ML22342B248
| ML22342B248 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 12/08/2022 |
| From: | James Holloway Virginia Electric & Power Co (VEPCO) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 22-374 | |
| Download: ML22342B248 (1) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 December 8, 2022 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNIT 1 ASME OM CODE INSERVICE TESTING PROGRAM 10 CFR 50.55a Serial No.:
22-374 NRA/GDM:
RO Docket No.: 50-280 License No.: DPR-32 REQUEST FOR APPROVAL OF ALTERNATIVE REQUEST V-01 USE OF MECHANICAL AGITATION PROCESS FOR PRESSURE ISOLATION VALVE 1-51-241 SEAT LEAKAGE TESTING 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 (AR) for Surry Power Station (SPS) Unit 1. The proposed 1ST AR applies to SPS Unit 1 pressure isolation valve (PIV) 1-Sl-241, which is a Low Head Safety Injection (LHSI) to Reactor Coolant System (RCS) cold leg isolation check valve.
Maintenance on 1-Sl-241 was planned and scheduled to be performed during the current SPS Unit 1 refueling outage (RFO); however, tagout isolation boundary leakage prohibited performance of the maintenance activity.
Recent test history of 1-Sl-241 suggests mechanical agitation may be required to achieve satisfactory test leakage results.
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 Unit 1 is the ASME OM Code 2004 Edition through 2006 Addenda.
The applicable ASME OM Code requirements associated with the request are:
Subsection ISTC-3630, "Leakage Rate for Other Than Containment Isolation Valves," requires testing of PIVs to verify their seat leakages are within acceptable limits and also states, "Valve closure before seat leakage testing shall be by using the valve operatorwith no additional closing force applied."
Subsection ISTC-3630(a) requires pressure isolation valve (PIV) leakage rate testing to be conducted at least once every two years.
Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request Page 2 of 4 Subsection ISTC-3630(f),
"Corrective Action,"
- states, "Valves or valve combinations with leakage rates exceeding values specified by the Owner per ISTC-3630(e) shall be declared inoperable and either repaired or replaced."
Subsection ISTC-5221 (a)(1 ), "Valve Obturator Movement," states, "Check valves that have a safety function in both the open and closed directions shall be exercised by initiating flow and observing that the obturator has traveled to either the full open position or to the position to perform its intended function(s) (see ISTA-1100), and verify on cessation or reversal of flow, the obturator has traveled to the seat."
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."
As discussed in Attachment 1, compliance with Subsections ISTC-3630, ISTC-3630(f), ISTC-5221 (a)(1 ), and ISTC-5224 for PIV 1-Sl-241 would cause a hardship or unusual difficulty without a compensating increase in the level of quality or safety to perform the repair or replacement activity required by ISTC-3630(f). Specifically, SPS Unit 1 is currently in an RFO, and PIV leakage testing is performed at the completion of the RFO as part of unit startup activities. Consequently, if PIV seat leakage were identified in excess of the acceptance criterion, repair/replacement of the PIV would be required thus necessitating the reversal of SPS Unit 1 startup activities, including cooldown, depressurization, reduction of RCS water level, etc.
By letter dated March 15, 2022 (ADAMS Accession No. ML22074A315), as supplemented by letter dated June 28, 2022 (ADAMS Accession No. ML22179A357),
Tennessee Valley Authority (TVA) recently submitted a similar AR (RV-02) for the Sequoyah Nuclear Plant (SQN). NRC approved the SQN AR in their Safety Evaluation Report (SER) dated September 29, 2022 (ADAMS Accession No. ML22263A375). The information included in these documents, as well as the associated NRC SQN AR Audit Summary dated September 28, 2022 (ADAMS Accession No. ML22263A008), was appropriately considered in the development of the SPS Unit 1 AR V-01. As the SQN AR was just recently approved by the NRC, adequate time to prepare a similar "all-inclusive" PIV submittal in advance was not possible. A Dominion Energy fleet AR addressing the entire PIV population is currently planned for submittal in 2023.
The proposed alternative V-01 is provided in Attachment 1 and has been approved by the Facility Safety Review Committee.
Verbal authorization of the proposed alternative is requested by 0900 hrs on December 9, 2022, to support completion of the 1-Sl-241 seat leakage test in support of Unit 1 startup activities.
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request Page 3 of 4 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 Regulatory commitments contained in this correspondence: None Attachments:
- 1. Alternative Request V Use of Mechanical Agitation Process for Pressure Isolation Valve 1-Sl-241 Seat Leakage Testing
- 2. Engineering Assessment of Mechanical Agitation Process for 1-Sl-241
cc:
U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303 Mr. John J. 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 - North Anna NRC Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, Maryland 20852 NRC Senior Resident Inspector Surry Power Station Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request Page 4 of 4 Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 ALTERNATIVE REQUEST V-01 USE OF MECHANICAL AGITATION PROCESS FOR PRESSURE ISOLATION VALVE 1-51-241 SEAT LEAKAGE TESTING Virginia Electric and Power Company (Dominion Energy Virginia)
Surry Power Station Unit 1
Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 Alternative Request for Use of Mechanical Agitation Process on Pressure Isolation Valve 1-SI-241 Seat Leakage Testing Alternative Request V-01 SURRY POWER STATION UNIT 1 DOMINION ENERGY VIRGINIA
--In Accordance with 10 CFR 50.55a(z)(2), Hardship or Unusual Difficulty without a Compensating Increase in the Level of Quality and Safety--
- 1. ASME OM Code Component Affected Component Description Valve Type OM Code OM Component ID Class Category Low Head Safety Injection 6" Velan (LHSI) to Reactor Coolant AC 1-Sl-241 System (RCS) Cold Leg Swing Check 1
Isolation Check Valve Valve
3. Applicable Code Requirements
- ASME OM Code, Subsection ISTC-3630, "Leakage Rate for Other Than Containment Isolation Valves," states "Valve closure before seat leakage testing shall be by using the valve operator with no additional closing force applied."
- ASME OM Code, Subsection ISTC-3630(a) requires pressure isolation valve (PIV) leakage rate testing to be conducted at least once every two years.
- ASME OM Code, Subsection ISTC-3630(f), "Corrective Action," states "Valves or valve combinations with leakage rates exceeding values specified by the Owner per ISTC-3630(e) shall be declared inoperable and either repaired or replaced."
- ASME OM Code, Subsection ISTC-5221(a)(1), "Valve Obturator Movement,"
states, "Check valves that have a safety function in both the open and closed Page 1 of 10
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 directions shall be exercised by initiating flow and observing that the obturator has traveled to either the full open position or to the position to perform its intended function(s) (see ISTA-1100), and verify on cessation or reversal of flow, the obturator has traveled to the seat."
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."
4. Reason for Request
Background - Surry Power Station (SPS) Unit 1 has requirements for leakage rate testing of Pressure Isolation Valves (PIV) in the Technical Specifications (TS) and the lnservice Testing (1ST) Program.
TS Requirements - SPS TS 3.1.C, "RCS Operational Leakage," has the following requirements related to PIVs:
5.a. Prior to going critical all primary coolant system pressure isolation valves listed below shall be functional as a pressure isolation device, except as specified in 3.1.C.5.b. Valve leakage shall not exceed the amounts indicated.
Max. Allowable Description Unit 1 Unit 2 Leakage (see note (a) below)
Loop A, Cold Leg 1-Sl-79, 1-Sl-241 2-Sl-79, 2-Sl-241 s; 5. 0 gpm for each valve Loop B, Cold Leg 1-Sl-82, 1-Sl-242 2-Sl-82, 2-Sl-242 Loop C, Cold Leg 1-Sl-85, 1-Sl-243 2-Sl-85, 2-Sl-243
- b. If Specification 3.1.C.5.a cannot be met, an orderly shutdown shall be initiated and the reactor shall be in HOT SHUTDOWN within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
Note (a):
- 1.
Leakage rates less than or equal to 1. 0 gpm are considered acceptable.
- 2.
Leakage rates greater than 1.0 gpm but less than or equal to 5.0 gpm are considered acceptable if the latest measured rate has not exceeded the rate determined by the previous test by an amount that reduces the margin between measured leakage rate and the maximum permissible rate of 5. 0 gpm by 50% or greater.
Page 2 of 10
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01
- 3. Leakage rates greater than 1.0 gpm but less than or equal to 5.0 gpm are considered unacceptable if the latest measured rate exceeded the rate determined by the previous test by an amount that reduces the margin between measured leakage rate and the maximum permissible rate of 5.0 gpm by 50% or greater.
- 4. Leakage rates greater than 5.0 gpm are considered unacceptable.
Item 19 in TS Table 4.1-2A, "Minimum Frequency for Equipment Tests," provides the testing frequency for the PIVs as follows: "Periodic leakage testing on each valve listed in Specification 3.1.C.5.a shall be accomplished prior to entering POWER OPERATION after every time the plant is placed in COLD SHUTDOWN for refueling, after each time the plant is placed in COLD SHUTDOWN for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if testing has not been accomplished in the preceding 9 months, and prior to returning the valve to service after maintenance, repair or replacement work is performed."
The proposed alternative request does not affect the above TS requirements.
ASME OM Code Requirements - The SPS Unit 1 1ST Program implements the ASME OM Code as required by SPS TS 6.4.1, "lnservice Testing Program,"
and 10 CFR 50.55a(f). As previously noted, the Code of Record for SPS Unit 1 is the ASME OM Code 2004 Edition through 2006 Addenda, which requires the following:
o OM Code, Subsection ISTC-3630, requires PIV testing to verify seat leakages are within acceptable limits and states, "Valve closure before seat leakage testing shall be by using the valve operator with no additional closing force applied."
o OM Code, Subsection ISTC-3630(a), requires PIV leakage rate testing to be conducted at least once every two years.
o OM Code, Subsection ISTC-3630(b)(4), allows testing to be performed at reduced differential test pressure if the leakage result is correlated to leakage at an RCS pressure. SPS calculates this acceptance criterion by taking the square root of the ratio between the test and functional pressure and multiplies it by the TS leakage limit of 1 gpm as prescribed by this paragraph.
This equates to a leakage acceptance criterion of 0.259 gpm for each valve, and the leakage for all three valves must be less than 0.450 gpm.
o The leakage testing requirement of ISTC-3630 is utilized to satisfy the requirements of ISTC-5221 (a)(1) and ISTC-5224.
1-Sl-241 opens to provide a flow path for SI and recirculation from the LHSI pumps to the RCS cold legs. It is normally closed and remains closed until injection to Page 3 of 10
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 isolate the LHSI low pressure piping from the RCS and the High Head SI (HHSI) headers since the LHSI Pump Cold Leg Discharge MOV is normally open.
Historically, Low Head SI to RCS Cold Leg Isolation Check Valve PIVs have been leak tested during startup from refueling outages (RFOs) (and certain other non-RFOs) at lower differential test pressures (starting around 150 psi). Leak testing of 1-Sl-241, Low Head SI through flow element FE-100C to RCS Cold Leg Isolation Check Valve, is accomplished by using pressure from a partially pressurized SI Accumulator at the check valve, and leakage is collected and measured over time at an upstream low pressure drain valve.
Most PIVs tested at the lower pressures meet the leakage rate acceptance criteria when correlated to RCS pressure. However, some PIVs have required higher test pressures (up to nominal RCS pressure) to achieve acceptable leakage results, and test procedures allow testing at low or higher pressures. 1-Sl-241 is typically tested with a partially pressurized accumulator with test pressures typically between 275 and 300 psig.
In certain cases, mechanical agitation has been used to get the valve to seat to achieve an acceptable leakage rate. Dominion Energy Virginia recognizes that mechanical agitation is a troubleshooting activity rather than a repair method and also recognizes that OM Code, ISTC-3630(f), requires valves with leakage rates that exceed their acceptance criteria to be declared inoperable, either repaired or replaced, followed by a re-test to confirm acceptable operation prior to being returned to service. Dominion Energy Virginia is also aware of a recent precedent where the NRC approved an 1ST alternative request for the Tennessee Valley Authority (TVA) Sequoyah Nuclear Plant (SQN) to use mechanical agitation as a PIV leakage test troubleshooting activity, and for deferring repair or replacement of certain PIVs to the following RFO (see Section 8).
Reason for the Request - SPS is currently tracking 1-Sl-241 in the station corrective action program (CAP) for repair or replacement in a subsequent outage.
1-Sl-241 was declared operable but not fully qualified after an engineering evaluation concluded an acceptable leakage test result was achieved after mechanical agitation of the PIV on May 27, 2021.
Corrective maintenance for 1-Sl-241 was originally planned and scheduled to occur during the current RFO ( 1 R31 ). Efforts were made to isolate 1-Sl-241 from the cavity to facilitate the planned valve inspection; however, a tagout boundary could not be established during the current RFO due to leakage past the boundary valves.
To repair or replace 1-Sl-241 during the current RFO, the plant would have to reverse Unit 1 startup activities and cooldown, depressurize, reduce RCS water level, and remove fuel, as required, from the reactor vessel. This would have a significant impact on startup and outage duration and would require emergent plant maneuvering and an increased shutdown safety risk to achieve the Page 4 of 10
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 required configuration necessary for repair or replacement. This evolution would also subject plant personnel to increased dose rates in a high ambient heat stress environment for an extended period of time to perform the actual repair or replacement.
In addition, substantial emergent support activities [e.g., work order (WO) planning and issue, scaffolds, radiological control surveys and coverage, operations tag outs and system alignments, engineering (various) inspections and support, quality control and inservice inspection support] would be required.
Therefore, performance of the repair or replacement activity in compliance with Subsections ISTC-3630, ISTC-3630(f), ISTC-5221 (a)(1 ), and ISTC-5224, for 1-Sl-241 would cause a hardship or unusual difficulty without a compensating increase in the level of quality or safety in order to perform the repair or replacement activity required by ISTC-3630(f).
- 5. Proposed Alternative Dominion Energy Virginia is requesting an alternative to the ISTC-3630 requirements as they relate to use of additional closing force to achieve PIV closure before seat leakage testing; ISTC-3630(f) requirements as they relate to corrective action following a failed seat leakage test; ISTC-5221 (a)(1) requirements as they relate to demonstrating that a PIV check valve disc travel to its seat following cessation of flow; and ISTC-5224 requirements as they relate to retesting following any required corrective action before the valve is returned to service. The proposed alternative is solely applicable to PIV 1-Sl-241.
1-Sl-241 seat leakage testing occurs at low pressures to expedite startup activities. If 1-Sl-241 seat leakage does not meet the acceptance criteria, the following actions will be taken:
1-Sl-241 will be declared inoperable in accordance with the affected TS and the ASME OM Code and the failed PIV will be entered into the site corrective action program, which will allow the provisions of this alternative to be invoked.
Rather than doing an ASME Code repair or replacement, 1-Sl-241 may be mechanically agitated in accordance with the guidance provided in Section 6 of this alternative.
After 1-Sl-241 is mechanically agitated, it will be seat leakage tested using the normal test procedures. The incremental agitation and testing process may be repeated until seat leakage rate acceptance criteria are met or it is determined that corrective maintenance is required.
Page 5 of 10
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 o If the seat leakage test meets the acceptance criteria, then the PIV will be declared operable.
o If the seat leakage test does not meet the acceptance criteria, then the PIV will be repaired or replaced during the outage of discovery.
If 1-Sl-241 needs to be mechanically agitated and subsequently passes seat leakage testing, it will be repaired or replaced during the next Unit 1 RFO.
When 1-Sl-241 is either repaired or replaced during the next outage, it must pass post-maintenance tests (including seat leakage tests) before being declared operable.
Using the provisions of this alternative request as an alternative to the specific requirements of ISTC-3630, ISTC-3630(f), ISTC-5221 (a)(1) and ISTC-5224, which have been identified to be a hardship without a compensating increase in quality and safety pursuant to 10 CFR 50.55a(z)(2), will provide adequate indication of 1-Sl-241 function and operability.
- 6. Basis for the Proposed Alternative The basis for the proposed alternative is based on the following factors:
1-Sl-241 is a PIV that is a common check valve model and design that is used in the industry and typically performs well until operation eventually results in degradation of the seating surfaces.
Seating 1-Sl-241 requires pressure from an SI accumulator pressurized to 275 to 300 psig.
To test back-leakage characteristics, SI Accumulator pressure and flow is utilized to measure flow from drain valves upstream of the check valves which would demonstrate quantifiable leakage past the check valves. Unless there is a significant pressure differential across the seat, the disc may not be pushed into the seat with enough force to achieve full contact. The disc is slightly inclined so gravity does not help keep the disc closed to the extent it would for a vertically mounted check valve.
SPS has experienced problems achieving consistent pressure differential across the 1-Sl-241 seat due to the numerous connections and branches involved in the 1-Sl-241 configuration. SPS has been able to achieve the required pressure differential through valve realignment, venting and cycling of valves, but only after extensive troubleshooting and procedure changes.
However, a failed test for 1-Sl-241 would require the emergent activities discussed previously to effect repair or replacement.
Once 1-Sl-241 is closed with an acceptable seat leakage rate, the valve Page 6 of 10
Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 would not be required to open unless a large break loss of coolant accident (LBLOCA) occurred and would not be required to perform the PIV 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.
Further justification for the proposed alternative is provided below.
A) Review of Maintenance History of PIV 1-SI-241 Work Orders (WOs) and test history for 1-SI-241 were reviewed going back to the Cycle 20 RFO (1 R20). The results are listed below in Table V-01.1.
TABLE V-01.1 Outage 1-Sl-241 Seat Leakage (gpm) 1R30 Initially >25; (Spring 2021) 0.0 after agitation 1R29 0.0 (Fall 2019) 1R28 0.0164 (Spring 2018) 1R27 0.0 (Fall 2016) 1R26 0.0 (Spring 2015) 1R25 0.0 (Fall 2013) 1R24 0.009 (Spring 2012) 1R23 0.016 (Fall 2010) 1R22 0.0 (Spring 2009) 1R21 1.82/1.6/0/0 (Fall 2007) 1R20 Initially> 5 gpm, 0.0159 gpm after (Spring 2006) agitation Page 7 of 10
Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 As noted in the above table, in the spring of 2006 1-Sl-241 was mechanically agitated after leakage testing due to measured seat leakage >5 gpm. Following agitation, the as-left leakage rate was found to be 0.0159 gpm. A work order was generated after the agitation, and the valve was worked in the fall of 2007.
A vendor was brought in due to difficulties returning the valve to service which is the reason for the four test results during RFO 1 R21 noted in Table V-01.1. The vendor provided additional direction to improve maintenance practices and procedural guidance for rebuilding the 6" Velan swing check valve. Since that time, test results have consistently been approximately zero until the leakage test performed in 2021.
B) Description of the Mechanical Agitation Process to be Used. if Needed Similar to the TVA precedent discussed in Section 4 above and referenced in Section 8 below, for this proposed alternative, Dominion Energy Virginia has performed an engineering evaluation that determined using a 15 lb hammer in accordance with the following instructions to mechanically agitate the 1-Sl-241 6" Velan check valve will not cause any internal damage or degradation to the valve.
To avoid preconditioning the check valves, obtain as-found test results and declare the valve inoperable. Use other methods to try to seat the valve prior to use of mechanical agitation, such as varying pressure or venting.
Visually inspect the valve body prior to the use of mechanical agitation and record any pre-existing damage, markings, or defects.
Mechanical agitation of the check valve is to be performed by tapping the valve body using a 15-pound (maximum) soft-faced dead blow mallet, rubber mallet, or against a block of wood with a 15-pound (maximum) steel mallet, swung approximately 120 degrees about the elbow WITHOUT excessive use of the body to accelerate the hammer head.
- The surface to be mechanically agitated shall NOT include valve bolting or flanges.
The valve shall be visibly inspected after the application of mechanical agitation to ensure no physical external damage to the check valve has occurred.
The valve shall be scheduled for disassembly during the next RFO following application of mechanical agitation to inspect the valve for damage and determine whether the agitation caused any adverse effects on valve performance.
Page 8 of 10
Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 If the mechanically agitated check valve subsequently passes its seat leakage test, it shall be repaired or replaced during the next RFO.
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.
C) Design of 1-Sl-241 Failure of a check valve disc to open (stuck closed), or detachment of the disc 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 disc is closed for long periods of time, allowing corrosion to bond the disc to other parts of the valve internals. Another failure mechanism is when the disc operates long-term in a less than full open position, allowing hinge pin wear in a raw water environment. The process fluid for the PIVs at SPS is RCS 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 that the disc will fail to open, or become detached when flow is required D) Description of PIV Open Exercise Testing PIV 1-Sl-241 is tested in the open direction during comprehensive pump testing of the LHSI pumps with design basis accident flow rates. Flow through the LHSI piping branches are monitored by temporary flow instrumentation each refueling outage. There have been no valve failures during this testing.
SUMMARY
The proposed alternative would permit continued startup if 1-Sl-241 can be demonstrated to have acceptable seat leakage following mechanical agitation in 1 R30 and in 1 R31 if 1-Sl-241 has unacceptable seat leakage.
If 1-Sl-241 passes the seat leakage test with no mechanical agitation required, SPS will perform corrective maintenance during 1 R32.
The valve would only be acceptable for normal operation for one additional cycle and only if the final PIV seat leakage meets the TS leakage criteria. Should mechanical agitation be needed in 1 R31, the following restrictions will be in place:
Should the valve fail to meet the TS and ASME OM Code leakage requirements, 1-Sl-241 will be declared inoperable.
Should the valve fail to meet the TS and ASME OM Code leakage Page 9 of 10
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 requirements, mechanical agitation will be used to assist in troubleshooting 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 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 lb (maximum) rubber mallet or soft-faced dead blow mallet 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 refueling outage 1-SI-241 will be disassembled and inspected and will be repaired or replaced as necessary. Post maintenance testing will be performed in accordance with ASME OM requirements.
7. Duration of Proposed Alternative
The duration of the proposed alternative request will be through the remainder of the 1 R31 operating cycle which is scheduled to end in the spring of 2024.
- 8. Precedent A similar relief request was submitted to the NRG 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 10 of 10 Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 ENGINEERING ASSESSMENT OF MECHANICAL AGITATION PROCESS FOR 1-Sl-241 Virginia Electric and Power Company (Dominion Energy Virginia)
Surry Power Station Unit 1
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 ENGINEERING ASSESSMENT OF MECHANICAL AGITATION PROCESS FOR 1-51-241 SURRY POWER STATION UNIT 1 Purpose The purpose of this assessment is to evaluate the use of mechanical agitation that has been previously applied to 1-Sl-241 for purposes of seating the valve following failed leak tests, as well as the structural impact from mechanical agitation using methods that are consistent with those previously approved by NRG Safety Evaluation [5].
Once approved for use at Surry Power Station (SPS), this mechanical agitation methodology could be used when necessary for leak testing of 1-Sl-241 (FE-1 00G Outlet to Cold Leg A Check Valve).
Design Inputs and Assumptions Assumptions made regarding past use of a 20-pound maul per Reference [3] & [4] are reasonable and conservative.
Inputs for this assessment are captured within the References section. The 6" Class 1500 Velan swing check valves investigated herein for SPS are bounded by the 6" Velan swing check valves included within the TVA relief request [5] [6] [8].
Methodology Existing documented bases from SPS as to why the use of a 20-pound maul for purposes of mechanically agitating 1-Sl-241 (along with other 6" check valves) is reviewed and augmented by additional assessment herein. Specifically, to evaluate force imparted by use of the 20-pound maul during the last application of mechanical agitation to seat 1-Sl-241 on May 21, 2021 (as documented within [4]), 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 [8] 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 (12], 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; for conservatism; however, 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 [12], 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 NRG and concluded to provide reasonable assurance that use of mechanical Page 1 of 5
agitation won't damage the impacted check valves.
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 Recommendations herein are based on NRG-approved methods documented in the revised NRC Safety Evaluation for Sequoyah Nuclear Plant [5], including additional information extracted from References [6], [7], & [8].
SPS Check Valve 1-SI-241 is reviewed against the valves included within the TVA alternate request to confirm applicability.
Discussion A previous engineering evaluation for mechanical agitation using a 20-pound maul for 1-Sl-241 (and the similar Unit 1 and 2 Loop A/8/C TS primary coolant system pressure isolation valves (PIVs)) was reviewed, and it was confirmed that these valves are all 6" Velan inclined vertical seat swing check valves (as shown on Velan Drawing 78704
[10]). Valve material is Type 316 Stainless Steel and wall thickness can be conservatively estimated as 0.6", which is consistent with TVA in their Engineering Work Request [8], which was audited by the NRC as part of the TVA alternate request.
Assuming similar parameters as TVA in [8], the force imparted using the same load increase factor, is only about 115 lbs. For conservatism, this force is doubled since the guidance in [3] is limited and relies on "common sense".
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 = TT*L*[90°+a]/180°)
6.283 ft Height hammer falls (h = L + Lsina) 4.5 ft Gravitational constant (g) 32.2 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 = Afv) 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 maul), a valve length of a = 22" (consistent with TVA), and a Poisson's Ratio of v = 0.3, the moment applied using Roark's Formulas for a Flat Circular Plates of Constant Thickness (Table 11.2) is estimated to be:
Moment= (Force1/4TT) * (1+v)
- ln(a/r) = 106.532 lbf / in Page 2 of 5
Serial No. 22-37 4 Docket No. 50-280 Proposed 1ST Alternative Request V-01 Based on the above moment, calculated induced stress is:
Stress= (6 *Moment)/ t2 = 1.78 ksi << Allowable Stress@ 600°F for SA-182, F316 (17 ksi)
Therefore, conservatively assuming a large 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 using a 20-pound maul to agitate the valve for purposes of seating the disc. That evaluation documents that Velan 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 [3] is intended to minimize the potential to damage the valve.
Guidance recommends striking the thickest portion of the valve body while avoiding point contact and, if practical, the use of second piece of metal plate to distribute the impact force. Guidance is also provided to avoid striking the bonnet.
Recommendations for Future Application of Mechanical Agitation to Seat Valve 1-SI-241 Following approval of the Dominion Energy Virginia Alternative Request [2], guidance for applying mechanical agitation to 1-SI-241 has to be consistent with the NRC-reviewed and approved guidance.
Moving forward, the following changes are recommended, which results in different guidance than that provided within the previous engineering evaluation and historically used.
Mechanical Agitation Requirements2 To avoid PRECONDITIONING the check valves, obtain as-found test results, or declare the valve inoperable. Use other methods to try to seat the valve prior to use of mechanical agitation, such as varying pressure or venting.
- Visually inspect the valve body prior to the use of mechanical agitation and record any pre-existing damage, markings, or defects.
Mechanical agitation of the check valves is to be performed by tapping the valve body using a 15-pound (maximum) soft-faced dead blow mallet, rubber mallet, or against a block of wood with a 15-pound (maximum) steel mallet, swung approximately 120 degrees about the elbow WITHOUT excessive use of the body to accelerate the hammer head.
The surface to be mechanically agitated shall NOT include valve bolting or flanges.
1 Conservative to use calculated force (assumed per unit length) vs. using "W' as would be calculated using Roark, Table 11.2, Case 17.
2 Consistent with TVA Sequoyah NP RV-02 Safety Evaluation (5), Audit Report (6), and (8).
Page 3 of 5
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 The valve shall be visibly inspected after the application of mechanical agitation to ensure no physical external damage to the check valve has occurred.
The valve shall be scheduled for disassembly during the next refueling outage following application of mechanical agitation to inspect the valve for damage and determine whether or not the agitation caused any adverse effects on valve performance.
If 1-Sl-241 is mechanically agitated and subsequently passes its seat leakage test, it shall be repaired or replaced during the next refueling outage.
Conclusions Past mechanical agitation of 1-Sl-241 has been evaluated using the NRG approved methodology in [5) and it is concluded that previous methods used, consistent with the 1995 engineering evaluation [3], would not have damaged the valve.
Future mechanical agitation of 1-Sl-241 should be consistent with the methodology evaluated and approved by the NRG for the TVA Sequoyah Nuclear Plant.
References
[1]
Condition Report CR1214749, Prior NRG Approval Needed for Testing Methodology on 1-Sl-241
[2]
Alternative Request: Letter Serial No. 22-37 4, Virginia Electric and Power Company, Surry Power Station Unit 1, "ASME OM Code lnservice Testing Program, Request for Approval of Alternative Request V-01, Use of Mechanical Agitation Process For Pressure Isolation Valve 1-Sl-241"
[3)
Engineering Transmittal S-95-0455, Revision 0, "Mechanical Agitation of Check Valves"
[4)
Engineering Technical Evaluation ETE-SU-2021-0034, Revision 0, "Engineering Evaluation for Mechanical Agitation of 1-Sl-241"
[5]
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)
(6)
NRC Accession Number ML22312A352 (12/1/22) - Office of Nuclear Reactor Regulation, Revised Audit Summary in Support of NRC Review of Alternative Request RV-02, Tennessee Valley Authority, Sequoyah Nuclear Plant, Units 1 and 2, Docket Numbers 50-327 and 50-328 (EPID No. L-2022-LLR-0072)
[7]
NRC Accession Number ML22224A035 -
Regulatory Audit Questions, Request for Alternative to American Society of Mechanical Engineers Operation and Maintenance Page 4 of 5
Serial No.22-374 Docket No. 50-280 Proposed 1ST Alternative Request V-01 Code Subsection ISTC-3630, TVA, Sequoyah Nuclear Plant, Units 1 and 2, Docket Numbers 50-327 and 50-328
[8]
TVA Engineering Work Request EWR No. 22-DEC-063-050, CNL-22-024 SQN PIV Relief Request - Mechanical Agitation Allowances
[9]
Surry Operations Periodic Test Procedures a. 1-OPT-Sl-014, Rev. 24, Cold Shutdown Test of SI Check Valves to RCS Cold Legs b. 2-OPT-Sl-014, Rev. 30, Cold Shutdown Test of SI Check Valves to RCS Cold Legs
[10] Velan Drawing 78704, 6" SWING CHECK VALVE FOR SAFETY INJECTION SYSTEM (available via DocTop as SU-EDWG-000-11448-11548-6.39-8A)
[11] Plant Drawing References a. 11448-FM-0898, Sh. 4 of 4, Rev. 25 b. 11548-FM-0898, Sh.
4 of 4, Rev. 28
[12] Roark's Formulas for Stress and Strain, 7th Edition, Warren C. Young and Richard G.
Budynas, McGraw-Hill 2000 Page 5 of 5