05000281/LER-2019-002, Auxiliary Feedwater System Loss of Safety Function Due to Check Valve Failure to Close
| ML20028D616 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 01/17/2020 |
| From: | Mladen F Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 20-023 LER 2019-002-00 | |
| Download: ML20028D616 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2812019002R00 - NRC Website | |
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January 11, 2020 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555-0001
Dear Sir or Madam:
10CFR50.73 Virginia Electric and Power Company Surry Power Station 5570 Hog Island Road Surry, Virginia 23883 Serial No.:
20-023
- SPS:
SCN Docket No.: 50-281 License No.: DPR-37 Pursuant to 10CFR50.73, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to Surry Power Station Unit 2.
Report No. 50~281 / 2019-002~00 This report has been reviewed by the Station Facility Safety Review Committee and will be forwarded to the Management Safety Review Committee.
Enclosure Commitment contained in this letter: None Very truly yours,
>>~r;f_r-* ~RU\\ M~I,.,
F. Mladen Site Vice President Surry Power Station cc:
U.S. Nuclear Regulatory Commission, Region II Marquis One Tower, Suite.1200 245 Peachtree Center Ave., NE Atlanta, GA 30303-1257 NRG Senior Resident Inspector Surry Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
3.Page Surry Power Station Unit 2 05000 281 1
OF 4
- 4. Title Auxiliary Feedwater System Loss of Safety Function due to Check Valve Failure to Close
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rev Facility Name Docket Number Month Day Year Year Number No.
Month Day Year 05000 Facility Name Docket Number 11 20 2019 2019 -
002 -
00 01 17 2020 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 1 O CFR §: (Check all that apply)
D 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50. 73(a)(2)(viii)(A)
D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
N D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50. 73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50.73(a)(2)(iv)(A)
D 50. 73(a)(2)(x)
- 10. Power Level D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2) 0 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50. 73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi) 0 50. 73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in Additionally, because the pumps were determined to be inoperable longer than allowed by Technical Specification 3.6.F, this report is also being submitted pursuant to 1 O CFR 50.73 (a)(2)(i)(B), as any operation or condition which was prohibited by the plant's Technical Specifications.
C. Cause of Event
The direct cause of the check valve failure was due to excessive wear on the check valve disc assembly parts. The internal valve assembly for this valve was last replaced in 1993.
The root cause was that no scheduled preventative maintenance was being performed on the Unit 2 TDAFW pump discharge check valve due to decisions made in 1996 and 2005 to rely on back leakage checks vs. performing check valve open and inspect. As a result, the station was not monitoring the extent of the wear occurring on the valve internals.
D. Safety Consequences
The safety consequences of postulated accident scenarios rely on the availability of the AFW system to provide water to the steam generators for the purpose of removing core decay heat during and after the postulated accident scenarios.
Limiting analysis assumptions for evaluation of such scenarios include a loss of offsite power rendering the Main Feedwater (MFW) pumps unavailable. For the duration of the Unit 2 AFW system unavailability period in question, Surry Power Station retained offsite power. This ensured that the Unit 2 MFW system was available as an alternate method of providing water to the steam generators and, therefore, ensuring a source of secondary coolant. -;
A review of station logs identified that, if the Unit 2 MFW system were unavailable for any reason, additional defense-in-depth was provided by the station cross-tie piping. Using this piping, at least one (1) Unit 1 motor driven AFW pump was available to provide water to the Unit 2 steam generators for all but five (5) hours of the period in question, when the cross-tie was unavailable for testing on 11/15/2019. During this five (5) hours of unavailability, it is estimated that the capability to resupply water to Unit 2 would have taken less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> if needed.
Further, isolation of the unanalyzed flow path through the Unit 2 TDAFW pump discharge line, which restored the operability of the Unit 2 AFW system, was completed within 20 minutes of identifying the Unit 2 TDAFW pump was rotating backward on 11/20/2019. This demonstrates that operability of the Unit 2 AFW system could have been promptly restored in response to an actual event. Consequently, the safety consequences associated with this event were bounded by the safety analyses documented in UFSAR Chapter 14.
Risk Significance:
The initiating events most challenging for this event are Emergency Switchgear Room (ESGR) floods and plant transients.
ESGR floods have the potential to disable all emergency power, leaving only the Unit 1 or 2 TDAFW pumps to provide secondary cooling. Plant transients typically rely on AFW as the primary source of decay heat removal, so a challenge to AFW would require operators to either align the Auxiliary Feedwater cross-tie, Main Feedwater, Condensate, or use feed and bleed for decay heat removal.
E::. Corrective Actions Corrective Actions (Completed)
- 1. The Unit 2 TDAFW pump discharge check valve's internal assembly was replaced:
- 2. The Unit 1 Turbine Driven AFW pump discharge check valve's internal assembly was inspected and determined to be satisfactory.
Corrective Actions (Planned pending causal evaluation approval)
- 1. Until the Unit 1 and Unit 2 MDAFW pump discharge check valve internal assemblies are inspected and/or-replaced, as necessary, alternate methods will be used to ensure the check valve is closed after the performance of surveillance flow testing.
- 2. Revise the AFW pump discharge check valve maintenance program to periodically inspect and/or replace the check valve internals, as needed, on both units.
- 3. Determine if there are other vulnerable safety-related system check valves and implement similar maintenance program changes as required.
F. Previous Occurrences
No previous Licensee Event Reports which could be comparable to this event were found.
G. Component Failure Yes. ASME Class 600, 6" cast steel swing check valve with raised face ends. Manufactured by Walworth Project Engineering. Page 4
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