05000325/LER-2014-005, Regarding Setpoint Drift in Main Steam Line Safety/Relief Valves Results in Two Valves Inoperable
| ML14212A031 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 07/21/2014 |
| From: | Hamrick G Duke Energy Carolinas, Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 14-005-00 | |
| Download: ML14212A031 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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)(iii) 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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3252014005R00 - NRC Website | |
text
4DUKE
- ENERGY, George T. Hamrick Vice President Brunswick Nuclear Plant Duke Energy Progress P.O. Box 10429 Southport, NC 28461 o: 910.457.3698 10 CFR 50.73 July 21, 2014 Serial: BSEP 14-0074 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Brunswick Steam Electric Plant, Unit No. 1 Renewed Facility Operating License No. DPR-71 Docket No. 50-325 Licensee Event Report 1-2014-005 In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Duke Energy Progress, Inc., submits the enclosed Licensee Event Report (LER). This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.
Please refer any questions regarding this submittal to Mr. Lee Grzeck, Manager - Regulatory Affairs, at (910) 457-2487.
Sincerely, George Hamrick SWR/swr
Enclosure:
Licensee Event Report 639~
cc (with enclosure):
U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Victor M. McCree, Regional Administrator 245 Peachtree Center Ave, NE, Suite 1200 Atlanta, GA 30303-1257 U. S. Nuclear Regulatory Commission ATTN: Ms. Michelle P. Catts, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission ATTN: Mr. Andrew Hon (Mail Stop OWFN 8G9A) (Electronic Copy Only) 11555 Rockville Pike Rockville, MD 20852-2738 Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-0510
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 0113112017 (02-2014)
(02-2014)
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- 3. PAGE Brunswick Steam Electric Plant (BSEP) Unit 1 05000325 1 OF 4
- 4. TITLE Setpoint Drift in Main Steam Line Safety/Relief Valves Results in Two Valves Inoperable
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 05 20 2014 2014-005
- - 00 07 21 2014 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
Li 20.2201(b)
Li 20.2203(a)(3)(i)
Li 50.73(a)(2)(i)(C)
Li 50.73(a)(2)(vii)
Li 20.2201(d)
Li 20.2203(a)(3)(ii)
Li 50.73(a)(2)(ii)(A)
Li 50.73(a)(2)(viii)(A)
Li 20.2203(a)(1)
Li 20.2203(a)(4)
Li 50.73(a)(2)(ii)(B)
Li 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
Li 50.36(c)(1)(i)(A)
F1 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[I 50.36(c)(1)(ii)(A)
[I 50.73(a)(2)(iv)(A)
EL 50.73(a)(2)(x)
Li 20.2203(a)(2)(iii)
Li 50.36(c)(2)
[L 50.73(a)(2)(v)(A)
Li 73.71(a)(4)
Li 20.2203(a)(2)(iv)
Li 50.46(a)(3)(ii)
Li 50.73(a)(2)(v)(B)
Li 73.71(a)(5) 1L 20.2203(a)(2)(v)
Li 50.73(a)(2)(i)(A)
Li 50.73(a)(2)(v)(C)
Li OTHER Li 20.2203(a)(2)(vi)
Z 50.73(a)(2)(i)(B)
[L 50.73(a)(2)(v)(D)
Specify in Abstract below or in
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Introduction
Initial Conditions At the time the condition was found, Unit 1 was in Mode 1 at approximately 100 percent of rated thermal power.
Reportability Criteria Unit 1 Technical Specification (TS) 3.4.3 requires at least 10 of 11 main steam [SB] safety/relief valves (SRVs) to be operable. Per Surveillance Requirement (SR) 3.4.3.1, each valve is required to open within +/-3 percent of its opening setpoint. As-found testing of the valves indicated that two of the valves had lift setpoints outside this tolerance and were therefore determined to have been inoperable when the unit was in operation. Consequently, the plant was operated in a condition which is prohibited by the TS, that is, with fewer than the required number of SRVs having lift setpoints within the 3 percent tolerance. Therefore, the condition is being reported per 10 CFR 50.73(a)(2)(i)(B) for operation in a condition prohibited by the plant TSs.
Event Description
During the spring 2014 Unit 1 refueling outage, all 11 Model 7657F Target Rock Two-Stage pilot valve assemblies in the SRVs were replaced with certified spares. The removed SRV pilot valves were sent to National Technical Systems (NTS) to determine the as-found set pressure. On May 20, 2014, the as-found testing results were formally reported. The test results showed that two of the 11 valves actuated at pressures outside of the 3 percent tolerance allowed by Technical Specifications 3.4.3. The test data for the valves found out of tolerance are shown below.
Valve TS Setpoint As-Found Lift Percent Identification (psig)
Pressure (psig)
Difference SIN 1225 1150 1192.4
+3.7 SIN 1109 1130 1091.7
- - 3.4
Event Cause
SRV serial number 1225 experienced upward setpoint drift because of corrosion bonding of the pilot disc to its seat. The SRVs are refurbished using a process that deposits a thin film of platinum on the surface of the pilot disc. Applying the platinum to the disc requires a surface roughness of 8 microinches root-mean-square (RMS) or better. In this valve, the surface finish was left more coarse. Sharp edges in the coarse surface tend to cause the coating to thin out. This made the surface more susceptible to localized loss of the platinum coating due to stresses imposed by contact with the seat. The loss of coating, in turn, allowed conditions to develop which were conducive to corrosion bonding.
The root cause of the corrosion bonding of SRV serial number 1225 is that the engineering document which established the platinum coating process did not define the surface finish requirements for effective application of the coating.
SRV serial number 1109 experienced downward setpoint drift. Formal root cause determination techniques and careful examination of the pilot valve were not able to determine a cause for the reduced lift setpoint pressure. Pilot valve examination showed that critical dimensions, pilot spring rate, and spring geometry were within tolerances. Metallurgical examination showed no cracking in the spring.
Industry sources were consulted for input on possible causes for a low lift pressure. These included the manufacturer (Target Rock), boiling water reactor (BWR) industry engineering peers, and a BWR industry design expert on SRVs. Potential failure modes identified by these sources were systematically eliminated, but no cause for the low lift pressure was determined.
Safety Assessment
The as-found condition of the Unit 1 SRVs was compared to the cycle-specific analysis for Brunswick fuel cycle 19. That analysis assumes that of the four lowest pressure SRVs, one fails to open; two open at 6 percent above setpoint; one opens at 10 percent above setpoint, and the remaining seven open at 3 percent above setpoint. The analysis bounds the as-found condition in which all valves were capable of opening; one valve opened at 3.4 percent below its lift setpoint; one valve opened at 3.7 percent above its lift setpoint, and all other valves were within their 3 percent tolerance. Therefore, the SRVs always remained capable of performing their safety function of preventing overpressurization of the reactor vessel.
Based on the foregoing analysis, it is concluded that this event had no adverse impact on nuclear safety.
Corrective Actions
Any changes to the corrective actions and schedules noted below will be handled in accordance with the site's corrective action program.
The complete population of 11 Unit 1 SRV pilot valves was replaced with refurbished and certified spares during the spring 2014 refueling outage, and spares were verified to have the correct surface texture for applying the platinum coating in a durable manner.
Recurrence of SRV setpoint drift arising from failed platinum coatings will be prevented by a revision to procedure OCM-VSR509, "Main Steam Relief Valves Target Rock Model 7567 Air Operators and Pilot Assembly Disassembly, Inspection, and Reassembly." This revision requires the surface roughness in the pilot seating area to be 8 microinches RMS or better prior to applying the platinum coating. The revision has been completed such that SRV pilot valves installed in the future will meet this requirement.
Previous Similar Events
A review of LERs and corrective action program condition reports identified one previous similar occurrence within the past three years. The occurrence was reported in LER 2-2013-003, dated July 22, 2013. In that event, setpoint drift resulted from the same surface texture mechanism described previously in this report. Since the SRV pilot was already in service at the time the 2013 event was discovered, the corrective actions could not have prevented the 2014 event.
Commitments
No regulatory commitments are contained in this report.