05000278/LER-2018-004, Failure of a Main Steam Isolation Valve to Fully Close
| ML18334A035 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 11/30/2018 |
| From: | Pat Navin Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CCN: 18-122 LER 2018-004-00 | |
| Download: ML18334A035 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 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 |
| 2782018004R00 - NRC Website | |
text
Exelon Generation CCN: 18-122 November 30, 2018 U. S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, DC 20555-0001
Subject:
Peach Bottom Atomic Power Station (PBAPS) Unit 3 Renewed Facility Operating License No. DPR-56 NRG Docket No. 50-278 Licensee Event Report (LEA) 3-18-004 10CFR 50.73 Enclosed is a Licensee Event Report concerning a Main Steam Isolation Valve to fully close.
In accordance with NEI 99-04, the regulatory commitment contained in this correspondence is to restore compliance with the regulations. The specific methods that have been planned to restore and maintain compliance are discussed in the LEA. If you have any questions or require additional information, please do not hesitate to contact Matt Retzer at 717-456-4351.
Patrick D. Navin Site Vice President Peach Bottom Atomic Power Station PDN/dnd/I R 4178993 Enclosure cc:
US NRG, Regional Administrator, Region I US NRG, Senior Resident Inspector R.R. Janati, Commonwealth of Pennsylvania D. Tancabel, State of Maryland B. Watkins, PSE&G, Financial Controls and Co-Owner Affairs
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 03/31/2020 (04-2018)
Eslimaled burden per response lo compi'/ wilh this mandatory colleclion request BO hours c,'-'t._f\\ RfC(ll-f>
LICENSEE EVENT REPORT (LER)
Reported lessons learned are incol]loraled inlo the licensing process and fed back lo
-~~t industry. Send comments regarding burden eslimale lo !he lnfonnalion Services Branch (See Page 2 for required number of digits/characters for each block)
(T-2 F43). U.S. Nuclear Regulatory Commission, Washng1on, DC 20555-0001, or bye-ma
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n lo lofocollecls Resource@nrc.gov. and to !he Desk Dttl:er, Offl:e of lnfonnalron and
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(See NUREG-1022, R.3 for instruction and guidance for completing this form Regulalory Affairs, NEOB-10202, (3150-0104). OHK:e of Managemenl and Budge!
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Washng1on, DC 20503 If a means used 10 impose an nlonnalion collectoo does not
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+o' hll12://www.nrc.gov/reading-rm/doc-collectionslnuregs/stafflsr1022/r3i) display a currently valid OMB conlrol nurrber, !he NRC may no! conduct "' sponsor and a person is nol required lo respond lo, lhe ilfonnalion coleclion
- 3. Page Peach Bottom Atomic Power Station Unit 3 05000278 1
OF 4
- 4. Title Failure of a Main Steam Isolation Valve to Fully Close
- 5. Event Date
- 6. LEA Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequenliel I Rev Facility Name Docket Number Month Dey Veer Veer Number No.
Month Dey Veer 05000 Facility Name Docket Number 10 01 2018 2018 -
004 0
11 30 2018 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 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) 3 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)
D 50.73(a)(2)(v){B)
D 73.71 (a)(5)
D 20.2203(a)(2)(iv)
D 5o.46{a){3)(ii)
D 50.73(a)(2){v)(C)
D 73.77(a){1) 0%
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)
~ 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 SEQUENTIAL NUMBER 004 REV NO.
0 Technical Specification (TS) 3.6.1.3 requires each Primary Containment Isolation Valve (PCIV) to be operable during Modes 1, 2 and 3. With the condition described above, MSIV 808 would exceed the maximum allowed single MSIV leakage limit of 85 standard cubic feet per hour (scfh) and would be inoperable. With one MSIV inoperable, TS 3.6.1.3 Condition D requires leakage limits to be restored to within limits in 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, or be in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. At the time of discovery, the unit was in Mode 3, and entered Mode 4 within approximately 15 minutes of when the condition was discovered. Therefore, TS requirements were met following discovery of the condition.
The valve was last closed approximately 8 days prior to this event on 9/23/18, following a reactor shutdown.
The previous valve closure was on 10/23/17 during the last Unit 3 refueling outage. There was no indication of a degraded condition during either of these closures. However, the condition of the poppet cap guide suggests the degradation process had been occurring for a significant period of time. Although the successful closure of the valve 8 days prior to this event provides evidence it could perform its design function at that time, it does not provide firm evidence that the valve would have been able to continue to perform its design function. This results in the valve being inoperable for approximately 8 days, exceeding its TS allowed outage times.
This event is being reported in accordance with the following:
10 CFR 50.73(a)(2)(i)(B) - any condition prohibited by plant Technical Specifications. Because MSIV 808 was inoperable for a period of approximately 8 days, TS 3.6.1.3 Condition D was not met for restoring leakage limits within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and Condition F was not met for being in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> if Condition D is not met.
There were no safety consequences as a result of this event. The outboard MSIV for the 'B' main steam line (A0-3-01 A-0868) was operable and would have been able to perform its containment isolation function.
The as-left leakage rate during the last Unit 3 refueling outage (Fall of 2017) for MSIV 868 was below the TS allowable limit.
Cause of the Event
An in-body inspection of the valve found that an anti-rotation lug on the shaft had worn the guide in the poppet cap, creating a notch in one side of the guide. During normal operation, with the MSIVs open, the poppet is supported by the valve stem and is exposed to steam flow. The observed damage to the poppet cap guide is indicative of poppet vibration as a result of turbulent steam flow. The steam flow applied a consistent vibration to the poppet causing the poppet cap guide to wear against the anti-rotation lug, resulting in a notch in the poppet cap guide. During valve closure, the poppet traveled its normal path, but the last 1 inch of stem travel did not occur because the stem anti-rotation lugs were caught in the notch, which prevented the stem from reaching the pilot seating surface.
Corrective Actions
SEQUENTIAL NUMBER 004 REV NO.
0 The stem and the poppet cap guide were replaced, and the poppet was modified to improve stabilization for MSIV 808 and SOC. During the Unit 2 Fall 2018 refueling outage, which took place shortly after this event, three of the four Unit 2 inboard MSIVs were modified to improve stability. The fourth valve had the modification installed in a prior outage. As with Unit 3, the Unit 2 outboard MSIVs also do not have the anti-rotation lugs and are not susceptible to this particular failure mechanism.
Additional corrective actions are documented in the Corrective Action Program.
Previous Similar Occurrences MSIV leakage exceeding TS limits has occurred in the past, however, the failure mechanism was different than in this event. Unit 2 LER 06-001 identified high MSIV leakage due to the poppet not properly seating on the main seating surface. Unit 2 LER 08-001 identified high MSIV leakage due to main seat degradation. Page _4_ of _i_