ML22312A443

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NRC Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors Fleet Response to RAI
ML22312A443
Person / Time
Site: Millstone, Surry, North Anna  
(NPF-065, NPF-049, NPF-004, NPF-007, DPR-032, DPR-037)
Issue date: 11/07/2022
From: James Holloway
Dominion Energy Nuclear Connecticut, Dominion Energy Services, Virginia Electric & Power Co (VEPCO)
To:
Office of Nuclear Reactor Regulation, Document Control Desk
Shared Package
ML22312A441 List:
References
22-273, GL-04-002
Download: ML22312A443 (1)
v • d • e


Text

PROPRIETARY - WITHHOLD UNDER 10 CFR 2.390 Dominion Energy Services, Inc.

5000 Dominion Boulevard, Glen Allen, VA 23060 Dominion Energy.com November 7, 2022 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

VIRGINIA ELECTRIC AND POWER COMPANY MILLSTONE POWER STATION UNITS 2 AND 3 NORTH ANNA POWER STATION UNITS 1 AND 2 SURRY POWER STATION UNITS 1 AND 2 Serial No.:

22-273 NRA/GDM:

RO Docket Nos.:

50-336/423 50-338/339 50-280/281 License Nos.: DPR-65 NPF-49 NPF-4/7 DPR-32/37 NRC GENERIC LETTER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED-WATER REACTORS" FLEET RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION By letters dated May 27, 2021, [ADAMS Accession No. ML21147A477], April 15, 2021,

[ADAMS Accession No. ML21105A433], and February 25, 2021, [A_DAMS Accession Nos. ML21056A557 and ML21056A541 ], Dominion Energy Nuclear Connecticut, Inc. and Virginia Electric and Power Company (collectively, Dominion Energy) submitted final supplemental responses for Millstone Power Station (MPS) Units 2 and 3, and North Anna and Surry Power Stations (NAPS and SPS) Units 1 and 2, respectively, to Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors," dated September 13, 2004.

By letter dated September 9, 2022, the NRC provided a request for additional information (RAI) for each of the station submittals noted above. Dominion Energy's responses to the NRC RAls associated with MPS Units 2 and 3 are provided in Attachments 1 and 2, respectively, and the responses to the NRC RAls associated with NAPS and SPS Units 1 and 2 are provided in Attachments 3 and 4, respectively.

The SPS response to NRC RAI 4 included in Attachment 4 contains information proprietary to Framatome, Inc.; therefore, it is supported by an affidavit signed by the owner of the information, which is provided in Attachment 6. The affidavit sets forth the basis on which the information may be withheld from public disclosure by the Commission and addresses with specificity the considerations listed in paragraph (b)(4) of 10 CFR 2.390.

Accordingly, it is respectfully requested that the proprietary information be withheld from public disclosure in accordance with 10 CFR 2.390. A non-proprietary version of the SPS RAI response is provided in Attachment 5. contains information that is being withheld from public disclosure under 10 CFR 2.390. Upon separation from Attachment 4, this page is decontrolled.

5ii-Dominion

--' Energy

Serial No.22-273 Docket Nos. 50-336/423/338/339/280/281 GL 2004-02 RAI Response Page 2 of 3 Should you have any questions or require additional information, please contact Mr. Gary D. Miller at (804) 273-2771.

Respectfully, James E. Holloway Vice President - Nuclear Engineering and Fleet Support Commitments contained in this letter: None Attachments:

1. Response to Request for Additional Information, Generic Letter 2004-02 Final Supplemental Response - Millstone Power Station Unit 2
2. Response to Request for Additional Information, Generic Letter 2004-02 Final Supplemental Response - Millstone Power Station Unit 3
3. Response to Request for Additional Information, Generic Letter 2004-02 Final Supplemental Response - North Anna Power Station Units 1 and 2
4. Response to Request for Additional Information, Generic Letter 2004-02 Final Supplemental Response - Surry Power Station Units 1 and 2 [PROPRIETARY]
5. Response to Request for Additional Information, Generic Letter 2004-02 Final Supplemental Response - Surry Power Station Units 1 and 2 (Non-Proprietary)
6. Framatome Inc. Affidavit for Withholding Proprietary Information from Public Disclosure COMMONWEAL TH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by James E. Holloway, who is Vice President-Nuclear Engineering and Fleet Support of Dominion Energy Nuclear Connecticut, Inc., and Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true o the best of his knowledge and belief.

Acknowledged before me this 7-f'1 day of

.,.J.,,u-, 2022.

My Commission Expires: ~, J..- :!.I,~.

/

Notaf)I Ii

Serial No.22-273 Docket Nos. 50-336/423/338/339/280/281 GL 2004-02 RAI Response Page 3.of 3 cc:

U.S. Nuclear Regulatory Co_mmission - Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 U.S. Nuclear Regulatory Commission - Region II.

Marquis One Tower 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, GA 30303-1257 R. V. Guzman Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C-2 11555 Rockville Pike Rockville, MD 20852-2738 Mr. G. Edward Miller NRC Senior Project Manager - North Anna U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738 Mr. L. John Klos NRC Project Manager - Surry U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station NRC Senior Resident Inspector North Anna Power Station NRC Senior Resident Inspector Surry Power Station Old Dominion Electric Cooperative Electronically Distributed Serial No.22-273 Docket No. 50-336 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE Dominion Energy Nuclear Connecticut, Inc.

(DENC)

Millstone Power Station Unit 2

Serial No.22-273 Docket Nos. 50-336 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE MILLSTONE POWER STATION UNIT 2 NRCComment 10 GFR 50. 46 requires that plants maintain the ability to provide Jong-term core cooling following any initial LOGA response. To ensure that this cooling is available, licensees demonstrate that in-vessel fiber accumulation will not adversely affect the required function.

Millstone 2 In its most recent supplemental response for NRG Generic Letter 2004-02, dated May 27, 2021 (ADAMS Accession No. ML21147A477), Dominion Energy provided information regarding the debris amounts used in the fiber penetration calculation for Millstone 2 and explained the methodology used to determine the amount of fiber that could penetrate the emergency core cooling system strainer.

Regarding the basis for some of the assumptions used in the calculations, discuss the following aspects of the calculation so that the NRG staff can understand how the in-vessel debris amounts were calculated:

1) The method for implementing the bed thickness correction was unclear. It seems that the Point Beach values would be directly applicable to Millstone 2 up to the tested thickness. Beyond the tested thickness, the model would have to be extrapolated to a higher debris load. With respect to extrapolation to higher debris loads, address the items below.
a. Was the correction for bed thickness applied to the thickness that will occur at the "Initial Sump Fiber Load" amount or was it applied to the design basis load?

Dominion Energy Response The Point Beach Test 3 data was extrapolated for the Millstone Power Station Unit 2 (MPS2) maximum theoretical debris bed thickness of 2.665 inches, which was then used to determine the cumulative bypass fraction. The "design basis load" (fiber load transported to the strainer -

5429 lbm) was used to calculate the bed thickness.

Page 1 of 8

Serial No.22-273 Docket Nos. 50-336

b. Provide the characteristics of the fiber in the test compared to the characteristics of the fiber used to calculate the plant bed thickness for the penetration correction.

Explain why any differences would not have to be accounted for in the correction factor, if applicable.

Dominion Energy Response MPS2 debris includes low density fiberglass (LDFG), mineral wool, and mineral fiber, whereas the three Point Beach tests evaluated different debris compositions of fiberglass, mineral wool, and Temp-Mat. The MPS2 cumulative bypass fraction is based on an extrapolated all-fiberglass Point Beach test (Test 3), which provided the most bypass at any given fiber bed thickness. In the NextEra Point Beach Letter No.

2017-0045, "Updated Final Response to NRC GL 2004-02," dated December 29, 2017 (ADAMS Accession No. ML17363A253), it was stated that the all-fiberglass test (Test 3) mathematical model may be conservatively used for any debris composition since it results in larger fiber penetration quantities than the other two models under identical test conditions. Below is a plot of the three Point Beach tests (exact debris compositions were provided in Table 3 in the DENC MPS2 final supplemental response dated May 27, 2021 (ADAMS Accession No. ML21147A477)), which indicates Test 3 as having the highest fiber penetration at any given bed thickness:

35 30

~

7 25 0.B

~ 20 LL l/l l/l

~ 15 co E 10 u

5 0

0 0

\,\

'i

~ ~

~

0.2 0.4 Point Beach - All Tests

-4 1-Test 1 Test 2

~

0.6 0.8 1

1.2 1.4 Bed Thickness (in.)

Shows extrapolated data for Test 3 compared with full data sets for Tests 1 & 2 Page 2 of 8 1.6

Serial No.22-273 Docket Nos. 50-336

c. Provide plots of penetrated debris vs. accumulated debris for the plant strainer.

On the plot, or separately, provide points (timing/bed thickness) at which the operating state of the ECCS and CSS pumps change including swapover to recirculation, flow changes, and the end of injection from the RWST.

Dominion Energy Response The plot below was used to generate a power equation that was then used to calculate the cumulative fiber bypass fraction for the theoretical debris bed thickness of 2.665".

Note that the "+1 Og" signifies that the cumulative bypass fraction data points account for an extra 10 grams of fiber that bypassed the Point Beach strainer surface but settled in the collection tube and was not measured in the downstream in-line filter bags. The extra 10 grams was apportioned to each fiber batch addition based on the mass of each addition and its associated bypass fraction. The Point Beach test report identified that this adjustment should be performed for the most accurate bypass determination. Note that "Extrap. Data" on the plot was only extended to 1.5" bed thickness to compare the curve shape with the Point Beach Tests 1 and 2 curves (see plots in the response for RAI 1 b above).

Point Beach - Test 3 (+10g) 35% -----.---...-----.----r-----T---...-------.------,

Test Da a (+10g) 6 25% ------------------i---------

-:p u

ro it 20% +----W---+---+-----+---+----+-----t-----+------1 V')

V')

ro

.......

  • Power ( est Data (+l0g))

g: 15% +---

....,_,_._--+-----+---+----+-----t-----+------1 ca E a 10%

s% +/--, -, -, ~T:::;:;;:::=.===+=::t:~7 0% +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-1-+-11-+-11-+-11-+-11-+-1--+-t--+-t 0

0.2 0.4 0.6 0.8 1

1.2 1.4 1.6 Bed Thickness (in.)

The MPS2 strainer does not experience any flow (Emergency Core Cooling System (ECCS) and Containment Spray System (CSS)) until the Refueling Water Storage Tank (RWST) low level switchover to the sump occurs, which has a minimum time of 33 minutes. At that time, the ECCS and CSS pumps would be operating and drawing through the strainer. The changes in flow rates and the timing of the flow changes are not significant since a cumulative fiber bypass fraction at the design basis load of Page 3 of 8

Serial No.22-273 Docket Nos. 50-336 5429 lbm is used to determine the sump fiber load of 660.15 lbm. The sump fiber load is the starting point for calculating the post-Hot Leg Break fibrous debris load that accumulates in the core and at the core inlet.

d. Confirm that the bed thickness is assumed to be zero at the time that EGGS pump suctions are realigned to the sump.

Dominion Energy Response As discussed in the response to RAI 1 c above, there is zero flow through the strainer until the time of sump switchover for both the ECCS and CSS. Thus, there is no initial debris bed.

Note that the sump load of 660.15 lbm is derived from the strainer cumulative fiber bypass fraction at the maximum theoretical debris bed thickness associated with the design basis load of 5429 lbm.

e. Provide the assumptions used for flow rates, timing of flow rate changes, and other factors that could impact the calculation. Provide these for the various scenarios for which in-vessel fiber loads were calculated.

Dominion Energy Response As discussed in the response to RAI 1 c above, changes in flow rates and the timing of the flow changes are not relevant since a cumulative fiber bypass fraction at the design basis load of 5429 lbm rs used to determine the sump fiber load of 660.15 lbm.

f.

What is the basis for the total fiber load of 5429 lb? Was this value used to develop the bed thickness correction?

If yes, what is the basis for using this value considering that lower amounts of fiber may transport for many scenarios, a more realistic erosion rate, and the debris generation and transport assumptions in the analysis? The fiber bed thickness is too small if only /ow-density fiberglass (LDFG) is considered. Did the thickness account for fiber densities other than LDFG? If so, justify this considering the test used only LDFG.

i.

This could result in a thinner bed and higher penetration at the time that EGGS is realigned to the sump.

Dominion Energy Response The fiber load of 5429 lbm is based on the fiber quantity determined to transport to the strainer from the break location that generates the maximum fiber load.

This is consistent with NRC Staff Review Guidance for In-Vessel Effects (ADAMS Accession No. ML19228A011 ), which states that "Licensees should assume the largest fibrous debris amount arriving at the sump strainer, including transport and erosion (based on the bounding fiber break for the plant)." The LDFG only Point Beach test results were selected for use to determine the MPS2 cumulative bypass fraction for the 5429 lbm Page 4 of 8

Serial No.22-273 Docket Nos. 50-336 fiber load since it demonstrated higher fiber penetration than the other test results using mixed debris compositions (see response to RAI 1 b above). The theoretical bed thickness was calculated by summing the MPS2 as-fabricated fiber volumes for all insulation types (see Table 3 in the MPS2 final supplemental response dated May 27, 2021), and then dividing by the effective strainer area. The theoretical bed thickness was then compared with the Point Beach Test 3 extrapolated test curve for determining the cumulative fiber bypass fraction. Since the in-vessel effects analysis uses the cumulative bypass fraction of fiber, it accounts for the higher fiber penetration rates as the debris bed is building.

g. What does the Initial Sump Fiber Load of 660. 15 lb. represent? How was it calculated? What is its relevance and how is it used in the in-vessel debris loading calculation? How were the debris generation and transport analyses for this value performed?

Dominion Energy Response This sump fiber load represents the mass of fines at the strainer that can bypass the strainer after a specific period (10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />) of insulation erosion. It is derived from the 5429 lbm total fiber load evaluated to transport to the strainer. In particular, 65% of the fiberglass and 100% of the mineral wool and mineral fiber generated at the break location were evaluated to transport to the strainer. This total fiber load represents the largest fiber load, for all the break locations evaluated, that will transport to the strainer. Based on the fact that only fibrous debris that has a size classification of "fines" can bypass the strainer, and since small and large debris sizes can only bypass the strainer after first being eroded into fines, a time-dependent fines generation evaluation was performed. This was accomplished by using a fibrous debris 4-part size distribution (intact, large, small, and fines) for each debris type generated and then applying erosion rates to the small and large debris quantities. Intact pieces are noted to remain encased in their covers and consequentially are not subject to erosion. The fraction of small and large debris eroded was calculated using the equation from the Nuclear Energy Institute (NEI) 04-07, "Pressurized Water Reactor Sump Performance Evaluation Methodology Guidance Report (GR)" NRC Safety Evaluation Report that uses an erosion rate of 0.3% per hour.

The sump fiber load of 660.15 lbm is used as a design input to calculate the post-Hot Leg Break fibrous debris load that accumulates in the core and at the core inlet. It is assumed the entire 660.15 lbm load of fibrous fines can be transported to the core and core inlet, and whose transport rate is dictated by the sump recirculation flow rate as well as the cumulative sump strainer bypass fraction.

Page 5 of 8

Serial No.22-273 Docket Nos. 50-336

h. How are the bed thickness correction values calculated for each time step?

Dominion Energy Response Only the maximum full debris load theoretical bed thickness was calculated, which then uses the extrapolated Point Beach Test 3 data to determine the total accumulated fiber bypass fraction of the 5429 lbm fiber load.

i.

If only a single thickness correction is used, provide a justification considering that bed thickness changes as debris arrives at the strainer.

Dominion Energy Response Since the in-vessel effects analysis uses the cumulative bypass fraction of fiber at the final theoretical bed thickness, it accounts for the higher fiber penetration rates as the debris bed is building.

2) Verify that the list of references in the submittal is correct and ensure that the citations in the text are correct. For example, there is a reference to STP testing in the text, but no STP references in the list.

Dominion Energy Response The list of references and their citations were reviewed, and one typographical error was identified. On page 21 of 29, Design Input 12 identifies WCAP-17788-A, Rev. 1, but should actually be WCAP-17788-P, Rev. 1. With regard to the STP testing, the citation is for reference 4.12, and this is the correct reference as STP testing is discussed in WCAP-17788-P, Rev. 1.

3) Confirm that Containment Spray System (CSS) operates for all scenarios throughout the period during which transport to the reactor is calculated. Are there scenarios where the spray flow would be zero, or less than the flow rate analyzed? If so, justify the flow rate used.

Dominion Energy Response The CSS operates for all scenarios throughout the period during which transport to the reactor is calculated, i.e., at all times after sump recirculation begins. The possible CSS flow rates for recirculation mode and boron precipitation control were reviewed, and the bounding minimum flow rate was used in the in-vessel debris loading calculation. In no scenario would the CSS flow rate be zero because this would require failures of both CSS pump trains, which is non-credible. There is also no scenario for which the CSS flow rate would be lower than the bounding minimum flow rate analyzed. The minimum CSS flow Page 6 of 8

Serial No.22-273 Docket Nos. 50-336 rate analyzed comes from a scenario in which only one CSS pump is operating in a degraded condition.

4) In the listed conservatisms it is stated that the designated sacrificial area was included to minimize the thickness.

Confirm that this means that no sacrificial area was subtracted from the total strainer area for the penetration calculations.

Dominion Energy Response Once the debris bed thickness was determined, which is based on the 5429 lbm debris load and the total strainer area (including sacrificial area), the cumulative bypass fraction was determined from the extrapolated Point Beach Test 3 data.

Consequently, no sacrificial area was subtracted for the penetration calculations.

5) The Millstone 2 evaluation described the acceptability of a minimum EGGS flow rate below the analyzed values. The condition was accepted based on the maximum flow case resulting in higher fiber loading. If the fiber mass for the high flow case remains significantly below the total in-vessel limit a more refined evaluation would not be required. However, if the fiber value approaches the limit a more refined analysis could be required. Provide the calculated fiber load for the high flow case.

Dominion Energy Response The high flow case resulted in the maximum fiber load for MPS2 with a resulting in-vessel debris loading of 20.67 g/FA. The cumulative in-vessel debris load represents the fiber load in the reactor vessel at the time sump fiber load is less than 1 % of the initial sump fiber load and is consistent with the termination criteria documented in Section 6.5.5 of WCAP-17788, Volume 1, Revision 1. It is noted the total in-vessel debris load at the time the termination criteria was reached was also reported for the core inlet debris load at the time of tb1ock. The cumulative in-vessel debris load was reported for the core inlet debris load at MPS2 because the value bounds the core inlet debris load at the time of tb1ock and satisfies the acceptance criteria for both in-vessel effects and core inlet blockage.

6) Table 5 appears to contain an error for fbtock-The value is listed as 2.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, but the value for CE plants is 333 minutes or about 5. 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Please confirm the correct value.

Dominion Energy Response The correct value is 333 minutes. The correct value (333 minutes) was used in the supporting calculations, but a typographical error was made in generating the input for Table 5. Correction of this error was entered into Dominion Energy's corrective action system.

Page 7 of 8

Serial No.22-273 Docket Nos. 50-336

7) Provide the basis for the maximum EGGS flow rate of 4100 gpm in the last row in Table 5. Explain how this value was used to calculate the maximum in-vessel fiber load. Does the full 4100 gpm inject to the reactor vessel as implied by the 18. 9 gpm per fuel assembly flow rate or is some of this CSS flow?

Dominion Energy Response The maximum ECCS flow rate of 4100 gpm is based on the bounding maximum ECCS flow rate for all scenarios following the initiation of recirculation mode, including sump recirculation and boron precipitation control modes, and does not include CSS flow. The calculation of in-vessel debris loading models the entirety of the ECCS flow (4100 gpm, or 18.9 gpm/FA, for the maximum ECCS flow case) injecting directly into the reactor vessel. Prior to Hot Leg Switchover (HLSO), the entire ECCS flow injects directly into the core inlet.

Page 8 of 8 Serial No.22-273 Docket No. 50-423 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE Dominion Energy Nuclear Connecticut, Inc.

(DENC)

Millstone Power Station Unit 3

Serial No.22-273 Docket No. 50-423 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE MILLSTONE POWER STATION UNIT 3 NRCComment 10 GFR 50. 46 requires that plants maintain the ability to provide Jong-term core cooling following any initial LOGA response. To ensure that this cooling is available, licensees demonstrate that in-vessel fiber accumulation will not adversely affect the required function.

Millstone 3 In its most recent supplemental response for NRG Generic Letter 2004-02, dated April 15, 2021 (ADAMS Accession No. ML21105A433), Dominion Energy provided information regarding the debris amounts used in the fiber penetration calculation for Millstone 3 and explained the methodology used to determine the amount of fiber that could penetrate the emergency core cooling system strainer.

Regarding the basis for some of the assumptions used in the calculations, discuss the following aspects of the calculation so that the NRG staff can understand how the in-vessel debris amounts were calculated:

1) The method for implementing the bed thickness correction was unclear. It seems that the Point Beach values corrected by Vogtle velocity data would be directly applicable to Millstone 3 up to the tested thickness. From that point on, the model would have to be extrapolated to a higher debris load. The items below should be considered.
a. Was the correction for bed thickness applied to the thickness that will occur at the "EGGS strainer" (or the initial sump fiber load) amount or was it applied to the design basis load?

Dominion Energy Response The Point Beach Test 3 data was directly extrapolated for the Millstone Power Station Unit 3 (MPS3) maximum theoretical debris bed thickness of 2.037 inches, which was then used to determine the cumulative bypass fraction after applying a velocity correction factor associated with that bed thickness. The "design basis load" (fiber load transported to the strainer -

2053 lbm) was used to calculate the bed thickness.

Page 1 of 9

Serial No.22-273 Docket No. 50-423

b. Provide the characteristics of the fiber in the test compared to the characteristics of the fiber used to calculate the plant bed thickness for the penetration correction.

Explain why any differences would not have to be accounted for in the correction factor, if applicable.

Dominion Energy Response MPS3 debris includes only low density fiberglass (LDFG), whereas the three Point Beach tests evaluated different debris compositions of fiberglass, mineral wool, and Temp-Mat. The MPS3 cumulative bypass fraction is based on an extrapolated all-fiberglass Point Beach test (Test 3), which provided the most bypass at any given fiber bed thickness. In the NextEra Point Beach Letter No. 2017-0045, "Updated Final Response to NRC GL 2004-02," dated December 29, 2017 (ADAMS Accession No. ML17363A253), it was stated that the all-fiberglass test (Test 3) mathematical model may be conservatively used for any debris composition since it results in larger fiber penetration quantities than the other two models under identical test conditions.

Below is a plot of the three Point Beach tests (exact debris compositions were provided in Table 3 included in the DENG final supplemental response dated April 15, 2021 (ADAMS Accession No. ML21105A433)), which indicates Test 3 as having the highest fiber penetration at any given bed thickness:

35 30

'ii

~ 25 0

B

~ 20 LL V)

V)

~ 15

~

E 10

J u

5 0

Point Beach - All Tests 0

\,\ 'l

41 1-Test 1

~ ~

-c,-rest 2 1~~

~

~

0 0.2 0.4 0.6 0.8 1

1.2 1.4 1.6 Bed Thickness (in.)

Page 2 of 9

Serial No.22-273 Docket No. 50-423

c. Provide plots of penetrated debris vs. accumulated debris for the plant strainer.

On the plot or separately provide points (timing/bed thickness) at which the operating state of the RSS changes including RSS swapover to recirculation, swapping EGGS pump suctions from the RWST to the RSS, RSS flow changes, and the end of injection from the RWST.

Dominion Energy Response The plot below was used to generate a power equation that was then used to calculate the cumulative fiber bypass fraction for the theoretical debris bed thickness of 2.037".

Note that the "+1 0g" signifies the cumulative bypass fraction data points account for an extra 10 grams of fiber that bypassed the Point Beach strainer surface but settled in the collection tube and was not measured in the downstream in-line filter bags. The extra 10 grams was apportioned to each fiber batch addition based on the mass of each addition and its associated bypass fraction.

The Point Beach test report identified that this adjustment should be performed for the most accurate bypass determination. Note that "Extrap. Data" on the plot was only extended to 1.5" bed thickness to compare the curve shape with the Point Beach Tests 1 and 2 curves (see plots in the response for RAI 1 b above).

35%

30%

6 25%

u ro it 20%

Vl Vl ro

~ 15%

a::i

~ 10%

5%

0%

-~

I 0

Point Beach - Test 3 (+10g}

\

- Test Da a (+l0g)

\

- Extrap. )ata

\

.......

  • Power ( rest Data (+l0g))
    • ~

y = 0.0403( 3x-o.1sa434

""-~

L.......

0.2 0.4 0.6 0.8 1

1.2 1.4 1.6 Bed Thickness (in.)

The MPS3 strainer does not experience any flow (Emergency Core Cooling System (ECCS) and Containment Spray System (CSS)) until the Refueling Water Storage Tank (RWST) low level switchover to the sump occurs, which has a minimum time of 33 minutes. At that time all ECCS and RSS pumps would be operating and drawing through the strainer. The changes in flow rates and the timing of the flow changes are Page 3 of 9

Serial No.22-273 Docket No. 50-423 not significant since a velocity corrected cumulative fiber bypass fraction at the design basis load of 2053 lbm is used to determine the sump fiber load of 380.32 lbm. The sump fiber load is the starting point for calculating the post-Hot Leg Break fibrous debris load that accumulates in the core and at the core inlet.

d. Provide the bed thickness calculated at the time that EGGS pump suctions are realigned to the RSS.

Dominion Energy Response As discussed in the response to RAI 1 c above, the timing of the fiber bed development is not significant since a velocity corrected cumulative fiber bypass fraction at the design basis load of 2053 lbm is used to determine the sump fiber load of 380.32 lbm.

e. Provide the assumptions used for flow rates, timing of flow rate changes, and other factors that could impact the calculation. Provide these for each scenario for which in-vessel debris loads were calculated.

Dominion Energy Response As discussed in the response to RAI 1 c above, changes in flow rates and the timing of the fiber bed development are not relevant since a velocity corrected cumulative fiber bypass fraction at the design basis load of 2053 lbm is used to determine the sump fiber load of 380.32 lbm.

f.

What is the basis for the total fiber load of 2053 lb? Was this value used to develop the bed thickness correction?

If yes, what is the basis for using this value considering that lower amounts of fiber may transport for many scenarios, a more realistic erosion rate, and the debris generation and transport assumptions in the analysis?

i.

This could result in a thinner bed and higher penetration at the time that EGGS is realigned to the sump/RSS.

Dominion Energy Response The fiber load of 2053 lbm is based on the fiber quantity determined to transport to the strainer from the break location that generates the maximum fiber load.

This is consistent with NRC Staff Review Guidance for In-Vessel Effects (ADAMS Accession No. ML19228A011 ), which states that "Licensees should assume the largest fibrous debris amount arriving at the sump strainer, including transport and erosion (based on the bounding fiber break for the plant)." The LDFG only Point Beach test results were selected for use to determine the MPS3 cumulative bypass fraction for the 2053 lbm fiber load since it demonstrated higher fiber penetration than the other test results using mixed debris compositions (see response to RAI 1b above). The theoretical Page 4 of 9

Serial No.22-273 Docket No. 50-423 bed thickness was calculated by dividing the MPS3 as-fabricated fiberglass volume (see Table 3 in the MPS3 final supplemental response dated April 15, 2021) by the effective strainer area. The theoretical bed thickness was then compared with the Point Beach Test 3 extrapolated test curve for determining the cumulative fiber bypass fraction, which then had a velocity correction factor applied associated with that bed thickness. Since the in-vessel effects analysis uses the velocity corrected cumulative bypass fraction of fiber, it accounts for the higher fiber penetration rates as the debris bed is building.

g. What is the basis for the EGGS fiber amount (initial sump fiber load) of 380.32 lb?

How was it calculated? What is its relevance and how is it used in the in-vessel debris loading calculation?

How were the debris generation and transport analyses for this value performed?

Dominion Energy Response This sump fiber load represents the mass of fines at the strainer that can bypass the strainer after a specific period (5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />) of insulation erosion. It is derived from the 2053 lbm total fiber load evaluated to transport to the strainer. In particular, 65% of the fiberglass generated at the break location was evaluated to transport to the strainer.

This total fiber load represents the largest fiber load, for all the break locations evaluated, that will transport to the strainer. Based on the fact that only fibrous debris that has a size classification of "fines" can bypass the strainer, and since small and large debris sizes can only bypass the strainer after first being eroded into fines, a time-dependent fines generation evaluation was performed.

This was accomplished by using a fibrous debris 4-part size distribution (intact, large, small, and fines) for each debris type generated and then applying erosion rates to the small and large debris quantities. Intact pieces are noted to remain encased in their covers and consequentially are not subject to erosion. The fraction of small and large debris eroded was calculated using the equation from the Nuclear Energy Institute (NEI) 04-07, "Pressurized Water Reactor Sump Performance Evaluation Methodology Guidance Report (GR)," NRC Safety Evaluation Report that uses an erosion rate of 0.3% per hour.

The sump fiber load of 380.32 lbm is used as a design input to calculate the post-Hot Leg Break fibrous debris load that accumulates in the core and at the core inlet. It is assumed that the entire 380.32 lbm load of fibrous fines can be transported to the core and core inlet, and whose transport rate is dictated by the sump recirculation flow rate as well as the cumulative sump strainer bypass fraction.

Page 5 of 9

Serial No.22-273 Docket No. 50-423

h. How are the bed thickness correction values calculated for each time step?

Dominion Energy Response Only the maximum full debris load theoretical bed thickness was calculated, which then uses the extrapolated and velocity corrected Point Beach Test 3 data to determine the total accumulated fiber bypass fraction of the 2053 lbm fiber load.

i.

If only a single thickness correction is used, provide a justification considering that bed thickness changes as debris arrives at the strainer.

Dominion Energy Response Since the in-vessel effects analysis uses the velocity corrected cumulative bypass fraction of fiber at the final theoretical bed thickness, it accounts for the higher fiber penetration rates as the debris bed is building.

2) Verify that the list of references in the submittal is correct and ensure that the citations in the text are correct. In the text, near the bottom of page 16 of 30, reference 4.14 is to STP testing.

For example, in the list of references, 4.14 is to WCAP-17788.

References 4.4 through 4. 10 are referred to as Point Beach and Vogtle testing near the top of page 17 of 30. This appears to be an error.

Dominion Energy Response The list of references and their citations were reviewed, and no errors were identified. On the bottom of page 16 of 30, with regard to the STP testing, the citation is for reference 4.14. This is the correct reference as STP testing is discussed in WCAP-17788-P, Rev. 1. On the top of page 17 of 30, the citations for references 4.6 to 4.10 are correct for Point Beach and Vogtle testing. References 4.4 and 4.5 are also appropriate, but it should have also been identified that AREVA/Alden testing for fiber bypass length distribution and size characterization were also reviewed to gain additional understanding of factors related to fiber bypass.

3) Confirm that Containment Recirculation Spray System (RSS) operates for all scenarios throughout the period during which debris transport to the reactor is calculated. Are there scenarios where the spray flow would be zero, or Jess than the 4071 gpm analyzed?

Dominion Energy Response The Recirculation Spray System (RSS) operates for all scenarios throughout the period during which transport to the reactor is calculated, i.e., at all times after sump recirculation Page 6 of 9

Serial No.22-273 Docket No. 50-423 begins. The possible RSS flow rates were reviewed and scenarios were identified with more limiting ECCS and RSS flow rates during sump recirculation than those modeled in the underlying calculation supporting the MPS3 Final Supplemental Response dated April 15, 2021. The identification of more limiting scenarios has been documented within Dominion Energy's corrective action system. Fiber loads calculated with the most-limiting design basis scenario are provided below and affirm the conclusions of the April 15, 2021, response, i.e., maximum fiber loads are less than the applicable limits.

At MPS3, four RSS pumps supply both the RSS and ECCS cold leg injection during the recirculation phase. All four pumps take suction from a common source, and each train (consisting of two pumps) is powered by an independent emergency bus. One pump from each train supplies water directly to each spray header, and the other pump from each train supplies recirculation flow to both the suction of the safety injection and charging pumps (via the low pressure safety injection system) and the spray headers.

The supplied safety injection and charging pumps then provide flow to the reactor vessel.

Because of this RSS alignment, the ECCS flow rate and RSS flow rate are inherently coupled and directly proportional to one another. While scenarios exist in which spray flow could be lower than that analyzed, the ECCS flow rates for those cases would also be lower, and the resulting fiber loads would be less limiting than the case shown herein.

Table 1, below, gives the ECCS flow rate, containment spray flow rate, in-vessel fibrous debris load, and core inlet fibrous debris load at the time of tb1ock (143 minutes) for the limiting recirculation fiber loading case.

Out of the possible sump recirculation ECCS/RSS flow rate ratios, the analyzed case has the highest ECCS flow rate and largest ECCS flow to total flow ratio.

This results in the limiting core inlet fiber load and cumulative in-vessel fiber load.

Table 1: Maximum ECCS to RSS Flow Fiber Loads IN-VESSEL CORE INLET CASE ECCS [gpm]

SPRAY [gpm]

TOTAL [gpm]

FIBER LOAD FIBER LOAD

[g/FA]

[g/FA]

Maximum 3880.51 4058.86 7939.37 15.42 12.74 ECCS Note: The maximum in-vessel fiber load is taken at the time the sump fiber load is less than 1 % of the initial sump fiber load consistent with the termination criteria specified in Section 6.5.5 of WCAP-17788, Volume 1, Revision 1. The core inlet fiber load is taken at the time of tb1ock (i.e., the time at which complete core inlet blockage can be tolerated).

The resulting in-vessel and core inlet fibrous debris loads continue to meet the associated acceptance criteria at MPS3 for both RFA-2 and GAIA fuel products. Table 5 included in the MPS3 April 15, 2021, response is updated based on the revised limiting case presented above and is provided below as Table 2.

Page 7 of 9

Serial No.22-273 Docket No. 50-423 Table 2: Key Parameter Values for In-Vessel Debris Effects Parameter WCAP-17788 Value MPS3 Value Evaluation Maximum Total In-

< than the WCAP-Maximum in-vessel fiber Vessel Fiber Load Volume 1, Section 6.5 17788 value load is less than WCAP-(g/FA) 17788 limit.

Maximum Core Inlet Maximum core inlet fiber Fiber Load (g/FA)

Volume 1, Table 6-3 12.74 load is less than WCAP-17788 threshold.

Later switchover time results Minimum Sump in a lower decay heat at the Switchover Time 20 33 time of debris arrival, (min) reducing the potential for debris induced core uncovery and heatup.

Potential for complete core Minimum Chemical inlet blockage due to Precipitate Time 2.4 ( lblock) 24 (lchem) chemical product generation (hrs) would occur much later than assumed.

Latest hot leg switchover Maximum Hot Leg 24 (lchem) 5 occurs well before the Switchover Time (hr) earliest potential chemical product generation.

This value is not bounded by the WCAP-17788-P value Rated Thermal and is dispositioned in Power (MWt) 3658 3723 Section 3.n.13 of the MPS3 Final Supplemental Response dated April 15, 2021.

AFP resistance is less than MaximumAFP Volume4 Volume 4 the analyzed value, which Resistance Table 6-1 RAI Table 4.2-24 increases the effectiveness of the AFP.

Limiting ECCS ECCS recirculation flow rate Recirculation Flow Volume4 corresponding to the most Rate Resulting in 20.1 limiting fiber injection hot leg Maximum Core Inlet Table 6-1 break scenario is within the Fiber Load (gpm/FA) analyzed flow range.

Page 8 of 9

Serial No.22-273 Docket No. 50-423

4) The Millstone 3 evaluation described the acceptability of a minimum EGGS flow rate below the analyzed values. The condition was accepted based on the maximum flow case resulting in higher fiber loading. If the fiber mass for the high flow case remains significantly below the total in-vessel limit a more refined evaluation would not be required. However, if the fiber value approaches the limit a more refined analysis could be required. Provide the fiber value calculated for the high flow case.

Dominion Energy Response As indicated in Table 1 of the response to RAl-3, the limiting in-vessel fibrous debris load is calculated as 15.42 g/FA for a maximum ECCS flow of 3880.51 gpm (20.1 gpm/FA).

Page 9 of 9 Serial No.22-273 Docket Nos. 50-338/339 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE Virginia Electric and Power Company (Dominion Energy Virginia)

North Anna Power Station Units 1 and 2

Serial No.22-273 Docket Nos. 50-338/339 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE NORTH ANNA POWER STATION UNITS 1 AND 2 NRCComment 10 CFR 50.46 requires that plants maintain the ability to provide long-term core cooling following any initial LOCA response. To ensure that this cooling is available, licensees demonstrate that in-vessel fiber accumulation will not adversely affect the required function.

Norlh Anna In its most recent supplemental response for NRG Generic Letter 2004-02, dated February 25, 2021 (ADAMS Accession No. ML21056A557), Virginia Electric and Power Company provided information regarding the debris amounts used in the fiber penetration calculation for Norlh Anna Units 1 and 2 and explained the methodology used to determine the amount of fiber that could penetrate the emergency core cooling system strainer. Regarding the basis for some of the assumptions used in the calculations, discuss the following aspects of the calculation so that the NRG staff can understand how the in-vessel debris amounts were calculated:

1) The method for implementing the bed thickness correction is unclear. It seems that the Point Beach values corrected by Vogtle velocity data would be directly applicable to Norlh Anna up to the tested thickness. From that point on, the model would have to be extrapolated to a higher debris load. However, it appears to the staff that the in-vessel loading was simply calculated by multiplying the fine fiber amount by the corrected penetration fraction and dividing by the number of fuel assemblies. This may be appropriate if the correction factor was calculated correctly. To clarify the appropriateness of using a correction factor in lieu of extrapolation:
a. Was the correction for bed thickness applied to the thickness that will occur at the LHSI strainer or was it applied to the design basis load? Was it developed for the same load to which it was applied?

Dominion Energy Response The Point Beach Test 3 data was directly extrapolated for the North Anna Power Station (NAPS) maximum theoretical debris bed thickness of 1.066 inches, which was then used to determine the cumulative bypass fraction after applying a velocity correction factor associated with that bed thickness. The "design basis load" (fiber load transported to the Low Head Safety Injection (LHSI) strainer - 909 lbm) was used to calculate the bed thickness.

The correction for bed thickness was developed for the same load to which it was applied.

Page 1 of 6

Serial No.22-273 Docket Nos. 50-338/339

b. Provide the characteristics of the fiber in the Point Beach test compared to the characteristics of the fiber used to calculate the plant bed thickness for the penetration correction.

Explain why any differences would not have to be accounted for in the correction factor, if applicable.

Dominion Energy Response NAPS debris includes low density fiberglass (LDFG), Temp-Mat, and Paree, whereas the three Point Beach tests evaluated different debris compositions of fiberglass, mineral wool, and Temp-Mat. The NAPS cumulative bypass fraction is based on an extrapolated all-fiberglass Point Beach test (Test 3), which provided the most bypass at any given fiber bed thickness. In the NextEra Point Beach Letter No. 2017-0045, "Updated Final Response to NRC GL 2004-02," dated December 29, 2017 (ADAMS Accession No. ML17363A253), it was stated that the all-fiberglass test (Test 3) mathematical model may be conservatively used for any debris composition since it results in larger fiber penetration quantities than the other two models under identical test conditions.

Below is a plot of the three Point Beach tests (exact debris compositions were provided in Table 3 in the Dominion Energy Virginia final supplemental response for NAPS dated February 25, 2021), which indicates Test 3 as having the highest fiber penetration at any given bed thickness:

Point Beach - All Tests

?i:

~ 25 --------------------------1 0

B

~ 20 -

LL V)

V)

~ 15 +---~

+-----+---+----+----+---+---+--:=------:--=---I c::i E 10 ---~~

l-------+-------+----1-----1----=-.=-u:..:u.....i..._i

I u

0 0.2 0.4 0.6 0.8 1

1.2 1.4 1.6 Bed Thickness (in.)

I l

l

_f 1

I I

-t I Shows extrapolated data for T~st 3 compared with full data sets for Tests 1 & 21 Page 2 of 6

Serial No.22-273 Docket Nos. 50-338/339

c. Provide the assumptions used for flow rates in the fiber load calculation.

Dominion Energy Response It was assumed that both of the LHSI pumps would be operating, which provides the maximum design flow rate of 5,609 gpm for the LHSI strainer. For the Recirculation Spray (RS) strainer, it was assumed only one RS train was in service (i.e., one Outside Recirculation Spray (ORS) pump and one Inside Recirculation Spray (IRS) pump),

which provides a maximum flow rate of 7,015 gpm. However, the RS train flow rate is not used in the in-vessel debris loading calculation as it was conservatively set to 0 gpm. Assumed debris loading of the LHSI strainers (909 lbm) is 50% of the full (100%) debris loading of the RS strainers (1818 lbm).

d. Provide the basis for the total fiber load of 909 lb Loading. On which strainer(s) was this value used to develop the bed thickness correction? What is the basis for using this value considering that lower amounts or different sizes of fiber may transport for many scenarios?

Dominion Energy Response The 909 lbm total fiber load on the LHSI strainer is based on 50% of the design fiber load (1818 lbm) transported to the RS strainer. The calculated approach velocity and theoretical bed thickness are based on the LHSI strainer with the 909 lbm fiber load.

Using this full load is consistent with NRC Staff Review Guidance for In-Vessel Effects (ADAMS Accession No. ML19228A011), which states that "Licensees should assume the largest fibrous debris amount arriving at the sump strainer, including transport and erosion (based on the bounding fiber break for the plant)." The LDFG only Point Beach test results were selected for use to determine the NAPS cumulative bypass fraction for the 909 lbm fiber load since it demonstrated higher fiber penetration than the other test results using mixed debris compositions (see response to RAI 1 b above). The theoretical bed thickness was calculated by dividing the sum of the NAPS as-fabricated fiberglass volumes (see Table 3 in the NAPS February 25, 2021, Final Supplemental Response) by the effective strainer area. The theoretical bed thickness was then compared with the Point Beach Test 3 extrapolated test curve for determining the cumulative fiber bypass fraction, which then had a velocity correction factor applied associated with that bed thickness. Since the in-vessel effects analysis uses the velocity corrected cumulative bypass fraction of fiber, it accounts for the higher fiber penetration rates as the debris bed is building.

Page 3 of 6

Serial No.22-273 Docket Nos. 50-338/339

e. How is the initial sump fiber load of 219 lb used in the in-vessel debris loading calculation?

Dominion Energy Response The sump fiber load of 219 lbm is the total mass of fines available at the LHSI and RS strainers, and it is assumed that 50% of this mass (109.5 lbm) is at the LHSI strainer.

This 50% fiber load is used as a design input to calculate the post-Hot Leg Break fibrous debris load that accumulates in the core and at the core inlet. It is assumed the entire 109.5 lbm load of fibrous fines can be transported to the core and core inlet, and whose transport rate is dictated by the sump recirculation flow rate as well as the velocity corrected cumulative sump strainer bypass fraction.

f.

How are the bed thickness correction values calculated for each time step?

Dominion Energy Response Only the maximum full debris load theoretical bed thickness was calculated, which then uses the extrapolated and velocity corrected Point Beach Test 3 data to determine the total accumulated fiber bypass fraction of the 909 lbm fiber load.

g. If only a single thickness correction is used, provide a justification considering that bed thickness changes as debris arrives at the strainer.

Dominion Energy Response Since the in-vessel effects analysis uses the velocity corrected cumulative bypass fraction of fiber at the final theoretical bed thickness, it accounts for the higher fiber penetration rates as the debris bed is building.

2) Verify that the list of references in the submittal is correct and ensure that the citations in the text are correct. In the text, near the bottom of page 16 of 30, reference 4. 13 is to STP testing.

For example, in the list of references, 4.13 is to WCAP-17788.

References 4.4 through 4. 10 are referred to as Point Beach and Vogtle testing near the top of page 17 of 30. This appears to be an error.

Dominion Energy Virginia Response The list of references and their citations were reviewed and determined to be correct.

Regarding the STP testing, the citation on the bottom of page 16 of 30 of the NAPS February 25, 2021, final supplemental response is for reference 4.13, which is the correct reference as STP testing is discussed in WCAP-17788-P, Rev. 1. On the top of page 17 of 30, the citations for references 4.6 to 4.10 are correct for Point Beach and Vogtle testing.

References 4.4 and 4.5 are also appropriate, but it should have also been Page 4 of 6

Serial No.22-273 Docket Nos. 50-338/339 identified that AREVA/Alden testing for fiber bypass length distribution and size characterization were also reviewed to gain additional understanding of factors related to fiber bypass.

3) Confirm that RSS spray operates for all scenarios throughout the period during which transporl to the reactor is calculated. Are there scenarios where the spray flow would be zero as assumed in the analysis for conservatism? If spray is not in service more than 50% of the fiber could transporl to the Low Head Safety Injection (LHSI) strainer.

Dominion Energy Response Sprays in containment operate for all scenarios throughout the period during which transport to the reactor is calculated. For conservatism, spray flow is assumed to be zero gpm within the in-vessel debris transport calculation. This ensures that all fiber that is not caught on the sump screen is injected into the reactor vessel instead of being diverted to the RS strainer.

The Quench Spray (QS) system at NAPS is actuated upon receipt of a Containment Depressurization Actuation (CDA) signal, indicating a breach in the primary system pressure boundary (e.g., a LOCA). The Refueling Water Storage Tank (RWST) is the source of suction for the QS system. The QS system is comprised of two independent QS flow paths, pumped by two independent pumps from the RWST to spray rings inside of containment. While the QS system operates, RWST level continues to decrease due to QS flow as well as Safety Injection (SI) flow into the RCS. Containment sump level will continue to increase as inventory accumulates in the sump. No credit for QS is taken in the in-vessel debris analysis as the QS system does not take suction from the containment sump.

The RS system at NAPS is activated on a CDA signal coincident with RWST level less than 60%. The RS system is comprised of three interacting subsystems: IRS, ORS, and Casing Cooling (CC). Both IRS and ORS subsystems consist of two trains, each with approximately 50% capacity, that pump the sump water resulting from the accident through heat exchangers to spray headers located in the containment. The pumps for two trains are inside the containment (IRS) and two are outside (ORS). All four trains are independent of each other. One IRS and ORS train is powered by one emergency bus while the other IRS and ORS train is powered by a separate/independent emergency bus.

The CC subsystem provides cooler borated water to the suction of the ORS pumps to provide adequate NPSH for the ORS pumps. The CC subsystem is not credited in the in-vessel debris analysis as the CC system does not interface with the containment sump.

The LHSI pumps initially take suction from the RWST. Once the RWST depletes to 16%,

the automatic recirculation mode transfer (RMT) is activated which redirects LHSI suction from the RWST to the containment sump. Therefore, both IRS and ORS have been Page 5 of 6

activated prior to sump switchover for the ECCS pumps.

Serial No.22-273 Docket Nos. 50-338/339 As such, there is non-zero spray flow throughout the LOCA event. A scenario where spray flow is zero would necessitate the failure of all trains across the QS and RS systems or the loss of both emergency buses which are not credible scenarios for the in-vessel debris analysis.

Page 6 of 6 Serial No.22-273 Docket Nos. 50-280/281 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE

[Non-Proprietary]

Virginia Electric and Power Company (Dominion Energy Virginia)

Surry Power Station Units 1 and 2

Serial No.22-273 Docket Nos. 50-280/281 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2004-02 FINAL SUPPLEMENTAL RESPONSE SURRY POWER STATION UNITS 1 AND 2 NRCComment 10 CFR 50.46 requires that plants maintain the ability to provide long-term core cooling following any initial LOCA response. To ensure that this cooling is available, licensees demonstrate that in-vessel fiber accumulation will not adversely affect the required function.

Surry In its most recent supplemental response for NRG Generic Letter 2004-02, dated February 25, 2021 (ADAMS Accession No. ML21056A541), Virginia Electric and Power Company provided information regarding the debris amounts used in the fiber penetration calculation for Surry Units 1 and 2 and explained the methodology used to determine the amount of fiber that could penetrate the emergency core cooling system strainer.

Regarding the assumptions used in the calculations, discuss the following aspects of the calculation so that the NRG staff can understand how the in-vessel debris amounts were calculated:

1) The method for implementing the bed thickness correction is unclear. It seems that the Point Beach values corrected by Vogtle velocity data would be directly applicable to Surry up to the tested thickness. From that point on, the model would have to be extrapolated to a higher debris load. However, it appears to the staff that the in-vessel loading was simply calculated by multiplying the fine fiber amount by the corrected penetration fraction and dividing by the number of fuel assemblies.

This may be appropriate if the correction factor was calculated correctly. The items below should be considered as appropriate.

a. Was the correction for bed thickness applied to the thickness that will occur at the LHSI strainer or was it applied to the design basis load? Was it developed for the load to which it is applied?

Dominion Energy Response The Point Beach Test 3 data was directly utilized for the Surry Power Station (SPS) maximum theoretical debris bed thickness of 0.382 inches, which was then used to determine the cumulative bypass fraction after applying a velocity correction factor associated with that bed thickness. The "design basis load" (fiber load transported to the Low Head Safety Injection (LHSI) strainer - 526.08 lbm) was used to calculate the bed thickness. The correction for bed thickness was developed for the same load to which it was applied.

Page 1 of 8

Serial No.22-273 Docket Nos. 50-280/281

b. Provide the characteristics of the fiber in the Point Beach test compared to the characteristics of the fiber used to calculate the plant bed thickness for the penetration correction.

Explain why any differences would not have to be accounted for in the correction factor, if applicable.

Dominion Energy Response SPS debris includes Low Density Fiberglass (LDFG), Temp-Mat, and Asbestos whereas the three Point Beach tests evaluated different debris compositions of fiberglass, mineral wool, and Temp-Mat. The SPS cumulative bypass fraction is based on an all-fiberglass Point Beach test (Test 3), which provided the most bypass at any given fiber bed thickness. In the NextEra Point Beach Letter No. 2017-0045, "Updated Final Response to NRC GL 2004-02," dated December 29, 2017 (ADAMS Accession No. ML17363A253), it was stated that the all-fiberglass test (Test 3) mathematical model may be conservatively used for any debris composition since it results in larger fiber penetration quantities than the other two models under identical test conditions.

Below is a plot of the three Point Beach tests (exact debris compositions were provided in Table 3 in the Dominion Energy Virginia final supplemental response dated February 25, 2021 ), which indicates Test 3 as having the highest fiber penetration at any given bed thickness:

Point Beach - All Tests 35 30

~

'°; 25 0

+:

u

~ 20 u..

V)

V)

~ 15 ca E 10

J u

5 0

0 0.2 0.4 0.6 0.8 1

1.2 1.4 1.6 Bed Thickness (in.)

I J

I l

I 1 Shows extrapolated data for Test 3 compared with full data sets for Tests 1 & 2 Page 2 of 8

Serial No.22-273 Docket Nos. 50-280/281

c. Provide the assumptions used for flow rates in the fiber load calculation.

Dominion Energy Response It was assumed that both of the LHSI pumps would be operating, which provides the maximum design flow rate of 4,100 gpm for the LHSI strainer. For the Recirculation Spray (RS) strainer, it was assumed only one RS train was in service (i.e., one Outside Recirculation Spray (ORS) pump and one Inside Recirculation Spray (IRS) pump),

which provides a maximum flow rate of 6751 gpm. However, the RS train flow rate is not used in the in-vessel debris loading calculation as it was conservatively set to 0 gpm. Assumed debris loading of the LHSI strainers is 40% of the full (100%) debris loading of the RS strainers (1230.7 lbm, plus additional fiber added for conservatism for a total load of 1315.2 lbm).

d. What does the total fiber load of 526. 08 lb represent?

Loading on which strainer(s)? Was this value used to develop the bed thickness correction? If yes, what is the basis for using this value considering that lower amounts or different sizes of fiber may transport for many scenarios, debris characteristics, and the debris generation and transport assumptions in the analysis?

Dominion Energy Response The 526.08 lbm total fiber load on the LHSI strainer is based on 40% of the design fiber load (1230.7 lbm, plus additional fiber added for conservatism for a total load of 1315.2 lbm) transported to the RS strainer. The calculated approach velocity and theoretical bed thickness are based on the LHSI strainer with the 526.08 lbm fiber load. Using this full load is consistent with NRG Staff Review Guidance for In-Vessel Effects (ADAMS Accession No. ML19228A011), which states that "Licensees should assume the largest fibrous debris amount arriving at the sump strainer, including transport and erosion (based on the bounding fiber break for the plant)." The LDFG only Point Beach test results were selected for use to determine the Surry cumulative bypass fraction for the 526.08 lbm fiber load since it demonstrated higher fiber penetration than the other test results using mixed debris compositions (see response to RAI 1b above). The theoretical bed thickness was calculated by dividing the sum of the SPS as-fabricated insulation volumes (see Table 3 in the SPS February 25, 2021, Final Supplemental Response) by the effective strainer area. The theoretical bed thickness was then compared with the Point Beach Test 3 test curve for determining the cumulative fiber bypass fraction, which then had a velocity correction factor applied associated with that bed thickness. Since the in-vessel effects analysis uses the velocity corrected cumulative bypass fraction of fiber, it accounts for the higher fiber penetration rates as the debris bed is building.

Page 3 of 8

Serial No.22-273 Docket Nos. 50-280/281

e. How is the initial sump fiber load of 56. 98 lb. used in the in-vessel debris loading calculation?

Dominion Energy Response The sump fiber load of 142.46 lbm is the total mass of fines available at the LHSI and RS strainers, and it is assumed that 40% of this mass (56.98 lbm) is at the LHSI strainer. This 40% fiber load is used as a design input to calculate the post-Hot Leg Break fibrous debris load that accumulates in the core and at the core inlet. It is assumed the entire 56.98 lbm load of fibrous fines can be transported to the core and core inlet, and whose transport rate is dictated by the sump recirculation flow rate as well as the velocity corrected cumulative sump strainer bypass fraction.

f.

How are the bed thickness correction values calculated for each time step?

Dominion Energy Response Only the maximum full debris load theoretical bed thickness was calculated, which then uses the extrapolated and velocity corrected Point Beach Test 3 data to determine the total accumulated fiber bypass fraction of the 526.08 lbm fiber load.

g. If only a single thickness correction is used, provide a justification considering that bed thickness changes as debris arrives at the strainer.

Dominion Energy Response Since the in-vessel effects analysis uses the velocity corrected cumulative bypass fraction of fiber at the final theoretical bed thickness, it accounts for the higher fiber penetration rates as the debris bed is building.

2) Verify that the list of references in the submittal is correct and ensure that the citations in the text are correct. In the text, near the bottom of page 18 of 37, reference 4.15 is to STP testing.

However, in the list of references, 4. 15 appears to be a Surry calculation. References 4.4 through 4. 10 are referred to as Point Beach and Vogtle testing near the top of page 19 of 37. This appears to be an error.

Dominion Energy Response The list of references and their citations within the text were reviewed. On the bottom of page 18 of 37, with regard to the STP testing, the citation is for reference 4.15, but should have been for reference 4.14, which is the correct reference as STP testing is discussed in WCAP-17788-P, Rev. 1. On the top of page 19 of 37, the citations for references 4.6 to 4.10 are correct for Point Beach and Vogtle testing. References 4.4 and 4.5 are also appropriate, but it should have also been identified that AREVA/Alden testing for fiber Page 4 of 8

Serial No.22-273 Docket Nos. 50-280/281 bypass length distribution and size characterization were also reviewed to gain additional understanding of factors related to fiber bypass.

3) Confirm that RSS spray operates for all scenarios throughout the period during which transport to the reactor is calculated. Are there scenarios where the spray flow would be zero as assumed in the analysis for conservatism? If spray is not in service more than 40% of the fiber could transport to the LHSI strainer.

Dominion Energy Response Sprays in containment operate for all scenarios throughout the period during which transport to the reactor is calculated. For conservatism, spray flow is assumed to be zero gpm within the in-vessel debris transport calculation. This ensures that all fiber that is not caught on the sump screen is injected into the reactor vessel instead of being diverted to the RS strainer.

The Containment Spray (CS) system at SPS is actuated upon receipt of a Consequence Limiting Safeguards (CLS) signal, indicating a breach in the primary system pressure boundary (e.g., a LOCA). The Refueling Water Storage Tank (RWST) is the source of suction for the CS system. The CS system is comprised of two independent CS flow paths, pumped by two independent pumps from the RWST to spray rings inside of containment. While the CS system operates, RWST level continues to decrease due to CS flow, as well as safety injection (SI) flow into the RCS. Containment sump level will continue to increase as inventory accumulates in the sump. No credit for CS is taken in the in-vessel debris analysis as the CS system does not take suction from the containment sump.

The RS system at Surry is activated on a CLS signal coincident with RWST level less than 60%. The RS system is comprised of two interacting subsystems: IRS and ORS.

Both IRS and ORS subsystems consist of two trains, each with approximately 50%

capacity, that pump the sump water resulting from the accident through heat exchangers to spray headers located in the containment. The pumps for two trains are inside the containment (IRS) and two are outside (ORS). All four trains are independent of each other. One IRS and ORS train is powered by one emergency bus while the other IRS and ORS train is powered by a separate/independent emergency bus.

The LHSI pumps initially take suction from the RWST. Once the RWST depletes to 13.5%, automatic recirculation mode transfer (RMT) is activated which redirects LHSI suction from the RWST to the containment sump. Therefore, both IRS and ORS have been activated prior to sump switchover for the ECCS pumps.

As such, there is non-zero spray flow throughout the LOCA events. A scenario where spray flow is zero would necessitate the failure of all trains across the CS and RS systems or the loss of both emergency buses, which are not credible scenarios for the in-vessel debris analysis.

Page 5 of 8

Serial No.22-273 Docket Nos. 50-280/281 The NRG staff also identified that it requires additional information regarding the assumption for the debris limit assumed for the fuel assemblies. Please respond to the following:

4) In the submittal dated February 25, 2021, the licensee states that Framatome expects the fiber limit for the AGORA-5A-I fuel product with the coarse mesh TRAPPER debris filter to lie between the debris limits for HTP [High Thermal Performance] fuel with FUELGUARD debris filter and the GA/A fuel with the GRIP debris filter as noted in Reference 4. 11, Table 7-2. Explain why this limit would be expected to lie between the limits for the other two fuel debris filter designs or provide the relevant excerpt from Reference 4. 11 that provides this information.

Dominion Energy Response

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Page 7 of 8 Serial No.22-273 Docket Nos. 50-280/281

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Page 8 of 8 Serial No.22-273 Docket Nos. 50-280/281 Serial No.22-273 Docket Nos. 50-280/281 FRAMATOME INC. AFFIDAVIT FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE Virginia Electric and Power Company (Dominion Energy Virginia)

Surry Power Station Units 1 and 2

AFFIDAVIT

1.

My name is Morris Byram. I am Product Manager, Licensing & Regulatory Affairs for Framatome Inc. (Framatome) and as such I am authorized to execute this Affidavit.

2.

I am familiar with the criteria applied by Framatome to determine whether certain Framatome information is proprietary. I am familiar with the policies established by Framatome to ensure the proper application of these criteria.

3.

I am familiar with the Framatome information contained in the Document that is Attachment 4 with title "Response to Request for Additional Information Generic Letter 2004-02 Final Supplemental Response - Surry Power Station Units 1 and 2," to the Dominion Energy letter with Serial Number 22-273, RO, and referred to herein as "Document." Information contained in this Document has been classified by Framatome as proprietary in accordance with the policies established by Framatome for the control and protection of proprietary and confidential information.

4.

This Document contains information of a proprietary and confidential nature and is of the type customarily held in confidence by Framatome and not made available to the public. Based on my experience, I am aware that other companies regard information of the kind contained in this Document as proprietary and confidential.

5.

This Document has been made available to the U.S. Nuclear Regulatory Commission in confidence with the request that the information contained in this Document be withheld from public disclosure. The request for withholding of proprietary information is made in accordance with 10 CFR 2.390. The information for which withholding from disclosure is

requested qualifies under 10 CFR 2.390(a)(4) "Trade secrets and commercial or financial information."

6.

The following criteria are customarily applied by Framatome to determine whether information should be classified as proprietary:

(a)

The information reveals details of Framatome's research and development plans and programs or their results.

(b)

Use of the information by a competitor would permit the competitor to significantly reduce its expenditures, in time or resources, to design, produce, or market a similar product or service.

(c)

The information includes test data or analytical techniques concerning a process, methodology, or component, the application of which results in a competitive advantage for Framatome.

( d)

The information reveals certain distinguishing aspects of a process, methodology, or component, the exclusive use of which provides a competitive advantage for Framatome in product optimization or marketability.

(e)

The information is vital to a competitive advantage held by Framatome, would be helpful to competitors to Framatome, and would likely cause substantial harm to the competitive position of Framatome.

The information in this Document is considered proprietary for the reasons set forth in paragraph 6(c) and 6(d) above.

7.

In accordance with Framatome's policies governing the protection and control of information, proprietary information contained in this Document has been made available, on a limited basis, to others outside Framatome only as required and under suitable agreement providing for nondisclosure and limited use of the information.

8.

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

9.

The foregoing statements are true and correct to the best of my knowledge, information, and belief.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on: (11/3/2022)

By RAM MO r r.1 $ Digitally signed by BYRAM Morris Date: 2022.11.03 08:15:29 -07'00' (NAME)

Email: morris.byram@framatome.com Phone: 434-221-1082

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