05000298/LER-2015-001, Regarding Valve Test Failures Result in a Condition Prohibited by Technical Specifications and a Loss of Safety Function
| ML15091A312 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 03/26/2015 |
| From: | Limpias O Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2015035 LER 15-001-00 | |
| Download: ML15091A312 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982015001R00 - NRC Website | |
text
H Nebraska Public Power District Always there when you need us NLS2015035 March 26, 2015 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2015-001-00
. Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2015-001-00.
There are no new commitments contained in this letter.
Since ely, Osc
. Limpias ('
Vice President Nuclear-Chief Nuclear Officer hJo Attachment: Licensee Event Report 2015-001-00 cc:
Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/attachment USNRC - CNS SRAB Administrator w/attachment NPG Distribution w/attachment INPO Records Center w/attachment via ICES entry SORC Chairman w/attachment CNS Records w/attachment Ok Lj- ýA ý-L COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3817 / Fax: (402) 825-5271 www.nppd.com
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 0113112017 (02-2014)
,Estimated
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REV NUMBER NO Cooper Nuclear Station 05000298 2015
- - 001
- - 00 4 of 5 (MCPR) operating limit would have protected the MCPR safety limit in the event of an anticipated operational occurrence. As such, this event will not be counted as a Safety System Functional Failure for the Nuclear Regulatory Commission performance indicator since no loss of safety function occurred.
SAFETY SIGNIFICANCE
Although the TS related to the set point lift pressures of the SRV pilot valve assemblies were exceeded, an analysis of this event indicates that the design basis pressures to ensure safety of the reactor vessel and its pressure related appurtenances would not be challenged. Public safety was not at risk. Safety to plant personnel and plant equipment were not at risk.
CAUSE
The probable cause is corrosion bonding with time being a possible exacerbating factor. The following causes may have been present or played a role: binding of various kinds, foreign material inclusions, vibration, and other mechanical effects.
CORRECTIVE ACTIONS
The following corrective actions have been entered into CNS' corrective action program:
- 1. CNS shall inspect the SRVs during disassembly to ensure there are no indications of binding, vibration, or other mechanical problems that might cause effects similar to that of corrosion bonding.
- 2. Laboratory work, under the direction of CNS, shall be undertaken to confirm or deny corrosion bonding of the disc and seats as needed. A comparison with previous laboratory findings about SRV pilot valves will be performed to determine, if possible, the role time in-service played in the failures.
- 3. Based on the results of the inspection and laboratory work, specific findings and corrective action recommendations in the form of a revised root cause investigation report will be completed.
- 4. If no evidence to refute corrosion bonding is identified, ensure after machining and lapping processes have been completed, that the oxide, passive layer on the seat and disc are fully restored by pickling or an equivalent process.
PREVIOUS EVENTS Licensee Event Report (LER) 2011-005 On June 22, 2011, one of eight Target Rock SRV pilot valve assemblies failed to lift within TS lift setpoint requirements. Wyle Laboratories performed this testing. The pressure setpoint of the failed pilot assembly was 1090 +/- 32.7 psig; it lifted at 1199 psig. Two subsequent informational lifts were performed for the SRV pilot assembly and were within the TS pressure setpoint tolerances. The mechanistic cause was the same as reported in previous LERs, pilot disc-to-seat NRC U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/3112017 FORM 366
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REV NUMBER NO Cooper Nuclear Station 05000298 2015
- - 001
- - 00 5 of 5 corrosion bonding.
LER 2010-001 On January 12, 2010, two of eight Target Rock SRV pilot valve assemblies failed to lift within TS lift setpoint requirements. Wyle Laboratories performed this testing. The pressure setpoint for the first pilot assembly is 1100 +/- 33.0 psig; the SRV pilot assembly lifted at 1166 psig. The pressure setpoint for the second pilot assembly is 1090 +/- 32.7 psig; it lifted at 1139 psig. Two subsequent informational lifts were performed for both SRV pilot assemblies and were within the TS pressure setpoint tolerances. The mechanistic cause was the same as reported in previous LERs, pilot disc-to-seat corrosion bounding.
LER 2008-002 On July 7 through July 9, 2008, the results of Target Rock SRV test data performed at Wyle Laboratories identified that one of eight SRV pilot assemblies failed as-found pressure setpoint testing. The SRV pilot assembly lifted at 1165 psig, outside its TS setpoint tolerance of 1100 +/- 33.0 psig.
The mechanistic cause was pilot disc-to-seat corrosion bounding between the Stellite 21 pilot disc and Stellite 6B pilot body seat to cause the SRV pilot assembly to lift outside its TS setpoint tolerance.
LER 2007-002 On February 28 through March 2, 2007, the results of Target Rock SRV tests performed at Wyle Laboratories identified that one of eight SRV pilot valve assemblies failed to lift within its TS lift setpoint of 1090 +/- 32.7 psig. The failure was a result of sufficient corrosion bonding between the SRV pilot valve assembly Stellite 21 disc and the pilot valve Stellite 6B body seat to cause the SRV pilot valve to lift outside its TS setpoint tolerance.