westinghouse 4-loop design available in MAAP4. Two RCS loops are included in the standard MAAP4 model, with one loop including a single steam generator and associated piping, and the other loop including the composite behavior of the remaining three steam generators and associated piping. The spectrum of RCS break sizes evaluated include a Double Ended Cold Leg (DECL) and a variety of smaller breaks. The MAAP4 primary system break flow model determines mass and energy releases for steam and water flows leaving the reactor coolant system by assuming they are in thermodynamic equilibrium. This characterization of the break flows maximizes water enthalpy, and minimizes steam release to con~.D 'llent atmosphere that is available to melt ice.

The modeling assumptions for the containment minimum water level analysis considered those conditions that would result in the least amount of water being available for the containment sump.

These included use of a maximum procedurally driven cooldown rate of the RCS along with maximum refill of the RCS for those breaks where inventory in the RCS could be restored. The analysis also considered the accumulators at their minimum pressure and temperature with water addition from the accumulators being controlled by ReS pressure and pressure

- 33

head driven flow from the accumulators. The water levels provided for the DEGB, the DGBS, and 2 in. line break in the February 29, 2008 Supplemental Response to GL 2004-02 represent these conservatisms, where applicable.

Refer also to Section 8 of the Margins and Conservatisms Evaluation.

b) Please provide the basis for concluding that there are no small breaks near the top of the pressurizer that should be analyzed for sump performance.

Response: When this was first evaluated four years ago, the ability of the Operators to recognize, mitigate, and establish recovery determine~t~at for the maximum 6 in.

break, the plant would not be in a condition wher~ J te Cfrculation was required.

Discussions with members of the Licensed oper~tbrlraining staff confirmed the original conclusion. Unfortunately, we are currentft;(j~able to revalidate this on the simulator since both of the CNP units are in an~qytage aQ~.(Ie ithe r the training staff or the operators are available to perform thefsce"Fiarios.

Response: Refer to the rEtsponse to RAI 2

Response

lated minimum water level analysis does not require revision.

25.

O. C. Cook liSts"" both sodium tetraborate in the ice and sodium hydroxide in the containment spray.

Tables 301-1 and 301-2 indicate that only sodium tetraborate is added to the multi-functional test loop for in-situ chemical precipitate formation in the chemical effects head loss testing.

Please provide a justification for not including sodium hydroxide in these tests.

Response: The addition of NaOH was unnecessary for this test. Ample quantities of Na and OH existed in the test solution as a result of the sodium aluminate and Sodium

- 34

Tetraborate additions to the test loop. The sodium aluminate is a strong alkaline which maintains the pH at the specified level of 8.9.

26.

Please explain why the later batches of chemicals have no apparent impact on the measured head loss. The staff is concerned that the addition of extra chemicals may not provide a significant degree of conservative if the phenomena behind why later batches of chemicals in the testing don't seem to have a noticeable impact on head loss is not understood and known to be present in the plant condition also.

Response: The chemical additions in excess of the quantities specified did not have the other necessary chemicals to react with to form additio*

Cipitate. The conditions entered the large tank relative to the opening of the pocket strainer.

d. Please state whether photographs were taken of the tank floor at the completion of the test and whether the quantity of debris that settled on the tank floor was estimated. What is the estimated quantity of the debris that settled? Was any of the settled debris manually pushed into the strainer pockets?

- 35 expected for 140% chemical addition were met for.tOs,test.

VUEZ Testing

27.

a.

whether agitation or manual stirring of the tank was performed during the testing,.and please describe the direction that the recirculation discharge flow

e. Please discuss how the reduced velocities used during debris bed formation affected the settling of debris in the test tank. For instance, the response (e.g., page 74 of 100) indicates that debris settled in tank, particularly prior to the initiation of full recirculation flow.

What is the basis for allowing debris settlement at strainer approach velocities that are significantly less than the prototypical value?

28.

Please explain how the containment spray flow for the first 25 minutes of the experiment was scaled, and the basis for the flow rate that was chosen.

29.

Debris does not appear to be prepared as fines in the photogr..aph provided in the Alion test report (pg. 66). Fiber is conservatively expected to b~~ndividual fibers because it is all latent debris. Calcium silicate insulation at the straip~r is analytically expected to be 86% fines and 14% small pieces. Similar observ'M~\\wt;h.f!n~/SO be made for Marinite debris. These important debris sources do not app..egr to h~fJ.abeen prepared per the

30.

plant-specific debris transport results.

31.

SimJ/~p the cel tes1ifi?J, all of the debris for the VUEZ test appeared to be added during the P601~fiK Phase."e staff is concerned that this approach is non-conservative because~~~the 10W~'" velocities during the fill-up phase (213rds of the value during recirculatio'7lJf!r;q'J$l6wer flow rate through the strainer would lead to reduced debris bed compression. "fj::~ith ermore, it is not clear whether a representative water level modeling was used. The use of a non-representative water level would further reduce the velocity during bed formation and further contribute to reduced bed compression. Additionally, due to pump cavitation, the flow in the VUEZ loop had to be substantially reduced during the debris bed formation process, which resulted in a bed being formed at velocities substantially lower than even the reduced velocities during pool fill.

a) Please address the potential for a resultant non-uniform debris distribution on the 2x2 pocket strainer module, with more debris going toward the bottom pockets as well as some piling of debris at the pocket openings rather than the formation of a thin bed.

- 36

b) Please also address the potential for reduced debris bed compression due to non representative test conditions that had the potential to underestimate the potential limiting head loss for the plant condition.

32.

Similar to a staff observation for the small-scale VUEZ test loops, when taken in aggregate, uncertainties are not negligible on the VUEZ large scale test apparatus:

a. Approximately 1% of volume is discarded due to sampling

b. Approximately a 3% reduction in head loss because Illi.EJ;alcium silicate debris was added to test than revised calculations showed.

c. Temperature uncertainty is +/-5°F

d. Flow measurement uncertainty is 5%

e. Pump flow uncertainty is 5%

33.

34.

- 37

REQUESTS FOR ADDITIONAL INFORMATION DONALD C. COOK NUCLEAR PLANT, UNITS 1 AND 2 SUPPLEMENTAL RESPONSES TO GENERIC LETTER (GL) 2004-02 Debris Generation/Zone of Influence

1.

a) Identify what zone of influence (pipe diameters) was determined for the new D. C.

Cook RubatexlArmaflex configuration and how it was arrived at from the referenced Wyle Labs test report data.

b) Were there any potential break locations within this zone of influence? If so, how much debris would be generated from this source, how much would be expected to arrive at the strainers, and what would its contribution be to strainer blockage and head loss?

2.

Describe the basis for determining that the results of jet testing with the 2,45 inch diameter jet were prototypical of that which could be expected from the much larger jets potentially experienced during a loss of coolant accident (LOCA)?

Debris Characteristics

3.

a) Describe the scaling process used to apply the results of the debris generation testing of the Marinite, Armaflex, fire barrier tape, and other materials to the plant condition. In particular, the staff noted that the size of the nozzle (2A5 inches) used for the testing resulted in a significantly smaller jet than would be created by a large-break LOCA. As a result, large test targets may only have been exposed to the peak pressure at the jet centerline over a limited area due to the radial decay of the jet pressure. Thus, a significant area of the target material could have been exposed to much lower jet pressures than this peak pressure. This effect could be significant, not only with respect to ablation.of base material by the impinging jet, but also to applying the total force necessary to rip off insulation jacketing or break insulation banding.

b) Please describe how the radial decay of the jet pressure was accounted for in the analysis of the test results to demonstrate that the results have been prototypically or conservatively scaled to the plant condition.

4.

Please identify which destruction test or tests were used as the basis for the Marinite size distribution given in Table 3c1-2 of the supplemental response.

5.

Based upon discussions with manufacturers of calcium silicate, the staff understands that there were several different manufacturing processes used to make calcium silicate insulation in the U.S., and that the calcium silicate produced by the different processes may have significantly different characteristics with respect to exposure to jet impingement and erosion.

What verification or analysis was done to ensure similarity between the calcium silicate at D. C. Cook and the material tested for both erosion and for the jet destruction testing performed by Ontario Power Generation?

- 2 Debris Transport

6.

In the D. C. Cook debris transport analysis, both the total quantity of transported debris and the distribution of this transported debris to the main and remote strainers have an impact on the final system head loss.

Please describe the basis for considering the Loop 4 break to be bounding, not only from the standpoint of transporting the greatest total amount of debris, but also from the standpoint of the degree of uniformity in the debris distribution between the main and remote strainers.

7.

The debris transport analysis makes assumptions in deriving the flow and debris distributions between the main and remote strainers that appear to lack adequate basis, including the following:

a. During pool fill up, the flow resistance on the main strainer is assumed to be negligible, even though a substantive amount of debris is assumed to accumulate there during fill up. Given the reduced water levels along with the fact that static head is the only driving force to move water through the main strainer at this time, the neglect of this flow resistance could have a non-negligible impact on the flow distribution during fill up, resulting in increased flow to the remote strainer.

b. Ten percent of the area of the main strainer is assumed to remain clean during recirculation, even though large scale test results for D. C. Cook suggest a greater degree of flow resistance. Furthermore, a significant number of head loss tests with a variety of different strainer geometries have demonstrated the potential for debris to form a continuous bed over the entire strainer surface area rather than leaving part of the strainer area open (presuming a sufficient quantity is available).

Therefore, a more representative analytical model of head loss at the main strainer during recirculation would likely result in a significantly larger flow and debris fractions arriving at the remote strainer.

<? <:'Water drai.ning into the containment pool during the fill-up phase is clean. Such a

. condition is not realistic, and the time dependence of blowdown, washdown, and pool-fill-up transport modes is not well known and can vary significantly from one accident scenario to the next. For this reason, conservatively estimating time dependent debris transport is very challenging.

As a result of these observations, the staff does not consider the flow and debris distributions to the main and remote strainers (including the time-dependent transport modeling used to determine these distributions) to be adequately justified. The measured flow rates to the main and remote strainers in the large scale tank tests performed at Control Components Inc. (CCI) further provide support to the staffs view that the fraction of flow and debris transport to the main strainer were overestimated by the transport analysis. Since non-uniformity of the flow and debris loading tends to reduce the overall system head loss, this overestimate of flow and debris transport to the main strainer appears non-conservative.

Please provide adequate justification to support the above assumptions used to support the determination of flow and debris transport to the main and remote strainers.

- 3

8.

Please provide additional information concerning the erosion testing of calcium silicate insulation and Marinite board, including the following items:

a. The basis for not accounting for erosion and dissolution effects in combination. The presence of chemicals in the test fluid may enhance the erosion rate, and, conversely, a high erosion rate may lead to increased dissolution.

b. The basis for not including the plant buffer materials in the test fluid.

c. The basis for using a velocity of 0.4 ft/s, since calcium silicate pieces larger than those tested (i.e., in the large piece category) would not transport at this velocity.

d. The basis for considering the turbulence conditions prototypical or conservative, since defining a limiting condition for turbulence is difficult given that a variety of conditions may exist throughout the containment pool at different times following a LOCA.

9.

Please identify the basis for the assumed calcium silicate tumbling transport velocity metrics for small pieces (0.33 ft/s) and large pieces (0.52 ft/s). NUREG/CR-6772 identifies the incipient tumbling velocity of 0.25fVs for small pieces of calcium silicate.

Head Loss and Vortexing

10.

According to the submittal, the debris was added directly in front of the strainer to reduce near-field settling. The staff has found that this.debris introduction method can result in non-prototypical bed formation and non-conservative head loss values during testing.

Please provide justification that the debris introduction methods used during head loss testing resulted in prototypical or conservative head loss results.

11.

The submittal stated that the fibrous debris was shredded, and then blasted with a water jet to render it into fine debris. The submittal stated that the fibrous debris was verified to be less than 10 mm in size. It is not clear that the debris was easily suspendable which is the primary consideration for fine fibrous debris. In addition, the submittal did not state the extent to which the fibrous debris was diluted. Therefore, agglomeration of debris could have occurred resulting in non-prototypical debris bed formation and non conservative head losses.

Please provide information that shows that the debris preparation and introduction methods used during head loss testing were conducive to prototypical debris arrival at the strainer and resulted in prototypical or conservative head loss results, or evaluate the effects of the non-prototypical debris on the head loss results.

12.

Reflective metallic insulation (RMI) debris was added to the head loss tests. In pictures of the chemical testing in the multi-functional test loop (MFTL), the RMI was piled up in front of the strainer and transported into the bottom several rows of the strainer. The staff considers this non-prototypical and it could result in non-conservative head loss values. Pictures of the non-prototypical RMI debris bed can be seen in photos on pages 288-293. With the RMI present, a prototypical fiber and particulate bed could not have been created. In particular, some of the RMI was part of the earlier-transported "pool-fill" transported debris. This resulted in an RMI layer being formed between the fibers and

- 4 particulate that was added early representing pool-fill transport and that which was added later representing recirculation transport.

Please address this testing approach wherein the RMI was apparently responsible for reducing head loss but was added to the tank in a non-prototypical way.

13.

During head loss testing the flow rate was started at 60% of the maximum flow. The flow rate was then increased to 80%, then to 100% along with debris additions to the same percentages. It is not clear why flow was not maintained at 100% for the entire test.

Please provide the basis for increasing the flow rate during the ~beginning of the test and provide information that verifies that this practice did not res yHJ'ii '~non-conservat ive head loss results. Adding debris with the flow rate below 1OO%J~' nkely non-conservative due to lo~er bed compression, and ther~fore, head loss..rh~.J6 It§~in g provides.additional details on the staff concerns. Forming the bed at reduced floW:(60% of debris added at 60% f10~), ~~ was done in the large scale ext~n~1~yd~ration h6'3(D~.~s tests, does not appear Justified unless a reduced water level ts: ~J !?O simulated thatc0-!Jl~ help model the building of the bed from the base of the str~. ! r1~'t 5 its top at a higher~ap~r,qach velocity.

The staff also questions whether the addition of 60% of the debris during'.fill up can be justified, and notes that thi~ overestimates"~F~.~cense~:~~)lculati.ons..Fo"fi large scale event sequence testing, the concern IS e v:~n m9re;subst8ntlal, With 100% of the debris being added at flows representing betwee~ 38,;and 50% of the scaled plant flow rates. The staff is concerned tha't-the time-depe ~-a eh'Ce of the debris arrival sequence in IJ u ~

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the plant is not known with confidence".;and adding all.of.the debris at less than 100% of

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the desig~ flow is non-conse:vativ~ ;wni"eal~tiC:. l ~.£i,nd ul ti ~~~~~y leads.to lower bed compression and lower debris bed ~ead 10ss Jh.~n a r.nore

• q,g ~servatlve methodology that is better aligned with.the expected plant benav.ior':>:T.he statf questions whether the time based addition of.de'brrs*for,the main ~ra i ri~t'(L e., addYng1he "pool-fill" transported

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material first) hasJih adequate.technical,basis. It appears to be based on arbitrary transport assumptions. Deb~s )addition in tbis manner may lead to a stratified bed that is non-represe nta.~ive of the e );,Ct;E~'cted plant COn.dition. Since the water height in the test tank during the~poOb-fill debri~aaition $as'i ri8t prototypical, the local approach velocity

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14.

The'test sequences that resulted in the maximum tested head losses for the double-endG'~"gqillotine brea k 'spd debris generation break size scenarios were different. The doubl ~e nd.ed gUillotj ~e break limiting head loss was attained by adding a homogeneous debris mT*tor~ in st~~:of 60%, 80%, and 100% while increasing flow in the same steps.

The debris g~'l1e ratipn break size limiting head loss was attained during a sequence intended to m'iln.iC'the flows that would occur through the strainer following a LOCA.

There is no apparent reason that different test sequences for would result in the limiting head loss for these breaks.

Please provide the results of the similar tests run for each flow scenario and provide an evaluation/comparison of the results.

- 5

15.

During the chemical effects testing, non-chemical head losses were significantly greater than large scale non-chemical head loss testing with a similar debris mixture.

a) Please provide an explanation for this behavior and evaluate how a higher non chemical debris head loss could affect the calculated bump-up factor.

b) Provide a justification that the chemical test head loss should not be applied directly to the net positive suction head evaluation.

16.

Provide an evaluation of the sensitivity of overall system head loss to various debris loads split between the main and remote strainers as predicted by the transport evaluation. Because it is difficult to determine how much debris will arrive at each strainer, this is an important issue.

17.

The submittal (pg 227) stated that the debris-only he,ad loss would be considered to be 1.57 ft after being increased by 50%. It was notclear that the clean strainer head loss was included in this value.

i I Please provide the total head loss including the clean strainer portion or confirm that this value includes the clean strainer head loss.

is.

The head loss charts for the chemical effects testlnqshow a large rapid increase in head loss immediately following non-chemicaldebris addition: The increase is followed by an immediate decrease in head loss to a significantly lower value, then a slower decrease until chemical precipitates are added (see pages 303 and 3(4). This behavior is unexpected.

a) Please provide an explanation for the rapid increase and decrease in head loss that occurred during this testing.

b) Provide justification that the chemical precipitates were added at a time such that a prototypical or conservative bump-up factor would be calculated. The staff considers that adding chemicals when baseline head loss is continuing to decrease could result in a non-conservative bump-up factor.

19.

The submittal stated that the design maximum head loss is 2.S ft for a large-break LOCA based.on the available driving head of water at the recirculation sump. This limit was based :on NUREG-CR*6'SOS guidance that head loss should not exceed 112 of the strainer height (Of in this case g'ubmergence above the bottom of the strainer). A slightly lower limit for the debris generation break size was also listed. There was no limit provided for the small-break LOCA and no calculation of potential head losses associated with a small break.

Provide justification that the strainer will maintain its function under all required scenarios including a small-break LOCA.

20.

The basis for the comparison being made on page 306, that the resulting head loss for the large scale head loss on the main strainer only is 3 ft, which compares favorably to the MFTL debris only head loss of 2.67 ft is not clear.

Please clarify this statement, which helps to undergird the bump-up factor approach.

- 6 Address in your response whether the scaling back of this head loss result based on the reduced flow rate can be justified because flow rate determination in the large scale tank was based ultimately on arbitrary assumptions made during the transport analysis. In actuality, the discrepancy in flow rate for this test indicates that too little debris was assumed to transport to the remote strainer (versus the main strainer) and that a higher flow rate would occur at the main strainer, presumably with slightly less debris. In other words, it is a non-converged solution.

Coatings Evaluation

21.

In the submittal, non-original equipment manufacturer alkyds and epoxies fail as chips in accordance with Keeler and Long Report No. 06-0413. The Keeler and Long report is only applicable to degraded qualified epoxies and not unqualified epoxies or alkyds.

Please provide additional justification for the unquallfled non-original equipment manufacturer alkyd and epoxy coatings assumption to fail as chips.

22.

a) Please provide the characteristics of the paint chip surrogate including the density and type of paint used.

I b) Please clarify how the paint chip surrogate simulates the expected coating debris.

Downstream - in vessel

23.

Based upon the information provided in the response, it appears that the potential exists for a break location to be sut;>merged by the water in the containment pool, potentially resulting in a flow path for unfiltered poolwater to enter the reactor vessel. The centerline for the reactor inlet nozzle is at 614 ft elevation. The maximum containment pool water level is also 614 ft elevation.

a) Please address whether the potential for debris bypass into the reactor vessel through this pathway.has been analyzed.

,"° :1, b) Are there any adverse debris effects from submerging other RCS break locations?

NPSH

24.

The submittal stated that the minimum water level calculation included Y:1 of the RCS volume arid'the volume of the accumulators. It is not clear that these volumes should be credited for all:breaks. For example a small-break LOCA could result in the accumulators r~rnaining full for an extended period and the RCS maintaining more than Y:1 of its volume. *'n addition, the RCS would tend to refill as it cooled off. Based on these observations it is not clear that the levels used in the vortexing evaluation are conservative. It was not clear that the increasing density of RCS inventory as it cooled was considered in the sump level calculations.

a) Please provide information that justifies that the sump pool level calculations resulted in realistic or conservative levels for the large-and small-break LOCAs.

- 7 b) Please provide the basis for concluding that there are no sm811 breaks near the tor of the pressurizer that should be analyzed for sump performance.

c) Verify that operators have the ability to coo/down and depressurize in sufficient time to prevent switchover.

d) How is a single failure accounted for in this analysis?

e) If the currently calculated minimum water levels require revision, please provide updated vortexing and air entrainment evaluations using conservative submergence values.

Chemical Effects

25.

D. C. Cook uses both sodium tetra borate in the ice and sodium hydroxide in the containment spray. Tables 301-1 and 301-2 indicate that only sodium tetraborate is added to the multi-functional test loop for in-situ chemical precipitate formation in the chemical effects head loss testing.

Please provide a justification for not including sodium hydroxide in these tests.

26.

Please explain why the later batches of chemicals have no apparent impact on the measured head loss. The staff is concerned that the addition of extra chemicals may not provide a significant degree of conservative if the phenomena behind why later batches of chemicals in the testing don't seem to have a noticeable impact on head loss is not understood and known to be present in the plant condition also.

VUEZ Testing The NRC staff performed a detailed review of the test procedures used by Alion at the small loops at the VUEZ test facility in Slovakia.' The staff concluded that it was unlikely that the plants relying on this testing coulc use it as a basis for demonstrating strainer design adequacy to resolve Generic Letter 2004-02. The staffs review did not specifically address testing performed in the larger loop at VUEZ that was used for the D. C. Cook testing. Although some similarities existed in the small-scale and larger-loop test programs, there were also some significantdifferences. If VUsZ testing is being used as part of the basis to demonstrate the adequacy of the D. C. Cook strainers, then please address the following requests for additional information on this testing below:

27.

Please provide the Jollowing additional information concerning the modeling of debris transport fo? the,VUEZ testing:

a. Please explain the basis for the minimum flowrate of 1 Umin to preclude stagnant regions in the test tank.

b. Please provide a basis for the statement on pages 56 and 64 of 100 of the VUEZ appendix that states that the water volume was much smaller than the actual plant condition, and therefore the turbulence and velocity in the (test) pool is higher. The relative size of the fluid volumes does not appear to the staff to be directly related to the velocity and turbulence.

- 8 Please compare the test tank flow characteristics to the velocity and turbulence contour plots for the plant condition provided in the February 2008 supplemental response.

c. Please state whether agitation or manual stirring of the tank was performed during the testing, and please describe the direction that the recirculation discharge flow entered the large tank relative to the opening of the pocket strainer.

d. Please state whether photographs were taken of the tank floor at the completion of the test and whether the quantity of debris that settled on the tank floor was estimated. What is the estimated quantity of the debris that settled? Was any of the settled debris manually pushed into the strainer pockets?

e. Please discuss how the reduced velocities used during debris bed formation affected the settling of debris in the test tank. For instance, the response (e.g., page 74 of 100) indicates that debris settled in tank, particularly prior to the initiation of full recirculation flow. What is the basis for allowing debris settlement at strainer approach velocities that are significantly less than the prototypical value?

28.

Please explain how the containment spray flow for the first 25 minutes of the experiment was scaled, and the basis for the flow rate that was chosen.

29.

Debris does not appear to be prepared as fines in the photograph provided in the Alion test report (pg. 66). Fiber is conservatively expected to be only individual fibers because it is all latent debris. Calcium silicate insulation at the strainer is analytically expected to be 86% fines and 14% small pieces. Similar observations can also be made for Marinite debris. These important debris sources do not appear to have been prepared per the plant-specific debris transport results.

Are there photos of the as-prepared debris slurries or close-ups of the debris during the addition process that show the form of this debris immediately prior to the addition to the tank, which would demonstrate that these debris sources were eventually prepared into a representative form ?

30.

Debris predominately entered the bottom row of pockets as evidenced in the photo on

. Page 67 of the Alion test report. The debris used for this testing should have been very nearly 100% fines (although some calcium silicate is small pieces). Although there may be some bias toward the bottom pockets during a LOCA even for fines, based on the photo, the biasing toward the bottom pockets seems much more pronounced than expected by the staff: Such significant non-uniformity can be attributed to either non representative debris preparation or the introduction of the debris so close to the bottom strainer pockets that it approached the strainer on a non-representative flowstream into the bottom pockets nearest the debris addition line.

a) Please provide additional photos of the debris accumulation on the strainer to clarify the situation.

b) Please identify the level the water was when the debris was being added, and identify whether the water level was representative of the plant condition at that time.

- 9

31.

Similar to the CCI testing, all of the debris for the VUEZ test appeared to be added during the pool-fill phase. The staff is concerned that this approach is non-conservative because of the lower velocities during the fill-up phase (2/3rds of the value during recirculation). This lower flow rate through the strainer would lead to reduced debris bed compression. Furthermore, it is not clear whether a representative water level modeling was used. The use of a non-representative water level would further reduce the velocity during bed formation and further contribute to reduced bed compression. Additionally, due to pump cavitation, the flow in the VUEZ loop had to be substantially reduced during the debris bed formation process, which resulted in a bed being formed at velocities substantially lower than even the reduced velocities during poolftll.

a) Please address the potential for a resultant non-uniform-debris distribution on the 2x2 pocket strainer module, with more debris going toward -the' bottom pockets as well as some piling of debris at the pocket openings rather than'the formation of a thin bed.

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b) Please also address the potential for reducea,1~' ;;-bris bed com ~t~~sion due to non representative test conditions that had the pd~~ntial to underestimate' tti~, pptential limiting head loss for the plant condition.

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32.

Similar to a staff observation for the small-sca!e XUEZtest loops, when taken in aggregate, uncertainties are not negligible on theVUEZ large scale test apparatus:

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a. Approximately 1% of volume -is-discarded due io:'sampling

b. Approximately a 3% reductiori*i ';.,head *16~*s*bec~us~

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c. Tempera ~ute ':uncertairity is +/-5°F

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33.

a),Why did the head.loss increase early in the head loss test to a fraction of a kPa (see figur~k7~4-14) before Me,official start of the test?

b) Whati:~?s. \\he r"e,ason the head loss subsequently increased fairly rapidly to 11 kPa?

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34.

Please identify~ine' concentration of the debris slurry used for the VUEZ tests and the degree to which agglomeration of the debris in the slurry affected the prototypicality of the test debris.