05000346/LER-2016-003

LER-2016-003, Leak from Reactor Coolant Pump Seal Piping Flexible Hose due to Undetected Manufacture Weld Defect

Davis-Besse Nuclear Power Station, Unit 1
Event date:	03-30-2016
Report date:	05-31-2016
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
Initial Reporting
ENS 51837	10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded
3462016003R00 - NRC Website

LER 16-003-00 for Davis-Besse Nuclear Power Station, Unit 1 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 D FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-16-145 LER 16-003-00
Download: ML16154A148 (5)

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

System Description:

The Davis-Besse Nuclear Power Station (DBNPS) Reactor Coolant System (RCS) [AB] uses four Reactor Coolant Pumps (RCPs) [AB-P] to circulate the reactor coolant. Each RCP is a single-stage centrifugal pump designed to produce a flow of approximately 90,000 gallons per minute (gpm) and driven at 1200 revolutions per minute by a 13,200 volt motor [AB-MO]. The RCPs are shaft-sealed with a seal cartridge assembly [AB- SEAL] that consists of three mechanical face-type sealing stages. The design flow rate for each seal staging flow coil is 1.5 gpm at a differential pressure of 750 pounds per square inch (psi). Approximately 8 to 10 gpm of seal injection water from the Makeup and Purification System [CB] is injected below the first stage mechanical seal for lubricating and cooling the seals. Most of the injection water passes into the pump case through the close-running, spiral grooved shaft and cover restriction bushing into the RCS, and the remainder (1.5 gpm) flows upward through the three mechanical seals. Flow from the three pressure break-down devices leaves the RCP through the seal return connection to return to the Makeup and Purification System.

Leakage across the third seal face passes up the shaft and into a standpipe that drains to the containment normal sump.

Technical Specification(s):

Technical Specification (TS) Limiting Condition for Operation (LCO) 3.4.13 requires RCS operation leakage be limited to no Pressure Boundary leakage, 1 gpm unidentified leakage, 10 gpm identified leakage, and 150 gallons per day primary to secondary leakage through any one steam generator while the plant is in Modes 1 through 4. With operational leakage not within these limits for reasons other than pressure boundary leakage or primary to secondary leakage, TS LCO 3.4.13 Condition A requires the leakage to be reduced to within limits within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. If Condition A cannot be met within the required completion time, or if Pressure Boundary leakage exists, or primary to secondary leakage is not within limits, Condition B requires the plant be placed in Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

DESCRIPTION OF EVENT:

On March 26, 2016, the DBNPS shutdown for scheduled refueling and maintenance activities. On March 30, 2016, with the station in Mode 6 and the RCS depressurized, a scheduled engineering inspection identified leakage from the RCP 1-1 seal injection flexible hose assembly and the leakage was determined to be an unisolable leak from the reactor coolant pressure boundary. This leakage was characterized as one half teaspoon of dry boric acid crystals, no active leak was identified and there was no indication of boric acid on the rest of the RCP seal package. The seal cavity vent lines for the first, second, and third stage seals are opened during RCS fill evolutions to vent non-condensable gases to the containment vent header. The leak was located on the RCP 1-1 first stage seal cavity vent line flexible hose assembly (at the flange to hose / bellows attachment), which is classified as small bore American Society of Mechanical Engineers (ASME)Section III Class 2 piping (3/4 inch pipe) between the RCP and the first isolation valve [AB-PSF] in the RCP vent piping.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

05000-346 - 003 2016 00 The flexible hose assemblies, manufactured by Senior Flexonics Pathway, had been installed (12 assemblies, 3 per RCP) in April 2014 during the 18th 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:

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 / bellows tube to socket end. A similar through-wall weld solidification crack at the flange to hose / 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 10 minutes.

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 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 Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

' 05000-346 - 003 2016 00 Reportability Discussion: (continued) 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 (repeatable) issue.

CORRECTIVE ACTIONS:

Extent of condition walkdowns / 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. In 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 18th Refueling Outage. There have been no similar LERs at the DBNPS involving flexible hose defects in the past three years.