05000346/LER-2013-002, Regarding Leak from Reactor Coolant Pump Seal Piping Socket Weld Due to High Cycle Fatigue
| ML13247A661 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 08/27/2013 |
| From: | Lieb R FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-13-262 LER 13-002-00 | |
| Download: ML13247A661 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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 |
| 3462013002R00 - NRC Website | |
text
FENOC TM FirstEnergy Nuclear Operating Company 5501 North State Route 2 Oak Harbor, Ohio 43449 Raymond A. Lieb Vice President, Nuclear August 27, 2013 419-321-7676 Fax: 419-321-7582 L-1 3-262 10 CFR 50.73 ATTN: Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555-0001
SUBJECT:
Davis-Besse Nuclear Power Station Docket Number 50-346, License Number NPF-3 Licensee Event Report 2013-002 Enclosed is Licensee Event Report (LER) 2013-002, "Leak from Reactor Coolant Pump Seal Piping Socket Weld due to High Cycle Fatigue." This LER is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(A).
There are no regulatory commitments contained in this letter or its enclosure. The actions described represent intended or planned actions and are described for information only. If there are any questions or if additional information is required, please contact Mr. Patrick J. McCloskey, Manager, Site Regulatory Compliance, at (419) 321-7274.
Sincerely, GMW Enclosure: LER 2013-002 cc:
NRC Region III Administrator NRC Resident Inspector NRR Project Manager Utility Radiological Safety Board rý4
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/31/2013 (10-2010)
, the NRC may (See reverse for required number of not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 3. PAGE Davis-Besse Nuclear Power Station 05000346 1 OF4
- 4. TITLE Leak from Reactor Coolant Pump Seal Piping Socket Weld due to High Cycle Fatigue
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV IIFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO MONTH DAY YEAR 05000 07 201
- - f4 00 00 08 27 01 FACILITY NAME DOCKET NUMBER ZiZI~ ~
jjj 1 3 105000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[1 20.2201(b)
Ej 20.2203(a)(3)(i)
[]
50.73(a)(2)(i)(C)
E]
50.73(a)(2)(vii) 3
[] 20.2201 (d)
E] 20.2203(a)(3)(ii)
Z 50.73(a)(2)(ii)(A)
E]
50.73(a)(2)(viii)(A)
C] 20.2203(a)(1)
[] 20.2203(a)(4)
E]
50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
E]
20.2203(a)(2)(i)
E]
50.36(c)(1)(i)(A)
E]
50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL E]
20.2203(a)(2)(ii)
E]
50.36(c)(1)(ii)(A) 5 50.73(a)(2)(iv)(A)
[S 50.73(a)(2)(x) 5 20.2203(a)(2)(iii) 5 50.36(c)(2) 5 50.73(a)(2)(v)(A)
E5 73.71(a)(4) 000 5
20.2203(a)(2)(iv) 5 50.46(a)(3)(ii)
E]
50.73(a)(2)(v)(B)
E5 73.71(a)(5) 5 20.2203(a)(2)(v) 5 50.73(a)(2)(i)(A)
LI 50.73(a)(2)(v)(C)
S OTHER Specify in Abstract below
[] 20.2203(a)(2)(vi)
E]
50.73(a)(2)(i)(B) 5 50.73(a)(2)(v)(D) or in
==DESCRIPTION OF EVENT==The RCP 1-2 first stage seal vent line from the leaking flange at the pump seal to the next flanged connection was removed and replaced. The new spool piece welded connections were made with socket welds meeting the industry recommended 2x1 weld leg configuration (weld leg along the pipe side of the weld is equal to twice the Code-required weld leg dimension), which reduces the effects of high cycle vibration fatigue. All weldments and fittings associated with the removed spool piece were sent to a laboratory for failure analysis. This removed spool piece also included the elbow socket weld that was repaired as a result of leakage discovered on June 6, 2012 as documented in DBNPS LER 2012-002.
CAUSE OF EVENT
The laboratory failure analysis concluded that the cause of the RCP 1-2 seal cavity vent line flange socket weld failure was high cycle fatigue. This high cycle fatigue was due to a less than adequate consideration of piping vibration during a previous modification. The existing seal line vent configuration for RCP 1-2 has existed since 1990, when the piping was lengthened by approximately five inches to accept a new style of RCP seal. The piping modification performed at that time did not appear to consider the impact of changing the vent line piping to accommodate the new seals would have on the socket-welded pipe. Small changes to small bore piping can affect the piping resonance frequency, resulting in higher amplitude vibrations, potentially resulting in a high-cycle fatigue failure.
ANALYSIS OF EVENT
Because the RCP first stage seal cavity vent piping is classified as ASME Section III Class 2 piping, in the event of a postulated failure, per design the reactor can be shut down and cooled down in an orderly manner assuming seal injection is maintained by the Makeup System. The estimated leak rate at the time of discovery in Mode 3 was well within the capability of the Makeup System's capability.
Therefore this event was of very low safety significance.
Reportability Discussion:
Based on existing precedence, this leak was determined to be reportable per 10 CFR 50.72(b)(3)(ii)(A) as degradation of a principal safety barrier; namely, the RCS, due to the material degradation (weld leak). The NRC was verbally notified of this event per 10 CFR 50.72(b)(3)(ii)(A) at 1527 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.810235e-4 months <br /> on July 1, 2013, via Event Number 49163. This issue is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(A) as degradation of a principal safety barrier. No safety functions were lost as a result of this issue, and all TS required actions were met.
CORRECTIVE ACTIONS
The RCP 1-2 first stage seal vent line from the leaking flange at the pump seal to the next flanged connection was removed and replaced with socket welds meeting the industry recommended 2x1 weld leg configuration.
Extent of condition walkdowns were performed on similar small bore piping (first, second, and third stage sear cavity vent lines, seal injection, and seal return piping) for all four RCPs. No other weld leaks were identified.
==CORRECTIVE ACTIONS==Vibration readings were taken with all four RCPs in operation to verify the seal injection lines, the seal return lines, and the three seal cavity vent lines for each RCP (besides the RCP 1-2 first stage seal vent line) were below the ASME Code screening vibration criteria.
As a result of the RCP 1-2 first stage seal vent line leakage discovered on June 6, 2012 as documented in DBNPS LER 2012-002, an engineering change is planned to replace the existing piping for the RCP first, second, and third stage seal cavity vent lines with flexible hoses to minimize high cycle vibration fatigue. Additionally, the socket weld size for portions of the seal injection and seal return lines will be increased to the industry recommended 2x1 weld leg configuration. Based upon this most recent failure, the engineering change will be revised to include replacing the entire line associated with RCP 1-2 first stage seal cavity vent line back to the first isolation valve. This increase in scope will ensure the remaining socket welds in this previously susceptible line are replaced with new material and socket welded connections to meet the industry recommended 2xl weld leg configuration. This engineering change is planned to be implemented during the next refueling outage scheduled for 2014.
Based upon the 2012 event, changes were made to design process documents to account for potential vibration fatigue failures in susceptible socket welded piping. Plant walkdowns will be performed to identify risk significant socket welded piping susceptible to vibration fatigue failures.
PREVIOUS SIMILAR EVENTS
DBNPS LER 2012-002 documents the discovery of a leaking elbow socket weld in the same RCP 1-2 first stage seal vent line as this leaking flange socket weld. The corrective action for the 2012 event of an engineering change to install flexible hoses for the RCP seal cavity vent lines and to increase the socket weld size on portions of the seal injection and controlled bleed off lines was planned to be implemented during the next refueling outage, which is scheduled for Spring 2014.