05000254/LER-1917-002, Regarding Four Main Steam Isolation Valves (Msivs) Closure Times Exceeded
| ML17146A167 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 05/26/2017 |
| From: | Darin S Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVP-17-041 LER 17-002-00 | |
| Download: ML17146A167 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2541917002R00 - NRC Website | |
text
=~Exelon Generation SVP-17-041 May 26, 2017 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Units 1 and 2 10 CFR 50.73 Renewed Facility Operating License Nos. DPR-29 and DPR-30 NRC Docket Nos. 50-254 and 50-265
Subject:
Licensee Event Report 254/2017-002-00, "Four Main Steam Isolation Valves (MSIVs)
Closure Times Exceeded" Enclosed is Licensee Event Report (LER) 254/2017-002-00, "Four Main Steam Isolation Valves (MSIVs) Closure Times Exceeded," for Quad Cities Nuclear Power Station, Unit 1.
This report is submitted in accordance with 10 CFR 50.73 (a)(2)(i)(B) which requires the reporting of any operation or condition prohibited by Technical Specifications.
There are no regulatory commitments contained in this letter.
Should you have any questions concerning this report, please contact Mr. W. J. Beck at (309) 227-2800.
Re/~
Scott Darin Site Vice President Quad Cities Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
SVP-17-041 U.S. Nuclear Regulatory Commission Page 2 of 2 bee:
NRC Project Manager-NRR (electronic Ltr & LER) Kimberly.green@nrc.gov Illinois Emergency Management Agency - Department of Nuclear Safety (hard copy Ltr & LER)
Charlie Mathews, IEMA Resident (electronic Ltr & LER)
Senior Reactor Analyst - NRC Region Ill (hard copy Ltr & LER)
Glen T. Kaegi, Director, Licensing and Regulatory Affairs - Cantera (electronic Ltr & LER)
Patrick R. Simpson, Manager, Licensing, Dresden & Quad Cities Stations (electronic Ltr & LER)
Exelon Document Control Desk Licensing (Hard Copy Ltr & LER)
Exelon Document Control Desk Licensing (Included in LER Completed)
Spencer T. Moore-MidAmerican Energy Company (electronic Ltr & LER) STMoore@midamerican.com LER Completed (electronic Ltr & LER)
Bruce Franzen, RA Manager - Dresden Nuclear Power Station (electronic Ltr & LER)
Wally Beck, RA Manager - Quad Cities Nuclear Power Station (electronic Ltr & LER)
Tom Petersen, NRC Coordinator - Quad Cities Nuclear Power Station (electronic Ltr & LER)
Kara Koett, NSRB Site Coordinator & INPO Site Coordinator - Quad Cities (electronic Ltr & LER)
INPO Records Center (included in LER Completed)
SVP Letter File (Q:\\SVP\\20YY)
Reg Assurance Clerk (for record turnover in EDMS)
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 03/31/2020 (04-2017)
, the httQ://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Quad Cities Nuclear Power Station Unit 1 05000254 1 OF 5
- 4. TITLE Four Main Steam Isolation Valves (MSIVs) Closure Times Exceeded
- 5. EVENT DATE
- 6. LEA NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR N/A N/A FACILITY NAME DOCKET NUMBER 03 27 2017 2017 - 002
- - 00 05 26 2017 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: {Check all that apply)
D 20.2201 (bl D 20.2203(a)(3)(il D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201(d)
D 20.2203(a)(3)(iil D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 4 D
D 20.2203(a)(4l D so.73(a)(2)(iiil 20.2203(a)(1)
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)(2J(ii)
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 13.11(a)(4)
D 20.2203(a)(2)(iiil D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 13.11(a)(sJ D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1J 000 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)(il D 20.2203(a)(2)(vi)
~ 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(iil
./'.;.':;
D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in C.
CAUSE OF EVENT
SEQUENTIAL NUMBER 002 REV NO.
00 The cause of the slow closure timing for MSIVs 1-0203-18, 1-0203-1 D and 1-0203-20 is due to a less than optimal replacement frequency of the MSIV actuator. The basis of this decision was because ten Unit 1 MSIVs have had slow closure times since the valve actuator replacement PM frequency was extended in 2002.
The vendor recommended replacement frequency is eight years (every fourth outage) and the Exelon PM Template replacement frequency is eight years as well. The current PM frequency is either every sixth (twelve years) or every seventh (fourteen years) refueling outage.
The cause of the slow closure for the 1-0203-2C MSIV was due to a less than optimal replacement frequency of the MSIV springs. The springs were replaced for the 1-0203-2C MSIV after being in-service for nearly 15 years. The MSIVs are normally open valves, which have their springs in compression for the entire cycle. If a spring is in compression for nearly 15 years continuously, the overall free length and spring rate decrease with age.
D.
SAFETY ANALYSIS
System Design
The design of the MSIVs is to prevent reactor coolant [AD] inventory loss and protect plant personnel in the event of steam line breakage outside the isolation valves, and to complete the primary containment [NH] boundary after a Loss of Coolant Accident (LOCA). The MSIVs are 20-inch air/spring operated, balanced "Y"-type globe valves. There are four main steam lines and each steam line has two isolation valves, one inside (inboard MSIV) and one outside (outboard MSIV) of primary containment.
Updated Final Safety Analysis Report (UFSAR) Section 6.2.4.1 provides the valve closure time for the main steam line is based on the main steam line break accident discussed in Section 15.6. Ensuring the MSIV closure time less than or equal to five seconds, sufficient coolant will remain in the reactor vessel to provide adequate core cooling. The valves are designed to close and to be leak-tight during the worst conditions of pressure, temperature, and steam flow following a break in the main steam line outside the containment. The MSIVs are leak tested in accordance with the 1 O CFR 50 Appendix J program. UFSAR Section 15.6 provides that a maximum MSIV closure time of 10.5 seconds would limit the total amount of liquid and steam lost from the primary system to prevent the core from being uncovered, and this closure time will ensure the radiological doses are well below the guidelines set forth in 1 O CFR 100.
Proper adjustment of the MSIV closure times prevents operation outside of the operational and design limits.
Safety Impact Technical Specifications and the In-Service Testing program require the MSIVs to close in a three to five second time range. Five seconds is fast enough to prevent a gross release of fission products, and three seconds is slow enough to minimize the severity of the pressure transient resulting from isolating the main steam lines during full power operation.
Slow MSIV stroke times would challenge the steam release limits of a steam line break outside of containment should the corresponding inboard valve simultaneously fail to close.
The Unit 1 MSIVs 1-0203-18, 1-0203-10, 1-0203-2C, and 1-0203-20 failed to close within the required Technical Specification limit of less than or equal to five seconds. The closure times for those four MSIVs were 5.7, 5.2, 5.1, and 5.6 seconds, respectively, however, the four MSIVs all closed inside the UFSAR limit of less than or equal to 10.5 seconds. Although the required five second Technical Specification limit was not met for these four MSIVs, the MS IVs were ca able of erformin the re uired UFSAR safet function durin the o eratin c cle rior to 01 R24.
Furthermore, since the MSIVs were not required to be operable or available at the time of discovery, this condition did not create any actual plant or safety consequences since the unit was not in an accident or transient condition requiring the use of main steam line isolation valves during this period of time.
Risk Insights The closure times for the four MSIVs were 5.7, 5.2, 5.1, and 5.6 seconds and recorded as slow, but the MSIVs did fully close. The MSIV success criterion in the Plant Probabilistic Risk Assessment (PRA) model, however, does not depend on closure time. Therefore, a difference of a fraction of a second between actual MSIV closure time and the acceptance criterion for the Technical Specification closure time has no effect on the PRA model. As a result, there is no effect on Core Damage Frequency (GDF) or Large Early Release Frequency (LERF).
In conclusion, the failure of the four MSIVs to close within the required time would not have caused the station to exceed the inventory and dose release limits. Furthermore, the impact on risk of this event is negligible. Therefore, the overall safety significance of this event was minimal.
E.
CORRECTIVE ACTIONS
Immediate:
- 1. The 1-0203-1 Band 1-0203-1 D MSIV actuators were replaced during the outage, Q1 R24 in 2017.
- 2. The 1-0203-2C MSIV springs were replaced during the outage, Q1 R24 in 2017.
- 3.
All four MSIVs were adjusted for proper as-left closure times, and retested satisfactorily.
Follow-up:
- 1. The 1-0203-2D MSIV actuator will be replaced during the next refuel outage, Q1 R25, in 2019.
- 2. The PM frequency will be changed to eight years for replacing the Unit 1 and Unit 2 MSIV actuators with additional instructions to replace the MSIV springs during the actuator replacement.
F.
PREVIOUS OCCURRENCES
The station events database, LERs, and INPO ICES were reviewed for similar events at Quad Cities. Specifically, this event was primarily attributed to a less than optimal replacement frequency of the MSIV actuators and springs. Based on the causes of this event and associated corrective actions, the events listed below, assisted with the resolution of this event.
Station Issue Report (IR) 1213432, Unit 1 Outboard MSIV 1-0203-2C Failed QCOS 0250-04 (05/09/2011) - The 1-0203-2C outboard MSIV closure time exceeded the acceptance criteria for cold timing, which is less than or equal to five seconds. The stroke time recorded was 5.2 seconds. The cause was dirty contacts within the control circuitry creating an electrical time delay. This is one of the ten slow closure time events on Unit 1 since 2002, which led to the current action to reduce the valve actuator PM frequency. Therefore, IR 1213432 provided useful insights associated with this event.
Station Issue Report (IR) 333083, Unit 2 Inboard MSIV 2-0203-1 C Slow Closure (05/09/2005) - While performing QCOS 0250-04, "MSIV Closure Timing," the 2-0203-1 C MSIV closure time was 5.05 seconds, which is outside of the surveillance acceptance criteria of 3-5 seconds. The cause of the slow valve stroke time was determined to be within the human response time for actuating the stopwatch. This previous event is similar in that stopwatches continue to be used to perform the closure time surveillance. However, this past event is not directly applicable SEQUENTIAL NUMBER 002 REV NO.
00 and is not considered a significant station experience that would have directly contributed to preventing the event of this current LER.
LER 2013-002-00 Outboard Main Steam Isolation Valves (MSIVs) Stroke Times Exceeded (03/11 /2013) - All four Unit 1 outboard MSIVs closed slowly due to actuator seals had degraded due to age and wear. The vendor recommended a replacement frequency of eight years for the actuators. This event was four of the ten slow closure events on Unit 1 since 2002, which led to the current action to reduce the valve actuator PM frequency.
Therefore, LER 2013-002-00 provided useful insights associated with this event.
G.
COMPONENT FAILURE DATA
The failed component was the air/hydraulic actuator on three of the four MSIVs and springs on the fourth MSIV.
These actuators are Model Numbers SA-A 104 and SA-A 119 manufactured by Rotork Hiller.
The MS IVs are manufactured by Crane.
This event has been reported to ICES under record #407880. Page _5_ of _5_