ML24365A198

Units and 2 - Request for Approval of Alternative Request V-2 Use of Mechanical Agitation for Back Leakage Testing of Accumulator Discharge Check Valves

ML24365A198
Person / Time
Site:	Surry
Issue date:	12/30/2024
From:	James Holloway Virginia Electric & Power Co (VEPCO)
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
24-257
Download: ML24365A198 (1)

Text

VIRGINIA ELECTRIC AND PO',VER COMPANY RICHMOND, VIRGINIA 23261 December 30, 2024 10 CFR 50.55a Attn: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 Serial No.:

NRA/GDM:

Docket Nos.:

License Nos.:

24-257 RO 50-280 50-281 DPR-32 DPR-37 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION ENERGY VIRGINIA)

SURRY POWER STATION UNITS 1 AND 2 REQUEST FOR APPROVAL OF ALTERNATIVE REQUEST V-2 USE OF MECHANICAL AGITATION FOR BACK LEAKAGE TESTING OF ACCUMULATOR DISCHARGE CHECK VALVES In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, "Codes and Standards," paragraph (z)(2), Virginia Electric and Power Company (Dominion Energy Virginia) requests Nuclear Regulatory Commission (NRC) approval of the attached inservice testing (1ST) Alternative Request V-2 for Surry Power Station (SPS) Units 1 and 2. The proposed alternative request applies to the accumulator discharge check valves. Recent test history of the accumulator discharge check valves suggests mechanical agitation may be required to achieve satisfactory test leakage results going forward.

The proposed alternative request is provided in. An engineering assessment of the proposed mechanical agitation process to be used for the accumulator discharge check valves is provided in Attachment 2.

10 CFR 50.55a(f) requires nuclear power plant systems and components to meet the requirements of the American Society of Mechanical Engineers (ASME) Operation and Maintenance (OM) Code for inservice testing. The ASME Code of Record for SPS Units 1 and 2 is the ASME OM Code 2020 Edition. The applicable ASME OM Code requirements are provided in the attached alternative request.

Proposed Alternative Request V-2 has been approved by the Facility Safety Review Committee. NRC approval is requested by October 31, 2025.

Serial No.24-257 Docket Nos. 50-280/281 1ST Alternative Request V-2 Page 2 of 3 Should you have any questions or require additional information, please contact Mr. Gary D. Miller at (804) 273-2771.

Resp~~p 7

James E. Holloway Vice President - Nuclear Engineering and Fleet Support Regulatory commitments contained in this correspondence: None Attachments:

1. 1ST Alternative Request V Proposed Alternative to Use Mechanical Agitation for Performing Back Leakage Testing of Accumulator Discharge Check Valves

2. Engineering Assessment of Mechanical Agitation Process for Accumulator Discharge Check Valves

cc:

U.S. Nuclear Regulatory Commission, Region II Marquis One Tower 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, Georgia 30303-1257 Mr. L. John Klos - Surry NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, Maryland 20852 Mr. G. Edward Miller NRC Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, Maryland 20852-2738 NRC Senior Resident Inspector Surry Power Station Serial No.24-257 Docket Nos. 50-280/281 1ST Alternative Request V-2 Page 3 of 3 1ST ALTERNATIVE REQUEST V-2 Serial No.24-257 Docket Nos. 50-280/281 PROPOSED ALTERNATIVE TO USE MECHANICAL AGITATION FOR PERFORMING BACK LEAKAGE TESTING OF ACCUMULATOR DISCHARGE CHECK VALVES Virginia Electric and Power Company (Dominion Energy Virginia)

Surry Power Station Units 1 and 2

SURRY POWER STATION UNITS 1 AND 2 ALTERNATIVE REQUEST V-2 Serial No.24-257 Docket Nos 50-280/281 Proposed Alternative in Accordance with 10 CFR 50.55a(z)(2)

- Hardship Without a Compensating Increase in Quality and Safety -

1.

ASME Code Components Affected Component Component Description*

ASME Category ID Class 1/2-SI-107 "A" Accumulator Discharge Check Valve 1

C 1/2-SI-109 "A" Accumulator Cold Leg Admission Check Valve 1

C 1/2-SI-128 "B" Accumulator Discharge Check Valve 1

C 1/2-SI-130 "B" Accumulator Cold Leg Admission Check Valve 1

C 1/2-SI-145 "C" Accumulator Discharge Check Valve 1

C 1/2-SI-147 "C" Accumulator Cold Leg Admission Check Valve 1

C

• Each valve in this table is a 12-inch Anchor Darling 304 stainless steel swing check valve.

Function:

The Safety Injection (SI) Accumulator Discharge Check Valves and the Accumulator Cold Leg Admission Check Valves (collectively, ADCVs) together make a series pair check valve configuration where at least one of the two valves establishes the Reactor Coolant (RC) pressure boundary for each of the three SI accumulators on each unit. These normally closed check valves open upon depressurization of the Reactor Coolant System (RCS) during a Loss of Coolant Accident (LOCA) to provide a flow path from the SI accumulators to the RCS cold legs.

The pressure boundary between the RCS and the accumulators is established by one of the two in series check valves during plant heat up following an outage.

If the valves do not seat properly, the plant cannot proceed to power operation.

Only one in series check valve is required for isolation, and, after the accumulators have discharged during an accident, the check valves do not have a closed safety function.

Each check valve in this series pair configuration is a pressure isolation valve (PIV); however, the valves are classified as Category C with exams controlled by the Check Valve Condition Monitoring program. Since Surry Power Station (SPS) Units 1 and 2 received their operating licenses in 1972 and 1973, respectively, they were not subject to later General Design Criteria Page 1 of 11

Serial No.24-257 Docket Nos 50-280/281 requirements, and their licensing bases do not require test configurations to test the valves individually. Reactor coolant leakage is considered to be an overall system leakage requirement and does not require any specific leakage limit to be assigned to any one valve. The June 12, 1987, SPS response to Generic Letter (GL) 87-06, "Periodic Verification of Leak Tight Integrity of Pressure Isolation Valves," identified these valves as PIVs; however, no leakage testing acceptance criteria were specified. Specifically, the response noted that, "The integrity of the primary coolant pressure boundary is periodically tested in accordance with Technical Specifications and ASME Section XI hydrostatic test requirements. This testing verifies the integrity of the boundary with the interfacing systems, but not the integrity of each of the individual valves which form the boundary."

2.

Applicable Code Edition and Addenda

American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code) 2020 Edition.

3.

Applicable Code Requirement

ASME OM Code, Subsection ISTC-5224, "Corrective Action," states, "If a check valve fails to exhibit the required change of obturator position, it shall be declared inoperable. A retest showing acceptable performance shall be run following any required corrective action before the valve is returned to service."

This paragraph also states, "Series valve pairs tested as a unit in accordance with ISTC-5223 that fail to prevent reverse flow shall be declared inoperable, and both valves shall be either repaired or replaced."

ASME OM Code, Mandatory Appendix II, 11-4000, "Condition Monitoring Activities," states, "Valve obturator movement during applicable test or examination activities shall be sufficient to determine the bidirectional functionality of the moving parts. A full open exercise test, or an open test to the position required to perform its intended function, is not required for this assessment."

4.

Reason for Request

The SPS Units 1 and 2 series pair ADCVs are not capable of being consistently tested individually. The piping configuration on the discharge of the accumulators is such that testing methodologies in the closed position are limited. A back leakage test is preferable to ensure that no inleakage to the accumulators will be present during power operation. The ADCVs receive a closed test every refueling outage and are partially flowed open at least every other refueling outage in accordance with their check valve condition monitoring plans. These swing check valves are installed horizontally, and the disk is mounted vertically which is perpendicular to the Page 2 of 11

Serial No.24-257 Docket Nos 50-280/281 pipe centerline. Due to this design, during valve closure the top of the swing check valve disk contacts the top of the seat, but the bottom of the disk is not always capable of achieving a proper seal with the seat without the full differential pressure of the RCS.

The series pair ADCVs are tested during startup from refueling outages (RFOs) at lower differential test pressures (starting around 300 psig). Back leakage testing of the ADCVs is accomplished by using pressure from the RCS for the valves connected to the loops, and Residual Heat Removal (RHR) system pressure for the valves located closest to the "B" and "C" accumulators. The presence of any back leakage is then measured by a flow indicator. Most ADCVs tested at the lower pressures meet the leakage rate acceptance criterion of two gallons per minute.

However, some ADCVs have required higher test pressures, between 900 and 2000 psig, to achieve acceptable leakage results. The test procedures allow testing at low or higher pressures. The RHR system discharges in between the series valve pairs associated with either the "B or "C" SI accumulators to provide cooling flow to the cold legs. For these ADCVs there are methods in place in the test procedure to determine which specific ADCV requires mechanical agitation.

The ADCVs associated with the "A" SI accumulator do not have any methods to make this determination.

In certain cases, mechanical agitation has been used to facilitate seating of a valve to achieve an acceptable back leakage test result.

Dominion Energy Virginia recognizes that mechanical agitation is a troubleshooting activity rather than a repair method and also recognizes that for series valve pairs tested as a unit that fail to prevent reverse flow, OM Code, ISTC-5224, "Corrective Action," requires the valve pair to be declared inoperable and to either be repaired or replaced. Consequently, if ADCV back leakage was identified in excess of the acceptance criterion, repair or replacement of the ADCV would be required, thus necessitating the reversal of SPS restart activities, including cooldown, depressurization, reduction of RCS water level, etc.

Therefore, compliance with ISTC-5224 to perform the repair or replacement activity for the valves listed in Section 1.0 of this request, as applicable, would cause a hardship or unusual difficulty without a compensating increase in the level of quality or safety. Dominion Energy Virginia is also aware of precedents where the NRG approved 1ST alternative requests to use mechanical agitation as a leakage test troubleshooting tool to facilitate valve seating and for deferring repair or replacement of certain check valves to the following RFO. See Section 8 below for a list of precedents.

5.

Proposed Alternative Dominion Energy Virginia is requesting an alternative to ISTC-5224 requirements as they relate to corrective action when the obturator position cannot be confirmed to be in the closed position, i.e., the valve must be declared inoperable, and a retest must be performed following any corrective action; series valve pairs that fail to prevent reverse flow shall be declared inoperable; and both valves shall be either Page 3 of 11

Serial No.24-257 Docket Nos 50-280/281 repaired or replaced. The proposed alternative is applicable to the valves listed in Section 1.0 of this alternative request.

Back leakage testing for the ADCVs occurs at low or high pressures to facilitate startup activities. When back leakage testing does not meet the acceptance criteria, the following actions will be taken:

Each ADCV, or series pair, that does not meet the back leakage test acceptance criteria will be declared inoperable and the failed ADCV, or series pair, will be entered into the site corrective action program, which will allow the provisions of this alternative to be invoked.

Rather than performing an ASME Code repair or replacement, the ADCV, or series pair, may be mechanically agitated. Attachment 2 provides a Dominion Energy Virginia engineering evaluation that determined using a 20-pound hammer to mechanically agitate the check valves in accordance with the restrictions specified therein will not cause any internal damage or degradation to the valves. For conservatism, mechanical agitation will be restricted to the use of a 15-pound hammer with the following instructions:

o To avoid preconditioning the check valves, obtain as-found test results and declare the valve(s) inoperable, as required. Use other methods to try to seat the valve prior to use of mechanical agitation, such as variance of pressure or venting.

o Visually inspect the valve body prior to the use of mechanical agitation and record any pre-existing damage, markings, or defects.

o Mechanical agitation of the check valve is to be performed by tapping the valve body using a 15-pound (maximum) rubber or dead blow hammer swung approximately 120 degrees about the elbow WITHOUT excessive use of the body to accelerate the hammer head. The diameter of the hammer face shall be 1/2 inch or greater.

o The surface to be mechanically agitated shall NOT include valve bolting or flanges. Only the lower two-thirds of the valve body shall be struck.

o The valve shall be visibly inspected after the application of mechanical agitation to ensure no physical external damage to the check valve has occurred.

o The valve shall only be struck one time with leakage reassessed prior to striking again.

o Should mechanical agitation need to be reapplied, the hammer can be applied to different areas of the valve body above minimum force within the noted limitations above.

After mechanical agitation, the valve will be retested using normal test procedures. The incremental agitation and testing process may be repeated until Page 4 of 11

Serial No.24-257 Docket Nos 50-280/281 back leakage test acceptance criteria are met or if it is determined that corrective action is required.

o If the back leakage or closure test meets the acceptance criteria, then the ADCV, or series pair, will be declared operable.

o If the back leakage or closure test does not meet the acceptance criteria, the ADCV, or series pair, as applicable, will be repaired or replaced during the outage of discovery.

If an ADCV, or series pair, as applicable, needs to be mechanically agitated and subsequently passes the back leakage or closure test, the ADCV, or series pair, will be repaired or replaced during the next applicable Unit's RFO.

When the ADCV, or series pair, is either repaired or replaced during the next outage, it must pass post-maintenance tests (including back leakage test, as applicable) before being declared operable.

The above controls will ensure mechanical agitation will only be applied to the valve body, and no edges or sharp points will be impacted. These controls will prevent damage to the valve and injury to personnel. Because mechanical agitation is not a repair or replacement activity, this alternative is needed to avoid potential unnecessary emergent demands on plant equipment, resources, and personnel. An evaluation of the mechanical agitation process is provided in Attachment 2. Using the provisions of this request as an alternative to the specific requirements of ISTC-5224, which have been identified as a hardship without compensating increase in quality and safety pursuant to 10 CFR 50.55(z)(2), will provide adequate indication of the function and operability of these ADCVs.

6.

Basis for the Proposed Alternative The acceptability of the proposed alternative is based on the following factors:

The ADCVs are a standard design check valve model for RCS system conditions and typically perform well until operation eventually results in degradation of the seating surfaces.

Back leakage testing requires the application of pressure from either the RCS or the RHR system. To test back leakage characteristics, any leakage is measured from a flow indicator located upstream of the check valves which would demonstrate quantifiable leakage past the check valves. The disks are mounted vertically so the top of the disk contacts the seat first but does not always seat properly at the bottom of the disk.

Unless there is a significant pressure differential across the seat, the disk may not be pushed into the seat with enough force to achieve full contact.

SPS has experienced problems achieving consistent differential pressure across the seats due to the original design of the piping configuration. It is believed the piping arrangement used to create the differential pressure across the valves Page 5 of 11

Serial No.24-257 Docket Nos 50-280/281 during testing was originally designed for RCS sampling. The needle valves in this test arrangement have a very small cross sectional flow area and are not capable of providing enough flow to create a large differential pressure across the ADCVs to consistently seat the valves. A design change was implemented on the "C" SI accumulator test loop configuration in the fall of 2022 to enhance seating of the ADCVs during the low pressure test by installing additional drain/test valves to allow a higher initial flow rate, which more rapidly establishes the differential pressure across 1-Sl-145 and 1-Sl-147. However, this design change has not improved testing capability.

Once the check valves are closed with an acceptable back leakage rate, the valves would not be required to open unless a large break loss of coolant accident (LBLOCA) occurred and would not be required to perform the RC pressure boundary or closure function again following a LBLOCA. Should a LBLOCA occur, the plant would be shut down for an extended period of time, which would allow the maintenance planned for the next refueling outage to be performed prior to startup following the LBLOCA.

A) Review of Test and Maintenance History for Valves in Section 1.0 Table V-2.1 Testing History of Unit 1 Valves (gpm)

Outage 1-SI-107 I 1-S1-109 1-SI-128 1-SI-130 1-SI-145 1-SI-147 1R32 0.0

>5 0.0 0.0 0.0 (Spring 2024) 0.01 1R31 0.0

>5 0.0 0.0 0.0 (Fall 2022) 0.01 1R30 0.0

>5 (Spring 2021) 0.0 0.0 0.0 0.01 4.75 0.0 1R29 4.82 (Fall 2019) 0.0 0.0 0.0 0.01 1R28

>5 0.0 0.0 0.0 0.0

{Spring 2018) 0.0 Page 6 of 11

Table V-2.1 Testing History of Unit 1 Valves (gpm)

Outage 1-SI-107 I 1-SI-109 1-SI-128 1-SI-130 1R27 0.0 0.0 0.0 (Fall 2016) 1R26 0.0 0.0 0.0 (Spring 2015) 1R25 0.0 0.0 0.0 (Fall 2013) 1R24 0.0 0.0 0.0 (Spring 2012) 1R23 0.0 0.0 0.0 (Fall 2010)

Serial No.24-257 Docket Nos 50-280/281 1-SI-145 1-SI-147 4.8 4.8 4.71 4.81 0.031-3 4.8 4.8 0.01 4.75 4.25 2.91 0.01 1 4.9 4.9 0.01 4.8 4.75 4.81 0.01 Note 1: This test was performed with a high pressure test method on the series pair at either 900 psig or 2000 psig.

Note 2: Indicates mechanical agitation was performed on the valve one time. After being agitated the valve was still not seating properly during the low pressure test. Valve was declared SAT when tested as a series pair.

1-Sl-147 is scheduled to be opened and inspected in the fall of 2025.

Note 3: After two unsuccessful attempts to seat the series pair valves at 900 psig, the back leakage test was performed again at 2000 psig after opening the "C" accumulator Discharge Isolation MOV to equalize the "C" accumulator pressure upstream of 1-Sl-145. After opening the MOV, the leak rate decreased to 0.0267 gpm.

Due to excessive performances of recirculation and sampling of the SI accumulator to maintain the level within Technical Specification requirements, 1-Sl-145 was mechanically agitated five times with monitoring of the inleakage rate after each attempt. The leak rate remained stable at 0.0266 gpm. Both 1-SI-145 and 1-Sl-147 were repaired in the following refueling outage.

Page 7 of 11

Maintenance History of Unit 1 Valves:

Serial No.24-257 Docket Nos 50-280/281 No major maintenance was identified for 1-Sl-107 or 1-Sl-109 going back to 1995.

1-Sl-128 was disassembled in February 1994. Valve seat was lapped.

1-Sl-130 was disassembled in March 1997. Valve was rebuilt.

1-Sl-145 was disassembled in September 1995 and found to be in good condition. Valve seat was lapped in March 1998. Valve was disassembled in April 2009 and shim clearance adjusted; disassembled in May 2018 and the seat was lapped; disassembled in November of 2022 and found SAT.

1-Sl-147 was disassembled in September 1995 and valve body seat and disk were cleaned; disassembled in March 1997 and seat was lapped; disassembled in October 1998 and blue check performed SAT; disassembled in May 2006 and new arm and disk assembled; disassembled in April of 2009 and new disk installed; new valve installed in November 201 O; disassembled valve in May 2018 and found a cracked disk, disk and hanger arm assembly were replaced; disassembly is currently scheduled for fall 2025 RFO.

Table V-2.2 Testing History of Unit 2 Valves (gpm)

Outage 2-SI-107 I 2-SI-109 2-SI-128 2-Sl-130 2-SI-145 2-SI-147 2R32 0.0 0.0 (Fall 2024) 1.7 a.a 0.7 2R31 0.0 0.0

{Spring 2023) 1.7 0.0 1.25 2R30 0.0 3.3 0.0 0.0 1.8 (Fall 2021) 0.01 2R29 0.0 0.0 1.35 0.0 1.0 (Spring 2020) 2R28 0.3 0.0 1.7 0.0 1.05 (Fall 2018) 2R27 0.9 0.6 1.7 0.65 1.2 (Spring 2017) 2R26 1.8 0.0 1.8 0.0 1.5 (Fall 2015)

Page 8 of 11

Table V-2.2 Serial No.24-257 Docket Nos 50-280/281 Testing History of Unit 2 Valves (gpm)

Outage 2-SI-107 l 2-SI-109 2-51-128 2-SI-130 2-SI-145 2-SI-147 2R25 0.0 0.0 1.0 0.0 0.5 (Spring 2014) 0.7 2.6 2R24 0.8 0.75 0.8 (Fall 2012) 0.01 0.0 2.4 0.5

>5.0 2R23 0.0 (Spring 2011) 0.61 0.61 Note 1: This test was performed with a high pressure test method on the series pair at either 900 psig or 2000 psig.

Maintenance History of Unit 2 Valves:

No major maintenance was identified for 2-SI-107, 2-SI-109, 2-SI-128, 2-SI-145, or 2-SI-147 going back to 1995.

2-SI-130 was disassembled and a new valve disk was installed in May 2008.

BJ Design of the Accumulator Discharge Check Valves Failure of a check valve disk to open (stuck closed), or detachment of the disk from valve internals, is normally due to service conditions and/or process fluid.

Most failures are associated with carbon steel valves in raw water systems where the disk is closed for long periods of time, allowing corrosion to bond the disk to other parts of the valve internals. Another failure mechanism is when the disk operates long-term in a less than full open position, allowing hinge pin wear in a raw water environment.

The process fluid for the ADCVs is borated water, which is maintained within strict chemistry and cleanliness standards. The valves are designed for service in a boric acid solution and are comprised of stainless steel materials. Because the conditions for corrosion are not present by design, and open position occurs a small percentage of the time, it is unlikely the disk will fail to open or become detached when flow is required.

Page 9 of 11

C)

Description of Check Valve Open Exercise Testing Serial No.24-257 Docket Nos 50-280/281 The ADCV open test is performed at least every other RFO as prescribed by the check valve condition monitoring plan. The partial open test is performed by discharging the contents of the accumulators through the ADCVs to demonstrate the valves are capable of performing their open safety functions. The ADCVs have consistently performed their open safety function with no issues identified.

SUMMARY

The subject ADCVs have an open safety function during accident conditions and a closed safety function during power operation. The ADCVs have historically proven to be reliable in performing these functions. The ADCVs only experience seating issues during back leakage testing, which takes place at a much lower pressure than when the ADCVs are performing their RC pressure boundary function. Furthermore, no issues have been identified with the ADCVs performing their open safety function.

Contingency work orders are in place to open and inspect any ADCV that fails an inservice back leakage test to determine if corrective maintenance is needed. There are no active preventative maintenance tasks in place for these valves because they have proven to be reliable in performing their safety functions and are not subject to inservice conditions that would cause degradation or wear on the valve internals. If a degradation mechanism were to be identified for these valves, a preventative maintenance task would be established on a periodic frequency to replace any internal components that exhibited excessive wear.

The proposed alternative would permit continued startup if any of the valves listed in Section 1.0 of this alternative request can demonstrate acceptable back leakage following mechanical agitation.

If any valve passes the back leakage test after mechanical agitation is applied, SPS will perform corrective maintenance during the next refueling outage after mechanical agitation has been applied. The valve would only be acceptable for normal operation for one additional cycle and only if the final back leakage test meets the prescribed acceptance criteria.

Should any of the valves in Section 1.0 fail to meet the acceptance criteria, the valve, or series pair, shall be declared inoperable.

Should any of the valves fail to meet the test requirements when verifying the closed position, mechanical agitation will be used to assist in trouble shooting the failure.

Mechanical agitation assists in ascertaining the condition of the valve seat. Prior to using mechanical agitation, SPS will obtain as-found test results and apply other measures, where possible, such as varying pressure or venting, to seat the check valve.

An engineering evaluation has been performed (Attachment 2) that provides a reasonable determination that the mechanical agitation process will not create damage to the valve. Mechanical agitation may be performed by tapping the valve body using a 15-pound (maximum) rubber mallet or soft-faced dead blow mallet Page 10 of 11

Serial No.24-257 Docket Nos 50-280/281 swung at a maximum of approximately 120 degrees about the elbow, without excessive use of the body to accelerate the hammer head. The surface to be agitated will not include any bolting or flanges. The valve will be visibly inspected prior to and after the mechanical agitation to ensure that no physical external damage to the check valve has occurred.

During the next RFO, the valve, or series pair, will be disassembled and inspected and will be repaired or replaced as necessary.

Post maintenance testing will be performed in accordance with the ASME OM requirements.

The NRG previously approved a similar alternative request for the SPS Units 1 and 2 sixth 1ST interval for the testing of PIVs and the use of mechanical agitation to resolve any closure issues. NRG approval was granted pursuant to 10 GFR 50.55a(z)(2) on the basis of being a hardship without a compensating increase in quality and safety.

The NRG further concluded that granting the relief did not endanger life or property or the common defense and security of the public. (See Section 8.)

7.

Duration of Proposed Alternative The proposed alternative described in Alternative Request V-2 will be used for the SPS Units 1 and 2 Sixth and Seventh lnservice Testing Interval.

8.

Precedents 9.1 A similar alternative request was submitted for Surry Power Station, Units 1 and 2, Alternative Request V-1, approved by the NRG by letter dated August 12, 2024 (ADAMS Accession No. ML24164A001).

9.2 A similar alternative request was submitted by TVA for the Sequoyah Nuclear Plant, Units 1 and 2, Relief Request RV-02, dated March 15, 2022, and supplemented June 28, 2022 (ADAMS Accession Nos. ML22074A315 and ML22179A357, respectively) and approved by the NRG by letter dated September 29, 2022 (ADAMS Accession No. ML22263A375).

Page 11 of 11 Serial No.24-257 Docket Nos 50-280/281 ENGINEERING ASSESSMENT OF MECHANICAL AGITATION PROCESS FOR ACCUMULATOR DISCHARGE CHECK VALVES Virginia Electric and Power Company (Dominion Energy Virginia)

Surry Power Station Unit 1 and Unit 2

Serial No.24-257 Docket Nos. 50-280/281 1ST Alternative Request V-2 ENGINEERING ASSESSMENT OF MECHANICAL AGITATION PROCESS FOR ACCUMULATOR DISCHARGE CHECK VALVES SURRY POWER STATION UNITS 1 AND 2 Purpose The purpose of this assessment is to evaluate the use of mechanical agitation for purposes of seating the Accumulator Discharge Check Valves (ADCVs) following failed back leakage tests, as well as the structural impact from mechanical agitation using methods that are consistent with those previously approved by NRC Safety Evaluations

[1) & [2]. Once approved for use at Surry Power Station (SPS), this mechanical agitation methodology could be used when necessary for back leakage testing of the ADCVs.

Methodology Existing documented bases from SPS as to why the use of a 20-pound hammer for purposes of mechanically agitating ADCVs is reviewed and augmented by additional assessment herein. Specifically, to evaluate force imparted by use of the 20-pound hammer during the last application of mechanical agitation to seat ADCVs, a similar methodology as was used by Tennessee Valley Authority (TVA) to estimate stresses induced in the body of the valves for supporting their Alternative Request RV-02 for the Sequoyah Nuclear Plant [2] is used. The TVA method estimates induced impact force and localized stress using an equation for a pendulum.

Employing Section 16.4 of Roark's Formulas for Stress and Strain [3], the method assumes the stress resulting from the impact of the falling hammer as two times the stress produced by its weight applied as static load. This implies a dynamic load factor of two; however, for conservatism, a factor of four is used to account for probable variations in hammer velocity. Localized stress induced in the valve wall is estimated (ignoring any dampening effects), also using Roark's Formulas [3], Table 11.2, Case 17, assuming a circular flat plate using a radius of the valve length and the thickness equal to a conservatively assumed wall thickness with an applied force. Again, this approach was submitted to the NRC and concluded to provide reasonable assurance that use of mechanical agitation won't damage the impacted check valves.

Recommendations herein are based on NRG-approved methods documented in the revised NRC Safety Evaluation for Sequoyah Nuclear Plant [2] and the NRC Safety Evaluation for SPS [1].

Discussion Valve design information for the Units 1 and 2 ADCVs was reviewed, and it was confirmed that these valves are 12-inch Anchor Darling swing check valves. Valve material is Type 304 Stainless Steel, and wall thickness can be conservatively estimated as 1.3 inches, which is consistent with the TVA Engineering Work Request that was audited by the NRC Page 1 of 3

Serial No.24-257 Docket Nos. 50-280/281 1ST Alternative Request V-2 as part of the TVA alternative request [2]. Assuming similar parameters as TVA in [2],

the force imparted using the same load increase factor, is only about 115 lbs.

For conservatism, this force is doubled in this evaluation.

Mass of the hammer (m):

20 lbm Length of the pendulum (L):

3 ft Angle of translation (a =120° - 90°):

30 deg Arc length (A = n*L *[90°+0)/180°)

6.283 ft Height hammer falls (h = L + Lsina) 4.5 ft Gravitational constant (g) 32.3 lbm-ft/lbf-s2 Hammer velocity at impact (v =

17.024 fps

[2*g*h]0.5) 204.282 ips Est. time to make contact (t = A/v) 0.369 s Acceleration at impact (a= v/t) 553.477 in/s2 Max Force @ contact (F = 4 x m

• a) 114.7103 lbf Using a maximum force of 230 lbf (conservative, see above), a contact radius (r) of 0.25 inch (which should be conservative for a 20-pound hammer), a valve length of a= 29 inches (conservative and consistent with TVA), and a Poisson's Ratio of v = 0.3, the moment applied using Roark's Formulas for a Flat Circular Plate of Constant Thickness (Table 11.2) [3] is estimated to be:

M1 = (Force/4rr) * (1 +v)

• ln(a/r) = 113.105 in-lbf / in Based on the above unit radial bending moment, calculated induced stress is:

Stress= (6

• M1) / t2 =.4 ksi << Allowable Stress@ 600°F for SA-351, CF8 (16.6 ksi)

Therefore, conservatively assuming a 230-pound force imparted to the valve body over a limited area, stresses in the valve body remain very low, which is a good indicator that no damage would be expected.

A previous engineering evaluation further reinforces why no damage would be expected 1 M is the unit radial bending moment, a is the outer radius of the circular plate, t is the thickness of plate, and r is the contact radius as defined in Roark's Formula, Table 11.2, Case 17 (3). It is conservative to use rand the total valve length, which is also consistent with TVA.

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Serial No.24-257 Docket Nos. 50-280/281 1ST Alternative Request V-2 using a 20-pound hammer to agitate the valve for purposes of seating the disk. That evaluation documents that Anchor Darling was contacted and expressed no concern for damaging the valve as a consequence of this practice.

SPS operating history also corroborates lack of damage. It is also noted that guidance provided in the previous engineering evaluation is intended to minimize the potential to damage the valve. The guidance recommends striking the thickest portion of the valve body while avoiding point contact, not to strike the bonnet, and, if practical, the use of a second piece of metal plate to distribute the impact force.

Conclusions Past mechanical agitation of ADGVs has been evaluated using the NRG approved methodology in [1] and [2], and it is concluded that previous methods used with a 20-pound hammer would not have damaged the valve. For conservatism, future mechanical agitation of the ADGVs will be restricted to the use of a 15-pound hammer.

Upon approval of this proposed alternative, mechanical agitation will follow the strict guidance given in Section 5 of this proposed alternative on the ADGVs.

References

[1]

NRG ADAMS Accession Number ML24164A001 (8/13/2024)-Surry Power Station, Unit Nos. 1 and 2 - Proposed Alternative Relief Request V-1 lnservice Testing of Pressure Isolation Valves (EPID L-2023-LLR-0060).

[2]

NRG ADAMS Accession Number ML22304A186 (12/1/22) -

Revised Safety Evaluation by the Office of Nuclear Reactor Regulation for Alternative Request RV-02 Related to the Fourth 10-year lnservice Testing Program Interval, Tennessee Valley Authority, Sequoyah Nuclear Plant, Units 1 and 2, Docket Numbers 50-327 and 50-328 (EPID No. L-2022-LLR-0034).

[3]

Roark's Formulas for Stress and Strain, 7th Edition, Warren G. Young and Richard G. Budynas, McGraw-Hill 2002.

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