05000346/LER-2016-003, Regarding Leak from Reactor Coolant Pump Seal Piping Flexible Hose Due to Undetected Manufacture Weld Defect
| ML16154A148 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/31/2016 |
| From: | Boles B FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-16-145 LER 16-003-00 | |
| Download: ML16154A148 (5) | |
| 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 |
| 3462016003R00 - NRC Website | |
text
FE NOC' RrstEnergy Nuclear Operating Company 5501 North State Route 2 Oak Harbor, Ohio 43449 Brian D. Boles Vice President, Nuclear May 31, 2016 L-16-145 ATTN: Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Davis-Besse Nuclear Power Station, Unit 1 Docket Number 50-346, License Number NPF-3 Licensee Event Report 2016-003 10 CFR 50.73 419-321-7676 Fax: 419-321-7582 Enclosed is Licensee Event Report (LER) 2016-003, "Leak from Reactor Coolant Pump Seal Piping Flexible Hose due to Undetected Manufacture Weld Defect." This LER is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) and 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, Brian D. Boles
'JCS Enclosure: LER 2016-003 cc: NRG Region Ill Administrator NRG Resident Inspector NRR Project Manager Utility Radiological Safety Board
NRC FORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)
Eslimated, the NRC may not conduct or sponsor, and a nerson is not renuired to resnond to the information collection.
Davis-Besse Nuclear Power Station Unit 1 05000-346
==DESCRIPTION OF EVENT==YEAR 2016
- 3. LER NUMBER SEQUENTIAL NUMBER
- - 003
\\
The flexible hose assemblies, manufactured by Senior Flexonics Pathway, had been installed (12 assemblies, 3 per RCP) in April 2014 during the 1'81h Refueling Outage as corrective action for DBNPS LER 2013-002, "Leak from Reactor Coolant Pump Seal Piping Socket Weld due to High Cycle Fatigue," therefore, the hoses had been pressurized for a twenty-four month operating cycle.
CAUSE OF EVENT
REV NO.
00 A laboratory failure examination was unable to confirm the pressure boundary leak path, but a partial depth weld solidification crack was observed in the Alloy 625 pressure boundary material at the hose I bellows tube to socket end. A similar through-wall weld solidification crack at the flange to hose I bellows tube pressure boundary weld was likely the source for the boric acid leakage for the RCP 1-1 first stage seal cavity vent line.
Therefore, the direct cause of the RCP 1-1. first stage seal cavity vent line pressure boundary leakage was likely a weld solidification crack during manufacture. Each of the other identified failure modes from operation, installation, manufacture, and design were refuted.
The DBNPS had three (3) uninstalled spare flexible hose assemblies also supplied in the same batch as the leaking hose for the RCP 1-1 first stage seal cavity vent line. These spare hose assemblies were subsequently bubble tested (30 psig air pressure for 10 minutes) and helium tracer probe leak tested. All three (3) uninstalled spare flexible hose assemblies passed the bubble test, but one (1) failed the helium tracer probe leak test acceptance criteria. Helium tracer probe leak testing of the uninstalled spare hose assemblies permits increased sensitivity for detection of extremely small leaks. Helium tracer probe leak testing was proven an effective barrier that could have mitigated or prevented shipment of the flexible hose assembly with pressure boundary leakage. Therefore, the root cause of the pressure boundary leak path (weld solidification crack) not being detected during manufacture was less than adequate quality control inspection after manufacture of the flexible hose assemblies such that an extremely small pressure boundary defect was not detected by liquid penetrant and hydrostatic testing at 1.5 times design pressure (3750 psig) for 1 O minutes.
ANALYSIS OF EVENT
Because the RCP first stage seal cavity vent piping is classified. as ASME Section Ill 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 irijection is maintained by the Makeup System. The estimated leak rate 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 at 0014 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> on March 31, 2016, via Event Number 51837. This issue is being reported in accordance with 10 CFR 50. 73(a)(2)(ii)(A) as degradation of a principal safety barrier. Additionally, as this is RCS Pressure Boundary leakage and it potentially could have existed with the plant in operation, contrary to TS LCO 3.4.13, which does not allow any Pressure Boundary leakage, this issue is also being reported pursuant to 10 CFR 50. 73(a)(2)(i)(B) as operation or condition prohibited by Technical Specifications. No safety functions were lost as a result of this issue and all TS required actions Page 4of4 (11-2015)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BYOMB: NO. 3150-0104 EXPIRES: 10/31/2018 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
, the NRC may not conduct or sponsor, and a oerson is not reauired to resoond to the information collection.
Davis-Besse Nuclear Power Station Unit 1
. 05000-346 YEAR 2016
- 3. LER NUMBER SEQUENTIAL NUMBER
- - 003 REV NO.
00 were met at the time of discovery. The flexible hose assembly manufacturer determined no 10 CFR 21 reportable condition existed since there was no failure in the design, materials, inspection, or testing per code requirements, and no evidence of a systemic (repeat~ble) issue.
. CORRECTIVE ACTIONS:
Extent of condition walkdowns I engineering inspections were performed on the other eleven (11) installed RCP seal cavity vent line flexible hose assemblies, and no other leaks were identified. There were no other '
flexible hose assemblies identified in the nuclear piping system specification, The RCP 1-1 first stage seal cavity vent line flexible hose assembly was replaced with one ( 1) of the spare hose assemblies that passed the helium tracer probe test to resolve the reactor coolant pressure boundary leakage and the operational mode restraint was closed on April 22, 2016.
The procurement requirements for the RCP seal cavity vent line flexible hose assemblies will be revised to add a new required helium tracer probe leak test with acceptance criteria of at least 1 E-5 Standard cubic centimeters/second, or other equivalent helium leak test method. Also, the procurement requirements will be revised to reference to this event's Condition Report so that this preventive action will be retained. Additionally, the flexible hose assemblies had the material status changed to Hold pending the change to the procurement requirements to add that the helium tracer probe leak test be completed.
PREVIOUS SIMILAR EVENTS
Licensee Event Report (LER).2012-002 and LER 2013-002 reported the discovery of a leaking elbow socket weld in the RCP 1-2 first stage seal vent line resulting from high cycle fatigue. )n response to LER 2013-002, the DBNPS RCPs first, second, and third stage seal cavity vent lines were replaced with flexible hoses in April 2014 during the 181h Refueling Outage. There have been no similar LERs at the DBNPS involving flexible hose defects in the past three years.